Exhibit 10

                       COLLABORATIVE EVALUATION AGREEMENT

This Agreement is made by and between Maxygen, Inc., 515 Galveston Drive,
Redwood City, California 94063 ("Maxygen"), and SIGA Technologies, Inc., 420
Lexington Avenue, Suite 620, New York, NY 10170 ("SIGA"), effective October 17,
2000 (the "Effective Date"), as follows:

                                   BACKGROUND

A. Maxygen has rights in certain genes useful for the production of proteins
that may be useful for vaccines; and

B. SIGA has rights in certain gram-positive commensal bacteria and related
technology useful for the production of proteins on the surface of bacteria that
may be useful for vaccines; and

C. SIGA and Maxygen wish to enter in to this Agreement in order to research and
evaluate the utility of gram-positive commensal bacteria as vectors for
inducing mucosal immunity.

NOW, THEREFORE, in consideration of the mutual covenants contained herein, and
for other good and valuable consideration, the parties hereby agree as follows:

      1. Evaluation. Subject to the terms and conditions set forth herein,
Maxygen and SIGA shall use commercially reasonable efforts to conduct mutually
agreed collaborative research (the "Evaluation") on the utility of gram-positive
commensal bacteria as vectors for inducing mucosal immunity as set forth in the
SIGA/Maxygen Research Project proposal attached hereto as Exhibit A and
incorporated herein (the "Project Proposal"). The parties shall review the
Project Proposal on an ongoing basis and may make mutually agreed upon changes
to the Project Proposal then in effect. SIGA and Maxygen shall conduct research
in accordance with the Project Proposal in a professional manner and each agrees
to commit the personnel, facilities and other resources reasonably necessary to
perform the research. Each party shall be responsible for its own costs in
performing the Evaluation.

      2. Materials:

            2.1 Maxygen Materials: Maxygen shall transfer to SIGA reasonable
quantities of biological materials identified on Exhibit B, and such other
additional materials as Maxygen and SIGA may from time-to-time agree during the
term of the Evaluation (the "Maxygen Materials") for the sole purpose of
performing the Evaluation. All right, title and interest to the Maxygen
Materials shall at all times remain with and be vested in Maxygen.

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                  2.1.1 Restriction on Use and Control. SIGA shall use the
Maxygen Materials for the sole purpose of performing the Evaluation at its
facility located at 420 Lexington Avenue, Suite 620 New York, NY 10170 and/or
SIGA's facility at 4575 SW Research Way, Suite 230, Corvallis, OR 97333 under
the direction of one or more SIGA employees, under scientifically reasonable
containment conditions, and not for any commercial, business or other use or
purpose other than the Evaluation without the prior written consent of Maxygen.
SIGA shall not transfer or provide access to the Maxygen Materials to any other
persons or entity or to any location other than its addresses specified above,
without the prior written consent of Maxygen (which consent may be conditioned
inter alia upon such person or entity duly executing and delivering Maxygen
standard form of material transfer agreement therefor).

                  2.1.2 SIGA represents and warrants that all personnel,
including employees of SIGA and Oregon State University who will be involved in
the performance of the Evaluation are and shall be bound by: (a) confidentiality
obligations at least as strict as those set forth herein; and (b) an obligation
to assign all Inventions (as defined in Section 5 herein) to SIGA and to
cooperate with SIGA in connection with patenting such Inventions. SIGA agrees
that it will not permit persons not bound by such obligations to work on the
Evaluation.

            2.2 SIGA Materials: SIGA owns and/or has licensed certain
gram-positive commensal bacteria and related technology, including without
limitation the gram-positive commensal bacteria and related technology licensed
from Rockefeller University, Oregon State University and/or Emory University and
will make certain of those materials (the "SIGA Materials") available for use in
the Evaluation. All right, title and interest to the SIGA Materials shall at all
times remain with and be vested in SIGA.

