<PAGE>
                                   APPENDIX C

                          PLAN OF ARRANGEMENT INCLUDING
                            SPECIAL SHARE PROVISIONS
<PAGE>

                                TABLE OF CONTENTS

                                                                            Page

                                    ARTICLE 1
                                 INTERPRETATION

1.1   Definitions............................................................1
1.2   Sections and Headings..................................................4
1.3   Number, Gender and Persons.............................................5

                                    ARTICLE 2
                                   ARRANGEMENT

2.1   Binding Effect.........................................................5
2.2   Arrangement............................................................5
2.3   Elections..............................................................6

                                    ARTICLE 3
                       CERTIFICATES AND FRACTIONAL SHARES

3.1   Issuance of Certificates Representing Company Special Shares...........7
3.2   Distributions with Respect to Unsurrendered Certificates...............8
3.3   Lost Certificates......................................................8
3.4   Extinction of Rights...................................................8
3.5   Withholding Rights.....................................................9

                                    ARTICLE 4
       CERTAIN RIGHTS OF ABGENIX CANADA TO ACQUIRE COMPANY SPECIAL SHARES

4.1   Abgenix Canada Liquidation Call Right..................................9
4.2   Abgenix Canada Redemption Call Right..................................11
4.3   No Fractional Abgenix Common Shares...................................12

                                    ARTICLE 5
                                   AMENDMENTS

5.1   Amendments to Plan of Arrangement.....................................13

                                    ARTICLE 6
                               FURTHER ASSURANCES

6.1   Further Assurances....................................................13


                                       -i-
<PAGE>

                               PLAN OF ARRANGEMENT
                                UNDER SECTION 252
                      OF THE COMPANY ACT (BRITISH COLUMBIA)

                                    ARTICLE 1
                                 INTERPRETATION

1.1 Definitions

In this Plan of Arrangement, unless there is something in the subject matter or
context inconsistent therewith, the following terms shall have the respective
meanings set out below and grammatical variations of such terms shall have
corresponding meanings:

"Acquisition Agreement" means the agreement made as of the 25th day of
September, 2000 among the Company, Abgenix Canada and Abgenix, as amended,
supplemented and/or restated in accordance therewith prior to the Effective
Date, providing for, among other things, the Arrangement;

"Abgenix" means Abgenix, Inc., a corporation existing under the laws of the
State of Delaware;

"Abgenix Canada" means Abgenix Canada Corporation, an unlimited liability
company existing under the laws of the Province of Nova Scotia;

"Abgenix Common Shares" means the common shares in the capital of Abgenix;

"Abgenix Stock Price" shall be equal to the average of the closing prices of one
Abgenix Common Share, as quoted on NASDAQ, for the five (5) trading days ending
on the Business Day before the SEC Effective Date;

"Arrangement" means an arrangement under section 252 of the BC Act on the terms
and subject to the conditions set out in this Plan of Arrangement, subject to
any amendments or variations thereto made in accordance with section 7.4 of the
Acquisition Agreement or Article 5 or made at the direction of the Court in the
Final Order;

"Arrangement Resolutions" means the special resolutions of the Company
Securityholders;

"BC Act" means the Company Act (British Columbia), as amended;

"Business Day" means any day other than a Saturday or Sunday or any day on which
commercial banks located in each of the Province of British Columbia, the State
of California and the State of Delaware are authorized or obligated to close.

"Canadian Resident" means a resident of Canada for purposes of the ITA;

"Circular" means the notice of the Company Meeting and accompanying management
information circular, including all appendices thereto, to be sent to the
Company Securityholders in connection with the Company Meeting;

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                                      -2-


"Company" means ImmGenics Pharmaceuticals Inc., a corporation existing under the
laws of British Columbia;

"Company Class A Shares" means the Class A preferred shares without par value in
the capital of the Company outstanding from time to time;

"Company Class B Shares" means the Class B preferred shares with a par value of
CDN$1.00 per share in the capital of the Company outstanding from time to time;

"Company Common Shares" means the outstanding common shares in the capital of
the Company;

"Company Convertible Debenture" means that certain debenture convertible into
343,595 shares of Company Class A Shares held by Corixa Corporation;

"Company Fully Diluted Shares" shall be the aggregate number of Company Special
Shares outstanding as of the Effective Date, plus the aggregate number of
Company Common Shares that would have been purchasable upon exercise of all
Company Options that are vested as of the Closing Date (after giving effect to
the acceleration of such Company Options contemplated hereby) were such Company
Options not replaced in accordance with the terms of the Option Replacement
Agreement;

