Document and Entity Information
Document and Entity Information - USD ($) | 12 Months Ended | ||
Dec. 31, 2018 | Mar. 08, 2019 | Jun. 29, 2018 | |
Document And Entity Information [Abstract] | |||
Document Type | 10-K | ||
Amendment Flag | false | ||
Document Period End Date | Dec. 31, 2018 | ||
Document Fiscal Year Focus | 2018 | ||
Document Fiscal Period Focus | FY | ||
Trading Symbol | SPRO | ||
Entity Registrant Name | Spero Therapeutics, Inc. | ||
Entity Central Index Key | 0001701108 | ||
Current Fiscal Year End Date | --12-31 | ||
Entity Filer Category | Accelerated Filer | ||
Entity Common Stock, Shares Outstanding | 17,215,976 | ||
Entity Well-known Seasoned Issuer | No | ||
Entity Voluntary Filers | No | ||
Entity Current Reporting Status | Yes | ||
Entity Public Float | $ 210,900,000 | ||
Entity Small Business | true | ||
Entity Emerging Growth Company | true | ||
Entity Ex Transition Period | true | ||
Entity Shell Company | false |
CONSOLIDATED BALANCE SHEETS
CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands | Dec. 31, 2018 | Dec. 31, 2017 |
Current assets: | ||
Cash and cash equivalents | $ 34,080 | $ 87,288 |
Marketable securities | 81,363 | |
Other receivables | 376 | 1,011 |
Tax incentive receivable, current | 922 | 1,932 |
Prepaid expenses and other current assets | 7,478 | 1,828 |
Total current assets | 124,219 | 92,059 |
Property and equipment, net | 2,893 | 1,164 |
Deposits | 153 | 206 |
Deferred offering costs | 316 | |
Other assets | 1,192 | |
Tax incentive receivable | 233 | |
Restricted cash | 50 | |
Total assets | 129,006 | 93,479 |
Current liabilities: | ||
Accounts payable | 3,603 | 3,470 |
Accrued expenses and other current liabilities | 8,263 | 4,321 |
Derivative liabilities | 223 | 223 |
Deferred rent | 229 | 143 |
Total current liabilities | 12,318 | 8,157 |
Deferred rent, net of current portion | 833 | 365 |
Total liabilities | 13,151 | 8,522 |
Commitments and contingencies (Note 11) | ||
Stockholders' equity: | ||
Preferred stock, $0.001 par value; 10,000,000 shares authorized, 3,220 shares issued and outstanding as of December 31, 2018 and zero shares issued and outstanding as of December 31, 2017 | ||
Common stock, $0.001 par value; 60,000,000 shares authorized as of December 31, 2018 and December 31, 3017; 17,205,962 shares issued and outstanding as of December 31, 2018 and 14,369,182 shares issued and outstanding as of December 31, 2017 | 17 | 14 |
Additional paid-in capital | 254,013 | 181,428 |
Accumulated deficit | (138,502) | (96,840) |
Accumulated other comprehensive loss | (28) | |
Total Spero Therapeutics, Inc. stockholders' equity | 115,500 | 84,602 |
Non-controlling interests | 355 | 355 |
Total stockholders' equity | 115,855 | 84,957 |
Total liabilities and stockholders' equity | $ 129,006 | $ 93,479 |
CONSOLIDATED BALANCE SHEETS (Pa
CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares | Dec. 31, 2018 | Dec. 31, 2017 |
Statement Of Financial Position [Abstract] | ||
Preferred stock, par value | $ 0.001 | $ 0.001 |
Preferred stock, shares authorized | 10,000,000 | 10,000,000 |
Preferred stock, shares/units issued | 3,220 | 0 |
Preferred stock, shares/units outstanding | 3,220 | 0 |
Common stock, par value | $ 0.001 | $ 0.001 |
Common stock, shares authorized | 60,000,000 | 60,000,000 |
Common stock, shares/units issued | 17,205,962 | 14,369,182 |
Common stock, shares/units outstanding | 17,205,962 | 14,369,182 |
CONSOLIDATED STATEMENTS OF OPER
CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands | 12 Months Ended | ||
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | |
Income Statement [Abstract] | |||
Grant revenue | $ 3,966 | $ 1,979 | $ 335 |
Operating expenses: | |||
Research and development | 33,885 | 32,869 | 26,333 |
General and administrative | 12,887 | 10,840 | 7,223 |
Total operating expenses | 46,772 | 43,709 | 33,556 |
Loss from operations | (42,806) | (41,730) | (33,221) |
Other income (expense): | |||
Change in fair value of derivative liabilities | 1,541 | 580 | |
Interest income and other income (expense), net | 1,144 | 303 | |
Total other income (expense), net | 1,144 | 1,844 | 580 |
Net loss | (41,662) | (39,886) | (32,641) |
Less: Net loss attributable to non-controlling interest | (1,143) | (7,150) | |
Net loss attributable to Spero Therapeutics, Inc. | (41,662) | (38,743) | (25,491) |
Cumulative dividends on redeemable convertible preferred shares | (6,146) | (3,441) | |
Accretion of redeemable bridge units and redeemable convertible preferred shares to redemption value | (1,208) | (996) | |
Net loss attributable to common shareholders of Spero Therapeutics, Inc. | $ (41,662) | $ (46,097) | $ (29,928) |
Net loss per share attributable to common shareholders per share, basic and diluted | $ (2.60) | $ (17.82) | $ (95.87) |
Weighted average shares outstanding, basic and diluted: | 16,001,832 | 2,586,865 | 312,169 |
Comprehensive loss: | |||
Net loss | $ (41,662) | $ (39,886) | $ (32,641) |
Other comprehensive loss: | |||
Unrealized loss on marketable securities | (28) | ||
Total other comprehensive gain loss | (28) | ||
Total comprehensive loss | $ (41,690) | $ (39,886) | $ (32,641) |
CONSOLIDATED STATEMENTS OF BRID
CONSOLIDATED STATEMENTS OF BRIDGE UNITS, REDEEMABLE CONVERTIBLE PREFERRED SHARES AND STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands | Total | Initial Public Offering [Member] | Spero Europe, Ltd. [Member]Exchange for Licensed Technology [Member] | Spero Cantab [Member] | Spero Cantab [Member]Exchange for Licensed Technology [Member] | Spero Potentiator, Inc. [Member] | Spero Gyrase, Inc. [Member]Acquired Technology [Member] | Class C Preferred Units [Member] | Class B Preferred Unit [Member] | Class A Preferred Unit [Member] | Series A Preferred Stock [Member] | Bridge Units [Member] | Bridge Units [Member]Class C Preferred Units [Member] | Preferred Units [Member] | Preferred Units [Member]Class C Preferred Units [Member] | Preferred Units [Member]Class B Preferred Unit [Member] | Preferred Stock [Member] | Preferred Stock [Member]Series C Preferred Stock [Member] | Common Units [Member] | Series A and B Convertible Preferred Stock [Member] | Series A and B Convertible Preferred Stock [Member]Series B Preferred Stock [Member] | Series A and B Convertible Preferred Stock [Member]Series A Preferred Stock [Member] | Common Stock [Member] | Common Stock [Member]Initial Public Offering [Member] | Common Stock [Member]Series B Preferred Stock [Member] | Common Stock [Member]Series A Preferred Stock [Member] | Additional Paid-in Capital [Member] | Additional Paid-in Capital [Member]Initial Public Offering [Member] | Additional Paid-in Capital [Member]Spero Cantab [Member] | Additional Paid-in Capital [Member]Class A Preferred Unit [Member] | Additional Paid-in Capital [Member]Series B Preferred Stock [Member] | Additional Paid-in Capital [Member]Series A Preferred Stock [Member] | Accumulated Deficit [Member] | Accumulated Deficit [Member]Spero Europe, Ltd. [Member] | Accumulated Deficit [Member]Spero Potentiator, Inc. [Member] | Spero Therapeutics, Inc. Stockholders' Equity [Member] | Spero Therapeutics, Inc. Stockholders' Equity [Member]Initial Public Offering [Member] | Spero Therapeutics, Inc. Stockholders' Equity [Member]Spero Europe, Ltd. [Member] | Spero Therapeutics, Inc. Stockholders' Equity [Member]Spero Cantab [Member] | Spero Therapeutics, Inc. Stockholders' Equity [Member]Spero Potentiator, Inc. [Member] | Spero Therapeutics, Inc. Stockholders' Equity [Member]Class A Preferred Unit [Member] | Spero Therapeutics, Inc. Stockholders' Equity [Member]Series A Preferred Stock [Member] | Non-controlling Interests [Member] | Non-controlling Interests [Member]Spero Europe, Ltd. [Member] | Non-controlling Interests [Member]Spero Europe, Ltd. [Member]Exchange for Licensed Technology [Member] | Non-controlling Interests [Member]Spero Cantab [Member] | Non-controlling Interests [Member]Spero Cantab [Member]Exchange for Licensed Technology [Member] | Non-controlling Interests [Member]Spero Potentiator, Inc. [Member] | Non-controlling Interests [Member]Spero Gyrase, Inc. [Member]Acquired Technology [Member] |
Balances at Dec. 31, 2015 | $ (18,553) | $ (18,100) | $ (18,100) | $ (453) | |||||||||||||||||||||||||||||||||||||||||||||
Balance, Units at Dec. 31, 2015 | 7,640,596 | ||||||||||||||||||||||||||||||||||||||||||||||||
Balance at Dec. 31, 2015 | $ 18,296 | ||||||||||||||||||||||||||||||||||||||||||||||||
Balance, Shares at Dec. 31, 2015 | 356,397 | ||||||||||||||||||||||||||||||||||||||||||||||||
Conversion of bridge units into preferred units | $ 8,500 | ||||||||||||||||||||||||||||||||||||||||||||||||
Deemed contribution of capital | 2,408 | $ 2,408 | $ 2,408 | $ 2,408 | |||||||||||||||||||||||||||||||||||||||||||||
Issuance of units | $ 7,897 | $ 24,979 | |||||||||||||||||||||||||||||||||||||||||||||||
Issuance of units, Shares | 5,321,112 | 1,609,846 | 8,500 | 5,909,089 | |||||||||||||||||||||||||||||||||||||||||||||
Repurchase of unvested common units, shares | (21,116) | ||||||||||||||||||||||||||||||||||||||||||||||||
Cumulative dividends on redeemable convertible preferred units | (3,441) | 3,441 | $ (2,503) | (938) | (3,441) | ||||||||||||||||||||||||||||||||||||||||||||
Accretion of redeemable preferred units to redemption value | (969) | $ 969 | (58) | (911) | (969) | ||||||||||||||||||||||||||||||||||||||||||||
Accretion of units to redemption value | $ 27 | ||||||||||||||||||||||||||||||||||||||||||||||||
Accretion of bridge units to redemption value | (27) | (27) | (27) | ||||||||||||||||||||||||||||||||||||||||||||||
Issuance of non-controlling interest in subidiary | $ 100 | $ 1,635 | $ 1,080 | $ 100 | $ 1,635 | $ 1,080 | |||||||||||||||||||||||||||||||||||||||||||
Issuance of additional shares to minority investor under anti-dilution rights | $ 980 | $ 980 | |||||||||||||||||||||||||||||||||||||||||||||||
Share-based compensation expense | 180 | 180 | 180 | ||||||||||||||||||||||||||||||||||||||||||||||
Net loss | (32,641) | (25,491) | (25,491) | (7,150) | |||||||||||||||||||||||||||||||||||||||||||||
Balances at Dec. 31, 2016 | (49,248) | (45,440) | (45,440) | (3,808) | |||||||||||||||||||||||||||||||||||||||||||||
Balance, Units at Dec. 31, 2016 | 8,500 | 13,549,685 | |||||||||||||||||||||||||||||||||||||||||||||||
Balance at Dec. 31, 2016 | $ 7,924 | $ 47,685 | |||||||||||||||||||||||||||||||||||||||||||||||
Balance, Shares at Dec. 31, 2016 | 335,281 | ||||||||||||||||||||||||||||||||||||||||||||||||
Conversion of bridge units into preferred units | 8,500 | $ (8,500) | $ 9,444 | ||||||||||||||||||||||||||||||||||||||||||||||
Conversion of bridge units into preferred units, Shares | (8,500) | 5,321,112 | |||||||||||||||||||||||||||||||||||||||||||||||
Purchase of non-controlling interest | $ (175) | $ (1,000) | $ 928 | $ (14) | $ (7,395) | $ (14) | $ 928 | $ (7,395) | $ 14 | $ (1,103) | $ 6,395 | ||||||||||||||||||||||||||||||||||||||
Exchange of units in Spero Therapeutics, LLC for shares in Spero Therapeutics, Inc. on a one-for-one basis | $ (103,760) | $ 103,760 | |||||||||||||||||||||||||||||||||||||||||||||||
Exchange of units in Spero Therapeutics, LLC for shares in Spero Therapeutics, Inc. on a one-for-one basis, Shares | 43,197,267 | 43,197,267 | (335,281) | 335,281 | |||||||||||||||||||||||||||||||||||||||||||||
Issuance of stock | $ 74,175 | $ 110 | $ 6 | $ 74,169 | $ 74,175 | ||||||||||||||||||||||||||||||||||||||||||||
Issuance of stock, shares | 61,880 | 5,971,498 | |||||||||||||||||||||||||||||||||||||||||||||||
Accretion of preferred stock to redemption value | $ 263 | ||||||||||||||||||||||||||||||||||||||||||||||||
Issuance of Common Stock, conversion of Preferred Stock to Common Stock | 107,018 | $ (107,018) | $ 8 | 107,010 | 107,018 | ||||||||||||||||||||||||||||||||||||||||||||
Issuance of Common Stock, conversion of Preferred Stock to Common Stock, shares | (43,259,147) | 8,062,403 | |||||||||||||||||||||||||||||||||||||||||||||||
Accretion of preferred stock to redemption value | (263) | (263) | (263) | ||||||||||||||||||||||||||||||||||||||||||||||
Cumulative dividends on redeemable convertible preferred shares | (2,885) | $ 2,885 | (1,983) | (902) | (2,885) | ||||||||||||||||||||||||||||||||||||||||||||
Issuance of units | $ 43,001 | ||||||||||||||||||||||||||||||||||||||||||||||||
Issuance of units, Shares | 24,326,470 | ||||||||||||||||||||||||||||||||||||||||||||||||
Cumulative dividends on redeemable convertible preferred units | (3,261) | $ 3,261 | (3,261) | (3,261) | |||||||||||||||||||||||||||||||||||||||||||||
Accretion of redeemable preferred units to redemption value | (369) | $ 369 | (369) | (369) | |||||||||||||||||||||||||||||||||||||||||||||
Accretion of units to redemption value | $ 576 | ||||||||||||||||||||||||||||||||||||||||||||||||
Accretion of bridge units to redemption value | (576) | (123) | (453) | (576) | |||||||||||||||||||||||||||||||||||||||||||||
Share-based compensation expense | 1,427 | 1,427 | 1,427 | ||||||||||||||||||||||||||||||||||||||||||||||
Net loss | (39,886) | (38,743) | (38,743) | (1,143) | |||||||||||||||||||||||||||||||||||||||||||||
Balances at Dec. 31, 2017 | 84,957 | $ 14 | 181,428 | (96,840) | 84,602 | 355 | |||||||||||||||||||||||||||||||||||||||||||
Balance, Shares at Dec. 31, 2017 | 14,369,182 | ||||||||||||||||||||||||||||||||||||||||||||||||
Issuance of common stock upon the exercise of stock options | 335 | 335 | 335 | ||||||||||||||||||||||||||||||||||||||||||||||
Issuance of common stock upon the exercise of stock options, shares | 56,780 | ||||||||||||||||||||||||||||||||||||||||||||||||
Issuance of stock | $ 69,504 | $ 4 | $ 69,500 | $ 69,504 | |||||||||||||||||||||||||||||||||||||||||||||
Issuance of stock, shares | 2,220 | 3,780,000 | |||||||||||||||||||||||||||||||||||||||||||||||
Issuance of preferred stock in exchange for common stock | $ (1) | $ 1 | |||||||||||||||||||||||||||||||||||||||||||||||
Issuance of preferred stock in exchange for common stock, shares | 1,000 | (1,000,000) | |||||||||||||||||||||||||||||||||||||||||||||||
Share-based compensation expense | 2,749 | 2,749 | 2,749 | ||||||||||||||||||||||||||||||||||||||||||||||
Unrealized loss on marketable securities | (28) | (28) | |||||||||||||||||||||||||||||||||||||||||||||||
Net loss | (41,662) | (41,662) | (41,662) | ||||||||||||||||||||||||||||||||||||||||||||||
Balances at Dec. 31, 2018 | $ 115,855 | $ 17 | $ 254,013 | $ (138,502) | $ 115,500 | $ 355 | |||||||||||||||||||||||||||||||||||||||||||
Balance, Shares at Dec. 31, 2018 | 3,220 | 17,205,962 |
CONSOLIDATED STATEMENTS OF BR_2
CONSOLIDATED STATEMENTS OF BRIDGE UNITS, REDEEMABLE CONVERTIBLE PREFERRED SHARES AND STOCKHOLDERS' EQUITY (DEFICIT) (Parenthetical) - USD ($) $ in Thousands | 12 Months Ended | |
Dec. 31, 2018 | Dec. 31, 2016 | |
Spero Gyrase, Inc. [Member] | Aviragen Therapeutics, Inc. [Member] | ||
Ownership percentage | 20.00% | |
Spero Europe, Ltd. [Member] | Promiliad Biopharma, Inc. [Member] | ||
Ownership percentage | 5.00% | |
Spero Cantab [Member] | Pro Bono Bio PLC [Member] | ||
Ownership percentage | 12.50% | |
Class B Preferred Units [Member] | ||
Issuance of tranche rights derivative liability with preferred units | $ 909 | |
Payment of offering costs | 112 | |
Common Stock [Member] | Series A Preferred Stock [Member] | ||
Payment of offering costs | $ 996 | |
Bridge Units [Member] | ||
Contingent prepayment option derivative liability | $ 908 |
CONSOLIDATED STATEMENTS OF CASH
CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands | 12 Months Ended | ||
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | |
Cash flows from operating activities: | |||
Net loss | $ (41,662) | $ (39,886) | $ (32,641) |
Adjustments to reconcile net loss to net cash used in operating activities: | |||
Non-cash research and development expense | 4,595 | ||
Depreciation and amortization | 409 | 363 | 279 |
Loss on disposal of fixed assets | 248 | ||
Change in fair value of derivative liabilities | (1,541) | (580) | |
Share-based compensation | 2,749 | 1,427 | 180 |
Unrealized foreign currency transaction loss | 373 | 83 | |
Accretion of discount on marketable securities | (671) | ||
Changes in operating assets and liabilities: | |||
Other receivables | 635 | (707) | (294) |
Prepaid expenses and other current assets | (5,497) | (575) | (966) |
Tax incentive receivables | 770 | (1,811) | (144) |
Deposits | (53) | ||
Accounts payable | 84 | 2,349 | (644) |
Accrued expenses and other current liabilities | 3,575 | 1,315 | 2,322 |
Deferred rent | 554 | (128) | (84) |
Other assets | (1,192) | ||
Advance payments from collaborator | (929) | ||
Net cash used in operating activities | (39,625) | (39,111) | (28,959) |
Cash flows from investing activities: | |||
Purchases of marketable securities | (130,175) | ||
Proceeds from maturities of marketable securities | 49,455 | ||
Purchases of property and equipment | (2,436) | (27) | (830) |
Net cash used in investing activities | (83,156) | (27) | (830) |
Cash flows from financing activities: | |||
Payment of offering costs | (3,574) | ||
Proceeds from stock option exercises | 335 | ||
Proceeds from initial public offering of common stock, net of commissions and underwriting discounts | 77,749 | ||
Cash payment for non-controlling interests | (1,175) | ||
Net cash provided by financing activities | 69,523 | 116,111 | 34,413 |
Net (decrease) increase in cash and cash equivalents | (53,258) | 76,973 | 4,624 |
Cash, cash equivalents and restricted cash at beginning of period | 87,338 | 10,365 | 5,741 |
Cash, cash equivalents and restricted cash at end of period | 34,080 | 87,338 | 10,365 |
Supplemental disclosure of non-cash investing and financing activities: | |||
Purchases of property and equipment included in accounts payable and accrued expenses | 54 | ||
Conversion of bridge units into preferred units | 8,500 | ||
Conversion of preferred stock to common stock | 107,018 | ||
Settlement of derivative liabilities upon issuance of preferred units | 944 | ||
Issuance of tranche rights with preferred units | 909 | ||
Deemed contribution of capital | 2,408 | ||
Settlement of derivative liability upon issuance of bridge units | 305 | ||
Issuance of contingent prepayment option with bridge units | 908 | ||
Cumulative dividends on redeemable convertible preferred shares | 6,146 | 3,441 | |
Accretion of redeemable convertible preferred units and stock to redemption value | 632 | 969 | |
Accretion of bridge units to redemption value | 576 | 27 | |
Issuance of additional shares of common stock to minority investors under anti-dilution rights | 980 | ||
2018 Equity Offering [Member] | |||
Cash flows from financing activities: | |||
Proceeds from equity offering | 70,500 | ||
Payment of offering costs | (996) | ||
2018 Registration Statement and At-the-Market Facility [Member] | |||
Cash flows from financing activities: | |||
Payment of offering costs | $ (316) | ||
Bridge Units [Member] | |||
Cash flows from financing activities: | |||
Proceeds from issuance of bridge units | 8,500 | ||
Series B Preferred Stock [Member] | |||
Cash flows from financing activities: | |||
Proceeds from issuance of preferred units, net of issuance costs | $ 25,913 | ||
Series C Preferred Stock [Member] | |||
Cash flows from financing activities: | |||
Payment of offering costs | (176) | ||
Proceeds from issuance of preferred units, net of issuance costs | $ 43,111 |
Nature of the Business and Basi
Nature of the Business and Basis of Presentation | 12 Months Ended |
Dec. 31, 2018 | |
Accounting Policies [Abstract] | |
Nature of the Business and Basis of Presentation | 1. Nature of the Business and Basis of Presentation Spero Therapeutics, Inc., together with its consolidated subsidiaries (the “Company”), is a multi-asset, clinical-stage biopharmaceutical company focused on identifying, developing and commercializing novel treatments for multi-drug resistant (“MDR”) bacterial infections. The Company’s most advanced product candidate, SPR994, is designed to be the first broad-spectrum oral carbapenem-class antibiotic for use in adults to treat MDR Gram-negative infections. Treatment with effective orally administrable antibiotics may prevent hospitalizations for serious infections and enable earlier, more convenient and cost-effective treatment of patients after hospitalization. The Company also has a platform technology known as its Potentiator Platform that it believes will enable it to develop drugs that will expand the spectrum and potency of existing antibiotics, including formerly inactive antibiotics, against Gram-negative bacteria. The Company’s lead product candidates generated from its Potentiator Platform are two intravenous, or IV,-administered agents, SPR206 and SPR741, designed to treat MDR Gram-negative infections in the hospital setting. In addition, the Company is developing SPR720, an oral antibiotic designed for the treatment of pulmonary non-tuberculous mycobacterial infections. The Company believes that its novel product candidates, if successfully developed and approved, would have a meaningful patient impact and significant commercial applications for the treatment of MDR infections in both the community and hospital settings. The Company was formed as Spero Therapeutics, LLC in December 2013 under the laws of the State of Delaware. On June 30, 2017, through a series of transactions, Spero Therapeutics, LLC merged with and into Spero Therapeutics, Inc. (formerly known as Spero OpCo, Inc.), a Delaware corporation. As part of the transactions, holders of preferred units and common units of Spero Therapeutics, LLC exchanged their units for shares of Spero Therapeutics, Inc. on a one-for-one basis. These transactions are collectively referred to as the Reorganization. Upon completion of the Reorganization, the historical consolidated financial statements of Spero Therapeutics, LLC became the historical consolidated financial statements of Spero Therapeutics, Inc. because the Reorganization was accounted for as a reorganization of entities under common control. The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, development by competitors of new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations and the ability to secure additional capital to fund operations. Product candidates currently under development will require significant additional research and development efforts, including preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel and infrastructure and extensive compliance-reporting capabilities. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales. On December 3, 2018, the Company filed a universal shelf registration statement on Form S-3 (Registration No. 333-228661) with the SEC, which was declared effective on December 11, 2018, and pursuant to which it registered for sale up to $200.0 million of any combination of its common stock, preferred stock, debt securities, warrants, rights and/or units from time to time and at prices and on terms that we may determine, including up to $50.0 million of our common stock available for issuance pursuant to an at-the-market offering program sales agreement that it entered into with Cantor Fitzgerald & Co., or Cantor. Under the sales agreement, Cantor may sell the shares by any method permitted by law deemed to be an “at the market” offering as defined in Rule 415 of the Securities Act. The accompanying consolidated financial statements of the Company have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of the Company and its consolidated subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation. In accordance with Accounting Standards Update (“ASU”) 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern (Subtopic 205-40) The accompanying consolidated financial statements do not include any adjustments that might result from the outcome of this uncertainty. Accordingly, the consolidated financial statements have been prepared on a basis that assumes the Company will continue as a going concern and which contemplates the realization of assets and satisfaction of liabilities and commitments in the ordinary course of business. |
Summary of Significant Accounti
Summary of Significant Accounting Policies | 12 Months Ended |
Dec. 31, 2018 | |
Accounting Policies [Abstract] | |
Summary of Significant Accounting Policies | 2. Summary of Significant Accounting Policies Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting periods. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, the accrual for research and development expenses, the valuation of common shares prior to the Company’s IPO, the valuation of share-based awards and the valuation of derivative liabilities. The Company bases its estimates on historical experience, known trends and other market-specific or other relevant factors that it believes to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates, as there are changes in circumstances, facts and experience. Actual results may differ from those estimates or assumptions. Consolidation The Company consolidates entities in which it has a controlling financial interest. The Company evaluates each of its subsidiaries to determine whether the entity represents a variable interest entity (“VIE”), for which consolidation should be evaluated under the VIE model, or, alternatively, if the entity is a voting interest entity, for which consolidation should be evaluated using the voting interest model. The Company has concluded that none of its subsidiaries is a VIE and has consolidated each subsidiary under the voting interest model because it has majority voting control of each subsidiary. Ownership interests in the Company’s subsidiaries that are held by entities other than the Company are reported as non-controlling interests in the consolidated balance sheets. Losses attributed to non-controlling interests and to the Company are reported separately in the consolidated statements of operations and comprehensive loss. As of December 31, 2018 and 2017, the Company consolidated its non-controlling interest in Spero Gyrase, Inc. Concentrations of Credit Risk and of Significant Suppliers Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash and cash equivalents. The Company maintains most of its cash and cash equivalents at one accredited financial institution. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships. The Company is dependent on third-party manufacturers to supply products for research and development activities in its programs. In particular, the Company relies and expects to continue to rely on a small number of manufacturers to supply it with its requirements for the active pharmaceutical ingredients and formulated drugs related to these programs. These programs could be adversely affected by a significant interruption in the supply of active pharmaceutical ingredients and formulated drugs. Deferred Offering Costs The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded in stockholders’ deficit as a reduction of additional paid-in capital generated as a result of the offering. Should the planned equity financing be abandoned, the deferred offering costs will be expensed immediately as a charge to operating expenses in the consolidated statement of operations and comprehensive loss. Cash Equivalents The Company considers all highly liquid investments with original maturities of three months or less at the date of purchase to be cash equivalents. Marketable Securities Marketable securities consist of investments with original maturities greater than 90 days. The Company considers its investment portfolio of investments to be available-for-sale. Accordingly, these investments are recorded at fair value, which is based on quoted market prices. Investments with maturities beyond one year are generally classified as short term, based on their highly liquid nature and because such marketable securities represent the investment of cash that is available for current operations. Unrealized gains and losses are reported as a component of accumulated other comprehensive income (loss) in stockholders’ equity. Realized gains and losses and declines in value judged to be other than temporary are included as a component of other income (expense), net based on the specific identification method. When determining whether a decline in value is other than temporary, the Company considers various factors, including whether the Company has the intent to sell the security, and whether it is more likely than not that the Company will be required to sell the security prior to recovery of its amortized cost basis. Property and Equipment Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation and amortization expense is recognized using the straight-line method over the estimated useful life of each asset as follows: Estimated Useful Life Laboratory equipment 5 years Computer software and equipment 3 years Office furniture and equipment 7 years Manufacturing equipment 5 years Leasehold improvements Shorter of life of lease or 5 years Costs for capital assets not yet placed into service are capitalized as construction in progress and are depreciated in accordance with the above guidelines once placed into service. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation and amortization are removed from the accounts and any resulting gain or loss is included in loss from operations. Expenditures for repairs and maintenance are charged to expense as incurred. Other Assets Other assets consist of long-term prepayments and deposits. Impairment of Long-Lived Assets Long-lived assets consist of property and equipment. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset group for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset group to its carrying value. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of an asset group are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset group over its fair value, determined based on discounted cash flows. During the year ended December 31, 2018, the Company recorded a loss of $0.2 million related to the write-off of fixed assets at its Watertown, Massachusetts laboratory facility. The Company did not record any impairment losses on long-lived assets during the years ended December 31, 2017 or 2016. Fair Value Measurements Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: • Level 1—Quoted prices in active markets for identical assets or liabilities. • Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. • Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. The Company’s cash equivalents and derivative liabilities are carried at fair value, determined according to the fair value hierarchy described above (see Note 3). The carrying values of the Company’s accounts payable and accrued expenses approximate their fair values due to the short-term nature of these liabilities. Derivative Liabilities In connection with certain equity financings, licensing transactions and research collaborations, the Company has identified certain embedded and freestanding derivatives, which are recorded as liabilities on the Company’s consolidated balance sheet and are remeasured to fair value at each reporting date until the derivative is settled. Changes in the fair value of the derivative liabilities are recognized as other income (expense) in the consolidated statement of operations and comprehensive loss. Classification and Accretion of Bridge Units and Redeemable Convertible Preferred Shares The Company has classified bridge units and redeemable convertible preferred shares outside of stockholders’ equity (deficit) because the shares contain certain redemption features that are not solely within the control of the Company. The carrying values of these instruments are accreted to their respective redemption values from the date of issuance through the earliest date of redemption. Segment Information The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The Company’s singular focus is on identifying, developing and commercializing novel treatments for MDR bacterial infections. All of the Company’s tangible assets are held in the United States. Government Contracts and Revenue Recognition The Company generates revenue from government contracts that reimburse the Company for certain allowable costs for funded projects. For contracts with government agencies, when the Company has concluded that it is the principal in conducting the research and development expenses and where the funding arrangement is considered central to the Company’s ongoing operations, the Company classifies the recognized funding received as revenue. The Company has concluded to recognize funding received from the Biomedical Advanced Research and Development Authority (“BARDA”), the U.S. Department of Defense (“DoD”), the National Institute of Allergy and Infectious Diseases (“NIAID”) of the National Institutes of Health (“NIH”) and Combating Antibiotic Resistant Bacteria Biopharmaceutical Accelerator (“CARB-X”) as revenue, rather than as a reduction of research and development expenses, because the Company is the principal in conducting the research and development activities and these contracts are central to its ongoing operations. Revenue is recognized as the qualifying expenses related to the contracts are incurred. Revenue recognition commences once the Company has substantially accomplished what it must do to be entitled to the benefits represented by the revenues. Revenue recognized upon incurring qualifying expenses in advance of receipt of funding is recorded in the Company’s consolidated balance sheet as other receivables. The related costs incurred by the Company are included in research and development expense in the Company’s consolidated statements of operations and comprehensive loss. Government Tax Incentives For available government tax incentives that the Company may earn without regard to the existence of taxable income and that require the Company to forego tax deductions or the use of future tax credits and net operating loss carryforwards, the Company classifies the funding recognized as a reduction of the related qualifying research and development expenses incurred. Since the fourth quarter of 2016 and through December 31, 2018, the Company’s operating subsidiary in Australia has met the eligibility requirements to receive a 43.5% tax incentive for qualifying research and development activities (see Note 14). The Company recognizes these incentives as a reduction of research and development expenses in the consolidated statements of operations and comprehensive loss in the same period that the related qualifying expenses are incurred. Reductions of research and development expense recognized upon incurring qualifying expenses in advance of receipt of tax incentive payments are recorded in the consolidated balance sheet as tax incentive receivables. Collaboration Agreements For collaboration agreements with a third party, to determine the appropriate statement of operations classification of the recognized funding, the Company first assesses whether the collaboration arrangement is within the scope of the accounting guidance for collaboration arrangements. If it is, the Company evaluates the collaborative arrangement for proper classification in the statement of operations based on the nature of the underlying activity and the Company assesses the payments to and from the collaborative partner. If the payments to and from the collaborative partner are not within the scope of other authoritative accounting guidance, the Company bases the statement of operations classification for the payments received on a reasonable, rational analogy to authoritative accounting guidance, applied in a consistent manner. Conversely, if the collaboration arrangement is not within the scope of accounting guidance for collaboration arrangements, the Company assesses whether the collaboration arrangement represents a vendor/customer relationship. If the collaborative arrangement does not represent a vendor/customer relationship, the Company then classifies the funding payments received in the statement of operations and comprehensive loss as a reduction of the related expense that is incurred. In 2014, the Company entered into a research and development services and support agreement with Hoffmann-La Roche Inc. and certain of its affiliates (“Roche”) and concluded that the agreements were not within the scope of the accounting guidance for collaboration arrangements (see Note 13). Due to the co-funded nature of the payments and the Company’s assessment that it did not have a vendor/customer relationship with Roche, the Company recognized the nonrefundable payments received under the agreement as a reduction to the research and development expenses incurred, based on a proportional methodology comparing the total expenses incurred in the period under the project to the total expenses expected to be incurred under the project. The Company terminated the agreement with Roche in August 2016. Research and Development Costs Research and development costs are expensed as incurred. Research and development expenses are comprised of costs incurred in performing research and development activities, including personnel salaries, share-based compensation and benefits, allocated facilities costs, depreciation, manufacturing expenses, costs related to the Company’s government contract and grant arrangements, and external costs of outside vendors engaged to conduct preclinical development activities, clinical trials as well as the cost of licensing technology. Upfront payments and milestone payments made for the licensing of technology are expensed as research and development in the period in which they are incurred. Advance payments for goods or services to be received in the future for use in research and development activities are recorded as prepaid expenses. The prepaid amounts are expensed as the related goods are delivered or the services are performed. Clinical Trial and other Research Contract Costs and Accruals The Company has entered into various research and development contracts with clinical research organizations and other companies both inside and outside of the United States. These agreements are generally cancelable, and related payments are recorded as research and development expenses as incurred. There may be instances in which payments made to these vendors exceed the level of service provided and will result in a prepayment of the expense. The Company records accruals for estimated ongoing research and clinical trial costs based on the services received and efforts expended pursuant to multiple contracts with these vendors. When evaluating the adequacy of the accrued liabilities, the Company analyzes the progress of the studies or trials, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs. Patent Costs All patent-related costs incurred in connection with filing and prosecuting patent applications are expensed as incurred due to the uncertainty about the recovery of the expenditure. Amounts incurred are classified as general and administrative expenses. Share-Based Compensation The Company measures all share-based awards granted to employees and directors based on the fair value on the date of grant using the Black-Scholes option-pricing model. Compensation expense of those awards is recognized over the requisite service period, which is generally the vesting period of the respective award. Generally, the Company issues awards with only service-based vesting conditions and records the expense for these awards using the straight-line method over the requisite service period, net of any actual forfeitures. The Company classifies share-based compensation expense in its consolidated statements of operations and comprehensive loss in the same manner in which the award recipient’s payroll costs are classified or in which the award recipient’s service payments are classified. Comprehensive Loss Comprehensive loss includes net loss as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those with shareholders. For the year ended December 31, 2018, these changes related to unrealized gains and losses on the Company’s available-for-sale marketable securities. There were no reclassifications out of comprehensive loss for the year ended December 31, 2018. There was no difference between net loss and comprehensive loss for the years ended December 31, 2017 and 2016. Net Income (Loss) per Share Attributable to Spero Therapeutics, Inc. The Company follows the two-class method when computing net income (loss) per share, as the Company has issued shares that meet the definition of participating securities. The two-class method determines net income (loss) per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed. Net income (loss) per share attributable to common stockholders is calculated based on net income (loss) attributable to Spero Therapeutics, Inc. and excludes net income (loss) attributable to non-controlling interests. Basic net income (loss) per share attributable to common stockholders is computed by dividing the net income (loss) attributable to common stockholders by the weighted average number of shares of common stock outstanding for the period. Diluted net income (loss) attributable to common stockholders is computed by adjusting net income (loss) attributable to common stockholders to reallocate undistributed earnings based on the potential impact of dilutive securities. Diluted net income (loss) per share attributable to common stockholders is computed by dividing the diluted net income (loss) attributable to common stockholders by the weighted average number of common shares outstanding for the period, including potential dilutive common shares assuming the dilutive effect of common stock equivalents. The Company’s preferred stock contractually entitles the holders of such shares to participate in dividends but does not contractually require the holders of such shares to participate in losses of the Company. Accordingly, in periods in which the Company reports a net loss, such losses are not allocated to such participating securities. In periods in which the Company reports a net loss attributable to common stockholders of Spero Therapeutics, Inc., diluted net loss per share attributable to common stockholders of Spero Therapeutics, Inc. is the same as basic net loss per share attributable to common stockholders of Spero Therapeutics, Inc., since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive. The Company reported a net loss attributable to common stockholders of Spero Therapeutics, Inc. for the years ended December 31, 2018, 2017 and 2016. Income Taxes The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the consolidated financial statements or in the Company’s tax returns. Deferred tax assets and liabilities are determined on the basis of the differences between the financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies. The Company accounts for uncertainty in income taxes recognized in the consolidated financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more-likely-than-not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the consolidated financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties. Recently Adopted Accounting Pronouncements In May 2014, the FASB”) issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) (“ASU 2014-09”), which supersedes existing revenue recognition guidance under GAAP. The standard’s core principle is that a company will recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. The standard outlines a five-step process to achieve this principle, and will require companies to use more judgment and make more estimates than under the current guidance. The Company expects that these judgments and estimates will include identifying performance obligations in the customer contract, estimating the amount of variable consideration to include in the transaction price and allocating the transaction price to each separate performance obligation. ASU 2014-09 also requires additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts. In August 2015, the FASB issued ASU 2015-14, Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date , which delays the effective date of ASU 2014-09 such that the standard is effective for public entities for annual periods beginning after December 15, 2017 and for interim periods within those fiscal years. In March 2016, the FASB issued ASU No. 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations (“ASU 2016-08”), which further clarifies the implementation guidance on principal versus agent considerations in ASU 2014-09. In April 2016, the FASB issued ASU No. 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensin g, clarifying the implementation guidance on identifying performance obligations and licensing. Specifically, the amendments in this update reduce the cost and complexity of identifying promised goods or services and improve the guidance for determining whether promises are separately identifiable. The amendments in this update also provide implementation guidance on determining whether an entity’s promise to grant a license provides a customer with either a right to use the entity’s intellectual property (which is satisfied at a point in time) or a right to access the entity’s intellectual property (which is satisfied over time). In May 2016, the FASB issued ASU No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients (“ASU 2016-12”), which clarifies the objective of the collectability criterion, presentation of taxes collected from customers, non-cash consideration, contract modifications at transition, completed contracts at transition and how guidance in ASU 2014-09 is retrospectively applied. ASU 2016-08, ASU 2016-10 and ASU 2016-12 have the same effective dates and transition requirements as ASU 2014-09. The Company adopted this standard using the modified retrospective approach, however the Company determined that government grant revenue is outside the scope of ASC 606. Therefore, the adoption of ASC 606 did not impact the Company’s financial position, results of operations or cash flows as its only existing revenue source as of December 31, 2018 is government grants. In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows: Classification of Certain Cash Receipts and Cash Payments In November 2016, the FASB issued ASU 2016-18 Statement of Cash Flows (Topic 230) The inclusion of restricted cash increased the beginning and ending balances of the consolidated statement of cash flows by $50,000 for the years ended December 31, 2017 and 2016. In January 2017, FASB issued ASU No. 2017-01, Business Combinations (Topic 805): Clarifying the Definition of a Business In May 2017, the FASB issued ASU No. 2017-09, Compensation—Stock Compensation (Topic 718): Scope of Modification Accounting Recently Issued Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842 Leases Codification Improvements to Topic 842, Leases Leases (Topic 842): Targeted Improvements The Company has elected to adopt ASU 2016-02 effective January 1, 2019 through a cumulative-effect adjustment under ASU 2018-11. This standard provides a number of optional practical expedients in transition. The Company plans to apply the package of practical expedients to leases that commenced prior to the effective date whereby it will elect to not reassess the following: (i) whether any expired or existing contracts contain leases; (ii) the lease classification for any expired or existing leases; and (iii) initial direct costs for any existing leases. The Company expects to elect the short-term lease recognition exemption for all leases that qualify, where a right-of-use asset or lease liability will not be recognized for short term leases. The Company has substantially completed its assessment of the adoption of ASU 2016-02 and expects that the most significant effects of adoption will be to the recognition of material new ROU assets and corresponding liabilities on its consolidated balance sheet related to its existing facility operating leases (see Note 11). In July 2017, the FASB issued ASU 2017-11, Earnings Per Share (Topic 260), Distinguishing Liabilities from Equity (Topic 480), Derivatives and Hedging (Topic 815) I. Accounting for Certain Financial Instruments with Down Round Features II. Replacement of the Indefinite Deferral for Mandatorily Redeemable Financial Instruments of Certain Nonpublic Entities and Certain Mandatorily Redeemable Noncontrolling Interests with a Scope Exception In June 2018, the FASB issued ASU 2018-07, Ímprovements to Nonemployee Share-Based Payment Accounting, which sets forth amendments to simplify the accounting for share-based payment awards to nonemployees by aligning the measurement and classification guidance, with certain exceptions, to that for share-based payment awards to employees. The amendments expand the scope of the accounting standard for share-based payment awards to include share-based payment awards granted to non-employees in exchange for goods or services used or consumed in an entity’s own operations and supersedes the guidance related to equity-based payments to non-employees. The amendments in this ASU are effective for fiscal years beginning after December 15, 2018, including interim periods within that fiscal year. The Company does not expect the adoption of this standard will have a material impact to its consolidated statement of operations, as awards to non-employees are not material. |
Fair Value of Financial Assets
Fair Value of Financial Assets and Liabilities | 12 Months Ended |
Dec. 31, 2018 | |
Fair Value Disclosures [Abstract] | |
Fair Value of Financial Assets and Liabilities | 3. Fair Value of Financial Assets and Liabilities The following tables present information about the Company’s assets and liabilities that are measured at fair value on a recurring basis (in thousands): Fair Value Measurements at December 31, 2018 Using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ — $ 22,327 $ — $ 22,327 Commercial paper — 6,389 — 6,389 Total cash equivalents — 28,716 — 28,716 Marketable securities: U.S. government securities — 37,815 — 37,815 Corporate bonds — 26,672 — 26,672 Commercial paper — 16,876 — 16,876 Total marketable securities — 81,363 — 81,363 Total cash equivalents and marketable securities $ — $ 110,079 $ — $ 110,079 Liabilities: Derivative liabilities: Anti-dilution rights $ — $ — $ 223 $ 223 $ — $ — $ 223 $ 223 Fair Value Measurements at December 31, 2017 Using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ — $ 83,121 $ — $ 83,121 $ — $ 83,121 $ — $ 83,121 Liabilities: Derivative liabilities: Anti-dilution rights $ — $ — $ 223 $ 223 $ — $ — $ 223 $ 223 The tables above do not include cash of $5.4 million and $4.2 million as of December 31, 2018 and 2017, respectively. During the years ended December 31, 2018 and 2017, there were no transfers between Level 1, Level 2 and Level 3. Marketable Securities The Company’s marketable securities are classified as Level 2 assets under the fair value hierarchy as these assets were primarily determined from independent pricing sources, which generally derive security prices from recently reported trades for identical or similar securities. The following table summarizes the gross unrealized gains and losses of the Company’s marketable securities as of December 31, 2018 (in thousands): December 31, 2018 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Assets: U.S. government securities $ 37,819 $ — $ (4 ) $ 37,815 Corporate bonds 26,696 — (24 ) 26,672 Commercial paper 16,876 — — 16,876 $ 81,391 $ — $ (28 ) $ 81,363 As of December 31, 2018, all of the Company’s marketable securities had remaining contractual maturity dates of one year or less from the consolidated balance sheet date. The Company did not own any marketable securities as of December 31, 2017. Tranche Rights The Company’s sales of Class A-1 preferred units (“Class A preferred units”) and Class B-1 preferred units (“Class B preferred units”) (see Note 6) provided investors with the right to participate in subsequent offerings of Class A and Class B preferred units in the event specified development and regulatory milestones were achieved. The Company classified each of the tranche rights as a derivative liability on its consolidated balance sheet because they met the definition of freestanding financial instruments that could have required the Company to transfer assets upon exercise. The Company remeasured the derivative liabilities associated with tranche rights to fair value at each reporting date, and recognized changes in the fair value of the derivative liabilities as a component of other income (expense) in the consolidated statement of operations and comprehensive loss. The fair value of these derivative liabilities was determined using the probability-weighted expected return method (“PWERM”), which considered as inputs the probability and time that a milestone would be achieved, the potential fair value of preferred stock upon the exercise of the tranche right and the risk-adjusted discount rate. Class A Tranche Rights The fair value of the tranche right related to the Company’s Class A preferred unit financing (see Note 6) upon issuance in June 2015 was $2.4 million, which increased slightly as of December 31, 2015. Upon the issuance of the Class B preferred units in February 2016, the tranche right was cancelled and the settlement of the fair value of the derivative liability of $2.4 million was recorded as an increase to additional paid-in capital as a deemed capital contribution from the Class A preferred unit investors. Class B Tranche Rights The fair value of the tranche right related to the Company’s Class B preferred unit financing upon issuance in February 2016 was $0.9 million. Upon the issuance of bridge units in December 2016, the tranche rights were cancelled and the fair value of the derivative liability, which had decreased by $0.6 million to $0.3 million as of the date of settlement due to a decrease in the fair value of the Company’s underlying units, was settled (see Note 6). Anti-Dilution Rights In connection with the issuance of non-controlling interests in certain of the Company’s subsidiaries (see Note 9), specifically Spero Potentiator, Inc., Spero Europe, Ltd. and Spero Gyrase, Inc., the Company granted anti-dilution rights to the minority investors. The Company classifies the anti-dilution rights as a derivative liability on its consolidated balance sheet because they are freestanding instruments that represent a conditional obligation to issue a variable number of shares. The Company remeasures the derivative liability associated with the anti-dilution rights to fair value at each reporting date, and recognizes changes in the fair value of the derivative liability as a component of other income (expense) in the consolidated statement of operations and comprehensive loss. The fair value of these derivative liabilities was determined using a discounted cash flow model. Spero Potentiator In connection with the Company’s issuance of a non-controlling interest in its subsidiary, Spero Potentiator Inc. (“Spero Potentiator”), to Northern Antibiotics Oy Ltd. (“Northern”) in February 2015, the Company granted to Northern certain anti-dilution rights (see Note 9). The fair value of the derivative liability related to the anti-dilution rights upon issuance in February 2015 was $2.4 million. In November 2015, the Company issued an additional 2,736 shares of Spero Potentiator’s common shares for no additional cost to Northern as a result of the anti-dilution rights. Upon issuance, the fair value of the additional shares of Spero Potentiator issued to Northern of $1.5 million was recorded as a reduction of the derivative liability and as an increase to the non-controlling interest. In January and August 2016, the Company issued an additional 2,160 shares of Spero Potentiator’s common shares for no additional cost to Northern as a result of the anti-dilution rights. Upon issuance, the fair value of the additional shares of Spero Potentiator issued to Northern of $1.0 million was recorded as a reduction of the derivative liability and as an increase to the non-controlling interest. At that time, the derivative liability related to the anti-dilution rights issued to Northern was fully settled as Northern had received the maximum number of shares it was entitled to under the anti-dilution rights. The most significant assumption impacting the fair value of the anti-dilution rights was the probability that the Company would fund the maximum amount of investment providing anti-dilution protection. Upon issuance of the rights and through August 2016, the date the maximum anti-dilution protection was reached, the Company’s assumption for the probability of such funding was 100%. Spero Europe, Ltd . In January 2016, in connection with the issuance of a non-controlling interest in its subsidiary, Spero Europe, Ltd. (“Spero Europe”), to Promiliad Biopharma Inc. (“Promiliad”), the Company granted to Promiliad certain anti-dilution rights (see Note 9). The fair value of the derivative liability related to the anti-dilution rights upon issuance in January 2016 was $0.2 million. The change in the fair value of the derivative liability associated with the anti-dilution rights was insignificant during the year ended December 31, 2016. During 2017, the fair value of the derivative liability decreased by $0.2 million to $0 by May 2017. In May 2017, the non-controlling interest in Spero Europe, Ltd. was repurchased and the anti-dilution rights were settled. The most significant assumption impacting the fair value of the anti-dilution rights was the probability that the Company would fund the maximum amount of investment providing anti-dilution protection. Upon the issuance of the rights and through December 31, 2016, the probability of such funding was determined to be 100%. During 2017, the probability of funding Spero Europe, Ltd. was reduced to 0% due to the Company’s decision to no longer pursue development of the licensed technology. Spero Gyrase, Inc. In March 2016, in connection with the issuance of a non-controlling interest in its subsidiary, Spero Gyrase, Inc. (“Spero Gyrase”), to Biota Pharmaceuticals, Inc. (now Aviragen Therapeutics, Inc.) (“Aviragen”), the Company granted to Aviragen certain anti-dilution rights (see Note 9). The fair value of the derivative liability related to the anti-dilution rights upon issuance in March 2016 was $1.6 million. The change in the fair value of the derivative liability associated with the anti-dilution rights was insignificant during the year ended December 31, 2016. During 2017, the fair value of the derivative liability decreased by $1.4 million to $0.2 million by June 30, 2017, and remained unchanged as of December 31, 2017. The most significant assumption impacting the fair value of the anti-dilution rights was the probability that the Company would fund the maximum amount of investment providing anti-dilution protection. Upon issuance of the rights and through December 31, 2016, the probability of such funding was determined to be 100%. During 2017, the probability of such funding was reduced to 0% due to the Company’s decision to no longer pursue development of the acquired technology. As of December 31, 2018 and 2017, the value of the derivative liability of $0.2 million represents amounts funded to the entity that could be settled by the issuance of equity. Contingent Prepayment Options Bridge units issued to investors in January 2015 and December 2016 contained contingent prepayment options whereby such units were automatically convertible into equity units sold in a subsequent round of qualified financing at a discounted rate. The Company classified the contingent prepayment options as derivative liabilities on its consolidated balance sheet because the bridge units were deemed to be more akin to debt than equity and the embedded prepayment options were at a substantial discount, thus meeting the definition of derivative liabilities. The Company remeasured the derivative associated with the contingent prepayment options to fair value at each reporting date, and recognized changes in the fair value of the derivative liabilities as a component of other income (expense) in its consolidated statement of operations and comprehensive loss. The fair value of these derivative liabilities was determined using the PWERM, which considered as inputs the probability and time that a subsequent round of preferred stock financing would occur and the risk-adjusted discount rate. January 2015 Bridge Units The fair value of the derivative liability related to the contingent prepayment option associated with bridge units issued in January 2015 was $2.3 million. The option was settled in June 2015 upon the issuance of Class A preferred units. As a condition to the June 2015 financing, the Company and the holders of the bridge units agreed to reduce the previously agreed-upon discount to the per unit conversion price from 20% to 10% of the per unit price of $3.90 to be paid for the sale of the Class A preferred units. The reduction of the discount resulted in a decrease to the fair value of the derivative liability of $1.4 million, which was recorded as an increase to additional paid-in capital as a deemed capital contribution by the holders of the bridge units. The remaining fair value of the derivative liability of $0.9 million was settled upon conversion of the bridge notes into Class A preferred units. December 2016 Bridge Units The fair value of the derivative liability related to the contingent prepayment option associated with bridge units issued in December 2016 was $0.9 million. The change in the fair value of the derivative liability associated contingent prepayment option was not material during the year ended December 31, 2016. The fair value of the derivative liability increased by less than $0.1 million as of March 2017, at which time the contingent prepayment option was settled upon the issuance of Class C preferred units. The following table provides a roll forward of the aggregate fair values of the Company’s derivative liabilities, for which fair value was determined by Level 3 inputs (in thousands): Contingent Prepayment Options Tranche Rights Anti-Dilution Rights Total Balance at December 31, 2015 $ — $ 2,404 $ 980 $ 3,384 Fair value at issuance 908 909 1,780 3,597 Change in fair value (6 ) (600 ) 26 (580 ) Settlement — (2,713 ) (980 ) (3,693 ) Balance at December 31, 2016 902 — 1,806 2,708 Change in fair value 42 — (1,583 ) (1,541 ) Settlement (944 ) — — (944 ) Balance at December 31, 2017 — — 223 223 Change in fair value — — — — Balance at December 31, 2018 $ — $ — $ 223 $ 223 |