            2.3 Joint Materials: Using the SIGA Materials, SIGA shall make
materials as set forth in the Evaluation, including without limitation
recombinant constructs expressing heterologous genes contained within the
Maxygen Materials (the "Joint Materials"). SIGA shall provide, and shall ensure
that Oregon State University provides, reasonable quantities of the Joint
Materials to Maxygen on an ongoing basis during the term of this Agreement.
Subject to Section 7, Maxygen shall use such Joint Materials solely for the
purpose of performing the Evaluation at its facility at 515 Galveston Dr.,
Redwood City, CA 94063 under the direction of one or more Maxygen employees.
Subject to the terms of this Agreement, Maxygen and SIGA shall jointly own the
Joint Materials. Subject to Section 7, neither Maxygen nor SIGA may take, send
or otherwise provide the Joint Materials to any third party without the prior
written approval of both Maxygen and SIGA.

      3. Reports and Records.

            3.1 Reports. Each party shall keep the other party informed of the
progress of the research under the Evaluation and shall provide reasonable
access to all source data and information relating to the Joint Materials and
shall provide the other party with summary written reports of any research under
the Evaluation upon reasonable request. The parties will consult with each other
as needed regarding the proposed course

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of the Evaluation. Within twenty (20) days after completion of the Evaluation,
or termination of the Evaluation in accordance with Article 15, SIGA and Maxygen
will prepare and submit to the other a report that sets forth the results of the
Evaluation and a summary of all data and information related to the Joint
Materials. Such information shall be considered Confidential Information of the
disclosing party as defined in Section 4.

            3.2 Records. SIGA and Maxygen agree to maintain, and SIGA shall
ensure that Oregon State University maintains, records of the activities
conducted in performing the Evaluation (or cause such records to be maintained)
in sufficient detail and in accordance with good scientific practices as will
properly reflect all work done and results achieved in the performance of the
Evaluation (including all data in the form required under any applicable
governmental regulations).

      4. Confidentiality and Non-Use Obligations. During the course of the
Evaluation, Maxygen and SIGA may each provide confidential information,
including but not limited to each party's proprietary materials, research and
development data and plans, proprietary technologies, business or research
strategies, trade secrets and material embodiments thereof (each party's
"Confidential Information"), to the other solely for the recipient's conduct of
the Evaluation. Each party may disclose Confidential Information of the other
party to its employees, agents and consultants, but only to the extent
reasonably required to accomplish the purposes of this Agreement. Each party
will use at least the same standard of care as it uses to protect proprietary or
confidential information of its own to ensure that such employees, agents,
consultants and licensees do not disclose or make any unauthorized use of the
Confidential Information.

            4.1 Confidential Information shall be provided in writing, marked
"confidential", or if disclosed orally, reduced to writing, marked
"confidential", and provided to the recipient within thirty (30) days of such
oral disclosure.

            4.2 The recipient shall maintain the disclosing party's Confidential
Information in confidence during the term of this Agreement and for a period of
five (5) years following the expiration or earlier termination hereof. The
recipient shall use the disclosing party's Confidential Information solely for
its conduct of the Evaluation, unless the recipient has received the prior
written approval of the disclosing party.

            4.3 The recipient's obligations hereunder shall not apply to any
information which: (i) can be shown by contemporaneous documentation of the
recipient to have been in its possession prior to receipt from the disclosing
party; (ii) is or becomes, through no fault of the recipient, publicly known;
(iii) is furnished to the recipient by a third party which is lawfully in
possession of such information and without breach of a duty to the disclosing
party; or (iv) is independently developed by the recipient without access to the
disclosing party's Confidential Information. Notwithstanding the foregoing,
either party may disclose the Confidential Information of the other to the
extent required by an applicable court order or by law; provided, however, that
either party that is so required to disclose the Confidential Information of

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the other party shall give the other party reasonable advance notice of such
disclosure and use reasonable efforts to secure confidential treatment of such
Confidential Information (whether through protective order or otherwise).