"Company Meeting" means the special meetings of the Company Securityholders,
including any adjournment thereof, to be called and held in accordance with the
Interim Order to consider the Arrangement;

"Company Options" means the Company Common Share purchase options granted under
the Company Stock Option Plan, as amended, and under separate agreements with
one senior officer of the Company, and being outstanding and unexercised on the
Effective Date;

"Company Securities" means the Company Common Shares and any other securities
issued by the Company which are converted into Company Common Shares under or
pursuant to the Arrangement;

"Company Securityholders" means the holders of Company Common Shares, Company
Class A Shares and Company Class B Shares, the Company Options and the Company
Convertible Debenture, collectively;

"Company Special Shares" means the non-voting shares in the capital of the
Company, having substantially the rights, privileges, restrictions and
conditions set out in the Special Share Provisions;

"Company Stock Option Plan" means the Company's 1996 Stock Option Plan;

"Court" means the Supreme Court of British Columbia;

"Current Market Price" has the meaning ascribed thereto in the Special Share
Provisions;

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                                      -3-


"Dividend Amount" means an amount equal to and in satisfaction of all declared
and unpaid dividends on a Company Special Share held by a holder on any dividend
record date which occurred prior to the date of exchange of such share for
Abgenix Common Shares;

"Drop Dead Date" means December 1, 2000, or such later date as may be mutually
agreed by the parties to the Arrangement Agreement;

"Effective Date" means the date on which the Final Order is filed with and
accepted by the Registrar, provided that such date occurs on or prior to the
Drop Dead Date;

"Effective Time" means 12:01 a.m. (Vancouver time) on the Effective Date;

"Exchange Ratio" means the ratio of Abgenix Common Shares deliverable on
exchange of each Company Special Share that will be delivered for each Company
Common Share pursuant to the Recapitalization, which will be determined on the
SEC Effective Date. The "Exchange Ratio" shall be equal to the Purchase Price
per Share divided by the Abgenix Stock Price;

"Final Order" means the final order of the Court approving the Arrangement;

"Governmental Entity" means any (a) multinational, federal, provincial, state,
regional, municipal, local or other government, governmental or public
department, court or tribunal, domestic or foreign, (b) any subdivision,
arbitral body, commission, board, bureau, agency or authority of any of the
foregoing, or (c) any quasi-governmental or private body exercising any
regulatory, expropriation or taxing authority under or for the account of any of
the foregoing;

"holders" means, when used with reference to any class of Company Securities,
the holders of Company Securities shown from time to time in the register
maintained by or on behalf of the Company in respect of those Company
Securities;

"Interim Order" means the interim order of the Court, as the same may be
amended, in respect of the Arrangement, as contemplated by section 2.3 of the
Acquisition Agreement;

"ITA" means the Income Tax Act (Canada), as amended;

"Liquidation Amount" has the meaning ascribed thereto in the Special Share
Provisions;

"Liquidation Call Purchase Price" has the meaning ascribed thereto in section
4.1(a);

"Liquidation Call Right" has the meaning ascribed thereto in section 4.1(a);

"Liquidation Date" has the meaning ascribed thereto in the Special Share
Provisions;

"Meeting Date" means the date of the Company Meeting;

"NASDAQ" means the Nasdaq National Market;

<PAGE>
                                      -4-


"Person" includes any individual, firm, partnership, joint venture, venture
capital fund, limited liability company, unlimited liability company,
association, trust, trustee, executor, administrator, legal personal
representative, estate, group, body corporate, corporation, unincorporated
association or organization, Governmental Entity, syndicate or other entity,
whether or not having legal status;

"Purchase Price per Share" means seventy-five million United States dollars
(US$75,000,000) plus the aggregate exercise price of all vested Company Options
to be replaced on the Closing Date and then divided by the number of Company
Fully Diluted Shares as of the Closing Date;

"Redemption Call Purchase Price" has the meaning ascribed thereto in section
4.2(a);

"Redemption Call Right" has the meaning ascribed thereto in section 4.2(a);

"Redemption Date" has the meaning ascribed thereto in the Special Share
Provisions;

"Registrar" means the Registrar of Companies appointed pursuant to section 320
of the BC Act;

"SEC Effective Date" means the date on which the registration statement on Form
S-1 (or S-3, as the case may be) filed by Abgenix with the United States
Securities and Exchange Commission in connection with the issuance of Abgenix
Common Shares upon exchange of the Company Special Shares becomes effective;

"Special Share Provisions" means the rights, privileges, restrictions and
conditions attaching to the Company Special Shares, which rights, privileges,
restrictions and conditions shall be substantially as set out in Appendix 1
hereto;

