<PAGE>

                              LETTER OF INTENT



     THIS LETTER OF INTENT is made on the 11th day of June 1998, by and between
Agouron Pharmaceuticals, Inc., a corporation duly organized and existing under
the laws of the state of California, having a principal place of business at
10350 North Torrey Pines Road, La Jolla, California 92037 (hereinafter called
"Agouron"), and The Immune Response Corporation, a corporation duly organized
and existing under the laws of the state of Delaware, having a principal place
of business at 5935 Darwin Court, Carlsbad, California 92008 (hereinafter called
"Immune Response").  Agouron and Immune Response are sometimes hereinafter
referred to as a party (collectively "parties") to this Agreement.

                                     BACKGROUND

In accordance with the terms of this Letter of Intent, Immune Response has
agreed to license to Agouron the exclusive rights necessary or useful for the
registration and/or commercialization of the product known as REMUNE, a non-
infectious intact Human Immunodeficiency Virus ("HIV") devoid of outer envelope
proteins.  This Letter of Intent, which shall be binding on the parties, sets
forth the basic license terms upon which the parties have agreed.  The full
terms of the license will be set forth in a definitive agreement to be prepared
as described below.


     NOW, THEREFORE, the parties agree as follows:

1.   TERMS.  The parties hereby enter into this Letter of Intent to confirm 
their entering into a license agreement on terms substantially in accordance 
with those contained in Exhibit A hereto.  The parties acknowledge that 
Exhibit A states the basic terms of the understanding between the parties and 
anticipate the further negotiation and preparation of an agreement containing 
the full terms of the license between the parties ("Definitive Agreement").  
Each party agrees to act in good faith in an effort to negotiate, execute and 
deliver the Definitive Agreement on or before September 1, 1998.  If the 
Definitive Agreement is not executed by September 1, 1998, the provisions of 
this Letter of Intent shall continue in effect until the Definitive Agreement 
is executed, and the parties will continue to negotiate in good faith in an 
effort to execute and deliver the Definitive Agreement as soon as possible.

2.   DISCLOSURE.  The parties shall jointly prepare and release a statement
about the existence of this Letter of Intent and of the license between Agouron
and Immune Response.  Except as agreed to by the parties, neither Agouron nor
Immune Response shall release any further information to any third party who is
not under an obligation of confidentiality with respect thereto about any of the
terms of this Letter of Intent, or of the license, or of results of clinical
trials of REMUNE, without the prior written consent of the other, which consent
shall not unreasonably be withheld.  This prohibition includes, but is not
limited to, press releases, educational and scientific conferences, promotional
materials and discussions with the media.  If a party determines that it is
required by law to release information to any third party regarding such
matters, it shall notify the other party of this fact prior to releasing the
information.  The notice to the other party shall include the text of the
information proposed for release.  The

* * * - Confidential treatment requested. Sections of text which have been
omitted and for which confidential treatment is requested are noted with "***".
An unredacted version of this document has been filed separately with the
Securities and Exchange Commission.


                                     1


<PAGE>

other party shall have the right to confer with the notifying party regarding 
the necessity for the disclosure and the text of the information proposed for 
release.

3.   MISCELLANEOUS.  This Letter of Intent contains the entire agreement between
the parties as of the date hereinabove written on the matters set forth herein
and shall be governed by and construed in accordance with the laws of the State
of California.  Exhibit A describes the parties' understanding with respect to
the registration and commercialization of the "Product" as defined therein. This
Letter of Intent, including Exhibit A, shall not be amended, supplemented or
otherwise modified, except by an instrument in writing signed by duly authorized
officers of both parties.  Each party shall bear all of the expenses incurred by
it in connection with the negotiation and preparation of this Letter of Intent
and the Definitive Agreement.  Each party represents and warrants that it is not
presently bound by any agreement with any third party which limits its
performance of any of the obligations or activities provided for under this
Letter of Intent or contemplated by the Definitive Agreement.  Immune Response
represents and warrants that it is not aware of any patents, patent applications
and/or know-how that it does not have the right to license to Agouron which is
necessary or useful for commercialization of Product by Agouron.  Immune
Response further represents and warrants that it will not enter into any
agreements which limit Immune Response's performance of any of the obligations
or activities provided for under this Letter of Intent or contemplated by the
Definitive Agreement.  Immune Response, at its expense, shall obtain any
government approval(s) not related to drug product registration, which are
required to enable this Agreement to become effective.  At any time after
October 15, 1998, Agouron may elect to immediately terminate, in their entirety,
all of its rights and obligations under this Letter of Intent and the Definitive
Agreement, except that Agouron may exercise this right to terminate only on the
basis of its concerns related to the safety, efficacy, competitiveness, or
commercial feasibility of Product.


