As filed with the Securities and Exchange Commission on March 30, 2017December 31, 2020

Registration No. 333-                    

REGISTRATION NO. 333-

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, DCD.C. 20549

FORM S-3

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

Registration Statement Under the Securities Act of 1933

PHARMATHENE,ALTIMMUNE, INC.

(Exact nameName of registrantRegistrant as specifiedSpecified in its charter)Charter)

One Park Place,Delaware

(State or Other Jurisdiction of Incorporation or Organization)

20-2726770

(I.R.S. Employer Identification No.)

910 Clopper Road, Suite 450201S

Annapolis, MD 21401Gaithersburg, Maryland

(410) 269-2600Telephone: (240) 654-1450

(Address, including zip code,Including Zip Code, and telephone number, including area

code,Telephone Number, Including Area Code, of Registrant’s principal executive offices)Principal Executive Offices)

John M. Gill

Dr. Vipin K. Garg

Chief Executive Officer

PharmAthene,Altimmune, Inc.

One Park Place,910 Clopper Road, Suite 450201S

Annapolis, MD 21401Gaithersburg, Maryland

(410) 269-2600Telephone: (240) 654-1450

(Name, address, including zip code, and telephone number,

including area code, of agent for service)

With a copy

Copy to:

Jeffrey A. Baumel,Joseph C. Theis, Esq.

Dentons USGoodwin Procter LLP

1221100 Northern Avenue of the Americas

New York, New York 10020-1089Boston, Massachusetts 02210

(212) 768-6700Telephone: (617) 570-1000

Approximate date of commencement of proposed sale to the public:

From time to time after the effective date of this Registration Statement.registration statement.

If the only securities being registered on this Formform are being offered pursuant to dividend or interest reinvestment plans, please check the following box.¨  ☐

If any of the securities being registered on this Formform are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, other than securities offered only in connection with dividend or interest reinvestment plans, check the following box.x  ☒

If this Formform is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.o  ☐

If this Formform is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.o  ☐

If this Formform is a registration statement pursuant to General Instruction I.D. or a post-effective amendment thereto that shall become effective upon filing with the Commission pursuant to Rule 462(e) under the Securities Act, check the following box.o  ☐

If this Formform is a post-effective amendment to a registration statement filed pursuant to General Instruction I.D. filed to register additional securities or additional classes of securities pursuant to Rule 413(b) under the Securities Act, check the following box.o  ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer” andfiler,” “smaller reporting company” and “emerging growth company” in Rule 12b-2 of the Exchange Act. (Check one):Act:

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of Securities Act.  ☐

CALCULATION OF REGISTRATION FEE

(1) There are being registered an indeterminate number of securities as shall have an aggregate offering price not to exceed $100,000,000. The securities registered hereunder may be sold separately or with other securities registered hereunder. The proposed maximum aggregate offering price per class of security will be determined from time to time by the registrant in connection with the issuance by the registrant of the securities registered underhereby amends this registration statement and is not specified as to each class of security being registered under this registration statement pursuant to General Instruction II.D. of Form S-3 under the Securities Act of 1933, as amended (the “Securities Act”).

(2)  The proposed maximum offering price has been estimated solely for the purpose of calculating the registration fee in accordance with Rule 457(o) under the Securities Act.

(3)  Subject to note 1 above, there is being registered hereunder an indeterminate number of shares of common and preferred stock of the registrant as may be sold from time to time by the registrant. Pursuant to Rule 416 under the Securities Act, the shares being registered hereunder include such indeterminate number of shares of common and preferred stock as may be issuable from time to time with respect to the shares being registered hereunder as a result of stock splits, stock dividends or similar transactions. Pursuant to Rule 457(i) under the Securities Act, the shares being registered hereunder include such indeterminate number of shares of common and preferred stock as may be issuable from time to time upon conversion, exercise or exchange of any preferred stock or warrants issued under this registration statement.

(4)  Subject to note 1 above, there is being registered hereunder an indeterminate number of warrants to purchase common stock or preferred stock of one or more series. Pursuant to Rule 457(i) under the Securities Act, the warrants being registered hereunder include such indeterminate number of warrants as may be issuable upon conversion or exchange of any preferred stock issued under this registration statement.

The Registrant hereby amends this Registration Statement on such date or dates as may be necessary to delay its effective date until the Registrantregistrant shall file a further amendment whichthat specifically states that this Registration Statementregistration statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933, as amended, or until the Registration Statementthis registration statement shall become effective on such date as the Commission, acting pursuant to said Section 8(a), may determine.

ALTIMMUNE, INC.

This summary highlights selected information from this prospectus and does not contain all of the information that you need to consider in making your investment decision. You should carefully read the entire prospectus, the applicable prospectus supplement and any related free writing prospectus, including the risks of investing in our securities discussed under the heading “Risk Factors” contained in the applicable prospectus supplement onand any related free writing prospectus, and under similar headings in the other hand, you should rely on the information in the prospectus supplement.

You should carefully read both this prospectus and the applicable prospectus supplement, as well as any documents that are incorporated by reference ininto this prospectus (as described underprospectus. You should also carefully read the heading “Incorporation by Reference”) and/or the applicable prospectus supplement, before you make your investment decision. The information incorporated by reference includes important business and financial information about us that is not included nor delivered with this document. This information is available without charge on the SEC’s website at www.sec.gov or upon written or oral request to PharmAthene, Inc., One Park Place, Suite 450, Annapolis, MD 21401, (410) 269-2600. If any statement ininto this prospectus, including our financial statements, and the applicable prospectus supplement or any document incorporated by reference into oneexhibits to the registration statement of these documents is inconsistent with a statement in another of those document having a later date, the statement in the document having the later date modifies or supersedes the earlier statement.

Unless otherwise mentioned or unless the context requires otherwise, all references to “PharmAthene,” “the Company,” “we,” “us,” “our,” and similar terms refer to PharmAthene, Inc. and its subsidiaries on a consolidated basis. The phrase “this prospectus” refers towhich this prospectus and any applicable prospectus supplement, unless the context otherwise requires. Whenever we refer to “you” or “yours”, we mean the persons to whom offers are made under this prospectus.

is a part.

SUMMARY

Overview

We are a biodefense company engaged in developing next generation anthrax vaccine. These next generation vaccines are intended to have more rapid time to protection, fewer doses for protection and less stringent requirements for temperature controlled storage and handling than the currently used vaccine.

On September 9, 2014, we signed a contract with the National Institutes of Allergy and Infectious Diseases (“NIAID") for the development of a next generation lyophilized anthrax vaccine (“SparVax-L”) based on the Company’s proprietary technology platform which contributes the recombinant protective antigen (“rPA”) bulk drug substance that is used in the liquid SparVax® formulation. The contract is incrementally funded. Over the base period of the contract, we were awarded initial funding of approximately $5.2 million, which includes a cost reimbursement component and a fixed fee component payable upon achievement of certain milestones. NIAID has exercised four options under this agreement to provide additional funding of approximately $8.8 million and an extension of the period of performance through December 31, 2017. The contract has a total value of up to approximately $28.1 million, if all technical milestones are met and all eight contract options are exercised by NIAID. If NIAID exercises all options, the contract would last approximately five years. If NIAID does not exercise any additional options, the contract would expire by its terms on December 31, 2017.

From 2006 through 2016, we were engaged in legal proceedings with SIGA Technologies, Inc. (“SIGA”). On December 23, 2015, the Delaware Supreme Court affirmed the Delaware Court of Chancery’s judgment against SIGA. On November 16, 2016, the Company received a final payment from SIGA which fully satisfied the judgment owed to PharmAthene. In total, the Company received payment of approximately $217.1 million (including interest) from SIGA.

On November 17, 2016, PharmAthene declared a special one-time cash dividend of $2.91 per share of common stock. PharmAthene funded the one-time special dividend with approximately 98% of the after tax net cash proceeds that PharmAthene received from SIGA in satisfaction of the judgment owed to PharmAthene. On February 3, 2017, PharmAthene paid the one-time dividend in an aggregate amount of $200.3 million.

The receipt of the award from SIGA generated substantial taxable income to the Company, a portion of which was offset by the Company’s tax net operating loss carryforwards (“NOLs”). At December 31, 2016, we had available $176.1 million in accumulated domestic losses available to offset income, subject to limitations imposed by the Internal Revenue Code of 1986 (the “Code”) and a 382 limitation of approximately $1 million, of which approximately $175 million was utilized to offset current year income. On November 25, 2015, the Company had adopted a Shareholders Rights Plan to help ensure that the NOLs remained available to help maximize the value for our shareholders of any amount received from the SIGA litigation.

On January 18, 2017, PharmAthene entered into an Agreement and Plan of Merger and Reorganization (as amended from time to time, the “Merger Agreement”), pursuant to which Altimmune, Inc. (“Altimmune”) will merge into Mustang Merger Sub Corp I Inc., a Delaware corporation and a direct wholly owned subsidiary of PharmAthene (“Merger Sub Corp”), with Altimmune as the surviving entity in such merger (“Merger 1”), and immediately thereafter, Altimmune will be merged with and into Mustang Merger Sub II LLC, a Delaware limited liability company and a direct wholly owned subsidiary of PharmAthene (“Merger Sub LLC”), with Merger Sub LLC as the surviving entity in such merger (“Merger 2”, and together with Merger 1, the “Mergers”). Upon consummation of the Mergers, Merger Sub Corp and Altimmune will cease to exist, and Merger Sub LLC will continue as a direct wholly owned subsidiary of PharmAthene. Upon completion of the Mergers, former PharmAthene security holders will own approximately 41.8% of the outstanding equity of the combined company, and former Altimmune security holders will own approximately 58.2% of the outstanding equity of the combined company, in each case, on an as converted and fully diluted basis. Following the anticipated consummation of the Mergers, PharmAthene will change its name to “Altimmune, Inc.”.

