Document:

[*] indicates that a confidential portion of the text of this agreement has been
omitted.

AMENDMENT NUMBER ONE TO TECHNOLOGY ACQUISITION AGREEMENT

     THIS AMENDMENT NUMBER ONE TO TECHNOLOGY ACQUISITION AGREEMENT is entered
into as of December 8, 1999, by and between XOMA (US) LLC ("XOMA") and Connetics
Corporation ("Connetics" or "CT").

     A.   XOMA (under the name "XOMA Corporation") and Connetics (under the name
          "Connective Therapeutics, Inc.") are parties to a Technology
          Acquisition Agreement effective as of June 3, 1994 (the
          "XOMA/Connetics Agreement"), and an Assignment and Assumption
          Agreement effective as of June 3, 1994, pursuant to which XOMA
          assigned to Connetics and Connetics assumed XOMA's rights and
          obligations under that certain Research Collaboration and License
          Agreement between XOMA and Dr. Arthur A. Vandenbark ("Vandenbark")
          effective February 27, 1990 (the "1990 Research Agreement") and that
          certain License Agreement between XOMA and Vandenbark effective
          February 27, 1990 (the "1990 License Agreement") (collectively, the
          "Assigned Agreements").

     B.   Connetics desires to assign all of its rights, title and interest in
          and to the Agreements to The Immune Response Corporation ("IRC") and
          XOMA is willing to agree to such assignment.

     C.   Prior to assuming Connetics' obligations under the Assigned
          Agreements, IRC has requested that certain amendments be made to the
          Assigned Agreements, and XOMA and Connetics agree to such changes in
          return for consideration from IRC.

     NOW, THEREFORE XOMA and Connetics hereby agree as follows:

                                    AGREEMENT

     Section 1. Section 1 of the XOMA/Connetics Agreement is hereby amended to
add the following sections:

<PAGE>
                                      -2-

          1.23 "Affiliate" shall mean, with respect to any Person, any other
     Person which directly or indirectly controls, is controlled by, or is under
     common control with, such Person. A Person shall be regarded as in control
     of another Person if it owns, or directly or indirectly controls, greater
     than fifty percent (50%) of the voting stock or other ownership interest of
     the other Person, or if it directly or indirectly possesses the power to
     direct or cause the direction of the management and policies of the other
     Person by any means whatsoever.

          1.24 "New Drug Application" or "NDA" shall mean a New Drug
     Application, as defined in the U.S. Food, Drug and Cosmetic Act and its
     regulations promulgated thereunder, and any corresponding foreign
     application, registration or certification.

          1.25 "Pivotal Trial" shall mean a clinical trial that is designed to
     provide data establishing the safety and efficacy of a Product in support
     of an NDA, PLA or BLA.

          1.26 "Product License Application" or "PLA" shall mean a Product
     License Application, as defined in the U.S. Food, Drug and Cosmetic Act and
     the regulations promulgated thereunder, and any corresponding foreign
     application, registration or certification.

          1.27 "Valid Claim" shall mean (a) an issued claim under an issued
     patent within the Patent Rights, which has not (i) expired or been
     canceled, (ii) been declared invalid by an unreversed and unappealable
     decision of a court or other appropriate body of competent jurisdiction,
     (iii) been admitted to be invalid or unenforceable through reissue,
     disclaimer otherwise, or (iv) been abandoned, and (b) a claim of a patent
     application included within the Patent Rights as of the Effective Date.

     Section 2. Section 1.2 of the XOMA/Connetics Agreement is hereby amended to
read in its entirety as follows:

          1.2 "Agreement" shall mean this Technology Acquisition Agreement dated
     as of June 3, 1994, as amended December 8, 1999.

     Section 3. Section 1.3 of the XOMA/Connetics Acquisition Agreement is
hereby amended to read in its entirety as follows:

<PAGE>
                                      -3-

          1.3 "Assignment and Assumption Agreement" shall mean the agreement
     whereby XOMA assigned to CT its rights under and CT assumes XOMA's
     obligations under the Vandenbark License Agreement as provided in Section
     3.3 which is attached as Exhibit A to the XOMA/Connetics Agreement and
     incorporated by reference therein.

     Section 4. Section 1.6 of the XOMA/Connetics Agreement is hereby deleted.

     Section 5. Section 1.9 of the XOMA/Connetics Agreement is hereby deleted.

     Section 6. Section 1.10 of the XOMA/Connetics Agreement is hereby amended
to read in its entirety as follows:

          1.10 "Net Sales" shall mean, with respect to any Product, the invoiced
     sales price of such Product billed by CT, its Affiliates or licensees of
     the TCR Technology to customers who are not Affiliates, less (to the extent
     incurred and absorbed by CT, its Affiliates or any such licensee) (a)
     credits, allowances, discounts and rebates to, and chargebacks from the
     account of, such customers for spoiled, damaged, out-dated, rejected or
     returned Product; (b) transportation and insurance costs incurred in
     transporting such Product in final form to such customers; (c) actual cash,
     quantity and trade discounts, rebates and other price adjustments or
     reduction programs; (d) sales, use, value-added and other direct taxes, or
     any other governmental charge imposed upon the production, importation, use
     or sale of the Product; (e) customs, duties, surcharges and other
     governmental charges incurred in the exportation or importation of such
     Product; and (f) bad debts accruals.

     Section 7. Section 1.13 of the XOMA/Connetics Agreement is hereby amended
to read in its entirety as follows:

          1.13 "Patents" shall mean (a) all United States and foreign (including
     regional authorities such as the European Patent Office) regular or
     provisional patent applications and issued patents listed on Schedule A;
     (b) all United States and foreign patents that have issued or issue from
     such patent applications, including utility, model and design patents and
     certificates of invention; (c) all divisionals, continuations,
     continuations-in-part, reissues, reexaminations, renewals, extensions or
     additions to any such patents and patent applications described in clauses
     (a) or (b) above.

     Section 8. Section 1.14 of the XOMA/Connetics Agreement is hereby deleted.