     IN WITNESS WHEREOF, the parties hereto have executed this Letter of Intent
by their respective officers thereunto duly authorized, as of the date
hereinabove written.  This Letter of Intent may be executed in counterparts and
all of such counterparts taken together shall be deemed to constitute one and
the same instrument.



 THE IMMUNE RESPONSE CORPORATION         AGOURON PHARMACEUTICALS, INC.


By:       s/Dennis J. Carlo             By:       s/Peter Johnson
          --------------------                    --------------------
Name:     Dennis J. Carlo               Name:     Peter Johnson
          --------------------                    --------------------
Title:    President                     Title:    President 
          --------------------                    --------------------


By:       s/Charles J. Cashion          By:       s/Gary Friedman     
          --------------------                    --------------------
Name:     Charles J. Cashion            Name:     Gary Friedman  
          --------------------                    --------------------
Title:    Senior VP                     Title:    Secretary  
          --------------------                    --------------------


                                      2 


<PAGE>
                                         
                                     EXHIBIT A


Immune Response, under the terms and conditions specified below, hereby 
grants Agouron the exclusive right to use, offer for sale, sell and/or 
import, in or into the Licensed Territory, the Product under applicable 
Immune Response Patent Rights (including claims therein relating to 
compositions and methods of use) and using applicable Immune Response 
Know-How. 

1.   Definitions:  Except as otherwise set forth herein, items containing an
     initial capitalized letter shall have the meaning stated below or in the
     Letter of Intent to which this Exhibit A is an attachment ("LOI"). 

     (a)  "Product" means a pharmaceutical product comprising a non-infectious
          intact HIV devoid of outer envelope proteins whose manufacture, use or
          sale infringes (in the absence of the license rights granted under
          this Exhibit A) a valid claim (which has not been abandoned,
          disclaimed or declared invalid in a non-appealable order) included in
          an issued patent within the Immune Response Patent Rights.
     
     (b)  "Licensed Territory" means all countries of the world except the
          countries listed in Schedule 1. 
     
     (c)  "Affiliate" means any person, organization or entity which is,
          directly or indirectly, controlling, controlled by, or under common
          control with Agouron or Immune Response, as the case may be.  The term
          "control" (including, with correlative meaning, the terms "controlled
          by" and "under common control with"), as used with respect to any
          person or entity, means the possession, directly or indirectly, of the
          power to direct or cause the direction of the management and policies
          of such person, organization or entity, whether through the ownership
          of voting securities, or by contract, or court order, or otherwise. 
          The ownership of voting securities of a person, organization or entity
          shall not, in and of itself, constitute "control" for purposes of this
          definition, unless said ownership is of a majority of the outstanding
          securities entitled to vote of such person, organization or entity. 
          Affiliate shall also mean a limited partnership in which a subsidiary
          of Agouron and/or Immune Response is a general partner.
     
     (d)  "Immune Response Patent Rights" means (i) the patents and the patent
          applications referred to in Schedule 2 of this Exhibit A; (ii) all
          patents arising from said applications, and all patents and patent
          applications based on, claiming the priority date(s) of, or
          corresponding to any of the foregoing; or (iii) any reissues,
          extensions (or other governmental actions that provide exclusive
          rights to the patent holder in the patented subject matter beyond the
          original patent expiration date), substitutions, confirmations,
          registrations, revalidations, re-examinations, additions,
          continuations, continuations-in-part, or divisions of or to any of the
          foregoing. 


*** - Confidential treatment requested.  Sections of text which have been
omitted and for which confidential treatment is requested are noted with "***". 
An unredacted version of this document has been filed separately with the
Securities and Exchange Commission.