Property and Equipment, Net
Property and Equipment, Net | 12 Months Ended |
Dec. 31, 2018 | |
Property Plant And Equipment [Abstract] | |
Property and Equipment, Net | 4. Property and Equipment, Net Property and equipment, net consisted of the following (in thousands): December 31, 2018 2017 Computer software and equipment $ 166 $ 181 Office furniture and equipment 210 201 Leasehold improvements 863 915 Laboratory equipment — 510 Construction-in-progress 897 — Manufacturing equipment 1,584 — 3,720 1,807 Less: Accumulated depreciation and amortization (827 ) (643 ) $ 2,893 $ 1,164 Property and equipment additions during the year ended December 31, 2018, primarily related to leased manufacturing equipment which was fully paid by the Company, as well as construction-in-progress and leasehold improvements related to the expansion of Company’s leased office space (see Note 11). Depreciation and amortization expense was $0.4 million, $0.4 million and less than $0.3 million for the years ended December 31, 2018, 2017 and 2016, respectively. During the year ended December 31, 2018, the Company recorded a loss of $0.2 million related to the write off of laboratory equipment and certain leasehold improvements at its Watertowm, Massachusetts laboratory facility. |
Accrued Expenses and Other Curr
Accrued Expenses and Other Current Liabilities | 12 Months Ended |
Dec. 31, 2018 | |
Payables And Accruals [Abstract] | |
Accrued Expenses and Other Current Liabilities | 5. Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consisted of the following (in thousands): December 31, 2018 2017 Accrued external research and development expenses $ 4,541 $ 1,770 Accrued payroll and related expenses 2,379 1,369 Accrued professional fees 917 878 Accrued other 426 304 $ 8,263 $ 4,321 |
Convertible Preferred Shares
Convertible Preferred Shares | 12 Months Ended |
Dec. 31, 2018 | |
Equity [Abstract] | |
Convertible Preferred Shares | 6. Convertible Preferred Shares Series A Convertible Preferred Shares The Company’s amended and restated certificate of incorporation authorizes its Board of Directors to issue up to 10,000,000 shares of preferred stock, par value $0.001 per share. As part of the Company’s July 2018 underwritten public offering, 2,220 shares were designated as Series A Convertible Preferred Stock and issued at a price of $12,500 per share. Each share of Series A Convertible Preferred Stock is convertible into 1,000 shares of the Company’s common stock at any time at the option of the holder, provided that the holder will be prohibited from converting the Series A Convertible Preferred Stock into shares of common stock if, as a result of such conversion, the holder, together with its affiliates, would own more than 9.99% of the total number of shares of the Company’s common stock then issued and outstanding. In the event of the Company’s liquidation, dissolution, or winding up, holders of Series A Convertible Preferred Stock will receive a payment equal to $0.001 per share of Series A Convertible Preferred Stock, plus an additional amount equal to any dividends declared but unpaid on such shares, any of our securities that by their terms are junior to the Series A Preferred Stock Series B Convertible Preferred Shares On November 15, 2018, the Company and Biotechnology Value Fund, L.P., Biotechnology Value Fund II, L.P., Biotechnology Value Trading Fund OS, L.P. and MSI BVF SPV LLC (collectively, “BVF”) entered into an Exchange Agreement (the “Exchange Agreement”) pursuant to which BVF agreed to exchange (the “Exchange”) an aggregate of 1,000,000 shares of the Company’s common stock, par value $0.001, owned by BVF for an aggregate of 1,000 shares of the Company’s newly designated Series B Convertible Preferred Stock, par value $0.001 per share. On November 16, 2018, as part of this exchange, 1,000 shares of the Company’s authorized and unissued preferred stock were designated as Series B Convertible Preferred Stock and issued at a price of $7,950 per share. The Series B Preferred Stock has substantially the same terms as the Company’s Series A Convertible Preferred Stock. Each share of Series B Preferred Stock is convertible into 1,000 shares of Common Stock at any time at the option of the holder, provided that the holder will be prohibited from converting the Series B Preferred Stock into shares of Common Stock if, as a result of such conversion, the holder, together with its affiliates, would own more than 9.99% of the total number of shares of Common Stock then issued and outstanding, subject to certain exceptions. In the event of the Company’s liquidation, dissolution, or winding up, holders of Series B Preferred Stock will receive a payment equal to $0.001 per share of Series B Preferred Stock before any proceeds are distributed to the holders of Common Stock and equal to any distributions to the holders of the Series A Convertible Preferred Stock. The Series B Convertible Preferred Stock does not have any mandatory redemption rights or other redemption rights that would be outside of the Company’s control. As such, the Company has classified the Series B Convertible Preferred Stock within permanent equity in its consolidated balance sheet. Redeemable Convertible Preferred Shares Prior to the Reorganization (see Note 1), the operating agreement of Spero Therapeutics, LLC, as amended and restated, provided for the issuance of Junior preferred units, Class A preferred units, Class B preferred units and bridge units, but did not specify an authorized number of each for issuance. Subsequent to the Company’s Reorganization on June 30, 2017, the Company’s amended and restated certificate of incorporation authorized the issuance of 43,297,267 shares of preferred stock, par value $0.001 per share, and holders of outstanding preferred units of Spero Therapeutics, LLC exchanged their units for preferred stock of Spero Therapeutics, Inc. on a one-for-one basis. The rights and preferences of each class of stock were the same both before and after the Reorganization. On October 20, 2017, the Company effected a one-for-6.0774 reverse stock split of its issued and outstanding shares of common stock and a proportional adjustment to the existing conversion rations for each series or the Company’s Preferred Stock. Upon the closing of the Company’s IPO in November 2017, all of the then outstanding convertible preferred shares automatically converted into shares of common stock. 2015 Bridge Units In January 2015, the Company issued and sold 8,000 bridge units to existing investors at a price of $1,000 per unit for gross proceeds of $8.0 million (the “2015 bridge units”). The bridge units did not have any stated rate of return and were automatically convertible into the same type of units issuable upon a qualified financing at a discount of either 20.0% or 25.0% to the per unit price paid by investors in a qualified financing, depending on the timing of such financing. The Company classified this contingent prepayment option as a derivative liability on its consolidated balance sheet on the date of issuance (see Note 3), and the fair value of contingent prepayment option on the date of issuance of $2.3 million was recorded as both a derivative liability and as a reduction to the carrying value of the bridge units. The option was settled in June 2015 upon the issuance of Class A preferred units, as discussed below. Class A Preferred Unit Financing In June 2015, the Company issued and sold 1,923,076 Class A preferred units at a price of $3.90 per unit for proceeds of $7.3 million, net of issuance costs of $0.2 million. The sale of Class A preferred units met the definition of a qualified financing under the 2015 bridge unit agreements. As a condition to the June 2015 Class A preferred unit financing, the Company and the holders of the 2015 bridge units agreed to reduce the previously agreed-upon discount to the per unit conversion price from 20% to 10% of the price to be paid for the sale of Class A preferred units of $3.90 per unit. Accordingly, the Company issued 2,279,202 Class A preferred units upon the conversion of the 2015 bridge units in the amount of $8.0 million, at a conversion price of $3.51 per unit. The conversion was accounted for as an extinguishment for accounting purposes. Accordingly, the Company recorded the Class A preferred units issued upon conversion of the 2015 bridge units at their aggregate fair value of $8.9 million and recorded a corresponding adjustment to extinguish the then-current carrying value of the 2015 bridge units of $8.0 million and the then-current fair value of the derivative liability related to the contingent prepayment option associated with the 2015 bridge units of $0.9 million (see Note 3). There was no gain or loss recognized upon the extinguishment. The Class A preferred unit financing included a provision for the issuance of an additional 3,295,455 Class A preferred units at a price of $4.40 per unit in exchange for gross proceeds of $14.5 million in the event the Company achieved a regulatory milestone. The Company classified this tranche right as a derivative liability on its consolidated balance sheet on the date of issuance, and the fair value of tranche right on the date of issuance of $2.4 million was recorded as both a derivative liability and as a reduction to the carrying value of the Class A preferred units. Upon issuance of the Class B preferred units in February 2016, the tranche right was cancelled (see Note 3). Class B Preferred Unit Financing In February 2016, the Company issued and sold 5,909,089 Class B preferred units at a price of $4.40 per unit for proceeds of $25.9 million, net of issuance costs of $0.1 million. The Class B preferred unit financing included a provision for the issuance of an additional 1,609,846 Class B preferred units at a price of $5.28 per unit in exchange for gross proceeds of $8.5 million in the event the Company achieved a regulatory milestone. The Company classified this tranche right as a derivative liability on its consolidated balance sheet on the date of issuance, and the fair value of the tranche right on the date of issuance of $0.9 million was recorded as both a derivative liability and as a reduction to the carrying value of the Class B preferred units. 2016 Bridge Units The regulatory milestone related to the Class B tranche right was achieved in the fourth quarter of 2016; however, the Company and the holders of the Class B preferred units agreed to replace the second closing of Class B preferred units with the issuance of bridge units that would be convertible in the next qualified financing at a 10% discount. Accordingly, in December 2016, the Company issued and sold 8,500 bridge units to existing investors at a price of $1,000 per unit for gross proceeds of $8.5 million (the “2016 bridge units”). Upon issuance of the 2016 bridge units, the fair value of the derivative liability associated with the Class B tranche right of $0.3 million was settled, resulting in a decrease to the carrying value of the derivative liability and an increase to the carrying value of the 2016 bridge units (see Note 3). The bridge units did not provide for any stated rate of return and were automatically convertible into the same type of units issuable upon a qualified financing at a 10% discount to the per unit price paid by investors in a qualified financing. The Company classified this contingent prepayment option as a derivative liability on its consolidated balance sheet on the date of issuance, and the fair value of the contingent prepayment option on the date of issuance of $0.9 million was recorded as both a derivative liability and as a reduction to the carrying value of the bridge units. Class C Preferred Unit Financing In March 2017, the Company issued and sold 24,326,470 Class C preferred units at a price of $1.7749 per unit for proceeds of $43.0 million, net of issuance costs of $0.2 million. The sale of Class C preferred units met the definition of a qualified financing under the 2016 bridge unit agreements. The Company issued 5,321,112 Class C preferred units upon the conversion of the 2016 bridge units in the amount of $8.5 million, at a conversion price of $1.60 per unit, which represented a discount of 10% to the price per unit paid by other investors in the Class C preferred unit financing. The conversion was accounted for as an extinguishment for accounting purposes. Accordingly, the Company recorded the Class C preferred units issued upon conversion of the 2016 bridge units at their aggregate fair value of $9.4 million and recorded a corresponding adjustment to extinguish the then-current carrying value of the 2016 bridge units of $8.5 million and the then-current fair value of the derivative liability related to the contingent prepayment option associated with the 2016 bridge units of $0.9 million (see Note 3). There was no gain or loss recognized upon the extinguishment. In July 2017 the Company sold to its Chief Financial Officer 61,880 shares of the Company’s Series C preferred stock at a price of $1.7749 per share, for proceeds of $0.1 million. The Junior preferred stock, the Series A preferred stock, the Series B preferred stock and the Series C preferred stock that were outstanding prior to the Company’s IPO in November 2017 are collectively referred to as the “Preferred Stock”. |
Common Stock
Common Stock | 12 Months Ended |
Dec. 31, 2018 | |
Equity [Abstract] | |
Common Stock | 7. Common Stock As of December 31, 2016, the operating agreement of Spero Therapeutics, LLC, as amended and restated, provided for the issuance of common units, but did not specify an authorized number for issuance. Subsequent to the Reorganization on June 30, 2017 (see Note 1), the Company’s amended and restated certificate of incorporation authorized the issuance of 61,917,986 shares of common stock, par value $0.001 per share. Subsequent to the Company’s IPO on November 6, 2017 (See Note 1), the Company’s amended and restated certificate of incorporation authorized the issuance of 60,000,000 shares of common stock, par value $0.001 per share. Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders. Common stockholders are not entitled to receive dividends, unless declared by the board of directors. In 2014, the Company issued and sold restricted common units, which were subject to vesting requirements. In 2016, the Company repurchased 21,116 unvested common units upon forfeiture at the original issuance price of $0.001 per unit. On November 6, 2017, Spero Therapeutics, Inc. completed an IPO of its common stock, and issued and sold 5,500,000 shares of common stock at a public offering price of $14.00 per share, resulting in net proceeds of $71.6 million after deducting underwriting discounts and commissions but before deducting offering costs. On November 14, 2017, Spero Therapeutics, Inc., issued and sold an additional 471,498 shares of its common stock at the IPO price of $14.00 per share pursuant to the underwriters’ partial exercise of their option to purchase additional shares of common stock, resulting in additional net proceeds of $6.1 million after deducting underwriting discounts and commissions. Upon the closing of the IPO in November 2017, the Company’s outstanding convertible preferred shares automatically converted into shares of common stock (see Note 6). On July 17, 2018, the Company completed an underwritten public offering of its common and preferred stock, which resulted in the sale of 3,780,000 shares of common stock at a price of $12.50 per share, and 2,220 shares of Series A Convertible Preferred Stock at a price of $12,500 per share. Each share of Series A Convertible Preferred Stock sold in the offering is convertible into 1,000 shares of the Company’s common stock. The Company received net proceeds from the offering of approximately $70.5 million after deducting underwriting discounts and commissions but before deducting $1.0 million of offering expenses payable by the Company. On December 3, 2018, the Company filed a universal shelf registration statement on Form S-3 (Registration No. 333-228661) with the SEC, which was declared effective on December 11, 2018, and pursuant to which the Company registered for sale up to $200.0 million of any combination of its common stock, preferred stock, debt securities, warrants, rights and/or units from time to time and at prices and on terms that it may determine, including up to $50.0 million of its common stock available for issuance pursuant to an at-the-market offering program sales agreement that it entered into with Cantor Fitzgerald & Co. Under the sales agreement, Cantor may sell shares of the Company’s common stock by any method permitted by law deemed to be an “at the market” offering as defined in Rule 415 of the Securities Act, subject to the terms of the sales agreement. As of December 31, 2018, there have been no sales of the Company’s common stock under the sales agreement. The Company incurred approximately $0.3 million of costs related to the shelf registration statement and at the market offering. These costs have been classified as deferred offering costs on the Company’s balance sheet as of December 31, 2018, and will be charged to additional paid-in-capital on a prorated basis upon the issuance of the associated equity. |
Share-Based Compensation
Share-Based Compensation | 12 Months Ended |
Dec. 31, 2018 | |
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract] | |
Share-Based Compensation | 8. Share-Based Compensation Incentive Stock Units Prior to the Reorganization, the Company’s operating agreement, as amended and restated, provided for the granting of incentive units to officers, directors, employees, consultants and advisors. Under the terms of the incentive unit grant agreements, such incentive units were subject to a vesting schedule, with 25% of the incentive units vesting following one year of continued employment or service and the balance vesting in equal monthly installments for 36 months beginning on the one-year anniversary of the holder’s employment or service with the Company. Holders of incentive units were entitled to receive distributions in proportion to their ownership percent interest, when and if distributed, that were in excess of the strike price of the award set by the board of directors on the date of grant. The Company determined that the underlying terms of the incentive units and the intended purpose of the awards were more akin to an equity-based compensation award than a performance bonus or profit-sharing arrangement and, therefore, the incentive units were equity-classified awards. The total number of incentive units that could have been issued under the Company’s operating agreement was 573,156 as of December 31, 2016, of which 159,890 units remained available for future issuance as of December 31, 2016. Upon the Reorganization on June 30, 2017 (see Note 1), the Company could no longer issue incentive units. In addition, in June 2017, in connection with the Reorganization, the Company cancelled the then-outstanding 402,857 incentive units. As of December 31, 2017, all of the incentive units were cancelled; however, the Company will continue to recognize compensation costs related to these awards (see below). 2017 Stock Incentive Plan On June 28, 2017, the Company’s stockholders approved the 2017 Stock Incentive Plan (the “2017 Plan”). The 2017 Plan provides for the grant of incentive stock options, nonstatutory stock options, stock grants and stock-based awards. The 2017 Plan is administered by the board of directors, or at the discretion of the board of directors, by a committee of the board. The exercise prices, vesting and other restrictions are determined at the discretion of the board of directors, or their committee if so delegated, except that the exercise price per share of stock options may not be less than 100% of the fair market value of the share of common stock on the date of grant and the term of stock option may not be greater than ten years. The number of shares initially reserved for issuance under the 2017 Plan was 1,785,416 shares of common stock. The shares of common stock underlying any awards that are forfeited, cancelled, repurchased or are otherwise terminated by the Company under the 2017 Plan will be added back to the shares of common stock available for issuance under the 2017 Plan. In July 2017, the Company additionally granted options for the purchase of 1,154,989 shares of common stock at an exercise price of $5.90 per share under the 2017 Plan. The options vest over four years and the fair value of these option grants was $3.96 per share. In July 2017, previous holders of the cancelled incentive units who were still employed by the Company at the time of the Reorganization received stock options under the 2017 Stock Incentive Plan (described below). Such stock options were granted for the same number of shares of common stock as the number of incentive units cancelled, and the stock options were granted on the same vesting terms as the incentive units. All such stock options have an exercise price of $5.90 per share. The Company accounted for the cancellation of the incentive units and the issuance of new awards as a modification of the awards for accounting purposes in the three months ended September 30, 2017. Unrecognized compensation expense related to the original award is being recognized over the remaining service period of the modified award. The incremental fair value of the replacement options, based on the positive difference between the fair value of the modified award and the fair value of the original award immediately before it was modified was not material. On October 18, 2017, the Company’s stockholders approved an amendment to the 2017 Plan, which became effective upon the completion of the Company’s IPO, to increase the total number of shares reserved for issuance under the 2017 Plan from 1,785,416 to 2,696,401. Additionally, the number of shares of common stock that may be issued under the 2017 Plan will automatically increase on each January 1, beginning with the fiscal year ending December 31, 2019 and continuing for each fiscal year until, and including, the fiscal year ending December 31, 2027, equal to the lowest of (i) 607,324 shares of common stock, (ii) 4% of the outstanding shares of common stock on such date and (iii) an amount determined by the Company’s board of directors or compensation committee. As of December 31, 2018, there were 341,811 shares remaining available to be issued under the 2017 Plan. Incentive Unit and Stock Option Valuation The fair value of each incentive unit award and stock options are estimated using the Black-Scholes option-pricing model. The Company does not have sufficient company-specific historical and implied volatility information and it therefore estimates its expected share volatility based on the historical volatility of a set of publicly traded peer companies. The Company expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded share price. The Company has estimated the expected term of the Company’s incentive units utilizing the “simplified” method for awards that qualify as “plain-vanilla.” The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future. The assumptions that the Company used in the Black-Scholes option-pricing model to determine the fair value of incentive unit and stock option awards granted to employees and directors were as follows, presented on a weighted average basis: Year Ended December 31, 2018 2017 2016 Risk-free interest rate 2.7 % 2.0 % 1.3 % Expected term (in years) 6.3 6.1 6.3 Expected volatility 74.1 % 77.1 % 76.5 % Expected dividend yield 0.0 % 0.0 % 0.0 % The following table summarizes stock option activity during 2018: Number of Shares Weighted Average Exercise Price Weighted Average Contractual Term Aggregate Intrinsic Value (in years) (in thousands) Outstanding as of December 31, 2017 2,011,296 $ 7.24 9.38 $ 9,074 Granted 503,730 11.30 Exercised (56,780 ) 5.90 Forfeited (160,436 ) 9.13 Cancelled — — Outstanding as of December 31, 2018 2,297,810 $ 8.03 8.77 $ 354 Outstanding as of December 31, 2018 - vested and expected to vest 2,294,629 $ 8.03 8.62 $ 354 Exercisable at December 31, 2018 845,851 $ 6.69 8.57 $ 183 The weighted average grant-date fair value of stock options granted during the year ended December 31, 2018 was $7.63 per share. The weighted average grant-date fair value of awards granted during the years ended December 31, 2017 and 2016 was $4.72 per share and $3.40 per unit, respectively. The aggregate intrinsic value of stock options exercised during the year ended December 31, 2018 was approximately $0.3 million. There were no stock options exercised during the years ended December 31, 2017 and 2016. The Company satisfies stock option exercises with newly issued shares of its common stock. As of December 31, 2018, total unrecognized compensation cost related to unvested stock option grants was approximately $7.9 million. This amount is expected to be recognized over a weighted average period of approximately 2.7 years. The Company recorded share-based compensation expense, for both incentive units and stock options in the following expense categories of its consolidated statements of operations and comprehensive loss (in thousands): Year Ended December 31, 2018 2017 2016 Research and development expenses $ 1,072 $ 371 $ 66 General and administrative expenses 1,677 1,056 114 Total $ 2,749 $ 1,427 $ 180 |
Non-Controlling Interests
Non-Controlling Interests | 12 Months Ended |
Dec. 31, 2018 | |
Noncontrolling Interest [Abstract] | |