      5. Intellectual Property Rights. Maxygen and SIGA acknowledge that the
conduct of the Evaluation may result in Inventions of commercial value, and they
agree to collaborate so as to protect the proprietary nature of such Inventions.
For purposes of this Agreement, "Inventions" shall mean any and all technology,
now existing or hereafter arising, conceived or reduced to practice by Maxygen
and/or SIGA in the performance of the Evaluation, including without limitation,
any idea, discovery, data, compound, molecule, cell line, biological or other
material, know-how, technique, method, process, use, composition, skill,
Confidential Information, trade secret or configuration of any kind, whether or
not any such information or materials would be (i) enforceable as a trade
secret, (ii) protected from copying on the basis of copyright infringement or
unfair competition, or (iii) eligible for protection under the patent laws of
the United States or elsewhere. Inventorship of any Inventions arising from the
conduct of the Evaluation shall be determined by the patent laws of the United
States and, subject to the terms of this Agreement, rights of ownership shall
follow therefrom. SIGA represents and warrants that its conduct of the
Evaluation will not result in the creation of any rights to any third parties.

            5.1 Ownership of Inventions.

                  5.1.1 "Maxygen Inventions" shall mean Inventions invented
solely by Maxygen employees or persons obligated to assign their Inventions to
Maxygen. Maxygen retains all right, title, and interest in and to all Maxygen
Inventions.

                  5.1.2 "SIGA Inventions" shall mean Inventions invented solely
by employees of SIGA or persons obligated to assign their Inventions to SIGA,
including without limitation employees of Oregon State University involved in
the performance of the Evaluation. Subject to the provisions of Section 7
herein, SIGA retains all right, title, and interest in and to all SIGA
Inventions.

                  5.1.3 "Joint Inventions" shall mean Inventions invented
jointly by employees of Maxygen or persons obligated to assign Inventions to
Maxygen, and employees of SIGA or persons obligated to assign Inventions to
SIGA, including without limitation employees of Oregon State University involved
in the performance of he Evaluation. Subject to the provisions of Section 7
herein, Maxygen and SIGA shall jointly own all Joint Inventions.

            5.2 Invention Disclosure; Inventorship. Each party shall promptly
provide a full written disclosure to the other describing any SIGA Inventions
and/or Joint Invention arising out of its conduct of the Evaluation (each an
"Invention Disclosure"). Such disclosure by SIGA shall contain sufficient detail
to enable Maxygen to evaluate the advisability of exercising its option granted
hereunder with respect to each such Invention.

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      6. Right to File Patents: Enforcement of Patents/Patent Applications
         Relating to Joint Inventions:

            6.1 Maxygen and SIGA Sole Inventions. Each party shall have the sole
right, but not the obligation, to file, prosecute and maintain patent
applications and patents with respect to its solely owned materials and
Inventions, at its sole expense, in countries selected by such party, and for
conducting interferences, reexaminations, reissues, oppositions, or request for
patent term extension relating thereto. Notwithstanding the foregoing, in the
event that SIGA does not file a patent application covering one or more SIGA
Inventions disclosed in an Invention Disclosure in one or more countries, SIGA
shall so notify Maxygen, and Maxygen may request that SIGA file, and SIGA agrees
to file, a patent application in countries selected by Maxygen to protect
Maxygen's interest in any such SIGA Invention during the Option Period, and
Maxygen agrees to assume SIGA's reasonable costs associated with the filing and
prosecution of such patent applications during the Option Period set forth in
Section 7.2; provided, if prior to the end of such Option Period, Maxygen
notifies SIGA that Maxygen does not wish to acquire a license to such SIGA
Invention, Maxygen's obligation to reimburse SIGA for such costs, and SIGA's
obligation to seek patent protection with respect to such applications, shall
terminate upon such notification.