                                  A-1


<PAGE>

     (e)  "Immune Response Know-How" means any know-how, trade secret,
          experimental data, formula, expert opinion, experimental procedure,
          and other confidential and/or proprietary information specifically
          concerning the Product that is Controlled by Immune Response and that
          is necessary or useful for either:  (i) the formulation, manufacture,
          use and/or application of the Product; or (ii) obtaining registration
          of the Product. 

     (f)  "Control" and "Controlled" mean possession of the ability to grant a
          license or sublicense as provided for herein without violating the
          terms of any agreement with, or arrangement with, any third party. 
     
     (g)  The terms "Net Sales," "Pre-Tax Profits," "Allowable Expenses" and
          "Manufacturing Transfer Markup" shall be fully defined in the
          Definitive Agreement.  The terms "Net Sales and "Allowable Expenses"
          shall be determined in accordance with generally accepted accounting
          principles and the usual and customary practices of the parties.

2.   As provided below, Immune Response and Agouron shall collaborate to
     complete the current program of clinical trials of the Product, including
     those aimed at achieving registration of the Product in the Licensed
     Territory, in an expeditious manner.  Immune Response and Agouron agree to
     the following basic approaches to the registration of Product in the
     Licensed Territory and the conduct of a committee to be formed to
     coordinate the parties' registration of Product in the Licensed Territory:

     (a)  Immune Response and Agouron shall use reasonable diligence in the
          registration of the Product.
     
     (b)  A committee, co-chaired by representatives of Immune Response and
          Agouron and comprised of representatives from Immune Response and
          Agouron, shall be formed to coordinate the registration of the Product
          in the Licensed Territory and such other matters that the parties
          mutually agree to assign to it.  Decisions of the committee shall be
          made by a unanimous vote of the committee, with each party having one
          (1) vote, regardless of the number of representatives attending a
          meeting.  The committee shall meet regularly, at least four times per
          year, and shall assign study or other registration activities between
          the parties as described in this Paragraph 2. 

     (c)  The committee shall review and discuss the registration plans for any
          countries involved, as well as a coordinated general strategy and
          priorities for preclinical and clinical registration of Product in the
          Licensed Territory.  Each party's members of the committee will
          reasonably consider the adoption of the other party's suggestions and
          will accept as many of such suggestions as are reasonable, based upon
          medical rationale, drug supply, and the need to conduct the studies in
          an expeditious and cost-efficient manner.

     (d)  The parties will share responsibility and authority to obtain
          regulatory approvals for the Product in the Licensed Territory.  If
          there is a disagreement among the parties concerning an issue related
          to the registration of the Product in the Licensed Territory, the
          issue shall be resolved in accordance with the provisions of Paragraph
          17.
     

*** - Confidential treatment requested.


                                    A-2

<PAGE>

     (e)  Agouron, at its expense (except for the cost of clinical supplies of
          Product to be provided to Agouron pursuant to the provisions of
          Paragraph 9), shall, using reasonable efforts, initiate and conduct a
          200-plus patient viral load study to support registration of the
          Product.
     
     (f)  In partial consideration for the rights granted to Agouron, Agouron
          will make up to six (6) quarterly payments of three million dollars
          ($3,000,000) each to support clinical and manufacturing development
          and scale-up of the Product beginning on October 15, 1998, and every
          ninety (90) days thereafter, until the earlier of: (i) January 15,
          2000; or (ii) the approval of a Product License Application ("PLA")
          for the Product in the United States.  The above quarterly payments of
          three million dollars ($3,000,000) each to support clinical and
          manufacturing development and scale-up of the Product shall only be
          due and payable by Agouron if Agouron has not elected to terminate, in
          its entirety, all of its rights and obligations under the LOI and the
          Definitive Agreement before the last permitted payment date for the
          applicable quarterly payment.
     
     (g)  Immune Response will complete, at its expense, the current worldwide
          program of clinical trials of the Product, including the studies
          listed in Schedule 3, and will promptly and fully disclose to Agouron
          the results of the interim and final analyses of data from these
          clinical trials.

