ANERGEN INC
SC 13D, 1999-02-09
BIOLOGICAL PRODUCTS, (NO DIAGNOSTIC SUBSTANCES)
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<PAGE>   1
                                  SCHEDULE 13D

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CUSIP NO. 034602-10-2                            PAGE 1 OF 9 PAGES
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                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                  -------------

                                  SCHEDULE 13D
                                 (RULE 13d-101)

                    UNDER THE SECURITIES EXCHANGE ACT OF 1934


                                  Anergen, Inc.
               ---------------------------------------------------
                                (Name of Issuer)

                    Common Stock, par value $0.001 per share
               ---------------------------------------------------
                         (Title of Class of Securities)

                                   034602-10-2
               ---------------------------------------------------
                                 (CUSIP Number)

                             Barry M. Sherman, M.D.
                      President and Chief Executive Officer
                                  Anergen, Inc.
                               301 Penobscot Drive
                         Redwood City, California 94063
                                 (650) 361-8901
         ---------------------------------------------------------------
           (Name, Address and Telephone Number of Person Authorized to
                      Receive Notices and Communications)

                                December 11, 1998
         ---------------------------------------------------------------
             (Date of Event which Requires Filing of this Statement)

If the filing person has previously filed a statement on Schedule 13G to report
the acquisition which is the subject of this Schedule 13D, and is filing this
schedule because of Rule 13d-1(b)(3) or (4), check the following box [ ].

The information required on the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the Securities Exchange Act of
1934 ("Act") or otherwise subject to the liabilities of that section of the Act
but shall be subject to all other provisions of the Act (however, see the
Notes).




<PAGE>   2

                                 SCHEDULE 13D

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CUSIP NO. 034602-10-2                                   PAGE 2 OF 9 PAGES
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- ------------ -------------------------------------------------------------------
1            NAME OF REPORTING PERSON
             S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

             CORIXA CORPORATION

             91-1654387
- ------------ -------------------------------------------------------------------
2            CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*           (a) [ ]
                                                                         (b) [X]
- ------------ -------------------------------------------------------------------
3            SEC USE ONLY

- ------------ -------------------------------------------------------------------
4            SOURCE OF FUNDS*
             OO
- ------------ -------------------------------------------------------------------
5            CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT 
             TO ITEMS 2(d) or 2(e) [ ]
- ------------ -------------------------------------------------------------------
6            CITIZENSHIP OR PLACE OF ORGANIZATION
             DELAWARE
- ------------ -------------------------------------------------------------------
                    7     SOLE VOTING POWER
                          0
    NUMBER OF
                    ----- ------------------------------------------------------
      SHARES        8     SHARED VOTING POWER
   BENEFICIALLY           9,146,294(1)
     OWNED BY
                    ----- ------------------------------------------------------
       EACH         9     SOLE DISPOSITIVE POWER
    REPORTING             0
      PERSON
                    ----- ------------------------------------------------------
       WITH         10    SHARED DISPOSITIVE POWER
                          9,146,294(1)

- ------------ -------------------------------------------------------------------
11           AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
             9,146,294
- ------------ -------------------------------------------------------------------
12           CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN 
             SHARES*     |X|

- ------------ -------------------------------------------------------------------
13           PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
             48.3% (1)
- ------------ -------------------------------------------------------------------
14           TYPE OF REPORTING PERSON*
             CO
- ------------ -------------------------------------------------------------------

(1) 9,146,294 of the shares of the Issuer Common Stock (excluding warrant shares
held by certain stockholders and option shares exercisable within 60 days of
January 8, 1999, which are included on Schedule II) covered by this report are
subject to a Voting Agreement entered into by certain stockholders of the Issuer
with the Reporting Person pursuant to which such stockholders have agreed to
vote all of the 

<PAGE>   3

                                  SCHEDULE 13D

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CUSIP NO. 034602-10-2                                    PAGE 3 OF 9 PAGES
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shares of Issuer Common Stock beneficially owned by such stockholders in favor
of the proposed merger of Yakima Acquisition Corporation ("Yakima") with and
into the Issuer pursuant to the Agreement and Plan of Reorganization dated as of
December 11, 1998 by and among the Issuer, the Reporting Person and Yakima, a
wholly-owned subsidiary of the Reporting Person (the "Merger Agreement"). The
Reporting Person expressly disclaims beneficial ownership of any of the shares
of Issuer Common Stock covered by the Voting Agreement. Based on the number of
shares of Issuer Common Stock outstanding on December 11, 1998 as represented by
the Issuer in the Merger Agreement, the number of shares of Issuer Common Stock
indicated represents approximately 48.3% of the outstanding shares of Issuer
Common Stock (subject to adjustment for fractional shares and option exercises).


ITEM 1 - SECURITY AND ISSUER

        This statement on Schedule 13D (the "Schedule 13D") relates to the
common stock, par value $0.001 per share (the "Shares" or the "Issuer Common
Stock"), of Anergen, Inc., a Delaware corporation (the "Issuer"). The principal
executive office of the Issuer is located at 301 Penobscot Drive, Redwood City,
California 94063.


ITEM 2 - IDENTITY AND BACKGROUND

(a)-(c) This Schedule 13D is filed by Corixa Corporation, a Delaware corporation
(the "Reporting Person"). The address of the principal business and principal
office of the Reporting Person is 1124 Columbia Street, Suite 200, Seattle,
Washington 98104. The Reporting Person is a biotechnology company that applies
its advanced immunological expertise and proprietary technology platforms to
discover and optimize vaccines and other antigen or adjuvant-based products.

        As a result of entering into the Voting Agreement described in Items 3
and 4 below, the Reporting Person may be deemed to have formed a "group" with
each of the Stockholders (as defined in Item 3 below), for purposes of Section
13(d)(3) of the Act and Rule 13d-5(b)(1) thereunder. The Reporting Person
expressly declares that the filing of this Schedule 13D shall not be construed
as an admission by the Reporting Person that it has formed any such group.

        To the best knowledge of the Reporting Person, the name of each
Stockholder, each Stockholder's resident address and the number of Shares owned
by each Stockholder is set forth in Schedule II, which is incorporated herein in
its entirety by reference. To the best knowledge of the Reporting Person, based
on the Issuer's 1998 Proxy Statement on Schedule 14A filed with the Securities
and Exchange Commission on April 6, 1998 and the information provided by each
Stockholder on the Voting Agreement, the following Stockholders were, as of the
date of the Voting Agreement, employed by the Issuer in the following
capacities: Barry Sherman, M.D., President, Chief Executive Officer, Secretary
and Director; Nick Lowcock, Director; Jeff Winkelhake, Vice President,
Pharmaceutical Development; Maureen Howard, Vice President, Research; Michael
Shulman, Vice President, Clinical Development; David Smith, Vice President,
Finance and Chief Financial Officer; Harden McConnell, Director; Harry Penner,
Director; James Thomas, Director; Bruce Carter, Director; and Nicole Vitullo,
Director.

<PAGE>   4

                                  SCHEDULE 13D

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CUSIP NO. 034602-10-2                                   PAGE 4 OF 9 PAGES
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        To the best of the Reporting Person's knowledge as of the date hereof,
the name, business address, present principal occupation or employment and
citizenship of each executive officer and director of the Reporting Person, and
the name, principal business and address of any corporation or other
organization in which such employment is conducted is set forth in Schedule I
hereto. The information contained in Schedule I is incorporated herein by
reference.

         (d)-(e) During the last five years, neither the Reporting Person nor,
to the best knowledge of the Reporting Person, any of the executive officers or
directors of the Reporting Person, has been convicted in a criminal proceeding
(excluding traffic violations or similar misdemeanors), or been a party to a
civil proceeding of a judicial or administrative body of competent jurisdiction
and as a result of such proceeding was or is subject to a judgment, decree or
final order enjoining future violations of, or prohibiting or mandating
activities subject to, Federal or State securities laws or finding any violation
with respect to such laws.

ITEM 3 - SOURCE AND AMOUNT OF FUNDS OR OTHER CONSIDERATION

        The Reporting Person entered into an Agreement and Plan of Merger dated
as of December 11, 1998 by and among the Reporting Person, Yakima and the Issuer
(the "Merger Agreement"), providing for the merger (the "Merger") of Yakima with
and into the Issuer with the Issuer as the surviving corporation, pursuant to
which each outstanding Share will be converted into the right to receive .058751
shares of common stock, par value $0.001 per share, of the Reporting Person,
subject to adjustment for certain potential pre-closing events. The Merger is
subject to the approval of the Merger Agreement by the Issuer's stockholders and
the satisfaction or waiver of certain other conditions as more fully described
in the Merger Agreement.

        As a further inducement for the Reporting Person to enter into the
Merger Agreement and in consideration thereof, Warburg, Pincus Ventures, L.P.,
International Biotechnology Trust PLC, Novo Nordisk A/S, Nicole Vitullo, Jeff
Winkelhake, Maureen Howard, Barry Sherman, M.D., Nick Lowcock, Michael Shulman,
David Smith, Harden McConnell, Harry Penner, James Thomas and Bruce Carter
(collectively, the "Stockholders"), entered into a Voting Agreement (the "Voting
Agreement"), dated as of December 11, 1998, with the Reporting Person whereby
the Stockholders agreed, severally and not jointly, to vote all of the Shares
beneficially owned by them in favor of approval and adoption of the Merger
Agreement. The Reporting Person did not pay additional consideration to any
Stockholder in connection with the execution and delivery of the Voting
Agreement.

         References to, and descriptions of, the Merger Agreement and the Voting
Agreement, respectively, as set forth above in this Item 3, are qualified in
their entirety by reference to the copies of the Merger Agreement and the Voting
Agreement, respectively, included as Exhibits 1 and 2, respectively, to this
Schedule 13D, and are incorporated in this Item 3 in their entirety,
respectively, where such references and descriptions appear.

<PAGE>   5

                                  SCHEDULE 13D

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CUSIP NO. 034602-10-2                                   PAGE 5 OF 9 PAGES
- ------------------------------                   -------------------------------


ITEM 4 - PURPOSE OF TRANSACTION

(a)-(j) The information set forth, or incorporated by reference, in Item 3 is
hereby incorporated herein by reference.

         Pursuant to the Voting Agreement, the Stockholders have agreed to vote
all of the Shares beneficially owned by them in favor of the approval and
adoption of the Merger Agreement. The Voting Agreement terminates upon the
earlier to occur of the completion of the Merger or the termination of the
Merger Agreement. The name of each Stockholder and the number of outstanding
shares of Issuer Common Stock held by each Stockholder are set forth on Schedule
II hereto, which is incorporated herein by reference.

         The purpose of the Voting Agreement is to facilitate consummation of
the Merger.

         Upon consummation of the Merger as contemplated by the Merger
Agreement, (a) Yakima will be merged into the Issuer, (b) the sole officer and
director of Anergen will be Steven Gillis, Ph.D, (c) the Certificate of
Incorporation and Bylaws of the Issuer will be replaced by the Certificate of
Incorporation and Bylaws of Yakima, (d) the Shares will cease to be authorized
for listing on the Nasdaq National Market and (e) the Shares will become
eligible for termination of registration pursuant to Section 12(g)(4) of the
Securities Exchange Act of 1934, as amended.

         References to, and descriptions of, the Merger Agreement and the Voting
Agreement, respectively, as set forth above in this Item 4, are qualified in
their entirety by reference to the copies of the Merger Agreement and the Voting
Agreement, respectively, included as Exhibits 1 and 2, respectively, to this
Schedule 13D, and are incorporated in this Item 4 in their entirety,
respectively, where such references and descriptions appear.


ITEM 5 - INTEREST IN SECURITIES OF THE ISSUER

        (a) - (b) The number of Shares covered by the Voting Agreement is
9,146,294 (excluding warrant shares held by certain Stockholders and option
shares exercisable within 60 days of January 8, 1999, which are included on
Schedule II), which constitutes approximately 48.3% of the Issuer Common Stock,
based on the number of Shares outstanding on December 11, 1998, as represented
by the Issuer in the Merger Agreement.

        By virtue of the Voting Agreement, the Reporting Person may be deemed to
share with the respective Stockholders the power to vote Shares subject to the
Voting Agreement. However, the Reporting Person (i) is not entitled to any
rights as a stockholder of Issuer as to the Shares covered by the Voting
Agreement and (ii) disclaims any beneficial ownership of the shares of Issuer
Common Stock which are covered by the Voting Agreement. See the information in
Item 2 with respect to the Stockholders and the information in Items 3 and 4
with respect to the Voting Agreement, which information is incorporated herein
by reference.

<PAGE>   6

                                  SCHEDULE 13D

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CUSIP NO. 034602-10-2                                  PAGE 6 OF 9 PAGES
- ------------------------------                   -------------------------------

        (c) Other than as set forth in this Item 5(a)-(b), to the best of the
Reporting Person's knowledge as of the date hereof (i) neither the Reporting
Person nor any subsidiary or affiliate of the Reporting Person nor any of the
Reporting Person's executive officers or directors, beneficially owns any shares
of Issuer Common Stock, and (ii) there have been no transactions in the shares
of Issuer Common Stock effected during the past 60 days by the Reporting Person,
nor to the best of the Reporting Person's knowledge, by any subsidiary or
affiliate of the Reporting Person or any of the Reporting Person's executive
officers of directors.

        (d) No other person is known by the Reporting Person to have the right
to receive or the power to direct the receipt of dividends from, or the proceeds
from the sale of, the Issuer Common Stock obtainable by the Reporting Person.

        (e) Not applicable.

        Reference to, and descriptions of, the Merger Agreement and Voting
Agreement, respectively, as set forth in this Item 5, are qualified in their
entirety by reference to the copies of the Merger Agreement and the Voting
Agreement, respectively, included as Exhibits 1 and 2, respectively, to this
Schedule 13D, and incorporated in this Item 5 in their entirety, respectively,
where such references and descriptions appear.


ITEM 6 - CONTRACTS, ARRANGEMENTS, UNDERSTANDINGS OR RELATIONSHIPS WITH RESPECT 
         TO SECURITIES OF THE ISSUER

        The information set forth, or incorporated by reference, in Items 3
through 5 is hereby incorporated herein by reference. Copies of the Merger
Agreement and the Voting Agreement are included as Exhibits 1 and 2,
respectively, to this Schedule 13D. To the best of the Reporting Person's
knowledge, except as described in this Schedule 13D, there are at present no
contracts, arrangements, understandings or relationship (legal or otherwise)
among the persons named in Item 2 above and between any such persons and any
person with respect to any securities of the Issuer.

ITEM 7 - MATERIAL TO BE FILED AS EXHIBITS

<TABLE>
<CAPTION>
EXHIBIT    DESCRIPTION
- -------    -----------

<S>        <C>  
1.         Agreement and Plan of Merger, dated as of December 11, 1998 by and
           among Corixa Corporation, Yakima Acquisition Corporation and
           Anergen, Inc. (without exhibits).

2.         Voting Agreement, dated as of December 11, 1998, by and between
           Corixa Corporation and each of the following stockholders of Anergen,
           Inc.: Warburg, Pincus Ventures, L.P., International Biotechnology
           Trust PLC, Novo Nordisk A/S, Nicole Vitullo, Jeff Winkelhake, Maureen
           Howard, Barry Sherman, Nick Lowcock, Michael Shulman, David Smith,
           Harden McConnell, Harry Penner, James Thomas and Bruce Carter.
</TABLE>
           
<PAGE>   7
                                  SCHEDULE 13D

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CUSIP NO. 034602-10-2                                   PAGE 7 OF 9 PAGES
- ------------------------------                   -------------------------------

SIGNATURE

        After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.


Date:  February 9, 1999                      /s/ MICHELLE BURRIS          
                                             -----------------------------------
                                             By:     Michelle Burris
                                             Title:  Vice President and Chief  
                                                     Financial Officer


        The original statement shall be signed by each person on whose behalf
the statement is filed or his authorized representative. If the statement is
signed on behalf of a person by his authorized representative (other than an
executive officer or general partner of this filing person), evidence of the
representative's authority to sign on behalf of such person shall be filed with
the statement, provided, however, that a power of attorney for this purpose
which is already on file with the Commission may be incorporated by reference.
The name and any title of each person who signs the statement shall be typed or
printed beneath his signature.



<PAGE>   8

                                  SCHEDULE 13D

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CUSIP NO. 034602-10-2                                  PAGE 8 OF 9 PAGES
- ------------------------------                   -------------------------------


                                   SCHEDULE I

        The following sets forth the name, business address and present
principal occupation or employment of each director and executive officer of the
Reporting Person. Except as indicated below, each such person is a U.S. citizen,
and the business address of each such person is 1124 Columbia Street, Suite 200,
Seattle, Washington 98104.

                               BOARD OF DIRECTORS

<TABLE>
<CAPTION>
NAME AND TITLE                              PRESENT PRINCIPAL OCCUPATION
- --------------                              ----------------------------
<S>                                         <C>
Joseph S. Lacob, Chairman of the Board      Partner, Kleiner Perkins Caufield & Byers

Steven Gillis, Ph.D                         President and Chief Executive Officer, Corixa
                                            Corporation

Mark McDade                                 Executive Vice President and, Chief Operating
                                            Officer, Corixa Corporation

Arnold L. Oronsky, Ph.D                     General Partner, InterWest Partners

Andrew E. Senyei, M.D.                      General Partner, Enterprise Partners
</TABLE>


                    EXECUTIVE OFFICERS WHO ARE NOT DIRECTORS

<TABLE>
<CAPTION>
NAME AND TITLE                              PRESENT PRINCIPAL OCCUPATION
- --------------                              ----------------------------
<S>                                         <C>

Steven Reed, Ph.D                           Executive Vice President and Chief Scientific
                                            Officer, Corixa Corporation

Kenneth Grabstein, Ph.D                     Vice  President and Director of Immunology, Corixa
                                            Corporation

Michelle Burris                             Vice President and Chief Financial Officer, Corixa Corporation

Martin Cheever, M.D.                        Vice President and Director of Medical Affairs,
                                            Corixa Corporation
</TABLE>


<PAGE>   9

                                  SCHEDULE 13D

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CUSIP NO. 034602-10-2                                   PAGE 9 OF 9 PAGES
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                                   SCHEDULE II

        The following sets forth the name of each Stockholder that is a party to
the Voting Agreement and the number of shares of Common Stock of Anergen, Inc.
beneficially owned by each such Stockholder. Except as indicated below, each
such person that is an individual is a U.S. citizen, and the business address of
each such person is 301 Penobscot Drive, Redwood City, California 94063.

<TABLE>
<CAPTION>
PARTY                                                      SHARES             OPTION SHARES/
                                                                               WARRANT
                                                                               SHARES(1)
<S>                                                       <C>                 <C>

Warburg, Pincus Ventures, L.P                             5,478,049                    -
    466 Lexington Avenue
    New York, NY  10017
International Biotechnology Trust PLC                     2,439,024                    -
    c/o Rothschild Asset Management Limited
    St. Swithin's Lane
    London, EC4N 8NR
    England
Novo Nordisk A/S                                          1,219,745                    -
    Novo Alle
    2880 Bagsvaerd
    Denmark
Jeff Winkelhake                                                 362              113,442
Maureen Howard                                                    -               56,660
Barry Sherman                                                 9,114              299,987
Nick Lowcock(2)                                                   -                    -
Michael Shulman                                                   -               32,508
David Smith                                                       -               37,178
Harden McConnell                                                  -               37,588
Harry Penner                                                      -               37,588
James Thomas(3)                                           5,478,049                    -
Bruce Carter(4)                                           1,219,745                    -
</TABLE>


(1)     Includes warrant shares held by such Stockholder and option shares
        exercisable within sixty (60) days of January 8, 1999.

(2)     Does not include shares held by Warburg, Pincus Ventures, L.P., with
        which Mr. Lowcock is affiliated. Mr. Lowcock disclaims beneficial
        ownership of these shares.

(3)     Represents 5,478,049 shares held by Warburg, Pincus Ventures, L.P., with
        which Mr. Thomas is affiliated. Mr. Thomas disclaims beneficial
        ownership of these shares.

(4)     Represents 1,219,745 shares held by Novo Nordisk A/S, of which Dr.
        Carter is an executive officer. Dr. Carter disclaims beneficial
        ownership of these shares.

<PAGE>   1
 
                                  APPENDIX A:
 
                      AGREEMENT AND PLAN OF REORGANIZATION
 
                                  BY AND AMONG
 
                              CORIXA CORPORATION,
                            A DELAWARE CORPORATION;
 
                        YAKIMA ACQUISITION CORPORATION,
                            A DELAWARE CORPORATION;
 
                                      AND
 
                                 ANERGEN, INC.
                            A DELAWARE CORPORATION.
 
                         Dated as of December 11, 1998.
 
                                       A-1
<PAGE>   2
 
                               INDEX OF EXHIBITS
 
<TABLE>
<S>        <C>
Exhibit A  Form of Anergen Voting Agreement
Exhibit B  Form of Escrow Fund Agreement
Exhibit C  Form of Anergen Affiliate Agreement
Exhibit D  Form of Opinion of Counsel to Corixa
Exhibit E  Form of Opinion of Counsel to Anergen
</TABLE>
 
                                       A-2
<PAGE>   3
 
                      AGREEMENT AND PLAN OF REORGANIZATION
 
     THIS AGREEMENT AND PLAN OF REORGANIZATION is made and entered into as of
December 11, 1998, by and among CORIXA CORPORATION, a Delaware corporation
("Corixa"), Yakima Acquisition Corporation, a Delaware corporation and a
wholly-owned subsidiary of Corixa ("Merger Sub"), and ANERGEN, INC., a Delaware
corporation ("Anergen").
 
                                    RECITALS
 
     A. Upon the terms and subject to the conditions of this Agreement (as
defined in Section 1.2 below) and in accordance with the Delaware General
Corporation Law ("Delaware Law"), Corixa, Merger Sub and Anergen intend to enter
into a business combination transaction.
 
     B. The respective boards of directors of Anergen and Corixa (1) have
determined that the Merger (as defined in Section 1.1) is consistent with and in
furtherance of their respective long-term business strategies and fair to, and
in the best interests of, their respective stockholders and (2) have approved
this Agreement, the Merger and the other transactions contemplated in this
Agreement.
 