<PAGE>
                                      -4-

     Section 9. Section 1.16 of the XOMA/Connetics Agreement is hereby amended
to read in its entirety as follows:

          1.16 "Product" shall mean a composition or a product the manufacture,
     use, offer for sale, sale or import of which is within the scope of a Valid
     Claim.

     Section 10. Section 1.18 of the XOMA/Connetics Agreement is hereby amended
to read in its entirety as follows:

          1.18 "TCR Related Improvements" shall mean all technology and know-how
     developed by or on behalf of CT prior to December 8, 1999, to the extent
     such technology and know-how are related to the TCR Technology, other than
     TCR Sole Improvements.

     Section 11. Section 1.19 of the XOMA/Connetics Agreement is hereby amended
to read in its entirety as follows:

          1.19 "TCR Sole Improvements" shall mean all technology and know-how
     developed by or on behalf of CT prior to December 8, 1999, to the extent
     such technology and know-how are improvements of the TCR Technology and may
     have applications related to the TCR Technology.

     Section 12. Section 1.20 of the XOMA/Connetics Agreement is hereby amended
to read in its entirety as follows:

          1.20 "TCR Technology" shall mean the Patents and all other technology
     and know-how developed, owned or controlled by XOMA, including that
     technology acquired by XOMA pursuant to the Vandenbark Agreements and that
     technology described in Exhibit E to this Agreement.

     Section 13. Section 1.21 of the XOMA/Connetics Agreement is hereby amended
to read in its entirety as follows:

          1.21 "Vandenbark License Agreements" shall mean the Research
     Collaboration and License Agreement, between Dr. Vandenbark and XOMA dated
     as of February 27, 1990, and any and all amendments thereto.

     Section 14. Article 2 of the XOMA/Connetics Agreement is hereby amended to
read in its entirety as follows:

<PAGE>
                                      -5-

     2. Assignment of TCR Technology.

          Subject to the terms and conditions of, and for the consideration set
     forth in this Agreement, XOMA, effective as of the Closing, did sell,
     convey, assign, transfer and deliver to CT and CT shall purchase and
     acquire from XOMA all right, title and interest in and to the TCR
     Technology, including without limitation the right to sue for and collect
     upon past infringements (the "Assignment"). The Assignment includes the
     right to all preclinical and clinical data related to a Product, which XOMA
     owned or controlled as of the Closing. XOMA agrees to execute and deliver
     to CT all instruments necessary to evidence and document such Assignment to
     CT as set forth in Section 6.5. XOMA hereby appoints CT its
     attorney-in-fact to execute and deliver on behalf of XOMA all such
     instruments upon XOMA's breach of its obligations under this Section 2,
     which breach is not cured within 30 days of receipt by XOMA of written
     notice from CT.

     Section 15. Section 3.2 of the XOMA/Connetics Agreement is hereby deleted.

     Section 16. Section 3.3 of the XOMA/Connetics Agreement is hereby amended
to read in its entirety as follows:

          3.3 Assumption of Vandenbark License Agreement. As partial
     consideration for the purchase of the TCR Technology, CT shall assume and
     agree to perform all of the obligations of XOMA under the Vandenbark
     License Agreement; and, at Closing, CT shall execute and deliver to XOMA
     for delivery to Vandenbark the Assignment and Assumption Agreement in the
     form attached as Exhibit A to this Agreement. From and after the Closing
     Date, CT shall indemnify and hold harmless (except as set forth below) XOMA
     from all claims of loss or damage of any nature whatsoever arising out of
     or in connection with the Vandenbark License Agreement; provided, however,
     that XOMA shall indemnify and hold harmless CT from all claims of loss or
     damage of any nature whatsoever arising out of or in connection with any
     breach by XOMA of its obligations under the Vandenbark License Agreement.

     Section 17. Section 5.1 of the XOMA/Connetics Agreement is hereby amended
to read in its entirety as follows:

          5.1 Amount of Royalty.

          5.1.1 CT shall pay XOMA a royalty equal to [*] of Net Sales in each
     country where Products are sold by CT, its Affiliates and licensees.

<PAGE>
                                      -6-

          For purposes of Connetics' royalty obligations pursuant to Section
     5.1.1, in the event that Connetics materially narrows the scope of or
     abandons a claim within the Patent Rights, then the narrowed claim in the
     form existing as of the Effective Date or the abandoned claim in the form
     existing as of the Effective Date, as applicable, shall be considered a
     Valid Claim with respect to such Product for purposes of this Agreement for
     a period of [*] after the first commercial sale of such Product.
     Notwithstanding the foregoing, Connetics shall not abandon claims within
     the Patent Rights prior to [*].

     Section 18. Section 5.2 of the XOMA/Connetics Agreement is hereby amended
to read in its entirety as follows:

          5.2 Term of Royalty Payments. Royalty payments shall continue to
     accrue and be payable with respect to Net Sales of Products and will
     automatically expire on a country-by-country basis on the later of (i) [*]
     from first commercial sale of a Product in any country or (ii) the
     expiration (or revocation) of the last to expire (or be revoked) of the
     Valid Claims in such country with respect to a Product.

     Section 19. Section 5.3 of the XOMA/Connetics Agreement is hereby deleted.

     Section 20. Section 5.4 of the XOMA/Connetics Agreement is hereby amended
to read in its entirety as follows:

          5.4 Reports. During the term of this Agreement following the first
     commercial sale of a Product by CT or its Affiliates, or the grant of a
     sublicense hereunder by CT or its Affiliates, CT shall furnish to XOMA a
     quarterly written report showing in reasonably specific detail the
     calculation of amounts payable, if any, which shall have accrued hereunder
     during the reporting period. With respect to sales of Products invoiced or
     revenues received in United States dollars, all amounts shall be expressed
     in United States dollars. With respect to sales of Products invoiced or
     revenues received in a currency other than United States dollars, all
     amounts shall be expressed in the domestic currency of the party making the
     sale together with the United States dollar equivalent of the amounts
     payable, calculated using the average closing buying rate for such currency
     published in the United States Western Edition of The Wall Street Journal
     under the heading "Currency Trading - Exchange Rates" on the last business
     day of each month in the quarter prior to the date of payment. Reports
     shall be due on the thirtieth (30th) day following the close of each
     calendar quarter. CT shall keep complete and accurate records in sufficient
     detail to properly permit the calculation of amounts payable hereunder to
     be determined.

