<PAGE>

                                                                    Exhibit 10.9
                                                                    ------------

                                   Agreement

     Medarex, Inc. and GenPharm International (Medarex, Inc. and GenPharm
     International are referred to hereinafter as "Provider") agree to provide
     Immuno-Designed Molecules S.A., ("Recipient") with certain research
     material requested by Recipient for use, subject to the terms and
     conditions set forth in this Agreement (the "Agreement"). Provider
     (collectively on the one hand) and Recipient (on the other hand) are each
     referred to herein singularly as a "Party" and collectively as the
     "Parties" to this Agreement.

     1.   This Agreement applies to the transfer by Provider to Recipient of
          transgenic mice ("Mice") and to any biological materials (including
          human and murine antibodies and immunized Mice) derived from the
          Recipient's use of those Mice hereunder (collectively, the "Derived
          Material"). The Mice and the Derived Materials are referred to herein
          collectively as the "Materials". Recipient shall use the Mice solely
          for purposes of conducting research expected to result in Derived
          Materials (and data, results and information relating thereto),
          [*****]. The Research is expected to include the immunization of the
          Mice with antigens supplied by Recipient (each an "Antigen"), and any
          such antigens or other materials provided or used by Recipient for
          purposes of the Research are referred to herein collectively as the
          "Recipient Materials". Recipient shall be under no obligation to
          disclose the nature of or provide any Recipient Materials to Provider.

     2.   Legal title to all Mice shall be and remain solely with Provider, and
          nothing in this Agreement grants Recipient any rights under any
          patents or patent applications of Provider. Recipient shall not
          transfer the mice. Recipient will use the Mice solely for the purposes
          contemplated under this Agreement, and in no event will attempt to
          breed or duplicate in any way the Mice provided to Recipient by
          Provider hereunder. Any information of Provider that is disclosed to
          Recipient by Provider in connection with the transfer of the Mice or
          the Research hereunder shall be used by Recipient solely for the
          purposes of Research, and shall be held in confidence by Recipient
          subject to the terms and conditions of Schedule A ("Confidentiality
          Provisions"). Legal title to any and all Recipient Materials shall be
          and remain solely with Recipient, and nothing in this Agreement grants
          Provider any rights under any patents or patent applications of
          Recipient. Any information of Recipient

***** REPRESENTS CONFIDENTIAL PORTION WHICH HAS BEEN OMITTED AND FILED
SEPARATELY WITH THE SECURITIES AND EXCHANGE COMMISSION. CONFIDENTIAL TREATMENT
HAS BEEN REQUESTED WITH RESPECT TO THE OMITTED PORTIONS.
<PAGE>

          relating to any Recipient Materials that is disclosed to Provider by
          Recipient shall not be used by Provider for any purpose, and shall be
          held in confidence by Provider subject to the terms and conditions of
          the Schedule A.

     3.   [*****] Recipient shall be under no obligation to provide any such
          Derived Materials to Provider. During the Materials Term (as
          hereinafter defined), Recipient shall not make any use of any such
          Derived Materials except for purposes of the Research, and thereafter
          Recipient shall not make any use of the Derived Materials, shall not
          transfer any Derived Materials to any third party, and shall not file
          any patent applications covering any Derived Materials or based on the
          Research without Provider's prior written consent, [*****]. Upon
          expiration or termination of the Materials Term, unless the Parties
          have entered into a definitive agreement, Recipient shall return or
          destroy the Mice and destroy all Derived Materials; provided, however,
          that legal title to any data, research results or other information
          relating to the Derived Materials shall be and remain with Recipient,
          but such shall be treated as confidential information and shall be
          held in confidence by Recipient subject to the terms and conditions of
          Schedule A. Recipient shall be under no obligation to disclose any
          such data, research results or other information to Provider, but if
          and to the extent that Recipient does make any such disclosure, any
          such information of Recipient disclosed to Provider by Recipient shall
          not be used by Provider for any purpose and shall be held in
          confidence by Provider subject to the terms and conditions of the
          Schedule A.