     C. Anergen has, subject to the provisions of this Agreement, determined to
recommend that the stockholders of Anergen adopt and approve this Agreement and
approve the Merger.
 
     D. Concurrently with the execution of this Agreement, and as a condition
and inducement to Corixa's willingness to enter into this Agreement, certain
affiliates of Anergen are entering into Voting Agreements in substantially the
form attached hereto as Exhibit A (the "Anergen Voting Agreements").
 
     E. The parties intend, by executing this Agreement, to adopt a plan of
reorganization within the meaning of Section 368 of the Internal Revenue Code of
1986, as amended (the "Code").
 
     NOW, THEREFORE, in consideration of the covenants, promises,
representations and warranties set forth herein, and for other good and valuable
consideration, the receipt and sufficiency of which are hereby acknowledged, the
parties agree as follows:
 
                                   ARTICLE I
 
                                   THE MERGER
 
     1.1  The Merger. At the Effective Time (as defined in Section 1.2) and
subject to and upon the terms and conditions of this Agreement and the
applicable provisions of Delaware Law, Merger Sub shall be merged with and into
Anergen (the "Merger"), the separate corporate existence of Merger Sub shall
cease and Anergen shall continue as the surviving corporation. Anergen, in its
capacity as the surviving corporation after the Merger, is hereinafter sometimes
referred to as the "Surviving Corporation."
 
     1.2  Effective Time; Closing. Subject to the provisions of this Agreement,
the parties hereto shall cause the Merger to be consummated by filing a
Certificate of Merger with the Secretary of State of the State of Delaware in
accordance with the relevant provisions of Delaware Law (the "Certificate of
Merger") (the time of such filing (or such later time as may be agreed in
writing by Anergen and Corixa and specified in the Certificate of Merger) being
the "Effective Time") as soon as practicable on or after the Closing Date
                                       A-3
<PAGE>   4
 
(as herein defined). Unless the context otherwise requires, the term "Agreement"
as used herein refers collectively to this Agreement and Plan of Reorganization
and the Certificate of Merger. The closing of the Merger (the "Closing") shall
take place at the offices of Venture Law Group, a Professional Corporation, 4750
Carillon Point, Kirkland, Washington 98033-7355, or via facsimile, at a time and
date to be specified by the parties, which shall be no later than the second
business day after the satisfaction or waiver of the conditions set forth in
Article VI of this Agreement, or at such other time, date and location as the
parties hereto agree in writing (the "Closing Date").
 
     1.3  Effect of the Merger. At the Effective Time, the effect of the Merger
shall be as provided in this Agreement and the applicable provisions of Delaware
Law. Without limiting the generality of the foregoing, and subject thereto, at
the Effective Time all the property, rights, privileges, powers and franchises
of Anergen and Merger Sub shall vest in the Surviving Corporation, and all
debts, liabilities and duties of Anergen and Merger Sub shall become the debts,
liabilities and duties of the Surviving Corporation.
 
     1.4  Certificate of Incorporation; Bylaws.
 
     (a) At the Effective Time, the certificate of incorporation of Merger Sub,
as in effect immediately prior to the Effective Time, shall be the certificate
of incorporation of the Surviving Corporation until thereafter amended as
provided by law and such certificate of incorporation of the Surviving
Corporation; provided, however, that at the Effective Time the certificate of
incorporation of the Surviving Corporation shall be amended so that the name of
the Surviving Corporation shall be "Anergen, Inc."
 
     (b) The bylaws of Merger Sub, as in effect immediately prior to the
Effective Time, shall be, at the Effective Time, the bylaws of the Surviving
Corporation until thereafter amended.
 
     1.5  Directors and Officers. The initial directors of the Surviving
Corporation shall be the directors of Merger Sub immediately prior to the
Effective Time, until their respective successors are duly elected or appointed
and qualified. The initial officers of the Surviving Corporation shall be the
officers of Merger Sub immediately prior to the Effective Time, until their
respective successors are duly appointed.
 
     1.6  Effect on Capital Stock. At the Effective Time, by virtue of the
Merger and without any action on the part of Merger Sub, Anergen or the holders
of any of the following securities:
 
          (a) Conversion of Anergen Common Stock. Each share of Common Stock,
     One-Tenth of One Cent ($0.001) par value per share, of Anergen (the
     "Anergen Common Stock") issued and outstanding immediately prior to the
     Effective Time, other than any shares of Anergen Common Stock to be
     canceled pursuant to Section 1.6(b), will be canceled and extinguished and
     automatically converted (subject to Sections 1.6(e) and (f)) into the right
     to receive the number of shares of Common Stock, One-Tenth of One Cent
     ($0.001) par value per share, of Corixa (the "Corixa Common Stock") equal
     to the Exchange Ratio (as defined below) upon surrender of the certificate
     representing such share of Anergen Common Stock in the manner provided in
     Section 1.7 (or in the case of a lost, stolen or destroyed certificate,
     upon delivery of an affidavit (and bond, if required) in the manner
     provided in Section 1.9), in each case subject to the provisions of Section
     1.6(g). The "Exchange Ratio" shall be equal to a fraction, the numerator of
     which is equal to the quotient resulting from dividing Eight Million Five
     Hundred Thousand Dollars ($8,500,000) (less all payments made to Anergen by
     Corixa pursuant to that certain
 
                                       A-4
<PAGE>   5
 
     amended and restated agreement, dated as of November 11, 1998, by and
     between Corixa and Anergen) by the average of the last reported sale price
     of Corixa Common Stock for the fifteen (15) trading days immediately
     preceding and including the date of the first public announcement of the
     Merger (the "Corixa Average"); provided, however, that in the event that
     the Corixa Average (i) is below Six Dollars ($6.00) per share, the Corixa
     Average will be deemed to be Six Dollars ($6.00) per share, and (ii) is
     above Eight Dollars ($8.00) per share, the Corixa Average will be deemed to
     be Eight Dollars ($8.00) per share, and the denominator of which is equal
     to all outstanding shares of Anergen capital stock on a fully-diluted basis
     assuming (1) conversion of all outstanding convertible securities and (2)
     exercise of all outstanding options and warrants to purchase Anergen Common
     Stock with an exercise price equal to or less than Two Dollars and Fifty
     Cents ($2.50) per share, in each case as of the date of this Agreement
     ("Fully-Diluted Basis"). It is acknowledged and agreed by the parties that
     all Anergen options and warrants with an exercise price greater than Two
     Dollars and Fifty Cents ($2.50) per share will be excluded from the
     calculation of Fully-Diluted Basis. As promptly as practicable, but in any
     event within five (5) business days, after the date of this Agreement, the
     parties will compile, sign and attach hereto as Schedule A a schedule
     setting forth the amount and computation of the Exchange Ratio.
 
          (b) Cancellation of Corixa-Owned Stock. Each share of Anergen Common
     Stock held by Anergen or owned by Merger Sub, Corixa or any direct or
     indirect wholly-owned subsidiary of Anergen or of Corixa immediately prior
     to the Effective Time shall be canceled and extinguished without any
     conversion thereof.
 
          (c) Stock Options; Employee Stock Purchase Plans. At the Effective
     Time, all options to purchase Anergen Common Stock then outstanding under
     the Anergen, Inc. 1988 Stock Option Plan (the "1988 Plan"), the Anergen,
     Inc. 1992 Consultant Stock Plan (the "1992 Plan"), the Anergen Inc. 1995
     Director Option Plan (the "Director Plan"), and the Anergen Inc. 1996 Stock
     Plan (the "1996 Plan," and together with the 1988 Plan, the 1992 Plan, the
     Director Plan and the 1996 Plan, the "Anergen Stock Option Plans") shall be
     assumed by Corixa in accordance with Section 5.8 hereof. Rights outstanding
     under the Anergen Inc. 1991 Employee Stock Purchase Plan (the "ESPP") shall
     be treated as set forth in Section 5.8.
 
          (d) Capital Stock of Merger Sub. Each share of Common Stock, One-Tenth
     of One Cent ($0.00l) par value per share, of Merger Sub (the "Merger Sub
     Common Stock") issued and outstanding immediately prior to the Effective
     Time shall be converted into one validly issued, fully paid and
     nonassessable share of Common Stock, One-Tenth of One Cent ($0.001) par
     value per share, of the Surviving Corporation. Each certificate evidencing
     ownership of shares of Merger Sub Common Stock shall evidence ownership of
     such shares of capital stock of the Surviving Corporation.
 
          (e) Adjustments to Exchange Ratio. The Exchange Ratio shall be
     adjusted to reflect appropriately the effect of any stock split, reverse
     stock split, stock dividend (including any dividend or distribution of
     securities convertible into Corixa Common Stock or Anergen Common Stock),
     reorganization, recapitalization, reclassification or other like change
     with respect to Corixa Common Stock or Anergen Common Stock occurring on or
     after the date hereof and prior to the Effective Time.
 
          (f) Fractional Shares. No fraction of a share of Corixa Common Stock
     will be issued by virtue of the Merger, but in lieu thereof each holder of
     shares of Anergen
 
                                       A-5
<PAGE>   6
 
     Common Stock who would otherwise be entitled to a fraction of a share of
     Corixa Common Stock (after aggregating all fractional shares of Corixa
     Common Stock that otherwise would be received by such holder) shall receive
     from Corixa an amount of cash (rounded to the nearest whole cent) equal to
     the product of (i) such fraction, multiplied by (ii) the average closing
     price of one share of Corixa Common Stock for the fifteen (15) trading days
     preceding and including December 14, 1998, as reported on the Nasdaq
     National Market System ("Nasdaq").
 
          (g) Escrow Shares, Escrow Fund Agreement. As soon as practicable after
     the Effective Date, Corixa will deposit into escrow certificates
     representing that number of shares of the Corixa Common Stock issued to
     holders of Anergen Common Stock in the Merger pursuant to Section 1.6(a)
     equal to the quotient resulting from dividing Four Hundred Thousand Dollars
     ($400,000) by the Corixa Average, on a pro rata basis. Such shares (the
     "Escrow Shares") will be held as collateral to secure Anergen's obligation
     to enter into an amendment to that certain Product Development and License
     Agreement, dated as of June 28, 1996, by and between Anergen and N.V.
     Organon ("Organon") (the "Organon Agreement") pursuant to this Section
     1.6(g) and the provisions of an escrow fund agreement in the form attached
     hereto as Exhibit B (the "Escrow Fund Agreement") to be executed and
     delivered by Corixa, Anergen and an escrow agent mutually acceptable to
     Corixa and Anergen (the "Escrow Agent"). The Escrow Shares will be held by
     the Escrow Agent pursuant to the Escrow Fund Agreement and will be released
     (i) to the holders of record of Anergen Common Stock immediately prior to
     the Effective Date if and only if Anergen executes and delivers to Corixa
     an amendment, signed by Organon and in a form reasonably acceptable to
     Corixa and Anergen and the respective counsel to Corixa and Anergen (the
     "Organon Amendment"), to the Organon Agreement on or prior to the later of
     (A) January 31, 1999 or (B) the Closing Date, but in any event prior to
     March 15, 1999 (the "Organon Termination Date"), or (ii) to Corixa (as
     treasury shares) if Anergen has not executed and delivered to Corixa the
     Organon Amendment prior to the Organon Termination Date. Corixa agrees to
     retain Michael Shulman, Jeff Winkelhake, Jan Baughman, Nancy Corbelatta,
     Simonetta Mocci and Nanette Solvason (and Maria Marmarinos of the Catalyst
     Group as a consultant) through the earlier to occur of (1) the delivery by
     Anergen to Corixa of the Organon Amendment or (2) the Organon Termination
     Date, and further agrees to review and provide comments on any drafts of
     the Organon Amendment as promptly as reasonably practicable.
 
     1.7  Surrender of Certificates.
 
     (a) Exchange Agent. Corixa shall select a bank or trust Company reasonably
acceptable to Anergen to act as the exchange agent (the "Exchange Agent") in the
Merger.
 
     (b) Corixa to Provide Common Stock. Promptly after the Effective Time,
Corixa shall make available to the Exchange Agent for exchange in accordance
with this Article I, the shares of Corixa Common Stock issuable pursuant to
Section 1.6 (less the Escrow Shares) in exchange for outstanding shares of
Anergen Common Stock, and cash in an amount sufficient for payment in lieu of
fractional shares pursuant to Section 1.6(f) and any dividends or distributions
to which holders of shares of Anergen Common Stock may be entitled pursuant to
Section 1.7(d).
 
     (c) Exchange Procedures. Promptly after the Effective Time, Corixa shall
cause the Exchange Agent to mail to each holder of record (as of the Effective
Time) of a
 
                                       A-6
<PAGE>   7
 
certificate or certificates (the "Certificates"), which immediately prior to the
Effective Time represented outstanding shares of Anergen Common Stock whose
shares were converted into shares of Corixa Common Stock pursuant to Section
1.6, cash in lieu of any fractional shares pursuant to Section 1.6(f) and any
dividends or other distributions pursuant to Section 1.7(d), (i) a letter of
transmittal in customary form (which shall specify that delivery shall be
effected, and risk of loss and title to the Certificates shall pass, only upon
delivery of the Certificates to the Exchange Agent and shall contain such other
provisions as Corixa may reasonably specify) and (ii) instructions for use in
effecting the surrender of the Certificates in exchange for certificates
representing shares of Corixa Common Stock, cash in lieu of any fractional
shares pursuant to Section 1.6(f) and any dividends or other distributions
pursuant to Section 1.7(d). Upon surrender of Certificates for cancellation to
the Exchange Agent or to such other agent or agents as may be appointed by
Corixa, together with such letter of transmittal, duly completed and validly
executed in accordance with the instructions thereto, the holders of such
Certificates shall be entitled to receive in exchange therefor certificates
representing the number of whole shares of Corixa Common Stock into which their
shares of Anergen Common Stock were converted at the Effective Time (less their
respective pro rata interests in the Escrow Shares), payment of cash in lieu of
fractional shares which such holders have the right to receive pursuant to
Section 1.6(f) and any dividends or distributions payable pursuant to Section
1.7(d), and the Certificates so surrendered shall forthwith be canceled. Until
so surrendered, outstanding Certificates will be deemed from and after the
Effective Time, for all corporate purposes, subject to Section 1.7(d) as to the
payment of dividends, to evidence only the ownership of the number of full
shares of Corixa Common Stock into which such shares of Anergen Common Stock
shall have been so converted (less the holder's respective pro rata interests in
the Escrow Shares) and the right to receive an amount in cash in lieu of the
issuance of any fractional shares in accordance with Section 1.6(f) and any
dividends or distributions payable pursuant to Section 1.7(d).
 
     (d) Distributions With Respect to Unexchanged Shares. No dividends or other
distributions declared or made after the date of this Agreement with respect to
Corixa Common Stock with a record date after the Effective Time will be paid to
the holders of any unsurrendered Certificates with respect to the shares of
Corixa Common Stock represented thereby until the holders of record of such
Certificates shall surrender such Certificates. Subject to applicable law,
following surrender of any such Certificates, the Exchange Agent shall deliver
to the record holders thereof, without interest, certificates representing whole
shares of Corixa Common Stock issued in exchange therefor (less their pro rata
interest in the Escrow Shares) along with payment in lieu of fractional shares
pursuant to Section 1.6(f) hereof and the amount of any such dividends or other
distributions with a record date after the Effective Time payable with respect
to such whole shares of Corixa Common Stock.
 
     (e) Transfers of Ownership. If certificates representing shares of Corixa
Common Stock are to be issued in a name other than that in which the
Certificates surrendered in exchange therefor are registered, it will be a
condition of the issuance thereof that the Certificates so surrendered will be
properly endorsed and otherwise in proper form for transfer and that the persons
requesting such exchange will have paid to Corixa or any agent designated by it
any transfer or other taxes required by reason of the issuance of certificates
representing shares of Corixa Common Stock in any name other than that of the
registered holder of the Certificates surrendered, or established to the
satisfaction of Corixa or any agent designated by it that such tax has been paid
or is not payable.
 
                                       A-7
<PAGE>   8
 
     (f) No Liability. Notwithstanding anything to the contrary in this Section
1.7, neither the Exchange Agent, the Escrow Agent, Corixa, the Surviving
Corporation nor any party hereto shall be liable to a holder of shares of Corixa
Common Stock or Anergen Common Stock for any amount properly paid to a public
official pursuant to any applicable abandoned property, escheat or similar law.
 
     1.8  No Further Ownership Rights in Anergen Common Stock. All shares of
Corixa Common Stock issued in accordance with the terms hereof (including any
cash paid in respect thereof pursuant to Section 1.6(f) and 1.7(d)) shall be
deemed to have been issued in full satisfaction of all rights pertaining to such
shares of Anergen Common Stock, and there shall be no further registration of
transfers on the records of the Surviving Corporation of shares of Anergen
Common Stock which were outstanding immediately prior to the Effective Time. If
after the Effective Time Certificates are presented to the Surviving Corporation
for any reason, they shall be canceled and exchanged as provided in this Article
I.
 
     1.9  Lost, Stolen or Destroyed Certificates. In the event that any
Certificates shall have been lost, stolen or destroyed, the Exchange Agent shall
issue in exchange for such lost, stolen or destroyed Certificates, upon the
making of an affidavit of that fact by the holder thereof, certificates
representing the shares of Corixa Common Stock into which the shares of Anergen
Common Stock represented by such Certificates were converted pursuant to Section
1.6 (less the applicable pro rata interest of the Escrow Shares), cash for
fractional shares, if any, as may be required pursuant to Section 1.6(f) and any
dividends or distributions payable pursuant to Section 1.7(d); provided,
however, that Corixa may, in its discretion and as a condition precedent to the
issuance of such certificates representing shares of Corixa Common Stock, cash
and other distributions, require the owner of such lost, stolen or destroyed
Certificates to deliver a bond in such sum as it may reasonably direct as
indemnity against any claim that may be made against Corixa, the Surviving
Corporation or the Exchange Agent with respect to the Certificates alleged to
have been lost, stolen or destroyed.
 
     1.10  Tax Consequences. It is intended by the parties hereto that the
Merger shall constitute a reorganization within the meaning of Section 368 of
the Code. The parties hereto adopt this Agreement as a "plan of reorganization"
within the meaning of Sections 1.368-2(g) and 1.368-3(a) of the United States
Income Tax Regulations.
 
     1.11  Taking of Necessary Action; Further Action. If, at any time after the
Effective Time, any further action is necessary or desirable to carry out the
purposes of this Agreement and to vest the Surviving Corporation with full
right, title and possession to all assets, property, rights, privileges, powers
and franchises of Anergen and Merger Sub, the officers and directors of Anergen
and Merger Sub will take all such lawful and necessary action. Corixa shall
cause Merger Sub to perform all of its obligations relating to this Agreement
and the transactions contemplated herein.
 
                                   ARTICLE II
 
                   REPRESENTATIONS AND WARRANTIES OF ANERGEN
 
     Anergen hereby represents and warrants to Corixa and Merger Sub, subject to
the exceptions specifically disclosed in writing in the disclosure letter and
referencing a specific representation made by Anergen to Corixa and Merger Sub
pursuant to this Article II
 
                                       A-8
<PAGE>   9
 
dated as of the date hereof and certified on behalf of Anergen by a duly
authorized officer of Anergen (the "Anergen Schedules"), as follows:
 
     2.1  Organization of Anergen.
 
     (a) Anergen and each of its subsidiaries (i) is a corporation or other
legal entity duly organized, validly existing and in good standing under the
laws of the jurisdiction in which it is organized, (ii) has the corporate or
other power and authority to own, lease and operate its assets and properties
and to carry on its business as now being conducted and (iii) is duly qualified
or licensed to do business in each jurisdiction where the character of the
properties owned, leased or operated by it or the nature of its activities makes
such qualification or licensing necessary, except for such failures to be so
duly qualified or licensed and in good standing that would not, either
individually or in the aggregate, have a Material Adverse Effect (as defined in
Section 8.3(c)) on Anergen.
 
     (b) Anergen has delivered or made available to Corixa a true and complete
list of all of Anergen's subsidiaries as of the date of this Agreement,
indicating the jurisdiction of organization of each subsidiary and Anergen's
equity interest therein.
 
     (c) Anergen has delivered or made available to Corixa a true and correct
copy of the certificate of incorporation and bylaws of Anergen and similar
governing instruments of each of its subsidiaries, each as amended to date, and
each such instrument is in full force and effect. Neither Anergen nor any of its
subsidiaries is in violation of any of the provisions of its certificate of
incorporation or bylaws or equivalent governing instruments.
 
     2.2  Anergen Capital Structure. The authorized capital stock of Anergen
consists of sixty million (60,000,000) shares of Common Stock, One-Tenth of One
Cent ($0.001) par value per share, of which there were eighteen million nine
hundred twenty-three thousand eight hundred-eight (18,923,888) shares issued and
outstanding as of December 8, 1998 (excluding shares held in treasury of which
there are none, and ten million (10,000,000) shares of Preferred Stock,
One-Tenth of One Cent ($0.001) par value per share, of which no shares are
issued or outstanding. All outstanding shares of Anergen Common Stock are duly
authorized, validly issued, fully paid and nonassessable and are not subject to
preemptive rights created by statute, the certificate of incorporation or bylaws
of Anergen or any agreement or document to which Anergen is a party or by which
it is bound. As of December 8, 1998, Anergen had reserved an aggregate of four
million fifty thousand (4,050,000) shares of Anergen Common Stock, for issuance
pursuant to the Anergen Stock Option Plans, of which four hundred sixty-seven
thousand eight hundred five (467,805) shares have been issued pursuant to option
exercises, and one million five hundred fifteen thousand four hundred
fifty-eight (1,515,458) shares are subject to outstanding, unexercised options.
As of December 8, 1998, Anergen had reserved one million eight hundred thousand
(1,800,000) shares of Anergen Common Stock for issuance to employees, directors
and consultants pursuant to the 1988 Plan, of which four hundred thirty-four
thousand seven hundred eight (434,708) shares have been issued pursuant to
option exercises, and seven hundred three thousand four hundred thirty-nine
(703,439) shares are subject to outstanding, unexercised options. As of December
8, 1998, Anergen had reserved fifty thousand (50,000) shares of Anergen Common
Stock for issuance to consultants pursuant to the 1992 Plan, of which
thirty-three thousand ninety-seven (33,097) shares have been issued pursuant to
option exercises, and fifteen thousand (15,000) shares are subject to
outstanding, unexercised options. As of December 8, 1998, Anergen had reserved
two hundred thousand (200,000) shares of Anergen Common Stock for issuance to
directors pursuant to the Director Plan, of which no shares have been issued
pursuant to option exercises, and forty thousand (40,000) shares are subject to
 
                                       A-9
<PAGE>   10
 
outstanding, unexercised options. As of December 8, 1998, Anergen had reserved
two million (2,000,000) shares of Anergen Common Stock for issuance to
employees, directors and consultants pursuant to the 1996 Plan, of which no
shares haven been issued pursuant to option exercises, and seven hundred
fifty-seven thousand and nineteen (757,019) shares are subject to outstanding,
unexercised options. As of December 8, 1998, Anergen had reserved an aggregate
of seven hundred fifty thousand (750,000) shares of Anergen Common Stock for
issuance pursuant to the ESPP, of which two hundred seventy-five thousand four
hundred ninety-seven (275,497) shares have been issued to employees. All shares
of Anergen Common Stock subject to issuance as aforesaid, upon issuance on the
terms and conditions specified in the instruments pursuant to which they are
issuable, would be duly authorized, validly issued, fully paid and
nonassessable. The Anergen Schedules list for each person who holds options to
acquire shares of Anergen Common Stock as of December 8, 1998, the name of the
holder of such option, the exercise price of such option, the number of shares
as to which such option had vested at such date and the vesting schedule for
such option.
 
