MFS VARIABLE INSURANCE TRUST
                            MFS/SUNLIFE SERIES TRUST

             500 Boylston Street, Boston, Massachusetts 02116-3741
                                  617-954-5000




                                        April 20, 2007

VIA EDGAR (as Correspondence)
United States Securities & Exchange Commission
100 F Street, N.E.
Washington, D.C.  20549

     Re:  Post-Effective  Amendment No. 25 to the Registration Statement on Form
          N-1A for MFS Variable  Insurance  Trust ("VIT") (Files Nos.  33-74668;
          811-8326)

          Post-Effective Amendment No. 38 to Registration Statement on Form N-1A
          for MFS/Sun Life Series Trust ("Series Trust";  together with VIT, the
          "Trusts") (File Nos. 2-83616; 811-3732)

Ladies and Gentlemen:

     As  requested,  in  connection  with the  filings  of the  above-referenced
Registration Statements, we acknowledge the following:

(i)           the comment process with the SEC or its staff, acting pursuant to
              delegated authority, does not foreclose the SEC from taking any
              action with respect to the filings;

(ii)          the comment process with the SEC or its staff, acting pursuant to
              delegated authority, does not relieve the Trusts from their full
              responsibility for the adequacy and accuracy of the disclosure in
              the filings; and

(iii)         the Trusts may not assert the comment process with the SEC or its
              staff in connection with the preliminary filings as a defense in
              any proceeding initiated by the SEC or any person under the
              federal securities laws of the United States.

     The Trusts note that, as indicated in the SEC's June 24, 2004 release
     regarding the public release of comment letters and responses, you are
     requesting such acknowledgements from all companies whose filings are being
     reviewed.

     If you have any questions, please call the undersigned at 617-954-4340.

                                        Very truly yours,


                                        MFS VARIABLE INSURANCE TRUST
                                        MFS/SUN LIFE SERIES TRUST



                                        /S/ Susan A. Pereira
                                        Susan A. Pereira
                                        Assistant Secretary