Exhibit 10.21

NOTE: Information in this document marked with an "[*]" has been omitted and
filed separately with the Commission. Confidential treatment has been requested
with respect to the omitted portions.

LICENSE AGREEMENT

between

TRANSKARYOTIC THERAPIES, INC.

and

CELL GENESYS, INC.

[*] Certain information on this page has been omitted and filed separately with
the Commission. Confidential treatment has been requested with respect to the
omitted portions.

LICENSE AGREEMENT

This License Agreement (the "Agreement"), effective as of June 7, 2002 (the
"Effective Date"), is between Transkaryotic Therapies, Inc., a corporation
organized and existing under the laws of Delaware and having its principal place
of business at 195 Albany Street, Cambridge, MA 02139 ("TKT"), and Cell Genesys,
Inc., a corporation organized and existing under the laws of Delaware and having
its principal place of business at 342 Lakeside Drive, Foster City, CA 94404
("Cell Genesys"). TKT and CELL GENESYS are sometimes hereinafter referred to
each as a "Party" and collectively as the "Parties."

WITNESSETH:

Whereas

, CELL GENESYS has certain Patent Rights (as hereinafter defined);

Whereas

, TKT desires to obtain a license under the CELL GENESYS Patent Rights upon the
terms and conditions set forth herein, and CELL GENESYS desires to grant such a
license;

Now, Therefore

, in consideration of the foregoing premises and the mutual covenants herein
contained, and intending to be legally bound, the Parties hereby agree as
follows:

ARTICLE I
DEFINITIONS

Unless specifically set forth to the contrary herein, the following terms,
whether used in the singular or plural, shall have the respective meanings set
forth below:

1.1 "Affiliate

" shall mean, with respect to a particular Party, a person, corporation,
partnership, or other entity that controls, is controlled by or is under common
control with such Party. For the purposes of the definition in this Section 1.1,
the word "control" (including, with correlative meaning, the terms "controlled
by" or "under the common control with") means the actual power, either directly
or indirectly through one or more intermediaries, to direct or cause the
direction of the management and policies of such entity, whether by the
ownership of at least fifty percent (50%) of the voting stock of such entity, or
by contract or otherwise.

1.2 "Designated Protein

" shall mean one of the [*], as described in or determined by the provisions set
forth in the letter dated June 7, 2002 from Robert H. Tidwell of CELL GENESYS to
Michael J. Astrue of TKT (the "Side Letter"), and subject to Sections 2.2 and
2.3 hereof.

1.3

[*]

2.

[*] Certain information on this page has been omitted and filed separately with
the Commission. Confidential treatment has been requested with respect to the
omitted portions.

1.4 "Licensed Product(s)

" shall mean [*] Licensed Products and [*] Licensed Products. "[*] Licensed
Product" shall mean [*] of a Designated Protein, the making, using, selling,
offering for sale or import of which is covered by a claim in the Patent Rights.
"[*] Licensed Product" shall mean [*], the making, using, selling, offering for
sale or import of which is covered by a claim in the Patent Rights. For clarity,
the term "Licensed Product(s)" does not include a composition that includes a
protein that is covered by, or that was made by a process covered by, a claim in
the Patent Rights, if that protein is not a Designated Protein.

1.5 "Patent Rights

" shall mean: (a) all patents and patent applications (including provisional and
utility applications) owned by CELL GENESYS, or licensed by CELL GENESYS with
the right to sublicense, as of the Effective Date that claim [*], including, but
not limited to: [*]; and also any new patent or patent application (i.e., not a
continuing application) filed after the Effective Date that is owned by CELL
GENESYS and [*] (b) divisions, continuations, continuations-in-part (but solely
as to claims that encompass subject matter disclosed in the parent application),
extensions, supplementary protection certificates, utility models,
reexaminations, reissues and renewals of the patents and patent applications in
clause (a) above,; and (c) foreign equivalents of the patents and applications
in clauses (a) and (b) above.

1.6 "Third Party

" shall mean a party other than TKT, CELL GENESYS, or their respective
Affiliates.

ARTICLE II
LICENSE GRANT

2.1 License Grant.

Subject to the terms and conditions of this Agreement, CELL GENESYS grants to
TKT (i) an [*] under the Patent Rights to [*], and (ii) a [*] under the Patent
Rights to [*] solely for use to [*].

2.2 Identification of Designated Proteins.

TKT shall designate in writing each additional protein that TKT desires to
designate as a Designated Protein pursuant to the Side Letter (up to the maximum
number and within the timeframes set forth therein), but subject to the
following. Until such time as TKT's rights to designate additional Designated
Proteins as provided in this Agreement have terminated, CELL GENESYS shall [*]
of any protein.

2.3 Substitution of Designated Proteins.

Notwithstanding Section 1.2, Section 2.2 and the Side Letter, if, on the [*] of
the Effective Date, CELL GENESYS has [*] then TKT shall have the right to
designate an [*]: (i) a method or composition for, or including, the activation
of a gene that is [*], (ii) a composition or a gene activation method that does
[*] and (iii) a method or composition for or including gene activation which
does [*]. Such additional [*] shall be identified on or before [*].

ARTICLE III
CONFIDENTIALITY/PRESS RELEASES

3.

[*] Certain information on this page has been omitted and filed separately with
the Commission. Confidential treatment has been requested with respect to the
omitted portions.

3.1 Nondisclosure Obligation.

All proprietary or confidential information disclosed by or on behalf of one
Party (the "Disclosing Party") to the other Party (the "Receiving Party")
hereunder in writing and marked "Confidential" or the equivalent (the
"Proprietary Information") shall be maintained in confidence by the Receiving
Party and shall not be disclosed to a Third Party or used for any purpose
whatsoever except as set forth herein without the prior written consent of the
Disclosing Party. All information disclosed by CELL GENESYS or TKT pursuant to
the Binding Letter of Intent dated April 21, 2002 (the "LOI") shall be deemed
Proprietary Information of CELL GENESYS or TKT, as the case may be, and shall be
subject to the terms of this Article 3. For purposes of clarity, it is the
intent of the Parties that general financial terms may be disclosed but that the
number of Licensed Products and the nature and category of proteins which may be
designated under this Agreement , as well as the nature of the milestones herein
shall be considered Proprietary Information of both Parties. The identity of the
Licensed Products and Designated Proteins shall be TKT Proprietary Information.
However, the foregoing obligations shall not apply to particular Proprietary
Information solely to the extent that the receiving Party can demonstrate with
written evidence that such information:

is known by the Receiving Party at the time of its receipt, and not through a
prior confidential disclosure by or on behalf of the Disclosing Party;

is properly in the public domain through no fault of the Receiving Party;

is subsequently disclosed to the receiving Party by a Third Party who may
lawfully do so and is not directly or indirectly under an obligation of
confidentiality to the Disclosing Party; or

is developed by the Receiving Party independently of, and without reference to
or use of, Proprietary Information received from the Disclosing Party.

3.2 Authorized Disclosures.

A Party may disclose the Proprietary Information of the other Party to the
extent such disclosure:

is required to be disclosed by any governmental or other regulatory agency in
order to obtain patents, to obtain approval to conduct clinical trials or to
market a Licensed Product;
provided, however
, that (i) prior written notice is promptly delivered to the disclosing Party in
order to provide an opportunity to challenge or limit the disclosure
obligations, (ii) such disclosure may be only to the extent necessary to obtain
such patents or approval, or to comply with regulations as appropriate and (iii)
confidential treatment shall be sought to the extent reasonably practicable;

is necessary to be disclosed to employees, agents, consultants and/or other
Third Parties for purposes related to the development and commercialization of
Licensed Products (or for such Third Parties to determine their interest in
performing such activities) in accordance with this Agreement on the condition
that such Third Parties agree to be bound by confidentiality obligations at
least as restrictive as the terms herein; or

4.

[*] Certain information on this page has been omitted and filed separately with
the Commission. Confidential treatment has been requested with respect to the
omitted portions.

is required to be disclosed by law or court order,
provided
that prior written notice is promptly delivered to the disclosing Party in order
to provide an opportunity to challenge or limit the disclosure obligations, and
provided
further that such disclosure may be only to the extent reasonably necessary to
comply with the applicable law or court order.

3.3 Press Releases.

Neither Party shall issue a press release relating to this Agreement without the
prior review and written consent of the other Party.

3.4 Confidential Treatment.

In the event that either Party is required to include this Agreement and any
agreements or letters referred to herein in any report, statement or other
document filed by such Party with the United States Securities and Exchange
Commission (the "SEC"), then the disclosing Party shall [*] to obtain, to the
maximum extent permitted by law, confidential treatment from the SEC of any
trade secrets and commercial or financial information of a privileged or
confidential nature, including without limitation all information relating to
the number or identity of the Designated Proteins under this Agreement and the
specific financial terms and the nature of the milestones herein, and shall
notify the other Party as to such efforts and all related communications with
the SEC. Notwithstanding the foregoing, neither Party shall submit a
confidentiality request for this Agreement or the agreements or letters referred
to herein without providing the other Party with an opportunity for prior review
and comment on such confidentiality request. The filing Party shall reasonably
consider and attempt to accommodate any such comments by such other Party in
submitting such confidentiality request.