     (h)  Agouron will provide, at its expense, regulatory staff support for
          preparation of registration documents as such support is reasonably
          requested by Immune Response.

     (i)  Agouron, notwithstanding the preceding, will be responsible for
          negotiating labeling, pricing and reimbursement for Product with the
          applicable regulatory authorities in the Licensed Territory, and after
          registration of the Product will have the primary responsibility for
          the ongoing correspondence and interaction with the applicable
          regulatory authorities.  Immune Response will provide reasonable
          assistance to Agouron in such interactions, if necessary.

     (j)  Except as provided above, the committee, in assigning the
          responsibility for performing specific tasks or activities related to
          a study or registration activity among the parties, shall make such
          assignments principally based on:  (i) the available resources each of
          the parties can commit to the task or activity; (ii) the expertise of
          each of the parties in conducting or monitoring the task or activity;
          (iii) which party can perform the task or activity in the most
          expeditious manner; and (iv) which party can perform the task or
          activity in the most cost-efficient manner.  A party not responsible
          for the performance of a task or activity may provide advisory and
          support services to the other party.  The committee may establish
          interdisciplinary project teams comprised of representatives of both
          parties having the specialized skills necessary to oversee the conduct
          of specific day-to-day registration 


*** - Confidential treatment requested


                                    A-3



<PAGE>
          activities.  The committee shall establish procedures concerning the
          scope and conduct of activities (including decision-making procedures)
          assigned to such project teams.  
          
     (k)  Each party shall keep the other party informed of its progress in the
          registration of Product, including making oral presentations of
          progress at the committee meetings and/or the preparing of such
          written progress reports as are agreed to by the parties summarizing
          such party's activities during each reporting period and its planned
          activities for the succeeding period.  Each of the parties will assign
          a representative to facilitate communications between the parties;
          each representative shall report to his/her management on the matters
          discussed at each of the meetings of the parties.
     
     (l)  Immune Response will disclose to Agouron all relevant Immune Response
          Know-How, including, but not limited to, data and information which it
          possesses from the pre-clinical and clinical studies of Product
          (including toxicology, pharmacokinetics and formulation studies) in a
          format which will facilitate the preparation for any regulatory
          filings or other correspondence to be filed or made by Agouron.  
     
     (m)  Immune Response will provide assistance to Agouron in accessing
          clinical investigators, clinical sites and testing laboratories for
          the purposes of data interpretation and/or evaluation and conduct of
          registration activities assigned to Agouron. 
     
     (n)  Immune Response shall use its reasonable efforts to coordinate its
          registration activities in any country(s) located outside the Licensed
          Territory with the registration activities of the parties in the
          Licensed Territory.

     (o)  If a licensee of Immune Response wishes to use the results of studies
          conducted by Agouron in such licensee's registration and
          commercialization activities in a country(s) located outside of the
          Licensed Territory, the parties shall enter into good-faith
          discussions about the sharing of the costs of such studies and/or the
          granting to Agouron of equivalent rights to use the results of any
          studies conducted by such licensee. 

     (p)  If development of the Product is discontinued in a country located in
          the Licensed Territory due to safety, efficacy or regulatory issues or
          by mutual agreement of the parties and Agouron is interested in
          developing a substitute drug product whose manufacture, use or sale
          would infringe (in the absence of the license rights granted under
          this Exhibit A) a valid claim (which has not been abandoned,
          disclaimed or declared invalid in a non-appealable order) included in
          an issued patent within the Immune Response Patent Rights, then Immune
          Response and Agouron shall enter into good faith negotiations
          regarding the terms of a license between Immune Response and Agouron
          for such substitute drug product.  During the period that Agouron is
          participating in the development and/or commercialization of the
          Product and/or another drug product whose manufacture, use or sale
          infringes (in the absence of the license rights granted under this
          Exhibit A) a valid claim (which has not been 



*** - Confidential treatment requested


                                    A-4


<PAGE>

          abandoned, disclaimed or declared invalid in a non-appealable order)
          included in an issued patent within the Immune Response Patent Rights,
          Immune Response agrees not to commercialize in the Licensed Territory
          other drug products whose manufacture, use or sale is covered by a
          valid claim (which has not been abandoned, disclaimed or declared
          invalid in a non-appealable order) in an issued patent within the
          Immune Response Patent Rights, on its own or with a third party, other
          than Agouron, its Affiliates or sublicensees. 