Non-Controlling Interests | 9. Non-Controlling Interests Spero Potentiator In February 2015, the Company’s wholly owned subsidiary, Spero Potentiator, issued 996 shares of its common stock with an aggregate fair value of $1.1 million to Northern in exchange for an exclusive license to develop and commercialize certain licensed compounds and licensed products. The Company recognized research and development expense of $1.1 million upon acquisition of the license and recorded a non-controlling interest in Spero Potentiator in a corresponding amount. In connection with the acquisition of the license, Northern obtained anti-dilution rights to maintain its 49.9% ownership percentage in Spero Potentiator at no additional cost to Northern in the event that Spero Potentiator completed subsequent equity financings, subject to a maximum amount of such financings. The maximum amount of gross proceeds from equity financings subject to the anti-dilution rights was $5.0 million through the date the Company filed an investigational new drug application (“IND”) related to the licensed technology. Subsequent to the filing of an IND, the maximum amount of gross proceeds from equity financings subject to the anti-dilution rights was $6.5 million. The Company accounted for the anti-dilution rights as a derivative liability on its consolidated balance sheet (see Note 3). The fair value of the derivative liability associated with the anti-dilution rights upon issuance in February 2015 of $2.4 million was recorded as research and development expenses as it was deemed to represent additional consideration for the license. In November 2015, Northern was issued an additional 2,736 common shares of Spero Potentiator for no additional cost as a result of the anti-dilution rights. The Company valued these shares at $1.5 million and recorded the amount as an increase in the non-controlling interest and a reduction in the carrying value of the derivative liability. In January and August 2016, Northern was issued an additional 2,160 common shares of Spero Potentiator for no additional cost. The Company valued these shares at $1.0 million and recorded the amount as an increase in the non-controlling interest and a reduction of the derivative liability. At that time, the anti-dilution rights issued to Northern were fully settled as Northern had received the maximum number of shares it was entitled to under the anti-dilution rights (See Note 3). In June 2017, the Company repurchased all of the shares of Spero Potentiator held by Northern in exchange for a cash payment of $1.0 million and contingent consideration of $0.1 million. As a condition of the repurchase of the shares from Northern, the Company amended the license agreement with Northern such that the Company will be obligated to make milestone payments of up to $7.0 million upon the achievement of specified clinical, commercial and other milestones, including a payment of $2.5 million upon the closing of an IPO, which occurred and was paid in November 2017. As a result of this transaction, during the six months ended June 30, 2017, the Company reclassified the balance of the non-controlling interest of $6.4 million as of the date of the transaction to accumulated deficit as an increase to that account. Additionally, the cash payment of $1.0 million was recorded as an increase to accumulated deficit. The Company will record the contingent payments as research and development expense when it becomes probable that the payments will be due. For periods subsequent to the acquisition, the Company no longer reports a non-controlling interest related to Spero Potentiator. Spero Europe In January 2016, the Company entered into an agreement with Promiliad whereby Promiliad granted to Spero Europe certain know-how and a sublicense to research, develop, manufacture and sell certain compounds. In exchange for the know-how and sublicense, Spero Europe provided Promiliad with a 5% equity ownership interest in Spero Europe, with a fair value of $0.1 million. In addition, Spero Europe agreed to make payments to Promiliad upon the achievement of future regulatory and commercial milestones of $4.1 million and to pay to Promiliad royalties of a mid single-digit percentage on net sales of licensed products under the agreement. Spero had the right to terminate the agreement with thirty days’ notice. The Company recognized research and development expense of $0.1 million upon the acquisition of the license and recorded a non-controlling interest in Spero Europe in a corresponding amount. In connection with the acquisition of the license, Promiliad obtained anti-dilution rights to maintain their 5% equity ownership in Spero Europe at no additional cost to Promiliad in the event that Spero Europe completed subsequent funding events, subject to a maximum amount of such funding of $5.0 million. The Company accounted for the anti-dilution rights as a derivative liability on its consolidated balance sheet (see Note 3). The fair value of the derivative liability associated with the anti-dilution rights upon issuance in January 2016 of $0.2 million was recorded as research and development expenses as it was deemed to represent additional consideration for the license. In May 2017, the Company repurchased all of the shares of Spero Europe from Promiliad in exchange for the return of the license. As a result of the transaction, the Company reclassified the balance of the non-controlling interest in Spero Europe of less than $0.1 million as of the date of the transaction to accumulated deficit as an increase to that account. For periods subsequent to the repurchase, the Company no longer reports a non-controlling interest related to Spero Europe. Spero Gyrase In March 2016, the Company entered into an agreement with Aviragen and its affiliates in order to acquire certain intellectual property and know-how related to certain compounds. In connection with the transaction, the Company established Spero Gyrase, a Delaware corporation, and issued to Aviragen 200 common shares of Spero Gyrase with a fair value of $1.1 million, which represented a 20% equity ownership interest in Spero Gyrase. In addition, Spero Gyrase agreed to make future milestone and royalty payments in exchange for the intellectual property. The Company accounted for the acquisition of technology as an asset acquisition because it did not meet the definition of a business. The Company recorded the acquired technology as research and development expense in the consolidated statement of operations and comprehensive loss in the amount of $1.1 million, because the acquired technology had not reached commercial feasibility and had no alternative future use, and recorded a non-controlling interest in Spero Gyrase in a corresponding amount. In connection with the agreement, Aviragen obtained anti-dilution rights to maintain their 20% equity ownership of Spero Gyrase at no additional cost to Aviragen in the event that Spero Gyrase completed subsequent funding events, subject to a maximum amount of such funding of $8.0 million. The Company accounted for the anti-dilution rights as a derivative liability on its consolidated balance sheet (see Note 3). The fair value of the derivative liability associated with the anti-dilution rights upon issuance in March 2016 of $1.6 million was recorded as research and development expenses as it was deemed to represent additional consideration for the license. Spero Cantab In June 2016, the Company entered into a stock purchase agreement and related agreements (the “Cantab Agreements”) with Pro Bono Bio PLC, a corporation organized under the laws of England, and certain of its affiliates, including PBB Distributions Limited (“PBB”), Cantab Anti-Infectives Ltd. (“CAI”) and New Pharma License Holdings Limited (“NPLH”) in order to acquire NPLH and its intellectual property rights and assets relating to the Company’s Potentiator Platform. Under the Cantab Agreements, CAI agreed to submit a request to NIAID to novate the then CAI-held NIAID contract to the Company, which was finalized in December 2017. The NIAID contract provides for development funding of up to $6.3 million over a base and three option periods. To date, funding for the base period and the first two option periods totaling $5.7 million have been committed. The Company shall pay PBB a percentage of funds received from NIAID up to a maximum of $1.3 million, of which $0.3 million was paid upfront to PBB as part of this agreement, as described below. During the year ended December 31, 2018, the Company recorded $0.4 million of expense related to amounts payable to PBB under this agreement. Consideration under Cantab Agreements consisted of: (i) 125 shares of Spero Cantab, the Company’s subsidiary, which represented a 12.5% ownership interest in Spero Cantab, and anti-dilution rights (as described below) issued to PBB, with a combined fair value of $1.6 million, (ii) upfront consideration of $0.3 million (to be credited against future payments payable to CAI), (iii) contingent milestone payments due upon the achievement of certain clinical, regulatory and commercial milestones (see Note 13), (iv) royalty payments of low single-digit percentages based on net sales of products from the licensed technology, and (v) a specified portion of funding payments made by NIAID. The Company accounted for the acquisition of NPLH as an asset acquisition because NPLH did not meet the definition of a business. The Company recognized research and development expense of $1.6 million upon the acquisition of NPLH because the acquired technology had not reached commercial feasibility and had no alternative future use. Upon the issuance of the shares and anti-dilution rights, the Company recorded a non-controlling interest in Spero Cantab of $1.6 million. The $0.3 million payment was recognized as research and development expenses as the services were performed by CAI. The Company records the contingent payments outlined in (iii), (iv) and (v) as research and development expense when it becomes probable that the payments will be due. Novation of the NIAID contract to Spero was finalized in December 2017. Prior to the contract novation, CAI performed research and development services at the Company’s direction and applied for reimbursement from NIAID. The Company paid CAI for such research and development services at an agreed-upon rate which took into consideration costs incurred by CAI, amounts reimbursed to CAI by NIAID and the portion of the NIAID reimbursement the Company paid to CAI. In connection with the Cantab Agreements, PBB obtained anti-dilution rights to maintain a certain equity ownership, ranging from 5% to 12.5%, of Spero Cantab at no additional cost to PBB in the event that Spero Cantab completed subsequent funding events, subject to maximum amount of such funding of $8.0 million. These anti-dilution rights represent a conditional obligation to issue a variable number of shares but are not freestanding and, therefore, do not require bifurcation for accounting purposes from the 125 shares issued. In July 2017, the Company repurchased all of the outstanding shares of Spero Cantab owned by PBB in exchange for a cash payment of $0.2 million and an amendment to the licensing agreement to increase the first two contingent milestone payments by a total of $0.1 million. For periods subsequent to the repurchase, the Company no longer reports a non-controlling interest related to Spero Cantab. As of December 31, 2018 and 2017, the Company’s only remaining non-controlling interest relates to Spero Gyrase, Inc., which totaled $0.4 million. |
Income Taxes
Income Taxes | 12 Months Ended |
Dec. 31, 2018 | |
Income Tax Disclosure [Abstract] | |
Income Taxes | 10. Income Taxes Prior to the Reorganization (see Note 1), the Company’s former parent company, Spero Therapeutics, LLC, was treated as a partnership for federal income tax purposes and, therefore, its owners, and not itself, were subject to U.S. federal or state income taxation on the income of Spero Therapeutics, LLC. Prior to the Reorganization, all of Spero Therapeutics, LLC’s directly held subsidiaries (including Spero Therapeutics, Inc.) were treated as corporations for U.S. federal income tax purposes and were subject to taxation in the United States or in other countries. Upon the Reorganization, Spero Therapeutics, Inc. became the parent company for Spero Therapeutics, LLC’s former subsidiaries and these entities continue to be subject to taxation in the United States or in other countries. In each reporting period, the Company’s tax provision includes the effects of consolidating the results of operations of its subsidiaries. During the years ended December 31, 2018, 2017 and 2016, the Company recorded no income tax benefits for the net operating losses incurred in each year or interim period due to its uncertainty of realizing a benefit from those items. The domestic and foreign components of loss before income taxes were as follows (in thousands): Year Ended December 31, 2018 2017 2016 Domestic $ (33,236 ) $ (38,706 ) $ (27,148 ) Foreign (8,426 ) (1,180 ) (5,493 ) Loss before income taxes $ (41,662 ) $ (39,886 ) $ (32,641 ) A reconciliation of the U.S. federal statutory income tax rate to the Company’s effective income tax rate is as follows: Year Ended December 31, 2018 2017 2016 Federal statutory income tax rate (21.0 ) (34.0 ) (34.0 ) Federal and state research and development tax credit (2.6 ) (3.3 ) (1.7 ) State taxes, net of federal benefit (5.4 ) (5.3 ) (4.4 ) Foreign rate differential 1.9 0.1 2.3 Nondeductible items 1.2 (0.1 ) 4.8 Effect of US tax reform — 23.8 — Increase in deferred tax asset valuation allowance 25.9 18.8 33.0 Effective income tax rate — — — Net deferred tax assets as of December 31, 2018 and 2017 consisted of the following (in thousands): December 31, 2018 2017 Net operating loss carryforwards $ 29,025 $ 21,754 Research and development tax credit carryforwards 3,385 2,022 Other 1,731 743 Total deferred tax assets 34,141 24,519 Valuation allowance (34,141 ) (24,519 ) Net deferred tax assets $ — $ — As of December 31, 2018, the Company had U.S. federal and state net operating loss carryforwards of $100.4 million and $100.3 million, respectively, which may be available to offset future income tax liabilities and begin to expire in 2033. In addition, as of December 31, 2018, the Company had foreign net operating loss carryforwards of $11.7 million, which may be available to offset future income tax liabilities and do not expire. As of December 31, 2018, the Company also had federal and state research and development tax credit carryforwards of $2.6 million and $0.8 million, respectively, which may be available to offset future income tax liabilities and begin to expire in 2033 and 2028, respectively. Utilization of the U.S. net operating loss carryforwards and research and development tax credit carryforwards may be subject to a substantial annual limitation under Section 382 of the Internal Revenue Code of 1986, and corresponding provisions of state law, due to ownership changes that have occurred previously or that could occur in the future. These ownership changes may limit the amount of carryforwards that can be utilized annually to offset future taxable income. In general, an ownership change, as defined by Section 382, results from transactions increasing the ownership of certain stockholders or public groups in the stock of a corporation by more than 50% over a three-year period. The Company has not conducted a study to assess whether a change of control has occurred or whether there have been multiple changes of control since inception due to the significant complexity and cost associated with such a study. If the Company has experienced a change of control, as defined by Section 382, at any time since inception, utilization of the net operating loss carryforwards or research and development tax credit carryforwards would be subject to an annual limitation under Section 382, which is determined by first multiplying the value of the Company’s stock at the time of the ownership change by the applicable long-term tax-exempt rate, and then could be subject to additional adjustments, as required. Any limitation may result in expiration of a portion of the net operating loss carryforwards or research and development tax credit carryforwards before utilization. Further, until a study is completed by the Company and any limitation is known, no amounts are being presented as an uncertain tax position. The Company has evaluated the positive and negative evidence bearing upon its ability to realize the deferred tax assets. Management has considered the Company’s history of cumulative net losses incurred since inception and its lack of commercialization of any products or generation of any revenue from product sales since inception and has concluded that it is more likely than not that the Company will not realize the benefits of the deferred tax assets. Accordingly, a full valuation allowance has been established against the deferred tax assets as of December 31, 2018 and 2017. Management reevaluates the positive and negative evidence at each reporting period. Changes in the valuation allowance for deferred tax assets during the years ended December 31, 2018 and 2017 related primarily to the increase in net operating loss carryforwards and research and development tax credit carryforwards, and were as follows (in thousands): December 31, 2018 2017 Valuation allowance as of beginning of year $ (24,519 ) $ (17,152 ) Decreases recorded as benefit to income tax provision — — Increases recorded to income tax provision (9,622 ) (7,367 ) Valuation allowance as of end of year $ (34,141 ) $ (24,519 ) The Company has not recorded any amounts for unrecognized tax benefits as of December 31, 2018 or 2017. The Company’s policy is to record interest and penalties related to income taxes as part of its income tax provision. As of December 31, 2018 or 2017, the Company had no accrued interest or penalties related to uncertain tax positions and no amounts had been recognized in the Company’s statement of operations and comprehensive loss. Prior to the Reorganization, the Company filed separate U.S. income tax returns return for each of its subsidiaries. As a result of the Reorganization, the Company will file U.S. income tax returns as a U.S. consolidated group. In Massachusetts, the Company files income tax returns as a combined group except for its Massachusetts Securities Corporation subsidiary, which is a separate income tax filing. The statute of limitations for assessment by the Internal Revenue Service and Massachusetts tax authorities remains open for all years since 2015. To the extent the Company has tax attribute carryforwards, the tax years in which the attribute was generated may still be adjusted upon examination by the Internal Revenue Service or state authorities to the extent utilized in a future period. No federal or state tax audits are currently in process. On December 22, 2017, President Trump signed into law the “the Tax Cuts and Jobs Act” ( “TCJA”). The TCJA includes a number of changes to existing tax law, including, among other things, a permanent reduction in the federal corporate income tax rate from a top marginal rate of 34% down to a flat rate of 21%, effective as of January 1, 2018, as well as limitation of the deduction for net operating losses to 80% of annual taxable income and elimination of net operating loss carrybacks, in each case, for losses arising in taxable years beginning after December 31, 2017 (though any such net operating losses may be carried forward indefinitely). As a result of the TCJA, the Company was required to revalue deferred tax assets and liabilities existing as of December 31, 2017 from the 34% federal rate in effect through the end of 2017, to the new 21%. This revaluation resulted in a reduction to the Company’s deferred tax asset of $9.4 million. This amount was offset by a corresponding reduction in the valuation allowance. There was no impact to the Company’s consolidated statements of operations and comprehensive loss as a result of the reduction in rates. The other provisions of the TCJA did not have a material impact on the Company’s consolidated financial statements. |
Commitments and Contingencies
Commitments and Contingencies | 12 Months Ended |
Dec. 31, 2018 | |
Commitments And Contingencies Disclosure [Abstract] | |
Commitments and Contingencies | 11. Commitments and Contingencies License Agreements The Company has entered into license agreements with various parties under which it is obligated to make contingent and non-contingent payments (see Note 13). Operating Leases In August 2015, the Company entered into an operating lease agreement for office space that commenced in January 2016 and expires in December 2020. The lease requires annual payments of $0.4 million over the five-year term. The lease provides for a renewal option to extend the lease for an additional five years. Under the terms of the lease, the Company provided a security deposit of $0.2 million to the landlord, which is included in long-term assets in the accompanying consolidated balance sheets. The lease includes annual rent escalations as well as tenant incentives in the amount of $0.7 million, of which $0.3 million is reimbursed to the landlord over the term of the lease. In July 2016, the Company entered into an agreement to lease laboratory space through November 30, 2019 from a sublessor, which requires annual lease payments of $0.3 million, subject to certain escalations. On January 17, 2018, the Company entered into an amendment (the “Amendment”) to the lease agreement with respect to its corporate headquarters located at 675 Massachusetts Avenue, Cambridge, Massachusetts. The Amendment makes certain changes to the original Lease Agreement, dated August 24, 2015 (the “Original Lease”), by and between the Company and U.S. REIF Central Plaza Massachusetts, LLC (the “Landlord”), including (i) the addition of approximately 7,800 square feet of office space in the same building (the “Expansion Premises”) and (ii) an extension of the expiration date of the Original Lease to seven years following the delivery date of the Expansion Premises (the “Lease Term”), which occurred on December 22, 2018. Under the Amendment, the Company has two consecutive options to extend the Lease Term for an additional period of five years (the “Option Terms”), subject to certain conditions, upon notice to the Landlord. The Amendment provides for annual base rent for the Expansion Premises of approximately $0.5 million in the first year of the Lease Term, which increases on an annual basis to approximately $0.6 million in the final year of the Lease Term, and annual base rent during the Option Terms to be calculated based on the Landlord’s good faith determination of 100% of the fair market rate for such Option Terms. The Company is also obligated to pay the Landlord certain costs, taxes and operating expenses, subject to certain exclusions. The Amendment also includes a provision from the landlord of $0.4 million for leasehold improvements on the Expansion Premises. Rent escalations and tenant incentives for operating leases are included in deferred rent in the consolidated balance sheet, and rent expense is recognized on a straight-line basis over the terms of occupancy. The following table summarizes the future minimum payments due under the operating leases as of December 31, 2018 (in thousands): Year Ending December 31, 2019 $ 1,361 2020 1,054 2021 995 2022 1,107 2023 1,123 2024 1,138 2025 1,108 $ 7,886 Rent expense for the years ended December 31, 2018, 2017 and 2016 was $0.8 million, $0.8 million and $0.4 million, respectively. Indemnification Agreements In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. The Company does not believe that the outcome of any claims under indemnification arrangements will have a material effect on its financial position, results of operations or cash flows, and it has not accrued any liabilities related to such obligations in its consolidated financial statements as of December 31, 2018, 2017 or 2016. Legal Proceedings The Company is not currently party to any material legal proceedings. At each reporting date, the Company evaluates whether or not a potential loss amount or a potential range of loss is probable and reasonably estimable under the provisions of the authoritative guidance that addresses accounting for contingencies. The Company expenses as incurred the costs related to such legal proceedings. |
Government Contracts
Government Contracts | 12 Months Ended |
Dec. 31, 2018 | |
Contractors [Abstract] | |
Government Contracts | 12. Government Contracts BARDA In July 2018, the Company was awarded a contract from BARDA of up to $44.2 million to develop SPR994 for the treatment of complicated urinary tract infections (“cUTIs”) caused by antibiotic resistant Gram-negative bacteria and for assessment against biodefense pathogens. The award commits initial funding of $15.7 million over a three-year base period from July 1, 2018 to June 30, 2021 for cUTI development activities. The balance of the award is subject to BARDA exercising two options. The exercise of the first option would entail funding of $13.6 million and is exercisable by BARDA subject to the Company achieving specified milestones related to, among other things, clinical progress and data. The exercise of the second option would entail funding of $14.9 million and is exercisable by BARDA subject to, among other things, satisfactory progress and results from the biodefense studies described below. As part of an inter-agency collaboration between BARDA and the Defense Threat Reduction Agency (“DTRA”), a series of studies to assess the efficacy of SPR994 in the treatment of infections caused by biodefense threats such as anthrax, plague and melioidosis will be conducted by the U.S. Army Medical Research Institute of Infectious Diseases (“USAMRIID”) under the direction of Spero. Because the FDA requires data from a human pneumonic disease as supportive of use of an antibiotic to treat a biothreat infection, the scope of the BARDA award includes the assessment of SPR994 levels in the lung of healthy volunteers as well as a proof of concept clinical trial in pneumonia patients, an indication for which tebipenem, SPR994's active pharmaceutical ingredient, is currently approved in Japan for pediatric use. The Company recorded $1.4 million of revenue under this agreement, of which $0.3 million was invoiced but unpaid and included in other receivables at December 31, 2018. U.S. Department of Defense In September 2016, the Company was awarded a cooperative agreement with the DoD to further develop anti-infective agents to combat Gram-negative bacteria. The agreement is structured as a single, two-year $1.5 million award. The Company is eligible for the full funding from the DoD, and there are no options to be exercised at a later date. The DoD funding supports next-generation potentiator discovery and screening of SPR741 partners. The Company recognizes revenue under this agreement as qualifying expenses are incurred. During the year ended December 31, 2018, the Company recognized $0.3 million of revenue under this agreement, of which less than $0.1 million was invoiced but unpaid and included in other receivables at December 31, 2018. NIAID In February 2017, the Company was awarded a grant from NIAID to conduct additional preclinical studies of SPR720, the Company’s novel oral bacterial gyrase inhibitor, for the treatment of non-tuberculous mycobacterial infections. The award is structured as a 12-month $0.6 million base period and $0.4 million option period. In February 2018 NIAID exercised the $0.4 million 12-month option period. In January 2019, the period of performance for this award was extended for an additional 12-month period. The Company recognized $0.5 million of revenue in the year ended December 31, 2018 under this agreement, of which less than $0.1 million was invoiced but unpaid and included in other receivables at December 31, 2018. In June 2016, the Company entered into agreements with Pro Bono Bio PLC (“PBB”), a corporation organized under the laws of England, and certain of its affiliates, including PBB Distributions Limited and Cantab Anti-Infectives Limited (“CAI”), in order to acquire certain intellectual property and government funding arrangements relating to SPR206. Under these agreements, CAI agreed to submit a request to NIAID to assign the then CAI-held NIAID contract to Spero, which was finalized in December 2017. The NIAID contract provides for development funding of up to $6.3 million over a base period and three option periods. As of December 31, 2018, funding for the base period and the first two option periods totaling $5.7 million have been committed. Spero shall pay PBB a percentage of funds received from NIAID up to a maximum of $1.3 million, of which $0.3 million was paid upfront to PBB as part of the agreement. The Company recorded $1.3 million of revenue under this agreement during the year ended December 31, 2018, of which less than $0.1 million was invoiced but unpaid and included in other receivables at December 31, 2018. During the year ended December 31, 2018, the Company recorded approximately $0.4 million in expense associated with amounts payable to PBB under this agreement, which has been included within research and development expenses within the consolidated statement of operations and comprehensive loss. CARB-X In April 2017, the Company was awarded a grant from CARB-X, a public-private partnership funded by BARDA within the U.S. Department of Health and Human Services to be used to screen, identify and complete Phase 1 trials with at least one partner compound for SPR741. The award committed to funding of $1.5 million over a 12-month period. On March 12, 2018, CARB-X committed an additional $0.4 million related to the first option for a period from December 1, 2017 to March 31, 2018. There will be no additional options exercised under the CARB-X award. The Company recognized $0.5 million of revenue in the year ended December 31, 2018 under this agreement. There are no amounts receivable under this agreement at December 31, 2018. |