ARTICLE IV
PAYMENTS

4.1 Upfront Fees.

In consideration for the license granted to TKT by CELL GENESYS under Section
2.1 and CELL GENESYS's fulfillment of its other obligations and undertakings
under this Agreement, within [*] of the Effective Date, TKT shall make a cash
payment to CELL GENESYS of Eleven Million U.S. Dollars (US $11,000,000), less
the credit provided for in Section 4.2, and shall issue and transfer to CELL
GENESYS three hundred sixty six thousand nine hundred twenty eight (366,928)
shares of TKT common stock (the "Shares") pursuant to an executed Stock Purchase
Agreement in the form attached hereto as Exhibit A (the "Stock Purchase
Agreement").

4.2 Cash Payment Credit.

The cash payment of Three Million U.S. Dollars (US $3,000,000) paid by TKT
pursuant to the LOI between the Parties effective April 21, 2002 shall be
credited towards the upfront cash fee of Eleven Million U.S. Dollars (US
$11,000,000), thereby reducing the payment required pursuant to Section 4.1 to
Eight Million U.S. Dollars (US $8,000,000).

4.3 Milestone Payments.

In further consideration for the license granted to TKT by CELL GENESYS under
Section 2.1 and CELL GENESYS's fulfillment of its other obligations and
undertakings under this Agreement, TKT shall make cash and stock payments to
CELL GENESYS in the respective amounts set forth below upon attainment of the
respective milestone events set forth below:

5.

[*] Certain information on this page has been omitted and filed separately with
the Commission. Confidential treatment has been requested with respect to the
omitted portions.

EVENT

AMOUNT

(a) [*].

[*].

(b) [*].

[*].

(c) [*].

[*].

4.4 Milestone Conditions.

No milestone shall be payable more than once by TKT. Further, milestones 4.3(b)
and 4.3(c) are exclusive of each other and only one can be achieved. For
clarity, TKT shall pay the amount designated above upon the achievement of
milestone 4.3(a) and upon the achievement of either of milestone 4.3(b) or
4.3(c). CELL GENESYS shall notify TKT in writing upon the achievement of any of
the milestone events set forth above and TKT shall have [*] to make the
corresponding cash payment or stock grant, as the case may be.

4.5 Late Payments.

For each payment or stock transfer not received by CELL GENESYS when due
pursuant to Section 4.4, TKT must pay to CELL GENESYS a simple interest charge
of [*] per annum, or such lower amount as is required by law, on the cash value
of such payment or stock transfer to be calculated from the date such payment or
stock transfer is due until it is actually received by CELL GENESYS.

ARTICLE V
REPRESENTATIONS, WARRANTIES AND INDEMNIFICATION

5.1 CELL GENESYS Representations and Warranties.

CELL GENESYS hereby represents and warrants to TKT that:

it has the full corporate power and authority to enter into this Agreement, to
perform its obligations under this Agreement and to grant the license granted
under Article 2 hereof, and this Agreement has been duly executed and
constitutes a legal, valid and binding obligation of it enforceable against it
in accordance with its terms and conditions, except as such enforceability may
be limited by applicable bankruptcy, insolvency, moratorium, reorganization or
similar laws, from time to time in effect, affecting creditor's rights generally
or by principles of equity;

as of the Effective Date, there are no claims, oppositions, litigations,
interferences, judgments or settlements against or owed by CELL GENESYS related
to the Patent Rights that would materially affect the license granted hereunder,
and there are no pending, and CELL GENESYS is not aware of any threatened,
claims, oppositions, litigations, or interferences relating to the Patent
Rights, other than those claims of record as of the Effective Date [*];

6.

[*] Certain information on this page has been omitted and filed separately with
the Commission. Confidential treatment has been requested with respect to the
omitted portions.

(i) CELL GENESYS is not aware that any of the data and information made
available to TKT for the diligence conducted by TKT pursuant to the LOI are
untrue or inaccurate to any material degree, and (ii) CELL GENESYS has made
available to TKT all Materials (as defined in Section 1(a) of the LOI) in CELL
GENESYS's or any of its agents' control or possession;

to CELL GENESYS' knowledge, it does not have any license rights granted to it by
Third Party under any patent that claims the activation of genes to produce
specific desired proteins, which license rights cannot be sublicensed to TKT for
the purposes of the license rights granted under Section 2.1; and

the execution and performance by it of its obligations hereunder does not and
will not constitute a material breach of, or materially conflict with, any
agreement or arrangement by which it is bound, and that it will not enter into
any agreement which materially conflicts with the terms hereof.

5.2 TKT Representations and Warranties.

TKT hereby represents and warrants to CELL GENESYS that:

it has the full corporate power and authority to enter into this Agreement and
to perform its obligations under this Agreement, and this Agreement has been
duly executed and constitutes a valid, binding and enforceable agreement in
accordance with its terms and conditions, except as such enforceability may be
limited by applicable bankruptcy, insolvency, moratorium, reorganization or
similar laws, from time to time in effect, affecting creditor's rights generally
or by principles of equity; and

the execution and performance by it of its obligations hereunder does not and
will not constitute a material breach of, or materially conflict with, any
agreement or arrangement by which it is bound, and that it will not enter into
any agreement which materially conflicts with the terms hereof.

5.3 CELL GENESYS Indemnification.

CELL GENESYS hereby agrees to defend, hold harmless and indemnify TKT, its
Affiliates, agents, directors, officers and employees from and against any and
all Third Party suits, claims, actions, demands, liabilities, costs, damages,
fees, expenses and/or losses, including without limitation reasonable legal
expenses and attorneys' fees (collectively "Third Party Claims") resulting from
a material breach by CELL GENESYS of any of the provisions of this Agreement,
including without limitation, the representations and warranties made in Section
5.1 by CELL GENESYS; except to the extent such Third Party Claims result from
the negligence or intentional misconduct of, or breach hereof by, TKT.

7.

[*] Certain information on this page has been omitted and filed separately with
the Commission. Confidential treatment has been requested with respect to the
omitted portions.

5.4 TKT Indemnification.

TKT hereby agrees to defend, hold harmless and indemnify CELL GENESYS, its
Affiliates, agents, directors, officers and employees from and against any and
all Third Party Claims (except to the extent such Third Party Claims result from
the negligence or intentional misconduct of, or breach hereof by, CELL GENESYS),
including any product liability claims, resulting:

from a material breach by TKT of any of the provisions of this Agreement; or

directly or indirectly from the manufacture, use, handling, storage, sale or
other disposition of Licensed Products by TKT, or its Affiliates, agents or
sublicensees.

5.5 Indemnification Procedure.

The Party seeking indemnification under this Section 5 (the "Indemnified Party")
shall (i) give prompt written notice to the other Party (the "Indemnifying
Party") of any Third Party Claim for which indemnification is sought, (ii)
permit the Indemnifying Party to assume full responsibility to investigate,
prepare for, defend against and/or compromise or settle (subject to the
provisions set forth below) the Third Party Claim and (iii) if the Indemnifying
Party assumes responsibility under clause (ii), reasonably assist the
Indemnifying Party, at the Indemnifying Party's reasonable expense, in the
investigation of, preparation for and defense of such Third Party Claim. If the
Indemnifying Party assumes control of the defense of a Third Party Claim, the
Indemnifying Party shall not be liable for any litigation costs or expenses
incurred by the Indemnified Party. If the Indemnifying Party does not assume
control of the defense of the Third Party Claim, the Indemnified Party shall
control such defense. The Indemnifying Party shall not compromise or settle such
Third Party Claim without the Indemnified Party's prior written consent if the
compromise or settlement does not include a complete and unconditional release
of the Indemnified Party from all liability with respect thereto or if the
compromise or settlement imposes any liability or obligation on the Indemnified
Party. The Indemnified Party shall not agree to any settlement of such action,
suit, proceeding or claim without the prior written consent of the Indemnifying
Party. The Indemnified Party shall have the right to participate, at its own
expense and with counsel of its choice, in the defense of any claim or suit the
defense of which has been assumed by the Indemnifying Party.

5.6 LIMITATION OF LIABILITY.

EXCEPT FOR OBLIGATIONS UNDER SECTIONS 5.3 AND 5.4 OR IN CASE OF BREACH OF
SECTION 3.1, IN NO EVENT SHALL EITHER PARTY, ITS DIRECTORS, OFFICERS, EMPLOYEES,
AGENTS OR AFFILIATES BE LIABLE TO THE OTHER PARTY FOR ANY INDIRECT, INCIDENTAL,
SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES, WHETHER BASED UPON A CLAIM OR
ACTION OR CONTRACT, WARRANTY, NEGLIGENCE, STRICT LIABILITY OR OTHER TORT, OR
OTHERWISE, ARISING OUT OF THIS AGREEMENT.