            6.2 Joint Inventions. With respect to Joint Inventions, the parties
shall confer in good faith to determine whether to seek patent protection for
each Joint Inventions and which party shall file, prosecute and maintain patent
applications and patents on behalf of the parties jointly, including conducting
interferences, reexaminations, reissues, oppositions, or request for patent term
extension relating thereto. For those inventions for which both parties agree to
seek patent protection, the parties shall share equally all reasonable
out-of-pocket patent costs with respect to such Joint Inventions, unless
otherwise agreed in writing. In the event that either party does not desire to
have any such activities undertaken with respect to a particular Joint
Invention, the other party shall have the right, in its discretion and at its
expense, to file, prosecute and/or maintain patent applications and patents with
respect to such joint invention, including conducting interferences,
reexaminations, reissues, oppositions, or request for patent term extension
relating thereto.

            6.3. Cooperation. Except as otherwise expressly provided herein,
applications filed on Joint Inventions shall be written and filed by outside
counsel acceptable to both parties, but under the control of the responsible
party. Each party shall be kept informed of all substantive matters relating to
the preparation and prosecution of all patent applications claiming or
disclosing Joint Inventions. Each party shall have the right to review and
comment upon such documentation and correspondence, as well as all
specifications, claims and responses to office actions related to Joint
Inventions prior to their submission to the relevant government patent office.
In addition, during the term of this Agreement and for ninety (90) days
thereafter, SIGA shall keep Maxygen informed of all substantive matters relating
to the preparation and prosecution of all patent applications claiming or
disclosing SIGA Inventions. Each party shall promptly provide the other with
copies of all patent prosecution and maintenance documentation and
correspondence so that the other shall be currently and promptly informed of the

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continuing prosecution and maintenance of patent applications and patents
claiming or disclosing Joint Inventions and/or, during the term of this
Agreement and for ninety (90) days thereafter, with respect to SIGA Inventions.

            6.4 Enforcement of Joint Inventions. Subject to Section 7, With
respect to any actual or threatened commercially material infringement or use of
any patent or patent applications claiming a Joint Invention (collectively, an
"Infringement"), the parties shall mutually determine which party will have the
rights and responsibilities of abating such an Infringement, and how the
expenses of abating any such Infringement shall be shared. Each party shall have
the right to be represented by counsel of its own selection and its own expense
in any suit initiated under this Section by the other party for an Infringement.
In the event only one party wishes to pursue in such proceeding, it shall have
the right to proceed alone, at its expense, and the other party agrees, at the
request and expense of the party initiating such action, to cooperate and join
in any proceedings in the event that a third party asserts that the co-owner of
such Joint Invention is necessary or indispensable to such proceedings;
provided, neither party may enter into any settlement with respect to any of the
jointly-owned Patent Rights, and may not make any statement which admits that
any of the jointly-owned Patent Rights are invalid or unenforceable, without the
prior consent of other party, which consent shall not be unreasonably withheld.

      7. License and Option Rights.

            7.1 Research License. Subject to the provisions of this Section 7
and each party's obligations hereunder regarding the Joint Materials and each
party's Confidential Information, Maxygen and SIGA each agree to grant to the
other, and hereby grant to the other, a royalty-free co-exclusive license,
without the right to sublicense, to use internally the results of the Evaluation
solely for research purposes.

            7.2 Maxygen Right of Negotiation. SIGA shall grant, and hereby
grants, to Maxygen the right of first negotiation to acquire, on commercially
reasonable terms, an exclusive or non-exclusive commercial license (at Maxygen's
election), with the right to grant and authorize sublicenses, in any patents or
patent applications or other intellectual property rights in and to any SIGA
Invention and/or SIGA's interest in any Joint Invention, and in any patents or
patent applications or other intellectual property rights owned or licensed by
SIGA necessary or reasonably useful to practice the SIGA Inventions and/or Joint
Inventions. Maxygen must notify SIGA in writing of its intent to negotiate such
license within (i) ninety (90) days after its receipt of SIGA's Invention
Disclosure, or (ii) ninety (90) days after completion of the Evaluation, or
(iii) ninety (90) days after the effective date of termination of this
Agreement, whichever is later (the "Option Period"). If Maxygen exercises its
right to negotiate a license to a particular Invention, SIGA shall use its best
efforts to enter into a license with Maxygen for the rights to such Invention
within six (6) months from the date of election, or such longer period as the
parties may agree. If Maxygen does not so notify SIGA that it wishes to acquire
a license to a particular Invention or if the parties are unable to enter into a
license agreement on mutually satisfactory terms with respect to a particular
Invention, then SIGA shall have the right to license any such patents or patent
applications claiming