On March 29, 2017, PharmAthene and Altimmune entered into amendment no. 1 to the Merger Agreement, pursuant to which PharmAthene and Altimmune agreed that: (i) the certificate of incorporation of PharmAthene after the effective time of the mergers will be the certificate of incorporation of PharmAthene immediately prior to the effective time of the mergers and that, at that time PharmAthene, will file an amendment to its certificate of incorporation to change its name to “Altimmune, Inc.” and (ii) PharmAthene’s bylaws will be amended and restated immediately after the effective time of the mergers, as agreed therein (which amended and restated Exhibit C to the Merger Agreement).

Altimmune is a privately-held clinical stage immunotherapeuticsbiopharmaceutical company focused on the development of products to stimulate robustdeveloping intranasal vaccines, immune modulating therapies and durabletreatments for liver disease. Our diverse pipeline includes proprietary intranasal vaccines for COVID-19 (AdCOVID), anthrax (NasoShield) and influenza (NasoVAX); an intranasal immune responsesmodulating therapeutic for the preventionCOVID-19 (T-COVID); and treatment of disease. Altimmune has two proprietary platform technologies, RespirVecnext generation peptide therapeutics for NASH (ALT-801) and Densigen, each of which has been shown, in preclinical studies and early clinical trials, to activate the immune system in distinctly different ways than traditional vaccine methods. Using these technologies, Altimmune has generated clinical product candidates which potentially represent an entirely new approach to harnessing the immune system. Altimmune’s most advance product candidate, NasoVAX, an intranasally administered recombinant influenza vaccine, uses an adenovector to achieve expression of the influenza antigen in the target cell, thereby potentially stimulating a broader and more rapid immune response than traditional influenza vaccines. Altimmune’s planned Phase 2 program for NasoVAX is expected to start in third quarter of 2017, with initial data anticipated approximately six months following the start of enrollment. Altimmune’s second most advanced product candidate, HepTcell, is being tested as an immunotherapy for patients chronically infected with thechronic hepatitis B virus (‘‘HBV’’),(HepTcell).

Corporate Information

We were incorporated in Delaware in April 2005 and hassubsequently changed our name to Altimmune, Inc. in May 2017, upon the potential to provide a functional cure, something that is not achievablecompletion of our merger with current treatments. HepTcell is currently in a Phase 1 trial in the United Kingdom in patients with chronic HBV. Initial results from this trial are expected by the end of 2017. With the support of the U.S. Biomedical Advanced Research and Development Authority (‘‘BARDA’’), Altimmune is developing a third product candidate, NasoShield, an anthrax vaccine designed to provide rapid, stable protection after one intranasal administration. Subject to continued financial and other support from BARDA, Altimmune anticipates launching a Phase 1 trial for NasoShield in the first quarter of 2018. The combined company will be a fully-integrated and diversified immunotherapeutics company with one preclinical stage and four clinical stage programs.

PharmAthene, Inc.

Our principal executive offices are located at One Park Place,910 Clopper Road, Suite 450, Annapolis,201S, Gaithersburg, Maryland 2140120878, and our telephone number is (410) 269-2600. After(240) 654-1450. Our Internet website is www.altimmune.com and our investor relations website is located under the consummation“Investors” tab. The information contained on, or that can be accessed through, our website is not incorporated by reference into this prospectus, and, therefore, is not part of this prospectus or any accompanying prospectus supplement.

Implications of Being a Smaller Reporting Company

We are a “smaller reporting company,” meaning that the Mergers,market value of our executive offices willstock held by non-affiliates is less than $700 million and our annual revenue was less than $100 million during our most recently completed fiscal year. We may continue to be located at 19 Firstfield Road, Suite 200, Gaithersburg, Maryland 20878.a smaller reporting company if either (i) the market value of our stock held by non-affiliates is less than $250 million or (ii) our annual revenue was less than $100 million during the most recently completed fiscal year and the market value of our stock held by non-affiliates is less than $700 million. For so long as we remain a smaller reporting company, we are permitted and intend to rely on exemptions from certain disclosure and other requirements that are applicable to other public companies that are not smaller reporting companies.

Forward-looking statements describe management’s current expectations regarding our future plans, strategiesthe estimated size of those markets, and objectivesthe incidence and are generally identifiable by useprevalence of certain medical conditions. All of the words “may,” “will,” “should,” “could,” “expect,” “anticipate,” “estimate,” “believe,” “intend,” “project,” “potential”market data used in this prospectus involve a number of assumptions and limitations, and the sources of such data cannot guarantee the accuracy or “plan” orcompleteness of such information. While we are not aware of any misstatements regarding the negativethird-party information and we believe that each of these words orstudies and publications is reliable, the industry in which we operate is subject to a high degree of uncertainty and risk due to a variety of important factors, including those described in the section titled “Risk Factors” in our Annual Report and in our other variations on these words or comparable terminology. Such statements include, but are not limitedreports with the SEC. These and other factors could cause results to statements relating to:differ materially from those expressed in the estimates made by third parties and by us.

Forward-looking statements are based on assumptionsYou should read this prospectus and the documents that we incorporate by reference in this prospectus completely and with the understanding that our actual future results may be incorrect, andmaterially different from what we cannot assure you that the projections included in theexpect. The forward-looking statements will come to pass.

in this prospectus and the documents we incorporate by reference herein represent our views as of their respective dates. All subsequent written and oral forward-looking statements included hereinattributable to us or persons acting on our behalf are expressly qualified in their entirety by our cautionary statements. We anticipate that subsequent events and developments will cause our views to change. However, while we may elect to update these forward-looking statements at some point in the cautionaryfuture, we have no current intention of doing so except to the extent required by applicable law. You should, therefore, not rely on these forward-looking statements contained or referredas representing our views as of any date subsequent to above.the date of this prospectus.

DESCRIPTION OF COMMONCAPITAL STOCK

The following descriptions are summaries of the material terms of our amended and restated certificate of incorporation and amended and restated bylaws. We refer in this section to our amended and restated certificate of incorporation as our charter, and we refer to our amended and restated bylaws as our bylaws.

General

Under our Amended and Restated Certificatecharter, our authorized capital stock consists of Incorporation, as amended, to which we refer as our “charter,” we are currently authorized to issue 100,000,000200,000,000 shares of common stock, par value $.0001$0.0001 per share, and 1,000,000 shares of preferred stock, par value $0.0001 per share. As of March 22, 2017,the date of this prospectus, we had 68,815,19537,142,946 shares of common stock outstanding and no shares of preferred stock outstanding.

Common Stock

Holders of our common stock are entitled to one vote for each share of common stock held of record on all matters to be voted on by stockholders, except as otherwise provided by law or in any preferred stock designation. Our bylaws specify that, except as otherwise required by law or our charter, the presence in person or by proxy of holders of a majority of the shares entitled to vote at a meeting of stockholders will be necessary, and will constitute a quorum, for the transaction of business at such meeting. Our bylaws furthermore specify that all elections of directors will be determined by a plurality of the votes and that, except as otherwise provided by law or in the charter or bylaws, any other matter will be determined by the vote of a majority of the shares which are voted with regard to it. Holders of our common stock have no conversion, preemptive or other subscription rights and there are no sinking fund or redemption provisions applicable to the common stock.

There is no cumulative voting with respect to the election of directors, with the result that the holders of more than 50% of the shares voting for the election of directors can elect all of the directors then up for election. Holders of our common stock are entitled to receive dividends when, as and if declared by our board of directors out of funds legally available therefor. In the event of our liquidation, dissolution or winding up, the holders of common stock are entitled to share in all assets remaining which are available for distribution to them after payment of liabilities and after provision has been made for each class of stock, if any, having preference over the common stock.

Preferred Stock

Under our charter, our board of directors is expressly granted authority to issue shares of preferred stock, in one or more series, and to fix for each series such voting powers, full or limited, and such designations, preferences and relative, participating, optional or other special rights and such qualifications, limitations or restrictions as it may determine in the resolution or resolutions providing for the issue of such series (to which we also refer as a “preferred stock designation”) and as may be permitted by the Delaware General Corporation Law. The number of authorized shares of preferred stock may be increased or decreased (but not below the number of shares of preferred stock then outstanding) by the affirmative vote of the holders of a majority of the voting power of all of the then outstanding shares of our capital stock entitled to vote generally in the election of directors, voting together as a single class, without a separate vote of the holders of the preferred stock, or any series of preferred stock, unless a vote of any such holders is required pursuant to any preferred stock designation.

This section describes the general terms of our preferred stock to which any prospectus supplement may relate. A prospectus supplement will describe the terms relating to any preferred stock to be offered by us in greater detail, and may provide information that is different from the information described in this prospectus. If the information in the prospectus supplement with respect to the particular preferred stock being offered differs from

the information in this prospectus, you should rely on the information in the prospectus supplement. A copy of our charter has been incorporated by reference from our filings with the SEC as an exhibit to the registration statement of which this prospectus is a part. A certificate of designations will specify the terms of the preferred stock being offered, and will be filed as an exhibit to the registration statement of which this prospectus is a part or incorporated by reference from a report that we file with the SEC.

The rights and terms relating to any new series of preferred stock could adversely affect the voting power or other rights of the holders of the common stock or could be utilized, under certain circumstances, as a method of discouraging, delaying or preventing a change in control of the Company.

The following description of our preferred stock, together with any description of our preferred stock in a related prospectus supplement, summarizes the material terms and provisions of the preferred stock that we may sell under this prospectus. We urge you to read the applicable prospectus supplement(s) related to the particular series of preferred stock that we sell under this prospectus and to the actual terms and provisions contained in our charter (certificate of designations) and bylaws, each as amended from time to time.