5.7 Limited Warranty.

Except for the warranties provided by CELL GENESYS in Section 5.1 AND TKT IN
SECTION 5.2, EACH PARTY disclaims all other warranties, express or implied, and
specifically, without limitation, any warranty of merchantability, fitness for a
particular purpose or any warranty that exercise by TKT of its rights under the
Patent Rights will not infringe any intellectual property rights of third
parties.

8.

[*] Certain information on this page has been omitted and filed separately with
the Commission. Confidential treatment has been requested with respect to the
omitted portions.

ARTICLE VI
INTELLECTUAL PROPERTY PROVISIONS

6.1 Filing, Prosecution and Maintenance of Patents.

Subject to Section 6.1(b) below, CELL GENESYS agrees to file, prosecute and
maintain all Patent Rights [*] and shall provide TKT with copies of all
documentation and correspondence related to the Patent Rights. To the extent
that such documents pertain to Licensed Products, CELL GENESYS shall give TKT an
opportunity to comment on any official communication related to the Patent
Rights before filing, shall [*], and shall consult with TKT thereon. CELL
GENESYS shall comply with any applicable duty to disclose information relevant
to the Patent Rights as required by the United States Patent and Trademark
Office during the prosecution of any of the Patent Rights. CELL GENESYS shall
[*] related to the scope of appropriate disclosure.

In the event that CELL GENESYS elects not to file, prosecute or maintain any
patent or patent application involving a particular patent or application in the
Patent Rights, then CELL GENESYS shall give TKT at least [*] notice thereof and
TKT shall have the right to elect to undertake such prosecution and maintenance.
In such case, CELL GENESYS shall, [*], either (i) assign such patent or
application (including any patent or application to which such patent or
application claims priority) to TKT, or (ii) allow TKT to prosecute and maintain
such patent in CELL GENESYS's name, and grant TKT an [*]. TKT shall, [*], file,
prosecute and maintain such patent or application (including any priority patent
or patent application) in the Patent Rights. CELL GENESYS shall execute such
documents and perform such acts as may be reasonably necessary to effect an
assignment or transfer of power of attorney to such Patent Rights to allow TKT
to continue in a timely manner such filing, prosecution or maintenance. Upon
completion of such assignment or transfer of power of attorney, TKT shall be
deemed automatically to have granted CELL GENESYS a [*] license under such
assigned Patent Rights [*]. Further, TKT agrees that it shall, upon CELL
GENESYS's request, negotiate in good faith with any Third Party to grant a
license [*] under such Patent Right to the extent needed for such Third Party to
practice license rights granted to it by CELL GENESYS under the Patent Rights
prior to CELL GENESYS's election not to file, prosecute or maintain such Patent
Right, provided that (a) such license rights do not include any right to make,
have made, use, sell, offer for sale or import any Licensed Products, and (b)
such Third Party is not, as of the date such election is made by CELL GENESYS
not to file, prosecute or maintain such Patent Right, [*]. CELL GENESYS shall
give notice to TKT as soon as practicable in advance of the grant, lapse,
revocation, surrender, invalidation or abandonment of any CELL GENESYS Patent
Right being prosecuted by CELL GENESYS.

6.2 Opposition, Reexamination and Reissue.

9.

[*] Certain information on this page has been omitted and filed separately with
the Commission. Confidential treatment has been requested with respect to the
omitted portions.

CELL GENESYS shall notify TKT, within [*] of learning of, and in any case, prior
to public disclosure of, any request for, or filing or declaration of, any
interference, opposition, reexamination, or the foreign equivalent of any of the
foregoing involving the Patent Rights.

CELL GENESYS shall not initiate any reexamination, interference or reissue
proceeding involving Patent Rights [*].

In connection with any interference, opposition, reissue, or reexamination
proceeding (or the foreign equivalent of any of the foregoing) involving the
Patent Rights, CELL GENESYS agrees to give TKT an opportunity to provide
comments on any official communication related to such interference, opposition,
reissue, or reexamination proceeding (or the foreign equivalent of any of the
foregoing) before filing, shall consider TKT's comments in good faith, and shall
consult with TKT thereon. Additionally, CELL GENESYS shall [*], and [*],
including to the extent permissible by law and contracts, the [*].
Notwithstanding the foregoing, CELL GENESYS shall not be required to make any
disclosure of any communication or other information that would destroy either
the attorney/client privilege or attorney work product privilege protecting such
communication or other information, provided that if such communication or other
information is material to TKT's interests under this Agreement, CELL GENESYS
shall, in good faith, use [*] to facilitate disclosure without destroying any
such privilege.

6.3 Enforcement and Defense

.

Each Party shall give the other Party notice of any unauthorized making, using,
selling, offering for sale or importing of a Licensed Product that may come to
such Party's attention (a "Field Infringement"). Each Party shall have the right
to bring suit against such alleged infringer in a Field Infringement, [*], and
either Party may [*]; provided, however, that in the event that TKT brings a
suit against an alleged infringer as the result of a possible Field
Infringement, but in its sole reasonable discretion believes that CELL GENESYS
is or may be a necessary or indispensable party under the applicable law, CELL
GENESYS agrees to become a party in such action , and shall execute all
documents and take all steps reasonably necessary to enable TKT to initiate,
prosecute and/or maintain such action, or for TKT to defend any declaratory
judgment action brought by the alleged infringer. Each Party shall be entitled
in any such action [*] to assert its own claims for damages and to defend it
interests in the Patent Rights. For any infringement of the Patent Rights other
than a Field Infringement, CELL GENESYS shall have the sole and exclusive right
to bring an action against the infringer.

Each Party shall [*] pursuant to an action brought under subclause (a) above.

Each Party shall notify the other of any certification regarding any Patent
Rights which it has received pursuant to 21 U.S.C. 355(b)(2)(A)(iv) or
(j)(2)(A)(vii)(IV) or its successor provisions or the foreign equivalent thereof
and shall provide the other with a copy of such certification within five (5)
days of receipt. CELL GENESYS's and TKT's rights with respect to the initiation
and prosecution of any legal action (or the defense of any such legal action) as
a result of such certification or any recovery obtained as a result of such
legal action shall be as defined above; provided, however, that if either Party
shall exercise its first right to initiate and prosecute any action or to
control the defense of any such action, such Party shall notify the other Party
of such decision within ten (10) days of receipt of the certification.

10.

[*] Certain information on this page has been omitted and filed separately with
the Commission. Confidential treatment has been requested with respect to the
omitted portions.

If any Licensed Product becomes the subject of a Third Party claim, or there is
the potential for a claim of patent infringement related to TKT's development,
use, sale, offer for sale or import of Licensed Products, TKT shall defend
against such claim [*]. CELL GENESYS and TKT shall fully cooperate and provide
assistance to each other, [*], with respect to any proceeding related to gene
activation patents owned or licensed by a Third Party and asserted, or
threatened to be asserted, by such Third Party, including without limitation,
[*].

6.4 Third Party License; Settlement.

Except as otherwise provided herein, CELL GENESYS shall [*] that [*] under the
Patent Rights [*].

ARTICLE VII
TERM AND TERMINATION

7.1 Term and Expiration.

This Agreement shall be effective as of the Effective Date and, unless
terminated earlier pursuant to the provisions of Section 7.2 below, shall
continue until the expiration of the last-to-expire Patent Right.

7.2 Termination by Either Party for Cause.

This Agreement may be terminated by written notice by either Party at any time
during the term of this Agreement if the other Party is in breach of a material
obligation hereunder and has not cured such breach within [*] after notice
requesting cure of the breach. If TKT terminates this Agreement pursuant to this
Section 7.2, then: (a) the license granted pursuant to Section 2.1 shall [*],
and provided that [*], and (b) in addition, TKT shall have (i) [*] under the
Patent Rights to [*] and (ii) a [*] under the Patent Rights to [*], but
excluding from the foregoing rights any [*] under the Patent Rights that have
been [*] prior to the date of breach.

7.3 Survivals.

Termination or expiration of this Agreement shall not relieve either Party of
any obligation of such Party accrued prior to such termination or expiration.
Any termination or expiration of this Agreement shall be without prejudice to
the rights of either Party against the other accrued under this Agreement prior
to termination or expiration hereof. The provisions of Articles 1, 3, 5, and 7
shall survive the termination or expiration of this Agreement. Notwithstanding
the termination of this Agreement pursuant to this Article VII, any sublicenses
of Patent Rights granted by TKT hereunder prior to such termination shall
survive such termination. In such event, CELL GENESYS shall have the right to
receive directly from the sublicensee any payments or other consideration
otherwise payable to TKT as the sublicensor under such sublicense, and to
otherwise exercise all of the rights of TKT as the sublicensor under such
sublicense; provided however that CELL GENESYS shall not assume, and shall not
be responsible for, any representations, warranties, promises or obligations of
TKT to any sublicensees other than the licenses under such sublicenses.