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such SIGA Inventions, and/or grant licenses under SIGA's interest in such Joint
Inventions, as the case may be, to any third party; provided that SIGA shall not
enter into an agreement which grants any rights to such Invention to any third
party on terms which, taken as a whole, are more favorable to such third party
than those offered to Maxygen, without first offering such terms to Maxygen. If
SIGA offers such terms to Maxygen, then Maxygen shall have sixty (60) business
days in which to notify SIGA as to whether Maxygen accepts such terms. If
Maxygen accepts such terms, then the parties shall promptly enter into such
agreement, granting such rights to Maxygen.

            7.3 Retained Rights. Except as expressly set forth in this
Agreement, no party shall obtain rights in or a license to any patent,
copyright, trademark or other property right of the other party by implication,
estoppel or otherwise.

      8. Publications. Maxygen and SIGA are free to present or publish the
findings of the Evaluation in a thesis, scientific publication, or public,
noncommercial conference provided that: (a) no Maxygen Confidential Information
is revealed by SIGA, and no SIGA Confidential Information is revealed by Maxygen
thereby; and (b) at least forty-five (45) days prior to submission thereof to a
publisher or any third party, the publishing party shall have delivered copies
of the proposed presentation or publication to the other party for review. Said
other party may, within forty five (45) days of such delivery, object to the
publication or presentation because there would be a disclosure of its
Confidential Information, or because there is patentable subject matter in which
said other party has an interest which needs protection. Upon written objection
regarding disclosure of Confidential Information or patentable subject matter,
the publishing party shall: (i) remove any information disclosing patentable
subject matter or, for up to ninety (90) days from initial delivery, delay
disclosing such patentable subject matter in order to permit the filing of
patent applications thereon and (ii) delete the Confidential Information of the
other party contained in the disclosure. The publishing party shall thereafter
be free to publish or disclose the information. The determination of authorship
for any paper shall be in accordance with accepted scientific practice, and the
parties shall, in any publication, acknowledge the contributions and
publications of the other as scientifically appropriate.

      9. Compliance with Law. Each party shall conduct the Evaluation in
compliance with all applicable laws and regulations including, where applicable,
those relating to the treatment of laboratory animals and current NIH
guidelines. Each party shall use any materials received from the other only in
laboratory animals or in in vitro experiments, and not in human beings.

      10. Warranties.

            10.1 Representation and Warranties. Each party hereby warrants and
represents that it has full right and power to enter into this Agreement. SIGA
represents and warrants that (i) the Maxygen Materials and the Joint Materials
will not be used in or for any research that is subject to consulting, licensing
or similar obligations to any third party, including any sponsor, unless written
permission is first obtained from Maxygen (ii) it has the right to grant the
rights, options and licenses herein, and that it has obtained

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any and all necessary written permissions, clearances and/or waivers from all
third parties required in order to grant such rights, options and licenses
herein. Each of Maxygen and SIGA hereby warrants that the rights and obligations
set forth herein do not, and during the term of the Agreement will not, conflict
with any other right or obligation provided under any other agreement that
Maxygen or SIGA, as applicable, has with any third party, including any sponsor
or government entity.