3.   In partial consideration for the rights granted to Agouron, Agouron will
     make the following license-fee milestone payments to Immune Response:


<TABLE>
<CAPTION>


     Milestones                                             Payment (US Dollars)
     ----------                                             -------------------
     <S>                                                    <C>
     Within 30 days of execution of the LOI                 $10,000,000

     ***                                                    $       ***

     ***                                                    $       ***

     ***                                                    $       ***
                                                            
     ***                                                    $       ***
                                                            -----------

          Total Milestone Payments                          $45,000,000
                                                            -----------
                                                            -----------
</TABLE>

The above license fee milestone payments shall be payable by Agouron one time
only and shall only be due if Agouron has not elected to terminate, in its
entirety, all of its rights and obligations under the LOI and the Definitive
Agreement before the last permitted payment date for the applicable milestone
payment.
     
4.   Prior to approval of the Product in the United States, Agouron will, "***."








5.   The right of Agouron to market Product in the Licensed Territory shall be
     subject to commercially reasonable marketing efforts by Agouron, on a
     country-by-country basis.  For purposes of this paragraph,
     commercialization efforts undertaken by Agouron's Affiliates and
     sublicensees shall be attributed to Agouron.  Agouron shall begin
     commercial sales of the in a country no later than "***" after the first
     registration of Product in such country; provided, however, that such
     period shall be extended for as long as commercially reasonable marketing
     efforts to begin commercial sales continue.  Following commencement of
     commercial sales in a country, Agouron shall keep Product reasonably
     available to the public; provided, however, that Agouron shall be released
     from this obligation if supply of Product is 


*** - Confidential treatment requested



                                    A-5


<PAGE>

     not available for such country and Agouron is not responsible for arranging
     for the commercial production and supply of Product for such country. 

6.   The term of the license rights granted hereunder will extend on a 
     country-by-country basis from the effective date of the signing of the 
     LOI until the last-to-expire of any patents within the Immune Response 
     Patent Rights covering the Product in such country (as extended by any 
     governmental actions which provide exclusive rights to the patent holder
     in the patented subject matter beyond the original patent expiration 
     date). 

7.   Agouron shall have the right to sublicense its rights in the Product in one
     or more countries of the Licensed Territory.  In the event that Immune
     Response or its Affiliates shall in the future obtain Control of one or
     more additional patent rights and/or know-how necessary or useful for the
     commercialization of the Product in the Licensed Territory, then Immune
     Response shall grant to Agouron an exclusive license consistent with the
     terms of this Exhibit A which adds such patent rights and know-how to the
     scope of the applicable Immune Response Patent Rights and Immune Response
     Know-How, without any additional obligations due from Agouron to Immune
     Response.  To the extent that Immune Response grants rights in the Product
     to a third party and such third party invents or discovers inventions
     and/or know-how necessary or useful for the commercialization of the
     Product in the Licensed Territory, then Immune Response shall use its
     reasonable efforts to secure rights for Agouron to use such inventions and
     know-how.

8.   Immune Response hereby grants to Agouron, its Affiliates and sublicensees a
     perpetual paid-up, royalty-free, worldwide, exclusive right to use Immune
     Response's trademark REMUNE-TM- in the marketing of the Product in the
     Licensed Territory.

9.   Immune Response shall supply Agouron, and Agouron shall purchase from
     Immune Response, sufficient commercial supplies of Product to support and
     sustain the launch and subsequent patient demand for Product in the
     Licensed Territory.  Immune Response hereby agrees to use its commercially
     reasonable efforts to have sufficient manufacturing capacity at its
     facilities to supply Agouron with commercial quantities of Product which
     are necessary for the launch of such Product in the Licensed Territory and
     agrees to have at least a monthly manufacturing capacity for the Licensed
     Territory of "***" unit doses/month of such Product at the time of launch
     of such Product.  Immune Response agrees, at its expense, to maintain
     commercially reasonable inventory and safety stock of Product for the
     Licensed Territory.  Immune Response further agrees to discuss with
     Agouron, in good faith, Immune Response's acquisition of additional
     manufacturing capacity required to meet the projected patient demand for
     the Product for the Licensed Territory.  Immune Response shall use
     diligence in its manufacturing activities and shall provide Agouron such
     technical support for the Product as it may reasonably requested. 
     Commercial supplies of Product shall be supplied to Agouron at Immune
     Response's "***." 