"Transfer Agent" means the transfer agent of the Company Special Shares;

"Trustee" means the trustee to be chosen by Abgenix and the Company, acting
reasonably, to act as trustee under the Voting, Exchange and Cash Put Trust
Agreement, being a corporation organized and existing under the laws of Canada
and authorized to carry on the business of a trust company in all of the
provinces of Canada, and any successor trustee appointed under the Voting,
Exchange and Cash Put Trust Agreement; and

"Voting, Exchange and Cash Put Trust Agreement" means an agreement to be made
between Abgenix, the Company and the Trustee in connection with the Plan of
Arrangement substantially in the form and content of Exhibit E annexed to the
Acquisition Agreement, with such changes thereto as the parties to the
Acquisition Agreement, acting reasonably, may agree.

1.2 Sections and Headings

The division of this Plan of Arrangement into sections and the insertion of
headings are for reference purposes only and shall not affect the interpretation
of this Plan of Arrangement. Unless otherwise indicated any reference in this
Plan of Arrangement to a section or an exhibit refers to the specified section
of or exhibit to this Plan of Arrangement.

<PAGE>
                                      -5-


1.3 Number, Gender and Persons

In this Plan of Arrangement, unless the context otherwise requires, words
importing the singular number include the plural and vice versa and words
importing any gender include all genders.

                                    ARTICLE 2
                                   ARRANGEMENT

2.1 Binding Effect

This Plan of Arrangement will become effective at, and be binding at and after,
the Effective Time on (i) the Company, (ii) all holders and all beneficial
holders of Company Common Shares, (iii) all holders and all beneficial holders
of Company Options, (iv) all holders and all beneficial holders of the Company
Class A Shares, (v) all holders and all beneficial holders of Company Class B
Shares, (vi) the holder of the Company Convertible Debenture, (vii) Abgenix and
(viii) Abgenix Canada.

2.2 Arrangement

Commencing at the Effective Time, the following shall occur and shall be deemed
to occur in the following order without any further act or formality:

      (a)   the Memorandum of the Company is altered by increasing the Company's
            authorized capital to consist of 500,000,000 shares divided into (i)
            100,000,000 common shares without par value; (ii) 100,000,000 Class
            A preferred shares without par value; (iii) 100,000,000 Class B
            preferred shares with a par value of CDN$1.00; (iv) 100,000,000
            Special Shares without par value; and (v) 100,000,000 Ordinary
            Shares without par value;

      (b)   the Articles of the Company be amended by adding the Special Rights
            and Restrictions Attached to the Special Shares, as set forth in
            Schedule A;

      (c)   the Articles of the Company be amended by adding the Special Rights
            and Restrictions Attached to the Ordinary Shares, as set forth in
            Schedule B;

      (d)   the Company Convertible Debenture shall be converted into 343,595
            Company Class A Shares in accordance with its terms;

      (e)   each of the Company Class A Shares shall be converted into one
            Company Common Share;

      (f)   each of the Company Class B Shares shall be converted into one
            Company Common Share;

      (g)   each Company Common Share shall be redesignated as a Company Special
            Share;

<PAGE>
                                      -6-


      (h)   each Company Option shall be exchanged for an option under the
            Abgenix 1999 Non-statutory Stock Option Plan (a "Replacement
            Option") to purchase a number of Abgenix Common Shares equal to the
            product of the Exchange Ratio multiplied by the number of Company
            Common Shares subject to such Company Option. Such Replacement
            Option shall provide for an exercise price per Abgenix Common Share
            equal to the exercise price per share of such Company Option
            immediately prior to the Effective Time divided by the Exchange
            Ratio. If the foregoing calculation results in a Replacement Option
            being exercisable for a fraction of an Abgenix Common Share, then
            the number of Abgenix Common Shares subject to such Replacement
            Option shall be rounded down to the next whole number of Abgenix
            Common Shares and the total exercise price for the Replacement
            Option will be reduced by the exercise price of the fractional
            Abgenix Common Shares. Such Replacement Option shall not be
            exercisable until the SEC Effective Date;

      (i)   the Memorandum of the Company is altered to decrease the Company's
            authorized capital to consist of 200,000,000 shares divided into (i)
            100,000,000 Special Shares without par value; and (ii) 100,000,000
            Ordinary Shares without par value;

      (j)   the Articles of the Company be amended by deleting Article 27,
            Special Rights and Restrictions attaching to the Class A Preferred
            Shares;