11.

[*] Certain information on this page has been omitted and filed separately with
the Commission. Confidential treatment has been requested with respect to the
omitted portions.

ARTICLE VIII
MISCELLANEOUS

8.1 Force Majeure.

Neither Party shall be held liable or responsible to the other Party nor be
deemed to have defaulted under or breached this Agreement for failure or delay
in fulfilling or performing any term of this Agreement when such failure or
delay is caused by or results from causes beyond the reasonable control of the
affected Party including, but not limited to, earthquakes, fire, floods,
embargoes, war, acts of war (whether war be 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. The affected Party shall notify the other Party of such force
majeure circumstances as soon as reasonably practical and shall make reasonable,
diligent efforts to remove the condition constituting force majeure or to avoid
its effects so as to resume performance as soon as practicable.

8.2 Sublicenses.

All sublicenses granted by TKT under the Patent Rights to Third Parties shall be
on such terms as are consistent with the provisions of this Agreement and shall
be subject to the rights of CELL GENESYS under this Agreement.

8.3 Assignment.

Except as otherwise expressly provided below, this Agreement may not be assigned
or otherwise transferred, nor may any right or obligation hereunder be assigned
or transferred, by either Party without the prior written consent of the other
Party; except that either Party may, without the prior written consent of the
other Party, assign this Agreement and such Party's rights and obligations
hereunder to its successor in interest in connection with the transfer or sale
of all or substantially all of such Party's assets or the business to which this
Agreement relates, or in the event of its merger, acquisition, consolidation,
change in control or similar transaction. Any permitted assignee shall assume
all obligations of its assignor under this Agreement except as otherwise
provided herein.

8.4 Severability.

If any provision hereof should be held invalid, illegal or unenforceable in any
respect, then, to the fullest extent permitted by law, (a) all other provisions
hereof shall remain in full force and effect and shall be liberally construed in
order to carry out the intentions of the Parties as nearly as may be possible
and (b) the Parties shall use their best efforts to replace the invalid, illegal
or unenforceable provision(s) with valid, legal and enforceable provision(s)
which, insofar as practical, implement the purposes of such provision(s) in this
Agreement.

8.5 Notices.

All notices or other communications which are required or permitted hereunder,
including any notices required pursuant to Section 2.2 hereof, shall be in
writing and addressed as follows:

12.

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the Commission. Confidential treatment has been requested with respect to the
omitted portions.

if to CELL GENESYS:

Cell Genesys, Inc.

 

342 Lakeside Drive

 

Foster City, CA 94404

Attention:

Robert Tidwell

 

Vice President, Corporate Development

With a copy to:

Cooley Godward LLP

3000 El Camino Real

 

Palo Alto, CA 94306-2155

Attention:

Barclay J. Kamb, Esq.

if to the Company:

Transkaryotic Therapies, Inc.

195 Albany Street

 

Cambridge, MA 02139

Attention:

Michael J. Astrue

 

Senior Vice President, Administration

With a copy to:

Kerry A. Flynn

Senior Director, Business Development

or to such other address as the Party to whom notice is to be given may have
furnished to the other Party in writing in accordance herewith. Any such
communication shall be deemed to have been given when delivered if personally
delivered or sent by facsimile (provided that the Party providing such notice
promptly confirms receipt of such transmission with the other Party by
telephone), on the business day after dispatch if sent by a
nationally-recognized overnight courier and on the third business day following
the date of mailing if sent by mail, postage prepaid, return receipt requested.

8.6 Applicable Law.

This Agreement shall be governed by and construed in accordance with the laws of
the State of Delaware, without reference to any rules regarding conflict of
laws. The Parties hereby consent to the jurisdiction of the state and federal
courts of the State of Delaware and agree that any disputes related hereto shall
be adjudicated therein.

8.7 Entire Agreement.

This Agreement, together with the Side Letter and the Stock Purchase Agreement,
contains the entire understanding of the Parties with respect to the subject
matter hereof and supercedes all prior agreements with respect to the subject
matter hereof, including without limitation the LOI. All express or implied
agreements and understandings, either oral or written, heretofore made are
expressly merged in and made a part of this Agreement. Except as expressly set
forth in this Agreement, this Agreement may be amended, or any term hereof
modified, only by a written instrument duly executed by both Parties.

13.

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the Commission. Confidential treatment has been requested with respect to the
omitted portions.

8.8 Headings.

The captions to the several Articles and Sections hereof are not a part of this
Agreement, but are merely guides or labels to assist in locating and reading the
several Articles and Sections hereof.

8.9 Independent Contractors.

It is expressly agreed that CELL GENESYS and TKT shall be independent
contractors and that the relationship between the two Parties shall not
constitute a partnership, joint venture or agency. Neither CELL GENESYS nor TKT
shall have the authority to make any statements, representations or commitments
of any kind, or to take any action, which shall be binding on the other, without
the prior written consent of the other Party.

8.10 Waiver.

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

8.11 Counterparts.

This Agreement may be executed in two (2) or more counterparts, each of which
shall be deemed an original, but all of which together shall constitute one and
the same instrument.

8.12 Waiver of Rule of Construction.

Each Party has had the opportunity to consult with counsel in connection with
the review, drafting and negotiation of this Agreement. Accordingly, the rule of
construction that any ambiguity in this Agreement shall be construed against the
drafting Party shall not apply.

8.13 Section 365(n) of the Bankruptcy Code.

All licenses granted under this Agreement are, and shall otherwise be, deemed to
be, for purposes of Section 365(n) of the Bankruptcy Code, licenses of rights to
"intellectual property" as defined under Section 101(35A) of the Bankruptcy
Code. The Parties shall retain and may fully exercise all of their respective
rights and elections under the Bankruptcy Code.

8.14 Third Party Beneficiaries.

Except as otherwise expressly provided in this Agreement, nothing herein
expressed or implied is intended or shall be construed to confer upon or to give
to any Third Party any rights or remedies by reason of this Agreement. Except as
otherwise expressly provided in this Agreement, there are no intended Third
Party beneficiaries under or by reason of this Agreement.

   *    *   *   

14.

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the Commission. Confidential treatment has been requested with respect to the
omitted portions.

In Witness Whereof

, the Parties have executed this License Agreement as of the date first set
forth above.

Transkaryotic Therapies, Inc.

Cell Genesys, Inc.

By:_______________________

By:_______________________

Name: Michael J. Astrue

Name:

Title: Senior Vice President
Administration & General Counsel

Title:

15.

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the Commission. Confidential treatment has been requested with respect to the
omitted portions.

--------------------------------------------------------------------------------

NOTE: Information in this document marked with an "[*]" has been omitted and
filed separately with the Commission. Confidential treatment has been requested
with respect to the omitted portions.

Exhibit A

FORM OF STOCK PURCHASE AGREEMENT

STOCK PURCHASE AGREEMENT

This Agreement

("Agreement") is made and entered into as of June 7, 2002 (the "Effective
Date"), by and among Transkaryotic Therapies, Inc., a Delaware corporation (the
"Company"), and Cell Genesys, Inc., a Delaware corporation ("CELL GENESYS").

A.

Concurrently with the execution of this Agreement, the Company is entering into
an Exclusive License Agreement with CELL GENESYS, (the "License Agreement"),
pursuant to which CELL GENESYS is licensing the rights to certain technology to
the Company; and

B.

In partial consideration for the execution and delivery of the License Agreement
by CELL GENESYS, the Company has agreed to issue to CELL GENESYS certain shares
of the Company's common stock in accordance with the terms and conditions of
this Agreement.

Agreement

In consideration of the mutual covenants contained in this Agreement and for
other good and valuable consideration, the receipt of which is hereby
acknowledged, the Company and CELL GENESYS hereby agree as follows:

SECTION 1

Authorization of Sale of Shares.

1.1 Authorization

. Subject to the terms and conditions of this Agreement, the Company has or
before the Closings (as defined below) will have authorized the sale and
issuance of up to the following number of shares of the Company's Common Stock,
par value $0.01 per share (the "Shares"):

Three-Hundred Sixty Six Thousand Nine Hundred Twenty Eight (366,928) Shares (the
"Up Front Shares"), subject to adjustment pursuant to Section 1.2;

that number of Shares equal to [*], divided by the average closing price of the
Company's Shares as reported on the Nasdaq National Market for the ten (10)
consecutive trading days ending two days prior to the date of the Second Tranche
Closing, as hereinafter defined (the "First Milestone Shares"), which shares
shall only be issued if the milestone in Section 4.3(a) of the License Agreement
is achieved; and

that number of Shares equal to [*], divided by the average closing price of the
Company's Shares as reported on the Nasdaq National Market for the ten (10)
consecutive trading days ending two days prior to the date of the Third Tranche
Closing, as hereinafter defined (the "Second Milestone Shares"), which shares
shall only be issued if the milestone in Section 4.3(b) of the License Agreement
is achieved.