<PAGE>
                                      -7-

     Section 21. Section 5.5 of the XOMA/Connetics Agreement is hereby amended
to read in its entirety as follows:

          5.5 Exchange Control. If at any time legal restrictions prevent the
     prompt remittance by CT of part or all amounts with respect to any country
     where a Product is sold, the parties shall use their reasonable commercial
     efforts, in cooperation with the applicable authorities in such country or
     otherwise, to facilitate payment of all royalties affected thereby. If,
     notwithstanding the good faith efforts of the parties, such remittance is
     prevented, CT shall have the right, in its sole discretion, to make such
     payments by depositing the amount thereof in local currency to XOMA's
     account in a bank or other depository institution in such country.

     Section 22. Section 5.6 of the XOMA/Connetics Agreement is hereby amended
to read in its entirety as follows:

          5.6 Records. CT shall keep for four (4) years from the date of each
     payment of amounts due pursuant to Section 5.1 complete and accurate
     records of sales and all other information necessary to calculate Net Sales
     of each Product in sufficient detail to allow the accrued royalties to be
     determined accurately. XOMA shall have the right to cause an independent,
     certified public accounting firm of nationally recognized standing (who has
     executed a confidentiality agreement with CT reasonably acceptable to CT)
     to audit such records at the place or places of business where such records
     are customarily kept in order to verify the accuracy of the reports of Net
     Sales and payments for the preceding four years. Such audits may be
     exercised during normal business hours once a year upon 30 days' advance
     written notice to CT. The accounting firm shall disclose to XOMA only
     whether the reports are correct or not and the specific details concerning
     any discrepancies. No other information shall be shared. XOMA shall bear
     the full cost of such audit unless such audit discloses a variance of more
     than 5% from the amount of the payments due under Section 4.1 of this
     Agreement, in which event, CT shall bear the full cost of such audit and
     shall pay to XOMA the amount payable. XOMA shall not disclose confidential
     information concerning payments and reports, and all information learned in
     the course of any audit or inspection unless such information is or becomes
     publicly known or available (unless such information becomes publicly known
     or available through breach of this Agreement), except to the extent
     necessary for XOMA to reveal such information in order to enforce its
     rights under this Agreement or if disclosure is required by law.

     Section 23. Section 5.7 of the XOMA/Connetics Agreement is hereby deleted.

<PAGE>
                                      -8-

     Section 24. Section 6.1 of the XOMA/Connetics Agreement is hereby amended
to read in its entirety as follows:

          6.1 CT hereby assumes sole responsibility for the prosecution,
     maintenance, enforcement and defense of the Patent Rights and the TCR
     Technology. CT shall use its commercially reasonable efforts to prosecute
     and maintain the Patent Rights consistent with CT's patent practices. XOMA
     shall assist CT, to the extent of any reasonable request of CT and at CT's
     expense, in CT's prosecution and maintenance of the Patent Rights in any
     and all countries, and to vest title thereto in CT or its successors and
     assigns. CT shall reimburse XOMA for all Costs incurred by XOMA under this
     Section 6.1; provided, however, that such assistance by XOMA which is
     reasonable and not costly shall be without charge to CT.

     Section 25. Section 6.2 of the XOMA/Connetics Agreement is hereby deleted.

     Section 26. Section 6.3 of the XOMA/Connetics Agreement is hereby deleted.

     Section 27. Section 7 of the XOMA/Connetics Agreement is hereby amended to
read in its entirety as follows:

          7. Diligence Milestones.

          7.1 CT shall use its commercially reasonable efforts to commence (or
     to cause its Affiliate or licensee of the TCR Technology to commence) the
     first Pivotal Trial of a Product on or before [*]. For purposes of this
     provision, "commence" shall mean the date the first patient is enrolled. CT
     shall use its commercially reasonable efforts to submit (or to cause its
     Affiliate or licensee of the TCR Technology to submit) an NDA, PLA or BLA
     to the FDA by or before [*] .

          7.2 If CT is unable to achieve either of the diligence milestones
     prior to the applicable dates set forth in Section 7.1 for reasons outside
     of CT's reasonable control, CT shall prepare and submit to XOMA a
     reasonable plan for the continued diligent development of Products and a
     revised schedule for achieving the remaining diligence milestones (which
     shall extend the applicable dates to accommodate the delay caused by such
     reasons outside of CT's reasonable control).

          7.3 If (a) CT is unable to achieve either of the diligence milestones
     prior to the applicable dates set forth in Section 7.1 other than for
     reasons outside of CT's control, or (b) CT is unable to achieve remaining
     diligence milestones prior to the revised

<PAGE>
                                      -9-

     schedule submitted under Section 7.2, CT shall either (i) at its option in
     its sole discretion, make a one-time payment to XOMA of [*], or (ii)
     otherwise, convey to XOMA CT's rights in the TCR Technology and TCR Sole
     Improvements (and transfer to XOMA of the know-how within the TCR
     Technology and TCR Sole Improvements). In either event, CT shall have no
     further diligence obligations under this Agreement.

     Section 28. Section 10 of the XOMA/Connetics Agreement is hereby deleted in
its entirety.

     Section 29. Section 15.2 of the XOMA/Connetics Agreement is hereby deleted.

     Section 30. During the term of the XOMA/Connetics Agreement, neither XOMA
nor any of its Affiliates shall take any action or initiate any proceeding to
prevent the issuance of, invalidate, revoke or otherwise render unenforceable
any of the Patent Rights (as defined in the Assignment Agreement dated as of
December 8, 1999, between IRC and Connetics). Within ninety (90) days after the
date hereof, XOMA and its Affiliates shall terminate, dismiss and withdraw all
such actions and proceedings which were taken or initiated by it or any of its
Affiliates on or before the date hereof.