Terms

Our board of directors will fix the rights, preferences, privileges, qualifications and restrictions of the preferred stock of each series that we sell under this prospectus and applicable prospectus supplements in the certificate of designations relating to that series. We will file as an exhibit to the registration statement of which this prospectus is a part or incorporate by reference the form of any certificate of designations that describes the terms of the series of preferred stock we are offering in connection with the issuance of the related series of preferred stock. This description of the preferred stock in the certificate of designations and any applicable prospectus supplement may include:

Rank

As set forth in the applicable supplement to this prospectus, shares of our preferred stock may rank, with respect to payment of distributions and rights upon our liquidation, dissolution or winding up, and allocation of our earnings and losses:

Distributions

Subject to any preferential rights of any outstanding stock or series of stock, holders of our preferred stock may be entitled to receive distributions, when and as authorized by our board of directors, out of legally available funds, and share pro rata based on the number of shares of preferred stock, common stock and other equity securities outstanding.

Voting Rights

As indicated in the applicable supplement to this prospectus, and as otherwise required under Delaware law, holders of our preferred stock may or may not have voting rights.

Liquidation Preference

As indicated in the applicable supplement to this prospectus, upon the voluntary or involuntary liquidation, dissolution or winding up of our affairs, then, before any distribution or payment shall be made to the holders of any common stock or any other class or series of stock ranking junior to the preferred stock in our distribution of assets upon any liquidation, dissolution or winding up, the holders of each series of our preferred stock may be entitled to receive, after payment or provision for payment of our debts and other liabilities, out of our assets legally available for distribution to shareholders, liquidating distributions in the amount of the liquidation preference per share (set forth in the applicable supplement to this prospectus), plus an amount, if applicable, equal to all distributions accrued and unpaid thereon (which shall not include any accumulation in respect of unpaid distributions for prior distribution periods if the preferred stock does not have a cumulative distribution). After payment of the full amount of the liquidating distributions to which they may be entitled, the holders of preferred stock may have no right or claim to any of our remaining assets. In the event that, upon our voluntary or involuntary liquidation, dissolution or winding up, the legally available assets are insufficient to pay the amount of the liquidating distributions on all of our outstanding preferred stock and the corresponding amounts payable on all of our stock of other classes or series of equity security ranking on a parity with the preferred stock in the distribution of assets upon liquidation, dissolution or winding up, then the holders of our preferred stock and all other such classes or series of equity securities may share ratably in the distribution of assets in proportion to the full liquidating distributions to which they would otherwise be respectively entitled.

If the liquidating distributions are made in full to all holders of preferred stock, our remaining assets may be distributed among the holders of any other classes or series of equity security ranking junior to the preferred

stock upon our liquidation, dissolution, or winding up, according to their respective rights and preferences and in each case according to their respective number of shares of stock.

Conversion Rights

The terms and conditions, if any, upon which shares of any series of preferred stock are convertible into, such as common stock, debt securities, warrants or units consisting of one or more of such securities will be set forth in the applicable supplement to this prospectus. These terms will include the amount and type of security into which the shares of preferred stock are convertible, the conversion price (or manner of calculation thereof), the conversion period, provisions as to whether conversion will be at the option of the holders of the preferred stock or us, the events, if any, requiring an adjustment of the conversion price and provisions, if any, affecting conversion in the event of the redemption of that preferred stock.

Redemption

If so provided in the applicable supplement to this prospectus, our preferred stock will be subject to mandatory redemption or redemption at our option, in whole or in part, in each case upon the terms, at the times and at the redemption prices set forth in such supplement to this prospectus.

Anti-takeover Effects of our Charter and Bylaws and Delaware Law

Our charter and bylaws include a number of provisions that may have the effect of delaying, deferring or preventing another party from acquiring control of us and encouraging persons considering unsolicited tender offers or other unilateral takeover proposals to negotiate with our board of directors rather than pursue non-negotiated takeover attempts. These provisions include the items described below.

Board Composition and Filling Vacancies

Our bylaws provide that directors may be removed only for cause and then only by the affirmative vote of the holders of majority of the shares then entitled to vote at an election of directors. Further, our charter provides that any vacancy on our board of directors, however occurring, including a vacancy resulting from an increase in the size of our board, may only be filled by the affirmative vote of a majority of our directors then in office even if less than a quorum. The classification of directors, together with the limitations on removal of directors and treatment of vacancies, has the effect of making it more difficult for stockholders to change the composition of our board of directors.

No Written Consent of Stockholders

Our charter provides that all stockholder actions are required to be taken by a vote of the stockholders at an annual or special meeting, and that stockholders may not take any action by written consent in lieu of a meeting. This limit may lengthen the amount of time required to take stockholder actions and would prevent the amendment of our bylaws or removal of directors by our stockholders without holding a meeting of stockholders.

Meetings of Stockholders

Our charter and bylaws provide that only a majority of the members of our board of directors then in office may call special meetings of stockholders and only those matters set forth in the notice of the special meeting may be considered or acted upon at a special meeting of stockholders. Our bylaws limit the business that may be conducted at an annual meeting of stockholders to those matters properly brought before the meeting.

Advance Notice Requirements

Our bylaws establish advance notice procedures with regard to stockholder proposals relating to the nomination of candidates for election as directors or new business to be brought before meetings of our stockholders. These

procedures provide that notice of stockholder proposals must be timely given in writing to our corporate secretary prior to the meeting at which the action is to be taken. Generally, to be timely, notice must be received at our principal executive offices not less than 90 days nor more than 120 days prior to the first anniversary date of the annual meeting for the preceding year. Our bylaws specify the requirements as to form and content of all stockholders’ notices. These requirements may preclude stockholders from bringing matters before the stockholders at an annual or special meeting.

Amendment to Certificate of Incorporation and Bylaws

Any amendment of our charter must first be approved by a majority of our board of directors, and if required by law or our certificate of incorporation, must thereafter be approved by a majority of the outstanding shares entitled to vote on the amendment and a majority of the outstanding shares of each class entitled to vote thereon as a class. Our bylaws may be amended by the affirmative vote of a majority of the directors then in office, subject to any limitations set forth in the bylaws; and may also be amended by the affirmative vote of a majority of the outstanding shares entitled to vote on the amendment, or, if our board of directors recommends that the stockholders approve the amendment, by the affirmative vote of the majority of the outstanding shares entitled to vote on the amendment, in each case voting together as a single class.

Undesignated Preferred Stock

Our certificate of incorporation provides for 1,000,000 authorized shares of preferred stock. The existence of authorized but unissued shares of preferred stock may enable our board of directors to discourage an attempt to obtain control of us by means of a merger, tender offer, proxy contest or otherwise. For example, if in the due exercise of its fiduciary obligations, our board of directors were to determine that a takeover proposal is not in the best interests of our stockholders, our board of directors could cause shares of preferred stock to be issued without stockholder approval in one or more private offerings or other transactions that might dilute the voting or other rights of the proposed acquirer or insurgent stockholder or stockholder group. In this regard, our certificate of incorporation grants our board of directors broad power to establish the rights and preferences of authorized and unissued shares of preferred stock. The issuance of shares of preferred stock could decrease the amount of earnings and assets available for distribution to holders of shares of common stock. The issuance may also adversely affect the rights and powers, including voting rights, of these holders and may have the effect of delaying, deterring or preventing a change in control of us.

Exclusive Jurisdiction for Certain Actions

Our bylaws provide that, unless we consent in writing to an alternative forum, the Court of Chancery of the State of Delaware will be the sole and exclusive forum for state law claims for (i) any derivative action or proceeding brought on our behalf, (ii) any action asserting a claim of breach of a fiduciary duty owed by any of our directors, officers and employees to us or our stockholders, (iii) any action asserting a claim arising pursuant to any provision of the Delaware General Corporation Law, our certificate of incorporation or our bylaws, or (iv) any action asserting a claim that is governed by the internal affairs doctrine, in each case subject to the Court of Chancery having personal jurisdiction over the indispensable parties named as defendants therein. This provision will not apply to actions arising under the Securities Act or the Exchange Act. Although we believe this provision benefits us by providing increased consistency in the application of Delaware law in the types of lawsuits to which it applies, the provision may have the effect of discouraging lawsuits against our directors and officers. The enforceability of similar exclusive forum provisions in other companies’ bylaws has been challenged in legal proceedings, and it is possible that a court could rule that this provision in our bylaws is inapplicable or unenforceable.

Section 203 of the Delaware General Corporation Law

We are subject to the provisions of Section 203 of the Delaware General Corporation Law. In general, Section 203 prohibits a publicly held Delaware corporation from engaging in a “business combination” with an

“interested stockholder” for a three-year period following the time that this stockholder becomes an interested stockholder, unless the business combination is approved in a prescribed manner. Under Section 203, a business combination between a corporation and an interested stockholder is prohibited unless it satisfies one of the following conditions:

Section 203 defines a business combination to include:

In general, Section 203 defines an interested stockholder as any entity or person beneficially owning 15% or more of the outstanding voting stock of the corporation and any entity or person affiliated with or controlling or controlled by the entity or person.

Exchange Listing

Our common stock is listed on the Nasdaq Global Market under the symbol “ALT.”

Transfer Agent

The transfer agent and registrar for the common stock is Continental Stock Transfer & Trust Company,Company. The transfer agent and registrar’s address is 1 State Street 30th Floor, New York, New York.York 10004.

DESCRIPTION OF PREFERRED STOCKDEBT SECURITIES

Under our charter, we are currently authorized to issue 1,000,000 shares of preferred stock, par value $.0001 per share. As of the date of this prospectus, we had no shares of preferred stock outstanding.

Under our charter, our board of directors is expressly granted authority to issue shares of preferred stock, in one or more series, and to fix for each series such voting powers, full or limited, and such designations, preferences and relative, participating, optional or other special rights and such qualifications, limitations or restrictions as it may determine in the resolution or resolutions providing for the issue of such series (to which we also refer as a “preferred stock designation”) and as may be permitted by the Delaware General Corporation Law. The number of authorized shares of preferred stock may be increased or decreased (but not below the number of shares of preferred stock then outstanding) by the affirmative vote of the holders of a majority of the voting power of all of the then outstanding shares of our capital stock entitled to vote generally in the election of directors, voting together as a single class, without a separate vote of the holders of the preferred stock, or any series of preferred stock, unless a vote of any such holders is required pursuant to any preferred stock designation.