     2.3  Obligations With Respect to Capital Stock. Except as set forth in
Section 2.2, there are no equity securities, partnership interests or similar
ownership interests of any class of Anergen equity security, or any securities
exchangeable or convertible into or exercisable for such equity securities,
partnership interests or similar ownership interests, issued, reserved for
issuance or outstanding. Except for securities Anergen owns free and clear of
all claims and encumbrances directly or indirectly through one or more
subsidiaries, as of the date of this Agreement, there are no equity securities,
partnership interests or similar ownership interests of any class of equity
security of any subsidiary of Anergen, or any security exchangeable or
convertible into or exercisable for such equity securities, partnership
interests or similar ownership interests, issued, reserved for issuance or
outstanding. Except as set forth in Section 2.2, there are no subscriptions,
options, warrants, equity securities, partnership interests or similar ownership
interests, calls, rights (including preemptive rights), commitments or
agreements of any character to which Anergen or any of its subsidiaries is a
party or by which it is bound obligating Anergen or any of its subsidiaries to
issue, deliver or sell, or cause to be issued, delivered or sold, or repurchase,
redeem or otherwise acquire, or cause the repurchase, redemption or acquisition
of, any shares of capital stock, partnership interests or similar ownership
interests of Anergen or any of its subsidiaries or obligating Anergen or any of
its subsidiaries to grant, extend, accelerate the vesting of or enter into any
such subscription, option, warrant, equity security, call, right, commitment or
agreement. As of the date of this Agreement, except as contemplated in this
Agreement, there are no registration rights and there is no voting trust, proxy,
rights plan, antitakeover plan or other agreement or understanding to which
Anergen is a party or by which it is bound with respect to any equity security
of any class of Anergen or with respect to any equity security, partnership
interest or similar ownership interest of any class of any of its subsidiaries.
Stockholders of Anergen will not be entitled to dissenters' rights under
applicable state law in connection with the Merger.
 
     2.4  Authority.
 
     (a) Anergen has all requisite corporate power and authority to enter into
this Agreement and to consummate the transactions contemplated herein. The
execution and delivery of this Agreement and the consummation of the
transactions contemplated herein have been duly authorized by all necessary
corporate action on the part of Anergen, subject only to the approval and
adoption of this Agreement and the approval of the Merger by Anergen's
stockholders and the filing of the Certificate of Merger pursuant to
 
                                      A-10
<PAGE>   11
 
Delaware Law. A vote of the holders of a majority of the outstanding shares of
the Anergen Common Stock is sufficient for Anergen's stockholders to approve and
adopt this Agreement and approve the Merger. This Agreement has been duly
executed and delivered by Anergen and, assuming the due authorization, execution
and delivery by Corixa and Merger Sub, constitutes a valid and binding
obligation of Anergen, enforceable against Anergen in accordance with its terms,
except as enforceability may be limited by bankruptcy and other similar laws and
general principles of equity. The execution and delivery of this Agreement by
Anergen do not, and the performance of this Agreement by Anergen will not, (i)
conflict with or violate the certificate of incorporation or bylaws of Anergen
or the equivalent governing instruments of any of its subsidiaries, (ii) subject
to obtaining the approval and adoption of this Agreement and the approval of the
Merger by Anergen's stockholders as contemplated in Section 5.2 and compliance
with the requirements set forth in Section 2.4(b) below, conflict with or
violate any law, rule, regulation, order, judgment or decree applicable to
Anergen or any of its subsidiaries or by which Anergen or any of its
subsidiaries or any of its or their respective properties is bound or affected
or (iii) result in any breach of or constitute a default (or an event that with
notice or lapse of time or both would become a default) under, or impair
Anergen's rights or alter the rights or obligations of any third party under, or
give to others any rights of termination, amendment, acceleration or
cancellation of, or result in the creation of a lien or encumbrance on any of
the properties or assets of Anergen or any of its subsidiaries pursuant to, any
note, bond, mortgage, indenture, contract, agreement, lease, license, permit,
franchise, concession, or other instrument or obligation to which Anergen or any
of its subsidiaries is a party or by which Anergen or any of its subsidiaries or
its or any of their respective assets are bound or affected which such breach,
default, impairment, alteration, giving of rights or creation of a lien or
encumbrance would result in material damages to Anergen. To the knowledge of
Anergen after reasonable inquiry, the Anergen Schedules list all consents,
waivers and approvals under any of Anergen's or any of its subsidiaries'
agreements, contracts, licenses or leases required to be obtained in connection
with the consummation of the transactions contemplated in this Agreement, which,
if individually or in the aggregate not obtained, would result in a material
loss of benefits to Anergen, Corixa or the Surviving Corporation as a result of
the Merger.
 
     (b) No consent, approval, order or authorization of, or registration,
declaration or filing with any court, administrative agency or commission or
other governmental authority or instrumentality, foreign or domestic
("Governmental Entity"), is required to be obtained or made by Anergen in
connection with the execution and delivery of this Agreement or the consummation
of the Merger, except for (i) the filing of the Certificate of Merger with the
Secretary of State of the State of Delaware, (ii) the filing of the Proxy
Statement/ Prospectus (as defined in Section 2.18) with the Securities and
Exchange Commission ("SEC") in accordance with the Securities Exchange Act of
1934, as amended (the "Exchange Act"), (iii) such consents, approvals, orders,
authorizations, registrations, declarations and filings as may be required under
applicable federal, foreign and state securities (or related) laws, and the
securities or antitrust laws of any foreign country and (iv) such other
consents, authorizations, filings, approvals and registrations which if not
obtained or made would not be material to Anergen or Corixa or have a material
adverse effect on the ability of the parties hereto to consummate the Merger.
 
     2.5  SEC Filings; Anergen Financial Statements.
 
     (a) Anergen has filed all forms, reports and documents required to be filed
by Anergen with the SEC since January 1, 1996 and has made available to Corixa
such forms, reports and documents in the form filed with the SEC. All such
required forms,
 
                                      A-11
<PAGE>   12
 
reports and documents (including those that Anergen may file subsequent to the
date hereof) are referred to herein as the "Anergen SEC Reports." As of their
respective dates, the Anergen SEC Reports (i) were prepared in accordance with
the requirements of the Securities Act of 1933, as amended (the "Securities
Act"), or the Exchange Act, as the case may be, and the rules and regulations of
the SEC thereunder applicable to such Anergen SEC Reports and (ii) did not at
the time they were filed (or if amended or superseded by a filing prior to the
date of this Agreement, then on the date of such filing) contain any untrue
statement of a material fact or omit to state a material fact required to be
stated therein or necessary in order to make the statements therein, in the
light of the circumstances under which they were made, not misleading. None of
Anergen's subsidiaries is required to file any forms, reports or other documents
with the SEC.
 
     (b) Each of the consolidated financial statements (including, in each case,
any related notes thereto) contained in the Anergen SEC Reports (the "Anergen
Financials"), including each Anergen SEC Reports filed after the date hereof
until the Closing, (i) complied as to form with the published rules and
regulations of the SEC with respect thereto, (ii) was prepared in accordance
with United States generally accepted accounting principles ("GAAP") applied on
a consistent basis throughout the periods involved (except as may be indicated
in the notes thereto or, in the case of unaudited interim financial statements,
as may be permitted by the SEC on Form 10-Q under the Exchange Act) and (iii)
fairly presented the consolidated financial position of Anergen and its
subsidiaries as at the respective dates thereof and the consolidated results of
Anergen's operations and cash flows for the periods indicated, except that the
unaudited interim financial statements may not contain footnotes and were or are
subject to normal and recurring year-end adjustments. The balance sheet of
Anergen contained in Anergen SEC Reports as of September 30, 1998 is hereinafter
referred to as the "Anergen Balance Sheet." Except as disclosed in the Anergen
Financials, since the date of the Anergen Balance Sheet neither Anergen nor any
of its subsidiaries has any liabilities required under GAAP to be set forth on a
balance sheet (absolute, accrued, contingent or otherwise) which are,
individually or in the aggregate, material to the business, results of
operations or financial condition of Anergen and its subsidiaries taken as a
whole, except for liabilities incurred since the date of the Anergen Balance
Sheet in the ordinary course of business consistent with past practices.
 
     (c) Anergen has heretofore furnished or made available to Corixa a complete
and correct copy of any amendments or modifications, which have not yet been
filed with the SEC but which are required to be filed, to agreements, documents
or other instruments which previously had been filed by Anergen with the SEC
pursuant to the Securities Act or the Exchange Act.
 
     2.6  Absence of Certain Changes or Events. Since the date of the Anergen
Balance Sheet there has not been: (a) any Material Adverse Effect (as defined in
Section 8.3(c)) on Anergen, (b) any declaration, setting aside or payment of any
dividend on, or other distribution (whether in cash, stock or property) in
respect of, any of Anergen's or any of its subsidiaries' capital stock, or any
purchase, redemption or other acquisition by Anergen of any of Anergen's capital
stock or any other securities of Anergen or its subsidiaries or any options,
warrants, calls or rights to acquire any such shares or other securities except
for repurchases from employees following their termination pursuant to the terms
of their pre-existing stock option or purchase agreements, (c) any split,
combination or reclassification of any of Anergen's or any of its subsidiaries'
capital stock, (d) any granting by Anergen or any of its subsidiaries of any
increase in compensation or fringe benefits, except for normal increases of cash
compensation in the ordinary course of
 
                                      A-12
<PAGE>   13
 
business consistent with past practice, or any payment by Anergen or any of its
subsidiaries of any bonus, except for bonuses made in the ordinary course of
business consistent with past practice, or any granting by Anergen or any of its
subsidiaries of any increase in severance or termination pay or any entry by
Anergen or any of its subsidiaries into any currently effective employment,
severance, termination or indemnification agreement or any agreement the
benefits of which are contingent or the terms of which are altered upon the
occurrence of a transaction involving Anergen of the nature contemplated herein,
(e) entry by Anergen or any of its subsidiaries into any licensing or other
agreement with regard to the acquisition or disposition of any Intellectual
Property (as defined in Section 2.9), (f) any change by Anergen in its
accounting methods, principles or practices, except as required by concurrent
changes in GAAP or (g) any revaluation by Anergen of any of its assets,
including, without limitation, writing down the value of capitalized inventory
or writing off notes or accounts receivable other than in the ordinary course of
business.
 
     2.7  Taxes.
 
     (a) Definition of Taxes. For the purposes of this Agreement, "Tax" or
"Taxes" refers to any and all federal, state, local and foreign taxes,
assessments and other governmental charges, duties, impositions and liabilities
relating to taxes, including taxes based upon or measured by gross receipts,
income, profits, sales, use and occupation, and value added, ad valorem,
transfer, franchise, withholding, payroll, recapture, employment, excise and
property taxes, together with all interest, penalties and additions imposed with
respect to such amounts and any obligations under any agreements or arrangements
with any other person with respect to such amounts and including any liability
for taxes of a predecessor entity.
 
     (b) Tax Returns and Audits.
 
          (i) To the knowledge of Anergen after reasonable inquiry, Anergen and
     each of its subsidiaries have timely filed all federal, state, local and
     foreign returns, estimates, information statements and reports ("Returns")
     relating to Taxes required to be filed by Anergen and each of its
     subsidiaries with any Tax authority, such Returns are true and correct and
     have been completed in all material respects in accordance with applicable
     law and Anergen and its subsidiaries have paid all Taxes shown to be due on
     such Returns.
 
          (ii) Anergen and each of its subsidiaries as of the Effective Time
     will have withheld with respect to its employees all federal and state
     income taxes, Taxes pursuant to the Federal Insurance Contribution Act
     ("FICA"), Taxes pursuant to the Federal Unemployment Tax Act ("FUTA") and
     other Taxes required to be withheld.
 
          (iii) Neither Anergen nor any of its subsidiaries has been delinquent
     in the payment of any Tax nor is there any Tax deficiency outstanding,
     proposed or assessed against Anergen or any of its subsidiaries, nor has
     Anergen or any of its subsidiaries executed any unexpired waiver of any
     statute of limitations on or extending the period for the assessment or
     collection of any Tax.
 
          (iv) No audit or other examination of any Return of Anergen or any of
     its subsidiaries by any Tax authority is presently in progress, nor has
     Anergen or any of its subsidiaries been notified of any request for such an
     audit or other examination.
 
          (v) No adjustment relating to any Returns filed by Anergen or any of
     its subsidiaries has been proposed in writing formally or informally by any
     Tax authority to Anergen or any of its subsidiaries or any representative
     thereof.
 
                                      A-13
<PAGE>   14
 
          (vi) To the knowledge of Anergen after reasonable inquiry, neither
     Anergen nor any of its subsidiaries has, or will as of the Effective Time
     have, any liability for unpaid Taxes which has not been accrued for or
     reserved on the Anergen Balance Sheet, whether asserted or unasserted,
     contingent or otherwise, other than any liability for unpaid Taxes that may
     have accrued since the date of the Anergen Balance Sheet in connection with
     the operation of the business of Anergen and its subsidiaries in the
     ordinary course.
 
          (vii) As of the date of this Agreement there is no, and as of the
     Effective Time there will not be any, contract, agreement, plan or
     arrangement to which Anergen is a party including but not limited to the
     provisions of this Agreement, covering any employee or former employee of
     Anergen or any of its subsidiaries that, individually or collectively,
     could give rise to the payment of any amount that would not be deductible
     pursuant to Sections 280G, 404 or 162(m) of the Code.
 
          (viii) Neither Anergen nor any of its subsidiaries has filed any
     consent agreement under Section 341(f) of the Code or agreed to have
     Section 341(f)(2) of the Code apply to any disposition of a subsection (f)
     asset (as defined in Section 341(f)(4) of the Code) owned by Anergen.
 
          (ix) Neither Anergen (except for customary arrangements relating to
     property taxes and sales taxes in leases) nor any of its subsidiaries is
     party to or has any obligation under any tax-sharing, tax indemnity or tax
     allocation agreement or arrangement.
 
          (x) Except as may be required as a result of the Merger, Anergen and
     its subsidiaries have not been and will not be required to include any
     adjustment in Taxable income for any Tax period (or portion thereof)
     pursuant to Section 481 or Section 263A of the Code or any comparable
     provision under state or foreign Tax laws as a result of transactions,
     events or accounting methods employed prior to the Closing.
 
          (xi) None of Anergen's or its subsidiaries' assets are tax exempt use
     property within the meaning of Section 168(h) of the Code.
 
          (xii) The Anergen Schedules list (A) any foreign Tax holidays, (B) any
     intercompany transfer pricing agreements, or other arrangements that have
     been established by Anergen or any of its subsidiaries with any Tax
     authority and (C) any expatriate programs or policies affecting Anergen or
     any of its subsidiaries.
 
          (xiii) To the knowledge of Anergen after reasonable inquiry, as of the
     Effective Time, there will be no liens or other encumbrances of any kind
     relating to Taxes on the assets of Anergen or any subsidiary of Anergen.
 
          (xiv) Each of Anergen and its subsidiaries have provided or made
     available to Corixa copies of all federal and state income and sales taxes,
     as applicable, and all Tax Returns for all periods since 1994.
 
     2.8  Title to Properties; Absence of Liens and Encumbrances.
 
     (a) The Anergen Schedules list the real property interests owned by Anergen
as of the date of this Agreement. The Anergen Schedules list all real property
leases to which Anergen is a party as of the date of this Agreement and each
amendment thereto that is in effect as of the date of this Agreement. All such
current leases are in full force and effect, are valid and effective in
accordance with their respective terms, and there is not, under any of such
leases, any existing default or event of default (or event which with notice or
                                      A-14
<PAGE>   15
 
lapse of time, or both, would constitute a default) that would give rise to a
claim in an amount greater than Fifteen Thousand Dollars ($15,000).
 
     (b) Anergen has good and valid title to, or, in the case of leased
properties and assets, valid leasehold interests in, all of its tangible
properties and assets, real, personal and mixed, used or held for use in its
business, free and clear of any liens, pledges, charges, claims, security
interests or other encumbrances of any sort ("Liens"), except as reflected in
the Anergen Financials and except for liens for taxes not yet due and payable
and such Liens or other imperfections of title and encumbrances, if any, which
are not material in character, amount or extent, and which do not materially
detract from the value, or materially interfere with the present use, of the
property subject thereto or affected thereby.
 
     2.9  Intellectual Property. For the purposes of this Agreement, the
following terms have the following definitions:
 
     "Intellectual Property" shall mean any or all of the following and all
     rights in, arising out of, or associated therewith: (i) all United States,
     international and foreign patents and applications therefor and all
     reissues, divisions, renewals, extensions, provisionals, continuations and
     continuations-in-part thereof, (ii) all inventions (whether patentable or
     not), invention disclosures, improvements, trade secrets, proprietary
     information, know how, technology, technical data and customer lists, and
     all documentation relating to any of the foregoing, (iii) all copyrights,
     copyrights registrations and applications therefor, and all other rights
     corresponding thereto throughout the world, (iv) all industrial designs and
     any registrations and applications therefor throughout the world, (v) all
     trade names, logos, common law trademarks and service marks, trademark and
     service mark registrations and applications therefor throughout the world,
     (vi) all databases and data collections and all rights therein throughout
     the world, (vii) all moral and economic rights of authors and inventors,
     however denominated, throughout the world, and (viii) any similar or
     equivalent rights to any of the foregoing anywhere in the world.
 
     "Anergen Intellectual Property" shall mean any Intellectual Property that
     is owned by, or exclusively licensed to, Anergen.
 
     "Registered Intellectual Property" means all United States, international
     and foreign: (i) patents and patent applications (including provisional
     applications), (ii) registered trademarks, applications to register
     trademarks, intent-to-use applications, or other registrations or
     applications related to trademarks, (iii) registered copyrights and
     applications for copyright registration and (iv) any other Intellectual
     Property that is the subject of an application, certificate, filing,
     registration or other document issued, filed with, or recorded by any
     state, government or other public legal authority.
 
     "Anergen Registered Intellectual Property" means all of the Registered
     Intellectual Property owned by, or filed in the name of, Anergen.
 
     (a) To the knowledge of Anergen after reasonable inquiry, no Anergen
Intellectual Property or product or service of Anergen is subject to any
proceeding or outstanding decree, order, judgment, agreement, or stipulation
restricting in any manner the use, transfer, or licensing thereof by Anergen, or
which may affect the validity, use or enforceability of such Anergen
Intellectual Property.
 
     (b) To the knowledge of Anergen after reasonable inquiry, each item of
Anergen Registered Intellectual Property is valid and subsisting, all necessary
registration,
 
                                      A-15
<PAGE>   16
 
maintenance and renewal fees currently due in connection with such Registered
Intellectual Property have been made, and all necessary documents, recordations
and certificates in connection with such Registered Intellectual Property have
been filed with the relevant patent, copyright, trademark or other authorities
in the United States or foreign jurisdictions, as the case may be, for the
purposes of maintaining such Registered Intellectual Property.
 
     (c) Anergen owns and has good and exclusive title to, or has license
(sufficient for the conduct of its business as currently conducted and as
proposed to be conducted) to, each material item of Anergen Intellectual
Property free and clear of any lien or encumbrance (excluding licenses and
related restrictions); and Anergen is the exclusive owner of all trademarks and
trade names used in connection with the operation or conduct of the business of
Anergen, including the sale of any products or the provision of any services by
Anergen, except where the failure to own such trade marks and trade names would
not result in a Material Adverse Effect on Anergen.
 
     (d) Anergen owns exclusively, and has good title to, all copyrighted works
that are Anergen products or which Anergen otherwise expressly purports to own,
except where the failure to own such copyrighted works would not result in a
Material Adverse Effect on Anergen.
 
     (e) To the extent that any Intellectual Property that is or was material to
Anergen's business has been developed or created by a third party for Anergen,
Anergen has a written agreement with such third party with respect thereto and
Anergen thereby either (i) has obtained ownership of, and is the exclusive owner
of or (ii) has obtained a license (sufficient for the conduct of its business as
currently conducted and as proposed to be conducted) to all such third party's
Intellectual Property in such work, material or invention by operation of law or
by valid assignment, to the extent it is necessary to do so.
 
     (f) Anergen has not transferred ownership of, or granted any exclusive
license with respect to, any Intellectual Property that is or was material
Anergen Intellectual Property, to any third party.
 
     (g) To the knowledge of Anergen after reasonable inquiry, the Anergen
Schedules list all material contracts, licenses and agreements currently in
force to which Anergen is a party (i) with respect to Anergen Intellectual
Property licensed or transferred to any third party (other than end-user
licenses in the ordinary course) or (ii) pursuant to which a third party has
licensed or transferred any material Intellectual Property to Anergen.
 