Collaboration and License Agree
Collaboration and License Agreements | 12 Months Ended |
Dec. 31, 2018 | |
Organization Consolidation And Presentation Of Financial Statements [Abstract] | |
Collaboration and License Agreements | 13. Collaboration and License Agreements The Company has certain obligations under license agreements with third parties that include annual maintenance fees and payments that are contingent upon achieving various development, regulatory and commercial milestones. Pursuant to these license agreements, the Company is required to make milestone payments if certain development, regulatory and commercial milestones are achieved, and may have certain additional research funding obligations. Also, pursuant to the terms of each of these license agreements, when and if commercial sales of a product commence, the Company will pay royalties to its licensors on net sales of the respective products. Roche Collaboration Agreements In April 2014, the Company and Roche entered into a research and development services and support agreement (“Research and Development Agreement”) and an option agreement (“Option Agreement”), whereby the Company was required to use its best efforts to research and develop a specified asset, while Roche would provide partial funding as well as participate on a joint steering committee for the development of this asset. As part of these agreements, the Company provided Roche with the option to participate in the Company’s next financing subsequent to April 2014 in an amount up to $2.0 million at 90.0% of the per unit price of the related financing (see Note 3). The subsequent financing occurred in June 2015 and, as Roche elected not to exercise its option, the option expired. As consideration for the agreements, Roche made nonrefundable upfront payments aggregating to $2.0 million in 2014 and paid annual nonrefundable maintenance fees of $1.0 million in 2015. Due to the cooperative nature of the development plans as driven by the joint steering committee and the partial defrayment of development costs, the nonrefundable payments were considered reductions to research and development expense. Upon receipt, the payments the Company received in 2014 and 2015 from Roche were deferred and were recognized as reductions to research and development expense. In June 2016, the Company provided notification to Roche that it intended to terminate its Research and Development Agreement with Roche based on its rights under the agreement, effective August 2016, resulting in a recognition of the remaining deferred advance research and development payments. There was no termination fee required under the agreement. Related to payments received under the concluded collaboration, the Company recognized reductions of research and development expense of $0.9 million for the year ended December 31, 2016. MGH License Agreement In March 2014, the Company entered into a license agreement with The General Hospital Corporation, doing business as Massachusetts General Hospital, (“MGH”) to obtain an exclusive worldwide license to research, develop, manufacture and sell products based on technology related to inhibitors of bacteria quorum sensing and technology pertaining to the methods for identifying compounds for treating, reducing or preventing pathogenic infections. Upon signing of the license agreement, the Company issued to MGH 24,681 common units. The Company also agreed to reimburse MGH for all patent costs related to the exclusive patent for the duration of the agreement. In November 2016, the Company terminated its license agreement with MGH. There were no termination payments required. Ascenion License Agreement In September 2014, the Company entered into a license agreement with Ascenion GmbH (formerly known as Helmholtz Zentrum fur Infektionsforschung GmbH) to obtain an exclusive worldwide license to research, develop, manufacture and sell products based on Ascenion’s PqsR modulator technology. Upon signing of the license agreement, the Company issued to Ascenion 9,625 common units. In November 2016, the Company terminated its license agreement with Ascenion. There were no termination payments required. Aviragen Agreement Under the Company’s agreement with Aviragen (see Note 9) for certain intellectual property and know-how relating to developing a gyrase inhibitor to develop therapies for Gram-negative infections, the Company is obligated to make milestone payments of up to an aggregate of $12.0 million upon the achievement of specified clinical, regulatory and commercial milestones and to pay royalties of low single-digit percentages based on net sales of products the Company acquired under the agreement. Cantab License Agreement Under the Cantab Agreements (see Note 9), the Company is obligated to make milestone payments of up to $5.8 million upon the achievement of specified clinical and regulatory milestones and a payment of £5.0 million ($6.4 million and $6.7 million as of December 31, 2018 and 2017, respectively)) upon the achievement of a specified commercial milestone. In addition, the Company has agreed to pay to PBB royalties, on a product-by-product and country-by-country basis, of a low single-digit percentage based on net sales of products licensed under the agreement. During the year ended December 31, 2018, the Company recorded $0.2 million in research and development expense related to the achievement of regulatory milestones for SPR206. The Cantab Agreements continue indefinitely, with royalty payment obligations thereunder continuing on a product-by-product and country-by-country basis until the later of ten years after the first commercial sale of such product in such country or the expiration in such country of the last to expire valid claim of any of the applicable patents. Vertex License Agreement In May 2016, the Company entered into an agreement with Vertex Pharmaceuticals Incorporated (“Vertex”) whereby Vertex granted the Company certain know-how and a sublicense to research, develop, manufacture and sell products for a proprietary compound, as well as a transfer of materials. In exchange for the know-how, sublicense and materials, Spero paid Vertex an upfront, one-time, nonrefundable, non-creditable fee of $0.5 million, which was recognized as research and development expense. As part of the agreement, the Company is obligated to make future milestone payments of up to $81.1 million upon the achievement of specified clinical, regulatory and commercial milestones and to pay Vertex tiered royalties, on a product-by-product and country-by-country basis, of a mid single-digit to low double-digit percentage based on net sales of products licensed under the agreement. During the year ended December 31, 2018, the Company recorded $0.2 million in research and development expense related to the achievement of regulatory milestones for SPR720. The agreement continues in effect until the expiration of all payment obligations thereunder, with royalty payment obligations continuing on a product-by-product and country-by-country basis until the later of ten years after the first commercial sale of such product in such country or the date of expiration in such country of the last to expire applicable patent. Further, Vertex has the right to terminate the agreement if provided with notification from the Company of intent to cease all development or if no material development or commercialization efforts occur for one year. Meiji License Agreement In June 2017, the Company entered into agreements with Meiji Seika Pharma Co. Ltd. (“Meiji”), a Japanese corporation, whereby Meiji granted to the Company certain know-how and a license to research, develop, manufacture and sell products for a proprietary compound in the licensed territory. In exchange for the know-how and license, the Company paid Meiji an upfront, one-time, nonrefundable, non-creditable fee of $0.6 million, which was recognized as research and development expense. As part of the agreement, the Company is obligated to make milestone payments of up to $3.0 million upon the achievement of specified clinical and regulatory milestones, to pay royalties, on a product-by-product and country-by-country basis, of a low single-digit percentage based on net sales of products licensed under the agreement and to pay Meiji a low double-digit percentage of any sublicense fees received by the Company up to $7.5 million. In October 2017, the Company paid a $1.0 million milestone payment to Meiji upon the enrollment of the first patient in the Company’s Phase 1 clinical trial of SPR994. The payment was recorded as research and development expense in the statement of operations and comprehensive loss for the year ended December 31, 2017. During the three months ended December 31, 2018, the Company paid Meiji $1.6 million related to fixed assets which will be used in manufacturing related activities at Meiji. This equipment has been capitalized as property and equipment in the consolidated balance sheet as of December 31, 2018. The agreement continues in effect until the expiration of all payment obligations thereunder (including royalty payments and licensee revenue) on a product-by-product and country-by-country basis, unless earlier terminated by the parties. Pursuant to the terms of the agreement, in addition to each party’s right to terminate the agreement upon the other party’s material breach (if not cured within a specified period after receipt of notice) or insolvency, the Company also has unilateral termination rights (i) in the event that the Company abandons the development and commercialization of SPR994 for efficacy, safety, legal or business factors, and (ii) under certain circumstances arising out of the head license with a global pharmaceutical company. Northern License Agreement In June 2017, in connection with the repurchase of all of the outstanding shares of Spero Potentiator (see Note 9), the Company amended its license agreement with Northern such that the Company agreed to pay Northern up to $7.0 million upon the achievement of specified clinical, regulatory and other milestones, including a total payment of $2.5 million upon the closing of an initial public offering. In addition, under an exchange agreement the Company entered into with Northern, the Company is obligated to make a payment to Northern of $0.1 million upon the closing of an initial public offering. The agreement has a perpetual term and no express termination rights. Upon the closing of the Company’s IPO in November 2017, the Company paid $2.6 million to Northern in connection with both the license and exchange agreements. This payment was recorded as research and development expense in the Company’s statement of operations and comprehensive loss for the year ended December 31, 2017. |
Australia Research and Developm
Australia Research and Development Tax Incentive | 12 Months Ended |
Dec. 31, 2018 | |
Research And Development [Abstract] | |
Australia Research and Development Tax Incentive | 14. Australia Research and Development Tax Incentive The Australian government has established a research and development tax incentive to encourage industry investment in research and development, which is available to companies incorporated under Australian law that have core research and development activities. In September 2016, the Company established Spero Potentiator Australia Pty Limited to carry out certain research and development activities. As this subsidiary meets the eligibility requirements of the Australian tax law, it is eligible to receive a 43.5% tax incentive for qualified research and development activities. For the years ended December 31, 2018, 2017 and 2016, $1.2 million, $1.8 million and $0.1 million, respectively, was recorded as a reduction to research and development expenses in the consolidated statements of operations and comprehensive loss associated with this tax incentive, representing 43.5% of the Company’s qualified research and development spending in Australia. The refund is denominated in Australian dollars and, therefore, the receivable is re-measured to U.S. dollars as of each reporting date. As of December 31, 2018 and 2017, the Company’s tax incentive receivables from the Australian government totaled $1.1 million and $1.9 million, respectively. |
Net Loss per Share
Net Loss per Share | 12 Months Ended |
Dec. 31, 2018 | |
Earnings Per Share [Abstract] | |
Net Loss per Share | 15. Net Loss per Share Basic and diluted net loss per share attributable to common stockholders of Spero Therapeutics, Inc. was calculated as follows (in thousands, except share and per share amounts): Year Ended December 31, 2018 2017 2016 Numerator: Net loss $ (41,662 ) $ (39,886 ) $ (32,641 ) Less: Net loss attributable to non-controlling interests — (1,143 ) (7,150 ) Plus: Cumulative dividends on redeemable convertible preferred shares — (6,146 ) (3,441 ) Plus: Accretion of bridge units and redeemable convertible preferred shares to redemption value — (1,208 ) (996 ) Net loss attributable to common stockholders of Spero Therapeutics, Inc. $ (41,662 ) $ (46,097 ) $ (29,928 ) Denominator: Weighted average common shares outstanding, basic and diluted 16,001,832 2,586,865 312,169 Net loss per share attributable to common stockholders of Spero Therapeutics, Inc., basic and diluted $ (2.60 ) $ (17.82 ) $ (95.87 ) The Company excluded potentially dilutive securities from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders of Spero Therapeutics, Inc. is the same. The Company excluded the following potential common shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect: December 31, 2018 2017 2016 Options to purchase common stock 2,297,810 2,011,296 — Series A convertible preferred stock (as converted to common shares) 2,220,000 — — Series B convertible preferred stock (as converted to common shares) 1,000,000 — — Redeemable convertible preferred shares (as converted to common shares) — — 2,229,518 Incentive units — — 413,266 5,517,810 2,011,296 2,642,784 |
Retirement Plan
Retirement Plan | 12 Months Ended |
Dec. 31, 2018 | |
Defined Benefit Pension Plans And Defined Benefit Postretirement Plans Disclosure [Abstract] | |
Retirement Plan | 16. Retirement Plan The Company has a defined-contribution plan under Section 401(k) of the Internal Revenue Code (the “401(k) Plan”). The 401(k) Plan covers all employees who meet defined minimum age and service requirements, and allows participants to defer a portion of their annual compensation on a pre-tax basis. As currently established, the Company is not required to make and to date has not made any contributions to the 401(k) Plan. The Company did not make any matching contributions during the years ended December 31, 2018, 2017 and 2016. |
Quarterly Financial Data
Quarterly Financial Data | 12 Months Ended |
Dec. 31, 2018 | |
Quarterly Financial Information Disclosure [Abstract] | |
Quarterly Financial Information | 17. Quarterly Financial Data (unaudited) March 31, 2018 June 30, 2018 September 30, 2018 December 31, 2018 Grant revenue $ 1,153 $ 463 $ 658 $ 1,692 Operating expenses 11,969 10,434 11,593 12,776 Net loss (10,644 ) (9,956 ) (10,463 ) (10,599 ) Net loss per share attributable to common shareholders per share, basic and diluted $ (0.74 ) $ (0.69 ) $ (0.60 ) $ (0.60 ) Weighted average shares outstanding, basic and diluted: 14,369,182 14,376,529 17,471,462 17,736,996 March 31, 2017 June 30, 2017 September 30, 2017 December 31, 2017 Grant revenue $ 140 $ 249 $ 597 $ 993 Operating expenses 7,739 10,414 10,563 14,993 Net loss (6,411 ) (9,763 ) (9,844 ) (13,868 ) Net loss attributable to Spero Therapeutics, Inc. (5,876 ) (9,169 ) (9,836 ) (13,862 ) Net loss attributable to common shareholders of Spero Therapeutics, Inc. (7,130 ) (12,121 ) (12,076 ) (14,770 ) Net loss per share attributable to common shareholders per share, basic and diluted $ (21.60 ) $ (36.21 ) $ (36.02 ) $ (1.59 ) Weighted average shares outstanding, basic and diluted: 330,075 334,788 335,285 9,273,783 |
Subsequent Events
Subsequent Events | 12 Months Ended |
Dec. 31, 2018 | |
Subsequent Events [Abstract] | |
Subsequent Events | 18. Subsequent Events On January 4, 2019, the Company, through its wholly owned subsidiary New Pharma License Holdings Limited (“NPLH”), entered into a license agreement (the “License Agreement”) with Everest Medicines II Limited (“Everest”), which License Agreement also includes an option granted by Spero’s wholly owned subsidiary Spero Potentiator, Inc. Under the terms of the License Agreement, the Company granted Everest an exclusive license to develop, manufacture and commercialize Spero’s product candidate SPR206 or products that contain the Compound (a “Licensed Product”) in Greater China (which includes Mainland China, Hong Kong and Macau), South Korea and certain Southeast Asian countries (collectively, the “Territory”). The Company retains development, manufacturing and commercialization rights with respect to the Compound and Licensed Products in the rest of the world and also retains the right to develop or manufacture the Compound and Licensed Products in the Territory for use outside the Territory. In addition to the license grant to SPR206, the Company also granted Everest a 12-month exclusive option to negotiate with the Company for an exclusive license to develop, manufacture and commercialize Spero’s product candidate SPR741 in the Territory. Under the terms of the License Agreement, the Company received an upfront payment of $3.0 million. The Company may also receive up to an additional $59.5 million in milestone payments upon Everest’s achievement of certain developmental, regulatory and sales milestone events related to SPR206, which achievement cannot be guaranteed. The Company is also entitled to receive high single-digit to low double-digit royalties on net sales, if any, of Licensed Products in the Territory following regulatory approval of the Compound. Everest has the right to sublicense to affiliates and third parties in the Territory. Everest is responsible for all costs related to developing, obtaining regulatory approval of and commercializing the Compound and Licensed Products in the Territory, and is obligated to use commercially reasonable efforts to develop, manufacture and commercialize Licensed Products, including to achieve certain specified diligence milestones within agreed-upon periods. Unless earlier terminated due to certain material breaches of the contract, or otherwise, the License Agreement will expire on a jurisdiction-by-jurisdiction and Licensed Product-by-Licensed Product basis until the latest to occur of expiration of the last valid claim under a licensed patent in such jurisdiction, the expiration of regulatory exclusivity in such jurisdiction or ten years after the first commercial sale of such Licensed Product in such jurisdiction. The License Agreement may be terminated in its entirety by Everest upon 90 or 180 days’ prior written notice, depending on the stage of development of the initial Licensed Product. |
Summary of Significant Accoun_2
Summary of Significant Accounting Policies (Policies) | 12 Months Ended |
Dec. 31, 2018 | |
Accounting Policies [Abstract] | |
Use of Estimates | Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting periods. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, the accrual for research and development expenses, the valuation of common shares prior to the Company’s IPO, the valuation of share-based awards and the valuation of derivative liabilities. The Company bases its estimates on historical experience, known trends and other market-specific or other relevant factors that it believes to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates, as there are changes in circumstances, facts and experience. Actual results may differ from those estimates or assumptions. |
Consolidation | Consolidation The Company consolidates entities in which it has a controlling financial interest. The Company evaluates each of its subsidiaries to determine whether the entity represents a variable interest entity (“VIE”), for which consolidation should be evaluated under the VIE model, or, alternatively, if the entity is a voting interest entity, for which consolidation should be evaluated using the voting interest model. The Company has concluded that none of its subsidiaries is a VIE and has consolidated each subsidiary under the voting interest model because it has majority voting control of each subsidiary. Ownership interests in the Company’s subsidiaries that are held by entities other than the Company are reported as non-controlling interests in the consolidated balance sheets. Losses attributed to non-controlling interests and to the Company are reported separately in the consolidated statements of operations and comprehensive loss. As of December 31, 2018 and 2017, the Company consolidated its non-controlling interest in Spero Gyrase, Inc. |
Concentrations of Credit Risk and of Significant Suppliers | Concentrations of Credit Risk and of Significant Suppliers Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash and cash equivalents. The Company maintains most of its cash and cash equivalents at one accredited financial institution. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships. The Company is dependent on third-party manufacturers to supply products for research and development activities in its programs. In particular, the Company relies and expects to continue to rely on a small number of manufacturers to supply it with its requirements for the active pharmaceutical ingredients and formulated drugs related to these programs. These programs could be adversely affected by a significant interruption in the supply of active pharmaceutical ingredients and formulated drugs. |
Deferred Offering Costs | Deferred Offering Costs The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded in stockholders’ deficit as a reduction of additional paid-in capital generated as a result of the offering. Should the planned equity financing be abandoned, the deferred offering costs will be expensed immediately as a charge to operating expenses in the consolidated statement of operations and comprehensive loss. |
Cash Equivalents | Cash Equivalents The Company considers all highly liquid investments with original maturities of three months or less at the date of purchase to be cash equivalents. |
Marketable Securities | Marketable Securities Marketable securities consist of investments with original maturities greater than 90 days. The Company considers its investment portfolio of investments to be available-for-sale. Accordingly, these investments are recorded at fair value, which is based on quoted market prices. Investments with maturities beyond one year are generally classified as short term, based on their highly liquid nature and because such marketable securities represent the investment of cash that is available for current operations. Unrealized gains and losses are reported as a component of accumulated other comprehensive income (loss) in stockholders’ equity. Realized gains and losses and declines in value judged to be other than temporary are included as a component of other income (expense), net based on the specific identification method. When determining whether a decline in value is other than temporary, the Company considers various factors, including whether the Company has the intent to sell the security, and whether it is more likely than not that the Company will be required to sell the security prior to recovery of its amortized cost basis. |
Property and Equipment | Property and Equipment Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation and amortization expense is recognized using the straight-line method over the estimated useful life of each asset as follows: Estimated Useful Life Laboratory equipment 5 years Computer software and equipment 3 years Office furniture and equipment 7 years Manufacturing equipment 5 years Leasehold improvements Shorter of life of lease or 5 years Costs for capital assets not yet placed into service are capitalized as construction in progress and are depreciated in accordance with the above guidelines once placed into service. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation and amortization are removed from the accounts and any resulting gain or loss is included in loss from operations. Expenditures for repairs and maintenance are charged to expense as incurred. |
Other Assets | Other Assets Other assets consist of long-term prepayments and deposits. |
Impairment of Long-Lived Assets | Impairment of Long-Lived Assets Long-lived assets consist of property and equipment. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset group for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset group to its carrying value. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of an asset group are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset group over its fair value, determined based on discounted cash flows. During the year ended December 31, 2018, the Company recorded a loss of $0.2 million related to the write-off of fixed assets at its Watertown, Massachusetts laboratory facility. The Company did not record any impairment losses on long-lived assets during the years ended December 31, 2017 or 2016. |
Fair Value Measurements | Fair Value Measurements Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: • Level 1—Quoted prices in active markets for identical assets or liabilities. • Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. • Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. The Company’s cash equivalents and derivative liabilities are carried at fair value, determined according to the fair value hierarchy described above (see Note 3). The carrying values of the Company’s accounts payable and accrued expenses approximate their fair values due to the short-term nature of these liabilities. |
Derivative Liabilities | Derivative Liabilities In connection with certain equity financings, licensing transactions and research collaborations, the Company has identified certain embedded and freestanding derivatives, which are recorded as liabilities on the Company’s consolidated balance sheet and are remeasured to fair value at each reporting date until the derivative is settled. Changes in the fair value of the derivative liabilities are recognized as other income (expense) in the consolidated statement of operations and comprehensive loss. |
Classification and Accretion of Bridge Units and Redeemable Convertible Preferred Shares | Classification and Accretion of Bridge Units and Redeemable Convertible Preferred Shares The Company has classified bridge units and redeemable convertible preferred shares outside of stockholders’ equity (deficit) because the shares contain certain redemption features that are not solely within the control of the Company. The carrying values of these instruments are accreted to their respective redemption values from the date of issuance through the earliest date of redemption. |
Segment Information | Segment Information The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The Company’s singular focus is on identifying, developing and commercializing novel treatments for MDR bacterial infections. All of the Company’s tangible assets are held in the United States. |
Government Contracts and Revenue Recognition | Government Contracts and Revenue Recognition The Company generates revenue from government contracts that reimburse the Company for certain allowable costs for funded projects. For contracts with government agencies, when the Company has concluded that it is the principal in conducting the research and development expenses and where the funding arrangement is considered central to the Company’s ongoing operations, the Company classifies the recognized funding received as revenue. The Company has concluded to recognize funding received from the Biomedical Advanced Research and Development Authority (“BARDA”), the U.S. Department of Defense (“DoD”), the National Institute of Allergy and Infectious Diseases (“NIAID”) of the National Institutes of Health (“NIH”) and Combating Antibiotic Resistant Bacteria Biopharmaceutical Accelerator (“CARB-X”) as revenue, rather than as a reduction of research and development expenses, because the Company is the principal in conducting the research and development activities and these contracts are central to its ongoing operations. Revenue is recognized as the qualifying expenses related to the contracts are incurred. Revenue recognition commences once the Company has substantially accomplished what it must do to be entitled to the benefits represented by the revenues. Revenue recognized upon incurring qualifying expenses in advance of receipt of funding is recorded in the Company’s consolidated balance sheet as other receivables. The related costs incurred by the Company are included in research and development expense in the Company’s consolidated statements of operations and comprehensive loss. |