This section describes the general terms and provisions of our preferred stockdebt securities that we may issue from time to whichtime. We may issue debt securities, in one or more series, as either senior or subordinated debt or as senior or subordinated convertible debt. While the terms we have summarized below will apply generally to any future debt securities we may offer under this prospectus, the applicable prospectus supplement may relate. Aor free writing prospectus supplement will describe the specific terms relatingof any debt securities offered through that prospectus supplement or free writing prospectus. The terms of any debt securities we offer under a prospectus supplement or free writing prospectus may differ from the terms we describe below. Unless the context requires otherwise, whenever we refer to the “indentures,” we are also referring to any preferred stock to be offered by us in greater detail, and may provide informationsupplemental indentures that is different fromspecify the information described in this prospectus. Ifterms of a particular series of debt securities.

We will issue any senior debt securities under the informationsenior indenture that we will enter into with the trustee named in the prospectus supplementsenior indenture. We will issue any subordinated debt securities under the subordinated indenture that we will enter into with respect to the particular preferred stock being offered differs from the information in this prospectus, you should rely on the informationtrustee named in the prospectus supplement. A copysubordinated indenture. We have filed forms of our charter has been incorporated by reference from our filings with the SECthese documents as an exhibitexhibits to the registration statement, of which this prospectus is a part. A certificatepart, and supplemental indentures and forms of designations will specifydebt securities containing the terms of the preferred stockdebt securities being offered and will be filed as an exhibitexhibits to the registration statement of which this prospectus is a part or will be incorporated by reference from a reportreports that we file with the SEC.

The rights and terms relatingindentures will be qualified under the Trust Indenture Act of 1939, as amended, or the Trust Indenture Act. We use the term “trustee” to any new series of preferred stock could adversely affectrefer to either the voting powertrustee under the senior indenture or other rights of the holders oftrustee under the common stock or could be utilized, under certain circumstances,subordinated indenture, as a method of discouraging, delaying or preventing a change in control of the Company.

applicable.

The following descriptionsummaries of our preferred stock, together with any description of our preferred stock in a related prospectus supplement, summarizes the material terms and provisions of the preferred stock that we may sell under this prospectus.senior debt securities, the subordinated debt securities and the indentures are subject to, and qualified in their entirety by reference to, all of the provisions of the indenture applicable to a particular series of debt securities. We urge you to read the applicable prospectus supplement(s)supplement or free writing prospectus and any related free writing prospectuses related to the particular series of preferred stockdebt securities that we sellmay offer under this prospectus, and toas well as the actualcomplete applicable indenture that contains the terms and provisions contained in our charter (certificate of designations) and bylaws, each as amended from time to time.

Terms

Our board of directors will fix the rights, preferences, privileges, qualifications and restrictions of the preferred stockdebt securities. Except as we may otherwise indicate, the terms of each series that we sell under this prospectusthe senior indenture and the subordinated indenture are identical.

General

We will describe in the applicable prospectus supplements in the certificate of designations relating to that series. We will file as an exhibit to the registration statement of which thissupplement or free writing prospectus is a part or incorporate by reference the form of any certificate of designations that describes the terms of the series of preferred stockdebt securities being offered, including:

payable immediately. If an event of default specified in the last bullet point above occurs with respect to us, the unpaid principal, premium, if any, and accrued interest, if any, of each issue of debt securities then outstanding shall be due and payable without any notice or other action on the part of the trustee or any holder.

The holders of a majority in principal amount of the outstanding debt securities of an affected series may waive any default or event of default with respect to the series and its consequences, except defaults or events of default regarding payment of principal, premium, if any, or interest, unless we have cured the default or event of default in accordance with the indenture. Any waiver shall cure the default or event of default.

Subject to the terms of the indentures, if an event of default under an indenture shall occur and be continuing, the trustee will be under no obligation to exercise any of its rights or powers under such indenture at the request or direction of any of the holders of the applicable series of debt securities, unless such holders have offered the trustee reasonable indemnity or security satisfactory to it against any loss, liability or expense. The holders of a majority in principal amount of the outstanding debt securities of any series will have the right to direct the time, method and place of conducting any proceeding for any remedy available to the trustee, or exercising any trust or power conferred on the trustee, with respect to the debt securities of that series, provided that:

A holder of the debt securities of any series will have the right to institute a proceeding under the indentures or to appoint a receiver or trustee, or to seek other remedies if:

These limitations do not apply to a suit instituted by a holder of debt securities if we default in the payment of the principal, premium, if any, or interest on, the debt securities, or other defaults that may be specified in the applicable prospectus supplement or free writing prospectus.

We will periodically file statements with the trustee regarding our compliance with specified covenants in the indentures.

Modification of Indenture; Waiver

Subject to this prospectus,the terms of the indenture for any series of debt securities that we may issue, we and as otherwise required under Delaware law,the trustee may change an indenture without the consent of any holders of our preferred stock may or may not have voting rights.with respect to the following specific matters:

In addition, under the indentures, the rights of holders of a series of debt securities may be changed by us and the trustee with the written consent of the holders of each series of our preferred stock may be entitled to receive, after payment or provision for payment of our debts and other liabilities, out of our assets legally available for distribution to shareholders, liquidating distributionsat least a majority in theaggregate principal amount of the liquidation preference per share (set forthoutstanding debt securities of each series that is affected. However, subject to the terms of the indenture for any series of debt securities that we may issue or as otherwise provided in the prospectus supplement or free writing prospectus applicable to a particular series of debt securities, we and the trustee may make the following changes only with the consent of each holder of any outstanding debt securities affected:

Discharge

Each indenture provides that, subject to the terms of the indenture and any limitation otherwise provided in the prospectus supplement or free writing prospectus applicable to a particular series of debt securities, we can elect to be discharged from our obligations with respect to one or more series of debt securities, except for specified obligations, including obligations to:

In order to exercise our rights to be discharged, we must deposit with the trustee money or government obligations sufficient to pay all the principal of, any premium and interest on, the debt securities of the series on the dates payments are due.

Form, Exchange and Transfer

We will issue the debt securities of each series only in fully registered form without coupons and, unless we otherwise specify in the applicable prospectus supplement or free writing prospectus, in denominations of $1,000 and any integral multiple thereof. The indentures provide that we may issue debt securities of a series in temporary or permanent global form and as book-entry securities that will be deposited with, or on behalf of, The Depository Trust Company or another depository named by us and identified in a prospectus supplement or free writing prospectus with respect to this prospectus), plus an amount, if applicable, equal to all distributions accrued and unpaid thereon (which shall not include any accumulation in respect of unpaid distributions for prior distribution periods ifthat series.

At the preferred stock does not have a cumulative distribution). After paymentoption of the full amountholder, subject to the terms of the liquidating distributionsindentures and the limitations applicable to which they may be entitled,global securities described in the holders of preferred stock may have no rightapplicable prospectus supplement or claim to any of our remaining assets. Infree writing prospectus, the event that, upon our voluntary or involuntary liquidation, dissolution or winding up, the legally available assets are insufficient to pay the amountholder of the liquidating distributions on all of our outstanding preferred stock and the corresponding amounts payable on all of our stock of other classes or series of equity security ranking on a parity with the preferred stock in the distribution of assets upon liquidation, dissolution or winding up, then the holders of our preferred stock and all other such classes or series of equitydebt securities may share ratably in the distribution of assets in proportion to the full liquidating distributions to which they would otherwise be respectively entitled.

If the liquidating distributions are made in full to all holders of preferred stock, our remaining assets may be distributed among the holders of any other classes or series of equity security ranking junior to the preferred stock upon our liquidation, dissolution, or winding up, according to their respective rights and preferences and in each case according to their respective number of shares of stock.

Conversion Rights

The terms and conditions, if any, upon which shares of any series of preferred stock are convertible into, such as common stock,can exchange the debt securities warrants or units consistingfor other debt securities of one or morethe same series, in any authorized denomination and of suchlike tenor and aggregate principal amount.

Subject to the terms of the indentures and the limitations applicable to global securities will be set forth in the applicable prospectus supplement to this prospectus. These terms will include the amount and type of security into which the shares of preferred stock are convertible, the conversion price (or manner of calculation thereof), the conversion period, provisions as to whether conversion will be at the option of theor free writing prospectus, holders of the preferred stockdebt securities may present the debt securities for exchange or for registration of transfer, duly endorsed or with the form of transfer endorsed thereon duly executed if so required by us or the events, if any, requiring an adjustmentsecurity registrar, at the office of the conversion price and provisions, ifsecurity registrar or at the office of any affecting conversion in the event of the redemption of that preferred stock.

Redemption

If sotransfer agent designated by us for this purpose. Unless otherwise provided in the debt securities that the holder presents for transfer or exchange, we will make no service charge for any registration of transfer or exchange, but we may require payment of any taxes or other governmental charges.

We will name in the applicable prospectus supplement or free writing prospectus the security registrar, and any transfer agent in addition to this prospectus, our preferred stockthe security registrar, that we initially designate for any debt securities. We may at any time designate additional transfer agents or rescind the designation of any transfer agent or approve a change in the office through which any transfer agent acts, except that we will be subjectrequired to mandatorymaintain a transfer agent in each place of payment for the debt securities of each series. If we elect to redeem the debt securities of any series, we will not be required to:

Information Concerning the terms, atTrustee

The trustee, other than during the timesoccurrence and at the redemption pricescontinuance of an event of default under an indenture, undertakes to perform only those duties as are specifically set forth in such supplementthe applicable indenture. Upon an event of default under an indenture, the trustee must use the same degree of care as a prudent person would exercise or use in the conduct of his or her own affairs.