     (h) All material contracts, licenses and agreements relating to the Anergen
Intellectual Property are in full force and effect. The consummation of the
transactions contemplated in this Agreement will neither violate nor result in
the breach, modification, cancellation, termination, or suspension of such
contracts, licenses and agreements. Anergen is in material compliance with, and
has not materially breached any term any of such contracts, licenses and
agreements and, to the knowledge of Anergen, all other parties to such
contracts, licenses and agreements are in compliance with, and have not
materially breached any term of, such contracts, licenses and agreements.
Following the Closing Date, the Surviving Corporation will be permitted to
exercise all of Anergen's material rights under such contracts, licenses and
agreements to the same extent Anergen would have been able to had the
transactions contemplated in this Agreement not occurred and without the payment
of any additional amounts or consideration other than ongoing fees, royalties or
payments which Anergen would otherwise be required to pay.
 
                                      A-16
<PAGE>   17
 
     (i) To the knowledge of Anergen after reasonable inquiry, the operation of
the business of Anergen as such business currently is conducted, including
Anergen's design, development, manufacture, marketing and sale of the products
or services of Anergen (including with respect to products currently under
development) has not, does not and will not infringe or misappropriate the
Intellectual Property of any third party (provided that with respect to patent
rights, such representation is limited to Anergen's knowledge) or, to its
knowledge, constitute unfair competition or trade practices under the laws of
any jurisdiction.
 
     (j) Anergen has not received notice from any third party that the operation
of the business of Anergen or any act, product or service of Anergen, infringes
or misappropriates the Intellectual Property of any third party or constitutes
unfair competition or trade practices under the laws of any jurisdiction.
 
     (k) To the knowledge of Anergen, no person has or is infringing or
misappropriating any Anergen Intellectual Property.
 
     (l) Anergen has taken commercially reasonable steps to protect Anergen's
rights in Anergen's confidential information and trade secrets that it wishes to
protect or any trade secrets or confidential information of third parties
provided to Anergen, and, without limiting the foregoing, Anergen has and
enforces a policy requiring each employee and contractor to execute a
proprietary information/confidentiality agreement substantially in the form
provided to Corixa and all current and former employees and contractors of
Anergen have executed such an agreement, except where the failure to do so is
not reasonably expected to be material to Anergen.
 
     2.10  Compliance; Permits; Restrictions.
 
     (a) To the knowledge of Anergen after reasonable inquiry, neither Anergen
nor any of its subsidiaries is, in any material respect, in conflict with, or in
default or in violation of (i) any law, rule, regulation, order, judgment or
decree applicable to Anergen or any of its subsidiaries or by which Anergen or
any of its subsidiaries or any of their respective properties is bound or
affected or (ii) any material note, bond, mortgage, indenture, contract,
agreement, lease, license, permit, franchise or other instrument or obligation
to which Anergen or any of its subsidiaries is a party or by which Anergen or
any of its subsidiaries or its or any of their respective properties is bound or
affected, except for conflicts, violations and defaults that (individually or in
the aggregate) would not cause Anergen to lose any material benefit or incur any
material liability. No investigation or review by any Governmental Entity is
pending or, to Anergen's knowledge, has been threatened in a writing delivered
to Anergen against Anergen or any of its subsidiaries, nor, to Anergen's
knowledge, has any Governmental Entity indicated an intention to conduct an
investigation of Anergen or any of its subsidiaries. There is no agreement,
judgment, injunction, order or decree binding upon Anergen or any of its
subsidiaries which has or could reasonably be expected to have a Material
Adverse Effect on Anergen.
 
     (b) Anergen and its subsidiaries hold, to the extent legally required, all
permits, licenses, variances, exemptions, orders and approvals from governmental
authorities that are material to and required for the operation of the business
of Anergen as currently conducted (collectively, the "Anergen Permits"). Anergen
and its subsidiaries are in compliance in all material respects with the terms
of the Anergen Permits, except where the failure to be in compliance with the
terms of the Anergen Permits would not have a Material Adverse Effect on
Anergen.
 
                                      A-17
<PAGE>   18
 
     2.11  Litigation. Except as disclosed in the Anergen Schedules, there are
no claims, suits, actions or proceedings pending or, to the knowledge of the
Anergen, threatened against, relating to or affecting Anergen or any of its
subsidiaries, before any court, governmental department, commission, agency,
instrumentality or authority, or any arbitrator that seeks to restrain or enjoin
the consummation of the transactions contemplated in this Agreement or which
could reasonably be expected, either singularly or in the aggregate with all
such claims, actions or proceedings, to have a Material Adverse Effect on
Anergen. No Governmental Entity has at any time challenged or questioned in a
writing delivered to Anergen the legal right of Anergen to design, manufacture,
offer or sell any of its products in the present manner or style thereof.
 
     2.12  Brokers' and Finders' Fee. Anergen has not incurred, nor will it
incur, directly or indirectly, any liability for brokerage or finders' fees or
agents' commissions or any similar charges in connection with this Agreement or
any transaction contemplated herein, except as otherwise set forth in that
certain Services and Consulting Agreement entered into as of July 15, 1998 by
and between Anergen and Maria Marmarinos as principal of Catalyst Group, a true
and accurate copy of which has been delivered by Anergen to Corixa.
 
     2.13  Employee Benefit Plans.
 
     (a) Definitions. With the exception of the definition of "Affiliate" set
forth in Section 2.13(a)(i) below (which definition shall apply only to this
Section 2.13), for purposes of this Agreement, the following terms shall have
the meanings set forth below:
 
          (i) "Affiliate" shall mean any other person or entity under common
     control with Anergen within the meaning of Section 414(b), (c), (m) or (o)
     of the Code and the regulations issued thereunder;
 
          (ii) "Anergen Employee Plan" shall mean any plan, program, policy,
     practice, contract, agreement or other arrangement providing for
     compensation, severance, termination pay, performance awards, stock or
     stock-related awards, fringe benefits or other employee benefits or
     remuneration of any kind, whether written or unwritten or otherwise, funded
     or unfunded, including without limitation, each "employee benefit plan,"
     within the meaning of Section 3(3) of ERISA which is or has been
     maintained, contributed to, or required to be contributed to, by Anergen or
     any Affiliate for the benefit of any Employee;
 
          (iii) "COBRA" shall mean the Consolidated Omnibus Budget
     Reconciliation Act of 1985, as amended;
 
          (iv) "DOL" shall mean the Department of Labor;
 
          (v) "Employee" shall mean any current, former, or retired employee,
     officer, or director of Anergen or any Affiliate;
 
          (vi) "Employee Agreement" shall mean each material management,
     employment, retention, severance, consulting, relocation, repatriation,
     expatriation, visas, work permit or similar agreement or contract between
     Anergen or any Affiliate and any Employee or consultant;
 
          (vii) "ERISA" shall mean the Employee Retirement Income Security Act
     of 1974, as amended;
 
          (viii) "FMLA" shall mean the Family Medical Leave Act of 1993, as
     amended;
 
                                      A-18
<PAGE>   19
 
          (ix) "International Employee Plan" shall mean each Anergen Employee
     Plan that has been adopted or maintained by Anergen, whether informally or
     formally, for the benefit of Employees outside the United States;
 
          (x) "IRS" shall mean the Internal Revenue Service;
 
          (xi) "Multiemployer Plan" shall mean any "Pension Plan" (as defined
     below) which is a "multiemployer plan," as defined in Section 3(37) of
     ERISA;
 
          (xii) "PBGC" shall mean the Pension Benefit Guaranty Corporation; and
 
          (xiii) "Pension Plan" shall mean each Anergen Employee Plan which is
     an "employee pension benefit plan," within the meaning of Section 3(2) of
     ERISA.
 
     (b) Schedules. The Anergen Schedules contain an accurate and complete list
of each Anergen Employee Plan and each Employee Agreement. Anergen does not have
any plan or commitment to establish any new Anergen Employee Plan, to modify any
Anergen Employee Plan or Employee Agreement (except to the extent required by
law or to conform any such Anergen Employee Plan or Employee Agreement to the
requirements of any applicable law, in each case as previously disclosed to
Corixa in writing, or as required by this Agreement), or to enter into any
Anergen Employee Plan or material Employee Agreement, nor does it have any
intention or commitment to do any of the foregoing.
 
     (c) Documents. Anergen has provided or made available to Corixa: (i)
correct and complete copies of all documents embodying to each Anergen Employee
Plan and forms of Employee Agreements, including all amendments thereto and
written interpretations thereof, (ii) the most recent annual actuarial
valuations, if any, prepared for each Anergen Employee Plan, (iii) the three (3)
most recent annual reports (Form Series 5500 and all schedules and financial
statements attached thereto), if any, required under ERISA or the Code in
connection with each Anergen Employee Plan or related trust, (iv) if the Anergen
Employee Plan is funded, the most recent annual and periodic accounting of
Anergen Employee Plan assets, (v) the most recent summary plan description
together with the summary of material modifications thereto, if any, required
under ERISA with respect to each Anergen Employee Plan, (vi) all IRS
determination, opinion, notification and advisory letters, and rulings relating
to Anergen Employee Plans and copies of all applications and correspondence to
or from the IRS or the DOL with respect to any Anergen Employee Plan, (vii) all
material written agreements and contracts relating to each Anergen Employee
Plan, including, but not limited to, administrative service agreements, group
annuity contracts and group insurance contracts, (viii) all communications
material to any Employee or Employees relating to any Anergen Employee Plan and
any proposed Anergen Employee Plans, in each case, relating to any amendments,
terminations, establishments, increases or decreases in benefits, acceleration
of payments or vesting schedules or other events which would result in any
material liability to Anergen, (ix) all COBRA forms and related notices and (x)
all registration statements and prospectuses prepared in connection with each
Anergen Employee Plan.
 
     (d) Employee Plan Compliance. (i) To the knowledge of Anergen after
reasonable inquiry, Anergen has performed in all material respects all
obligations required to be performed by it under, is not in default or violation
of and has no knowledge of any default or violation by any other party to each
Anergen Employee Plan, and each Anergen Employee Plan has been established and
maintained in all material respects in accordance with its terms and in
compliance with all applicable laws, statutes, orders, rules and regulations,
including but not limited to ERISA or the Code; (ii) each Anergen Employee Plan
intended to qualify under Section 401(a) of the Code and each trust intended to
 
                                      A-19
<PAGE>   20
 
qualify under Section 501(a) of the Code has either received a favorable
determination letter from the IRS with respect to each such Plan as to its
qualified status under the Code, including all amendments to the Code effected
by the Tax Reform Act of 1986 and subsequent legislation, or has remaining a
period of time under applicable Treasury regulations or IRS pronouncements in
which to apply for such a determination letter and make any amendments necessary
to obtain a favorable determination (iii) to the knowledge of Anergen after
reasonable inquiry, no "prohibited transaction," within the meaning of Section
4975 of the Code or Sections 406 and 407 of ERISA, and not otherwise exempt
under Section 408 of ERISA, has occurred with respect to any Anergen Employee
Plan, (iv) there are no actions, suits or claims pending, or, to the knowledge
of Anergen, threatened or reasonably anticipated (other than routine claims for
benefits) against any Anergen Employee Plan or against the assets of any Anergen
Employee Plan, (v) each Anergen Employee Plan can be amended, terminated or
otherwise discontinued after the Effective Time in accordance with its terms,
without liability to Corixa, Anergen or any of its Affiliates (other than
ordinary administration expenses typically incurred in a termination event),
(vi) there are no audits, inquiries or proceedings pending or, to the knowledge
of Anergen or any Affiliates, threatened by the IRS or DOL with respect to any
Anergen Employee Plan, and (vii) neither Anergen nor any Affiliate is subject to
any penalty or tax with respect to any Anergen Employee Plan under Section
402(i) of ERISA or Sections 4975 through 4980 of the Code.
 
     (e) Pension Plans. Anergen does not now, nor has it ever, maintained,
established, sponsored, participated in, or contributed to, any Pension Plan
which is subject to Title IV of ERISA or Section 412 of the Code.
 
     (f) Multiemployer Plans. At no time has Anergen contributed to or been
requested to contribute to any Multiemployer Plan.
 
     (g) No Post-Employment Obligations. No Anergen Employee Plan provides, or
has any liability to provide, retiree life insurance, retiree health or other
retiree employee welfare benefits to any person for any reason, except as may be
required by COBRA or other applicable statute, and Anergen has never
represented, promised or contracted (whether in oral or written form) to any
Employee (either individually or to Employees as a group) or any other person
that such Employee(s) or other person would be provided with retiree life
insurance, retiree health or other retiree employee welfare benefit, except to
the extent required by statute.
 
     (h) To the knowledge of Anergen after reasonable inquiry, neither Anergen
nor any Affiliate has, prior to the Effective Time, and in any material respect,
violated any of the health care continuation requirements of COBRA, the
requirements of FMLA or any similar provisions of state law applicable to its
Employees.
 
     (i) Effect of Transaction.
 
          (i) The execution of this Agreement and the consummation of the
     transactions contemplated herein will not (either alone or upon the
     occurrence of any additional or subsequent events) constitute an event
     under any Anergen Employee Plan, Employee Agreement, trust or loan that
     will or may result in any material payment (whether of severance pay or
     otherwise), acceleration, forgiveness of indebtedness, vesting,
     distribution, increase in benefits or obligation to fund benefits with
     respect to any Employee.
 
          (ii) To the knowledge of Anergen after reasonable inquiry, no payment
     or benefit which will or may be made by Anergen or its Affiliates with
     respect to any Employee
 
                                      A-20
<PAGE>   21
 
     as a result of the transactions contemplated by this Agreement will be
     characterized as an "excess parachute payment," within the meaning of
     Section 280G(b)(1) of the Code.
 
     (j) Employment Matters. Anergen: (i) is in compliance in all material
respects with all applicable foreign, federal, state and local laws, rules and
regulations respecting employment, employment practices, terms and conditions of
employment and wages and hours, in each case, with respect to Employees, (ii)
has withheld all amounts required by law or by agreement to be withheld from the
wages, salaries and other payments to Employees, (iii) is not liable for any
arrears of wages or any taxes or any penalty for failure to comply with any of
the foregoing, and (iv) is not liable for any material payment to any trust or
other fund or to any governmental or administrative authority, with respect to
unemployment compensation benefits, social security or other benefits or
obligations for Employees (other than routine payments to be made in the normal
course of business and consistent with past practice). There are no material
pending, or to the knowledge of Anergen either any threatened or reasonably
anticipated, claims or actions against Anergen under any worker's compensation
policy or long-term disability policy. To Anergen's knowledge, no employee of
Anergen has violated any employment contract, nondisclosure agreement or
noncompetition agreement by which such employee is bound due to such employee
being employed by Anergen and disclosing to Anergen or using trade secrets or
proprietary information of any other person or entity.
 
     (k) Labor. No work stoppage or labor strike against Anergen is pending,
threatened or reasonably anticipated. Anergen does not know of any activities or
proceedings of any labor union to organize any Employees. There are no actions,
suits, claims, labor disputes or grievances pending, or, to the knowledge of
Anergen, any threatened or reasonably anticipated, relating to any labor, safety
or discrimination matters involving any Employee, including, without limitation,
charges of unfair labor practices or discrimination complaints, which, if
adversely determined, would, individually or in the aggregate, result in any
material liability to Anergen. To the knowledge of Anergen after reasonable
inquiry, neither Anergen nor any of its subsidiaries has engaged in any unfair
labor practices within the meaning of the National Labor Relations Act. Anergen
is not presently, nor has it been in the past, a party to, or bound by, any
collective bargaining agreement or union contract with respect to Employees and
no collective bargaining agreement is being negotiated by Anergen.
 
     (l) International Employee Plan. Each International Employee Plan has been
established, maintained and administered in material compliance with its terms
and conditions and with the requirements prescribed by any and all statutory or
regulatory laws that are applicable to such International Employee Plan.
Furthermore, no International Employee Plan has unfunded liabilities, that as of
the Effective Time, will not be offset by insurance or fully accrued. Except as
required by law, no condition exists that would prevent Anergen or Corixa from
terminating or amending any International Employee Plan at any time for any
reason.
 
     2.14  Environmental Matters.
 
     (a) Hazardous Material. No underground storage tanks and no amount of any
substance that has been designated by any Governmental Entity or by applicable
federal, state or local law to be radioactive, toxic, hazardous or otherwise a
danger to health or the environment, including, without limitation, PCBs,
asbestos, petroleum, urea-formaldehyde and all substances listed as hazardous
substances pursuant to the Comprehensive Environmental Response, Compensation,
and Liability Act of 1980, as amended, or defined
 
                                      A-21
<PAGE>   22
 
as a hazardous waste pursuant to the United States Resource Conservation and
Recovery Act of 1976, as amended, and the regulations promulgated pursuant to
said laws, but excluding office and janitorial supplies, (a "Hazardous
Material") are present, as a result of the actions of Anergen or any of its
subsidiaries or any affiliate of Anergen, or, to Anergen's knowledge, as a
result of any actions of any third party or otherwise, in, on or under any
property, including the land and the improvements, ground water and surface
water thereof that Anergen or any of its subsidiaries has at any time owned,
operated, occupied or leased, except where the presence of any of the foregoing
substances (i) is authorized by permit or license in the ordinary course of
Anergen's business, or (ii) would not result in a Material Adverse Effect on
Anergen.
 
     (b) Hazardous Materials Activities. Neither Anergen nor any of its
subsidiaries has transported, stored, used, manufactured, disposed of released
or exposed its employees or others to Hazardous Materials in violation of any
law in effect on or before the Closing Date, except where any such violation,
individually or in the aggregate, would not result in a material adverse effect
on Anergen. Neither Anergen nor any of its subsidiaries has disposed of,
transported, sold, used, released, exposed its employees or others to or
manufactured any product containing a Hazardous Material (collectively
"Hazardous Materials Activities") in violation of any rule, regulation, treaty
or statute promulgated by any Governmental Entity in effect prior to or as of
the date hereof to prohibit, regulate or control Hazardous Materials or any
Hazardous Material Activity, except where any such violation, individually or in
the aggregate, would not result in a material adverse effect on Anergen.
 
     (c) Permits. Anergen and its subsidiaries currently hold all environmental
approvals, permits, licenses, clearances and consents (the "Anergen
Environmental Permits") necessary for the conduct of Anergen's and its
subsidiaries' Hazardous Material Activities and other businesses of Anergen and
its subsidiaries as such activities and businesses are currently being
conducted, except where the failure to hold such Anergen Environmental Permits
would not have a material adverse effect on Anergen.
 
     (d) Environmental Liabilities. No action, proceeding, revocation
proceeding, amendment procedure, writ or injunction is pending, and to Anergen's
knowledge, no action, proceeding, revocation proceeding, amendment procedure,
writ or injunction has been threatened by any Governmental Entity against
Anergen or any of its subsidiaries in a writing delivered to Anergen concerning
any Anergen Environmental Permit, Hazardous Material or any Hazardous Materials
Activity of Anergen or any of its subsidiaries. Anergen is not aware of any fact
or circumstance which could involve Anergen or any of its subsidiaries in any
environmental litigation or impose upon Anergen any material environmental
liability, except where the existence of such fact or circumstance would not
result in a material adverse effect on Anergen.
 
     2.15  Agreements, Contracts and Commitments. Except as otherwise set forth
in the Anergen Schedules, neither Anergen nor any of its subsidiaries is a party
to or is bound by:
 
          (a) any employment or consulting agreement, contract or commitment
     with any officer or director or higher level employee or member of
     Anergen's board of directors, other than those that are terminable by
     Anergen or any of its subsidiaries on no more than thirty (30) days notice
     without liability or financial obligation, except to the extent general
     principles of wrongful termination law may limit Anergen's or any of its
     subsidiaries' ability to terminate employees at will;
 
                                      A-22
<PAGE>   23
 
          (b) any material agreement or plan currently in force, including,
     without limitation, any stock option plan, stock appreciation right plan or
     stock purchase plan, any of the benefits of which will be increased, or the
     vesting of benefits of which will be accelerated, by the occurrence of any
     of the transactions contemplated in this Agreement or the value of any of
     the benefits of which will be calculated on the basis of any of the
     transactions contemplated in this Agreement;
 
          (c) any material agreement of indemnification or any guaranty
     currently in force other than any agreement of indemnification entered into
     in connection with the sale or license of software products in the ordinary
     course of business;
 
          (d) any material agreement, contract or commitment currently in force
     containing any covenant limiting in any respect the right of Anergen or any
     of its subsidiaries to engage in any line of business or to compete with
     any person or granting any exclusive distribution rights;
 
          (e) any material agreement, contract or commitment currently in force
     relating to the disposition or acquisition (by license or otherwise) by
     Anergen or any of its subsidiaries after the date of this Agreement of a
     material amount of assets not in the ordinary course of business or
     pursuant to which Anergen has any material ownership interest in any
     corporation, partnership, joint venture or other business enterprise other
     than Anergen's subsidiaries;
 
          (f) any material joint marketing or development agreement currently in
     force under which Anergen or any of its subsidiaries have continuing
     material obligations to jointly market any product, technology or service
     and which may not be canceled without penalty upon notice of ninety (90)
     days or less, or any material agreement pursuant to which Anergen or any of
     its subsidiaries have continuing material obligations to jointly develop
     any intellectual property that will not be owned, in whole or in part, by
     Anergen or any of its subsidiaries and which may not be canceled without
     penalty upon notice of ninety (90) days or less;
 
          (g) any material agreement, contract or commitment currently in force
     to license any third party to manufacture or reproduce any Anergen product,
     service or technology except as a distributor in the normal course of
     business.
 
     Neither Anergen nor any of its subsidiaries, nor to Anergen's knowledge any
other party to a Anergen Contract (as defined below), is in breach, violation or
default under, and neither Anergen nor any of its subsidiaries has received
written notice that it has breached, violated or defaulted under, any of the
material terms or conditions of any of the agreements, contracts or commitments
to which Anergen or any of its subsidiaries is a party or by which it is bound
that are required to be disclosed in the Anergen Schedules pursuant to clauses
(a) through (g) above or pursuant to Section 2.9 hereof (any such agreement,
contract or commitment, a "Anergen Contract") in such a manner as would permit
any other party to cancel or terminate any such Anergen Contract, or would
permit any other party to seek damages or other remedies.
 