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the Commission. Confidential treatment has been requested with respect to the
omitted portions.

If after the date hereof (i) the outstanding shares of the Company's Common
Stock shall be subdivided or split into a greater number of shares or a dividend
in Common Stock shall be paid in respect of such Common Stock, (ii) the
outstanding shares of Common Stock are combined, (iii) the Company shall pay a
dividend in securities of the Company (other than Common Stock) or of other
property (including cash) on the Common Stock, or (iv) there shall occur any
merger, consolidation, capital reorganization or reclassification in which the
Common Stock is converted or exchanged for securities, cash or other property,
all share quantities in this Agreement, as well as the class or series of stock
constituting the Common Stock for purposes of this Agreement, shall be
appropriately adjusted to reflect such stock splits, stock dividend,
combination, other dividend, merger, consolidation, capital reorganization or
reclassification. After any event referenced in clauses (i) through (iv) is
consummated, if applicable, all references herein to the Company's Common Stock
shall be deemed to refer to the capital stock or property (including cash) into
or for which the Common Stock was converted or exchanged, with the necessary
changes in detail.

1.2 Adjustment of Up Front Shares

. The number of Up Front Shares shall be adjusted as follows:

if the product of the average closing price of the Company's Shares as reported
on the Nasdaq National Market for the ten (10) trading days ending two days
prior to the effective date of the Registration Statement (as hereinafter
defined) with respect to the Up Front Shares multiplied by 366,928 is less than
Fifteen Million Dollars ($15,000,000), then the number of Up Front Shares shall
be increased by the number of Shares equal to (x) the difference between
$15,000,000 and such product divided by (y) such average closing price; and the
Company shall issue to CELL GENESYS such additional Up Front Shares promptly
following the end of such ten (10) day period for a price per share equal to the
par value of each such share, which price shall be deemed paid in partial
consideration for the execution and delivery by CELL GENESYS of the License
Agreement; provided further that the Company shall promptly cause any such
additional shares to be registered, through supplement or amendment, on the
Registration Statement with respect to the Up Front Shares; and

if the product of the average closing price of the Company's Shares as reported
on the Nasdaq National Market for the ten (10) trading days ending two days
prior to the effective date of the Registration Statement (as hereinafter
defined) with respect to the Up Front Shares multiplied by 366,928 is greater
than Fifteen Million Dollars ($15,000,000), then the number of Up Front Shares
shall be decreased by a number of Shares equal to (x) the difference between
such product and $15,000,000 divided by (y) such average closing price; and CELL
GENESYS shall surrender to the Company the number of Shares by which the Up
Front Shares are decreased, promptly following the end of such ten (10) day
period, at a price per share equal to the par value of each such share, which
price shall be deemed paid in partial consideration for the execution and
delivery by Company of the License Agreement.

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the Commission. Confidential treatment has been requested with respect to the
omitted portions.

SECTION 2

Closing and Delivery

2.1 Sale of Shares

. Subject to the terms and conditions of this Agreement and in reliance upon the
representations, warranties and agreements contained herein, the Company will
issue and sell to CELL GENESYS, and CELL GENESYS will purchase from the Company,
at each of the Closings, the applicable number of Shares, at a price per share
equal to the par value of each such share at such time, which price shall be
deemed paid in partial consideration for the execution and delivery by CELL
GENESYS of the License Agreement.

2.2 Closings

. The closings of the purchase and sale of the Shares to be issued pursuant to
this Agreement shall be held at the offices of Hale and Dorr LLP, 60 State
Street, Boston, Massachusetts, 02109 in three tranches, as follows:

Within ten days of execution of the License Agreement, at a date mutually agreed
by the parties hereto, the closing of the purchase and sale of the Up Front
Shares will occur (the "First Tranche Closing");

Within [*] of the achievement of the milestone in Section 4.3(a) of the License
Agreement, if achieved, at a date mutually agreed by the parties hereto, the
closing of the purchase and sale of the First Milestone Shares will occur (the
"Second Tranche Closing"); and

Within [*] of the achievement of the milestone in Section 4.3(b) of the License
Agreement, if achieved, at a date mutually agreed by the parties hereto, the
closing of the purchase and sale of the Second Milestone Shares will occur (the
"Third Tranche Closing").

Each of the First Tranche Closing, Second Tranche Closing and Third Tranche
Closing are collectively hereinafter referred to as the "Closings" and
individually as a "Closing".

2.3 Delivery of the Shares

. Promptly following a Closing, the Company shall deliver to CELL GENESYS a
certificate representing the number of Shares purchased at such Closing,
registered in the name of CELL GENESYS.

SECTION 3

Representations, Warranties and Covenants of the Company.

Subject to and except as set forth on the Schedule of Exceptions which is
arranged in sections corresponding to the sub-section numbered provisions
contained below in this Section and except as described in the SEC Reports (as
defined below), the Company hereby represents and warrants to, and covenants
with, CELL GENESYS as of the date hereof as follows:

3.1 Organization and Qualification

. The Company is a corporation duly organized, validly existing and in good
standing under the laws of the State of Delaware and has all requisite corporate
power and authority to perform its obligations hereunder and to consummate the
transactions contemplated hereby.

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the Commission. Confidential treatment has been requested with respect to the
omitted portions.

3.2 Due Execution, Delivery and Performance

. The Company's execution, delivery and performance of this Agreement and the
issuance and sale of the Shares have been duly authorized by all requisite
corporate action by the Company. Upon the execution and delivery by the Company,
and assuming the valid execution and delivery of this Agreement by CELL GENESYS,
this Agreement will constitute the valid and binding obligation of the Company,
enforceable in accordance with its terms, except as enforceability may be
limited by applicable bankruptcy, insolvency, reorganization, moratorium or
similar laws affecting creditors' and contracting parties' rights generally and
except as enforceability may be subject to general principles of equity
(regardless of whether such enforceability is considered in a proceeding in
equity or at law), including specific performance, and except as the
indemnification provisions contained in Section 8.3 hereof may be legally
unenforceable.

3.3 No Conflicts

. The Company's execution, delivery and performance of this Agreement and the
issuance of the Shares will not violate, conflict with, result in a breach of or
constitute (upon notice or lapse of time or both) a default under, or result in
the creation or imposition of any lien, security interest, mortgage, pledge,
charge or other encumbrance, of any material nature, upon any properties or
assets of the Company under any (a) law, regulation, rule, injunction, judgment,
order, decree, ruling, charge or other restriction of any government,
governmental agency, court or arbitrator to which the Company is subject, (b)
the Company's Amended Restated Certificate of Incorporation or Bylaws or (c) any
provision of any material indenture, mortgage, agreement, contract or other
material instrument to which the Company is a party or by which the Company or
any of its properties or assets is bound as of the date hereof, except in the
case of clause (a) and clause (c), where such violation, conflict, breach,
default, or imposition would not have a Material Adverse Effect. As used in this
Agreement, a "Material Adverse Effect" means (a) a material adverse effect upon
the business, operations, properties, assets or condition (financial or
otherwise) of the Company or, as the case may be, the Company and any of its
subsidiaries, taken as a whole or (b) a material impairment of the ability of
the Company to perform its obligations under this Agreement.

3.4 Governmental Consents

. Except for applicable filings with The Nasdaq Stock Market, Inc. (the "Nasdaq
Market"), under the Securities Act of 1933, as amended (the "Securities Act"),
or the Securities Exchange Act of 1934, as amended (the "Exchange Act"), or
state securities laws, no consent, approval, qualification, order or
authorization of, or filing with, any local, state, or federal governmental
authority is required on the part of the Company in connection with the
Company's valid execution, delivery, or performance of this Agreement, or the
offer, sale or issuance of the Up Front Shares by the Company, other than any
post-closing filings as may be required under applicable federal or state
securities laws, which will be timely filed within the applicable periods
therefor.

3.5 Issuance and Sale of the Securities

. When issued and paid for in accordance with this Agreement, the Shares to be
sold hereunder by the Company will be validly issued and outstanding, fully paid
and non- assessable.

3.6 SEC Reports

.

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the Commission. Confidential treatment has been requested with respect to the
omitted portions.