Subject to this prospectus.provision, the trustee is under no obligation to exercise any of the powers given it by the indentures at the request of any holder of debt securities unless it is offered reasonable security and indemnity against the costs, expenses and liabilities that it might incur.

Payment and Paying Agents

Unless we otherwise indicate in the applicable prospectus supplement or free writing prospectus, we will make payment of the interest on any debt securities on any interest payment date to the person in whose name the debt securities, or one or more predecessor securities, are registered at the close of business on the regular record date for the interest.

We will pay principal of and any premium and interest on the debt securities of a particular series at the office of the paying agents designated by us, except that unless we otherwise indicate in the applicable prospectus supplement or free writing prospectus, we will make interest payments by check that we will mail to the holder or by wire transfer to certain holders. Unless we otherwise indicate in the applicable prospectus supplement or free writing prospectus, we will designate the corporate trust office of the trustee as our sole paying agent for payments with respect to debt securities of each series. We will name in the applicable prospectus supplement or free writing prospectus any other paying agents that we initially designate for the debt securities of a particular series. We will maintain a paying agent in each place of payment for the debt securities of a particular series.

All money we pay to a paying agent or the trustee for the payment of the principal of or any premium or interest on any debt securities that remains unclaimed at the end of two years after such principal, premium or interest has become due and payable will be repaid to us, and the holder of the debt security thereafter may look only to us for payment thereof.

Governing Law

The indentures and the debt securities will be governed by and construed in accordance with the laws of the State of New York, except to the extent that the Trust Indenture Act is applicable.

Ranking of Debt Securities

The subordinated debt securities will be subordinate and junior in priority of payment to certain of our other indebtedness to the extent described in a prospectus supplement or free writing prospectus. The subordinated indenture does not limit the amount of subordinated debt securities that we may issue. It also does not limit us from issuing any other secured or unsecured debt.

The senior debt securities will rank equally in right of payment to all our other senior unsecured debt. The senior indenture does not limit the amount of senior debt securities that we may issue. It also does not limit us from issuing any other secured or unsecured debt.

DESCRIPTION OF WARRANTS

The following description, together with the additional information we may include in any applicable prospectus supplements, summarizes the material terms and provisions of the warrants that we may offer under this prospectus.prospectus and the related warrant agreements and warrant certificates. While the terms we have summarized below will apply generally to any warrants that we may offer, under this prospectus, we will describe the particular terms of any series of warrants in more detail in the applicable prospectus supplement. TheIf we indicate in the prospectus supplement, the terms of any warrants offered under athat prospectus supplement may differ from the terms described below.

We Specific warrant agreements will filecontain additional important terms and provisions and will be incorporated by reference as exhibitsan exhibit to the registration statement, which includes this prospectus.

General

We may issue warrants for the purchase of which this prospectus is a part, common stock, preferred stock and/or debt securities in one or more series. We may issue warrants independently or together with common stock, preferred stock and/or debt securities, and the warrants may be attached to or separate from these securities.

We will incorporate by reference from another report that we file with the SEC, the form of warrant agreement, which may include a form of warrant certificate, that describes the terms of the particularevidence each series of warrants by warrant certificates that we are offering. The following summary of material provisions of the warrants andwill issue under a separate warrant agreement. We will enter into the warrant agreements are subject to allagreement with a warrant agent. We will indicate the provisionsname and address of the warrant agreement and warrant certificateagent in the applicable prospectus supplement relating to a particular series of warrants. We urge you to read the applicable prospectus supplements related to the particular series of warrants that we sell under this prospectus, as well as the complete warrant agreements and/or warrant certificates that contain the terms of the warrants.

General

We will describe in the applicable prospectus supplement the terms relating toof the series of warrants, being offered, which may include:including:

Before exercising their warrants, holders of warrants will likely not have any of the rights of holders of the securities with which the warrants are issued and the number of warrants issued with each such security or each principal amount of such security;

DESCRIPTION OF UNITS

We may issue units comprised of shares of common stock, shares of preferred stock, debt securities and warrants in any combination. We may issue units in such amounts and in as many distinct series as we wish. This section outlines certain provisions of the units that we describemay issue. If we issue units, they will be issued under one or more unit agreements to be entered into between us and a bank or other financial institution, as unit agent. The information described in this section may not be complete in all respects and is qualified entirely by reference to the unit agreement with respect to the units of any particular series. The specific terms of any series of units offered will be described in the applicable prospectus supplement. UnlessIf so described in a particular supplement, the specific terms of any series of units may differ from the general description of terms presented below. We urge you to read any prospectus supplement related to any series of units we otherwise specifymay offer, as well as the complete unit agreement and unit certificate that contain the terms of the units. If we issue units, forms of unit agreements and unit certificates relating to such units will be incorporated by reference as exhibits to the registration statement, which includes this prospectus.

Each unit that we may issue will be issued so that the holder of the unit is also the holder of each security included in the unit. Thus, the holder of a unit will have the rights and obligations of a holder of each included security. The unit agreement under which a unit is issued may provide that the securities included in the unit may not be held or transferred separately, at any time or at any time before a specified date. The applicable prospectus supplement may describe:

The provisions described in this section, as well as those described under “Description of Capital Stock,” “Description of Debt Securities” and “Description of Warrants” will apply to the securities included in each unit, to the extent relevant and as may be updated in any prospectus supplements.

Issuance in Series

We may issue units in such amounts and in as many distinct series as we wish. This section summarizes terms of the units that apply generally to all series. Most of the financial and other specific terms of a particular series of units will be described in the applicable prospectus supplement.

Unit Agreements

We will issue the units under one or more unit agreements to be entered into between us and a bank or other financial institution, as stock purchase unit agent. We may add, replace or terminate stock purchase unit agents from time to time. We will identify the unit agreement under which each series of units will be issued and the unit agent under that agreement in the applicable prospectus supplement.

The following provisions will generally apply to all unit agreements unless otherwise stated in the applicable prospectus supplement:

Modification without Consent

We and the applicable unit agent may amend any unit or unit agreement without the consent of any holder:

We do not need any approval to make changes that affect only units to be issued after the changes take effect. We may also make changes that do not adversely affect a particular unit in any material respect, even if they adversely affect other units in a material respect. In those cases, we do not need to obtain the approval of the holder of the unaffected unit; we need only obtain any required approvals from the holders of the warrantsaffected units.

Modification with Consent

We may not amend any particular unit or a unit agreement with respect to any particular unit unless we obtain the consent of the holder of that unit, if the amendment would:

Any other change to a particular unit agreement and the units issued under that agreement would require the following approval:

These provisions regarding changes with majority approval also apply to changes affecting any securities issued under a stock purchase unit agreement, as the governing document.

In each case, the required approval must be given by written consent.

Unit Agreements Will Not Be Qualified under Trust Indenture Act

No unit agreement will be qualified as an indenture, and no unit agent will be required to qualify as a trustee, under the Trust Indenture Act. Therefore, holders of units issued under unit agreements will not have the protections of the Trust Indenture Act with respect to their units.

Mergers and Similar Transactions Permitted; No Restrictive Covenants or Events of Default

The unit agreements will not restrict our ability to merge or consolidate with, or sell our assets to, another corporation or other entity or to engage in any other transactions. If at any time upwe merge or consolidate with, or

sell our assets substantially as an entirety to, another corporation or other entity, the specified timesuccessor entity will succeed to and assume our obligations under the unit agreements. We will then be relieved of any further obligation under these agreements.

The unit agreements will not include any restrictions on our ability to put liens on our assets, nor will they restrict our ability to sell our assets. The unit agreements also will not provide for any events of default or remedies upon the expiration date thatoccurrence of any events of default.

Governing Law

The unit agreements and the units will be governed by Delaware law.

Form, Exchange and Transfer

We will issue each unit in global—i.e., book-entry—form only. Units in book-entry form will be represented by a global security registered in the name of a depositary, which will be the holder of all the units represented by the global security. Those who own beneficial interests in a unit will do so through participants in the depositary’s system, and the rights of these indirect owners will be governed solely by the applicable procedures of the depositary and its participants. We will describe book-entry securities, and other terms regarding the issuance and registration of the units in the applicable prospectus supplement.

Each unit and all securities comprising the unit will be issued in the same form.

If we set forthissue any units in registered, non-global form, the following will apply to them.

The units will be issued in the denominations stated in the applicable prospectus supplement. AfterHolders may exchange their units for units of smaller denominations or combined into fewer units of larger denominations, as long as the closetotal amount is not changed.

Holders may exchange or transfer their units at the office of businessthe unit agent. Holders may also replace lost, stolen, destroyed or mutilated units at that office. We may appoint another entity to perform these functions or perform them ourselves.

Holders will not be required to pay a service charge to transfer or exchange their units, but they may be required to pay for any tax or other governmental charge associated with the transfer or exchange. The transfer or exchange, and any replacement, will be made only if our transfer agent is satisfied with the holder’s proof of legal ownership. The transfer agent may also require an indemnity before replacing any units.

If we have the right to redeem, accelerate or settle any units before their maturity, and we exercise our right as to less than all those stock purchase units or other securities, we may block the exchange or transfer of those units during the period beginning 15 days before the day we mail the notice of exercise and ending on the expiration date, unexercised warrantsday of that mailing, in order to freeze the list of holders to prepare the mailing. We may also refuse to register transfers of or exchange any unit selected for early settlement, except that we will become void.

Holderscontinue to permit transfers and exchanges of the warrantsunsettled portion of any unit being partially settled. We may exercisealso block the warrants by deliveringtransfer or exchange of any unit in this manner if the warrant certificate representingunit includes securities that are or may be selected for early settlement.

Only the warrantsdepositary will be entitled to transfer or exchange a unit in global form, since it will be exercised togetherthe sole holder of the unit.