     2.16  Change of Control Payments. The Anergen Schedules set forth each plan
or agreement pursuant to which any amounts may become payable (whether currently
or in the future) to current or former officers and directors of Anergen as a
result of or in connection with the Merger.
 
     2.17  Statements; Proxy Statement/Prospectus. The information supplied by
Anergen for inclusion in the Registration Statement (as defined in Section
3.3(b)) shall not, at the
 
                                      A-23
<PAGE>   24
 
time the Registration Statement is filed with the SEC and at the time it becomes
effective under the Securities Act, contain any untrue statement of a material
fact or omit to state any material fact required to be stated therein or
necessary in order to make the statements therein, in light of the circumstances
under which they are made, not misleading. The information supplied by Anergen
for inclusion in the proxy statement/prospectus to be sent to (a) the
stockholders of Anergen in connection with the meeting of Anergen's stockholders
to consider the approval and adoption of this Agreement and the approval of the
Merger (the "Anergen Stockholders' Meeting") (such proxy statement/prospectus as
amended or supplemented is referred to herein as the "Proxy
Statement/Prospectus") shall not, on the date the Proxy Statement/Prospectus is
first mailed to Anergen's stockholders or at the time of the Anergen
Stockholders' Meeting, contain any untrue statement of a material fact or omit
to state any material fact required to be stated therein or necessary in order
to make the statements therein, in light of the circumstances under which they
are made, not false or misleading, or omit to state any material fact necessary
to correct any statement in any earlier communication with respect to the
solicitation of proxies for the Anergen Stockholders' Meeting which has become
false or misleading. The Proxy Statement/Prospectus will comply as to form in
all material respects with the provisions of the Securities Act, the Exchange
Act and the rules and regulations thereunder. If at any time prior to the
Effective Time any event relating to Anergen or any of its affiliates, officers
or directors should be discovered by Anergen which is required to be set forth
in an amendment to the Registration Statement or a supplement to the Proxy
Statement/Prospectus, Anergen shall promptly inform Corixa. Notwithstanding the
foregoing, Anergen makes no representation or warranty with respect to any
information supplied by Corixa or Merger Sub which is contained in any of the
foregoing documents.
 
     2.18  Board Approval. The board of directors of Anergen has, as of the date
of this Agreement, determined (a) that the Merger is fair to, and in the best
interests of Anergen and its stockholders and (b) to recommend that the
stockholders of Anergen approve and adopt this Agreement and approve the Merger.
 
     2.19  Fairness Opinion. Anergen's Board of Directors has received a written
opinion from Pacific Growth Equities dated as of the date hereof to the effect
that, as of the date hereof, the Merger and the Exchange Ratio are fair to
Anergen's stockholders from a financial point of view and has delivered to
Corixa a copy of such opinion.
 
     2.20  Section 203 of the Delaware General Corporation Law Not
Applicable. The Board of Directors of Anergen has taken all actions so that the
restrictions contained in Section 203 of the Delaware General Corporation Law
applicable to a "business combination" (as defined in such Section 203) will not
apply to the execution, delivery or performance of this Agreement or to the
consummation of the Merger or the other transactions contemplated by this
Agreement.
 
     2.21  Customs. Anergen has acted with reasonable care to properly value and
classify, in accordance with applicable tariff laws, rules and regulations, all
goods that Anergen or any of its subsidiaries import into the United States or
into any other country (the "Imported Goods"). To Anergen's knowledge, there are
currently no material claims pending against Anergen by the U.S. Customs Service
(or other foreign customs authorities) relating to the valuation, classification
or marking of the Imported Goods.
 
                                      A-24
<PAGE>   25
 
                                  ARTICLE III
 
            REPRESENTATIONS AND WARRANTIES OF CORIXA AND MERGER SUB
 
     Corixa and Merger Sub hereby represent and warrant to Anergen, subject to
the exceptions specifically disclosed in writing in the disclosure letter and
referencing a specific representation made by Corixa and Merger Sub to Anergen
pursuant to this Article III dated as of the date hereof and certified by a duly
authorized officer of Corixa and Merger Sub (the "Corixa Schedules"), as
follows:
 
     3.1  Organization of Corixa and Merger Sub.
 
     (a) Each of Corixa and Merger Sub (i) is a corporation duly organized,
validly existing and in good standing under the laws of the jurisdiction in
which it is organized, (ii) has the corporate or other power and authority to
own, lease and operate its assets and property and to carry on its business as
now being conducted and (iii) except as would not be material to Corixa, is duly
qualified or licensed to do business in each jurisdiction where the character of
the properties owned, leased or operated by it or the nature of its activities
makes such qualification or licensing necessary.
 
     (b) Corixa has delivered or made available to Anergen a true and correct
copy of the certificate of incorporation and bylaws of Corixa, each as amended
to date, and each such instrument is in full force and effect. Neither Corixa
nor any of its subsidiaries is in violation of any of the provisions of its
certificate of incorporation or bylaws or equivalent governing instruments.
 
     3.2  Corixa and Merger Sub Capital Structure. The authorized capital stock
of Corixa consists of forty million (40,000,000) shares of Common Stock,
One-Tenth of One Cent ($0.001) par value per share, of which there were twelve
million six hundred ninety three thousand eight hundred thirty seven
(12,693,837) shares issued and outstanding as of December 8, 1998, and ten
million (10,000,000) shares of Preferred Stock, One-Tenth of One Cent ($0.001)
par value per share, none of which shares are issued and outstanding. All
outstanding shares of Corixa Common Stock are duly authorized, validly issued,
fully paid and nonassessable, free of any liens or encumbrances and are not
subject to preemptive rights created by statute, the certificate of
incorporation or bylaws of Corixa or any agreement or document to which Corixa
is a party or by which it is bound. As of December 8, 1998, Corixa had reserved
an aggregate of two million seven hundred thirty nine thousand two hundred eight
(2,739,208) shares of Corixa Common Stock, net of exercises, for issuance under
the Corixa Corporation 1994 Amended and Restated Stock Option Plan (the "Corixa
Stock Option Plan"), the Corixa Corporation Directors' Stock Option Plan (the
"Corixa Directors' Plan"), and the Corixa Corporation 1997 Employee Stock
Purchase Plan (the "Corixa ESPP", and together with the Corixa Stock Option Plan
and the Corixa Directors' Plan, the "Corixa Plans"). As of December 8, 1998,
Corixa had reserved two million three hundred sixty four thousand two hundred
eight (2,364,208) shares of Corixa Common Stock for issuance to employees,
directors and consultants pursuant to the Corixa Stock Option Plan, of which two
hundred eighty three thousand eight hundred nine (283,809) shares have been
issued pursuant to option exercises, and one million three hundred ninety five
thousand five hundred eighty nine (1,395,589) shares are subject to outstanding,
unexercised options. As of December 8, 1998, Corixa had reserved two hundred
fifty thousand (250,000) shares of Corixa Common Stock for issuance to directors
pursuant to the Corixa Directors' Plan, of which sixty thousand (60,000) are
subject to outstanding, unexercised options. As of December 8, 1998, Corixa had
reserved one hundred twenty five thousand (125,000)
 
                                      A-25
<PAGE>   26
 
shares of Corixa Common Stock for issuance to employees pursuant to the Corixa
ESPP, of which five thousand eight hundred eighty seven (5,887) shares have been
issued to employees. The authorized capital stock of Merger Sub consists of one
thousand (1,000) shares of Common Stock, One-Tenth of One Cent ($0.001) par
value, all of which, as of the date hereof are issued and outstanding and are
held by Corixa. Merger Sub was formed on or about December 3, 1998 for the
purpose of consummating the Merger and has no material assets or liabilities
except as necessary for such purpose. Other than as set forth in the Corixa
Schedules or as contemplated in this Agreement, there are no other options,
warrants, calls, rights, commitments or agreements of any character to which
Corixa or Merger Sub is a party or by which either Corixa or Merger Sub is bound
obligating Corixa or Merger Sub to issue, deliver, sell, repurchase or redeem,
or cause to be issued, delivered, sold, repurchased or redeemed, any shares of
the capital stock of Corixa or obligating Corixa or Merger Sub to grant, extend
or enter into any such option, warrant, call, right, commitment or agreement.
 
     3.3  Authority.
 
     (a) Each of Corixa and Merger Sub, as applicable, has all requisite
corporate power and authority to enter into this Agreement and to consummate the
transactions contemplated herein. The execution and delivery of this Agreement
and the consummation of the transactions contemplated herein have been duly
authorized by all necessary corporate action on the part of Corixa and Merger
Sub, subject only to the filing of the Certificate of Merger pursuant to
Delaware Law. This Agreement has been duly executed and delivered by each of
Corixa and Merger Sub and, assuming the due authorization, execution and
delivery by Anergen, constitutes the valid and binding obligation of Corixa and
Merger Sub, enforceable against Corixa and Merger Sub in accordance with its
terms, except as enforceability may be limited by bankruptcy and other similar
laws and general principles of equity. The execution and delivery of this
Agreement by each of Corixa and Merger Sub does not, and the performance of this
Agreement by each of Corixa and Merger Sub will not, (i) conflict with or
violate the certificate of incorporation or bylaws of Corixa or Merger Sub, (ii)
conflict with or violate any law, rule, regulation, order, judgment or decree
applicable to Corixa or Merger Sub or by which any of their respective
properties is bound or affected or (iii) result in any material breach of or
constitute a material default (or an event that with notice or lapse of time or
both would become a material default) under, or impair Corixa's rights or alter
the rights or obligations of any third party under, or give to others any rights
of termination, amendment, acceleration or cancellation of, or result in the
creation of a material lien or encumbrance on any of the material properties or
assets of Corixa or Merger Sub pursuant to, any material note, bond, mortgage,
indenture, contract, agreement, lease, license, permit, franchise or other
instrument or obligation to which Corixa or Merger Sub is a party or by which
Corixa or Merger Sub or any of their respective properties are bound or
affected.
 
     (b) No consent, approval, order or authorization of, or registration,
declaration or filing with any Governmental Entity is required to be obtained or
made by Corixa or Merger Sub in connection with the execution and delivery of
this Agreement or the consummation of the Merger, except for (i) the filing of a
Form S-4 (or any similar successor form thereto) Registration Statement (the
"Registration Statement") with the SEC in accordance with the Securities Act,
(ii) the filing of the Certificate of Merger with the Secretary of State of the
State of Delaware, (iii) such consents, approvals, orders, authorizations,
registrations, declarations and filings as may be required under applicable
federal, foreign and state securities (or related) laws and the securities or
antitrust laws of any foreign country and (v) such other consents,
authorizations, filings, approvals and
 
                                      A-26
<PAGE>   27
 
registrations which if not obtained or made would not be material to Corixa or
Anergen or have a material adverse effect on the ability of the parties hereto
to consummate the Merger.
 
     3.4  SEC Filings; Corixa Financial Statements.
 
     (a) Corixa has filed all forms, reports and documents required to be filed
by Corixa with the SEC since January 1, 1997, and has made available to Anergen
such forms, reports and documents in the form filed with the SEC. All such
required forms, reports and documents (including those that Corixa may file
subsequent to the date hereof) are referred to herein as the "Corixa SEC
Reports." As of their respective dates, the Corixa SEC Reports (i) were prepared
in accordance with the requirements of the Securities Act or the Exchange Act,
as the case may be, and the rules and regulations of the SEC promulgated
thereunder applicable to such Corixa SEC Reports and (ii) did not at the time
they were filed (or if amended or superseded by a filing prior to the date of
this Agreement, then on the date of such filing) contain any untrue statement of
a material fact or omit to state a material fact required to be stated therein
or necessary in order to make the statements therein, in the light of the
circumstances under which they were made, not misleading. None of Corixa's
subsidiaries is required to file any forms, reports or other documents with the
SEC.
 
     (b) Each of the consolidated financial statements (including, in each case,
any related notes thereto) contained in the Corixa SEC Reports (the "Corixa
Financials"), including any Corixa SEC Reports filed after the date hereof until
the Closing, (i) complied as to form in all material respects with the published
rules and regulations of the SEC with respect thereto, (ii) was prepared in
accordance with GAAP applied on a consistent basis throughout the periods
involved (except as may be indicated in the notes thereto or, in the case of
unaudited interim financial statements, as may be permitted by the SEC on Form
10-Q under the Exchange Act) and (iii) fairly presented the consolidated
financial position of Corixa and its subsidiaries as at the respective dates
thereof and the consolidated results of Corixa's operations and cash flows for
the periods indicated, except that the unaudited interim financial statements
may not contain footnotes and were or are subject to normal and recurring
year-end adjustments. The balance sheet of Corixa contained in Corixa SEC
Reports as of December 31, 1997, is hereinafter referred to as the "Corixa
Balance Sheet." Except as disclosed in the Corixa Financials, since the date of
the Corixa Balance Sheet neither Corixa nor any of its subsidiaries has any
liabilities (absolute, accrued, contingent or otherwise) which are, individually
or in the aggregate, material to the business, results of operations or
financial condition of Corixa and its subsidiaries taken as a whole, except for
liabilities incurred since the date of the Corixa Balance Sheet in the ordinary
course of business consistent with past practices.
 
     3.5  Absence of Certain Changes or Events. Since the date of the Corixa
Balance Sheet there has not been any Material Adverse Effect on Corixa.
 
     3.6  Statements; Proxy Statement/Prospectus. The information supplied by
Corixa for inclusion in the Registration Statement shall not at the time the
Registration Statement is filed with the SEC and at the time it becomes
effective under the Securities Act, contain any untrue statement of a material
fact or omit to state any material fact required to be stated therein or
necessary in order to make the statements therein, in light of the circumstances
under which they are made, not misleading. The information supplied by Corixa
for inclusion in the Proxy Statement/Prospectus shall not, on the date the Proxy
Statement/Prospectus is first mailed to Anergen's stockholders or at the time of
the Anergen Stockholders' Meeting, contain any untrue statement of a material
fact or omit to
 
                                      A-27
<PAGE>   28
 
state any material fact required to be stated therein or necessary in order to
make the statements therein, in light of the circumstances under which they are
made, not false or misleading, or omit to state any material fact necessary to
correct any statement in any earlier communication with respect to the
solicitation of proxies for the Anergen Stockholders' Meeting which has become
false or misleading. If at any time prior to the Effective Time, any event
relating to Corixa or any of its affiliates, officers or directors should be
discovered by Corixa which is required to be set forth in an amendment to the
Registration Statement or a supplement to the Proxy Statement/Prospectus, Corixa
shall promptly so inform Anergen. Notwithstanding the foregoing, Corixa makes no
representation or warranty with respect to any information supplied by Anergen
which is contained in any of the foregoing documents.
 
     3.7  Valid Issuance. The Corixa Common Stock to be issued in the Merger,
when issued in accordance with the provisions of this Agreement: (a) will be
validly issued, fully paid and nonassessable and (b) will not be subject to any
restrictions on resale under the Securities Act other than restrictions imposed
by Rule 145 promulgated under the Securities Act.
 
                                   ARTICLE IV
 
                      CONDUCT PRIOR TO THE EFFECTIVE TIME
 
     4.1  Conduct of Business by Anergen. During the period from the date of
this Agreement and continuing until the earlier of the termination of this
Agreement pursuant to its terms or the Effective Time, Anergen and each of its
subsidiaries shall, except to the extent that Corixa shall otherwise consent in
writing (which consent shall not be unreasonably withheld, it being acknowledged
and agreed by the parties that Corixa will respond as promptly as reasonably
practicable to Anergen's requests for such consent), carry on its business, in
the usual, regular and ordinary course, in substantially the same manner as
heretofore conducted and in compliance with all applicable laws and regulations,
pay its debts and taxes when due subject to good faith disputes over such debts
or taxes, pay or perform other obligations when due, and use its commercially
reasonable efforts consistent with past practices and policies to (i) preserve
intact its present business organization, (ii) keep available the services of
its present officers and employees and (iii) preserve its relationships with
customers, suppliers, distributors, licensors, licensees, and others with which
it has business dealings. In addition, Anergen will promptly notify Corixa of
any material event involving its business or operations.
 
     In addition, except as permitted by the terms of this Agreement (including
entering into the Organon Amendment and the Bridge Financing), and except as
provided in Article IV of the Anergen Schedules, without the prior written
consent of Corixa not to be unreasonably withheld (it being acknowledged and
agreed by the parties that Corixa will respond reasonably promptly to Anergen's
requests for such prior written consent of Corixa), during the period from the
date of this Agreement and continuing until the earlier of the termination of
this Agreement pursuant to its terms or the Effective Time, Anergen shall not do
any of the following and shall not permit its subsidiaries to do any of the
following:
 
          (a) Waive any stock repurchase rights, accelerate, amend or change the
     period of exercisability of options or restricted stock, or reprice options
     granted under any employee, consultant, director or other stock plans or
     authorize cash payments in exchange for any options granted under any of
     such plans;
 
                                      A-28
<PAGE>   29
 
          (b) Except as otherwise provided in the Anergen Schedules, grant any
     severance or termination pay to any officer or employee except pursuant to
     written agreements outstanding, or policies existing, on the date hereof
     and as previously disclosed in writing or made available to Corixa, or
     adopt any new severance plan;
 
          (c) Transfer or license to any person or entity or otherwise extend,
     amend or modify in any material respect any rights to the Anergen
     Intellectual Property, or enter into grants to future patent rights;
 
          (d) Declare, set aside or pay any dividends on or make any other
     distributions (whether in cash, stock, equity securities or property) in
     respect of any capital stock or split, combine or reclassify any capital
     stock or issue or authorize the issuance of any other securities in respect
     of, in lieu of or in substitution for any capital stock;
 
          (e) Purchase, redeem or otherwise acquire, directly or indirectly, any
     shares of capital stock of Anergen or its subsidiaries, except repurchases
     of unvested shares at cost in connection with the termination of the
     employment relationship with any employee pursuant to stock option or
     purchase agreements in effect on the date hereof;
 
          (f) Issue, deliver, sell, authorize, pledge or otherwise encumber or
     propose any of the foregoing of, any shares of capital stock or any
     securities convertible into shares of capital stock, or subscriptions,
     rights, warrants or options to acquire any shares of capital stock or any
     securities convertible into shares of capital stock, or enter into other
     agreements or commitments of any character obligating it to issue any such
     shares or convertible securities, other than the issuance delivery and/or
     sale of (i) shares of Anergen Common Stock pursuant to the exercise of
     stock options therefor outstanding as of the date of this Agreement, and
     (ii) shares of Anergen Common Stock issuable to participants in the ESPP
     consistent with the terms thereof;
 
          (g) Cause, permit or propose any amendments to its certificate of
     incorporation, bylaws or similar charter documents of any of its
     subsidiaries;
 
          (h) Acquire or agree to acquire by merging or consolidating with, or
     by purchasing any equity interest in or a portion of the assets of, or by
     any other manner, any business or any corporation, partnership, association
     or other business organization or division thereof or otherwise acquire or
     agree to acquire any assets which are material, individually or in the
     aggregate, to the business of Anergen or enter into any material joint
     ventures, strategic partnerships or alliances;
 
          (i) Sell, lease, license, encumber or otherwise dispose of any
     properties or assets which are material, individually or in the aggregate,
     to the business of Anergen, except sales of inventory in the ordinary
     course of business consistent with past practice;
 
          (j) Incur any indebtedness for borrowed money or guarantee any such
     indebtedness of another person, issue or sell any debt securities or
     options, warrants, calls or other rights to acquire any debt securities of
     Anergen, enter into any "keep well" or other agreement to maintain any
     financial statement condition or enter into any arrangement having the
     economic effect of any of the foregoing other than (i) in connection with
     the financing of ordinary course trade payables consistent with past
     practice or (ii) pursuant to existing credit facilities in the ordinary
     course of business;
 
          (k) Except as otherwise disclosed in the Anergen Schedules, adopt or
     amend any employee benefit plan or employee stock purchase or employee
     stock option plan,
 
                                      A-29
<PAGE>   30
 
     or enter into any employment contract or collective bargaining agreement
     (other than offer letters and letter agreements entered into in the
     ordinary course of business consistent with past practice with employees
     who are terminable "at will,"), pay any special bonus or special
     remuneration to any director or employee, or increase the salaries or wage
     rates or fringe benefits (including rights to severance or indemnification)
     of its directors, officers, employees or consultants other than in the
     ordinary course of business, consistent with past practice, or change in
     any material respect any management policies or procedures;
 
          (l) Make any payments outside of the ordinary course of business;
 
          (m) Modify, amend or terminate any material contract or agreement to
     which Anergen or any subsidiary thereof is a party or waive, release or
     assign any material rights or claims thereunder;
 
          (n) Enter into any contracts, agreements, or obligations relating to
     the distribution, sale, license or marketing by third parties of Anergen's
     products or products licensed by Anergen other than in the ordinary course
     of business consistent with past practice;
 
          (o) Revalue any of its assets or, except as required by GAAP, make any
     change in accounting methods, principles or practices;
 
          (p) Engage in any action with the intent to directly or indirectly
     adversely impact any of the transactions contemplated in this Agreement;
 
          (q) Expend more than Fifteen Thousand Dollars ($15,000) for any
     individual purchase or lease of any capital assets or related services, or
     Thirty Thousand Dollars ($30,000) in the aggregate for all such purchases
     or leases; or
 
          (r) Agree in writing or otherwise to take any of the actions described
     in Article VI (a) through (q) above.
 
     4.2  Conduct of Business by Corixa. During the period from the date of this
Agreement and continuing until the earlier of the termination of this Agreement
pursuant to its terms or the Effective Time, except as permitted by the terms of
this Agreement and except as provided in Article IV of the Corixa Schedules,
without the prior written consent of Anergen which consent shall not be
unreasonably withheld, during the period from the date of this Agreement and
continuing until the earlier of the termination of this Agreement pursuant to
its terms or the Effective Time, Corixa shall not declare, set aside or pay any
dividends on or make any other distributions (whether in cash, stock, equity
securities or property) in respect of any capital stock or split, combine or
reclassify any capital stock or issue or authorize the issuance of any other
securities in respect of in lieu of or in substitution for any capital stock.
 