     Section 31. Without limiting the rights and remedies of IRC at law, in
equity or otherwise, if XOMA or any of its Affiliates (a) takes during the term
of the XOMA/Connetics Agreement any action or initiates any proceeding to
prevent the issuance of, invalidate, revoke or otherwise render unenforceable
any of the Patent Rights (as defined in the Assignment Agreement dated as of
December 8, 1999, between IRC and Connetics), or (b) fails within ninety (90)
days after the date hereof to terminate, dismiss and withdraw any such action or
proceeding which was taken or initiated by it or any of its Affiliates on or
before the date hereof, then, if IRC is not itself in material breach of the
XOMA/Connetics Agreement or the IRC/XOMA Agreement, within ten (10) days after
written notice from IRC, (x) XOMA shall refund to IRC all amounts paid by IRC to
XOMA under the Agreement dated as of the date hereof, between IRC and XOMA (the
"IRC/XOMA Agreement"); (y) XOMA shall sell, assign and transfer to IRC (at no
cost to IRC) the number of shares of Common Stock of IRC issued to XOMA under
Section 3.1.2 of the IRC/XOMA Agreement (or if XOMA no longer owns the IRC
shares, XOMA shall pay to IRC an amount equal to the full amount of
consideration received for the sale of such shares); and (z) IRC shall have no
further obligation to pay any amounts to XOMA under the XOMA/Connetics Agreement
or the IRC/XOMA Agreement.

<PAGE>
                                      -10-

     Section 32. Without limiting the rights and remedies of IRC at law, in
equity or otherwise, if Connetics, Vandenbark or any of their respective
Affiliates (a) takes during the term of the XOMA/Connetics Agreement any action
or initiates any proceeding to prevent the issuance of, invalidate, revoke or
otherwise render unenforceable any of the Patent Rights (as defined in the
Assignment Agreement dated as of December 8, 1999, between IRC and Connetics),
or (b) fails within ninety (90) days after the date hereof to terminate, dismiss
and withdraw any such action or proceeding which was taken or initiated by it or
any of its Affiliates on or before the date hereof, then, if IRC is not itself
in material breach of the XOMA/Connetics Agreement or the IRC/XOMA Agreement,
IRC shall have no further obligation to pay any amounts to XOMA under Section
3.1.1 of the IRC/XOMA Agreement.

     Section 33. IRC shall be a third party beneficiary of the provisions of
Sections 30, 31 and 32 of this Amendment.

     Section 34. Except as specifically modified or amended hereby, the
XOMA/Connetics Agreement shall continue in full force and effect and, as so
modified or amended, is hereby ratified, confirmed and approved. No provision of
this Amendment may be modified or amended except expressly in a writing signed
by both parties nor shall any terms be waived except expressly in a writing
signed by the party charged therewith. This Amendment shall be governed in
accordance with the laws of the State of California, without regard to
principles of conflicts of laws.

<PAGE>
                                      -11-

         IN WITNESS WHEREOF, XOMA and Connetics have entered into this Amendment
Number One to Technology Acquisition Agreement as of the date first written
above.

"XOMA"                                 "Connetics"

XOMA (US) LLC                          Connetics Corporation
                                       a Delaware corporation

By:____________________________        _____________________________________
     Name:                             Thomas G. Wiggans
     Title:                            President and Chief Executive Officer[*] indicates that a confidential portion of the text of this agreement has been
omitted

                                    AGREEMENT

     THIS AGREEMENT (this "Agreement") dated as of December 8, 1999 (the
"Effective Date"), is entered into between The Immune Response Corporation, a
Delaware corporation ("IRC"), having a place of business located at 5935 Darwin
Court, Carlsbad, California 92008, and XOMA (US) LLC, a Delaware limited
liability company ("XOMA"), having a place of business at 2910 Seventh Street,
Berkeley, California 94710, with reference to the following facts:

     A. In connection with an acquisition of technology by IRC, an assignment
agreement known as the Technology Acquisition Agreement between Connetics
Corporation ("Connetics") and XOMA and effective as of June 3, 1994 (the
"Original Agreement") must be amended.

     B. In consideration for XOMA's willingness to amend the Original Agreement,
which amendment shall be effective as of December 8, 1999, IRC will transfer to
XOMA shares of IRC stock and will pay to XOMA the amounts set forth herein, all
on the terms and conditions herein.

     NOW, THEREFORE, in consideration of the foregoing premises and the mutual
covenants herein, the parties agree as follows:

1.       DEFINITIONS.

     For purposes of this Agreement, the terms defined in this Article 1 shall
have the respective meanings set forth below:

     1.1 "Affiliate" shall mean, with respect to any Person, any other Person
which directly or indirectly controls, is controlled by, or is under common
control with, such Person. A Person shall be regarded as in control of another
Person if it owns, or directly or indirectly controls, greater than fifty
percent (50%) of the voting stock or other ownership interest of the other
Person, or if it directly or indirectly possesses the power to direct or cause
the direction of the management and policies of the other Person by any means
whatsoever.

     1.2 "Commission" shall mean the Securities and Exchange Commission or any
other federal agency at the time administering the Securities Act.

     1.3 "Person" shall mean an individual, corporation, partnership, limited
liability company, trust, business trust, association, joint stock company,
joint venture, pool, syndicate,

<PAGE>
                                      -2-

sole proprietorship, unincorporated organization, governmental authority or any
other form of entity not specifically listed herein.

     1.4 The terms "register," "registered" and "registration" shall mean a
registration effected by preparing and filing a registration statement in
compliance with the Securities Act and applicable rules and regulations
thereunder, and the declaration or ordering of the effectiveness of such
registration statement.

     1.5 "Registration Expenses" shall mean all expenses incurred in effecting
the registration of the Shares pursuant to this Agreement, including, without
limitation, all registration, qualification, and filing fees, printing expenses,
escrow fees, fees and disbursements of counsel for IRC, blue sky fees and
expenses, and expenses of any regular or special audits incident to or required
by any such registration, but shall not include Selling Expenses.