     4.   The transfer of the Mice constitutes a nonexclusive license to use the
          Mice solely for the purposes of the Research. This Agreement does not
          restrict Provider's right to distribute the Mice to other commercial
          or to non-commercial entities. Provider shall have no obligation to
          grant a license to Recipient, and may grant exclusive or nonexclusive
          licenses to others who may be investigating uses of the Mice.

     5.   The Mice are provided to Recipient to conduct experiments in animals
          or in vitro. The Materials will not be used in humans, including for
          purposes of diagnostic testing.

     6.   During the Materials Term and thereafter until the return or
          destruction of the Mice and destruction of the Derived Materials,
          written records will be maintained by Recipient of all uses made of,
          and all persons allowed access to Materials, and copies of such
          records will be furnished to Provider as

***** REPRESENTS CONFIDENTIAL PORTION WHICH HAS BEEN OMITTED AND FILED
SEPARATELY WITH THE SECURITIES AND EXCHANGE COMMISSION. CONFIDENTIAL TREATMENT
HAS BEEN REQUESTED WITH RESPECT TO THE OMITTED PORTIONS.

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<PAGE>

          confidential information of Recipient subject to the terms and
          conditions of Schedule A.

     7.   The Materials are experimental in nature and shall be used with
          prudence and appropriate caution, since not all of the characteristics
          are known. THE MATERIALS ARE PROVIDED "AS IS" WITHOUT WARRANTY OF
          MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE OR ANY OTHER
          WARRANTY, EXPRESS OR IMPLIED. PROVIDER MAKES NO REPRESENTATION OR
          WARRANTY THAT THE USE OF THE MATERIALS WILL NOT INFRINGE ANY PATENT OR
          OTHER PROPRIETARY RIGHT.

     8.   This Agreement shall commence as of December 27, 1999 (the "Effective
          Date"). Except for Schedule A, the term of this Agreement (the
          "Materials Term") shall expire on the date that is [*****] after the
          Effective Date, unless either extended by the Parties by written
          agreement, sooner terminated in accordance herewith or the Parties
          have entered into a definitive agreement. The term of Schedule A shall
          not expire until five (5) years after the Effective Date. Either Party
          may terminate the Materials Term of this Agreement for any reason
          effective thirty (30) days after written notice to the other Party.
          Upon expiration or termination of the Materials Term, unless the
          Parties have entered into a definitive agreement, Recipient shall
          return or destroy the Mice and destroy all Derived Materials, and
          Provider shall return or destroy any Recipient Materials (if any)
          received from Recipient and shall destroy any Derived Materials (if
          any) received from Recipient. The Parties anticipate that the
          definitive agreement will have a term of [*****].

     9.   If Recipient provides written notice to Provider of the identity of
          the Antigen for which Derived Materials have been obtained by
          Recipient, unless Provider has previously granted a third party rights
          to use the Mice with respect to such Antigen or has commenced or has
          the intent to commence an active research program on its own behalf
          with respect to such Antigen, as shown by written records, during the
          Materials Term Recipient shall have a right of first negotiation to
          obtain a commercial license from Provider with respect to the Derived
          Materials specific for such Antigen. During the Materials Term, if
          Recipient provides such notice and either a third party notifies
          Provider that such third party wishes to acquire a commercial license
          to antibodies directed against such Antigen or Provider wishes to
          commercialize antibodies against such Antigen itself, Provider shall
          notify Recipient; however, Provider shall not be obligated to identify
          such party,

***** REPRESENTS CONFIDENTIAL PORTION WHICH HAS BEEN OMITTED AND FILED
SEPARATELY WITH THE SECURITIES AND EXCHANGE COMMISSION. CONFIDENTIAL TREATMENT
HAS BEEN REQUESTED WITH RESPECT TO THE OMITTED PORTIONS.