Government Tax Incentives | Government Tax Incentives For available government tax incentives that the Company may earn without regard to the existence of taxable income and that require the Company to forego tax deductions or the use of future tax credits and net operating loss carryforwards, the Company classifies the funding recognized as a reduction of the related qualifying research and development expenses incurred. Since the fourth quarter of 2016 and through December 31, 2018, the Company’s operating subsidiary in Australia has met the eligibility requirements to receive a 43.5% tax incentive for qualifying research and development activities (see Note 14). The Company recognizes these incentives as a reduction of research and development expenses in the consolidated statements of operations and comprehensive loss in the same period that the related qualifying expenses are incurred. Reductions of research and development expense recognized upon incurring qualifying expenses in advance of receipt of tax incentive payments are recorded in the consolidated balance sheet as tax incentive receivables. |
Collaboration Agreements | Collaboration Agreements For collaboration agreements with a third party, to determine the appropriate statement of operations classification of the recognized funding, the Company first assesses whether the collaboration arrangement is within the scope of the accounting guidance for collaboration arrangements. If it is, the Company evaluates the collaborative arrangement for proper classification in the statement of operations based on the nature of the underlying activity and the Company assesses the payments to and from the collaborative partner. If the payments to and from the collaborative partner are not within the scope of other authoritative accounting guidance, the Company bases the statement of operations classification for the payments received on a reasonable, rational analogy to authoritative accounting guidance, applied in a consistent manner. Conversely, if the collaboration arrangement is not within the scope of accounting guidance for collaboration arrangements, the Company assesses whether the collaboration arrangement represents a vendor/customer relationship. If the collaborative arrangement does not represent a vendor/customer relationship, the Company then classifies the funding payments received in the statement of operations and comprehensive loss as a reduction of the related expense that is incurred. In 2014, the Company entered into a research and development services and support agreement with Hoffmann-La Roche Inc. and certain of its affiliates (“Roche”) and concluded that the agreements were not within the scope of the accounting guidance for collaboration arrangements (see Note 13). Due to the co-funded nature of the payments and the Company’s assessment that it did not have a vendor/customer relationship with Roche, the Company recognized the nonrefundable payments received under the agreement as a reduction to the research and development expenses incurred, based on a proportional methodology comparing the total expenses incurred in the period under the project to the total expenses expected to be incurred under the project. The Company terminated the agreement with Roche in August 2016. |
Research and Development Costs | Research and Development Costs Research and development costs are expensed as incurred. Research and development expenses are comprised of costs incurred in performing research and development activities, including personnel salaries, share-based compensation and benefits, allocated facilities costs, depreciation, manufacturing expenses, costs related to the Company’s government contract and grant arrangements, and external costs of outside vendors engaged to conduct preclinical development activities, clinical trials as well as the cost of licensing technology. Upfront payments and milestone payments made for the licensing of technology are expensed as research and development in the period in which they are incurred. Advance payments for goods or services to be received in the future for use in research and development activities are recorded as prepaid expenses. The prepaid amounts are expensed as the related goods are delivered or the services are performed. |
Clinical Trial and other Research Contract Costs and Accruals | Clinical Trial and other Research Contract Costs and Accruals The Company has entered into various research and development contracts with clinical research organizations and other companies both inside and outside of the United States. These agreements are generally cancelable, and related payments are recorded as research and development expenses as incurred. There may be instances in which payments made to these vendors exceed the level of service provided and will result in a prepayment of the expense. The Company records accruals for estimated ongoing research and clinical trial costs based on the services received and efforts expended pursuant to multiple contracts with these vendors. When evaluating the adequacy of the accrued liabilities, the Company analyzes the progress of the studies or trials, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs. |
Patent Costs | Patent Costs All patent-related costs incurred in connection with filing and prosecuting patent applications are expensed as incurred due to the uncertainty about the recovery of the expenditure. Amounts incurred are classified as general and administrative expenses. |
Share-Based Compensation | Share-Based Compensation The Company measures all share-based awards granted to employees and directors based on the fair value on the date of grant using the Black-Scholes option-pricing model. Compensation expense of those awards is recognized over the requisite service period, which is generally the vesting period of the respective award. Generally, the Company issues awards with only service-based vesting conditions and records the expense for these awards using the straight-line method over the requisite service period, net of any actual forfeitures. The Company classifies share-based compensation expense in its consolidated statements of operations and comprehensive loss in the same manner in which the award recipient’s payroll costs are classified or in which the award recipient’s service payments are classified. |
Comprehensive Loss | Comprehensive Loss Comprehensive loss includes net loss as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those with shareholders. For the year ended December 31, 2018, these changes related to unrealized gains and losses on the Company’s available-for-sale marketable securities. There were no reclassifications out of comprehensive loss for the year ended December 31, 2018. There was no difference between net loss and comprehensive loss for the years ended December 31, 2017 and 2016. |
Net Income (Loss) per Share Attributable to Spero Therapeutics, Inc. | Net Income (Loss) per Share Attributable to Spero Therapeutics, Inc. The Company follows the two-class method when computing net income (loss) per share, as the Company has issued shares that meet the definition of participating securities. The two-class method determines net income (loss) per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed. Net income (loss) per share attributable to common stockholders is calculated based on net income (loss) attributable to Spero Therapeutics, Inc. and excludes net income (loss) attributable to non-controlling interests. Basic net income (loss) per share attributable to common stockholders is computed by dividing the net income (loss) attributable to common stockholders by the weighted average number of shares of common stock outstanding for the period. Diluted net income (loss) attributable to common stockholders is computed by adjusting net income (loss) attributable to common stockholders to reallocate undistributed earnings based on the potential impact of dilutive securities. Diluted net income (loss) per share attributable to common stockholders is computed by dividing the diluted net income (loss) attributable to common stockholders by the weighted average number of common shares outstanding for the period, including potential dilutive common shares assuming the dilutive effect of common stock equivalents. The Company’s preferred stock contractually entitles the holders of such shares to participate in dividends but does not contractually require the holders of such shares to participate in losses of the Company. Accordingly, in periods in which the Company reports a net loss, such losses are not allocated to such participating securities. In periods in which the Company reports a net loss attributable to common stockholders of Spero Therapeutics, Inc., diluted net loss per share attributable to common stockholders of Spero Therapeutics, Inc. is the same as basic net loss per share attributable to common stockholders of Spero Therapeutics, Inc., since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive. The Company reported a net loss attributable to common stockholders of Spero Therapeutics, Inc. for the years ended December 31, 2018, 2017 and 2016. |
Income Taxes | Income Taxes The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the consolidated financial statements or in the Company’s tax returns. Deferred tax assets and liabilities are determined on the basis of the differences between the financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies. The Company accounts for uncertainty in income taxes recognized in the consolidated financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more-likely-than-not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the consolidated financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties. |
Recently Adopted Accounting Pronouncements | Recently Adopted Accounting Pronouncements In May 2014, the FASB”) issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) (“ASU 2014-09”), which supersedes existing revenue recognition guidance under GAAP. The standard’s core principle is that a company will recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. The standard outlines a five-step process to achieve this principle, and will require companies to use more judgment and make more estimates than under the current guidance. The Company expects that these judgments and estimates will include identifying performance obligations in the customer contract, estimating the amount of variable consideration to include in the transaction price and allocating the transaction price to each separate performance obligation. ASU 2014-09 also requires additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts. In August 2015, the FASB issued ASU 2015-14, Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date , which delays the effective date of ASU 2014-09 such that the standard is effective for public entities for annual periods beginning after December 15, 2017 and for interim periods within those fiscal years. In March 2016, the FASB issued ASU No. 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations (“ASU 2016-08”), which further clarifies the implementation guidance on principal versus agent considerations in ASU 2014-09. In April 2016, the FASB issued ASU No. 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensin g, clarifying the implementation guidance on identifying performance obligations and licensing. Specifically, the amendments in this update reduce the cost and complexity of identifying promised goods or services and improve the guidance for determining whether promises are separately identifiable. The amendments in this update also provide implementation guidance on determining whether an entity’s promise to grant a license provides a customer with either a right to use the entity’s intellectual property (which is satisfied at a point in time) or a right to access the entity’s intellectual property (which is satisfied over time). In May 2016, the FASB issued ASU No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients (“ASU 2016-12”), which clarifies the objective of the collectability criterion, presentation of taxes collected from customers, non-cash consideration, contract modifications at transition, completed contracts at transition and how guidance in ASU 2014-09 is retrospectively applied. ASU 2016-08, ASU 2016-10 and ASU 2016-12 have the same effective dates and transition requirements as ASU 2014-09. The Company adopted this standard using the modified retrospective approach, however the Company determined that government grant revenue is outside the scope of ASC 606. Therefore, the adoption of ASC 606 did not impact the Company’s financial position, results of operations or cash flows as its only existing revenue source as of December 31, 2018 is government grants. In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows: Classification of Certain Cash Receipts and Cash Payments In November 2016, the FASB issued ASU 2016-18 Statement of Cash Flows (Topic 230) The inclusion of restricted cash increased the beginning and ending balances of the consolidated statement of cash flows by $50,000 for the years ended December 31, 2017 and 2016. In January 2017, FASB issued ASU No. 2017-01, Business Combinations (Topic 805): Clarifying the Definition of a Business In May 2017, the FASB issued ASU No. 2017-09, Compensation—Stock Compensation (Topic 718): Scope of Modification Accounting |
Recently Issued Accounting Pronouncements | Recently Issued Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842 Leases Codification Improvements to Topic 842, Leases Leases (Topic 842): Targeted Improvements The Company has elected to adopt ASU 2016-02 effective January 1, 2019 through a cumulative-effect adjustment under ASU 2018-11. This standard provides a number of optional practical expedients in transition. The Company plans to apply the package of practical expedients to leases that commenced prior to the effective date whereby it will elect to not reassess the following: (i) whether any expired or existing contracts contain leases; (ii) the lease classification for any expired or existing leases; and (iii) initial direct costs for any existing leases. The Company expects to elect the short-term lease recognition exemption for all leases that qualify, where a right-of-use asset or lease liability will not be recognized for short term leases. The Company has substantially completed its assessment of the adoption of ASU 2016-02 and expects that the most significant effects of adoption will be to the recognition of material new ROU assets and corresponding liabilities on its consolidated balance sheet related to its existing facility operating leases (see Note 11). In July 2017, the FASB issued ASU 2017-11, Earnings Per Share (Topic 260), Distinguishing Liabilities from Equity (Topic 480), Derivatives and Hedging (Topic 815) I. Accounting for Certain Financial Instruments with Down Round Features II. Replacement of the Indefinite Deferral for Mandatorily Redeemable Financial Instruments of Certain Nonpublic Entities and Certain Mandatorily Redeemable Noncontrolling Interests with a Scope Exception In June 2018, the FASB issued ASU 2018-07, Ímprovements to Nonemployee Share-Based Payment Accounting, which sets forth amendments to simplify the accounting for share-based payment awards to nonemployees by aligning the measurement and classification guidance, with certain exceptions, to that for share-based payment awards to employees. The amendments expand the scope of the accounting standard for share-based payment awards to include share-based payment awards granted to non-employees in exchange for goods or services used or consumed in an entity’s own operations and supersedes the guidance related to equity-based payments to non-employees. The amendments in this ASU are effective for fiscal years beginning after December 15, 2018, including interim periods within that fiscal year. The Company does not expect the adoption of this standard will have a material impact to its consolidated statement of operations, as awards to non-employees are not material. |
Summary of Significant Accoun_3
Summary of Significant Accounting Policies (Tables) | 12 Months Ended |
Dec. 31, 2018 | |
Accounting Policies [Abstract] | |
Estimated Useful Lives of Assets | Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation and amortization expense is recognized using the straight-line method over the estimated useful life of each asset as follows: Estimated Useful Life Laboratory equipment 5 years Computer software and equipment 3 years Office furniture and equipment 7 years Manufacturing equipment 5 years Leasehold improvements Shorter of life of lease or 5 years |
Fair Value of Financial Asset_2
Fair Value of Financial Assets and Liabilities (Tables) | 12 Months Ended |
Dec. 31, 2018 | |
Fair Value Disclosures [Abstract] | |
Summary of Financial Assets and Liabilities Measured at Fair Value Recurring Basis | The following tables present information about the Company’s assets and liabilities that are measured at fair value on a recurring basis (in thousands): Fair Value Measurements at December 31, 2018 Using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ — $ 22,327 $ — $ 22,327 Commercial paper — 6,389 — 6,389 Total cash equivalents — 28,716 — 28,716 Marketable securities: U.S. government securities — 37,815 — 37,815 Corporate bonds — 26,672 — 26,672 Commercial paper — 16,876 — 16,876 Total marketable securities — 81,363 — 81,363 Total cash equivalents and marketable securities $ — $ 110,079 $ — $ 110,079 Liabilities: Derivative liabilities: Anti-dilution rights $ — $ — $ 223 $ 223 $ — $ — $ 223 $ 223 Fair Value Measurements at December 31, 2017 Using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ — $ 83,121 $ — $ 83,121 $ — $ 83,121 $ — $ 83,121 Liabilities: Derivative liabilities: Anti-dilution rights $ — $ — $ 223 $ 223 $ — $ — $ 223 $ 223 |
Summary of Gross Unrealized Gains and Losses of Marketable Securities | The following table summarizes the gross unrealized gains and losses of the Company’s marketable securities as of December 31, 2018 (in thousands): December 31, 2018 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Assets: U.S. government securities $ 37,819 $ — $ (4 ) $ 37,815 Corporate bonds 26,696 — (24 ) 26,672 Commercial paper 16,876 — — 16,876 $ 81,391 $ — $ (28 ) $ 81,363 |
Roll Forward of the Fair values of Derivative Liabilities | The following table provides a roll forward of the aggregate fair values of the Company’s derivative liabilities, for which fair value was determined by Level 3 inputs (in thousands): Contingent Prepayment Options Tranche Rights Anti-Dilution Rights Total Balance at December 31, 2015 $ — $ 2,404 $ 980 $ 3,384 Fair value at issuance 908 909 1,780 3,597 Change in fair value (6 ) (600 ) 26 (580 ) Settlement — (2,713 ) (980 ) (3,693 ) Balance at December 31, 2016 902 — 1,806 2,708 Change in fair value 42 — (1,583 ) (1,541 ) Settlement (944 ) — — (944 ) Balance at December 31, 2017 — — 223 223 Change in fair value — — — — Balance at December 31, 2018 $ — $ — $ 223 $ 223 |
Property and Equipment, Net (Ta
Property and Equipment, Net (Tables) | 12 Months Ended |
Dec. 31, 2018 | |
Property Plant And Equipment [Abstract] | |
Components of Property and Equipment, Net | Property and equipment, net consisted of the following (in thousands): December 31, 2018 2017 Computer software and equipment $ 166 $ 181 Office furniture and equipment 210 201 Leasehold improvements 863 915 Laboratory equipment — 510 Construction-in-progress 897 — Manufacturing equipment 1,584 — 3,720 1,807 Less: Accumulated depreciation and amortization (827 ) (643 ) $ 2,893 $ 1,164 |
Accrued Expenses and Other Cu_2
Accrued Expenses and Other Current Liabilities (Tables) | 12 Months Ended |
Dec. 31, 2018 | |
Payables And Accruals [Abstract] | |
Schedule of Accrued Expenses and Other Current Liabilities | Accrued expenses and other current liabilities consisted of the following (in thousands): December 31, 2018 2017 Accrued external research and development expenses $ 4,541 $ 1,770 Accrued payroll and related expenses 2,379 1,369 Accrued professional fees 917 878 Accrued other 426 304 $ 8,263 $ 4,321 |
Share-Based Compensation (Table
Share-Based Compensation (Tables) | 12 Months Ended |
Dec. 31, 2018 | |
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract] | |
Summary of Assumptions used to determine Fair Value of Incentive Unit and Stock Option Awards Granted to Employees and Directors | The assumptions that the Company used in the Black-Scholes option-pricing model to determine the fair value of incentive unit and stock option awards granted to employees and directors were as follows, presented on a weighted average basis: Year Ended December 31, 2018 2017 2016 Risk-free interest rate 2.7 % 2.0 % 1.3 % Expected term (in years) 6.3 6.1 6.3 Expected volatility 74.1 % 77.1 % 76.5 % Expected dividend yield 0.0 % 0.0 % 0.0 % |
Summary of Stock Option Activity | The following table summarizes stock option activity during 2018: Number of Shares Weighted Average Exercise Price Weighted Average Contractual Term Aggregate Intrinsic Value (in years) (in thousands) Outstanding as of December 31, 2017 2,011,296 $ 7.24 9.38 $ 9,074 Granted 503,730 11.30 Exercised (56,780 ) 5.90 Forfeited (160,436 ) 9.13 Cancelled — — Outstanding as of December 31, 2018 2,297,810 $ 8.03 8.77 $ 354 Outstanding as of December 31, 2018 - vested and expected to vest 2,294,629 $ 8.03 8.62 $ 354 Exercisable at December 31, 2018 845,851 $ 6.69 8.57 $ 183 |
Summary of Share-Based Compensation Expense | The Company recorded share-based compensation expense, for both incentive units and stock options in the following expense categories of its consolidated statements of operations and comprehensive loss (in thousands): Year Ended December 31, 2018 2017 2016 Research and development expenses $ 1,072 $ 371 $ 66 General and administrative expenses 1,677 1,056 114 Total $ 2,749 $ 1,427 $ 180 |
Income Taxes (Tables)
Income Taxes (Tables) | 12 Months Ended |
Dec. 31, 2018 | |
Income Tax Disclosure [Abstract] | |
Schedule of Domestic and Foreign Components of Loss before Income Taxes | The domestic and foreign components of loss before income taxes were as follows (in thousands): Year Ended December 31, 2018 2017 2016 Domestic $ (33,236 ) $ (38,706 ) $ (27,148 ) Foreign (8,426 ) (1,180 ) (5,493 ) Loss before income taxes $ (41,662 ) $ (39,886 ) $ (32,641 ) |
Reconciliation of U.S. Federal Statutory Income Tax Rate to Company's Effective Income Tax Rate | A reconciliation of the U.S. federal statutory income tax rate to the Company’s effective income tax rate is as follows: Year Ended December 31, 2018 2017 2016 Federal statutory income tax rate (21.0 ) (34.0 ) (34.0 ) Federal and state research and development tax credit (2.6 ) (3.3 ) (1.7 ) State taxes, net of federal benefit (5.4 ) (5.3 ) (4.4 ) Foreign rate differential 1.9 0.1 2.3 Nondeductible items 1.2 (0.1 ) 4.8 Effect of US tax reform — 23.8 — Increase in deferred tax asset valuation allowance 25.9 18.8 33.0 Effective income tax rate — — — |
Net Deferred Tax Assets | Net deferred tax assets as of December 31, 2018 and 2017 consisted of the following (in thousands): December 31, 2018 2017 Net operating loss carryforwards $ 29,025 $ 21,754 Research and development tax credit carryforwards 3,385 2,022 Other 1,731 743 Total deferred tax assets 34,141 24,519 Valuation allowance (34,141 ) (24,519 ) Net deferred tax assets $ — $ — |
Summary of Changes in Valuation Allowance for Deferred Tax Assets | Changes in the valuation allowance for deferred tax assets during the years ended December 31, 2018 and 2017 related primarily to the increase in net operating loss carryforwards and research and development tax credit carryforwards, and were as follows (in thousands): December 31, 2018 2017 Valuation allowance as of beginning of year $ (24,519 ) $ (17,152 ) Decreases recorded as benefit to income tax provision — — Increases recorded to income tax provision (9,622 ) (7,367 ) Valuation allowance as of end of year $ (34,141 ) $ (24,519 ) |
Commitments and Contingencies (
Commitments and Contingencies (Tables) | 12 Months Ended |
Dec. 31, 2018 | |
Commitments And Contingencies Disclosure [Abstract] | |
Summary of Future Minimum Payments Due Under Operating Leases | The following table summarizes the future minimum payments due under the operating leases as of December 31, 2018 (in thousands): Year Ending December 31, 2019 $ 1,361 2020 1,054 2021 995 2022 1,107 2023 1,123 2024 1,138 2025 1,108 $ 7,886 |
Net Loss per Share (Tables)
Net Loss per Share (Tables) | 12 Months Ended |
Dec. 31, 2018 | |
Earnings Per Share [Abstract] | |
Summary of Basic and Diluted Net Loss per Share Attributable to Common Stockholders | Basic and diluted net loss per share attributable to common stockholders of Spero Therapeutics, Inc. was calculated as follows (in thousands, except share and per share amounts): Year Ended December 31, 2018 2017 2016 Numerator: Net loss $ (41,662 ) $ (39,886 ) $ (32,641 ) Less: Net loss attributable to non-controlling interests — (1,143 ) (7,150 ) Plus: Cumulative dividends on redeemable convertible preferred shares — (6,146 ) (3,441 ) Plus: Accretion of bridge units and redeemable convertible preferred shares to redemption value — (1,208 ) (996 ) Net loss attributable to common stockholders of Spero Therapeutics, Inc. $ (41,662 ) $ (46,097 ) $ (29,928 ) Denominator: Weighted average common shares outstanding, basic and diluted 16,001,832 2,586,865 312,169 Net loss per share attributable to common stockholders of Spero Therapeutics, Inc., basic and diluted $ (2.60 ) $ (17.82 ) $ (95.87 ) |
Summary of Shares Excluded From the Computation of Diluted Net Loss Per Share Attributable to Common Stockholders | The Company excluded the following potential common shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect: December 31, 2018 2017 2016 Options to purchase common stock 2,297,810 2,011,296 — Series A convertible preferred stock (as converted to common shares) 2,220,000 — — Series B convertible preferred stock (as converted to common shares) 1,000,000 — — Redeemable convertible preferred shares (as converted to common shares) — — 2,229,518 Incentive units — — 413,266 5,517,810 2,011,296 2,642,784 |
Quarterly Financial Data (Table
Quarterly Financial Data (Tables) | 12 Months Ended |
Dec. 31, 2018 | |
Quarterly Financial Information Disclosure [Abstract] | |
Quarterly Financial Information | March 31, 2018 June 30, 2018 September 30, 2018 December 31, 2018 Grant revenue $ 1,153 $ 463 $ 658 $ 1,692 Operating expenses 11,969 10,434 11,593 12,776 Net loss (10,644 ) (9,956 ) (10,463 ) (10,599 ) Net loss per share attributable to common shareholders per share, basic and diluted $ (0.74 ) $ (0.69 ) $ (0.60 ) $ (0.60 ) Weighted average shares outstanding, basic and diluted: 14,369,182 14,376,529 17,471,462 17,736,996 March 31, 2017 June 30, 2017 September 30, 2017 December 31, 2017 Grant revenue $ 140 $ 249 $ 597 $ 993 Operating expenses 7,739 10,414 10,563 14,993 Net loss (6,411 ) (9,763 ) (9,844 ) (13,868 ) Net loss attributable to Spero Therapeutics, Inc. (5,876 ) (9,169 ) (9,836 ) (13,862 ) Net loss attributable to common shareholders of Spero Therapeutics, Inc. (7,130 ) (12,121 ) (12,076 ) (14,770 ) Net loss per share attributable to common shareholders per share, basic and diluted $ (21.60 ) $ (36.21 ) $ (36.02 ) $ (1.59 ) Weighted average shares outstanding, basic and diluted: 330,075 334,788 335,285 9,273,783 |
Nature of the Business and Ba_2
Nature of the Business and Basis of Presentation - Additional Information (Detail) $ in Thousands | 3 Months Ended | 12 Months Ended | ||||||
Dec. 31, 2017USD ($) | Sep. 30, 2017USD ($) | Jun. 30, 2017USD ($) | Mar. 31, 2017USD ($) | Dec. 31, 2018USD ($) | Dec. 31, 2017USD ($) | Dec. 31, 2016USD ($) | Dec. 11, 2018USD ($) | |
Nature Of Business And Basis Of Presentation [Line Items] | ||||||||
Entity incorporation month and year | 2013-12 | |||||||
State of incorporation | Delaware | |||||||
Merger date | Jun. 30, 2017 | |||||||
Business combination exchange ratio | 1 | |||||||
Net loss | $ 13,862 | $ 9,836 | $ 9,169 | $ 5,876 | $ 41,662 | $ 38,743 | $ 25,491 | |
Accumulated deficit | $ 96,840 | $ 138,502 | $ 96,840 | |||||
At-The-Market Offering Program [Member] | Sales Agreement [Member] | Cantor Fitzgerald & Co [Member] | Maximum [Member] | ||||||||
Nature Of Business And Basis Of Presentation [Line Items] | ||||||||
Authorized offering value | $ 200,000 | |||||||
Common stock available for issuance | $ 50,000 |
Summary of Significant Accoun_4
Summary of Significant Accounting Policies - Estimated Useful Lives of Assets (Details) | 12 Months Ended |
Dec. 31, 2018 | |
Laboratory Equipment [Member] | |
Property Plant And Equipment [Line Items] | |
Estimated useful life | 5 years |
Computer Software and Equipment [Member] | |
Property Plant And Equipment [Line Items] | |
Estimated useful life | 3 years |
Office Furniture and Equipment [Member] | |
Property Plant And Equipment [Line Items] | |
Estimated useful life | 7 years |
Manufacturing Equipment [Member] | |
Property Plant And Equipment [Line Items] | |
Estimated useful life | 5 years |
Leasehold Improvements [Member] | |
Property Plant And Equipment [Line Items] | |
Estimated useful life | Shorter of life of lease or 5 years |
Summary of Significant Accoun_5
Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) | 12 Months Ended | ||
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | |
Summary Of Significant Accounting Policies [Line Items] | |||
Cash, cash equivalents increased due to inclusion | $ (53,258,000) | $ 76,973,000 | $ 4,624,000 |
Accounting Standards Update 2016-18 [Member] | |||
Summary Of Significant Accounting Policies [Line Items] | |||
Cash, cash equivalents increased due to inclusion | $ 50,000 | $ 50,000 | |
Spero Potentiator Australia Pty Limited [Member] | Research and Development Expenses [Member] | |||
Summary Of Significant Accounting Policies [Line Items] | |||
Percentage of refundable tax incentive | 43.50% | ||
Laboratory Equipment and Leasehold Improvements [Member] | Massachusetts [Member] | |||
Summary Of Significant Accounting Policies [Line Items] | |||
Loss on write-off of fixed assets | $ 200,000 |
Fair Value of Financial Asset_3
Fair Value of Financial Assets and Liabilities - Summary of Financial Assets and Liabilities Measured at Fair Value Recurring Basis (Detail) - USD ($) $ in Thousands | Dec. 31, 2018 | Dec. 31, 2017 |
Cash equivalents: | ||
Total cash equivalents | $ 5,400 | $ 4,200 |
Fair Value, Measurements, Recurring [Member] | ||
Cash equivalents: | ||
Total cash equivalents | 28,716 | |
Marketable securities: | ||
Total marketable securities | 81,363 | |
Total cash equivalents and marketable securities | 110,079 | 83,121 |
Derivative liabilities: | ||
Derivative liabilities | 223 | 223 |
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member] | ||
Cash equivalents: | ||
Total cash equivalents | 22,327 | 83,121 |
Fair Value, Measurements, Recurring [Member] | Commercial Paper [Member] | ||
Cash equivalents: | ||
Total cash equivalents | 6,389 | |
Marketable securities: | ||
Total marketable securities | 16,876 | |
Fair Value, Measurements, Recurring [Member] | U.S. Government Securities [Member] | ||
Marketable securities: | ||
Total marketable securities | 37,815 | |
Fair Value, Measurements, Recurring [Member] | U.S. Corporate Bonds [Member] | ||
Marketable securities: | ||
Total marketable securities | 26,672 | |
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | ||
Cash equivalents: | ||
Total cash equivalents | 28,716 | |
Marketable securities: | ||
Total marketable securities | 81,363 | |
Total cash equivalents and marketable securities | 110,079 | 83,121 |
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Money Market Funds [Member] | ||
Cash equivalents: | ||
Total cash equivalents | 22,327 | 83,121 |
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Commercial Paper [Member] | ||
Cash equivalents: | ||
Total cash equivalents | 6,389 | |
Marketable securities: | ||
Total marketable securities | 16,876 | |
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | U.S. Government Securities [Member] | ||
Marketable securities: | ||
Total marketable securities | 37,815 | |
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | U.S. Corporate Bonds [Member] | ||
Marketable securities: | ||
Total marketable securities | 26,672 | |
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | ||
Derivative liabilities: | ||
Derivative liabilities | 223 | 223 |
Fair Value, Measurements, Recurring [Member] | Anti- dilution Rights [Member] | ||
Derivative liabilities: | ||
Derivative liabilities | 223 | 223 |
Fair Value, Measurements, Recurring [Member] | Anti- dilution Rights [Member] | Level 3 [Member] | ||
Derivative liabilities: | ||
Derivative liabilities | $ 223 | $ 223 |
Fair Value of Financial Asset_4
Fair Value of Financial Assets and Liabilities - Additional Information (Detail) - USD ($) | Jul. 01, 2015 | Mar. 31, 2017 | Dec. 31, 2016 | Aug. 31, 2016 | Feb. 29, 2016 | Jan. 31, 2016 | Nov. 30, 2015 | Jun. 30, 2015 | Feb. 28, 2015 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Jun. 30, 2017 | May 31, 2017 | Mar. 31, 2016 | Jan. 31, 2015 |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||||||||||||||||
Total cash | $ 5,400,000 | $ 4,200,000 | ||||||||||||||
Fair value assets level 1 to level 2 transfers | 0 | 0 | ||||||||||||||
Fair value assets level 2 to level 1 transfers | 0 | 0 | ||||||||||||||
Fair value liabilities level 1 to level 2 transfers | 0 | 0 | ||||||||||||||
Fair value liabilities level 2 to level 1 transfers | 0 | 0 | ||||||||||||||
Transfer of financial asset into level 3 of fair value | 0 | 0 | ||||||||||||||
Transfer of financial liabilities into level 3 of fair value | $ 0 | 0 | ||||||||||||||
Spero Potentiator, Inc. [Member] | ||||||||||||||||
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||||||||||||||||
Number of shares issued | 2,160 | 2,160 | 2,736 | |||||||||||||
Proceeds from issuing additional shares | $ 0 | $ 0 | $ 0 | |||||||||||||
Fair value inputs probability of funding | 100.00% | |||||||||||||||
Spero Potentiator, Inc. [Member] | Northern Antibiotics Oy Ltd. [Member] | ||||||||||||||||
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||||||||||||||||
Number of shares issued | 2,160 | 2,160 | 2,736 | 996 | ||||||||||||
Amount of shares issued | $ 1,000,000 | $ 1,000,000 | $ 1,500,000 | |||||||||||||
Spero Potentiator, Inc. [Member] | Anti- dilution Rights [Member] | ||||||||||||||||
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||||||||||||||||
Derivative liabilities | $ 2,400,000 | |||||||||||||||
Spero Potentiator, Inc. [Member] | Anti- dilution Rights [Member] | Northern Antibiotics Oy Ltd. [Member] | ||||||||||||||||
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||||||||||||||||
Proceeds from issuing additional shares | $ 0 | 0 | $ 0 | $ 0 | ||||||||||||
Spero Europe, Ltd. [Member] | Anti- dilution Rights [Member] | ||||||||||||||||
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||||||||||||||||
Derivative liabilities | $ 200,000 | $ 0 | ||||||||||||||
Increase (decrease) derivative liabilities | $ (200,000) | |||||||||||||||
Fair value inputs probability of funding | 0.00% | 100.00% | ||||||||||||||
Spero Gyrase, Inc. [Member] | Anti- dilution Rights [Member] | ||||||||||||||||
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||||||||||||||||
Derivative liabilities | $ 200,000 | $ 200,000 | $ 1,600,000 | |||||||||||||
Increase (decrease) derivative liabilities | $ (1,400,000) | |||||||||||||||
Fair value inputs probability of funding | 0.00% | 100.00% | ||||||||||||||
Class A Tranche Rights[Member] | ||||||||||||||||
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||||||||||||||||
Derivative liabilities | $ 2,400,000 | |||||||||||||||
Increase (decrease) derivative liabilities | $ (2,400,000) | |||||||||||||||
Class B Tranche Rights [Member] | ||||||||||||||||
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||||||||||||||||
Derivative liabilities | $ 300,000 | $ 900,000 | $ 300,000 | |||||||||||||
Increase (decrease) derivative liabilities | (600,000) | |||||||||||||||
January 2015 Bridge Units [Member] | ||||||||||||||||
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||||||||||||||||
Derivative liabilities | $ 900,000 | |||||||||||||||
Increase (decrease) derivative liabilities | $ (1,400,000) | |||||||||||||||
January 2015 Bridge Units [Member] | Contingent prepayment option [Member] | ||||||||||||||||
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||||||||||||||||
Derivative liabilities | $ 2,300,000 | |||||||||||||||
Class A Preferred Unit [Member] | ||||||||||||||||
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||||||||||||||||
Preferred units discount percentage | 10.00% | 20.00% | ||||||||||||||
Conversion price of redeemable preferred share | $ 3.51 | $ 3.90 | ||||||||||||||
December 2016 Bridge Units [Member] | Contingent prepayment option [Member] | ||||||||||||||||
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||||||||||||||||
Derivative liabilities | $ 900,000 | $ 900,000 | ||||||||||||||
December 2016 Bridge Units [Member] | Contingent prepayment option [Member] | Maximum [Member] | ||||||||||||||||
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||||||||||||||||
Increase (decrease) derivative liabilities | $ 100,000 |
Fair Value of Financial Asset_5
Fair Value of Financial Assets and Liabilities - Summary of Gross Unrealized Gains and Losses of Marketable Securities (Detail) $ in Thousands | Dec. 31, 2018USD ($) |
Schedule Of Available For Sale Securities [Line Items] | |
Amortized Cost | $ 81,391 |
Gross Unrealized Losses | (28) |
Fair Value | 81,363 |
U.S. Government Securities [Member] | |
Schedule Of Available For Sale Securities [Line Items] | |
Amortized Cost | 37,819 |
Gross Unrealized Losses | (4) |
Fair Value | 37,815 |
U.S. Corporate Bonds [Member] | |
Schedule Of Available For Sale Securities [Line Items] | |
Amortized Cost | 26,696 |
Gross Unrealized Losses | (24) |
Fair Value | 26,672 |
Commercial Paper [Member] | |
Schedule Of Available For Sale Securities [Line Items] | |
Amortized Cost | 16,876 |
Fair Value | $ 16,876 |
Fair Value of Financial Asset_6
Fair Value of Financial Assets and Liabilities - Roll Forward of the Fair values of Derivative Liabilities (Detail) - Level 3 [Member] - USD ($) $ in Thousands | 12 Months Ended | ||
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | |||
Balance at December 31, 2015 | $ 223 | $ 2,708 | $ 3,384 |
Fair value at issuance | 3,597 | ||
Change in fair value | 0 | (1,541) | (580) |
Settlement | (944) | (3,693) | |
Balance at December 31, 2016 | 223 | 223 | 2,708 |
Contingent prepayment option [Member] | |||
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | |||
Balance at December 31, 2015 | 902 | ||
Fair value at issuance | 908 | ||
Change in fair value | 0 | 42 | (6) |
Settlement | (944) | ||
Balance at December 31, 2016 | 902 | ||
Tranche Rights [Member] | |||
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | |||
Balance at December 31, 2015 | 2,404 | ||
Fair value at issuance | 909 | ||
Change in fair value | 0 | (600) | |
Settlement | (2,713) | ||
Anti- dilution Rights [Member] | |||
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | |||
Balance at December 31, 2015 | 223 | 1,806 | 980 |
Fair value at issuance | 1,780 | ||
Change in fair value | 0 | (1,583) | 26 |
Settlement | (980) | ||
Balance at December 31, 2016 | $ 223 | $ 223 | $ 1,806 |
Property and Equipment, Net - C
Property and Equipment, Net - Components of Property and Equipment, Net (Detail) - USD ($) $ in Thousands | Dec. 31, 2018 | Dec. 31, 2017 |
Property Plant And Equipment [Line Items] | ||
Property and equipment, gross | $ 3,720 | $ 1,807 |
Less: Accumulated depreciation and amortization | (827) | (643) |
Property and equipment, net | 2,893 | 1,164 |
Laboratory Equipment [Member] | ||
Property Plant And Equipment [Line Items] | ||
Property and equipment, gross | 510 | |
Computer Software and Equipment [Member] | ||
Property Plant And Equipment [Line Items] | ||
Property and equipment, gross | 166 | 181 |
Office Furniture and Equipment [Member] | ||
Property Plant And Equipment [Line Items] | ||
Property and equipment, gross | 210 | 201 |
Leasehold Improvements [Member] | ||
Property Plant And Equipment [Line Items] | ||
Property and equipment, gross | 863 | $ 915 |
Construction in Progress [Member] | ||
Property Plant And Equipment [Line Items] | ||
Property and equipment, gross | 897 | |
Manufacturing Equipment [Member] | ||
Property Plant And Equipment [Line Items] | ||
Property and equipment, gross | $ 1,584 |
Property and Equipment, Net - A
Property and Equipment, Net - Additional Information (Detail) - USD ($) | 12 Months Ended | ||
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | |
Property Plant And Equipment [Line Items] | |||
Depreciation and amortization expense | $ 409,000 | $ 363,000 | $ 279,000 |
Massachusetts [Member] | Laboratory Equipment and Leasehold Improvements [Member] | |||
Property Plant And Equipment [Line Items] | |||
Loss related to write off | $ 200,000 | ||
Maximum [Member] | |||
Property Plant And Equipment [Line Items] | |||
Depreciation and amortization expense | $ 300,000 |
Accrued Expenses and Other Cu_3
Accrued Expenses and Other Current Liabilities - Schedule of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands | Dec. 31, 2018 | Dec. 31, 2017 |
Payables And Accruals [Abstract] | ||
Accrued external research and development expenses | $ 4,541 | $ 1,770 |
Accrued payroll and related expenses | 2,379 | 1,369 |
Accrued professional fees | 917 | 878 |
Accrued other | 426 | 304 |
Accrued expenses and other current liabilities | $ 8,263 | $ 4,321 |
Convertible Preferred Shares -
Convertible Preferred Shares - Additional Information (Detail) | Nov. 16, 2018$ / sharesshares | Nov. 15, 2018$ / sharesshares | Jul. 17, 2018USD ($)$ / sharesshares | Oct. 20, 2017 | Jun. 30, 2017$ / sharesshares | Jul. 01, 2015USD ($)$ / sharesshares | Jul. 31, 2017USD ($)$ / sharesshares | Mar. 31, 2017USD ($)$ / sharesshares | Feb. 29, 2016USD ($)$ / sharesshares | Jun. 30, 2015USD ($)$ / sharesshares | Jan. 31, 2015USD ($)$ / sharesshares | Dec. 31, 2018$ / sharesshares | Dec. 31, 2017USD ($)$ / sharesshares | Dec. 31, 2016USD ($)$ / sharesshares | Dec. 31, 2015USD ($)$ / sharesshares |
Class Of Stock [Line Items] | |||||||||||||||
Preferred stock, shares authorized | shares | 10,000,000 | 10,000,000 | |||||||||||||
Preferred stock, par value | $ / shares | $ 0.001 | $ 0.001 | |||||||||||||
Share price | $ / shares | $ 0.001 | ||||||||||||||
Common stock, par value | $ / shares | $ 0.001 | $ 0.001 | $ 0.001 | $ 0.001 | |||||||||||
Share conversion ratio | 1 | ||||||||||||||
Conversion of bridge units in to preferred units | $ 8,500,000 | ||||||||||||||
Payment of offering costs | $ 3,574,000 | ||||||||||||||
Fair value of tranche right | $ 909,000 | ||||||||||||||
2015 Bridge Units [Member] | |||||||||||||||
Class Of Stock [Line Items] | |||||||||||||||
Bridge units issued and sold | shares | 8,000 | ||||||||||||||
Bridge units issued price per unit | $ / shares | $ 1,000 | ||||||||||||||
Conversion of bridge units in to preferred units | $ 8,000,000 | ||||||||||||||
Redeemable issuer option value | $ 2,300,000 | ||||||||||||||
2015 Bridge Units [Member] | Minimum [Member] | |||||||||||||||
Class Of Stock [Line Items] | |||||||||||||||
Bridge units discount percentage | 20.00% | ||||||||||||||
2015 Bridge Units [Member] | Maximum [Member] | |||||||||||||||
Class Of Stock [Line Items] | |||||||||||||||
Bridge units discount percentage | 25.00% | ||||||||||||||
Class A Preferred Unit [Member] | |||||||||||||||
Class Of Stock [Line Items] | |||||||||||||||
Redeemable convertible shares, par value | $ / shares | $ 3.90 | $ 4.40 | |||||||||||||
Conversion of bridge units in to preferred units | $ 8,000,000 | ||||||||||||||
Redeemable issuer option value | $ 900,000 | ||||||||||||||
Redeemable convertible shares issued and sold | shares | 2,279,202 | 1,923,076 | 3,295,455 | ||||||||||||
Proceeds from issuance of preferred units, net of issuance costs | $ 7,300,000 | $ 14,500,000 | |||||||||||||
Payment of offering costs | $ 200,000 | ||||||||||||||
Preferred units discount percentage | 10.00% | 20.00% | |||||||||||||
Conversion price of redeemable preferred share | $ / shares | $ 3.51 | $ 3.90 | |||||||||||||
Convertible debt fair value disclosures | $ 8,900,000 | ||||||||||||||
Liability fair value adjustment | 8,000,000 | ||||||||||||||
Gain on extinguishment | $ 0 | ||||||||||||||
Fair value of tranche right | $ 2,400,000 | ||||||||||||||
Class B Preferred Unit [Member] | |||||||||||||||
Class Of Stock [Line Items] | |||||||||||||||
Redeemable convertible shares, par value | $ / shares | $ 4.40 | $ 5.28 | |||||||||||||
Redeemable convertible shares issued and sold | shares | 5,909,089 | 1,609,846 | |||||||||||||
Proceeds from issuance of preferred units, net of issuance costs | $ 25,900,000 | $ 8,500,000 | |||||||||||||
Payment of offering costs | $ 100,000 | ||||||||||||||
Fair value of tranche right | $ 900,000 | ||||||||||||||
2016 Bridge Units [Member] | |||||||||||||||
Class Of Stock [Line Items] | |||||||||||||||
Bridge units issued and sold | shares | 8,500 | ||||||||||||||
Bridge units issued price per unit | $ / shares | $ 1,000 | ||||||||||||||
Conversion of bridge units in to preferred units | $ 8,500,000 | ||||||||||||||
Bridge units discount percentage | 10.00% | ||||||||||||||
Redeemable issuer option value | $ 900,000 | ||||||||||||||
Change in fair value | 300,000 | ||||||||||||||
Class C Preferred Units [Member] | |||||||||||||||
Class Of Stock [Line Items] | |||||||||||||||
Redeemable convertible shares, par value | $ / shares | $ 1.7749 | ||||||||||||||
Conversion of bridge units in to preferred units | 8,500,000 | ||||||||||||||
Redeemable issuer option value | $ 900,000 | ||||||||||||||
Redeemable convertible shares issued and sold | shares | 24,326,470 | 5,321,112 | |||||||||||||
Proceeds from issuance of preferred units, net of issuance costs | $ 43,000,000 | ||||||||||||||
Payment of offering costs | $ 200,000 | ||||||||||||||
Preferred units discount percentage | 10.00% | ||||||||||||||
Conversion price of redeemable preferred share | $ / shares | $ 1.60 | ||||||||||||||
Convertible debt fair value disclosures | $ 9,400,000 | ||||||||||||||
Liability fair value adjustment | 8,500,000 | ||||||||||||||
Gain on extinguishment | $ 0 | ||||||||||||||
Class C Preferred Units [Member] | Chief Financial Officer [Member] | |||||||||||||||
Class Of Stock [Line Items] | |||||||||||||||
Redeemable convertible shares, par value | $ / shares | $ 1.7749 | ||||||||||||||
Redeemable convertible shares issued and sold | shares | 61,880 | ||||||||||||||
Proceeds from issuance of preferred units, net of issuance costs | $ 100,000 | ||||||||||||||
Common Stock [Member] | |||||||||||||||
Class Of Stock [Line Items] | |||||||||||||||
Reverse stock split ratio | 0.164544 | ||||||||||||||
Reverse stock split | one-for-6.0774 | ||||||||||||||
BVF [Member] | |||||||||||||||
Class Of Stock [Line Items] | |||||||||||||||
Issuance of preferred stock in exchange for shares of common stock | shares | 1,000,000 | ||||||||||||||
Common stock, par value | $ / shares | $ 0.001 | ||||||||||||||
Series B Convertible Preferred Stock [Member] | BVF [Member] | |||||||||||||||
Class Of Stock [Line Items] | |||||||||||||||
Preferred stock, shares authorized | shares | 1,000 | ||||||||||||||
Preferred stock, par value | $ / shares | $ 0.001 | ||||||||||||||
Share price | $ / shares | $ 7,950 | ||||||||||||||
Number of shares issuable upon conversion | shares | 1,000 | 1,000 | |||||||||||||
Percentage of shares owned by share holders | 9.99% | ||||||||||||||
Preferred stock, liquidation per share | $ / shares | $ 0.001 | ||||||||||||||
Redeemable Convertible Preferred Shares [Member] | |||||||||||||||
Class Of Stock [Line Items] | |||||||||||||||
Redeemable convertible shares, authorized | shares | 43,297,267 | ||||||||||||||
Redeemable convertible shares, par value | $ / shares | $ 0.001 | ||||||||||||||
Underwritten Public Offering [Member] | |||||||||||||||
Class Of Stock [Line Items] | |||||||||||||||
Payment of offering costs | $ 1,000,000 | ||||||||||||||
Underwritten Public Offering [Member] | Common Stock [Member] | |||||||||||||||
Class Of Stock [Line Items] | |||||||||||||||
Issuance of stock, shares | shares | 3,780,000 | ||||||||||||||
Share price | $ / shares | $ 12.50 | ||||||||||||||
Underwritten Public Offering [Member] | Series A Convertible Preferred Stock [Member] | |||||||||||||||
Class Of Stock [Line Items] | |||||||||||||||
Issuance of stock, shares | shares | 2,220 | ||||||||||||||
Share price | $ / shares | $ 12,500 | ||||||||||||||
Number of shares issuable upon conversion | shares | 1,000 | 1,000 | |||||||||||||
Percentage of shares owned by share holders | 9.99% | ||||||||||||||
Preferred stock, liquidation per share | $ / shares | $ 0.001 | ||||||||||||||
Voting rights | no |
Common Stock - Additional Infor
Common Stock - Additional Information (Detail) $ / shares in Units, $ in Thousands | Jul. 17, 2018USD ($)$ / sharesshares | Nov. 14, 2017USD ($)$ / sharesshares | Nov. 06, 2017USD ($)$ / sharesshares | Oct. 20, 2017 | Jun. 30, 2017$ / sharesshares | Dec. 31, 2018USD ($)$ / sharesshares | Dec. 31, 2017USD ($)$ / sharesshares | Dec. 31, 2016$ / sharesshares | Dec. 11, 2018USD ($) |
Class Of Stock [Line Items] | |||||||||
Common stock, shares authorized | shares | 61,917,986 | 60,000,000 | 60,000,000 | ||||||
Common stock, par value | $ / shares | $ 0.001 | $ 0.001 | $ 0.001 | $ 0.001 | |||||
Common stock, voting rights | Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders. | ||||||||
Number of shares repurchased unvested common units upon forfeiture | shares | 21,116 | ||||||||
Share price | $ / shares | $ 0.001 | ||||||||
Net proceeds from issuance of common stock | $ 77,749 | ||||||||
Offering expenses payable | 3,574 | ||||||||
Deferred offering costs | $ 316 | ||||||||
Common Stock [Member] | |||||||||
Class Of Stock [Line Items] | |||||||||
Reverse stock split ratio | 0.164544 | ||||||||
Reverse stock split | one-for-6.0774 | ||||||||
Net proceeds from issuance of common stock | $ 6,100 | $ 71,600 | |||||||
Spero Therapeutics, LLC [Member] | |||||||||
Class Of Stock [Line Items] | |||||||||
Conversion of stock | shares | 1 | ||||||||
Initial Public Offering [Member] | |||||||||
Class Of Stock [Line Items] | |||||||||
Common stock, shares authorized | shares | 60,000,000 | ||||||||
Common stock, par value | $ / shares | $ 0.001 | ||||||||
Offering expenses payable | $ 3,574 | ||||||||
Initial Public Offering [Member] | Common Stock [Member] | |||||||||
Class Of Stock [Line Items] | |||||||||
Share price | $ / shares | $ 14 | $ 14 | |||||||
Issuance of stock, shares | shares | 471,498 | 5,500,000 | 5,971,498 | ||||||
Underwritten Public Offering [Member] | |||||||||
Class Of Stock [Line Items] | |||||||||
Net proceeds from issuance of common and preferred stock | $ 70,500 | ||||||||
Offering expenses payable | $ 1,000 | ||||||||
Underwritten Public Offering [Member] | Series A Convertible Preferred Stock [Member] | |||||||||
Class Of Stock [Line Items] | |||||||||
Share price | $ / shares | $ 12,500 | ||||||||
Issuance of stock, shares | shares | 2,220 | ||||||||
Number of shares issuable upon conversion | shares | 1,000 | 1,000 | |||||||
Underwritten Public Offering [Member] | Common Stock [Member] | |||||||||
Class Of Stock [Line Items] | |||||||||
Share price | $ / shares | $ 12.50 | ||||||||
Issuance of stock, shares | shares | 3,780,000 | ||||||||
At-The-Market Offering Program [Member] | Sales Agreement [Member] | Cantor Fitzgerald & Co [Member] | |||||||||
Class Of Stock [Line Items] | |||||||||
Deferred offering costs | $ 300 | ||||||||
At-The-Market Offering Program [Member] | Sales Agreement [Member] | Cantor Fitzgerald & Co [Member] | Maximum [Member] | |||||||||
Class Of Stock [Line Items] | |||||||||
Authorized offering value | $ 200,000 | ||||||||
Common stock available for issuance | $ 50,000 | ||||||||
At-The-Market Offering Program [Member] | Common Stock [Member] | Sales Agreement [Member] | Cantor Fitzgerald & Co [Member] | |||||||||
Class Of Stock [Line Items] | |||||||||
Issuance of stock, shares | shares | 0 |
Share-Based Compensation - Addi
Share-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions | Jul. 31, 2017 | Jun. 28, 2017 | Jun. 30, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Oct. 18, 2017 | Oct. 17, 2017 |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||||||
Exercise price of stock options | $ 5.90 | |||||||
Incentive Units | ||||||||
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||||||
Number of shares cancelled in connection with reorganization | 402,857 | |||||||
Stock Option [Member] | ||||||||
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||||||
Options additionally granted for purchase of common stock | 503,730 | |||||||
Weighted average grant-date fair value of awards granted | $ 7.63 | $ 4.72 | $ 3.40 | |||||
Aggregate intrinsic value of stock options exercised | $ 0.3 | |||||||
Stock option exercised | 56,780 | 0 | 0 | |||||
Total unrecognized compensation cost related to unvested share-based awards | $ 7.9 | |||||||
Weighted average period | 2 years 8 months 12 days | |||||||
Operating Agreement [Member] | ||||||||
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||||||
Number of shares authorized for issuance | 573,156 | |||||||
Common stock available for issuance | 159,890 | |||||||
2017 Plan [Member] | ||||||||
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||||||
Options vesting period | 4 years | |||||||
Number of shares authorized for issuance | 1,785,416 | 2,696,401 | 1,785,416 | |||||
Common stock available for issuance | 341,811 | |||||||
Options additionally granted for purchase of common stock | 1,154,989 | |||||||
Exercise price of stock options | $ 5.90 | |||||||
Fair value of option grants | $ 3.96 | |||||||
Number of shares to be incremented | 607,324 | |||||||
Percentage of outstanding shares of common stock to be incremented | 4.00% | |||||||
2017 Plan [Member] | Minimum [Member] | ||||||||
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||||||
Options vesting period | 10 years | |||||||
Exercise price per share of stock options as a percentage of fair market value of share of common stock | 100.00% | |||||||
25% Incentive Units Vesting [Member] | ||||||||
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||||||
Percentage of incentive units vesting | 25.00% | |||||||
Share-based compensation arrangement by share-based payment award, award requisite service period | 1 year | |||||||
Remaining Balance of Incentive Units Vesting [Member] | ||||||||
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||||||
Options vesting period | 36 months |
Share-Based Compensation - Summ
Share-Based Compensation - Summary of Fair Value of Incentive Unit and Stock Option Awards Granted to Employees and Directors (Detail) | 12 Months Ended | ||
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | |
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract] | |||
Risk-free interest rate | 2.70% | 2.00% | 1.30% |
Expected term (in years) | 6 years 3 months 18 days | 6 years 1 month 6 days | 6 years 3 months 18 days |
Expected volatility | 74.10% | 77.10% | 76.50% |
Expected dividend yield | 0.00% | 0.00% | 0.00% |
Share-Based Compensation - Su_2
Share-Based Compensation - Summary of Stock Option Activity (Detail) - Stock Option [Member] - USD ($) $ / shares in Units, $ in Thousands | 12 Months Ended | ||
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | |
Number of Shares | |||
Outstanding, Beginning Balance | 2,011,296 | ||
Granted | 503,730 | ||
Exercised | (56,780) | 0 | 0 |
Forfeited | (160,436) | ||
Outstanding Ending Balance | 2,297,810 | 2,011,296 | |
Outstanding- vested and expected to vest Ending Balance | 2,294,629 | ||
Exercisable Ending Balance | 845,851 | ||
Weighted Average Exercise Price | |||
Outstanding Beginning Balance | $ 7.24 | ||
Granted | 11.30 | ||
Exercised | 5.90 | ||
Forfeited | 9.13 | ||
Outstanding Ending Balance | 8.03 | $ 7.24 | |
Outstanding- vested and expected to vest Ending Balance | 8.03 | ||
Exercisable Ending Balance | $ 6.69 | ||
Weighted Average Contractual Term | |||
Outstanding | 8 years 9 months 7 days | 9 years 4 months 17 days | |
Outstanding - vested and expected to vest Ending Balance | 8 years 7 months 13 days | ||
Exercisable Ending Balance | 8 years 6 months 25 days | ||
Aggregate Intrinsic Value | |||
Outstanding Balance | $ 354 | $ 9,074 | |
Outstanding - vested and expected to vest Ending Balance | 354 | ||
Outstanding Ending Balance | $ 183 |
Share-Based Compensation - Su_3
Share-Based Compensation - Summary of Share-Based Compensation Expense (Detail) - USD ($) $ in Thousands | 12 Months Ended | ||
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
Share-based compensation expense | $ 2,749 | $ 1,427 | $ 180 |
Research and Development Expenses [Member] | |||
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
Share-based compensation expense | 1,072 | 371 | 66 |
Research and Development Expenses [Member] | |||
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
Share-based compensation expense | $ 1,677 | $ 1,056 | $ 114 |
Non-Controlling Interests - Spe
Non-Controlling Interests - Spero Potentiator - Additional Information (Detail) - USD ($) | 1 Months Ended | 12 Months Ended | ||||||
Jun. 30, 2017 | Aug. 31, 2016 | Jan. 31, 2016 | Nov. 30, 2015 | Feb. 28, 2015 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | |
Noncontrolling Interest [Line Items] | ||||||||
Research and development expense | $ 33,885,000 | $ 32,869,000 | $ 26,333,000 | |||||
Non-controlling interest | 355,000 | $ 355,000 | ||||||
Spero Potentiator, Inc. [Member] | ||||||||
Noncontrolling Interest [Line Items] | ||||||||
Common stock shares issued | 2,160 | 2,160 | 2,736 | |||||
Proceeds from the issuance of common stock, net of issuance costs | $ 0 | $ 0 | $ 0 | |||||
Non-controlling interest | $ 0 | |||||||
Spero Potentiator, Inc. [Member] | Anti- dilution Rights [Member] | ||||||||
Noncontrolling Interest [Line Items] | ||||||||
Fair value of derivative liability | $ 2,400,000 | |||||||
Spero Potentiator, Inc. [Member] | Northern Antibiotics Oy Ltd. [Member] | ||||||||
Noncontrolling Interest [Line Items] | ||||||||
Common stock shares issued | 2,160 | 2,160 | 2,736 | 996 | ||||
Common stock issued, aggregate fair value | $ 1,100,000 | |||||||
Increase in non-controlling interest and reduction of derivative liability | $ 1,000,000 | $ 1,000,000 | $ 1,500,000 | |||||
Cash payment for repurchase of shares | $ 1,000,000 | |||||||
