EXHIBIT 99.1


     AMENDMENT No. 3 (this "Amendment"), dated as of May 31, 2005, to the Share
Exchange Agreement dated as of March 15, 2005 and as amended by Amendment No. 1
dated as of March 15, 2005 and Amendment No. 2 dated as of April 21, 2005 (the
"Agreement"), by and among EPIMMUNE INC., a Delaware corporation (the "Issuer"),
and the shareholders of IDM S.A., a societe anonyme organized under the laws of
France (the "Company"), listed on Exhibit A attached thereto (the "Principal
Company Shareholders"). Capitalized terms used but not defined herein shall have
the meanings assigned to such terms in the Agreement.

                                    RECITALS:

     A. The Issuer and the Principal Company Shareholders have entered into the
Agreement;

     B. The Principal Company Shareholders have appointed Helene Ploix, as
Shareholder Representative, and have empowered her to execute amendments to the
Agreement which may be necessary or desirable to complete the Agreement; and

     C. The Issuer and the Shareholder Representative, on behalf of the
Principal Company Shareholders, have agreed to enter into this Amendment No. 3
to the Agreement.

     NOW, THEREFORE, in consideration of the foregoing and the rights and
obligations contained herein, and intending to be legally bound hereby, the
Issuer and the Shareholder Representative hereby agree as follows:

          Section 1. Issuer Reverse Stock Split. Section 6.11(d) of the
Agreement shall be deleted and replaced in its entirety by the following
paragraph:

          (d) Subject to the receipt of the requisite stockholder approval at
     the Issuer Stockholders' Meeting, the Issuer shall take all action as may
     be necessary immediately prior to the Closing to (i) effect a reverse stock
     split of the Issuer Common Stock pursuant to which four, five, six, seven,
     eight, nine or ten shares of Issuer Common Stock will be consolidated into
     one share of Issuer Common Stock (it being understood that the final
     determination of the number of shares of Issuer Common Stock to be
     consolidated under this Section 6.11(d) shall be made by the Issuer's board
     of directors in consultation with the Company, following the approval by
     the requisite affirmative vote of the stockholders of the Issuer of each
     proposed ratio for such reverse stock split) and (ii) cause the authorized
     capital stock of the Issuer after giving effect to such reverse stock split
     prescribed in clause (i) above to be increased to a total of 65,000,000
     shares, consisting of 55,000,000 shares of Issuer Common Stock and
     10,000,000 shares of Issuer Preferred Stock.

          Section 2. Entire Agreement. The Agreement, as amended by this
Amendment constitutes the entire agreement of the parties with respect to the
subject matter hereof and supersedes all prior agreements and undertakings, both
written and oral, between the

parties and the Principal Company Shareholders with respect to the subject
matter thereof and hereof. Except as amended by this Amendment, the Agreement
shall continue in full force and effect in accordance with its terms.

          Section 3. Severability. If any term or other provision of this
Amendment is invalid, illegal or incapable of being enforced by any rule of Law,
or public policy, all other conditions and provisions of this Amendment shall
nevertheless remain in full force and effect so long as the economic or legal
substance of the Transactions contemplated by this Amendment is not affected in
any manner materially adverse to any party. Upon such determination that any
term or other provision is invalid, illegal or incapable of being enforced, the
parties hereto shall negotiate in good faith to modify this Amendment so as to
effect the original intent of the parties as closely as possible in a mutually
acceptable manner in order that the Transactions be consummated as originally
contemplated by the Agreement as amended by this Amendment to the fullest extent
possible.

          Section 4. Counterparts. This Amendment may be executed and delivered
(including by facsimile transmission) in one or more counterparts, and by the
different parties hereto in separate counterparts, each of which when executed
shall be deemed to be an original but all of which taken together shall
constitute one and the same agreement.

          Section 5. Governing Law. (a) This Amendment shall be governed by, and
construed in accordance with, the laws of the State of Delaware applicable to
contracts executed in and to be performed in that jurisdiction, excluding (to
the greatest extent a Delaware court would permit) any rule of law that would
cause the application of the laws of any jurisdiction other than the State of
Delaware.

     (b) The parties irrevocably agree that any dispute, controversy or claim
arising out of or relating to this Amendment or the transactions contemplated
thereby, or the breach, termination or invalidity thereof, shall be settled by
arbitration in accordance with the Rules of Conciliation and Arbitration of the
International Chamber of Commerce as at present in force. The place of
arbitration shall be Orange County, California and the number of arbitrators
shall be three. Each of (i) the Shareholder Representative, on behalf of the
Principal Company Shareholders, on the one hand, and (ii) the Issuer, on the
other hand, shall designate one arbitrator and the two so designated arbitrators
shall jointly designate the third arbitrator. If such designation is not made
within fifteen (15) days of the designation of the second party designated
arbitrator, the Secretary General of the International Court of Arbitration of
the International Chamber of Commerce shall designate the third arbitrator. The
language of the arbitral proceedings shall be English, but all submissions and
written evidence may be in French or English.


                                       2

     IN WITNESS WHEREOF, the Issuer and the Principal Company Shareholders,
represented by the Shareholder Representative have executed, or have caused to
be executed by their respective officers thereunto duly authorized, this
Amendment as of the date first written above.

                                  EPIMMUNE INC.


                                  By: /s/ ROBERT DE VAERE
                                      ------------------------------------------
                                      Name:  Robert De Vaere
                                      Title: Vice President, Finance and
                                      Administration, Chief Financial Officer
                                      and Secretary


                                  PRINCIPAL COMPANY SHAREHOLDERS,
                                   Represented by the Shareholder Representative

                                  By: /s/ Helene Ploix
                                      ------------------------------------------
                                      Name:  Helene Ploix
                                      Title: Shareholder Representative