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                                                                   EXHIBIT 10.31

Dear Dr. Brettman:

     This letter describes me terms of your expanded advisory role with
GeneCraft, Inc. ("GeneCraft"). Please review the letter and, if the terms are
acceptable to you, sign it, and return a signed copy to me.

     As part of your expanded advisory role with GeneCraft, you agree to perform
the services described in the attached Exhibit A (the "Services"), for a period
commencing on January 1, 2003 and ending on January 1, 2007. Notwithstanding the
foregoing, either GeneCraft or you may terminate the advisory relationship
described herein prior to January 1, 2007 for any or no reason by giving the
other party thirty (30) days prior written notice. The confidentiality and
assignment obligations listed below will survive termination. As consideration
for your performance of the Services, GeneCraft will pay you the compensation
set forth in Exhibit A.

     You agree that your confidentiality obligations to GeneCraft arising in
connection with your service as a member of GeneCraft's Board of Directors apply
to your expanded advisory role with GeneCraft. Accordingly, you agree that you
will not disclose GeneCraft's confidential information or trade secrets or other
information GeneCraft is obligated to keep confidential to any third party or
use this information for any purpose other than in connection with the
performance of the Services and your obligations as a member of GeneCraft's
Board of Directors. You agree to take all reasonable precautions to prevent any
unauthorized disclosure of this information. In addition, you agree not to
disclose to GeneCraft any confidential information of any third party to whom
you owe non-disclosure obligations.

     As part of your expanded advisory role with GeneCraft, you may create works
of authorship and inventions for GeneCraft. Without a written commitment from
you, GeneCraft would not own these works and inventions. Therefore, you agree
that all works of authorship and inventions created by you specifically for
GeneCraft while performing the Services for GeneCraft will be the sole property
of GeneCraft. You hereby assign to GeneCraft all right, title, and interest in
and to these works and inventions, including all related intellectual property
rights. You also agree to assist GeneCraft to secure GeneCraft's rights in these
works and inventions and related intellectual property rights. You further agree
not to incorporate any pre-existing works or third party materials into the
works and inventions you create for GeneCraft while performing the Services
without the prior written consent of GeneCraft.

     Any term of this letter agreement and the attached Exhibit A may be amended
or waived only with the written consent of GeneCraft and you. This letter
agreement and the attached Exhibit A constitute the full and entire
understanding and agreement between GeneCraft and you with regard to the subject
hereof. This letter agreement shall be governed, construed and interpreted in
accordance with the laws of the State of Washington, without giving effect to
principles of conflicts of law. This letter agreement may be executed in two or
more counterparts, each of which shall be deemed an original and all of which
together shall constitute one instrument.

                                        Sincerely,



                                        /s/ Peter A. Thompson
                                        ----------------------------------------
                                        Peter A. Thompson, MD, FACP
                                        President and CEO of GeneCraft


Acknowledged and agreed:


/s/ Lee R. Brettman
-------------------------------------
Lee. R. Bettman, MD, FACP

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                                    EXHIBIT A

                            SERVICES AND COMPENSATION

     1. Services. Services include the following:

     -    Providing input on clinical development planning for GeneCraft product
          candidates at and between meetings of GeneCraft's clinical development
          planning team;

     -    Providing input on implementation of GeneCraft's clinical development
          strategies;

     -    Providing input on research and development prioritization at and
          between meetings of GeneCraft's research and development strategic
          planning team; and

     -    Other activities as mutually agreed upon by you and GeneCraft.

     2. Compensation. GeneCraft will recommend at the first meeting of
GeneCraft's Board of Directors following the date of this letter that GeneCraft
grant you the right to purchase 100,000 shares of GeneCraft's Common Stock (the
"Shares") at a price per share equal to the fair market value per share of the
Common Stock on the date of purchase. The Shares will be sold pursuant to
GeneCraft's standard form of Restricted Stock Purchase Agreement and will be
subject to a right of repurchase on the part of GeneCraft that will lapse as
follows: GeneCraft's repurchase right will lapse as to 25% of the Shares upon
the date of purchase and, as to the remaining Shares, at the rate of 1/36th of
such Shares each month thereafter, subject to your continued provision of the
Services on the applicable dates.