Contingent consideration | 100,000 | |||||||
Milestone payments | 7,000,000 | |||||||
Cash payment for repurchase of shares | 2,500,000 | |||||||
Non-controlling interest | 6,400,000 | |||||||
Increase to accumulated deficit | $ 1,000,000 | |||||||
Spero Potentiator, Inc. [Member] | Northern Antibiotics Oy Ltd. [Member] | Anti- dilution Rights [Member] | ||||||||
Noncontrolling Interest [Line Items] | ||||||||
Ownership percentage | 49.90% | |||||||
Proceeds from the issuance of common stock, net of issuance costs | $ 0 | $ 0 | $ 0 | $ 0 | ||||
Spero Potentiator, Inc. [Member] | Northern Antibiotics Oy Ltd. [Member] | Anti- dilution Rights [Member] | Prior to IND [Member] | ||||||||
Noncontrolling Interest [Line Items] | ||||||||
Maximum amounts of investments for anti-dilution protection | 5,000,000 | |||||||
Spero Potentiator, Inc. [Member] | Northern Antibiotics Oy Ltd. [Member] | Anti- dilution Rights [Member] | Post IND [Member] | ||||||||
Noncontrolling Interest [Line Items] | ||||||||
Maximum amounts of investments for anti-dilution protection | 6,500,000 | |||||||
Spero Potentiator, Inc. [Member] | Northern Antibiotics Oy Ltd. [Member] | Licensing Agreements [Member] | ||||||||
Noncontrolling Interest [Line Items] | ||||||||
Research and development expense | $ 1,100,000 |
Non-Controlling Interests - S_2
Non-Controlling Interests - Spero Europe - Additional Information (Detail) - USD ($) | 1 Months Ended | 12 Months Ended | |||
Jan. 31, 2016 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | May 31, 2017 | |
Noncontrolling Interest [Line Items] | |||||
Research and development expense | $ 33,885,000 | $ 32,869,000 | $ 26,333,000 | ||
Non-controlling interest | 355,000 | $ 355,000 | |||
Spero Europe, Ltd. [Member] | |||||
Noncontrolling Interest [Line Items] | |||||
Termination of agreement notice period | 30 days | ||||
Non-controlling interest | $ 0 | ||||
Spero Europe, Ltd. [Member] | Maximum [Member] | |||||
Noncontrolling Interest [Line Items] | |||||
Non-controlling interest | $ 100,000 | ||||
Spero Europe, Ltd. [Member] | Licensing Agreements [Member] | Anti- dilution Rights [Member] | |||||
Noncontrolling Interest [Line Items] | |||||
Research and development expense | $ 200,000 | ||||
Spero Europe, Ltd. [Member] | Promiliad Biopharma, Inc. [Member] | |||||
Noncontrolling Interest [Line Items] | |||||
Ownership percentage | 5.00% | 5.00% | |||
Common stock issued, aggregate fair value | $ 100,000 | ||||
Milestone payments | 4,100,000 | ||||
Proceeds from the issuance of common stock, net of issuance costs | 0 | ||||
Maximum amounts of investments for anti-dilution protection | $ 5,000,000 | ||||
Spero Europe, Ltd. [Member] | Promiliad Biopharma, Inc. [Member] | Anti- dilution Rights [Member] | |||||
Noncontrolling Interest [Line Items] | |||||
Ownership percentage | 5.00% | ||||
Spero Europe, Ltd. [Member] | Promiliad Biopharma, Inc. [Member] | Licensing Agreements [Member] | |||||
Noncontrolling Interest [Line Items] | |||||
Research and development expense | $ 100,000 |
Non-Controlling Interests - S_3
Non-Controlling Interests - Spero Gyrase - Additional Information (Detail) - USD ($) | 1 Months Ended | 12 Months Ended | ||
Mar. 31, 2016 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | |
Noncontrolling Interest [Line Items] | ||||
Research and development expense | $ 33,885,000 | $ 32,869,000 | $ 26,333,000 | |
Spero Gyrase, Inc. [Member] | Anti- dilution Rights [Member] | Research and Development Expenses [Member] | ||||
Noncontrolling Interest [Line Items] | ||||
Fair value of derivative liability | $ 1,600,000 | |||
Spero Gyrase, Inc. [Member] | Aviragen Therapeutics, Inc. [Member] | ||||
Noncontrolling Interest [Line Items] | ||||
Common stock shares issued | 200 | |||
Common stock issued, aggregate fair value | $ 1,100,000 | |||
Ownership percentage | 20.00% | 20.00% | ||
Spero Gyrase, Inc. [Member] | Aviragen Therapeutics, Inc. [Member] | Anti- dilution Rights [Member] | ||||
Noncontrolling Interest [Line Items] | ||||
Ownership percentage | 20.00% | |||
Proceeds from the issuance of common stock, net of issuance costs | $ 0 | |||
Spero Gyrase, Inc. [Member] | Aviragen Therapeutics, Inc. [Member] | Anti- dilution Rights [Member] | Maximum [Member] | ||||
Noncontrolling Interest [Line Items] | ||||
Gross proceeds from equity financings | 8,000,000 | |||
Spero Gyrase, Inc. [Member] | Aviragen Therapeutics, Inc. [Member] | Technology-Based Intangible Assets [Member] | ||||
Noncontrolling Interest [Line Items] | ||||
Research and development expense | $ 1,100,000 |
Non-Controlling Interests - S_4
Non-Controlling Interests - Spero Cantab - Additional Information (Detail) | 1 Months Ended | 12 Months Ended | |||
Jul. 31, 2017USD ($) | Jun. 30, 2016USD ($)Optionshares | Dec. 31, 2018USD ($)Option | Dec. 31, 2017USD ($) | Dec. 31, 2016USD ($) | |
Noncontrolling Interest [Line Items] | |||||
Research and development expense | $ 33,885,000 | $ 32,869,000 | $ 26,333,000 | ||
Non-controlling interest | 355,000 | 355,000 | |||
Spero Cantab [Member] | |||||
Noncontrolling Interest [Line Items] | |||||
Non-controlling interest | 0 | ||||
Spero Cantab [Member] | Pro Bono Bio PLC [Member] | |||||
Noncontrolling Interest [Line Items] | |||||
Ownership percentage | 12.50% | ||||
Spero Cantab [Member] | Cantab Agreements [Member] | |||||
Noncontrolling Interest [Line Items] | |||||
Common stock shares issued | shares | 125 | ||||
Common stock issued, aggregate fair value | $ 1,600,000 | ||||
Upfront consideration | 300,000 | ||||
Non-controlling interest | 1,600,000 | ||||
Cash payment for repurchase of shares | $ 200,000 | ||||
Spero Cantab [Member] | Cantab Agreements [Member] | Contingent Milestone Payments [Member] | |||||
Noncontrolling Interest [Line Items] | |||||
Cash payment for repurchase of shares | $ 100,000 | ||||
Spero Cantab [Member] | Cantab Agreements [Member] | Pro Bono Bio PLC [Member] | |||||
Noncontrolling Interest [Line Items] | |||||
Maximum amounts of investments for anti-dilution protection | $ 8,000,000 | ||||
Spero Cantab [Member] | Cantab Agreements [Member] | Pro Bono Bio PLC [Member] | Maximum [Member] | |||||
Noncontrolling Interest [Line Items] | |||||
Ownership percentage | 12.50% | ||||
Spero Cantab [Member] | Cantab Agreements [Member] | Pro Bono Bio PLC [Member] | Minimum [Member] | |||||
Noncontrolling Interest [Line Items] | |||||
Ownership percentage | 5.00% | ||||
Spero Cantab [Member] | Cantab Anti Infectives Ltd. [Member] | Cantab Agreements [Member] | |||||
Noncontrolling Interest [Line Items] | |||||
Research and development expense | $ 300,000 | ||||
Spero Cantab [Member] | Cantab Anti Infectives Ltd. [Member] | Cantab Agreements [Member] | Niaid [Member] | |||||
Noncontrolling Interest [Line Items] | |||||
Maximum potential funding from government contract | $ 6,300,000 | ||||
Number of option period for funding from government contract | Option | 3 | ||||
Maximum received fund | 1,300,000 | ||||
Amount paid upfront as part of agreement | $ 300,000 | ||||
Spero Cantab [Member] | Cantab Anti Infectives Ltd. [Member] | Cantab Agreements [Member] | Niaid [Member] | First Option [Member] | |||||
Noncontrolling Interest [Line Items] | |||||
Number of option period for funding from government contract | Option | 2 | ||||
Committed amount from government contract to date | $ 5,700,000 | ||||
Spero Cantab [Member] | Pro Bono Bio PLC [Member] | Cantab Agreements [Member] | Niaid [Member] | Research and Development Expenses [Member] | |||||
Noncontrolling Interest [Line Items] | |||||
Expense associated with amounts payable under agreement | 400,000 | ||||
Spero Cantab [Member] | New Pharma License Holding Limited [Member] | Cantab Agreements [Member] | |||||
Noncontrolling Interest [Line Items] | |||||
Research and development expense | $ 1,600,000 | ||||
Spero Gyrase, Inc. [Member] | |||||
Noncontrolling Interest [Line Items] | |||||
Non-controlling interest | $ 400,000 | $ 400,000 |
Income Taxes - Additional Infor
Income Taxes - Additional Information (Detail) - USD ($) | 12 Months Ended | ||
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | |
Income Taxes [Line Items] | |||
Income tax benefits for the net operating losses | $ 0 | $ 0 | $ 0 |
Federal net operating loss carryforwards | 100,400,000 | ||
State net operating loss carryforwards | $ 100,300,000 | ||
Federal and state operating loss carryforwards expiration period | 2033 | ||
Foreign net operating loss carryforwards | $ 11,700,000 | ||
Maximum increase in percentage ownership of stockholders or public groups | 50.00% | ||
Ownership change, increase in ownership percentage, term | 3 years | ||
Unrecognized tax benefits | $ 0 | 0 | |
Accrued interest or penalties related to uncertain tax positions | $ 0 | $ 0 | |
Federal corporate income tax rate | 21.00% | 34.00% | 34.00% |
Tax cut and jobs act net operating loss deduction limitation percentage | 80.00% | ||
Decrease in deferred tax asset | $ 9,400,000 | ||
Federal [Member] | |||
Income Taxes [Line Items] | |||
Tax credit carryforward | $ 2,600,000 | ||
Tax credit carryforward expiration period | 2033 | ||
State [Member] | |||
Income Taxes [Line Items] | |||
Tax credit carryforward | $ 800,000 | ||
Tax credit carryforward expiration period | 2028 |
Income Taxes - Schedule of Dome
Income Taxes - Schedule of Domestic and Foreign Components of Loss before Income Taxes (Detail) - USD ($) $ in Thousands | 12 Months Ended | ||
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | |
Income Tax Disclosure [Abstract] | |||
Domestic | $ (33,236) | $ (38,706) | $ (27,148) |
Foreign | (8,426) | (1,180) | (5,493) |
Loss before income taxes | $ (41,662) | $ (39,886) | $ (32,641) |
Income Taxes - Reconciliation o
Income Taxes - Reconciliation of U.S. Federal Statutory Income Tax Rate to Company's Effective Income Tax Rate (Detail) | 12 Months Ended | ||
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | |
Income Tax Disclosure [Abstract] | |||
Federal statutory income tax rate | (21.00%) | (34.00%) | (34.00%) |
Federal and state research and development tax credit | (2.60%) | (3.30%) | (1.70%) |
State taxes, net of federal benefit | (5.40%) | (5.30%) | (4.40%) |
Foreign rate differential | 1.90% | 0.10% | 2.30% |
Nondeductible items | 1.20% | (0.10%) | 4.80% |
Effect of US tax reform | 23.80% | ||
Increase in deferred tax asset valuation allowance | 25.90% | 18.80% | 33.00% |
Income Taxes - Net Deferred Tax
Income Taxes - Net Deferred Tax Assets (Detail) - USD ($) $ in Thousands | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 |
Income Tax Disclosure [Abstract] | |||
Net operating loss carryforwards | $ 29,025 | $ 21,754 | |
Research and development tax credit carryforwards | 3,385 | 2,022 | |
Other | 1,731 | 743 | |
Total deferred tax assets | 34,141 | 24,519 | |
Valuation allowance | $ (34,141) | $ (24,519) | $ (17,152) |
Income Taxes - Summary of Chang
Income Taxes - Summary of Changes in Valuation Allowance for Deferred Tax Assets (Detail) - USD ($) $ in Thousands | 12 Months Ended | |
Dec. 31, 2018 | Dec. 31, 2017 | |
Income Tax Disclosure [Abstract] | ||
Valuation allowance as of beginning of year | $ (24,519) | $ (17,152) |
Increases recorded to income tax provision | (9,622) | (7,367) |
Valuation allowance as of end of year | $ (34,141) | $ (24,519) |
Commitments and Contingencies -
Commitments and Contingencies - Additional Information (Detail) $ in Millions | Jan. 17, 2018USD ($)ft²Option | Jul. 31, 2016USD ($) | Aug. 31, 2015USD ($) | Dec. 31, 2018USD ($) | Dec. 31, 2017USD ($) | Dec. 31, 2016USD ($) |
Other Commitments [Line Items] | ||||||
Rent expense | $ 0.8 | $ 0.8 | $ 0.4 | |||
Office Space [Member] | ||||||
Other Commitments [Line Items] | ||||||
Operating lease beginning date | 2016-01 | |||||
Operating lease expiration date | 2020-12 | |||||
Annual lease payments | $ 0.4 | |||||
Term of lease | 5 years | |||||
Lease renewal term | 5 years | |||||
Security deposit | $ 0.2 | |||||
Annual rent escalations and tenant incentives | 0.7 | |||||
Amount reimbursed | $ 0.3 | |||||
Office Space [Member] | Lease Agreements [Member] | Cambridge, Massachusetts [Member] | U.S. REIF Central Plaza Massachusetts, LLC [Memebr] | ||||||
Other Commitments [Line Items] | ||||||
Term of lease | 7 years | |||||
Lease renewal term | 5 years | |||||
Lease expiration date | Dec. 22, 2018 | |||||
Area of office space | ft² | 7,800 | |||||
Number of renewal options | Option | 2 | |||||
Operating lease, option to extend | the Company has two consecutive options to extend the Lease Term for an additional period of five years (the “Option Terms”), subject to certain conditions, upon notice to the Landlord. | |||||
Operating leases annual base rent initial | $ 0.5 | |||||
Operating leases annual base rent final | $ 0.6 | |||||
Operating lease percentage of annual base rent | 100.00% | |||||
Leasehold improvements receivable from the landlord | $ 0.4 | |||||
Laboratory Space [Member] | ||||||
Other Commitments [Line Items] | ||||||
Annual lease payments | $ 0.3 | |||||
Lease expiration date | Nov. 30, 2019 |
Commitments and Contingencies_2
Commitments and Contingencies - Summary of Future Minimum Payments Due Under Operating Leases (Detail) $ in Thousands | Dec. 31, 2018USD ($) |
Operating Leases Future Minimum Payments Due [Abstract] | |
2019 | $ 1,361 |
2020 | 1,054 |
2021 | 995 |
2022 | 1,107 |
2023 | 1,123 |
2024 | 1,138 |
2025 | 1,108 |
Total | $ 7,886 |
Government Contracts - Addition
Government Contracts - Additional Information (Detail) | 1 Months Ended | 3 Months Ended | 12 Months Ended | ||||||||||||||||
Jan. 31, 2019 | Jul. 31, 2018USD ($)Option | Feb. 28, 2018USD ($) | Apr. 30, 2017USD ($) | Feb. 28, 2017USD ($) | Sep. 30, 2016USD ($) | Jun. 30, 2016USD ($)Option | Dec. 31, 2018USD ($) | Sep. 30, 2018USD ($) | Jun. 30, 2018USD ($) | Mar. 31, 2018USD ($) | Dec. 31, 2017USD ($) | Sep. 30, 2017USD ($) | Jun. 30, 2017USD ($) | Mar. 31, 2017USD ($) | Dec. 31, 2018USD ($)Option | Dec. 31, 2017USD ($) | Dec. 31, 2016USD ($) | Mar. 12, 2018USD ($) | |
Government Contracts [Line Items] | |||||||||||||||||||
Grant revenue | $ 1,692,000 | $ 658,000 | $ 463,000 | $ 1,153,000 | $ 993,000 | $ 597,000 | $ 249,000 | $ 140,000 | $ 3,966,000 | $ 1,979,000 | $ 335,000 | ||||||||
Amounts receivable under agreement | 376,000 | $ 1,011,000 | 376,000 | 1,011,000 | |||||||||||||||
BARDA [Member] | |||||||||||||||||||
Government Contracts [Line Items] | |||||||||||||||||||
Potential contract amount awarded | $ 44,200,000 | ||||||||||||||||||
Option exercise | Option | 2 | ||||||||||||||||||
BARDA [Member] | Maximum [Member] | Other Receivables [Member] | |||||||||||||||||||
Government Contracts [Line Items] | |||||||||||||||||||
Revenue invoiced but unpaid | 300,000 | 300,000 | |||||||||||||||||
BARDA [Member] | Base Period Contracts [Member] | |||||||||||||||||||
Government Contracts [Line Items] | |||||||||||||||||||
Potential amount initial funding awarded | $ 15,700,000 | ||||||||||||||||||
Contract term | 3 years | ||||||||||||||||||
BARDA [Member] | Grant [Member] | |||||||||||||||||||
Government Contracts [Line Items] | |||||||||||||||||||
Grant revenue | 1,400,000 | ||||||||||||||||||
BARDA [Member] | First Option [Member] | |||||||||||||||||||
Government Contracts [Line Items] | |||||||||||||||||||
Potential grant amount awarded | $ 13,600,000 | ||||||||||||||||||
BARDA [Member] | Second Option [member] | |||||||||||||||||||
Government Contracts [Line Items] | |||||||||||||||||||
Potential grant amount awarded | $ 14,900,000 | ||||||||||||||||||
U.S. Department of Defense [Member] | |||||||||||||||||||
Government Contracts [Line Items] | |||||||||||||||||||
Contract term | 2 years | ||||||||||||||||||
Potential grant amount awarded | $ 1,500,000 | ||||||||||||||||||
U.S. Department of Defense [Member] | Maximum [Member] | Other Receivables [Member] | |||||||||||||||||||
Government Contracts [Line Items] | |||||||||||||||||||
Revenue invoiced but unpaid | 100,000 | 100,000 | |||||||||||||||||
U.S. Department of Defense [Member] | Grant [Member] | |||||||||||||||||||
Government Contracts [Line Items] | |||||||||||||||||||
Grant revenue | 300,000 | ||||||||||||||||||
Niaid [Member] | |||||||||||||||||||
Government Contracts [Line Items] | |||||||||||||||||||
Contract term | 12 months | ||||||||||||||||||
Niaid [Member] | Spero Cantab [Member] | Cantab Anti Infectives Ltd. [Member] | Cantab Agreements [Member] | |||||||||||||||||||
Government Contracts [Line Items] | |||||||||||||||||||
Maximum potential funding from government contract | $ 6,300,000 | ||||||||||||||||||
Number of option period for funding from government contract | Option | 3 | ||||||||||||||||||
Maximum received fund | 1,300,000 | ||||||||||||||||||
Amount paid upfront as part of agreement | 300,000 | ||||||||||||||||||
Niaid [Member] | Spero Cantab [Member] | Pro Bono Bio PLC [Member] | Cantab Agreements [Member] | |||||||||||||||||||
Government Contracts [Line Items] | |||||||||||||||||||
Grant revenue | 1,300,000 | ||||||||||||||||||
Niaid [Member] | Spero Cantab [Member] | Pro Bono Bio PLC [Member] | Cantab Agreements [Member] | Research and Development Expenses [Member] | |||||||||||||||||||
Government Contracts [Line Items] | |||||||||||||||||||
Expense associated with amounts payable under agreement | 400,000 | ||||||||||||||||||
Niaid [Member] | Maximum [Member] | Other Receivables [Member] | |||||||||||||||||||
Government Contracts [Line Items] | |||||||||||||||||||
Revenue invoiced but unpaid | 100,000 | 100,000 | |||||||||||||||||
Niaid [Member] | Base Period Contracts [Member] | |||||||||||||||||||
Government Contracts [Line Items] | |||||||||||||||||||
Potential grant amount awarded | $ 600,000 | ||||||||||||||||||
Niaid [Member] | Grant [Member] | |||||||||||||||||||
Government Contracts [Line Items] | |||||||||||||||||||
Grant revenue | $ 500,000 | ||||||||||||||||||
Niaid [Member] | Option Period Contracts [Member] | |||||||||||||||||||
Government Contracts [Line Items] | |||||||||||||||||||
Contract term | 12 months | ||||||||||||||||||
Potential grant amount awarded | $ 400,000 | ||||||||||||||||||
Potential grant amount exercised | $ 400,000 | ||||||||||||||||||
Niaid [Member] | Option Period Contracts [Member] | Subsequent Event [Member] | |||||||||||||||||||
Government Contracts [Line Items] | |||||||||||||||||||
Contract term extended | 12 months | ||||||||||||||||||
Niaid [Member] | First Option [Member] | Spero Cantab [Member] | Cantab Anti Infectives Ltd. [Member] | Cantab Agreements [Member] | |||||||||||||||||||
Government Contracts [Line Items] | |||||||||||||||||||
Number of option period for funding from government contract | Option | 2 | ||||||||||||||||||
Committed amount from government contract | $ 5,700,000 | ||||||||||||||||||
CARB-X [Member] | |||||||||||||||||||
Government Contracts [Line Items] | |||||||||||||||||||
Contract term | 12 months | ||||||||||||||||||
Potential grant amount awarded | $ 1,500,000 | ||||||||||||||||||
Potential grant amount exercised | $ 0 | ||||||||||||||||||
Amounts receivable under agreement | $ 0 | $ 0 | |||||||||||||||||
CARB-X [Member] | First Option [Member] | |||||||||||||||||||
Government Contracts [Line Items] | |||||||||||||||||||
Potential grant amount awarded | $ 400,000 | ||||||||||||||||||
CARB-X [Member] | Grant [Member] | |||||||||||||||||||
Government Contracts [Line Items] | |||||||||||||||||||
Grant revenue | $ 500,000 |
Collaboration and License Agr_2
Collaboration and License Agreements - Additional Information (Detail) £ in Millions | 1 Months Ended | 3 Months Ended | 12 Months Ended | ||||||||||||||
Nov. 30, 2017USD ($) | Jun. 30, 2017USD ($) | Nov. 30, 2016USD ($) | Jun. 30, 2016USD ($) | Jun. 30, 2016GBP (£) | May 31, 2016USD ($) | Mar. 31, 2016USD ($) | Apr. 30, 2014USD ($) | Dec. 31, 2018USD ($) | Dec. 31, 2018USD ($) | Dec. 31, 2017USD ($) | Dec. 31, 2016USD ($) | Dec. 31, 2015USD ($) | Dec. 31, 2014USD ($) | Oct. 31, 2017USD ($) | Sep. 30, 2014shares | Mar. 31, 2014shares | |
Roche Collaboration Agreements [Member] | |||||||||||||||||
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items] | |||||||||||||||||
Research and development agreement, potential investment | $ 2,000,000 | ||||||||||||||||
Percentage of issuance price | 90.00% | ||||||||||||||||
Nonrefundable upfront payments | $ 2,000,000 | ||||||||||||||||
Nonrefundable maintenance fees | $ 1,000,000 | ||||||||||||||||
Termination fee | $ 0 | ||||||||||||||||
Reductions of research and development expense | $ 900,000 | ||||||||||||||||
MGH License Agreement [Member] | |||||||||||||||||
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items] | |||||||||||||||||
Termination fee | $ 0 | ||||||||||||||||
Common units issued | shares | 24,681 | ||||||||||||||||
Ascenion License Agreement [Member] | |||||||||||||||||
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items] | |||||||||||||||||
Termination fee | $ 0 | ||||||||||||||||
Common units issued | shares | 9,625 | ||||||||||||||||
Aviragen Agreement [Member] | |||||||||||||||||
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items] | |||||||||||||||||
Potential milestone payment upon achievement of specified clinical, regulatory and commercial milestones | $ 12,000,000 | ||||||||||||||||
Cantab Related Agreements [Member] | |||||||||||||||||
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items] | |||||||||||||||||
Potential milestone payment upon achievement of specified clinical and regulatory milestones | $ 5,800,000 | ||||||||||||||||
Potential milestone payment upon achievement of specified commercial milestone | £ 5 | $ 6,400,000 | $ 6,700,000 | ||||||||||||||
License agreement research and development expense related to achievement of regulatory milestones | 200,000 | ||||||||||||||||
Contract termination period | 10 years | 10 years | |||||||||||||||
Vertex License Agreement [Member] | |||||||||||||||||
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items] | |||||||||||||||||
Nonrefundable upfront payments | $ 500,000 | ||||||||||||||||
License agreement research and development expense related to achievement of regulatory milestones | $ 200,000 | ||||||||||||||||
Contract termination period | 10 years | ||||||||||||||||
Potential milestone payment upon achievement of specified clinical, regulatory and commercial milestones | $ 81,100,000 | ||||||||||||||||
Contract termination period if no material development or commercialization occurs | 1 year | ||||||||||||||||
Meiji License Agreement [Member] | |||||||||||||||||
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items] | |||||||||||||||||
Nonrefundable upfront payments | $ 600,000 | ||||||||||||||||
Potential milestone payment upon achievement of specified clinical and regulatory milestones | 3,000,000 | ||||||||||||||||
Potential milestone payments upon achievement of specified condition | $ 1,000,000 | ||||||||||||||||
License agreement fixed assets related payments | $ 1,600,000 | ||||||||||||||||
Meiji License Agreement [Member] | Maximum [Member] | |||||||||||||||||
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items] | |||||||||||||||||
Sublicense fee payable to counter party | 7,500,000 | ||||||||||||||||
Northern License Agreement [Member] | |||||||||||||||||
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items] | |||||||||||||||||
Potential milestone payment upon achievement of specified clinical, regulatory and other milestones | 7,000,000 | ||||||||||||||||
Potential milestone payment upon closing of initial public offering | 2,500,000 | ||||||||||||||||
Northern Exchange Agreement [Member] | |||||||||||||||||
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items] | |||||||||||||||||
Potential milestone payment upon closing of initial public offering | $ 100,000 | ||||||||||||||||
Northern License And Exchange Agreement [Member] | |||||||||||||||||
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items] | |||||||||||||||||
Potential milestone payment upon closing of initial public offering | $ 2,600,000 |
Australia Research and Develo_2
Australia Research and Development Tax Incentive - Additional Information (Detail) - Spero Potentiator Australia Pty Limited [Member] - USD ($) $ in Millions | 12 Months Ended | ||
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | |
Australia [Member] | |||
Schedule Of Income Tax [Line Items] | |||
Tax incentive receivable | $ 1.1 | $ 1.9 | |
Research and Development Expenses [Member] | |||
Schedule Of Income Tax [Line Items] | |||
Percentage of refundable tax incentive | 43.50% | ||
Reduction to research and development expenses | $ 1.2 | $ 1.8 | $ 0.1 |
Net Loss per Share - Summary of
Net Loss per Share - Summary of Basic and Diluted Net Loss per Share Attributable to Common Stockholders (Detail) - USD ($) $ / shares in Units, $ in Thousands | 3 Months Ended | 12 Months Ended | |||||||||
Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | |
Numerator: | |||||||||||
Net loss | $ (10,599) | $ (10,463) | $ (9,956) | $ (10,644) | $ (13,868) | $ (9,844) | $ (9,763) | $ (6,411) | $ (41,662) | $ (39,886) | $ (32,641) |
Less: Net loss attributable to non-controlling interests | (1,143) | (7,150) | |||||||||
Plus: Cumulative dividends on redeemable convertible preferred shares | (6,146) | (3,441) | |||||||||
Plus: Accretion of bridge units and redeemable convertible preferred shares to redemption value | (1,208) | (996) | |||||||||
Net loss attributable to common shareholders of Spero Therapeutics, Inc. | $ (14,770) | $ (12,076) | $ (12,121) | $ (7,130) | $ (41,662) | $ (46,097) | $ (29,928) | ||||
Denominator: | |||||||||||
Weighted average common shares outstanding, basic and diluted | 17,736,996 | 17,471,462 | 14,376,529 | 14,369,182 | 9,273,783 | 335,285 | 334,788 | 330,075 | 16,001,832 | 2,586,865 | 312,169 |
Net loss per share attributable to common stockholders of Spero Therapeutics, Inc., basic and diluted | $ (0.60) | $ (0.60) | $ (0.69) | $ (0.74) | $ (1.59) | $ (36.02) | $ (36.21) | $ (21.60) | $ (2.60) | $ (17.82) | $ (95.87) |
Net Loss per Share - Summary _2
Net Loss per Share - Summary of Shares Excluded From the Computation of Diluted Net Loss Per Share Attributable to Common Stockholders (Detail) - shares | 12 Months Ended | ||
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | |
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] | |||
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount | 5,517,810 | 2,011,296 | 2,642,784 |
Options to Purchase Common Stock [Member] | |||
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] | |||
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount | 2,297,810 | 2,011,296 | |
Series A Convertible Preferred Stock [Member] | |||
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] | |||
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount | 2,220,000 | ||
Redeemable Convertible Preferred Shares [Member] | |||
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] | |||
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount | 2,229,518 | ||
Series B Convertible Preferred Stock [Member] | |||
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] | |||
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount | 1,000,000 | ||
Incentive Units | |||
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] | |||
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount | 413,266 |
Retirement Plan - Additional In
Retirement Plan - Additional Information (Detail) | 12 Months Ended | ||
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | |
Defined Benefit Pension Plans And Defined Benefit Postretirement Plans Disclosure [Abstract] | |||
Matching contributions | 0.00% | 0.00% | 0.00% |
Quarterly Financial Data (Detai
Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands | 3 Months Ended | 12 Months Ended | |||||||||
Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | |
Quarterly Financial Information Disclosure [Abstract] | |||||||||||
Grant revenue | $ 1,692 | $ 658 | $ 463 | $ 1,153 | $ 993 | $ 597 | $ 249 | $ 140 | $ 3,966 | $ 1,979 | $ 335 |
Operating expenses | 12,776 | 11,593 | 10,434 | 11,969 | 14,993 | 10,563 | 10,414 | 7,739 | 46,772 | 43,709 | 33,556 |
Net loss | $ (10,599) | $ (10,463) | $ (9,956) | $ (10,644) | (13,868) | (9,844) | (9,763) | (6,411) | (41,662) | (39,886) | (32,641) |
Net loss attributable to Spero Therapeutics, Inc. | (13,862) | (9,836) | (9,169) | (5,876) | (41,662) | (38,743) | (25,491) | ||||
Net loss attributable to common shareholders of Spero Therapeutics, Inc. | $ (14,770) | $ (12,076) | $ (12,121) | $ (7,130) | $ (41,662) | $ (46,097) | $ (29,928) | ||||
Net loss per share attributable to common shareholders per share, basic and diluted | $ (0.60) | $ (0.60) | $ (0.69) | $ (0.74) | $ (1.59) | $ (36.02) | $ (36.21) | $ (21.60) | $ (2.60) | $ (17.82) | $ (95.87) |
Weighted average shares outstanding, basic and diluted: | 17,736,996 | 17,471,462 | 14,376,529 | 14,369,182 | 9,273,783 | 335,285 | 334,788 | 330,075 | 16,001,832 | 2,586,865 | 312,169 |
Subsequent Events - Additional
Subsequent Events - Additional Information (Detail) - Subsequent Event [Member] - License Agreement [Member] - Everest [Member] | Jan. 04, 2019USD ($) |
Subsequent Event [Line Items] | |
Period of option granted on an agreement | 12 months |
Upfront payment received | $ 3,000,000 |
Maximum additional milestone payments receivable | $ 59,500,000 |
Minimum [Member] | |
Subsequent Event [Line Items] | |
Agreement termination period upon written notice | 90 days |
Maximum [Member] | |
Subsequent Event [Line Items] | |
Agreement termination period upon written notice | 180 days |