      (k)   the Articles of the Company be amended by deleting Article 28,
            Special Rights and Restrictions attaching to the Class B Preferred
            Shares;

      (l)   the Memorandum of the Company, after giving effect to the foregoing
            provisions of this Plan of Arrangement, shall be in the form
            attached as Schedule C;

      (m)   the Articles of the Company, after giving effect to the foregoing
            provisions of this Plan of Arrangement, shall be in the form
            attached as Schedule D;

      (n)   Abgenix shall issue to and deposit with the Trustee the Special
            Voting Share, in consideration of the payment to Abgenix of US$1.00,
            to be thereafter held of record by the Trustee as trustee for and on
            behalf of, and for the use and benefit of, the holders of the
            Company Special Shares in accordance with the Voting, Exchange and
            Cash Put Trust Agreement; and

      (o)   the Company shall issue 20,000,000 Ordinary Shares to Abgenix Canada
            for an aggregate purchase price of $20 pursuant to and in accordance
            with the Acquisition Agreement.

2.3 Elections

Holders of Company Common Shares, shall be entitled to make an income tax
election pursuant to subsection 85 (1) of the ITA or, if the holder is a
partnership, subsection 85 (2) of the ITA

<PAGE>
                                      -7-


(and in each case, where applicable, the analogous provisions of provincial
income tax law) with respect to the redesignation of their Company Common Shares
to Company Special Shares by providing two signed copies of the necessary
prescribed election forms to the Company within ninety (90) days following the
Effective Date, duly completed with the details of the number of Company Common
Shares redesignated and the applicable agreed amounts for the purposes of such
elections. Thereafter, subject to the election forms being correct and complete
and complying with the provisions of the ITA (or applicable provincial income
tax law), the forms will be signed by the Company and returned to such holders
of Company Common Shares within thirty (30) days after the receipt thereof by
the Company for filing with Canada Customs and Revenue Agency (or the applicable
provincial taxing authority). The Company will not be responsible for the proper
completion of any election form and, except for the Company's obligation to
return duly completed election forms which are received by the Company within
ninety (90) days of the Effective Date, within thirty (30) days after the
receipt thereof by the Company, the Company will not be responsible for any
taxes, interest or penalties resulting from the failure by a holder of Company
Common Shares to properly complete or file the election forms in the form and
manner and within the time prescribed by the ITA (or any applicable provincial
legislation). In its sole discretion, the Company may choose to sign and return
an election form received more than ninety (90) days following the Effective
Date, but the Company will have no obligation to do so.

                                    ARTICLE 3
                       CERTIFICATES AND FRACTIONAL SHARES

3.1 Issuance of Certificates Representing Company Special Shares

At or promptly after the Effective Time, the Company shall deposit with the
Transfer Agent at its registered office, for the benefit of the holders of
Company Common Shares who will receive Company Special Shares in connection with
the Arrangement, certificates representing that number of whole Company Special
Shares to be delivered pursuant to section 2.2 upon the redesignation of Company
Common Shares. Upon surrender to the Company for cancellation of a certificate
which immediately prior to the Effective Time represented Company Common Shares
that were redesignated as Company Special Shares under the Arrangement, together
with such other documents and instruments as would have been required to effect
the transfer of the shares formerly represented by such certificate under the BC
Act and the articles of the Company and such additional documents and
instruments as the Company may reasonably require, the holder of such
surrendered certificate shall be entitled to receive in exchange therefor, and
the Company shall deliver to such holder, a certificate representing that number
of Company Special Shares which such holder has the right to receive (together
with any dividends or distributions with respect thereto pursuant to section
3.2, less any amounts withheld pursuant to section 3.5 hereof), and the
certificate so surrendered shall forthwith be cancelled. In the event of a
transfer of ownership of Company Securities that is not registered in the
transfer records of the Company, a certificate representing the proper number of
Company Special Shares may be issued to the transferee if the certificate
representing such Company Securities is presented to the Company, accompanied by
all documents required to evidence and effect such transfer. Until surrendered
as contemplated by this section 3.1, each certificate which immediately prior to
the Effective Time

<PAGE>
                                      -8-


represented Company Securities shall be deemed at all times after the Effective
Time to represent only the right to receive upon such surrender (i) the
certificate representing Company Special Shares as contemplated by this section
3.1, and (ii) any dividends or distributions with a record date after the
Effective Time theretofore paid or payable with respect to Company Special
Shares as contemplated by section 3.2.