     1.6 "Securities Act" shall mean the Securities Act of 1933, as amended, or
any similar successor federal statute and the rules and regulations thereunder,
all as the same shall be in effect from time to time.

     1.7 "Selling Expenses" shall mean all underwriting discounts and selling
commissions applicable to the sale of the Shares and fees and disbursements of
counsel for XOMA.

     1.8 "Shares" shall mean those Shares of IRC Common Stock issued to XOMA
pursuant to Section 3.1.2 of this Agreement.

     1.9 "Third Party" shall mean any Person other than IRC, XOMA and their
respective Affiliates.

     1.10 "Vandenbark" shall mean Dr. Arthur A. Vandenbark.

     2. REPRESENTATIONS AND WARRANTIES.

     2.1 Mutual Representations. Each party represents and warrants to the other
party as follows:

     2.1.1 Legal Existence. Such party is a corporation or limited liability
company, as the case may be, duly organized, validly existing and in good
standing under the laws of the state in which it is incorporated or formed, as
the case may be.

     2.1.2 Authorization and Enforcement of Obligations. Such party (a) has the
power and authority and the legal right to enter into this Agreement and to
perform its obligations hereunder, and (b) has taken all necessary action on its
part to authorize the execution and delivery of this Agreement and the
performance of its obligations hereunder. This

<PAGE>
                                      -3-

Agreement has been duly executed and delivered on behalf of such party, and
constitutes a legal, valid, binding obligation, enforceable against such party
in accordance with its terms.

     2.1.3 No Consents. All necessary consents, approvals and authorizations of
all governmental authorities and other Persons required to be obtained by such
party in connection with this Agreement have been obtained.

     2.1.4 No Conflict. The execution and delivery of this Agreement and the
performance of such party's obligations hereunder (a) do not conflict with or
violate any requirement of applicable laws or regulations, and (b) do not
conflict with, or constitute a default under, any contractual obligation of it.

     2.2 XOMA Representations. XOMA represents and warrants to IRC as follows:

     2.2.1 Accredited Investor. XOMA is an "accredited investor" as defined in
Rule 501(a) of Regulation D promulgated under the Securities Act.

     2.2.2 Investment Intent. XOMA is acquiring the Shares pursuant to Section
3.1.2(a) below for investment for its own account only and not with a view to
the resale or "distribution" thereof in violation of the Securities Act. XOMA
understands that such Shares have not been registered under the Securities Act
or registered or qualified under any state securities law in reliance on
specific exemptions therefrom, which exemptions may depend upon, among other
things, the bona fide nature of XOMA's investment intent as expressed herein.

     2.2.3 Investment Experience. XOMA has been furnished with all requested
materials relating to IRC's business affairs and financial condition and has
been afforded the opportunity to ask questions of IRC and received satisfactory
answers to any such inquiries. XOMA has such business and financial experience
as is required to give it the capacity to evaluate the merits and risks of the
acquisition of such Shares.

     2.2.4 Compliance with Securities Laws and Regulations. All subsequent
offers and sales of such Shares shall be made pursuant to registration under the
Securities Act and qualification under the applicable state securities laws or
pursuant to exemptions from registration and qualification.

     2.3 IRC Representations. IRC represents and warrants to XOMA as follows:

     2.3.1 Valid Issuance of Shares. The Shares which are being issued to XOMA
hereunder, when issued, sold and delivered in accordance with the terms hereof,
for the consideration expressed herein, will be duly and validly issued, fully
paid and nonassessable, free and clear of all security interests, liens or other
encumbrances, voting or other restrictions and

<PAGE>
                                      -4-

preemptive or similar rights and, based in part upon the representations of XOMA
in this Agreement, will be issued in compliance with all applicable federal and
state securities laws. The Common Stock of IRC is qualified for trading on the
Nasdaq Stock Market, and IRC and such Common Stock meet the criteria for
continuing qualification for such trading.

     2.3.2 Governmental Consents. The execution, delivery and performance by IRC
of this Agreement require no action by or in respect of, or filing with, any
governmental body, agency, or official other than (a) post-sale filings pursuant
to applicable state and federal securities laws, which IRC undertakes to file
within the applicable time periods and (b) any such action or filing as to which
the failure to make or obtain would not, individually or in the aggregate, have
a material adverse effect.

     2.3.3 SEC Filings; Financial Statements.

     (a) IRC has delivered to XOMA (i) its annual report on Form 10-K for its
fiscal year ended December 31, 1998, (ii) its proxy or information statement
relating to the annual meeting of the stockholders of the Company held on May
25, 1999, and (iii) all of its other reports, statements, schedules and
registration statements filed with the Commission since December 31, 1998. IRC
has filed on a timely basis all such reports, statements, schedules and
registration statements required to be filed with the Commission.

     (b) As of its filing date, each such report or statement filed pursuant to
the 1934 Act did not contain any untrue statement of a material fact or omit to
state any material fact necessary in order to make the statements made therein,
in the light of the circumstances under which they were made, not misleading.

     (c) The audited consolidated financial statements and unaudited
consolidated interim financial statements of IRC included in the annual and
other reports referred to in Section 2.3.3(a) fairly present, in conformity with
generally accepted accounting principles applied on a consistent basis, the
consolidated financial position of IRC and its consolidated subsidiaries as of
the dates thereof and their consolidated results of operations and changes in
financial position for the periods then ended.

     3. CONSIDERATION.

     3.1 Payments by IRC.

     3.1.1 Technology Access.

     (a) Upon the Effective Date, IRC shall pay to XOMA [*] in cash.

     (b) On or before [*] in cash.

<PAGE>
                                      -5-

     (c) If prior to July 31, 2000, IRC (i) sells or assigns to a Third Party
the Assigned Technology or grants to a Third Party a license under the Assigned
Technology, and (ii) receives cash consideration for such sale, assignment or
license, then within ten (10) business days after the receipt by IRC of such
cash consideration, IRC shall pay to XOMA an amount [*]. All amounts paid to
XOMA under this Section 3.1.1(c) shall be credited against the payments owing
under Section 3.1.1(b) above in the inverse order in which they are due.