Since January 1, 2001, the Company has filed in a timely manner with the
Securities and Exchange Commission (the "SEC") all reports ("SEC Reports")
required to be filed by it under the Exchange Act. All of the SEC Reports filed
by the Company comply in all material respects with the requirements of the
Exchange Act. To the knowledge of the Company, none of the SEC Reports contain,
as of the respective dates thereof, any untrue statement of a material fact or
omit to state any material fact required to be stated therein or necessary to
make the statements therein not misleading in light of the circumstances under
which they were made.

No event has occurred since January 1, 2002, requiring the filing of an SEC
Report that has not heretofore been filed and furnished to CELL GENESYS
(including, without limitation, any amendment to any such SEC Report).

3.7 Capitalization

. The authorized capital stock of the Company consists of (i) 100,000,000 shares
of Common Stock, par value $0.01 per share, of which 34,383,308 were issued and
outstanding as of April 10, 2002 and (ii) 10,000,000 shares of preferred stock,
par value $0.01 per share, of which no shares are issued and outstanding on the
date hereof. As of the date hereof, the Company has no intention, obligation or
commitment, fixed or contingent, to issue any shares of such Preferred Stock,
other than pursuant to its Stockholders' Rights Plan.

3.8 Nasdaq Compliance

. The Company's Common Stock is registered pursuant to Section 12(g) of the
Exchange Act, and is listed on the Nasdaq National Market (the "Nasdaq Stock
Market"), and the Company has taken no action designed to, or which to its
knowledge is likely to have the effect of, terminating the registration of the
Common Stock under the Exchange Act or delisting the Common Stock from the
Nasdaq Stock Market. The issuance of the shares does not require stockholder
approval, including, without limitation, pursuant to the Nasdaq Marketplace
Rules.

3.9 Form S-3 Eligibility

. The Company qualifies as a registrant whose securities may be resold pursuant
to Form S-3 promulgated by the SEC pursuant to the 1933 Securities Act, as
amended.

3.10 Absence of Litigation

. There is no action, suit, proceeding or investigation pending or, to the
Company's best knowledge, that has been filed, commenced or threatened, by or
before any governmental agency, court or arbitrator against the Company which
might have, either individually or in the aggregate, a Material Adverse Effect
(including, without limitation, any such action, suit, proceeding or
investigation that questions the validity of this Agreement or the issuance of
the Shares hereunder).

3.11 Legal Compliance

. To the Company's knowledge, the Company is not in default or violation of its
Amended Restated Certificate of Incorporation or Bylaws and has not violated any
applicable laws (including, without limitation, rules, regulations, codes,
plans, injunctions, judgments, orders, decrees, rulings and charges thereunder)
of federal, state, local and foreign governments (and all agencies thereof) in
respect of the conduct of its business or the ownership of its properties which
default violation would (either individually or in the aggregate) have a
Material Adverse Effect. To the knowledge of the Company, there exists no
condition, event or act which constitutes, or which after notice, lapse of time
or both, would constitute, such a default or violation under any of the
foregoing except where such a default is not reasonably expected to have a
Material Adverse Effect.

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the Commission. Confidential treatment has been requested with respect to the
omitted portions.

3.12 Securities Act Exemption

. Assuming and relying in part on the truth and accuracy of CELL GENESYS'
representations and warranties in Section 4 of this Agreement, the offer, sale
and issuance of the Shares is exempt from registration under the Securities Act.

3.13 No Manipulation of Stock

. The Company has not taken and will not, in violation of applicable law, take,
any action outside the ordinary course of business designed to or that might
reasonably be expected to cause or result in unlawful manipulation of the price
of the Common Stock to facilitate the sale or resale of the Shares by CELL
GENESYS.

3.14 Brokers

. Neither the Company nor any of the officers, directors or employees of the
Company has employed any broker or finder in connection with the transaction
contemplated by this Agreement. The Company shall indemnify CELL GENESYS from
and against any broker's, finder's or agent's fees for which the Company is
responsible.

SECTION 4

Representations, Warranties and Covenants of Cell Genesys.

4.1 Authority, Approval and Enforceability.

CELL GENESYS represents and warrants to and covenants with the Company that:

CELL GENESYS is a corporation duly organized, validly existing and in good
standing under the laws of the State of Delaware and has all requisite corporate
power and authority to perform its obligations hereunder and to consummate the
transactions contemplated hereby..

CELL GENESYS' execution, delivery and performance of this Agreement have been
duly authorized by all requisite corporate action by CELL GENESYS. Upon the
execution and delivery by CELL GENESYS, and assuming the valid execution and
delivery of this Agreement by the Company, this Agreement will constitute a
valid and binding obligation of CELL GENESYS, enforceable in accordance with its
terms, except as enforceability may be limited by applicable bankruptcy,
insolvency, reorganization, moratorium or similar laws affecting creditors' and
contracting parties' rights generally and except as enforceability may be
subject to general principles of equity (regardless of whether such
enforceability is considered in a proceeding in equity or at law), including
specific performance, and except as the indemnification provisions contained in
Section 8.3 hereof may be legally unenforceable.

4.2 Investment Representations

. CELL GENESYS understands that the Shares have not been registered under the
Securities Act. CELL GENESYS also understands that the Shares are being offered
and sold pursuant to an exemption from registration contained in the Securities
Act based in part upon CELL GENESYS' representations contained in the Agreement,
including this Section 4.2. CELL GENESYS represents and warrants to, and
covenants with, the Company that as of the date hereof and as of the date of any
issuance of Shares hereunder:

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omitted portions.

CELL GENESYS has substantial experience in evaluating and investing in private
purchases of securities in companies similar to the Company so that it is
capable of evaluating the merits and risks of its investment in the Company and
has the capacity to protect its own interests. CELL GENESYS must bear the
economic risk of this investment indefinitely unless the Shares are registered
pursuant to the Securities Act, or an exemption from registration is available.

CELL GENESYS has been advised or is aware of the provisions of Rule 144
promulgated under the Securities Act, which permits limited resale of shares
purchased in a private purchase subject to the satisfaction of certain
conditions.

CELL GENESYS agrees that it will not sell, assign or transfer, (collectively,
"Transfer") any of the Shares unless the Transfer will be made pursuant to an
exemption from the registration requirements of the Securities Act or pursuant
to an effective registration statement under the Securities Act and pursuant to
an exemption from any applicable state securities laws or an effective
registration or other qualification under any applicable state securities laws.
CELL GENESYS understands that exemptions from such registration requirements are
limited. The Company is under no obligation to register the Shares except as
provided in Section 8.

CELL GENESYS acknowledges and agrees that the Shares are subject to certain
restrictions as to resale under the federal and state securities laws. CELL
GENESYS agrees and understands that stop transfer instructions will be given to
the transfer agent for the Shares, and each share certificate and each
certificate delivered on transfer of or in substitution for any such
certificate, shall have affixed a legend in substantially the following form:

"The shares represented by this certificate have not been registered under the
Securities Act of 1933, as amended (the "Act"), and may not be offered, sold or
otherwise transferred, assigned, pledged or hypothecated unless and until
registered under the Act or unless the Company has received an opinion of
counsel satisfactory to the Company and its counsel that such registration is
not required."

CELL GENESYS is acquiring the Shares for its own account for investment only,
and not with a view towards their distribution or sale, nor with any present
intention of distributing or selling the same (except in compliance with
securities laws), and except as set forth herein, CELL GENESYS has no present or
contemplated agreement, understanding, obligation, or commitment providing for
the disposition thereof.

CELL GENESYS represents that by reason of its, or of its management's, business
or financial experience, it has the capacity to protect its own interests in
connection with the transactions contemplated in this Agreement. Further, CELL
GENESYS is aware of no publication of any advertisement in connection with the
transactions contemplated in the Agreement.

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the Commission. Confidential treatment has been requested with respect to the
omitted portions.

CELL GENESYS represents that it is an accredited investor within the meaning of
Regulation D under the Securities Act.

CELL GENESYS has had an opportunity to discuss the Company's business,
management and financial affairs with directors, officers and management of the
Company and has had the opportunity to review the Company's operations and
facilities. CELL GENESYS has also had the opportunity to ask questions of and
receive answers from, the Company and its management regarding the terms and
conditions of this investment.

4.3 No Manipulation of Stock

. CELL GENESYS has not taken and will not, in violation of applicable law, take,
any action outside the ordinary course of business designed to or that might
reasonably be expected to cause or result in unlawful manipulation of the price
of the Company's Common Stock to facilitate the sale or resale of the Shares.

SECTION 5

Survival of Representations, Warranties and Agreements.

Notwithstanding any investigation made by any party to this Agreement, all
covenants, agreements, representations and warranties made by the Company and
CELL GENESYS herein shall survive the execution of this Agreement and the
issuance and sale to CELL GENESYS of the Shares and shall terminate one year
after the achievement of, or failure to achieve, as the case may be, the last
remaining milestone under the License Agreement; provided, however, that the
representations and warranties in Section 3.6 and Section 3.10 shall survive the
execution of this Agreement for 18 months from the date of the First Tranche
Closing.