3.2 Distributions with Respect to Unsurrendered Certificates

No dividends or other distributions declared or made after the Effective Time
with respect to Company Special Shares with a record date after the Effective
Time shall be paid to the holder of any unsurrendered certificate which
immediately prior to the Effective Time represented outstanding Company
Securities, and no interest shall be earned or payable on these proceeds unless
and until the holder of such certificate shall surrender such certificate in
accordance with section 3.1. Subject to applicable law, at the time of such
surrender of any such certificate (or, in the case of clause (ii) below, at the
appropriate payment date), there shall be paid to the holder of the certificates
representing Company Securities without interest, (i) the amount of dividends or
other distributions with a record date after the Effective Time theretofore paid
with respect to the Company Special Shares to which such holder is entitled
pursuant hereto and (ii) on the appropriate payment date, the amount of
dividends or other distributions with a record date after the Effective Time but
prior to surrender and a payment date subsequent to surrender payable with
respect to such Company Special Shares.

3.3 Lost Certificates

In the event any certificate which immediately prior to the Effective Time
represented one or more outstanding Company Securities shall have been lost,
stolen or destroyed, upon the making of an affidavit of that fact by the Person
claiming such certificate to be lost, stolen or destroyed, the Company will
deliver in exchange for such lost, stolen or destroyed certificate one or more
certificates representing one or more Company Special Shares (and any dividends
or distributions with respect thereto) deliverable in accordance with such
holder's instructions. When authorizing such payment in exchange for any lost,
stolen or destroyed certificate, the Person to whom certificates representing
Company Special Shares are to be delivered shall, as a condition precedent to
the delivery thereof, give a bond satisfactory to the Company and its transfer
agents in such sum as the Company may direct or otherwise indemnify the Company
and Abgenix in a manner satisfactory to the Company against any claim that may
be made against the Company with respect to the certificate alleged to have been
lost, stolen or destroyed.

3.4 Extinction of Rights

Any certificate which immediately prior to the Effective Time represented
outstanding Company Securities that is not deposited with all other instruments
required by section 3.1 on or prior to the date of the notice referred to in
section 6(2) of the Special Share Provisions shall cease to represent a claim or
interest of any kind or nature as a shareholder of the Company. On such date,
the Company Special Shares to which the former holder of the certificate
referred to in the preceding sentence was ultimately entitled shall be deemed to
have been surrendered for no consideration to the Company together with all
entitlements to dividends, distributions and

<PAGE>
                                      -9-


interest in respect thereof held for such former holder. None of the Company,
Abgenix or Abgenix Canada shall be liable to any person in respect of any
Company Special Shares (or dividends, distributions and interest in respect
thereof) delivered to a public official pursuant to any applicable abandoned
property, escheat or similar law.

3.5 Withholding Rights

The Company, Abgenix and Abgenix Canada shall be entitled to deduct and withhold
from any dividend or consideration otherwise payable to any holder of Company
Securities or Company Special Shares such amounts as the Company, Abgenix or
Abgenix Canada is required or permitted to deduct and withhold with respect to
such payment under the ITA, the United States Internal Revenue Code of 1986 or
any provision of provincial, state, local or foreign tax law, in each case, as
amended. To the extent that amounts are so withheld, such withheld amounts shall
be treated for all purposes hereof as having been paid to the holder of the
securities in respect of which such deduction and withholding was made, provided
that such withheld amounts are actually remitted to the appropriate taxing
authority. To the extent that the amount so required to be deducted or withheld
from any payment to a holder exceeds the cash portion of the consideration
otherwise payable to the holder, the Company, Abgenix Canada and Abgenix are
hereby authorized to sell or otherwise dispose of such portion of the
consideration as is necessary to provide sufficient funds to the Company,
Abgenix Canada or Abgenix, as the case may be, to enable it to comply with such
deduction or withholding requirement and the Company, Abgenix Canada or Abgenix
shall notify the holder thereof and remit any unapplied balance of the net
proceeds of such sale.

                                    ARTICLE 4
                   CERTAIN RIGHTS OF ABGENIX CANADA TO ACQUIRE
                             COMPANY SPECIAL SHARES