     3.1.2 The Shares.

     (a) On the Effective Date, IRC shall issue to XOMA the number of shares of
Common Stock of IRC (rounded to the nearest whole number) which shall have an
aggregate value of [*], at a price per share equal to the average daily closing
price of the Common Stock of IRC as quoted on the Nasdaq Stock Market on each of
the twenty (20) trading days ending three (3) trading days prior to the
Effective Date.

     (b) The certificate or certificates for the Shares shall be subject to a
legend restricting transfer under the Securities Act of 1993 and referring to
restrictions on transfer of such certificate(s), which legend shall be
substantially as follows:

         THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED
         UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE "SECURITIES ACT"),
         AND HAVE BEEN ACQUIRED FOR INVESTMENT AND NOT WITH A VIEW TO, OR IN
         CONNECTION WITH, THE SALE, OFFERING OR DISTRIBUTION THEREOF. NO SUCH
         SALE, OFFERING OR DISPOSITION MAY BE EFFECTED WITHOUT (A) AN EFFECTIVE
         REGISTRATION STATEMENT RELATED THERETO, OR (B) AN OPINION OF COUNSEL
         FOR XOMA THAT SUCH REGISTRATION IS NOT REQUIRED UNDER THE SECURITIES
         ACT, OR (C) FULL COMPLIANCE WITH THE PROVISIONS OF RULE 144 UNDER THE
         SECURITIES ACT.

Any legend endorsed on a certificate pursuant to this section shall be removed
(i) if such shares may be transferred in compliance with Rule 144(k) promulgated
under the Securities Act, (ii) if such shares may be transferred in compliance
with subsection 3.1.2(c) below, and (iii) following registration of the Shares,
upon XOMA's request.

     (c) XOMA shall not directly or indirectly sell, assign, transfer or
otherwise dispose of the Shares or any interest therein (or enter into any
agreement to do any of the foregoing) until such time as (i) the Shares have
been registered and qualified under applicable federal and state securities
laws, or (ii) XOMA may sell, assign, transfer or otherwise dispose of the Shares
pursuant to an exemption from applicable federal and state securities laws.
Thereafter, XOMA shall not directly or indirectly sell, assign, transfer or
otherwise dispose of

<PAGE>
                                      -6-

in the aggregate more than one-third (1/3) of the aggregate number of the Shares
issued to XOMA under Section 3.1.2(a) above (or enter into any agreement to do
any of the foregoing) in any period of thirty (30) consecutive days.

     (d) Late Payments. Any payments or portions thereof due hereunder which are
not paid on the date such payments are due under this Agreement shall bear
interest at a rate equal to the lesser of the prime rate as published in the
United States Western Edition of The Wall Street Journal (or its successor in
interest) under the heading "Money Rates" plus two percent (2%), or the maximum
rate permitted by law, calculated on the number of days such payment is
delinquent.

     4. ACCOUNTING.

     4.1 Records. IRC shall keep for four (4) years from the date of each
payment of amounts due pursuant to Section 4.1 of the Assignment Agreement
between IRC and Connetics, complete and accurate records of sales and all other
information necessary to calculate Net Sales of each Product (as such terms are
defined in the Assignment Agreement) in sufficient detail to allow the accrued
royalties to be determined accurately. XOMA shall have the right to cause an
independent, certified public accounting firm of nationally recognized standing
(who may be XOMA's regularly retained independent accountants and who have
executed a confidentiality agreement with IRC reasonably acceptable to IRC) to
audit such records at the place or places of business where such records are
customarily kept in order to verify the accuracy of the reports of Net Sales and
payments for the preceding four years. Such audits may be exercised during
normal business hours once a year upon 30 days' advance written notice to IRC.
The accounting firm shall disclose to XOMA only whether the reports are correct
or not and the specific details concerning any discrepancies. No other
information shall be shared. XOMA shall bear the full cost of such audit unless
such audit discloses a variance of more than 5% from the amount of the payments
due under Section 4.1 of the Assignment Agreement, in which event, IRC shall
bear the full cost of such audit and shall pay to XOMA the amount payable. XOMA
shall not disclose confidential information concerning payments and reports, and
all information learned in the course of any audit or inspection unless such
information is or becomes publicly known or available other than through breach
of this Agreement, except to the extent necessary for XOMA to reveal such
information in order to enforce its rights under this Agreement or if disclosure
is required by law.

     5. REGISTRATION OF THE SHARES.

     5.1 Registration. Within thirty (30) days after the Effective Date, IRC
shall file a registration statement for the resale of the Shares on Form S-3
pursuant to the Securities Act and as would permit or facilitate the sale and
distribution of the Shares. IRC shall use its

<PAGE>
                                      -7-

commercially reasonable efforts to effect such registration as soon as
practicable thereafter. Additionally, IRC shall file appropriate post-effective
amendments to such registration statement and appropriate qualifications under
applicable blue sky or other state securities laws. IRC shall furnish XOMA with
copies of all correspondence to and from the Commission from the date of filing,
in connection with such registration, such copies to be forwarded no later than
five (5) business days after receipt by IRC or mailing by IRC or its agents, as
the case may be.

     5.1.1 IRC shall not be obligated to effect, or to take any action to
effect, any such registration pursuant to this Section 5.1 in any particular
jurisdiction in which IRC would be required to execute a general consent to
service of process in effecting such registration, qualification, or compliance,
unless IRC is already subject to service in such jurisdiction and except as may
be required by the Securities Act.

     5.1.2 The registration statement filed pursuant to this Section 5.1 shall
not include other securities of IRC with respect to which registration rights
have been granted (except those issued to Connetics pursuant to the Assignment
Agreement dated as of the date hereof, between IRC and Connetics), nor
securities of IRC being sold for the account of IRC, unless XOMA consents to
such inclusion, which consent shall not be unreasonably withheld or delayed.