SECTION 6

Conditions to Company's Obligations at the Closing.

The Company's obligation to complete the sale and issuance of the Shares at each
Closing shall be subject to the following conditions to the extent not waived by
the Company:

6.1 Representations and Warranties Correct

. The representations and warranties made by CELL GENESYS in Sections 4.1, 4.2
and 4.3 hereof shall be true and correct when made, and shall be true and
correct on the date of the First Tranche Closing. Moreover, with respect to the
Second Tranche Closing and Third Tranche Closing, the representations and
warranties made by CELL GENESYS in Section 4.2 hereof shall be true and correct
on the respective dates of such Closings.

6.2 Compliance Certificate; Certified Resolutions.

At the First Tranche Closing, CELL GENESYS shall have delivered to the Company a
compliance certificate, executed by the Chief Executive Officer of CELL GENESYS,
dated as of the date of the First Tranche Closing, to the effect that the
conditions, specified in Sections 6.1 have been satisfied.

SECTION 7

Conditions to Cell Genesys' Obligations At the Closing.

CELL GENESYS' obligation to purchase the Shares at each Closing shall be subject
to the following conditions to the extent not waived by CELL GENESYS:

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omitted portions.

7.1 Representations and Warranties Correct

. The representations and warranties made by the Company in Section 3 hereof
shall be true and correct when made, and shall be true and correct as of the
date of the First Tranche Closing.

7.2 Legal Opinion

. CELL GENESYS shall have received from counsel to the Company, an opinion
letter addressed to CELL GENESYS, with respect to the issuance of the Shares,
dated as of the date of each Closing, in a form customarily and usually
delivered by law firms of publicly traded companies in stock issuances of the
nature contemplated by this Agreement.

7.3 Covenants Performed

. All covenants, agreements and conditions contained herein to be performed by
the Company on or prior to the date of each Closing shall have been performed or
complied with in all material respects.

7.4 Qualifications

. All authorizations, approvals, or permits, if any, of any governmental
authority or regulatory body of the United States or of any state that are
binding upon the Company and that are required in connection with the lawful
sale and issuance of the Shares at such Closing pursuant to this Agreement shall
have been duly obtained and shall be effective on and as of the date of each
Closing. No stop order or other order enjoining the sale of the Shares shall
have been issued and no proceedings for such purpose shall be pending or, to the
knowledge of the Company, threatened by the SEC, or any commissioner of
corporations or similar officer of any state having jurisdiction over this
transaction.

7.5 Legal Investment

. At the time of each Closing, the sale and issuance of the Shares shall be
legally permitted by all laws and regulations to which CELL GENESYS and the
Company are subject.

7.6 Compliance Certificate; Certified Resolutions

. At the First Tranche Closing, the Company shall have delivered to CELL GENESYS
(i) a compliance certificate, executed by the Chief Executive Officer of the
Company, dated as of the First Tranche Closing, to the effect that the
conditions, specified in Sections 7.1, 7.3 and 7.4 have been satisfied; and (ii)
a certificate of the Secretary of the Company evidencing the effective
authorization of the issuance of the Stock by the Company's Board of Directors
as of the date of each Closing.

SECTION 8

Registration of the Shares; Compliance with the Securities Act.

8.1 Definitions

. As used in this Section 8 the following terms shall have the following
respective meanings:

"Registrable Shares" shall mean all Shares issued pursuant to this Agreement
(which, for greater certainty, shall include the Up Front Shares, the First
Milestone Shares and the Second Milestone Shares, when issued) and any other
shares of Common Stock issued or issuable in respect to the Shares (because of
stock splits, stock dividends, reclassifications, recapitalizations, adjustments
pursuant to this Agreement or similar events);

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"Untrue Statement" shall mean any untrue statement or alleged untrue statement,
or any omission or alleged omission to state in the Registration Statement a
material fact required to be stated therein or necessary to make the statements
therein, in the light of the circumstances under which they were made, not
misleading.

8.2 Registration Procedures and Expenses

. The Company shall:

within fourteen (14) days immediately following each Closing, such actual date
being referred to as the "Registration Date," prepare and file with the SEC a
registration statement on Form S-3 in order to register with the SEC under the
Securities Act a sale by CELL GENESYS on a delayed or continuous basis pursuant
to Rule 415 under the Securities Act any or all of the Registrable Shares then
issued at such Closing through the automated quotation system of the Nasdaq
National Market System or the facilities of any national securities exchange on
which the Company's Common Stock is then traded, or in privately-negotiated
transactions (a "Registration Statement") (notwithstanding anything to the
contrary expressed or implied herein, if a registration statement on Form S-3,
or any substitute form, is not then available for registration of the
Registrable Shares, the Company shall be obligated instead to prepare and file
with the SEC a registration statement on Form S-1 in order to register the
Registrable Shares under the Securities Act and such registration statement will
be a "Registration Statement" for the purposes of this Agreement);

subject to receipt of necessary information from CELL GENESYS, use its
commercially reasonably efforts to cause such Registration Statement to become
effective as soon as possible after the Registration Date, and take all other
reasonable actions necessary under any federal law or regulation to permit all
Registrable Shares to be sold or otherwise disposed of thereunder;

promptly notify CELL GENESYS, at any time when a prospectus relating to such
Registration Statement is required to be delivered under the Securities Act, of
the happening of any event as a result of which the prospectus included in or
relating to such Registration Statement contains an Untrue Statement;

promptly prepare and file with the SEC, and deliver to CELL GENESYS, such
amendments and supplements to such Registration Statement and the prospectus
used in connection therewith as may be necessary to keep such Registration
Statement effective until termination of such obligation as provided in Section
8.7 below;

furnish to CELL GENESYS such number of copies of prospectuses in conformity with
the requirements of the Securities Act, in order to facilitate the public sale
or other disposition of all or any of the Registrable Shares by CELL GENESYS;

file such documents as may be required of the Company for normal state
securities law clearance for the resale of the Registrable Shares in which
states of the United States as may be reasonably requested by CELL GENESYS
provided, however, that the Company shall not be required in connection with
this paragraph (f) to qualify as a foreign corporation or execute a general
consent to service of process in any jurisdiction;

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no later than the Registration Date, use its best efforts to cause all
Registrable Shares to be listed on each securities exchange, if any, on which
equity securities by the Company are then listed; and

bear all expenses in connection with the procedures in Section 8.2, other than
(i) fees and expenses, if any, of counsel or other advisers to CELL GENESYS, and
(ii) any expenses relating to the sale of the Registrable Shares by CELL
GENESYS, including broker's commission, discounts or fees and transfer taxes.

8.3 Indemnification

.

The Company agrees to indemnify and hold harmless CELL GENESYS (and each person,
if any, who controls CELL GENESYS within the meaning of Section 15 of the
Securities Act) from and against any losses, claims, damages or liabilities to
which CELL GENESYS may become subject (under the Securities Act or otherwise)
insofar as such losses, claims, damages or liabilities (or actions or
proceedings in respect thereof) arise out of, or are based upon, any Untrue
Statement contained in the Registration Statement on the effective date thereof,
or arise out of any failure by the Company to fulfill any undertaking included
in the Registration Statement and the Company will reimburse CELL GENESYS for
any reasonable legal or other expenses reasonably incurred in investigating,
defending or preparing to defend any such action, proceeding or claim; provided,
however, that the Company shall not be liable in any such case to the extent
that such loss, claim, damage or liability arises out of, or is based upon, an
Untrue Statement made in such Registration Statement in reliance upon and in
conformity with written information furnished to the Company by or on behalf of
CELL GENESYS specifically for use in preparation of the Registration Statement,
or the failure of CELL GENESYS to comply with the covenants and agreements
contained in Section 8.4 hereof respecting the sale of the Registrable Shares or
any statement or omission in any prospectus that is corrected in any subsequent
prospectus that was delivered to CELL GENESYS prior to the pertinent sale or
sales by CELL GENESYS.

CELL GENESYS agrees to indemnify and hold harmless the Company and underwriter
(and each person, if any, who controls the Company within the meaning of
Section 15 of the Securities Act, each officer of the Company who signs the
Registration Statement and each director of the Company) from and against any
losses, claims, damages or liabilities to which the Company (or any such
underwriter, officer, director or controlling person) may become subject (under
the Securities Act or otherwise), insofar as such losses, claims, damages or
liabilities (or actions or proceedings in respect thereof) arise out of, or are
based upon, any failure to comply with the covenants and agreements contained in
Section 8.4 hereof respecting sale of the Registrable Shares, or any Untrue
Statement made in the Registration Statement on the effective date thereof if
such Untrue Statement was made in reliance upon and in conformity with written
information furnished by or on behalf of CELL GENESYS specifically for use in
preparation of the Registration Statement, and CELL GENESYS will reimburse the
Company (or such underwriter, officer, director or controlling person), as the
case may be, for any legal or other expenses reasonably incurred in
investigating, defending or preparing to defend any such action, proceeding or
claim; provided that in no event shall any indemnity by CELL GENESYS under this
Section 8.3 exceed the net proceeds received by CELL GENESYS from the sale of
the Registrable Shares covered by such Registration Statement.