                                   ARTICLE V
 
                             ADDITIONAL AGREEMENTS
 
     5.1  Proxy Statement/Prospectus; Registration Statement; Other Filings;
Board Recommendations.
 
     (a) As promptly as practicable after the execution of this Agreement,
Anergen and Corixa will prepare, and file with the SEC, the Proxy
Statement/Prospectus and Corixa will prepare and file with the SEC the
Registration Statement in which the Proxy Statement/Prospectus will be included
as a prospectus. Each of Anergen and Corixa will
 
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respond to any comments of the SEC and will use its respective commercially
reasonable efforts to have the Registration Statement declared effective under
the Securities Act as promptly as practicable after such filing, Anergen will
cause the Proxy Statement/ Prospectus to be mailed to its stockholders at the
earliest practicable time after the Registration Statement is declared effective
by the SEC. As promptly as practicable after the date of this Agreement, each of
Anergen and Corixa will prepare and file any other filings required to be filed
by it under the Exchange Act, the Securities Act or any other Federal, foreign
or Blue Sky or related laws relating to the Merger and the transactions
contemplated in this Agreement (the "Other Filings"). Each of Anergen and Corixa
will notify the other promptly upon the receipt of any comments from the SEC or
its staff or any other government officials and of any request by the SEC or its
staff or any other government officials for amendments or supplements to the
Registration Statement, the Proxy Statement/Prospectus or any Other Filing or
for additional information and will supply the other with copies of all
correspondence between such party or any of its representatives, on the one
hand, and the SEC, or its staff or any other government officials, on the other
hand, with respect to the Registration Statement, the Proxy
Statement/Prospectus, the Merger or any Other Filing. Each of Anergen and Corixa
will cause all documents that it is responsible for filing with the SEC or other
regulatory authorities under this Section 5.1(a) to comply in all material
respects with all applicable requirements of law and the rules and regulations
promulgated thereunder. Whenever any event occurs which is required to be set
forth in an amendment or supplement to the Proxy Statement/Prospectus, the
Registration Statement or any Other Filing, Anergen or Corixa, as the case may
be, will promptly inform the other of such occurrence and cooperate in filing
with the SEC or its staff or any other government officials, and/or mailing to
stockholders of Anergen, such amendment or supplement.
 
     (b) The Proxy Statement/Prospectus will include the recommendation of the
Board of Directors of Anergen in favor of adoption and approval of this
Agreement and approval of the Merger.
 
     5.2  Meeting of Anergen Stockholders.
 
     (a) Promptly after the date hereof, Anergen will take all action necessary
in accordance with the Delaware Law and its certificate of incorporation and
bylaws to convene the Anergen Stockholders' Meeting to be held as promptly as
practicable, and in any event (to the extent permissible under applicable law)
within thirty (30) days after the declaration of effectiveness of the
Registration Statement; provided, however, that in the event Anergen's board of
directors receives a Superior Offer during the last five (5) business days of
such thirty (30) day period, such thirty (30) day period shall be extended for
seven (7) calendar days from the time Anergen's board of directors receives such
Superior Offer (the "Anergen Stockholder's Meeting Period"), for the purpose of
voting upon this Agreement and the Merger or the issuance of shares of Corixa
Common Stock pursuant to the Merger, respectively. Anergen will use its
commercially reasonable efforts to solicit from its stockholders proxies in
favor of the adoption and approval of this Agreement and the approval of the
Merger and will take all other action reasonably necessary or advisable to
secure the vote or consent of its stockholders required by the rules of Nasdaq
or Delaware Law to obtain such approvals. Notwithstanding anything to the
contrary contained in this Agreement, Anergen may adjourn or postpone the
Anergen Stockholders' Meeting to the extent necessary to ensure that any
necessary supplement or amendment to the Prospectus/Proxy Statement is provided
to Anergen's stockholders in advance of a vote on the Merger and this Agreement
or, if as of the time for which Anergen Stockholders' Meeting is originally
scheduled (as set forth in the Prospectus/
 
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<PAGE>   32
 
Proxy Statement) there are insufficient shares of Anergen Common Stock
represented (either in person or by proxy) to constitute a quorum necessary to
conduct the business of the Anergen's Stockholders' Meeting. Anergen shall
ensure that the Anergen Stockholders' Meeting is called, noticed, convened, held
and conducted, and subject to Section 5.2(c) that all proxies solicited by
Anergen in connection with the Anergen Stockholders' Meeting are solicited, in
compliance with the Delaware Law, its certificate of incorporation and bylaws,
the rules of Nasdaq and all other applicable legal requirements. Anergen's
obligation to call, give notice of, convene and hold the Anergen Stockholders'
Meeting in accordance with this Section 5.2(a) shall not be limited to or
otherwise affected by the commencement, disclosure, announcement or submission
to Anergen of any Acquisition Proposal (as defined in Section 5.4(a)), or by any
withdrawal, amendment or modification of the recommendation of Anergen's board
of directors with respect to the Merger.
 
     (b) Subject to Section 5.2(c): (i) Anergen's board of directors shall
unanimously recommend that Anergen's stockholders vote in favor of and adopt and
approve this Agreement and the Merger at the Anergen Stockholders' Meeting, (ii)
the Prospectus/ Proxy Statement shall include a statement to the effect that
Anergen's board of directors has unanimously recommended that Anergen's
stockholders vote in favor of and adopt and approve this Agreement and the
Merger at the Anergen Stockholders' Meeting and (iii) neither Anergen's board of
directors nor any committee thereof shall withdraw, amend or modify, or propose
or resolve to withdraw, amend or modify in a manner adverse to Corixa, the
unanimous recommendation of Anergen's board of directors that Anergen's
stockholders vote in favor of and adopt and approve this Agreement and the
Merger.
 
     (c) Nothing in this Agreement shall prevent Anergen's board of directors
from withholding, withdrawing, amending or modifying its unanimous
recommendation in favor of the Merger if (i) a Superior Offer (as defined below)
is made to Anergen and is not withdrawn, (ii) neither Anergen nor any of its
representatives shall have violated any of the restrictions set forth in Section
5.4, and (iii) Anergen's board of directors or any committee thereof concludes
in good faith, after consultation with its outside counsel, that, in light of
such Superior Offer, the withholding, withdrawal, amendment or modification of
such recommendation is required in order for Anergen's board of directors or any
committee thereof to comply with its fiduciary obligations to Anergen's
stockholders under applicable law. Subject to applicable laws, nothing contained
in this Section 5.2 shall limit Anergen's obligation to hold and convene the
Anergen Stockholders' Meeting (regardless of whether the unanimous
recommendation of the Anergen's board of directors shall have been withdrawn,
amended or modified). For purposes of this Agreement, the term "Superior Offer"
shall mean an unsolicited, bona fide written offer made by a third party to
consummate any of the following transactions: (1) a merger, consolidation,
business combination, recapitalization, liquidation, dissolution or similar
transaction involving Anergen pursuant to which the stockholders of Anergen
immediately preceding such transaction hold less than fifty percent (50%) of the
equity interest in the surviving or resulting entity of such transaction, (2) a
sale or other disposition by Anergen of assets (excluding inventory and used
equipment sold in the ordinary course of business) representing in excess of
fifty percent (50%) of the fair market value of Anergen's business immediately
prior to such sale, (3) the acquisition by any person or group (including by way
of a tender offer or an exchange offer or issuance by Anergen), directly or
indirectly, of beneficial ownership or a right to acquire beneficial ownership
of shares representing in excess of fifty percent (50%) of the voting power of
the then-outstanding shares of capital stock of Anergen or (4) any public
announcement of a proposal, plan or intention to do any of the foregoing or any
agreement to engage in any of the foregoing, on terms that
 
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<PAGE>   33
 
Anergen's board of directors determines, in its judgment consistent with
applicable corporate law, after consultation with its financial advisor, is
reasonably likely to be financially superior to the Anergen stockholders than
the terms of the Merger.
 
     5.3  Confidentiality: Access to Information.
 
     (a) The parties acknowledge that Anergen and Corixa have previously
executed a Confidential Disclosure Agreement, dated as of September 29, 1998
(the "Confidentiality Agreement"), which Confidentiality Agreement will continue
in full force and effect in accordance with its terms.
 
     (b) Access to Information. Anergen will afford Corixa and its accountants,
counsel and other representatives reasonable access during normal business hours
to the properties, books, records and personnel of Anergen during the period
prior to the Effective Time to obtain all information concerning the business,
including the status of product development efforts, properties, results of
operations and personnel of Anergen, as Corixa may reasonably request. No
information or knowledge obtained by Corixa in any investigation pursuant to
this Section 5.3 will affect or be deemed to modify any representation or
warranty contained herein or the conditions to the obligations of the parties to
consummate the Merger. Corixa will cooperate reasonably with Anergen and respond
to reasonable requests for information from Anergen's accountants, counsel and
other representatives.
 
     5.4  No Solicitation.
 
     (a) From and after the date of this Agreement until the earlier of the
Effective Time or termination of this Agreement pursuant to Article VII, Anergen
and its subsidiaries will not, nor will they authorize or permit any of their
respective officers, directors, affiliates or employees or any investment
banker, attorney or other advisor or representative retained by any of them to,
directly or indirectly, (i) solicit, initiate, encourage or induce the making,
submission or announcement of any Acquisition Proposal (as hereinafter defined),
(ii) participate in any discussions or negotiations regarding, or furnish to any
person any non-public information with respect to, or take any other action to
facilitate any inquiries or the making of any proposal that constitutes or may
reasonably be expected to lead to, any Acquisition Proposal, (iii) subject to
Section 5.2(c), engage in discussions with any person with respect to any
Acquisition Proposal, except as to the existence of these provisions, (iv)
subject to Section 5.2(c), approve, endorse or recommend any Acquisition
Proposal or (v) subject to Section 5.2(c), enter into any letter of intent or
similar document or any contract agreement or commitment contemplating or
otherwise relating to any Acquisition Transaction (as hereinafter defined);
provided, however, that prior to the approval of this Agreement by the required
Anergen Stockholder Vote, this Section 5.4(a) shall not prohibit Anergen from
furnishing nonpublic information regarding Anergen and its subsidiaries to,
entering into a confidentiality agreement with or entering into discussions
with, any person or group in response to a Superior Offer submitted by such
person or group (and not withdrawn) if (1) neither Anergen nor any
representative of Anergen and its subsidiaries shall have violated any of the
restrictions set forth in this Section 5.4, (2) Anergen's board of directors
concludes in good faith, after consultation with its outside legal counsel, that
such action is required in order for Anergen's board of directors to comply with
its fiduciary obligations to Anergen's stockholders under applicable law, (3)
prior to furnishing any such nonpublic information to, and as promptly as
reasonably practicable after having any discussions with, such person or group,
Anergen gives Corixa written notice of the identity of such person or group and
of Anergen's intention to furnish nonpublic information to, or enter into
discussions with, such person or group and Anergen receives from such person or
group an executed confidentiality
 
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<PAGE>   34
 
agreement containing customary limitations on the use and disclosure of all
nonpublic written and oral information furnished to such person or group by or
on behalf of Anergen, and (4) contemporaneously with furnishing any such
nonpublic information to such person or group, Anergen furnishes such nonpublic
information to Corixa (to the extent such nonpublic information has not been
previously furnished by Anergen to Corixa); and provided further, however, that
upon compliance with clauses (1) - (4) and Anergen determines to accept a
Superior Offer, all Anergen Affiliate Agreements and all Anergen Voting
Agreements shall terminate, and Anergen shall be entitled to enter into an
agreement with such third party concerning such Superior Proposal, provided that
Anergen has made payment in full to Corixa of the Termination Fee subject and
pursuant to Section 7.3(b). Anergen and its subsidiaries will immediately cease
any and all existing activities, discussions or negotiations with any parties
conducted heretofore with respect to any Acquisition Proposal. Without limiting
the foregoing, it is understood that any violation of the restrictions set forth
in the preceding two sentences by any officer, director or employee of Anergen
or any of its subsidiaries or any investment banker, attorney or other advisor
or representative of Anergen or any of its subsidiaries shall be deemed to be a
material breach of this Section 5.4 by Anergen. In addition to the foregoing,
Anergen shall provide Corixa with at least the same notice as provided to the
members of Anergen's board of directors of any meeting of Anergen's board of
directors at which Anergen's board of directors is reasonably expected to
consider a Superior Offer or to recommend a Superior Offer to its stockholders
and together with such notice a copy of the definitive documentation relating to
such Superior Offer.
 
     For purposes of this Agreement, "Acquisition Proposal" shall mean any offer
or proposal (other than an offer or proposal by Corixa) relating to any
Acquisition Transaction. For the purposes of this Agreement, "Acquisition
Transaction" shall mean any transaction or series of related transactions other
than the transactions contemplated in this Agreement involving: (A) any
acquisition or purchase from Anergen by any person or "group" (as defined under
Section 13(d) of the Exchange Act and the rules and regulations thereunder) of
more than a fifteen percent (15%) interest in the total outstanding voting
securities of Anergen or any of its subsidiaries or any tender offer or exchange
offer that if consummated would result in any person or "group" (as defined
under Section 13(d) of the Exchange Act and the rules and regulations
thereunder) beneficially owning fifteen percent (15%) or more of the total
outstanding voting securities of Anergen or any of its subsidiaries or any
merger, consolidation, business combination or similar transaction involving
Anergen pursuant to which the stockholders of Anergen immediately preceding such
transaction hold less than eighty-five percent (85%) of the equity interests in
the surviving or resulting entity of such transaction, (B) any sale, lease
(other than in the ordinary course of business), exchange, transfer, license
(other than in the ordinary course of business), acquisition or disposition of
more than fifty percent (50%) of the assets of Anergen, or (C) any liquidation
or dissolution of Anergen.
 
     (b) In addition to the obligations of Anergen set forth in paragraph (a) of
this Section 5.4, Anergen as promptly as practicable shall advise Corixa orally
and in writing of any request for non-public information which Anergen
reasonably believes would lead to an Acquisition Proposal or of any Acquisition
Proposal, or any inquiry with respect to or which Anergen reasonably should
believe would lead to any Acquisition Proposal, the material terms and
conditions of such request, Acquisition Proposal or inquiry and the identity of
the person or group making any such request, Acquisition Proposal or inquiry.
Anergen will keep Corixa informed in all material respects of the status and
details
 
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<PAGE>   35
 
(including material amendments or proposed amendments) of any such request,
Acquisition Proposal or inquiry.
 
     5.5  Public Disclosure. Corixa and Anergen will consult with each other,
and to the extent practicable, agree, before issuing any press release or
otherwise making any public statement with respect to the Merger, this Agreement
or an Acquisition Proposal and will not issue any such press release or make any
such public statement prior to such consultation, except as may be required by
law or any listing agreement with a national securities exchange. The parties
have agreed to the text of the joint press release announcing the signing of
this Agreement.
 
     5.6  Reasonable Efforts Notification.
 
     (a) Upon the terms and subject to the conditions set forth in this
Agreement, each of the parties agrees to use all commercially reasonable efforts
to take, or cause to be taken, all actions, and to do, or cause to be done, and
to assist and cooperate with the other parties in doing, all things necessary,
proper or advisable to consummate and make effective, in the most expeditious
manner practicable, the Merger and the other transactions contemplated in this
Agreement, including using reasonable efforts to accomplish the following: (i)
the taking of all reasonable acts necessary to cause the conditions precedent
set forth in Article VI to be satisfied, (ii) the obtaining of all necessary
actions or nonactions, waivers, consents, approvals, orders and authorizations
from Governmental Entities and the making of all necessary registrations,
declarations and filings (including registrations, declarations and filings with
Governmental Entities, if any) and the taking of all reasonable steps as may be
necessary to avoid any suit, claim, action, investigation or proceeding by any
Governmental Entity, (iii) the obtaining of all necessary consents, approvals or
waivers from third parties, (iv) the defending of any suits, claims, actions,
investigations or proceedings, whether judicial or administrative, challenging
this Agreement or the consummation of the transactions contemplated herein,
including seeking to have any stay or temporary restraining order entered by any
court or other Governmental Entity vacated or reversed and (v) the execution or
delivery of any additional instruments necessary to consummate the transactions
contemplated in, and to fully carry out the purposes of, this Agreement. In
connection with and without limiting the foregoing, Anergen and its board of
directors shall, if any state takeover statute or similar statute or regulation
is or becomes applicable to the Merger, this Agreement or any of the
transactions contemplated in this Agreement, use all reasonable efforts to
ensure that the Merger and the other transactions contemplated in this Agreement
may be consummated as promptly as practicable on the terms contemplated in this
Agreement and otherwise to minimize the effect of such statute or regulation on
the Merger, this Agreement and the transactions contemplated herein.
Notwithstanding anything herein to the contrary, nothing in this Agreement shall
be deemed to require Corixa or Anergen or any subsidiary or affiliate thereof to
agree to any divestiture by itself or any of its affiliates of shares of capital
stock or of any business, assets or property, or the imposition of any material
limitation on the ability of any of them to conduct their businesses or to own
or exercise control of such assets, properties and stock.
 
     (b) Anergen shall give prompt notice to Corixa of any representation or
warranty made by it contained in this Agreement becoming untrue or inaccurate in
any material respect, or any failure of Anergen to comply with or satisfy in any
material respect any covenant, condition or agreement to be complied with or
satisfied by it under this Agreement, in each case, such that the conditions set
forth in Section 6.3(a) or 6.3(b) would not be satisfied; provided, however,
that no such notification shall affect the
 
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<PAGE>   36
 
representations, warranties, covenants or agreements of the parties or the
conditions to the obligations of the parties under this Agreement.
 
     (c) Corixa shall give prompt notice to Anergen of any representation or
warranty made by it or Merger Sub contained in this Agreement becoming untrue or
inaccurate in any material respect, or any failure of Corixa or Merger Sub to
comply with or satisfy in any material respect any covenant, condition or
agreement to be complied with or satisfied by it under this Agreement, in each
case, such that the conditions set forth in Section 6.2(a) or 6.2(b) would not
be satisfied, provided, however, that no such notification shall affect the
representations, warranties, covenants or agreements of the parties or the
conditions to the obligations of the parties under this Agreement.
 
     5.7  Third Party Consents. As soon as practicable following the date
hereof, Corixa and Anergen will each use its commercially reasonable efforts to
obtain any consents, waivers and approvals under any of its or its subsidiaries'
respective agreements, contracts, licenses or leases required to be obtained in
connection with the consummation of the transactions contemplated herein.
 
     5.8  Stock Options and Employee Benefits.
 
     (a) At the Effective Time, each outstanding option to purchase shares of
Anergen Common Stock (each an "Anergen Stock Option") under the Anergen Stock
Option Plans, whether or not exercisable, will be assumed by Corixa. Each
Anergen Stock Option so assumed by Corixa under this Agreement will continue to
have, and be subject to, the same terms and conditions set forth in the
applicable Anergen Stock Option Plan immediately prior to the Effective Time
(including, without limitation, any repurchase rights or vesting provisions),
except that (i) each Anergen Stock Option will be exercisable (or will become
exercisable in accordance with its terms) for that number of whole shares of
Corixa Common Stock equal to the product of the number of shares of Anergen
Common Stock that were issuable upon exercise of such Anergen Stock Option
immediately prior to the Effective Time multiplied by the Exchange Ratio,
rounded down to the nearest whole number of shares of Corixa Common Stock and
(ii) the per share exercise price for the shares of Corixa Common Stock issuable
upon exercise of such assumed Anergen Stock Option will be equal to the quotient
determined by dividing the exercise price per share of Anergen Common Stock at
which such Anergen Stock Option was exercisable immediately prior to the
Effective Time by the Exchange Ratio, rounded up to the nearest whole cent.
 
     (b) It is intended that Anergen Stock Options assumed by Corixa shall
qualify following the Effective Time as incentive stock options as defined in
Section 422 of the Code to the extent Anergen Stock Options qualified as
incentive stock options immediately prior to the Effective Time and the
provisions of this Section 5.8 shall be applied consistent with such intent.
 
     (c) Rights outstanding under the ESPP shall be treated in a manner
reasonably acceptable to Corixa and Anergen.
 
     5.9  Form S-8. Corixa agrees to file a registration statement on Form S-8
for the shares of Corixa Common Stock issuable with respect to assumed Anergen
Stock Options as soon as is reasonably practicable after the Effective Time and
intends to maintain the effectiveness of such registration statement thereafter
for so long as any of such options or other rights remain outstanding.
 
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<PAGE>   37
 
     5.10  Indemnification.
 
     (a) From and after the Effective Time, Corixa will cause the Surviving
Corporation to fulfill and honor in all respects the obligations of Anergen
pursuant to any indemnification agreements between Anergen and its directors and
officers as of the Effective Time (the "Indemnified Parties") and any
indemnification provisions under Anergen's certificate of incorporation or
bylaws as in effect on the date hereof. The certificate of incorporation and
bylaws of the Surviving Corporation will contain provisions with respect to
exculpation and indemnification that are at least as favorable to the
Indemnified Parties as those contained in the certificate of incorporation and
bylaws of Anergen as in effect on the date hereof, which provisions will not be
amended, repealed or otherwise modified for a period of six (6) years from the
Effective Time in any manner that would adversely affect the rights thereunder
of individuals who, immediately prior to the Effective Time, were directors,
officers, employees or agents of Anergen, unless such modification is required
by law.
 
     (b) For a period of five (5) years after the Effective Time, Corixa will
cause the Surviving Corporation to use its commercially reasonable efforts to
maintain in effect, if available, directors' and officers' liability insurance
covering those persons who are currently covered by Anergen's directors' and
officers' liability insurance policy on terms comparable to those applicable to
the current directors and officers of Anergen; provided, however, that in no
event will Corixa or the Surviving Corporation be required to expend in excess
of one hundred twenty-five percent (125%) of the annual premium currently paid
by Anergen for such coverage (or such coverage as is available for such one
hundred twenty-five percent (125%) of such annual premium).
 
     5.11  Nasdaq Listing. Corixa agrees to authorize for listing on Nasdaq the
shares of Corixa Common Stock issuable, and those required to be reserved for
issuance, in connection with the Merger, upon official notice of issuance.
 