     5.2 Expenses. All Registration Expenses incurred in connection with any
registration, qualification or compliance pursuant to Section 5.1 above shall be
borne by IRC. All Selling Expenses shall be borne by XOMA.

     5.3 Registration Procedures. IRC will provide XOMA with a draft of the
registration statement and give due consideration to their comments three (3)
days prior to the filing. IRC will keep XOMA advised in writing as to the
initiation of the registration of the Shares and as to the completion thereof.
At its expense, IRC will use its commercially reasonable efforts to:

     5.3.1 Keep such registration effective for a period of one (1) year from
the Effective Date or until XOMA has completed the distribution described in the
registration statement relating thereto, whichever first occurs;

     5.3.2 Prepare and file with the Commission such amendments and supplements
to such registration statement and the prospectus used in connection with such
registration statement as may be necessary to comply with the provisions of the
Securities Act with respect to the disposition of all securities covered by such
registration statement;

<PAGE>
                                      -8-

     5.3.3 Furnish such number of prospectuses and other documents incident
thereto, including any amendment of or supplement to the prospectus, as XOMA
from time to time may reasonably request;

     5.3.4 Notify XOMA of the happening of any event as a result of which the
prospectus included in such registration statement, as then in effect, includes
an untrue statement of a material fact or omits to state a material fact
required to be stated therein or necessary to make the statements therein not
misleading or incomplete in the light of the circumstances then existing, and at
the request of XOMA, prepare and furnish to XOMA a reasonable number of copies
of a supplement to or an amendment of such prospectus as may be necessary so
that, as thereafter delivered to the purchasers of Shares, such prospectus shall
not include an untrue statement of a material fact or omit to state a material
fact required to be stated therein or necessary to make the statements therein
not misleading or incomplete in the light of the circumstances then existing;
and

     5.3.5 Cause the Shares to be listed or qualified on each securities
exchange or inter-dealer quotation system on which similar securities issued by
IRC are then listed and thereafter maintain such listing or quotation.

     5.4 Indemnification.

     5.4.1 IRC shall indemnify XOMA, its directors, officers, employees, legal
counsel and accountants and each Person controlling XOMA within the meaning of
Section 15 of the Securities Act, against all losses, liabilities, damages and
expenses incurred as a result of any claim, demand, action or proceeding by any
Third Party arising out of or based on any untrue statement (or alleged untrue
statement) made by or on behalf of IRC of a material fact contained in any
prospectus, offering circular, or other document (including any related
registration statement, notification, or the like), or based on any omission (or
alleged omission) to state therein a material fact required to be stated therein
or necessary to make the statements therein not misleading, or any violation by
IRC of the Securities Act or any rule or regulation thereunder applicable to IRC
and will reimburse each such XOMA, its officers, directors, employees, legal
counsel and accountants and each Person controlling XOMA within the meaning of
Section 15 of the Securities Act, for any legal or any other expenses reasonably
incurred in connection with investigating or defending or settling any such
claim, demand, action or other proceeding; provided, however, that IRC will not
be liable in any such case to the extent that any such loss, liability, damage
or expense arises out of or is based on any untrue statement or omission based
upon written information furnished to IRC by XOMA and stated to be specifically
for use therein; provided, further, that the obligations of IRC hereunder shall
not apply to amounts paid in settlement of any such claims, demands, actions or
other proceedings if such settlement is effected without the consent of IRC
(which consent shall not be unreasonably withheld or delayed).

<PAGE>
                                      -9-

     5.4.2 XOMA shall indemnify IRC, its directors, officers, employees, legal
counsel and accountants and each Person controlling IRC within the meaning of
Section 15 of the Securities Act, against all losses, liabilities, damages and
expenses incurred as a result of any claim, demand, action or proceeding by any
Third Party arising out of or based on any untrue statement (or alleged untrue
statement) made by or on behalf of XOMA of a material fact contained in any
prospectus, offering circular, or other document (including any related
registration statement, notification, or the like) incident to any such
registration, qualification, or compliance, or based on any omission (or alleged
omission) to state therein a material fact required to be stated therein or
necessary to make the statements therein not misleading, or any violation by
XOMA of the Securities Act or any rule or regulation thereunder applicable to
XOMA, and will reimburse IRC, its directors, officers, employees, legal counsel
and accountants and each Person controlling IRC within the meaning of Section 15
of the Securities Act, for any legal or any other expenses reasonably incurred
in connection with investigating or defending or settling any such claim,
demand, action or other proceeding, in each case to the extent, but only to the
extent, that such untrue statement (or alleged untrue statement) or omission (or
alleged omission) is made in such registration statement, prospectus, offering
circular, or other document in reliance upon and in conformity with written
information furnished to IRC by XOMA and stated to be specifically for use
therein; provided, however, that the obligations of XOMA hereunder shall not
apply to amounts paid in settlement of any such claims, demands, actions or
other proceedings if such settlement is effected without the consent of XOMA
(which consent shall not be unreasonably withheld or delayed).

     5.4.3 The indemnified party shall promptly notify the other party hereto of
any claim, demand, action or proceeding for which it intends to claim such
indemnification, and the indemnifying party shall have the right to participate
in, and, to the extent it so desires, jointly with any other indemnifying party
similarly noticed, to assume the defense thereof with counsel selected by the
indemnifying party; provided, however, that the indemnified party shall have the
right to retain its own counsel if representation of the indemnified party by
the counsel retained by the indemnifying party would be inappropriate due to
actual or potential differing interests between the indemnified party and any
other party represented by such counsel in such proceedings, the reasonable
costs of such independent counsel to be borne by the indemnifying party. The
failure to deliver notice to the indemnifying party within a reasonable time
after notice of any such claim or demand, or commencement of any such action or
proceeding, if materially prejudicial to its ability to defend, shall relieve
the indemnifying party of any liability to the indemnified party under this
Article 5, but the omission so to deliver notice to the indemnifying party will
not relieve it of any liability that it may have to the indemnified party
otherwise than under this Article 5. The indemnified party under this Article 5
and its agents, shall cooperate fully with the indemnifying party and its legal
representatives in the investigation and defense of any claim, demand, action or
proceeding covered by this indemnification.