4.1 Abgenix Canada Liquidation Call Right

      (a)   Abgenix Canada shall have the overriding right (the "Liquidation
            Call Right"), in the event of and notwithstanding the proposed
            liquidation, dissolution or winding-up of the Company, to purchase
            from all but not less than all of the holders of Company Special
            Shares (other than any holder of Company Special Shares which is an
            affiliate of Abgenix) on the Liquidation Date all but not less than
            all of the Company Special Shares held by each such holder on
            payment by Abgenix Canada of an amount per share (the "Liquidation
            Call Purchase Price") equal to the Current Market Price of an
            Abgenix Common Share on the last Business Day prior to the
            Liquidation Date multiplied by the Exchange Ratio, which shall be
            satisfied in full by Abgenix Canada causing to be delivered to such
            holder such number of Abgenix Common Shares calculated in accordance
            with the Exchange Ratio for each Company Special Share held by such
            holder, plus any Dividend Amount. In the event of the exercise of
            the Liquidation Call Right by Abgenix Canada each holder shall be
            obligated to sell all the Company Special Shares held by the holder
            to Abgenix Canada on the Liquidation Date on payment by Abgenix
            Canada to the holder of the Liquidation Call Purchase Price for each
            such share,

<PAGE>
                                      -10-


            and the Company shall have no obligation to pay any Liquidation
            Amount to the holders of such shares so purchased by Abgenix Canada.

      (b)   To exercise the Liquidation Call Right, Abgenix Canada must notify
            the holders of Company Special Shares, and the Company of Abgenix
            Canada's intention to exercise such right at least forty-five (45)
            days before the Liquidation Date in the case of a voluntary
            liquidation, dissolution or winding-up of the Company and at least
            five (5) Business Days before the Liquidation Date in the case of an
            involuntary liquidation, dissolution or winding-up of the Company.
            If Abgenix Canada exercises the Liquidation Call Right, then on the
            Liquidation Date Abgenix Canada will purchase and the holders will
            sell all of the Company Special Shares then outstanding for a price
            per share equal to the Liquidation Call Purchase Price.

      (c)   For the purposes of completing the purchase of the Company Special
            Shares pursuant to the Liquidation Call Right, Abgenix Canada shall
            deposit with the Transfer Agent, on or before the Liquidation Date,
            certificates representing the aggregate number of Abgenix Common
            Shares deliverable by Abgenix Canada and a cheque or cheques of
            Abgenix Canada payable at par at any branch of the bankers of
            Abgenix Canada representing the aggregate Dividend Amount, if any,
            in payment of the total Liquidation Call Purchase Price, less any
            amounts withheld pursuant to section 3.5 hereof. Provided that
            Abgenix Canada has complied with the immediately preceding sentence,
            on and after the Liquidation Date the rights of each holder of
            Company Special Shares will be limited to receiving such holder's
            proportionate part of the total Liquidation Call Purchase Price
            payable by Abgenix Canada upon presentation and surrender by the
            holder of certificates representing the Company Special Shares held
            by such holder and the holder shall on and after the Liquidation
            Date be considered and deemed for all purposes to be the holder of
            the Abgenix Common Shares to which it is entitled. Upon surrender to
            the Transfer Agent of a certificate or certificates representing
            Company Special Shares, together with such other documents and
            instruments as may be required to effect a transfer of Company
            Special Shares under the governing corporate statute and the
            articles of the Company and such additional documents and
            instruments as the Transfer Agent may reasonably require, the holder
            of such surrendered certificate or certificates shall be entitled to
            receive in exchange therefor, and the Transfer Agent on behalf of
            Abgenix Canada shall deliver to such holder, certificates
            representing the Abgenix Common Shares to which the holder is
            entitled and a cheque or cheques of Abgenix Canada payable at par at
            any branch of the bankers of Abgenix Canada in payment of the
            remaining portion, if any, of the total Liquidation Call Purchase
            Price, less any amounts withheld pursuant to section 3.5 hereof. If
            Abgenix Canada does not exercise the Liquidation Call Right in the
            manner described above, on the Liquidation Date the holders of the
            Company Special Shares will be entitled to receive in exchange
            therefor the Liquidation Amount otherwise

<PAGE>
                                      -11-


            payable by the Company in connection with the liquidation,
            dissolution or winding-up of the Company pursuant to Article 5 of
            the Special Share Provisions.

4.2 Abgenix Canada Redemption Call Right

In addition to Abgenix Canada's rights contained in the Special Share
Provisions, including, without limitation, the Retraction Call Right (as defined
in the Special Share Provisions), Abgenix Canada shall have the following rights
in respect of the Company Special Shares:

      (a)   Abgenix Canada shall have the overriding right (the "Redemption Call
            Right"), notwithstanding the proposed redemption of the Company
            Special Shares by the Company pursuant to Section 6(2) of the
            Special Share Provisions, to purchase from all but not less than all
            of the holders of Company Special Shares (other than any holder of
            Company Special Shares which is an affiliate of Abgenix) on the
            Redemption Date all but not less than all of the Company Special
            Shares held by each such holder on payment by Abgenix to each holder
            of an amount per Company Special Share (the "Redemption Call
            Purchase Price") equal to the Current Market Price of an Abgenix
            Common Share on the last Business Day prior to the Redemption Date
            multiplied by the Exchange Ratio, which shall be satisfied in full
            by Abgenix Canada causing to be delivered to such holder such number
            of Abgenix Common Shares calculated in accordance with the Exchange
            Ratio for each Special Share held by such holder, plus any Dividend
            Amount. In the event of the exercise of the Redemption Call Right by
            Abgenix Canada each holder shall be obligated to sell all the
            Company Special Shares held by the holder to Abgenix Canada on the
            Redemption Date on payment by Abgenix Canada to the holder of the
            Redemption Call Purchase Price for each such share, and the Company
            shall have no obligation to redeem, or to pay any Dividend Amount in
            respect of, such shares so purchased by Abgenix Canada.

      (b)   To exercise the Redemption Call Right, Abgenix Canada must notify
            the Transfer Agent, as agent for the holders of Company Special
            Shares, and the Company of Abgenix Canada's intention to exercise
            such right at least sixty (60) days before the Redemption Date,
            except in the case of a redemption occurring as a result of a
            Abgenix Control Transaction, an Exchangeable Share Voting Event or
            an Exempt Exchangeable Share Voting Event (each as defined in the
            Special Share Provisions), in which case Abgenix Canada shall so
            notify the Transfer Agent and the Company on or before the
            Redemption Date. The Transfer Agent will notify the holders of the
            Company Special Shares as to whether or not Abgenix Canada has
            exercised the Redemption Call Right forthwith after the expiry of
            the period during which the same may be exercised by Abgenix Canada.
            If Abgenix Canada exercises the Redemption Call Right, on the
            Redemption Date Abgenix Canada will purchase and the holders will
            sell all of the Company Special Shares then outstanding for a price
            per share equal to the Redemption Call Purchase Price.

      (c)   For the purposes of completing the purchase of the Company Special
            Shares pursuant to the Redemption Call Right, Abgenix Canada shall
            deposit with the

<PAGE>
                                      -12-


            Transfer Agent, on or before the Redemption Date, certificates
            representing the aggregate number of Abgenix Common Shares
            deliverable by Abgenix Canada and a cheque or cheques of Abgenix
            Canada payable at par at any branch of the bankers of Abgenix Canada
            representing the aggregate Dividend Amount, if any, in payment of
            the total Redemption Call Purchase Price, less any amounts withheld
            pursuant to section 3.5 hereof. Provided that Abgenix Canada has
            complied with the immediately preceding sentence, on and after the
            Redemption Date the rights of each holder of Company Special Shares
            will be limited to receiving such holder's proportionate part of the
            total Redemption Call Purchase Price payable by Abgenix Canada upon
            presentation and surrender by the holder of certificates
            representing the Company Special Shares held by such holder and the
            holder shall on and after the Redemption Date be considered and
            deemed for all purposes to be the holder of the Abgenix Common
            Shares to which it is entitled. Upon surrender to the Transfer Agent
            of a certificate or certificates representing Company Special
            Shares, together with such other documents and instruments as may be
            required to effect a transfer of Company Special Shares under the
            governing corporate statute and the articles of the Company and such
            additional documents and instruments as the Transfer Agent may
            reasonably require, the holder of such surrendered certificate or
            certificates shall be entitled to receive in exchange therefor, and
            the Transfer Agent on behalf of Abgenix Canada shall deliver to such
            holder, certificates representing the Abgenix Common Shares to which
            the holder is entitled and a cheque or cheques of Abgenix Canada
            payable at par at any branch of the bankers of Abgenix Canada in
            payment of the remaining portion, if any, of the total Redemption
            Call Purchase Price, less any amounts withheld pursuant to section
            3.5 hereof. If Abgenix Canada does not exercise the Redemption Call
            Right in the manner described above, on the Redemption Date the
            holders of the Company Special Shares will be entitled to receive in
            exchange therefor the redemption price otherwise payable by the
            Company in connection with the redemption of the Company Special
            Shares pursuant to Section 7 of the Special Share Provisions.

4.3 No Fractional Abgenix Common Shares

No fraction of an Abgenix Common Share will be delivered in connection with the
exercise of the Liquidation Call Right or the Redemption Call Right by Abgenix
Canada. In lieu thereof any holder of Company Special Shares who would otherwise
be entitled to receive a fraction of an Abgenix Common Share (after aggregating
all fractional Abgenix Common Shares that would otherwise be received by such
holder) shall receive from Abgenix Canada an amount of cash (rounded to the
nearest cent) without interest, equal to the product of (x) such fraction and
(y) the Current Market Price of an Abgenix Common Share.