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<PAGE>

          whether Provider or a third party. If Recipient has not notified
          Provider within ten (10) business days of such Provider's notice that
          Recipient will enter a definitive agreement with Provider for a non-
          exclusive commercial license for the Derived Materials on the terms
          set forth on Schedule B, or if Recipient and Provider have failed to
          enter into a definitive license agreement consistent with such terms
          within ninety (90) days from the date of Provider's notice to
          Recipient, then Recipient's right of first negotiation shall terminate
          with respect to the Derived Materials and the related Antigen. In any
          such case, Provider may grant one or more third parties commercial
          licenses with respect to antibodies specific for the applicable
          Antigen, or conduct commercialization of such antibodies itself.

     10.  In no event shall Provider be liable for any use by Recipient of the
          Materials or for any loss, claim, damage, or liability, of any kind or
          nature, that may arise from or in connection with this Agreement or
          the use, handling, or storage of the Materials. The Recipient agrees
          to indemnify and hold harmless Provider and Provider's officers,
          agents, and employees from any liability, loss, or damage they may
          suffer as a result of claims, demands, costs, or judgments against
          them arising out of the use and disposition of the Materials by the
          Recipient, except insofar as such liability arises out of the
          negligence or wrongdoing of Provider or its officers, agents or
          employees.

     11.  Recipient will use the Materials in compliance with all laws,
          governmental regulations and guidelines, including without limitation
          current NIH guidelines and any regulations or guidelines pertaining to
          research with recombinant DNA that may be applicable to the Materials.

     12.  Provider and Recipient agree in principal, subject to the terms of a
          definitive agreement, for Provider to license to Recipient on a non-
          exclusive basis the right to develop and commercialize Medarex's in-
          licensed anti-CTLA-4 intellectual property, technology and Provider's
          anti-CTLA-4 human antibody in connection with cellular vaccines and
          cellular therapy. The terms of such license will [*****] include
          milestone payments, beginning upon [*****], equal to [*****] and
          royalties equal to [*****]. To the extent that Recipient may develop
          patents or patent applications on the use of anti-CTLA-4 antibodies in
          connection with cellular vaccines or cellular therapy, Recipient and
          Provider agree that Provider will have the right to out-license the
          relevant patents and patent applications to potential licensees,
          [*****].

***** REPRESENTS CONFIDENTIAL PORTION WHICH HAS BEEN OMITTED AND FILED
SEPARATELY WITH THE SECURITIES AND EXCHANGE COMMISSION. CONFIDENTIAL TREATMENT
HAS BEEN REQUESTED WITH RESPECT TO THE OMITTED PORTIONS.

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<PAGE>

     13.  [*****]

     14.  This Agreement, including its Schedule A and Schedule B, contains the
          entire agreement between the Parties with respect to the subject
          matter contained herein and supersedes any previous understandings,
          commitments or agreements, oral or written. This Agreement may only be
          amended with a written agreement signed by authorized representatives
          of the Parties hereto.

     15.  This Agreement shall be governed by New Jersey law. The Parties hereby
          submit to the exclusive jurisdiction of the courts of New Jersey in
          all matters concerning this Agreement.


FOR MEDAREX INC. AND                    FOR IMMUNO-DESIGNED MOLECULES S.A.
GENPHARM INTERNATIONAL


Signature: /s/ D. Drakeman              Signature: /s/ J. Romet-Lemonne
           -----------------------                 ---------------------------

Name:  DONALD L. DRAKEMAN               Name:  JEAN-LOUP ROMET-LEMONNE

Title: CHIEF EXECUTIVE OFFICER          Title: PRESIDENT

Date:  December 27, 1999                Date:  December 27, 1999

***** REPRESENTS CONFIDENTIAL PORTION WHICH HAS BEEN OMITTED AND FILED
SEPARATELY WITH THE SECURITIES AND EXCHANGE COMMISSION. CONFIDENTIAL TREATMENT
HAS BEEN REQUESTED WITH RESPECT TO THE OMITTED PORTIONS.

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<PAGE>

                                  SCHEDULE A

                          CONFIDENTIALITY PROVISIONS

     Each Party (herein referred to as the "Disclosing Party") is in possession
     of certain non-public confidential and/or proprietary information (such
     information, whether in written or oral form and including summaries or
     notes thereof, is hereinafter defined as the "Information") that it is
     willing to disclose to the other Party (herein referred to as the
     "Receiving Party") for the purpose of discussing a possible collaboration
     involving Medarex's transgenic mouse and antibody technology.