<PAGE>
                                      -10-

     5.5 Information by XOMA. XOMA shall furnish to IRC such information
regarding XOMA and the distribution of the Shares as IRC may reasonably request
in writing and as shall be reasonably required in connection with any
registration, qualification, or compliance referred to in this Article 5.

     6. MISCELLANEOUS.

     6.1 Termination of Payment Obligations.

     6.1.1 During the term of this Agreement, neither XOMA nor any of its
Affiliates shall take any action or initiate any proceeding to prevent the
issuance of, invalidate, revoke or otherwise render unenforceable any of the
Patent Rights (as defined in the Assignment Agreement dated as of December 8,
1999, between IRC and Connetics). Within ninety (90) days after the date hereof,
XOMA and its Affiliates shall terminate, dismiss and withdraw all such actions
and proceedings which were taken or initiated by it or any of its Affiliates on
or before the date hereof.

     6.1.2 Without limiting the rights and remedies of IRC at law, in equity or
otherwise, if XOMA or any of its Affiliates (a) takes during the term of this
Agreement any action or initiates any proceeding to prevent the issuance of,
invalidate, revoke or otherwise render unenforceable any of the Patent Rights
(as defined in the Assignment Agreement dated as of December 8, 1999, between
IRC and Connetics), or (b) fails within ninety (90) days after the date hereof
to terminate, dismiss and withdraw any such action or proceeding which was taken
or initiated by it or any of its Affiliates on or before the date hereof, then,
if IRC is not itself in material breach of the Original Agreement or this
Agreement, within ten (10) days after written notice from IRC, (x) XOMA shall
refund to IRC all amounts paid by IRC to XOMA under this Agreement; (y) XOMA
shall sell, assign and transfer to IRC (at no cost to IRC) the number of shares
of Common Stock of IRC issued to XOMA under Section 3.1.2 of this Agreement (or
if XOMA no longer owns the IRC shares, XOMA shall pay to IRC an amount equal to
the full amount of consideration received for the sale of such shares); and (z)
IRC shall have no further obligation to pay any amounts to XOMA under the
Original Agreement or this Agreement.

     6.1.3 Without limiting the rights and remedies of IRC at law, in equity or
otherwise, if Connetics, Vandenbark or any of their respective Affiliates (a)
takes during the term of this Agreement any action or initiates any proceeding
to prevent the issuance of, invalidate, revoke or otherwise render unenforceable
any of the Patent Rights (as defined in the Assignment Agreement dated as of
December 8, 1999, between IRC and Connetics), or (b) fails within ninety (90)
days after the date hereof to terminate, dismiss and withdraw any such action or
proceeding which was taken or initiated by it or any of its Affiliates on or
before the date hereof, then, if IRC is not itself in material breach of the
Original Agreement or this

<PAGE>
                                      -11-

Agreement, IRC shall have no further obligation to pay any amounts to XOMA under
Section 3.1.1 of this Agreement.

     6.2 Notices. Any consent, notice or report required or permitted to be
given or made under this Agreement by one of the parties hereto to the other
party shall be in writing, addressed to such other party at its address
indicated below, or to such other address as the addressee shall have last
furnished in writing to the addressor and (except as otherwise provided in this
Agreement) shall be effective upon receipt by the addressee.

         If to IRC:                         The Immune Response Corporation
                                            5935 Darwin Court
                                            Carlsbad, California 92008
                                            Attention:  President
                                            Fax: (760) 431-8636

         If to XOMA:                        XOMA (US) LLC
                                            2910 Seventh Street
                                            Berkeley, California 94710
                                            Attention: Legal Department

     6.3 Governing Law. This Agreement shall be governed by and construed in
accordance with the laws of the State of California, without regard to
principles of conflicts of law.

     6.4 Attorneys' Fees. In the event that the parties incur attorneys' fees as
a result of an action arising from IRC's failure to pay the amounts due
hereunder, the prevailing party shall be entitled to attorneys' fees.

     6.5 Assignment. Neither IRC nor XOMA shall assign its rights or obligations
under this Agreement without the prior written consent of the other party
hereto; provided, however, that party may, without such consent, assign this
Agreement and its rights and obligations hereunder (a) to its Affiliates, or (b)
in connection with the transfer or sale of all or substantially all of its
business, or in the event of its merger or consolidation or change in control or
similar transaction. Any permitted assignee shall assume all obligations of its
assignor under this Agreement.

     6.6 Amendments. No change, modification, extension or termination of this
Agreement, or any of the provisions herein contained, shall be valid unless made
in writing and signed by duly authorized representatives of the parties hereto.

     6.7 Entire Agreement. This Agreement embodies the entire understanding
between the parties and supersedes any prior representations, understanding and
agreements between

<PAGE>
                                      -12-

them regarding the subject matter hereof. There are no representations,
agreements or understandings, oral or written, between the parties regarding the
subject matter of this Agreement which are not fully expressed herein.

     6.8 Waiver. The waiver by either party hereto of any right hereunder or the
failure to perform or of a breach by the other party shall not be deemed a
waiver of any other right hereunder or of any other breach or failure by said
other party whether of a similar nature or otherwise.

     6.9 Headings. The headings and captions used in this Agreement are for
convenience of reference only, and shall not in any way affect the
interpretation of the provisions of this Agreement.

     6.10 Counterparts. This Agreement may be executed in counterparts, each of
which shall be an original and all of which together shall constitute one and
the same instrument.

     IN WITNESS WHEREOF, the parties have executed this Agreement as of the date
first set forth above.

                         THE IMMUNE RESPONSE CORPORATION

                         By
                              ----------------------------------------
                              Dennis J Carlo, Ph.D.
                              President and Chief Executive Officer

                          XOMA (US) LLC

                          By
                              -----------------------------------------
                               Title

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