<PAGE>
                                      -13-


                                    ARTICLE 5
                                   AMENDMENTS

5.1 Amendments to Plan of Arrangement

The Company reserves the right to amend, modify and/or supplement this Plan of
Arrangement at any time and from time to time prior to the Effective Date,
provided that each such amendment, modification and/or supplement must be (i)
set out in writing, (ii) approved by Abgenix, (iii) filed with the Court and, if
made following the Company Meeting, approved by the Court and (iv) communicated
to holders of Company Common Shares, the Company Class A Shares, the Company
Class B Shares, the Company Convertible Debenture and the Company Options if and
as required by the Court.

Any amendment, modification or supplement to this Plan of Arrangement may be
proposed by the Company at any time prior to the Company Meeting (provided that
Abgenix shall have consented thereto) with or without any other prior notice or
communication, and if so proposed and accepted by the Persons voting at the
Company Meeting (other than as may be required under the Interim Order), shall
become a part of this Plan of Arrangement for all purposes.

Any amendment, modification or supplement to this Plan of Arrangement that is
approved by the Court following the Company Meeting shall be effective only if
(i) it is consented to by each of the Company and Abgenix and (ii) if required
by the Court, it is consented to by holders of the Company Common Shares, the
Company Class A Shares, the Company Class B Shares, the Company Convertible
Debenture and the Company Options voting in the manner directed by the Court.

Any amendment, modification or supplement to this Plan of Arrangement may be
made following the Effective Date unilaterally by the Company, provided that it
concerns a matter which, in the reasonable opinion of Company, is of an
administrative nature required to better give effect to the implementation of
this Plan of Arrangement and is not adverse to the financial or economic
interests of any Company Securityholder.

                                    ARTICLE 6
                               FURTHER ASSURANCES

6.1 Further Assurances

Notwithstanding that the transactions and events set out herein shall occur and
be deemed to occur in the order set out in this Plan of Arrangement without any
further act or formality, each of the parties to the Acquisition Agreement shall
make, do and execute, or cause to be made, done and executed, all such further
acts, deeds, agreements, transfers, assurances, instruments or documents as may
reasonably be required by any of them in order further to document or evidence
any of the transactions or events set out herein.

<PAGE>

                                   SCHEDULE A

                               Special Share Terms

<PAGE>

                                   SCHEDULE B

                              Ordinary Share Terms

                         SPECIAL RIGHTS AND RESTRICTIONS
                                 ATTACHED TO THE
                                 ORDINARY SHARES

The Ordinary Shares shall have the following rights, privileges, restrictions
and conditions:

30.1 For the purposes of these share provisions:

      "Ordinary Shares" means the ordinary shares of the Company to which will
      be attached the rights, privileges, restrictions and conditions as set
      forth herein;

      "Special Shares" mean the special shares in the capital of the Company,
      having the rights, privileges, restrictions and conditions set forth at
      Article 29;

30.2 The Ordinary Shares shall rank junior to the Special Shares with respect to
the payment of dividends and the distribution of assets in the event of the
liquidation, dissolution or winding-up of the Company, whether voluntary or
involuntary, or any other distribution of the assets of the Company, among its
members for the purpose of winding up its affairs.

30.3 The Ordinary Shares will entitle holders to one vote for each Ordinary
Share held at all meetings of members except meetings at which only holders of
another specified class of shares are entitled to vote.

30.4  The Ordinary Shares will entitle holders:

      (a)   to receive, subject to the rights of the holders of other classes of
            shares of the Company, any dividend declared by the Board; and

      (b)   to receive, also subject to the rights on holders of other classes
            of shares of the Company, the remaining property of the Company upon
            its liquidation, dissolution or winding up, whether voluntary or
            involuntary.
<PAGE>

                                   SCHEDULE C

                               Altered Memorandum

                       (As altered by Plan of Arrangement)

                                       OF

                         IMMGENICS PHARMACEUTICALS INC.

1.    The name of the Company is ImmGenics Pharmaceuticals Inc.

2.    The authorized capital of the Company consists of 200,000,000 shares
      divided into:

      (a)   100,000,000 Special Shares without par value; and

      (b)   100,000,000 Ordinary Shares without par value.

3.    The rights and restrictions attached to the classes of shares in the
      capital of the Company are as set out in the articles of the Company.
<PAGE>

                                   SCHEDULE D

                                Altered Articles