Payments and Notices

In making payments and giving notices with specified information, and payingrespect to our units, we will follow the required amount to the warrant agent in immediately available funds,procedures as provideddescribed in the applicable prospectus supplement.

PLAN OF DISTRIBUTION

We intend to set forth in any warrant agreement and in the applicable prospectus supplement the information that the holder of the warrant will be required to deliver to the warrant agent.may sell securities:

In addition, we may issue the securities as a dividend or distribution or in a subscription rights offering to our existing security holders.

We may directly solicit offers to purchase securities, or agents may be designated to solicit such offers. In the prospectus supplement relating to such offering, we will name any agent that could be viewed as an underwriter under the Securities Act and describe any commissions that we must pay to any such agent. Any such agent will be acting on a best efforts basis for the period of its appointment or, if indicated in the applicable prospectus supplement, we will issue and deliver theon a firm commitment basis. This prospectus may be used in connection with any offering of our securities purchasable upon such exercise. If fewer than allthrough any of the warrants represented by the warrantthese methods or warrant certificate are exercised, then we will issue a new warrant or warrant certificate for the remaining amount of warrants. If we so indicateother methods described in the applicable prospectus supplement, holders of the warrants may surrender securities as all or part of the exercise price for warrants.

PLAN OF DISTRIBUTION

These securities may be offered and sold directly by us, through dealers or agents designated from time to time, or to or through underwriters or may be offered and sold directly by us through a specific bidding or auction process, a rights offering or through a combination of these methods. The prospectus supplement with respect to the securities being offered will set forth the terms of the offering, including the names of the underwriters, dealers or agents, if any, the purchase price of the securities, our net proceeds, any underwriting discounts and other items constituting underwriters’ compensation, public offering price and any discounts or concessions allowed or reallowed or paid to dealers and any securities exchanges on which such securities may be listed. These securities may also be offered by us to our shareholders in lieu of dividends.

supplement.

The distribution of the securities may be effected from time to time in one or more transactions, including:transactions:

Each prospectus supplement will describe the parties. Agents, underwriters or broker-dealers may be paid compensation for offering and selling the securities. That compensation may be in the formmethod of discounts, concessions or commissions to be received from us or from the purchasers of the securities. Dealers and agents participating in the distribution of the securities may be deemedand any applicable restrictions.

The prospectus supplement with respect to be underwriters, and compensation received by them on resale of the securities may be deemed to be underwriting discounts and commissions under the Securities Act. If such dealers or agents were deemed to be underwriters, they may be subject to statutory liabilities under the Securities Act.

We may also make direct sales through subscription rights distributed to our existing shareholders onof a pro rata basis, which may or may not be transferable. In any distribution of subscription rights to our shareholders, if all of the underlying securities are not subscribed for, we may then sell the unsubscribed securities directly to third parties or may engage the services of one or more underwriters, dealers or agents, including standby underwriters, to sell the unsubscribed securities to third parties.

If underwriters are used in an offering, we may execute an underwriting agreement with such underwriters andparticular series will specify the name of each underwriter anddescribe the terms of the transaction (includingoffering of the securities, including the following:

If any underwriters or agents are used in the sale of the offered securities in respect of which this prospectus is delivered, we will be acquired by the underwriters for their own accounts and may be resold from time to time in oneenter into an underwriting agreement, sales agreement or more transactions, including negotiated transactions, at a fixed public offering price or at varying prices determinedother agreement with them at the time of sale. Any public offering pricesale to them, and any discounts or concessions allowed or reallowed or paid to dealers may be changed from time to time. Unless otherwisewe will set forth in the prospectus supplement relating to such offering the obligationsnames of the underwriters or agents and the terms of the related agreement with them.

In connection with the offering of securities, we may grant to the underwriters an option to purchase additional securities with an additional underwriting commission, as may be set forth in the offered securitiesaccompanying prospectus supplement. If we grant any such option, the terms of such option will be subject to conditions precedent andset forth in the underwriters will be obligated to purchase allprospectus supplement for such securities.

If a dealer is used in the sale of the offered securities if any are purchased.

If dealers are used in an offering,respect of which the prospectus is delivered, we will sell thesuch securities to the dealersdealer, as principals.principal. The dealersdealer, who may be deemed to be an “underwriter” as that term is defined in the Securities Act, may then resell thesuch securities to the public at varying prices which they determineto be determined by such dealer at the time of resale. The names of

If we offer securities in a subscription rights offering to our existing security holders, we may enter into a standby underwriting agreement with dealers, acting as standby underwriters. We may pay the standby underwriters a commitment fee for the securities they commit to purchase on a standby basis. If we do not enter into a standby underwriting arrangement, we may retain a dealer-manager to manage a subscription rights offering for us.

Agents, underwriters, dealers and the terms of the transaction will be specified in a prospectus supplement.

The securitiesother persons may be sold directly byentitled under agreements which they may enter into with us or through agents we designate. If agents are used in an offering, the names of the agents and the terms of the agency will be specified in a prospectus supplement. Unless otherwise indicated in a prospectus supplement, the agents will act on a forts basis for the period of their appointment.

Dealers and agents named in a prospectus supplement may be deemed to be underwriters (within the meaning of the Securities Act) of the securities described therein. In addition, we may sell the securities directly to institutional investors or others who may be deemed to be underwriters within the meaning of the Securities Act with respect to any resales thereof.

In compliance with the guidelines of the Financial Industry Regulatory Authority (“FINRA”), the aggregate value of all compensation to be received by participating FINRA members in any offering will not exceed 8% of the offering proceeds.

Underwriters, dealers and agents, may be entitled to indemnification by us against specificcertain civil liabilities, including liabilities under the Securities Act, or to contribution with respect to payments which the underwriters or agentsand may be required to make in respect thereof, under underwriting or other agreements. The termscustomers of, any indemnification provisions will be set forth in a prospectus supplement. Certain underwriters, dealers or agents and their associates may engage in transactions with andor perform services for us in the ordinary course of business.

If so indicated in athe applicable prospectus supplement, we will authorize underwriters or other persons acting as our agents to solicit offers by institutional investorscertain institutions to purchase securities from us pursuant to delayed delivery contracts providing for payment and delivery on a future date. Wethe date stated in the prospectus supplement. Each contract will be for an amount not less than, and the aggregate amount of securities sold pursuant to such contracts shall not be less nor more than, the respective amounts stated in the prospectus supplement. Institutions with whom the contracts, when authorized, may enter contracts withbe made include commercial and savings banks, insurance companies, pension funds, investment companies, educational and charitable institutions and other institutional investors. The obligations of any institutional investor willinstitutions, but shall in all cases be subject to the condition that its purchase of the offered securitiesour approval. Delayed delivery contracts will not be illegalsubject to any conditions except that:

EachOffered securities may also be offered and sold, if so indicated in the prospectus supplement, in connection with a remarketing upon their purchase, in accordance with a redemption or repayment pursuant to their terms, or otherwise, by one or more remarketing firms, acting as principals for their own accounts or as agents for us. Any remarketing firm will indicatebe identified and the terms of its agreement, if any, with us and its compensation will be described in the applicable prospectus supplement. Remarketing firms may be deemed to be underwriters in connection with their remarketing of offered securities.

Certain agents, underwriters and dealers, and their associates and affiliates, may be customers of, have borrowing relationships with, engage in other transactions with, or perform services, including investment banking services, for us or one or more of our respective affiliates in the ordinary course of business.

In order to facilitate the offering of the securities, any underwriters may engage in transactions that stabilize, maintain or otherwise affect the price of the securities or any other securities the prices of which may be used to determine payments on such securities. Specifically, any underwriters may over-allot in connection with the offering, creating a short position for their own accounts. In addition, to cover overallotments or to stabilize the price of the securities or of any such other securities, the underwriters may bid for, and purchase, the securities or any such other securities in the open market. Finally, in any offering of the securities through a syndicate of underwriters, the underwriting syndicate may reclaim selling concessions allowed to an underwriter or a dealer for distributing the securities in the offering if the syndicate repurchases previously distributed securities offered therebyin transactions to cover syndicate short positions, in stabilization transactions or otherwise. Any of these activities may stabilize or maintain the market price of the securities above independent market levels. Any such underwriters are not required to engage in these activities and may end any of these activities at any time.

We may engage in at-the-market offerings into an existing trading market in accordance with Rule 415(a)(4) under the Securities Act. In addition, we may enter into derivative transactions with third parties, or sell securities not covered by this prospectus to third parties in privately negotiated transactions. If the applicable prospectus supplement so indicates, in connection with those derivatives, the third parties may sell securities covered by this prospectus and the applicable prospectus supplement, including in short sale transactions. If so, the third party may use securities pledged by us or borrowed from us or others to settle those sales or to close out any related open borrowings of stock, and may use securities received from us in settlement of those derivatives to close out any related open borrowings of stock. The third party in such sale transactions will be an underwriter and, if not identified in this prospectus, will be named in the applicable prospectus supplement (or a post-effective amendment). In addition, we may otherwise loan or pledge securities to a financial institution or other third party that in turn may sell the securities short using this prospectus and an applicable prospectus supplement. Such financial institution or other third party may transfer its economic short position to investors in our securities or in connection with a concurrent offering of other securities.

Under Rule 15c6-1 of the Exchange Act, trades in the secondary market generally are required to settle in two business days, unless the parties to any such trade expressly agree otherwise. The applicable prospectus supplement may provide that the original issue date for your securities may be more than two scheduled business days after the trade date for your securities. Accordingly, in such a case, if you wish to trade securities on any date prior to the second business day before the original issue date for your securities, you will be required, by virtue of the fact that your securities initially are expected to settle in more than two scheduled business days after the trade date for your securities, to make alternative settlement arrangements to prevent a failed settlement.

