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                                                                   Exhibit 10.62


*Certain confidential information contained in this document, marked by
brackets, has been omitted and filed with the Securities and Exchange Commission
pursuant to Rule 24b-2 of the Securities Exchange Act of 1934, as amended

                                                November 19, 2001
Inpharzam, S.A.
Via Industria 1
6814 Cadempino
Switzerland
Attention:  Managing Director

RE:  COLLABORATION AGREEMENT, DATED MAY 21, 1999, BETWEEN CORIXA CORPORATION
AND INPHARZAM INTERNATIONAL, S.A., A WHOLLY OWNED SUBSIDIARY OF ZAMBON GROUP
SPA (THE "AGREEMENT")

Dear Mr. Rettani:

This Letter Agreement sets forth our understanding regarding the certain changes
to the Agreement, all as set forth herein below. All capitalized terms not
otherwise defined herein shall have the definitions given them in the Agreement.

      1.    Except as set forth herein or otherwise modified in accordance with
            the Agreement, the Research Program during the [*] of the Research
            Program Term shall be as set forth in the [*] Work Plan attached
            hereto as Exhibit A and incorporated herein by this reference (the
            "Work Plan"). Zambon shall be responsible for [*] set forth therein,
            as well as [*]. Within ten (10) days following the execution in full
            of this Letter Agreement, Zambon shall pay to Corixa [*] payable by
            Zambon to Corixa as forecast in Exhibit A pursuant to the
            immediately preceding sentence, for Corixa's use in payment of such
            [*]. After Corixa has used the foregoing initial payment, Corixa
            shall thereafter invoice Zambon for [*]. Such invoices shall be
            payable by Zambon within thirty days of receipt.

      2.    Corixa shall continue to [*] aimed at achieving the preclinical
            milestone set forth in Section 6.4(i) of the Agreement in connection
            with [*]. In relation to the above Corixa shall issue two invoices
            to Zambon, each in the amount of [*] as follows: Corixa shall issue
            the first invoice upon [*], to be paid by Zambon to Corixa by wire
            transfer of immediately available funds, and Corixa shall issue the
            second invoice, [*]. In the event that by [*], Corixa has not
            delivered to Zambon [*], Zambon shall have no obligation to make
            such addition payment and the above second invoice submitted by
            Corixa to Zambon shall be deemed to be cancelled.

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* Confidential treatment requested
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      3.    The [*] as defined in Section 4.5 of the Agreement shall hereafter
            be amended [*]. In the event the parties [*] as contemplated in
            Section 4.5 of the Agreement, [*].

            Upon execution in full of this Letter Agreement, [*] shall, with no
            further action required by either party, [*]. Corixa acknowledges
            and agrees that the foregoing shall not operate to return to Corixa
            any rights in any Antigens for application in [*] and as a
            consequence Corixa undertakes not to engage in any activity
            whatsoever in conflict with the Agreement concerning the above
            Antigens without the prior consent of Zambon. Notwithstanding
            Section 19.4 of the Agreement, [*].

Except as modified hereby, the Agreement shall continue to be in full force and
effect in accordance with its terms.

If Zambon agrees to the foregoing, please have the enclosed duplicate original
of this letter executed as indicated below and returned to my attention.

                                          Sincerely,

                                          /s/ STEVEN GILLIS, PH.D.
                                          Chairman, Chief Executive Officer

                                          Acknowledged and Agreed:

                                          INPHARZAM INTERNATIONAL, S.A.

                                          /s/ ROBERTO RETTANI
                                          Vice President

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* Confidential treatment requested
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                              EXHIBIT A - WORK PLAN

[*]

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* Confidential treatment request