            10.2 Disclaimer of Warranties. Maxygen and SIGA each specifically
disclaim that the Evaluation will be successful, in whole or part. MAXYGEN AND
SIGA EXPRESSLY DISCLAIM ANY WARRANTIES OR CONDITIONS, EXPRESS, IMPLIED,
STATUTORY OR OTHERWISE, WITH RESPECT TO THE CONFIDENTIAL INFORMATION,
INVENTIONS, PATENTS OR KNOW-HOW, MAXYGEN MATERIALS, SIGA MATERIALS, OR JOINT
MATERIALS, INCLUDING, WITHOUT LIMITATION, ANY WARRANTY OF MERCHANTABILITY, OR
FITNESS FOR A PARTICULAR PURPOSE, VALIDITY OF ANY MAXYGEN TECHNOLOGY OR SIGA
TEHCNOLOGY, PATENTED OR UNPATENTED, OR NON-INFRINGEMENT OF THE INTELLECTUAL
PROPERTY RIGHTS OF THIRD PARTIES.

      11. Indemnification.

            11.1 Each party (the "Indemnitor") shall indemnify and hold harmless
the other party and their respective employees, agents, officers, directors and
permitted assigns (each an "Indemnitee") from and against any claims by a third
party resulting in any liabilities, damages, settlements, claims, actions,
suits, penalties, fines, costs or expenses incurred (including without
limitation, reasonable attorneys' fees and other expenses of litigation) (any of
the foregoing, a "Claim") arising out of or resulting from (i) the Indemnitor's
conduct of the Evaluation; (ii) a breach of any representations or warranties of
the Indemnitor hereunder, or (iii) the negligence or willful misconduct by the
Indemnitor, except, in each case, to the extent such Claim arises out of the
negligence or willful misconduct of the Indemnitee.

            11.2 An Indemnitee under this Article 11 shall promptly notify the
Indemnitor in writing of any loss, claim, damage, liability or action in respect
of which the Indemnitee intends to claim such indemnification, and the
Indemnitor shall have the right to participate in, and, to the extent the
Indemnitor so desires, to assume the defense thereof with counsel chosen by
Indemnitor, with consent of Indemnitee, which consent shall not be unreasonably
withheld. The Indemnitee shall not enter into negotiations or enter into any
agreement with respect to the settlement of any Claim without the prior written
approval of the Indemnitor, and the indemnity agreement in this Article 11 shall
not apply to amounts paid in settlement of any loss, claim, damage, liability or
action if such settlement is made without the consent of the Indemnitor, which
consent shall not be withheld unreasonably. The failure to deliver written
notice to the Indemnitor within a reasonable time after the commencement of any
such action, if prejudicial to its ability to defend such action, shall relieve
such Indemnitor of any liability to the Indemnitee under this Article 11. At the
Indemnitor's request, the Indemnitee under this Article 11, and its employees
and agents, shall cooperate fully with the Indemnitor and its legal

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representatives in the investigation and defense of any action, claim or
liability covered by this indemnification and provide full information with
respect thereto.

      12. Press Release. All publicity, press releases and other announcements
relating to this Agreement or the transaction contemplated hereby shall be
reviewed in advance by, and shall be subject to the approval of, both parties;
provided, however, that either party may disclose the terms of this Agreement to
the extent required to comply with applicable regulations and laws, without the
prior consent of the other party. Once a particular disclosure has been approved
for disclosure, either party may make disclosures which do not differ materially
therefrom without any need for further consents.

      13. Notices. Routine notices of conditions or situations affecting the
Evaluation shall be given in writing between Drs. Hruby, Fischetti, and/or Jones
of SIGA and Stanley Goldman of Maxygen. All other notices, requests and other
communications hereunder shall be in writing and shall be personally delivered
or sent by nationally recognized overnight express delivery service, registered
or certified mail, return receipt requested, postage prepaid, in each case to
the respective address specified below, or such other address as may be
specified in writing to the other parties hereto as follows:

      In the case of SIGA:

                  SIGA Technologies, Inc.
                  420 Lexington Avenue, Suite 620
                  New York, NY 10170
                  Attn: Joshua D. Schein, Chief Executive Officer

      In the case of Maxygen:

                  Maxygen, Inc.
                  515 Galveston Drive
                  Redwood City, CA 94063
                  Attn: President

      14. Independent Contractor. Neither party, nor their respective employees,
consultants or representatives, shall be considered employees, partners, or
agents of the other party. Neither party may make any representations or
commitments on the other party's behalf nor may one party use the other party's
name or trademarks in any public disclosure, without the named party's prior
written consent.