The securities may be new issues of securities and may have no established trading market. The securities may or may not be listed on a national securities exchange. We can make no assurance as to the liquidity of or the existence of trading markets for any securities exchange; however, we anticipate thatof the securities.

The specific terms of any common shares sold pursuant to a prospectus supplementlock-up provisions in respect of any given offering will be eligible for trading on the NYSE MKT, subject to official notice of issuance. Any underwriters to whom securities are sold by us for Public offering and sale may make a market in the securities, but such underwriters will not be obligated to do so and may discontinue any market making at any time without notice.

LEGAL MATTERS

Certain legal matters relating to the issuance and sale of the securities hereby will be passed upon by Dentons US LLP, New York, New York. Additional legal matters may be passed upon for us or any underwriters, dealers or agents, by counsel that we will namedescribed in the applicable prospectus supplement.

The underwriters, dealers and agents may engage in transactions with us, or perform services for us, in the ordinary course of business for which they receive compensation.

The anticipated date of delivery of offered securities will be set forth in the applicable prospectus supplement relating to each offer.

LEGAL MATTERS

Certain legal matters in connection with this offering will be passed upon for us by Goodwin Procter LLP, Boston, Massachusetts. Any underwriters will also be advised about the validity of the securities and other legal matters by their own counsel, which will be named in the prospectus supplement.

EXPERTS

The consolidated financial statements of PharmAtheneAltimmune, Inc. appearing in PharmAtheneAltimmune, Inc.’s Annual Report (Form 10-K) for the year ended December 31, 2016, and the effectiveness of PharmAthene Inc.’s internal control over financial reporting as of December 31, 20162019, have been audited by ErnestErnst & Young LLP, independent registered public accounting firm, as set forth in their reportsreport thereon, incorporated by referenceincluded therein, and incorporated herein by reference. Such consolidated financial statements are incorporated herein by reference in reliance upon such reportsreport given on the authority of such firm as experts in accounting and auditing.

WHERE YOU CAN FIND MORE INFORMATION

This prospectus is part of a registration statement we filed with the SEC. This prospectus does not contain all of the information set forth in the registration statement and the exhibits to the registration statement. For further information with respect to us and the securities we are offering under this prospectus, we refer you to the registration statement and the exhibits and schedules filed as a part of the registration statement. You should rely only on the information contained in this prospectus or incorporated by reference. We have not authorized anyone else to provide you with different information. We are subject tonot making an offer of these securities in any state where the informational reporting requirementsoffer is not permitted. You should not assume that the information in this prospectus is accurate as of any date other than the date on the front page of this prospectus, regardless of the Exchange Act andtime of delivery of this prospectus or any sale of the securities offered by this prospectus.

We file annual, quarterly and current reports, proxy statements, and other information with the SEC. You may readThe SEC maintains a web site at http://www.sec.gov that contains reports, proxy statements and copy any materials weother information about issuers, such as us, who file electronically with the SEC at the SEC’s Public Reference Room located at 100 F Street, N.E., Washington, D.C. 20549. Please callSEC. The address of the SEC website is www.sec.gov.

We maintain a website at 1-800-SEC -0330 for furtherhttp://www.altimmune.com. The information contained on, or accessible through, our website is not incorporated by reference into this prospectus and, therefore is not part of this prospectus or part of the accompanying prospectus supplement.

Our common stock is listed on the Public Reference Room. You may also access filed documents atNasdaq Global Market under the SEC’s website at www.sec.gov.ticker “ALT.”

INCORPORATION BY REFERENCE

We are incorporatingThe SEC allows us to incorporate by reference important business and financialmuch of the information about us that we file with the SEC. AnySEC, which means that we can disclose important information to you by referring you to those publicly available documents. The information that we incorporate by reference in this prospectus is considered to be part of this prospectus. Information that

Because we fileare incorporating by reference future filings with the SEC, this prospectus is continually updated and those future filings may modify or supersede some of the information included or incorporated in this prospectus. This means that you must look at all of the SEC filings that we incorporate by reference to determine if any of the statements in this prospectus or in any document previously incorporated by reference have been modified or superseded. This prospectus incorporates by reference the documents listed below and any future filings we make with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act (in each case, other than those documents or the portions of those documents not deemed to be filed) between the date of the initial registration statement and the effectiveness of the registration statement and following the effectiveness of the registration statement until the offering of the securities under the registration statement is terminated or completed:

We also incorporate by reference into this prospectus all documents (other than current reports furnished under Item 2.02 or Item 7.01 of Form 8-K and exhibits filed on such form that are related to such items) that are filed by us with the SEC pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act (i) after the date of the initial filing of the registration statement of which this prospectus forms a part and prior to effectiveness of the registration statement, and (ii) after the date of this prospectus but prior to the termination of the offering pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Securities Exchange Act of 1934, shall be deemed to be incorporated by reference in the registration statement and to be part thereof from the date of filing of such information and automatically adds to, updates or supersedes the information listed below.

We incorporate by reference the followingoffering. These documents we have filed, or may file, with the SEC:

To the extent that any information contained in any Current Report on Form 10-K, Quarterly Reports on Form 10-Q, Current Reports on Form 8-K, or any exhibit thereto, is furnished to, rather than filed with, the SEC, such information or exhibit is specifically not incorporated by reference in this prospectus.

We make available free of charge through our website at www.pharmathene.com our press releases and all of the documents that we are required to file electronically with the SEC, including all amendments thereto, as soonwell as reasonably practical after they are electronically filed with, or furnished to, the SEC. Our website also contains our Code of Ethics. The information on our website is not part of nor incorporated by reference into this prospectus.

proxy statements.

You may also read andrequest a copy any materials we file with the SECof these filings, at no cost, by contacting us, either orally or in writing, at the SEC’s Public Reference Room at 100 F Street, N.E., Washington, D.C. 20549. You may obtain information on the operation of the Public Reference Room by calling the SEC at 1-800-SEC -0330. The SEC also maintains an Internet site that contains reports, proxy and information statements, and other information regarding issuers, like PharmAthene, that file electronically with the SEC at http://www.sec.gov.following:

Altimmune, Inc.

910 Clopper Road, Suite 201S

Gaithersburg, Maryland

Attention: Chief Financial Officer

(240) 654-1450

$250,000,000

In addition, we will provide, without charge to each person, including any beneficial owner, to whomPROSPECTUS

The date of this prospectus is                  delivered, upon written or oral request of such person, a copy of any or all of the documents incorporated by reference in this prospectus other than exhibits, unless such exhibits specifically are incorporated by reference into such documents or this prospectus. Requests for such documents should be addressed in writing or by telephone to: PharmAthene, Inc., One Park Place, Suite 450, Annapolis, MD 21401, (410) 269-2600.2020.

PART II.

II

INFORMATION NOT REQUIRED IN PROSPECTUS

Item 14. Other Expenses of Issuance and Distribution.

Item 14.

Other Expenses of Issuance and Distribution

The following is a statement oftable sets forth the estimated costs and expenses, other than underwriting compensation, incurred or expected to be incurreddiscounts and commissions, payable by us in connection with the issuance and distributionoffering of the securities being registered pursuant to this registration statement.registered. All of the amounts shown are estimates, except for the SEC registration fee. The amounts do not include the costs of preparing any prospectus supplements, NYSE MKT listing fees,fee and FINRA filing fees, transfer agent fees or other expenses relating to the sale and distribution of particular securities registered pursuant to this registration statement, as those costs and expenses cannot be estimated at this time.fee.

Item 15. Indemnification of Officers and Directors.

*	The amount of securities and number of offerings are indeterminable and the expenses cannot be estimated at this time. An estimate of the aggregate expenses in connection with the sale and distribution of securities being offered will be included in any applicable prospectus supplement.

Our Amended and Restated Certificate of Incorporation, as amended, provides that the Company, to the full extent permitted by Section 145 of the Delaware General Corporation Law, or the DGCL, authorizes a corporation to indemnify its directors and officers against liabilities arising out of actions, suits and proceedings to which they are made or threatened to be made a party by reason of the fact that they have served or are currently serving as amended from timea director or officer to time, shall indemnify all persons whom ita corporation. The indemnity may indemnify pursuantcover expenses (including attorneys’ fees) judgments, fines and amounts paid in settlement actually and reasonably incurred by the director or officer in connection with any such law. It further provides thataction, suit or proceeding if the director or officer acted in good faith and in a manner the director or officer reasonably believed to be in or not opposed to the best interests of the corporation, and, with respect to any criminal action or proceeding, had no reasonable cause to believe the director or officer’s conduct was unlawful. Section 145 permits corporations to pay expenses (including attorneys’ fees) incurred by an officer or director in defending any civil, criminal, administrative, or investigative action, suit or proceeding for which such officer or director may be entitled to indemnification under our Amendeddirectors and Restated Certificate of Incorporation, as amended, shall be paid by the Companyofficers in advance of the final disposition of such action, suit or proceeding upon receipt of an undertaking by or on behalf of such director or officer to repay such amount if it shall ultimately be determined that hesuch director or officer is not entitled to be indemnified by the Companycorporation as authorized thereby.in Section 145. In addition, Section 145 provides that a corporation has the power to purchase and maintain insurance on behalf of its directors and officers against any liability asserted against them and incurred by them in their capacity as a director or officer, or arising out of their status as such, whether or not the corporation would have the power to indemnify the director or officer against such liability under Section 145.

We have adopted provisions in both our certificate of incorporation and bylaws that limit or eliminate the personal liability of our directors to the fullest extent permitted by the DGCL, as it now exists or may in the future be amended. Consequently, a director is not personally liable to us or our stockholders for monetary damages or breach of fiduciary duty as a director, except for liability for:

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These limitations of liability do not alter director liability under the federal securities laws and do not affect the availability of equitable remedies such as an injunction or rescission.

In addition, our Bylaws, as amended, provide the Company with the power to to:

We have entered into indemnification agreements with each of our directors and officers are covered by insurance policies maintained by the Company against certain liabilities for actions taken in their capacities as such, including liabilities under the Securities Act.