     The Receiving Party agrees on behalf of itself and its affiliates,
     successors and assigns to accept such Information, which may be disclosed
     in written or oral form, in accordance with the following terms:

     1.   The Receiving Party agrees not to disclose to anyone and to protect
          the confidentiality of any and all Information disclosed to it under
          this Agreement, with the exception of the following:

               a)   Information that, at the time of disclosure to the Receiving
                    Party, is generally known to the public;

               b)   Information that, after disclosure by the Disclosing Party
                    becomes part of the public knowledge by publication or
                    otherwise, except by breach of this Agreement;

               c)   Information that was in the Receiving Party's possession at
                    the time of disclosure but not acquired, directly or
                    indirectly, from the Disclosing Party, provided the
                    Receiving Party furnishes the Disclosing Party with
                    satisfactory written documentation thereof prior to any
                    disclosure of such Information to a third party;

               d)   Information that the Receiving Party receives from third
                    parties who have the legal right to disclose such
                    information, provided such Information was not obtained to
                    the knowledge of the Receiving Party by said third parties,
                    directly or indirectly, from the Disclosing Party on a
                    confidential basis.

     2.   The Receiving Party agrees that it will not use the Information that
          it is required hereunder to keep confidential for any purpose other
          than for the purpose described above.

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<PAGE>

                                  SCHEDULE B

                                  TERM SHEET
                         HuMAb-Mouse /(TM)/ Technology


     The Collaboration

     Medarex proposes to make the HuMAb-Mouse technology available to Immuno-
     Designed Molecules S.A. to create antibodies for an antigen, or antigens,
     of Immuno-Designed Molecules S.A. choice.

     Demonstration Project

     Medarex offers a free demonstration project to allow to work with the HuMAb
     mice and develop a pool of high affinity, human antibodies for [*****]
     antigens. The exact number of mice needed is to be determined. At Immuno-
     Designed Molecules S.A.'s option, Medarex will perform immunizations,
     derive hybridomas and characterize the resulting antibodies, using Immuno-
     Designed Molecules S.A.'s antigen and assays, for a fee of [*****] per
     antigen. Medarex can also develop assays, at a price to be determined.

     Research License

     Following the demonstration project, if Immuno-Designed Molecules S.A.
     chooses to enter into a business collaboration, for a fee of [*****] per
     antigen target, Medarex will grant a research license on a non-exclusive
     basis for a [*****] period to allow Immuno-Designed Molecules S.A. to
     evaluate the human antibodies to the antigen. This license may be renewed
     for an additional fee of [*****] per antigen target for [*****].

     Commercial License

     An exclusive commercial license for the antibodies created by Immuno-
     Designed Molecules will be granted for a fee of [*****] per antigen. If the
     commercial license is obtained during the research license renewal period,
     the renewal fee will be pro-rated and credited against the commercial
     license fee. Immuno-Designed Molecules S.A. may proceed directly to the
     commercial license for a target antigen without obtaining a research
     license first. Commercial licenses are subject to availability.

***** REPRESENTS CONFIDENTIAL PORTION WHICH HAS BEEN OMITTED AND FILED
SEPARATELY WITH THE SECURITIES AND EXCHANGE COMMISSION. CONFIDENTIAL TREATMENT
HAS BEEN REQUESTED WITH RESPECT TO THE OMITTED PORTIONS.

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<PAGE>

Milestones

[*****]

Royalties

Annual Worldwide Sales

[*****]

***** REPRESENTS CONFIDENTIAL PORTION WHICH HAS BEEN OMITTED AND FILED
SEPARATELY WITH THE SECURITIES AND EXCHANGE COMMISSION. CONFIDENTIAL TREATMENT
HAS BEEN REQUESTED WITH RESPECT TO THE OMITTED PORTIONS.

                                       8