      15. Term, Termination. Amendment and Survival.

            15.1 Term. This Agreement shall commence on the Effective Date and,
unless terminated earlier pursuant to the other provisions of this Article 15,
shall continue in full force and effect until the first anniversary of the
Effective Date, or such later date as the parties may mutually agree in writing.
This Agreement may be modified, amended or renewed only with the written
agreement of both parties.

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            15.2 Permissive Termination. This Agreement may be terminated by
either party upon thirty (30) days prior written notice to the other party.

            15.3 Effect of Termination.

                  15.3.1 Accrued Rights and Obligations. Termination of this
Agreement for any reason shall not release any party hereto from any liability
which, at the time of such termination, has already accrued to the other party
or which is attributable to a period prior to such termination, nor preclude
either party from pursuing any rights and remedies it may have hereunder or at
law or in equity which accrued or are based upon any event occurring prior to
such termination.

                  15.3.2 Materials. Upon expiration or any termination of the
Agreement, (i) SIGA and Maxygen will cease conducting work on the Evaluation,
(ii) SIGA shall promptly destroy or, at Maxygen's option, return to Maxygen all
Maxygen Materials (except to the extent incorporated into Joint Materials),
(iii) Maxygen shall promptly destroy or, at Maxygen's option, return to SIGA all
SIGA Materials (except to the extent incorporated into Joint Materials), and
(iv) subject to Section 7, each party may retain the Joint Materials generated
in the performance of the Evaluation for internal research and evaluation;
provided, however, that in the event that Maxygen Materials provided to SIGA
hereunder contain genetic material or proteins claimed by Maxygen to be
proprietary and covered by the claims of one or more patent applications or
patents owned or controlled by Maxygen (such materials referred to as
"Proprietary Maxygen Materials"), Maxygen may elect by written notice to have
all Joint Materials incorporating or made from such Proprietary Maxygen
Materials destroyed by both parties, and the parties shall promptly destroy such
Joint Materials upon SIGA's receipt of such notice.

                  15.3.3 Return of Confidential Information. Upon the expiration
or earlier termination of this Agreement, or upon request by the disclosing
party, the recipient shall return to the disclosing party, or provide
satisfactory evidence of the destruction of, all Confidential Information
furnished hereunder and any notes, copies, summaries or extracts thereof,
provided that the recipient may retain one (1) copy of the disclosing party's
Confidential Information in its legal archives in order solely for purposes of
monitoring its obligations hereunder.

                  15.3.4 Survival. Upon the expiration or termination of this
Agreement for any reason, Sections 2, 3, 4, 5, 6, and 7 shall survive; provided,
Section 7.2 shall survive for only ninety (90) days following such expiration or
termination; provided further, Section 11(i) and (ii) shall survive only to the
extent such claims arise from acts or omissions that occurred prior to the
effective date of termination of this Agreement.

      16. Assignment. Neither party may assign or transfer this Agreement
without the written consent of the other party, which consent shall be not be
unreasonably withheld; provided, either party may assign this Agreement, without
such consent, to an entity that acquires all or substantially all of the
business or assets of such party to which

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this Agreement pertains, whether by merger, reorganization, acquisition, sale,
or otherwise. The terms and conditions of this Agreement shall be binding on and
inure to the benefit of the permitted successors and assigns of the parties.

      17. Entire Agreement. This Agreement is the entire agreement of the
parties relating to the Evaluation and supersedes any previous understandings,
representations, acknowledgements, commitments or agreements, oral or written,
regarding such subject matter. This Agreement shall be governed by and construed
under laws of the State of California, without regard to its conflicts of laws
principles. If any provision of this Agreement is held to be unenforceable, the
remaining provisions shall continue unaffected.