*** - Confidential treatment requested


                                    A-6

<PAGE>

10.  Immune Response agrees not to enter into any contractual arrangement with
     its licensees outside the Licensed Territory which would limit Immune
     Response's ability to fully fulfill Agouron's product requirements for the
     Licensed Territory, or which would require Immune Response to allocate its
     manufacturing capacity among such licensees and Agouron.  If supply
     shortages of Product are expected to occur during a calendar quarterly
     period, and Immune Response's available supply of drug product is required
     to be allocated among Immune Response's licensees, Immune Response shall
     allocate the available supply of drug product among Immune Response's
     licensees during such calendar quarterly period on a pro-rata basis, based
     upon:  (i) the relative utilization of such Product in each licensee's
     respective territories during the twelve (12) month period ending on the
     first day of such calendar quarterly period (based on historical sales data
     during such twelve (12) month, to the extent such data is available); and
     (ii) the projected sales of such Product in each licensee's respective
     territories during the twelve (12) month period commencing with the first
     day of such calendar quarterly period.

11.  If Immune Response is unable to provide Agouron with its requirements of
     Product in a timely and cost-efficient manner, Immune Response agrees to
     assist Agouron in the identification of alternative low-cost manufacturing
     sources for the Product, including but not limited to, access to current
     suppliers of starting materials, intermediates, bulk material and/or
     finished Product.  Immune Response in such circumstances will grant Agouron
     the non-exclusive worldwide right to make and have made Product under
     applicable Immune Response Patent Rights and Immune Response Know-How
     relating to processes, intermediates and materials for manufacturing
     Product, and will provide to Agouron without charge, to the extent
     available, technical and manufacturing assistance and use of its technology
     and proprietary information for the Product, including information on its
     analytical methods, validation reports and manufacturing processes. 

12.  Pre-Tax Profits generated from aggregate Net Sales and royalties from
     Products in the Licensed Territory on a country-by-country basis shall be
     shared equally by Immune Response and Agouron on a fifty-fifty basis. 
     "***."



*** - Confidential treatment requested

                                     A-7

<PAGE>

13.  At any time after October 15, 1998, Agouron may elect to immediately
     terminate its development obligations in the Licensed Territory for Product
     under the LOI and the Definitive Agreement, except that Agouron may
     exercise this right to terminate only on the basis of its concerns related
     to the safety, efficacy, competitiveness, or commercial feasibility of
     Product.  In the event that Agouron elects to terminate its development
     obligations for Product under the LOI and the Definitive Agreement, Immune
     Response, its Affiliates and sublicensees shall be free, without any
     further action by Immune Response or Agouron, to develop and/or
     commercialize Product in the Licensed Territory, on their own, or with any
     third party, and to retain, use and disclose to any such third party
     information and materials that have been developed by Agouron in its
     development activites for Product; provided, that Immune Response shall not
     disclose to such third party the confidential and proprietary information
     of Agouron (other than clinical, regulatory and manufacturing information
     and materials specifically relating to Product).  In the event of the
     termination of Agouron's development obligations in the Licensed Territory
     for Product under the LOI and the Definitive Agreement, the licenses
     granted to Agouron to use, offer for sale, sell and/or import, in or into
     the Licensed Territory, the Product under applicable Immune Response Patent
     Rights and using applicable Immune Response Know-How, shall be terminated. 
     Agouron shall transfer ownership of any dossiers for Product in the
     Licensed Territory to Immune Response, and shall cooperate with Immune
     Response to effect an orderly transition of Agouron's development 
     responsibilities in the Licensed Territory to Immune Response.