     5.12  Anergen Affiliate Agreements and Voting Agreements. Set forth on the
Anergen Schedules is a list of those persons who may be deemed to be, in
Anergen's reasonable judgment, affiliates of Anergen within the meaning of Rule
145 promulgated under the Securities Act (each a "Anergen Affiliate"). Anergen
will provide Corixa with such information and documents as Corixa reasonably
requests for purposes of reviewing such list. Anergen will use its commercially
reasonable efforts to deliver or cause to be delivered to Corixa, as promptly as
practicable on or immediately following the date hereof, from each Anergen
Affiliate an executed affiliate agreement in substantially the form attached
hereto as Exhibit C (the "Anergen Affiliate Agreement"), and an executed voting
agreement in substantially the form attached hereto as Exhibit A (the "Anergen
Voting Agreement"), each of which will be in full force and effect as of the
Effective Time. Corixa will be entitled to place appropriate legends on the
certificates evidencing any Corixa Common Stock to be received by a Anergen
Affiliate pursuant to the terms of this Agreement, and to issue appropriate stop
transfer instructions to the transfer agent for the Corixa Common Stock,
consistent with the terms of the Anergen Affiliate Agreement.
 
     5.13  Corixa Guarantee of Certain Employment Agreement Benefits. Corixa
shall guarantee the performance by Anergen of all obligations due to Barry
Sherman, M.D. under that certain letter agreement dated December 3, 1998 to the
Employment Agreement of Barry Sherman, M.D., dated as of May 1996, true and
accurate copies of which have been delivered to Corixa by Anergen.
 
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                                   ARTICLE VI
 
                            CONDITIONS TO THE MERGER
 
     6.1  Conditions to Obligations of Each Party to Effect the Merger. The
respective obligations of each party to this Agreement to effect the Merger
shall be subject to the satisfaction at or prior to the Closing Date of the
following conditions:
 
          (a) Anergen Stockholder Approval. This Agreement shall have been
     approved and adopted, and the Merger shall have been duly approved, by the
     requisite vote under applicable law, by the stockholders of Anergen.
 
          (b) Registration Statement Effective; Proxy Statement. The SEC shall
     have declared the Registration Statement effective. No stop order
     suspending the effectiveness of the Registration Statement or any part
     thereof shall have been issued, and no proceeding for that purpose, and no
     similar proceeding in respect of the Proxy Statement/Prospectus, shall have
     been initiated or threatened in writing by the SEC.
 
          (c) No Order. No Governmental Entity shall have enacted, issued,
     promulgated, enforced or entered any statute, rule, regulation, executive
     order, decree, injunction or other order (whether temporary, preliminary or
     permanent) which is in effect and which has the effect of making the Merger
     illegal or otherwise prohibiting consummation of the Merger.
 
          (d) Escrow Fund Agreement. Each of Corixa, Anergen and the Escrow
     Agent shall have executed and delivered the Escrow Fund Agreement.
 
          (e) Nasdaq Listing. The shares of Corixa Common Stock issuable to
     stockholders of Anergen pursuant to this Agreement and such other shares
     required to be reserved for issuance in connection with the Merger shall
     have been authorized for listing on the Nasdaq National Market upon
     official notice of issuance.
 
          (f) Tax Opinion. Corixa shall have received a written opinion from its
     tax counsel, Venture Law Group, a Professional Corporation, and Anergen
     shall have received a written opinion from its tax counsel, Wilson Sonsini
     Goodrich & Rosati, Professional Corporation, to the effect that the Merger
     will constitute a reorganization within the meaning of Section 368(a) of
     the Code and such opinion shall not have been withdrawn; provided, however,
     that if tax counsel to either Corixa or Anergen does not render such
     opinion, this condition will nonetheless be deemed to be satisfied with
     respect to such party if counsel to the other party renders such opinion to
     such party. The parties to this Agreement agree to make such reasonable
     representations as requested by such counsel for the purpose of rendering
     such opinions.
 
     6.2  Additional Conditions to Obligations of Anergen. The obligation of
Anergen to consummate and effect the Merger shall be subject to the satisfaction
at or prior to the Closing Date of each of the following conditions, any of
which may be waived, in writing, exclusively by Anergen:
 
          (a) Representations and Warranties. Each representation and warranty
     of Corixa and Merger Sub contained in this Agreement (i) shall have been
     true and correct as of the date of this Agreement and (ii) shall be true
     and correct on and as of the Closing Date with the same force and effect as
     if made on the Closing Date, except (A) in the case of either clause (i) or
     clause (ii), individually or in the aggregate, as does not constitute a
     Material Adverse Effect on Corixa and Merger Sub, (B) for changes
     contemplated in this Agreement and (C) for those representations and
     warranties which address matters only as of a particular date
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<PAGE>   39
 
     (which representations shall have been true and correct except as does not
     constitute a Material Adverse Effect on Corixa and Merger Sub as of such
     particular date) (it being understood that, for purposes of determining
     whether or not a breach or inaccuracy of a representation or warranty of
     Corixa or Merger Sub contained in this Agreement constitutes a Material
     Adverse Effect as contemplated in Section 6.2(a)(A), (1) all "Material
     Adverse Effect" qualifications and other qualifications based on the word
     "material" or similar phrases contained in such representations and
     warranties shall be disregarded and (2) any update of or modification to
     the Corixa Schedules made or purported to have been made after the date of
     this Agreement shall be disregarded). Anergen shall have received a
     certificate with respect to the foregoing signed on behalf of Corixa and
     Merger Sub by an authorized officer of Corixa and Merger Sub.
 
          (b) Agreements and Covenants. Corixa and Merger Sub shall have
     performed or complied in all material respects with all agreements and
     covenants required by this Agreement to be performed or complied with by
     them on or prior to the Closing Date, and Anergen shall have received a
     certificate to such effect signed on behalf of Corixa and Merger Sub by an
     authorized officer of Corixa and Merger Sub.
 
          (c) Opinion of Corixa's Counsel. Anergen shall have received from
     counsel to Corixa an opinion substantially in the form attached hereto as
     Exhibit D ("Opinion of Counsel to Corixa").
 
          (d) Material Adverse Effect. No Material Adverse Effect with respect
     to Corixa and its subsidiaries shall have occurred since the date of this
     Agreement.
 
     6.3  Additional Conditions to the Obligations of Corixa and Merger Sub. The
obligations of Corixa and Merger Sub to consummate and effect the Merger shall
be subject to the satisfaction at or prior to the Closing Date of each of the
following conditions, any of which may be waived, in writing, exclusively by
Corixa and Merger Sub:
 
          (a) Representations and Warranties. Each representation and warranty
     of Anergen contained in this Agreement (i) shall have been true and correct
     as of the date of this Agreement and (ii) shall be true and correct on and
     as of the Closing Date with the same force and effect as if made on and as
     of the Closing Date, except (A) in the case of either clause (i) or clause
     (ii), individually or in the aggregate, as does not constitute a Material
     Adverse Effect on Anergen (B) for changes contemplated in this Agreement
     and (C) for those representations and warranties which address matters only
     as of a particular date (which representations shall have been true and
     correct except as does not constitute a Material Adverse Effect on Anergen
     as of such particular date) (it being understood that, for purposes of
     determining whether or not a breach or inaccuracy of a representation or
     warranty of Anergen contained in this Agreement constitutes a Materiel
     Adverse Effect as contemplated in Section 6.3(a)(A), (1) all "Material
     Adverse Effect" qualifications and other qualifications based on the word
     "material" or similar phrases contained in such representations and
     warranties shall be disregarded and (2) any update of or modification to
     the Anergen Schedules made or purported to have been made after the date of
     this Agreement shall be disregarded). Corixa shall have received a
     certificate with respect to the foregoing signed on behalf of Anergen by an
     authorized officer of Anergen.
 
          (b) Agreements and Covenants. Anergen shall have performed or complied
     in all material respects with all agreements and covenants required by this
     Agreement to
 
                                      A-39
<PAGE>   40
 
     be performed or complied with by it at or prior to the Closing Date, and
     Corixa shall have received a certificate to such effect signed on behalf of
     Anergen by the Chief Executive Officer and the Chief Financial Officer of
     Anergen.
 
          (c) Material Adverse Effect. No Material Adverse Effect with respect
     to Anergen and its subsidiaries shall have occurred since the date of this
     Agreement.
 
          (d) Consents. Anergen shall have obtained all consents, waivers and
     approvals required in connection with the consummation of the transactions
     contemplated herein in connection with the agreements, contracts, licenses
     or leases set forth on Schedule 6.3(d).
 
          (e) Bridge Investment. Each of Anergen, Warburg, Pincus Ventures, L.P.
     ("WPV"), and International Biotechnology Trust PLC ("IBT") shall have
     executed and delivered that certain Note Purchase Agreement in a form
     reasonably acceptable to counsel to Corixa, and each of Corixa, WPV and IBT
     shall have executed and delivered a Common Stock Purchase Agreement in a
     form reasonably acceptable to counsel to Corixa.
 
          (f) Silicon Valley Bank Loan. Silicon Valley Bank shall not have (i)
     foreclosed on its loan(s) made to Anergen pursuant to that certain Loan and
     Security Agreement, dated as of June 23, 1995, as amended from time to
     time, and taken action to encumber, obtain a lien in respect of, obtain
     title or otherwise take control of (A) any Anergen Intellectual Property,
     (B) equipment utilized in Anergen's research and development efforts or (C)
     cash balances in an aggregate amount exceeding Two Hundred Fifty Thousand
     Dollars ($250,000) or (ii) exercised legal remedies which (x) cause Anergen
     to seek voluntary relief under Chapter 7 or 11 of the United State
     Bankruptcy Code (the "Bankruptcy Code"), (y) have placed Anergen
     involuntarily in a proceeding under Chapter 7 or 11 under the Bankruptcy
     Code or (z) cause Anergen to become insolvent i.e., unable to meet its
     current obligations as such obligations become due.
 
          (g) Opinion of Anergen's Counsel. Corixa shall have received from
     counsel to Anergen an opinion substantially in the form attached hereto as
     Exhibit E ("Opinion of Counsel to Anergen").
 
          (h) Note Purchase Agreement. Silicon Valley Bank shall have executed
     and delivered that certain Note Purchase Agreement dated as of December 11,
     1998, by and between Anergen, Warburg, Pincus Ventures, L.P., International
     Biotechnology Trust PLC and Silicon Valley Bank.
 
                                  ARTICLE VII
 
                       TERMINATION, AMENDMENT AND WAIVER
 
     7.1 Termination. This Agreement may be terminated at any time prior to the
Effective Time, whether before or after the requisite approvals of the
stockholders of Anergen or Corixa:
 
          (a) by mutual written consent duly authorized by the boards of
     directors of Corixa and Anergen;
 
          (b) by either Anergen or Corixa if the Merger shall not have been
     consummated by February 15, 1999 (or March 31, 1999, in the event that the
     SEC has notified the parties that the Proxy Statement/Prospectus will be
     reviewed by the SEC for any
 
                                      A-40
<PAGE>   41
 
     reason); provided, however, that the right to terminate this Agreement
     under this Section 7.1(b) shall not be available to any party whose action
     or failure to act has been a principal cause of or resulted in the failure
     of the Merger to occur on or before such date and such action or failure to
     act constitutes a breach of this Agreement;
 
          (c) by either Anergen or Corixa if a Governmental Entity shall have
     issued an order, decree or ruling or taken any other action, in any case
     having the effect of permanently restraining, enjoining or otherwise
     prohibiting the Merger, which order, decree, ruling or other action is
     final and nonappealable;
 
          (d) by either Anergen or Corixa if the required approval of the
     stockholders of Anergen contemplated in this Agreement shall not have been
     obtained by reason of the failure to obtain the required vote at a meeting
     of Anergen stockholders duly convened therefor or at any adjournment
     thereof (provided that the right to terminate this Agreement under this
     Section 7.1(d) shall not be available to Anergen where the failure to
     obtain Anergen stockholder approval shall have been caused by the action or
     failure to act of Anergen and such action or failure to act constitutes a
     breach by Anergen of this Agreement);
 
          (e) by Corixa or Anergen (at any time prior to the adoption and
     approval of this Agreement and the Merger by the required vote of the
     stockholders of Anergen) if a Triggering Event (as defined below) shall
     have occurred;
 
          (f) by Corixa (at any time prior to the adoption and approval of this
     Agreement and the Merger by the required vote of the stockholders of
     Anergen) if a Termination Event (as defined below) shall have occurred;
 
          (g) by Anergen, upon a breach of any representation, warranty,
     covenant or agreement on the part of Corixa set forth in this Agreement, or
     if any representation or warranty of Corixa shall have become untrue, in
     either case such that the conditions set forth in Section 6.2(a) or Section
     6.2(b) would not be satisfied as of the time of such breach or as of the
     time such representation or warranty shall have become untrue; provided,
     however, that if such inaccuracy in Corixa's representations and warranties
     or breach by Corixa is curable by Corixa through the exercise of its
     commercially reasonable efforts, then Anergen may not terminate this
     Agreement under this Section 7.1(g) for ten (10) days after delivery of
     written notice from Anergen to Corixa of such breach; and provided further,
     however, Corixa continues to exercise commercially reasonable efforts to
     cure such breach (it being understood that Anergen may not terminate this
     Agreement pursuant to this paragraph (g) if it shall have materially
     breached this Agreement or if such breach by Corixa is cured during such
     ten (10) day period); or
 
          (h) by Corixa, upon a breach of any representation, warranty, covenant
     or agreement on the part of Anergen set forth in this Agreement, or if any
     representation or warranty of Anergen shall have become untrue, in either
     case such that the conditions set forth in Section 6.3(a) or Section 6.3(b)
     would not be satisfied as of the time of such breach or as of the time such
     representation or warranty shall have become untrue; provided, however,
     that if such inaccuracy in Anergen's representations and warranties or
     breach by Anergen is curable by Anergen through the exercise of its
     commercially reasonable efforts, then Corixa may not terminate this
     Agreement under this Section 7.1(h) for ten (10) days after delivery of
     written notice from Corixa to Anergen of such breach, and provided further,
     however, Anergen continues to exercise commercially reasonable efforts to
     cure such breach (it being
 
                                      A-41
<PAGE>   42
 
     understood that Corixa may not terminate this Agreement pursuant to this
     paragraph (h) if it shall have materially breached this Agreement or if
     such breach by Anergen is cured during such ten (10) day period).
 
     For the purposes of this Agreement, a "Termination Event" shall be deemed
to occur if Anergen shall not have used commercially reasonable efforts to hold
the Anergen Stockholders' Meeting as promptly as practicable and in any event
within the later of (A) the Anergen Stockholders' Meeting Period or (B) fifteen
(15) days after any amendments or supplement to the Proxy Statement/Prospectus
are mailed to stockholders of Anergen.
 
     For the purposes of this Agreement, a "Triggering Event" shall be deemed to
have occurred if: (i) Anergen's board of directors or any committee thereof
shall for any reason have withdrawn or shall have amended or modified in a
manner adverse to Corixa its unanimous recommendation in favor of the adoption
and approval of this Agreement or the approval of the Merger, (ii) Anergen shall
have failed to include in the Proxy Statement/ Prospectus the unanimous
recommendation of Anergen's board of directors in favor of the adoption and
approval of the Agreement and the approval of the Merger, (iii) Anergen's board
of directors fails to reaffirm its unanimous recommendation in favor of the
adoption and approval of the Agreement and the approval of the Merger within
seven (7) calendar days after Corixa requests in writing that such
recommendation be reaffirmed at any time following the public announcement of an
Acquisition Proposal, (iv) Anergen's board of directors or any committee thereof
shall have approved or publicly recommended any Acquisition Proposal, (v)
Anergen shall have entered into any letter of intent or similar document or any
agreement, contract or commitment accepting any Acquisition Proposal or (vi) a
tender or exchange offer relating to securities of Anergen shall have been
commenced by a Person unaffiliated with Corixa and Anergen shall not have sent
to its securityholders pursuant to Rule 14e-2 promulgated under the Securities
Act, within ten (10) business days after such tender or exchange offer is first
published sent or given, a statement disclosing that Anergen recommends
rejection of such tender or exchange offer.
 
     7.2  Notice of Termination Effect of Termination. Any termination of this
Agreement under Section 7.1 above will be effective immediately upon the
delivery of written notice of the terminating party to the other parties hereto.
In the event of the termination of this Agreement as provided in Section 7.1,
this Agreement shall be of no further force or effect, except (i) as set forth
in this Section 7.2, Section 7.3 and Article VIII (Miscellaneous), each of which
shall survive the termination of this Agreement and (ii) nothing herein shall
relieve any party from liability for any willful breach of this Agreement. No
termination of this Agreement shall affect the obligations of the parties
contained in the Confidentiality Agreement, all of which obligations shall
survive termination of this Agreement in accordance with their terms.
 
     7.3  Fees and Expenses.
 
     (a) General. Except as set forth in this Section 7.3, all fees and expenses
incurred in connection with this Agreement and the transactions contemplated
herein shall be paid by the party incurring such fees and expenses whether or
not the Merger is consummated; provided, however, that Corixa shall pay all fees
and expenses, other than attorneys', accountants' and fairness opinion fees and
expenses, incurred in relation to the printing and filing (with the SEC) of the
Proxy Statement/Prospectus (including any preliminary materials related thereto)
and the Registration Statement (including financial statements and exhibits) and
any amendments or supplements thereto; and provided further, however, that (i)
any legal fees and expenses of Anergen exceeding One Hundred Thousand Dollars
 
                                      A-42
<PAGE>   43
 
($100,000), any accounting fees and expenses of Anergen exceeding Fifty Thousand
Dollars ($50,000), and any investment banking fees for Anergen's fairness
opinion exceeding One Hundred Thousand Dollars ($100,00), shall be deemed
expenses of Anergen's stockholders and not Anergen.
 
     (b) Anergen Payments. In the event that this Agreement is terminated by
Corixa or Anergen, as applicable, pursuant to (i) Section 7.1(d), (e) or (f),
Anergen shall promptly, but in no event later than five (5) business days after
the date of such termination, pay Corixa a fee equal to Four Hundred Thousand
Dollars ($400,000) in immediately available funds (the "Termination Fee") or
(ii) Section 7.1(h), Anergen shall promptly but in no event later than five (5)
business days after the date of such termination, pay Corixa a fee equal to Two
Hundred Thousand Dollars ($200,000) in immediately available funds (the "M.A.E.
Termination Fee"); provided, however, that the Termination Fee shall not be due
if in the case of termination under Section 7.1(d), the failure to obtain the
required stockholder approval is primarily the result of a Material Adverse
Effect on Corixa. Anergen acknowledges and agrees that the agreements contained
in this Section 7.3(b) are an integral part of the transactions contemplated in
this Agreement, and that, without these agreements, Corixa would not enter into
this Agreement; accordingly, if Anergen fails promptly to pay the amounts due
pursuant to this Section 7.3(b), and, in order to obtain such payment, Corixa
commences a suit which results in a judgment against Anergen for the amounts set
forth in this Section 7.3(b), Anergen shall pay to Corixa its reasonable costs
and expenses (including reasonable attorneys' fees and expenses) in connection
with such suit, together with interest on the amounts set forth in this Section
7.3(b) at the prime rate of The Chase Manhattan Bank in effect on the date such
payment was required to be made.
 
     (c) Payment of the fees described in Section 7.3(b) above shall not be in
lieu of damages incurred in the event of willful breach of this Agreement.
 
     7.4  Amendment. Subject to applicable law, this Agreement may be amended by
the parties hereto at any time by execution of an instrument in writing signed
on behalf of each of Corixa and Anergen.
 
     7.5  Extension; Waiver. At any time prior to the Effective Time any party
hereto may, to the extent legally allowed, (a) extend the time for the
performance of any of the obligations or other acts of the other parties hereto,
(b) waive any inaccuracies in the representations and warranties made to such
party contained herein or in any document delivered pursuant hereto and (c)
waive compliance with any of the agreements or conditions for the benefit of
such party contained herein. Any agreement on the part of a party hereto to any
such extension or waiver shall be valid only if set forth in an instrument in
writing signed on behalf of such party. Delay in exercising any right under this
Agreement shall not constitute a waiver of such right.
 
                                  ARTICLE VIII
 
                               GENERAL PROVISIONS
 
     8.1  Non-Survival of Representations and Warranties. The representations
and warranties of Anergen, Corixa and Merger Sub contained in this Agreement
shall terminate at the Effective Time, and only the covenants that by their
terms survive the Effective Time shall survive the Effective Time.
 
                                      A-43
<PAGE>   44
 
     8.2  Notices. All notices and other communications hereunder shall be in
writing and shall be deemed given if delivered personally or by commercial
delivery service, or sent via telecopy (receipt confirmed) to the parties at the
following addresses or telecopy numbers (or at such other address or telecopy
numbers for a party as shall be specified by like notice):
 
     (a) if to Corixa or Merger Sub, to:
 
         Corixa Corporation
         1124 Columbia Street
         Seattle, Washington 98104
         Attention: Steven Gillis, Ph.D., President and Chief Executive Officer
         Telephone No.: (206) 754-5711
         Telecopy No.: (206) 754-5994
 
         with a copy to:
 
         Venture Law Group
         A Professional Corporation
         4750 Carillon Point
         Kirkland, Washington 98033-7355
         Attention: William W. Ericson
         Telephone No.: (425) 739-8731
         Telecopy No.: (425) 739-8750
 
     (b) if to Anergen, to:
 
         Anergen Inc.
         301 Penobscot Drive
         Redwood City, California 94063
         Attention: Barry Sherman, M.D., President
         Telephone No.: (650) 361-8901
         Telecopy No.: (650) 361-8958
 
         with a copy to:
 
         Wilson Sonsini Goodrich & Rosati
         Professional Corporation
         650 Page Mill Road
         Palo Alto, California 94304-1050
         Attention: Barry Taylor, Esq.
         Telephone No.: (650) 493-9300
         Telecopy No.: (650) 493-6811
 
     8.3  Interpretation Knowledge.
 
     (a) When a reference is made in this Agreement to Exhibits, such reference
shall be to an Exhibit to this Agreement unless otherwise indicated. When a
reference is made in this Agreement to Sections, such reference shall be to a
Section of this Agreement unless otherwise indicated the words "include,"
"includes" and "including" when used herein shall be deemed in each case to be
followed by the words "without limitations." The table of contents and headings
contained in this Agreement are for reference purposes only and shall not affect
in any way the meaning or interpretation of this Agreement. When reference is
made herein to "the business of" an entity, such reference shall be deemed to
include the business of all direct and indirect subsidiaries of such entity.
Reference to the
 
                                      A-44
<PAGE>   45
 
subsidiaries of an entity shall be deemed to include all direct and indirect
subsidiaries of such entity.
 