On January 21, 2009, the Company’s board of directors approved a form of indemnification agreement (the “Indemnification Agreement”) and authorized the Company to enter into such Indemnification Agreement with each of the Company’s current directors and executive officers, as well as other key employees to be identified by the chief executive officer from time to time.

Pursuant to the Indemnification Agreements, the Company generally agreed,officers. These agreements provide that, in exchange for each person’s continued service as a director, officer or other employee, as applicable, towe will indemnify each of our directors, certain of our executive officers and, hold harmless each such personat times, their affiliates to the fullest extent permitted by law against certainDelaware law. We will advance expenses, including attorneys’ fees (but excluding judgments, penalties, fines and settlement payments incurredamounts), to each indemnified director, executive officer or affiliate in connection with any proceeding in which indemnification is available and we will indemnify our directors and officers for any action or proceeding arising out of that person’s services as a director or officer brought on behalf of us or in furtherance of our rights. Additionally, certain of our directors or officers may have certain rights to indemnification, advancement of expenses or insurance provided by their affiliates or other than a derivative suit (and against certain expenses in connection with a derivative suit)third parties, which indemnification relates to and resulting from his or her servicemight apply to the Company.

same proceedings arising out of such director’s or officer’s services as a director referenced herein. Nonetheless, we have agreed in the indemnification agreements that our obligations to those same directors or officers are primary and any obligation of such affiliates or other third parties to advance expenses or to provide indemnification for the expenses or liabilities incurred by those directors are secondary.

The foregoing description of the Indemnification Agreements does not purport to be complete and is qualified in its entirety by reference to the actual agreement, a form of which is attached as an exhibit to the Company’s Current Report on Form 8-K, filed on January 27, 2009.

Item 16. Exhibits.We also maintain general liability insurance which covers certain liabilities of our directors and officers arising out of claims based on acts or omissions in their capacities as directors or officers, including liabilities under the Securities Act.

See the indexExhibit Index attached to exhibits, which isthis Registration Statement and incorporated herein by reference.

Item 17. Undertakings.

(a) The undersigned registrant hereby undertakes:

(1) to file, during the

(1)

To file, during any period in which offers or sales are being made, a post-effective amendment to this registration statement:

(i) to include any prospectus required by Section 10(a)(3) of the Securities Act of 1933, as amended (the “Securities Act” or “Securities Act of 1933”);II-2

provided, however, that the undertakings set forth in the registration statement. Notwithstanding the foregoing, any increase or decrease in volume of securities offered (if the total dollar value of securities offered would not exceed that which was registered) and any deviation from the low or high end of the estimated maximum offering range may be reflected in the form of prospectus filed with the Commission pursuant to Rule 424(b) if, in the aggregate, the changes in volume and price represent no more than 20 percent change in the maximum aggregate offering price set forth in the “Calculation of Registration Fee” table in the effective registration statement;

(iii) to include any material information with respect to the plan of distribution not previously disclosed in the registration statement or any material change to such information in the registration statement;

provided, however, that paragraphs (a)(1)(i), (a)(1)(ii) and (a)(1)(iii) above do not apply if the information required to be included in a post- effectivepost-effective amendment by those paragraphs is contained in periodic reports filed with or furnished to the CommissionSEC by the registrant pursuant to Section 13 or Section 15(d) of the Securities Exchange Act of 1934, as amended, (the “Exchange Act”)or the Exchange Act, that are incorporated by reference in thethis registration statement or isare contained in a form of prospectus filed pursuant to Rule 424(b) that is part of thethis registration statement;statement.

(2) that, for the purpose of determining any liability under the Securities Act, each such post-effective amendment shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initialbona fide offering thereof;

(3) to remove from registration by means of a post-effective amendment any of the securities being registered which remain unsold at the termination of the offering.II-3

(5) that, for the purpose of determining liability under the Securities Act of 1933 to any purchaser:

(i)

any preliminary prospectus or prospectus of the undersigned registrant relating to the offering required to be filed pursuant to Rule 424;

(i) (A) Each prospectus filed by the registrant pursuant to Rule 424(b)(3) shall be deemed to be part of the registration statement as of the date the filed prospectus was deemed part of and included in the registration statement; and

(ii)

any free writing prospectus relating to the offering prepared by or on behalf of the undersigned registrant or used or referred to by the undersigned registrant;

(B) Each prospectus required to be filed pursuant to Rule 424(b)(2), (b)(5) or (b)(7) as part of a registration statement in reliance on Rule 430B relating to an offering made pursuant to Rule 415(a)(1)(i), (vii) or (x) for the purpose of providing the information required by Section 10(a) of the Securities Act of 1933 shall be deemed to be part

(iii)

the portion of any other free writing prospectus relating to the offering containing material information about the undersigned registrant or its securities provided by or on behalf of the undersigned registrant; and included in the registration statement as of the earlier of the date such form of prospectus is first used after effectiveness or the date of the first contract of sale of securities in the offering described in the prospectus. As provided in Rule 430B, for liability purposes of the issuer and any person that is at that date an underwriter, such date shall be deemed to be a new effective date of the registration statement relating to the securities in the registration statement to which the prospectus relates, and the offering of such securities at that time shall be deemed to be the initialbona fide offering thereof.Provided, however, that no statement made in a registration statement or prospectus that is part of the registration statement or made in a document incorporated or deemed incorporated by reference into the registration statement or prospectus that is part of the registration statement will, as to a purchaser with a time of contract of sale prior to such effective date, supersede or modify any statement that was made in the registration statement or prospectus that was part of the registration statement or made in any such document immediately prior to such effective date.

(6) that, for the purpose of determining liability of the registrant under the Securities Act of 1933 to any purchaser in the initial distribution of the securities, the undersigned registrant undertakes that in a primary offering of securities of the undersigned registrant pursuant to this registration statement, regardless of the underwriting method used to sell the securities to the purchaser, if the securities are offered or sold to such purchaser by means of any of the following communications, the undersigned registrant will be a seller to the purchaser and will be considered to offer or sell such securities to such purchaser:

(7)

That, for purposes of determining any liability under the Securities Act:

(i) Any preliminary prospectus or prospectus of the undersigned registrant relating to the offering required to be filed pursuant to Rule 424 (§230.424 of this chapter);

(i)

the information omitted from the form of prospectus filed as part of this registration statement in reliance upon Rule 430A and contained in a form of prospectus filed by the registrant pursuant to Rule 424(b)(1) or (4) or 497(h) under the Securities Act shall be deemed to be part of this registration statement as of the time it was declared effective; and

(ii) Any free writing prospectus relating to the offering prepared by or on behalf of the undersigned registrant or used or referred to by the undersigned registrant;

(ii)

each post-effective amendment that contains a form of prospectus shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

(iii) The portion of any other free writing prospectus relating to the offering containing material information about the undersigned registrant or its securities provided by or on behalf of the undersigned registrant; and

(iv) Any other communication that is an offer in the offering made by the undersigned registrant to the purchaser.

(b) The undersigned registrant hereby undertakes that, for purposes of determining any liability under the Securities Act of 1933, each filing of the registrant’s annual report pursuant to Section 13(a) or 15(d) of the Securities Exchange Act of 1934 (and, where applicable, each filing of an employee benefit plan’s annual report pursuant to Section 15(d) of the Securities Exchange Act of 1934) that is incorporated by reference in the registration statement shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initialbona fide offering thereof.

(h) Insofar as indemnification for liabilities arising under the Securities Act of 1933 may be permitted to directors, officers and controlling persons of the registrant pursuant to the foregoing provisions, or otherwise, the registrant has been advised that in the opinion of the Securities and Exchange CommissionSEC such indemnification is against public policy as expressed in the Securities Act and is, therefore, unenforceable. In the event that a claim for indemnification against such liabilities (other than the payment by the registrant of expenses incurred or paid by a director, officer or controlling person of the registrant in the successful defense of any action, suit or proceeding) is asserted by such director, officer or controlling person in connection with the securities being registered, the registrant will, unless in the opinion of its counsel the matter has been settled by controlling precedent, submit to a court of appropriate jurisdiction the question whether such indemnification by it is against public policy as expressed in the Securities Act and will be governed by the final adjudication of such issue.

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SIGNATURES

Pursuant to the requirements of the Securities Act, of 1933, the RegistrantAltimmune, Inc. certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-3 and has duly caused this Registration Statement on Form S-3 to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Annapolis,Gaithersburg, State of Maryland, on March 30, 2017.the 31st day of December, 2020.

POWER OF ATTORNEY

KNOW ALL MENPERSONS BY THESE PRESENTS, that each of the undersignedperson whose signature appears below constitutes and appoints John M. Gill,Vipin K. Garg and Philip MacNeill,Will Brown, and each of them, as his or her attorneys-in-fact and agents, each with fullthe power of substitution, and resubstitution, for and in the name, place and stead of the undersigned,him or her in any and all capacities, to sign this Registration Statement, any and all amendments thereto (including post- effectivepost-effective amendments) to this Registration Statement or any Registration Statement for this offering that is to be effective upon the filing pursuant to Rule 462(b) under the Securities Act of 1933, as amended, and all post-effective amendments thereto,, and to file the same, with all exhibits thereto and all other documents in connection therewith, with the Securities and Exchange Commission, granting unto said attorneys-in-fact and agents full power and authority to do and perform each and every act and thing requisite and necessary to be done in and about the premises, as fully to all intents and purposes as the undersigned might or could do in person,SEC, hereby ratifying and confirming all that each of said attorney-in-factattorneys-in fact, or his substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

Pursuant to the requirements of the Securities Act, of 1933, this Registration Statement has been signed below by the following persons in the capacities indicated, on March 30, 2017.listed opposite their respective names.

Index to Exhibits

* Filed herewith.II-6