14.  At any time after October 15, 1998, Agouron may elect to immediately
     terminate, on a country-by-country basis, its marketing rights for Product
     in the Licensed Territory under the LOI and the Definitive Agreement,
     except that Agouron may exercise this right to terminate only on the basis
     of its concerns related to the safety, efficacy, competitiveness, or
     commercial feasibility of Product.  In the event that Agouron elects to
     terminate its marketing rights for Product in a country:  (i) the licenses
     granted to Agouron to use, offer for sale, sell and/or import, in or into
     such country, the Product under applicable Immune Response Patent Rights
     and using applicable Immune Response Know-How, shall be terminated, and
     Immune Response and its Affiliates and sublicensees shall be free to market
     such Product in such country, on its own, or with any third party; (ii)
     Agouron shall transfer ownership to Immune Response of any dossiers for
     Product in such country; and (iii) Agouron shall cooperate with to Immune
     Response to effect an orderly transition of Agouron's marketing
     responsibilities in such country to Immune Response.

15.  Immune Response, in accordance with the reasonable directions of Agouron,
     shall prepare, file, prosecute, maintain and extend:  (i) patent
     applications and patents included in the Immune Response Patent Rights; and
     (ii) applicable Immune Response trademarks.  Immune Response shall own any
     Immune Response Patent Rights and Immune Response trademarks and shall be
     responsible for all preparation, filing, prosecution, maintenance,
     extension and enforcement expenses for such Immune Response Patent Rights
     and Immune Response trademarks.  Within fourteen (14) days after the
     execution of the LOI, Immune Response shall provide Agouron with copies of
     the material patent prosecution file histories for the Immune Response
     Patent Rights.  Immune Response shall be solely responsible for  any 


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                                      A-8

<PAGE>

     royalties or other payments due to Rhone-Poulenc Rorer Inc. (including
     payments due because of license fees or commercial sales of the Product)
     because of their previously contractual arrangement (or the termination
     thereof) involving the Product.  "***."






16.  This Agreement shall be assignable by a party with the prior written
     consent of the other party.  Any assignment (other than to an Affiliate)
     without the prior written consent of the other party shall be void.  If
     this Agreement is assigned to an Affiliate of a party, the assigning party
     shall still be responsible for all of its obligations specified in this
     Agreement.  Notwithstanding the preceding, the LOI shall be assignable to
     the transferee or successor company in the event of:  (i) a sale or
     transfer of all or substantially all of a party's assets; or (ii) the
     merger or consolidation of the party with another company.

17.  If the representatives of the parties are unable to reach agreement on a
     decision required under the terms of the LOI, the issue shall be submitted
     for consideration, in the case of Immune Response, to a designee of its
     Chief Executive Officer, and, in the case of Agouron, to a designee of its
     Chief Executive Officer.  If they are unable to agree, then the Chief
     Executive Officers of the parties shall agree upon the appropriate
     decision.  If the Chief Executive Officers of the parties are unable to
     reach agreement on a decision required of them, then the issue shall be
     settled by arbitration in San Diego, California in accordance with the
     Commercial Arbitration Rules of the American Arbitration Association then 
     in effect.  The decision of the arbitrator(s) shall be final and binding on
     all parties.  The cost of such arbitration shall be borne by the 
     non-prevailing party, unless otherwise decided by the arbitrator(s). 
     
18.  "***." 









19.  Neither party shall be held liable or responsible to the other party nor be
     deemed to have defaulted under or breached the LOI for the failure or delay
     in fulfilling or performing any term of the LOI to the extent, and for so
     long as, such failure or delay is caused by or results from causes beyond
     the reasonable control of the affected party, including but not limited to
     fire, floods, embargoes, war, acts of war (whether war is declared or not),
     insurrections, riots, civil commotions, strikes, lockouts or other labor
     disturbances, acts of God, or acts, omissions or delays in acting by any
     governmental authority or the other party.