     (b) For purposes of this Agreement the term "knowledge" means with respect
to a Anergen, with respect to any matter in question, that any of the President
and Chief Executive Officer, Chief Financial Officer, Controller, the Vice
President of Research, the Vice President of Clinical Development and the Vice
President of Pharmaceutical Development of Anergen, has actual knowledge of such
matter, and with respect to Corixa, with respect to any matter in question, that
any of the President and Chief Executive Officer, Chief Operating Officer, Chief
Financial Officer and the General Counsel of Corixa, has actual knowledge of
such matter.
 
     (c) For purposes of this Agreement, the term "Material Adverse Effect" when
used in connection with an entity means any change, event, violation,
inaccuracy, circumstance or effect that is materially adverse to the business,
assets (including intangible assets), capitalization, financial condition or
results of operations of such entity and its subsidiaries taken as a whole,
except for those changes, events, violations, inaccuracies, circumstances and
effects that (i) are caused by conditions affecting the United States economy as
a whole or affecting the industry in which such entity competes as a whole,
which conditions do not affect such entity in a disproportionate manner, or (ii)
are related to or result from announcement or pendency of the Merger or (iii)
with respect to Anergen result from continued losses and declines in the cash
balances of Anergen which occur in the ordinary course of business and as
reasonably contemplated in the business plans of Anergen delivered by Anergen to
Corixa, which include but are not limited to, any disputes with or actions
undertaken by current creditors of Anergen as disclosed on the Anergen
Schedules.
 
     (d) For purposes of this Agreement, the term "person" shall mean any
individual, corporation (including any non-profit corporation), general
partnership, limited partnership, limited liability partnership, joint venture,
estate, trust, Anergen or Corixa, as applicable, (including any limited
liability Anergen or Corixa, as applicable, or joint stock Anergen or Corixa, as
applicable), firm or other enterprise, association, organization, entity or
Governmental Entity.
 
     8.4  Counterparts. This Agreement may be executed in one or more
counterparts, all of which shall be considered one and the same agreement and
shall become effective when one or more counterparts have been signed by each of
the parties and delivered to the other party, it being understood that all
parties need not sign the same counterpart.
 
     8.5  Entire Agreement; Third Party Beneficiaries. This Agreement and the
documents and instruments and other agreements among the parties hereto as
contemplated by or referred to herein, including the Anergen Schedules and the
Corixa Schedules (a) constitute the entire agreement among the parties with
respect to the subject matter hereof and supersede all prior agreements and
understandings, both written and oral, among the parties with respect to the
subject matter hereof, it being understood that the Confidentiality Agreement
shall continue in full force and effect until the Closing and shall survive any
termination of this Agreement; and (b) are not intended to confer upon any other
person any rights or remedies hereunder except as otherwise provided in Section
5.10.
 
     8.6  Severability. In the event that any provision of this Agreement or the
application thereof, becomes or is declared by a court of competent jurisdiction
to be illegal, void or unenforceable, the remainder of this Agreement will
continue in lull force and effect and the application of such provision to other
persons or circumstances will be
 
                                      A-45
<PAGE>   46
 
interpreted so as reasonably to effect the intent of the parties hereto. The
parties further agree to replace such void or unenforceable provision of this
Agreement with a valid and enforceable provision that will achieve, to the
extent possible, the economic, business and other purposes of such void or
unenforceable provision.
 
     8.7  Other Remedies; Specific Performance. Except as otherwise provided
herein, any and all remedies herein expressly conferred upon a party will be
deemed cumulative with and not exclusive of any other remedy conferred hereby,
or by law or equity upon such party, and the exercise by a party of any one
remedy will not preclude the exercise of any other remedy. The parties hereto
agree that irreparable damage would occur in the event that any of the
provisions of this Agreement were not performed in accordance with their
specific terms or were otherwise breached. It is accordingly agreed that the
parties shall be entitled to seek an injunction or injunctions to prevent
breaches of this Agreement and to enforce specifically the terms and provisions
hereof in any court of the United States or any state having jurisdiction, this
being in addition to any other remedy to which they are entitled at law or in
equity.
 
     8.8  Governing Law. This Agreement shall be governed by and construed in
accordance with the laws of the State of Delaware, regardless of the laws that
might otherwise govern under applicable principles of conflicts of law thereof;
provided, however, that issues involving the corporate governance of any of the
parties hereto shall be governed by their respective jurisdictions of
incorporation. Each of the parties hereto irrevocably consents to the exclusive
jurisdiction of any state or federal court within the Western District of
Washington, in connection with any matter based upon or arising out of this
Agreement or the matters contemplated herein, other than issues involving the
corporate governance of any of the parties hereto, agrees that process may be
served upon them in any manner authorized by the laws of the State of Washington
for such persons and waives and covenants not to assert or plead any objection
which they might otherwise have to such jurisdiction and such process.
 
     8.9  Rules of Construction. The parties hereto agree that they have been
represented by counsel during the negotiation and execution of this Agreement
and, therefore, waive the application of any law, regulation, holding or rule of
construction providing that ambiguities in an agreement or other document will
be construed against the party drafting such agreement or document.
 
     8.10  Assignment. No party may assign either this Agreement or any of its
rights, interests, or obligations hereunder without the prior written approval
of the other parties. Subject to the preceding sentence, this Agreement shall be
binding upon and shall inure to the benefit of the parties hereto and their
respective successors and permitted assigns.
 
     8.11  WAIVER OF JURY TRIAL. EACH OF CORIXA, ANERGEN AND MERGER SUB HEREBY
IRREVOCABLY WAIVES ALL RIGHT TO TRIAL BY JURY IN ANY ACTION, PROCEEDING OR
COUNTERCLAIM (WHETHER BASED ON CONTRACT, TORT OR OTHERWISE) ARISING OUT OF OR
RELATING TO THIS AGREEMENT OR THE ACTIONS OF CORIXA, ANERGEN OR MERGER SUB IN
THE NEGOTIATION, ADMINISTRATION, PERFORMANCE AND ENFORCEMENT HEREOF.
 
                                      A-46
<PAGE>   47
 
     IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be
executed by their duly authorized respective officers as of the date first
written above.
 
                                          CORIXA CORPORATION,
                                          a Delaware corporation
 
                                          By:
 
                                          Name:
 
                                          Title:
 
                                          YAKIMA ACQUISITION CORPORATION,
                                          a Delaware corporation
 
                                          By:
 
                                          Name:
 
                                          Title:
 
                                          ANERGEN, INC.,
                                          a Delaware corporation
 
                                          By:
 
                                          Name:
 
                                          Title:
 
                                      A-47

<PAGE>   1
 
                                   EXHIBIT A
 
                                 ANERGEN, INC.
 
                                VOTING AGREEMENT
 
     This Voting Agreement (this "Voting Agreement") is made and entered into as
of December 11, 1998, by and between Corixa Corporation, a Delaware corporation
("Acquiror"), and the undersigned stockholder ("Holder") of Anergen, Inc., a
Delaware corporation ("Target").
 
                                    RECITALS
 
     Pursuant to an Agreement and Plan of Reorganization dated as of December
11, 1998 (the "Reorganization Agreement") by and among Acquiror, Yakima
Acquisition Corporation, a Delaware corporation and wholly-owned subsidiary of
Acquiror ("Sub"), and Target, Sub is merging with and into Target (the
"Acquisition") and Target, as the surviving corporation of the Acquisition, will
thereby become a wholly-owned subsidiary of Acquiror. Pursuant to Section 6.2(f)
of the Reorganization Agreement, Target has agreed to cause certain significant
stockholders of Target to execute and deliver to Acquiror voting agreements in
the form hereof. The Holder is the beneficial owner (as defined in Rule 13d-3
under the Securities Exchange Act of 1934, as amended (the "Exchange Act")) of
such number of shares of the outstanding capital stock and all rights, warrants
and options to acquire shares of capital stock of Target as is indicated on the
final page of this Voting Agreement (the "Shares").
 
     In consideration of the execution of the Reorganization Agreement by
Acquiror, Holder agrees not to transfer or otherwise dispose of any of the
Shares, or any other shares of capital stock of Target acquired by Holder
hereafter and prior to the Expiration Date (as defined in Section 1(a) below),
and agrees to vote the Shares and any other such shares of capital stock of
Target in favor of and so as to facilitate consummation of the Acquisition.
 
                                   AGREEMENT
 
     The parties agree as follows:
 
     1. Agreement to Retain Shares.
 
     (a) Transfer and Encumbrance. Holder agrees not to transfer (except as may
be specifically required by court order), sell, exchange, pledge (except in
connection with a bona fide loan transaction, provided that any pledgee agrees
not to transfer, sell, exchange, pledge or otherwise dispose of or encumber the
Shares or any New Shares (as defined in Section 1(b)) prior to the Expiration
Date and also agrees to be subject to the Proxy (as defined in Section 3)), or
otherwise dispose of or encumber the Shares or any New Shares, or to make any
offer or agreement relating thereto, at any time prior to the Expiration Date.
As used herein, the term "Expiration Date" shall mean the earlier to occur of
(i) such date and time as the Acquisition shall become effective in accordance
with the terms and provisions of the Reorganization Agreement, and (ii) upon the
termination of the Reorganization Agreement pursuant to its terms.
 
     (b) New Shares. Until the Expiration Date, Holder agrees that any shares of
capital stock of Target that Holder purchases or with respect to which Holder
otherwise acquires beneficial ownership after the date of this Voting Agreement
and prior to the Expiration
 
                                      A-48
<PAGE>   2
 
Date ("New Shares") shall be subject to the terms and conditions of this Voting
Agreement to the same extent as if they constituted Shares.
 
     (c) Superior Offer. In the event that (A) Target's board of directors
approves, and recommends that Target's stockholders approve, a Superior Offer
(as defined in the Reorganization Agreement), (B) Target's board of directors
provides written notice of such approval and recommendation to Acquiror and (C)
Target has paid in full Acqurior the Termination Fee (as defined in the
Reorganization Agreement), Holder's obligations under this Voting Agreement
shall immediately terminate.
 
     2. Agreement to Vote Shares. Until the Expiration Date, at every meeting of
the stockholders of Target called with respect to any of the following, and at
every adjournment thereof, and on every action or approval by written consent of
the stockholders of Target with respect to any of the following, Holder shall
vote the Shares and any New Shares (a) in favor of approval of the
Reorganization Agreement and the Acquisition and any matter that could
reasonably be expected to facilitate the Acquisition, and (b) against any
proposal for any recapitalization, merger, sale of assets or other business
combination (other than the Acquisition) between Target and any person or entity
other than Acquiror or any other action or agreement that would result in a
breach of any covenant, representation or warranty or any other obligation or
agreement of Target under the Reorganization Agreement or which could result in
any of the conditions to Target's obligations under the Reorganization Agreement
not being fulfilled. This Voting Agreement is intended to bind Holder as a
stockholder of Target only with respect to the specific matters set forth
herein.
 
     3. Irrevocable Proxy. Until the Expiration Date, concurrently with the
execution of this Voting Agreement, Holder agrees to deliver to Acquiror a proxy
in the form attached hereto as Exhibit A (the "Proxy"), which shall be
irrevocable (until the Expiration Date) to the extent provided in Section 212 of
the Delaware General Corporation Law, covering the total number of Shares and
New Shares beneficially owned or as to which beneficial ownership is acquired
(as such term is defined in Rule 13d-3 under the Exchange Act) by Holder set
forth therein.
 
     4. Representations, Warranties and Covenants of Holder. Holder hereby
represents, warrants and covenants to Acquiror that Holder (a) is the beneficial
owner of the Shares, which at the date of this Voting Agreement and at all times
up until the Expiration Date will be free and clear of any liens, claims,
options, charges or other encumbrances, (b) does not beneficially own any shares
of capital stock of Target other than the Shares (excluding shares as to which
Holder currently disclaims beneficial ownership in accordance with applicable
law) and (c) has full power and authority to make, enter into and carry out the
terms of this Voting Agreement and the Proxy.
 
     5. Additional Documents. Holder hereby covenants and agrees to execute and
deliver any additional documents necessary or desirable, in the reasonable
opinion of Acquiror, to carry out the purpose and intent of this Voting
Agreement.
 
     6. Consent and Waiver. Holder hereby gives any consents or waivers that are
reasonably required for the consummation of the Acquisition under the terms of
any agreement to which Holder is a party or pursuant to any rights Holder may
have.
 
     7. Termination. This Voting Agreement and the Proxy delivered in connection
herewith shall terminate and shall have no further force or effect as of the
Expiration Date.
 
                                      A-49
<PAGE>   3
 
     8. Miscellaneous.
 
     (a) Amendments and Waivers. Any term of this Voting Agreement may be
amended or waived with the written consent of the parties or their respective
successors and assigns. Any amendment or waiver effected in accordance with this
Section 8(a) shall be binding upon the parties and their respective successors
and assigns.
 
     (b) Governing Law. This Voting Agreement and all acts and transactions
pursuant hereto and the rights and obligations of the parties hereto shall be
governed, construed and interpreted in accordance with the laws of the State of
Delaware, without giving effect to principles of conflicts of law.
 
     (c) Counterparts. This Voting 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.
 
     (d) Titles and Subtitles. The titles and subtitles used in this Voting
Agreement are used for convenience only and are not to be considered in
construing or interpreting this Voting Agreement.
 
     (e) Notices. Any notice required or permitted by this Voting Agreement
shall be in writing and shall be deemed sufficient upon receipt, when delivered
personally or by courier, overnight delivery service or confirmed facsimile, or
forty-eight (48) hours after being deposited in the regular mail as certified or
registered mail (airmail if sent internationally) with postage prepaid, if such
notice is addressed to the party to be notified at such party's address or
facsimile number as set forth on the final page of this Voting Agreement, or as
subsequently modified by written notice.
 
     (f) Severability. If one or more provisions of this Voting Agreement are
held to be unenforceable under applicable law, the parties agree to renegotiate
such provision in good faith, in order to maintain the economic position enjoyed
by each party as close as possible to that under the provision rendered
unenforceable. In the event that the parties cannot reach a mutually agreeable
and enforceable replacement for such provision, then (i) such provision shall be
excluded from this Voting Agreement, (ii) the balance of this Voting Agreement
shall be interpreted as if such provision were so excluded and (iii) the balance
of this Voting Agreement shall be enforceable in accordance with its terms.
 
     (g) Attorneys' Fees. Should suit be brought to enforce or interpret any
part of this Voting Agreement, the prevailing party will be entitled to recover,
as an element of the costs of suit and not as damages, reasonable attorneys'
fees to be fixed by the court (including without limitation, costs, expenses and
fees on any appeal). The prevailing party will be entitled to recover its costs
of suit proceeds to final judgment.
 
     (h) Specific Performance; Injunctive Relief. The parties hereto acknowledge
and agree that Acquiror will be irreparably harmed and that there will be no
adequate remedy at law for a violation of any of the covenants or agreements of
Stockholder set forth herein. Therefore, the parties acknowledge and agree that,
in addition to any other remedies that may be available to Acquiror upon any
such violation, Acquiror shall have the right to enforce such covenants and
agreements by specific performance, injunctive relief or by any other means
available to Acquiror at law or in equity.
 
                                      A-50
<PAGE>   4
 
     The parties have caused this Voting Agreement to be duly executed on the
date first above written.
 
                                          "ACQUIROR"
 
                                          CORIXA CORPORATION,
                                          a Delaware corporation
 
                                          By:
                                          --------------------------------------
 
                                          Name:
                                          --------------------------------------
                                                            (print)
 
                                          Title:
                                          --------------------------------------
 
                                          Address:
                                          --------------------------------------
 
                                                --------------------------------
 
                                          Facsimile:
                                          --------------------------------------
 
                                          "HOLDER"
 
                                          By:
                                          --------------------------------------
 
                                          Name:
                                          --------------------------------------
                                                            (print)
 
                                          Title:
                                          --------------------------------------
 
                                          Holder's Address for Notice:
 
                                          --------------------------------------
 
                                          --------------------------------------
 
                                          --------------------------------------
 
                                          Facsimile:
                                          --------------------------------------
 
                                          Shares beneficially owned:
 
                                                         shares of Common Stock
                                                         of Anergen, Inc.
 
                                                         shares of Common Stock
                                                         of Anergen, Inc.
                                                         issuable upon exercise
                                                         of outstanding options
                                                         and warrants
 
                                      A-51
<PAGE>   5
 
                                   EXHIBIT A
 
                               IRREVOCABLE PROXY
                                TO VOTE STOCK OF
                                 ANERGEN, INC.
 
     Subject to the terms of that certain Voting Agreement, dated as of December
11, 1998, by and between Acquiror (as defined below) and Stockholder (as defined
below), (the "Voting Agreement") the undersigned stockholder ("Stockholder") of
Anergen, Inc., a Delaware corporation ("Target"), hereby irrevocably (to the
full extent permitted by Section 212 of the Delaware General Corporation Law)
appoints the members of the board of directors of Corixa Corporation, a Delaware
corporation ("Acquiror"), and each of them, as the sole and exclusive attorneys
and proxies of the undersigned, with full power of substitution and
resubstitution, to vote and exercise all voting and related rights (to the full
extent that the undersigned is entitled to do so) with respect to all of the
shares of capital stock of Target that now are or hereafter may be beneficially
owned by the undersigned, and any and all other shares or securities of Target
issued or issuable in respect thereof on or after the date hereof (collectively,
the "Shares") in accordance with the terms of this Proxy. The Shares
beneficially owned by the undersigned stockholder of Target as of the date of
this Proxy are listed on the final page of this Proxy. Upon the undersigned's
execution of this Proxy, any and all prior proxies given by the undersigned with
respect to any Shares are hereby revoked and the undersigned agrees not to grant
any subsequent proxies with respect to the Shares until after the earlier to
occur of (i) the Expiration Date (as defined below) and (ii) Superior Offer
Event (as defined below).
 
     This Proxy is irrevocable (to the extent permitted by Section 212 of the
Delaware General Corporation Law) is granted pursuant to that certain Voting
Agreement of even date herewith, by and among Acquiror and the undersigned
stockholder (the "Voting Agreement"), and is granted in consideration of
Acquiror entering into that certain Agreement and Plan of Reorganization, of
even date herewith, by and among Target, Acquiror and Yakima Acquisition
Corporation, a Delaware corporation ("Sub") and wholly-owned subsidiary of
Acquiror (the "Reorganization Agreement"). The Agreement provides for the merger
of Sub with and into Target (the "Acquisition"). As used herein, the term
"Expiration Date" shall mean the earlier to occur of (i) such date and time as
the Acquisition shall become effective in accordance with the terms and
provisions of the Reorganization Agreement and (ii) upon termination of the
Reorganization Agreement pursuant to its terms. As used herein, the term
"Superior Offer Event" shall mean the determination of Target's board of
directors to accept an unsolicited, bona fide written offer made by a third
party to consummate any of the following transactions: (1) a merger,
consolidation, business combination, recapitalization, liquidation, dissolution
or similar transaction involving Target's pursuant to which the stockholders of
Target immediately preceding such transaction hold less than fifty percent (50%)
of the equity interest in the surviving or resulting entity of such transaction,
(2) a sale or other disposition by Target of assets (excluding inventory and
used equipment sold in the ordinary course of business) representing in excess
of fifty percent (50%) of the fair market value of Target's business immediately
prior to such sale, (3) the acquisition by any person or group (including by way
of a tender offer or an exchange offer or issuance by Target), directly or
indirectly, of beneficial ownership or a right to acquire beneficial ownership
of shares representing in excess of fifty percent (50%) of the voting power of
the then-outstanding shares of capital stock of the Target or (4) any public
announcement of a proposal, plan or intention to do any of the foregoing or any
agreement to engage in any of the foregoing, on terms that Target's board of
directors determines, in its judgment consistent with applicable corporate
 
                                      A-52
<PAGE>   6
 
law, after consultation with its financial advisor, is reasonably likely to be
financially superior to the Target stockholders than the terms of the Merger.
 
     Subject to the terms of the Voting Agreement, the attorneys and proxies
named above, and each of them, are hereby authorized and empowered by the
undersigned, at any time prior to the Expiration Date, to act as the
undersigned's attorney and proxy to vote the Shares, and to exercise all voting
and other rights of the undersigned with respect to the Shares (including,
without limitation, the power to execute and deliver written consents pursuant
to Section 228 of the Delaware General Corporation Law), at every annual,
special or adjourned meeting of the stockholders of Target and in every written
consent in lieu of such meeting (i) in favor of approval of the Acquisition and
the Merger Agreement and in favor of any matter that could reasonably be
expected to facilitate the Acquisition, and (ii) against any proposal for any
recapitalization, merger, sale of assets or other business combination (other
than the Acquisition) between Target and any person or entity other than
Acquiror or any other action or agreement that would result in a breach of any
covenant, representation or warranty or any other obligation or agreement of
Target under the Merger Agreement or which could result in any of the conditions
to Target's obligations under the Merger Agreement not being fulfilled. The
attorneys and proxies named above may not exercise this Proxy on any other
matter except as provided above. The undersigned stockholder may vote the Shares
on all other matters.
 
     Any obligation of the undersigned hereunder shall be binding upon the
successors and assigns of the undersigned.
 
     This Proxy is irrevocable (to the extent provided in Section 212 of the
Delaware General Corporation Law) subject to the limitations set forth in the
Voting Agreement.
 
Dated: December 11, 1998
 
                                                  (Signature of Holder)
 
                                                  (Print Name of Holder)
 
                                          Shares beneficially owned:
 
                                                    Shares of Common Stock of
                                                    Anergen Inc. owned by Holder
                                                    as of the date of this
                                                    Voting Agreement
 
                                                    Shares of Common Stock of
                                                    Anergen, Inc. issuable upon
                                                    exercise or conversion of
                                                    outstanding options,
                                                    warrants or other securities
                                                    owned by Holder as of the
                                                    date of this Voting
                                                    Agreement
 
                                      A-53


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