      18. Severability. In the event that any provisions of this Agreement are
determined to be invalid or unenforceable by a court of competent jurisdiction,
the remainder of the Agreement shall remain in full force and effect without
said provision. The parties shall in good faith negotiate a substitute clause
for any provision declared invalid or unenforceable, which shall most nearly
approximate the intent of the parties in entering this Agreement; provided, if
the parties are unable to agree on such a substitute clause and the deletion of
the provision held invalid or unenforceable would produce material adverse
financial consequences for one party, such party shall have the right to
terminate the Agreement with thirty (30) days notice.

      19. Compliance with Laws. Each party shall use reasonable efforts to
furnish the other party any information requested or required by that party
during the term of this Agreement or any extensions hereof to enable that party
to comply with the requirements of any U.S. or foreign federal, state and/or
government agency. Each party shall comply with all applicable U.S., foreign,
state, regional and local laws, rules and regulations relating to its activities
to be performed pursuant to this Agreement, including without limitation, the
United States Foreign Corrupt Practices Act, United States export regulations
and such other United States and foreign laws and regulations as may be
applicable, and to obtaining all necessary approvals, consents and permits
required by the applicable agencies of the government of the United States and
foreign jurisdictions.

      20. Headings. The captions to the several Sections and Articles hereof are
not a part of this Agreement, but are included merely for convenience of
reference only and shall not affect its meaning or interpretation.

      21. Binding Effect. This Agreement shall be binding upon and inure to the
benefit of the parties and their respective legal representatives, successors
and permitted assigns.

      22. Counterparts. This Agreement may be executed in two counterparts, each
of which shall be deemed an original and which together shall constitute one
instrument.

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

MAXYGEN, INC.                             SIGA TECHNOLOGIES, INC.


By: /s/ Michael Rabson                    By: /s/ Joshua D. Schein
    ----------------------------------        ----------------------------------
    Michael Rabson                            Joshua D. Schein

Title: Sr. Vice President and             Title: Chief Executive Officer
       General Counsel

MAXY BD Review _____

MAXY Legal Review /s/ DWS
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                                   EXHIBIT A

                                PROJECT PROPOSAL

Objective: Express the Yersinia V antigen on the surface of Streptococcus
gordonii and testing of the derived recombinant as a candidate vaccine.

Procedure:

      1)    Discussions will be held between Maxygen and SIGA research groups to
            determine the exact structure and boundaries of the Yersinia V
            antigen to be expressed.

      2)    Maxygen will provide to SIGA the plasmid containing the gene for the
            Yersinia V antigen along with the necessary sequence information
            pertaining to the gene. Maxygen will also provide purified V antigen
            and antisera to the protein, if available.

      3)    SIGA will construct a recombination plasmid containing the gene for
            the V antigen fused in an appropriate configuration to achieve
            genomic integration and surface expression in Streptococcus
            gordonii. Structure and authenticity of the plasmid will be verified
            by restriction endonuclease digestion and nucleotide sequencing.

      4)    SIGA will transform the recombination plasmid containing the V
            antigen into a recipient Streptococcus gordonii strain. A
            recombinant strain will be selected by acquisition of appropriate
            antibiotic resistance (erythromycin) and surface expression of
            desired protein as measured by streak blot, western blot and ELISA
            if applicable.

      5)    SIGA will provide to Maxygen the verified Streptococcus gordonii V
            antigen recombinant strain in the form of a glycerol stock.

      6)    Maxygen to perform animal studies in mice using the Streptococcus
            gordonii V antigen recombinant strain and perform the necessary
            immunological assays and challenge studies.

      7)    Following the animal trials, Maxygen and SIGA representatives will
            review data and discuss the advisability of continued development of
            this and/or related products.
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                                   EXHIBIT B

                               MAXYGEN MATERIALS

Wild-type V antigen gene from Yersinia pestis