*** - Confidential treatment requested


                                      A-9


<PAGE>

20.  In partial consideration for the rights granted to Agouron, Agouron will
     purchase from Immune Response two million dollars ($2,000,000) of
     unregistered Immune Response Common Stock on each of the purchase dates
     listed below at the premiums to Fair Market Value ("FMV") set forth
     opposite the applicable purchase date: 

<TABLE>
<CAPTION>


      Purchase Date                                     Premium
      ---------------------                             --------
      <S>                                               <C>
      Execution Date of LOI                             50%
      10/15/98                                          ***
      1/15/99                                           ***
      4/15/99                                           ***
      7/15/99                                           ***
      10/15/99                                          ***
      1/17/00                                           ***
</TABLE>

FMV shall mean the average closing price of Immune Response Common Stock
for the five trading days immediately preceding the above purchase dates;
provided, however, that if the FMV of Immune Response Common Stock is "***"
on the applicable purchase date, the premium to FMV shall be "***."
Agouron's obligation to purchase Immune Response Common Stock shall
terminate with respect to any purchase obligations whose applicable
purchase dates occur after Agouron has elected to terminate, in its
entirety, all of its rights and obligations under the LOI and the
Definitive Agreement.





*** - Confidential treatment requested

                                      A-10


<PAGE>

                                   SCHEDULE 1

                 COUNTRIES NOT INCLUDED IN THE LICENSED TERRITORY


The following countries, subject to the provisions of Paragraph 18 of Exhibit A,
are excluded from the Licensed Territory "***:"

***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***


The following countries, subject to the provisions of Paragraph 18 of Exhibit 
A, are excluded from the Licensed Territory "***."

***
***
***
***
***
***
***
***
***
***



*** - Confidential treatment requested

                                   S-1


<PAGE>

                            SCHEDULE 2

                  IMMUNE RESPONSE PATENT RIGHTS


U.S. Patent No. 5,256,767, issued October 26, 1993, from U.S. Patent
Application Serial No. 07/975,899, filed November 10, 1992.

"***."

"***."












*** - Confidential treatment requested

                                    S-2


<PAGE>

                                SCHEDULE 3

SUMMARY OF CLINICAL TRIALS OF PRODUCT BEING CONDUCTED BY IMMUNE RESPONSE


1.   Trial 806 is a multi-center, double-blind, Phase III clinical end point
     study.  Patients are HIV positive with CD4 counts between 300 and 549
     cells/mul.

2.   Trial 816 is a multi-center, double-blind, Phase II study intended to
     evaluate the combination of REMUNE-TM- and triple antiviral drug therapy
     (AZT, 3TC and Crixivan) on the induction of an HIV-1 specific immune
     response.  Patients are HIV positive with CD4 counters > 350 cells/ul.

3.   Trial 2102 is a multi-center, double-blind, adjuvant-controlled, Phase II
     study of REMUNE plus AZT and ddI versus AZT and ddI alone in HIV-infected
     subjects.  The trial is being conducted in Spain and patients have CD4
     counts between 300 and 700 cells/mul.

4.   Trial 808 is a Phase I study to evaluate the safety and immunogenicity of
     REMUNE in children with HIV-infection.

5.   The Switzerland trial is a single center, randomized, open label, Phase II
     study combining antiviral therapy (1592U89) plus Nelfinavir plus Saquinavir
     or 141W94) alone or antiviral therapy plus immune-based therapy
     (subcutaneous interleukin-2 or REMUNE) in antiviral naive HIV-1 infected
     subjects with CD-4 + counts > 250 cells/mul.
     
6.   The England trial is a single center, randomized, open labeled Phase I
     study of antiviral therapy (two nucleoside analogues and at least one
     protease inhibitor) versus antiviral therapy plus IL-2; antiviral therapy
     plus IL-2 plus REMUNE; antiviral therapy plus REMUNE.  Patients are HIV
     positive with CD4 counts > 300 cells/mul.

7.   Trial 818 is a Phase II study intended to evaluate the combination of
     interferon-alpha (IFN) and REMUNE on HIV-1 specific immunogenicity in HIV-1
     infected subjects with CD-4 counts > 300 cells/mul.
     
8.   Trial 2101B is a Phase II, double-blind, randomized, adjuvant controlled
     study of REMUNE.

9.   Trial 822 is a randomized, double-blind, adjuvant controlled, research
     study to evaluate the combination of REMUNE and HAART on the induction of
     HIV-1 specific immune responses.
     

                               S-3