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Promptly after receipt by any indemnified person of a written notice of a claim
or the beginning of any action in respect of which indemnity is to be sought
against an indemnifying person pursuant to this Section 8.3, such indemnified
person shall notify the indemnifying person in writing of such claim or of the
commencement of such action, and, subject to the provisions hereinafter stated,
in case any such action shall be brought against an indemnified person and such
indemnifying person shall have been notified thereof, such indemnifying person
shall be entitled to participate therein, and, to the extent it shall wish, to
assume the defense thereof, with counsel reasonably satisfactory to such
indemnified person. After notice from the indemnifying person to such
indemnified person of its election to assume the defense thereof, such
indemnifying person shall not be liable to such indemnified person for any legal
expenses subsequently incurred by such indemnified person in connection with the
defense thereof; provided, however, that if there exists or shall exist a
conflict of interest that would make it inappropriate, in the opinion of counsel
to the indemnified person, for the same counsel to represent both the
indemnified person and such indemnifying person or any affiliate or associate
thereof, the indemnified person shall be entitled to retain its own counsel at
the expense of such indemnifying person; provided, however, that no indemnifying
person shall be responsible for the fees and expenses of more than one separate
counsel for all indemnified parties; provided, however, that no person guilty of
fraudulent misrepresentation (within the meaning of Section 11(f) of the
Securities Act) shall be entitled to contribution from any person who was not
guilty of such fraudulent misrepresentation. No indemnifying party, in the
defense of any such claim or litigation shall, except with the consent of each
indemnified party, consent to entry of any judgment or enter into any settlement
which does not include as an unconditional term thereof the giving by the
claimant or plaintiff to such indemnified party of a release from all liability
in respect to such claim or litigation. No indemnified party may settle or agree
to settle any claim or litigation as to which indemnification may be sought
hereunder without the prior written consent of the indemnifying party. Each
indemnified party shall furnish such information regarding itself or the claim
in question as an indemnifying party may reasonably request in writing as shall
be reasonably required in connection with the defense of such claim and
litigation resulting therefrom.

If the indemnification provided for in this Section 8.3 is held by a court of
competent jurisdiction to be unavailable to an indemnified party with respect to
any loss, liability, claim, damage, or expense referred to therein, then the
indemnifying party, in lieu of indemnifying such indemnified party hereunder,
shall contribute to the amount paid or payable by such indemnified party as a
result of such loss, liability, claim, damage, or expense in such proportion as
is appropriate to reflect the relative fault of the indemnifying party on the
one hand and of the indemnified party on the other in connection with the
statements or omissions that resulted in such loss, liability, claim, damage, or
expense as well as any other relevant equitable considerations. The relative
fault of the indemnifying party and of the indemnified party shall be determined
by reference to, among other things, whether the untrue or alleged untrue
statement of material fact or the omission to state a material fact relates to
information supplied by the indemnifying party or by the indemnified party and
the parties' relative intent, knowledge, access to information, and opportunity
to correct or prevent such statement or omission; provided, that in no event
shall any contribution by CELL GENESYS hereunder exceed the net proceeds
received by CELL GENESYS from the sale of the Shares covered by the Registration
Statement.

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8.4 Transfer of Shares After Registration; Notice

. CELL GENESYS hereby covenants with the Company not to make any sale of the
Registrable Shares after registration without effectively causing the prospectus
delivery requirement under the Securities Act to be satisfied, and not to make
sale of the Registrable Shares under the Registration Statement if the Company
has notified it that the Registration Statement contains an Untrue Statement.

8.5 Reporting Requirements

. The Company agrees to use its best efforts to:

make and keep public information available, as those terms are understood and
defined in Rule 144 under the Securities Act;

file with the SEC in a timely manner all reports and other documents required of
the Company under the Securities Act and the Securities Exchange Act of 1934;
and

so long as CELL GENESYS own Registrable Shares, to furnish to CELL GENESYS
forthwith upon request (1) a written statement by the Company as to whether it
complies with the reporting requirements of said Rule 144, the Securities Act
and Securities Exchange Act of 1934, and whether it qualifies as a registrant
whose securities may be resold pursuant to SEC Form S- 3, and (2) such other
information as may be reasonably requested in availing CELL GENESYS of any rule
or regulation of the SEC that would permit the selling of the Registrable Shares
without registration.

8.6 Limitations on Registration Rights.

Notwithstanding the provisions of this Section 8, the Company may be written
notice to CELL GENESYS require that CELL GENESYS immediately cease sales of
shares under the Registration Statement ("Suspended Registration Statement"), in
any period during which the Company is engaged in any activity or transaction or
preparations or negotiations for any activity or transaction ("Company
Activity") that the Company desires to keep confidential for business reasons,
if the Company determines in good faith that the public disclosure requirements
imposed on the Company under the Securities Act in connection with any such
Registration Statement would require disclosure of the Company Activity;
provided, that (i) that the Company shall not suspend the use of said prospectus
more than two times in any twelve month period and the duration of any one such
suspension shall not be more than thirty (30) days and (ii) the Company shall
cause any Suspended Registration Statement to remain effective for one
additional day for each day, or any portion of a day, that CELL GENESYS was
required to cease sales of shares thereunder, and provided further, that the
Company shall use its commercially reasonable efforts to minimize the duration
of any such suspension; and

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If the Company requires CELL GENESYS to cease sales of shares pursuant to
Section 8.6(a) above, the Company shall, as promptly as practicable following
the termination of the circumstance which entitled the Company to do so, give
prompt written notice to CELL GENESYS that such circumstance has terminated and
that it may resume sales pursuant to the Suspended Registration Statement has
been amended to comply with the requirements of the Securities Act, the Company
shall enclose such revised prospectus with the notice to CELL GENESYS given
pursuant to this section 8.6(b) and CELL GENESYS shall make no offers or sales
of shares pursuant to such Suspended Registration Statement other than by means
of such revised prospectus. The foregoing provisions of this Section 8.6 shall
in no manner diminish or otherwise impair the Company's obligations under
Section 8.2 and Section 8.3 hereof.

8.7 Termination of Obligations

. The obligations of the Company pursuant to Sections 8.2 through 8.5 hereof
with respect to Registrable Shares issued at a Closing and the Registration
Statement covering such Shares shall cease and terminate at such time as all of
such Registrable Shares (i) have been resold or (ii) such time as all of such
Registrable Shares held by such Purchaser may be sold during any 90 day period
pursuant to Rule 144, including Rule 144 (k), without being restricted by the
volume limitations of Rule 144(e).

SECTION 9 Notices

.

All notices or other communications which are required or permitted hereunder
shall be in writing and addressed as follows:

if to CELL GENESYS:

Cell Genesys, Inc.

 

342 Lakeside Drive

 

Foster City, CA 94404

Attention:

Robert Tidwell

 

Vice President, Corporate Development

With a copy to:

Cooley Godward LLP

3000 El Camino Real

 

Palo Alto, CA 94306-2155

Attention:

Barclay J. Kamb, Esq.

if to the Company:

Transkaryotic Therapies, Inc.

195 Albany Street

 

Cambridge, MA 02139

Attention:

Richard F Selden

 

President and Chief Executive Officer

With a copy to:

Kerry A. Flynn

Senior Director, Business Development

or to such other address as the party to whom notice is to be given may have
furnished to the other party in writing in accordance herewith. Any such
communication shall be deemed to have been given when delivered if personally
delivered or sent by facsimile (provided that the party providing such notice
promptly confirms receipt of such transmission with the other party by
telephone), on the business day after dispatch if sent by a
nationally-recognized overnight courier and on the third business day following
the date of mailing if sent by mail, postage prepaid, return receipt requested.

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SECTION 10 Miscellaneous

.

10.1 Waivers and Amendments

. Neither this Agreement nor any provision hereof may be changed, waived,
discharged, terminated, modified or amended except upon the written consent of
the parties hereto.

10.2 Headings

. The headings of the various sections of this Agreement have been inserted for
convenience of reference only and shall not be deemed to be part of this
Agreement.

10.3 Severability

. If any provision hereof should be held invalid, illegal or unenforceable in
any respect, then, to the fullest extent permitted by law, (a) all other
provisions hereof shall remain in full force and effect and shall be liberally
construed in order to carry out the intentions of the Parties as nearly as may
be possible and (b) the parties shall use their best efforts to replace the
invalid, illegal or unenforceable provision(s) with valid, legal and enforceable
provision(s) which, insofar as practical, implement the purposes of such
provision(s) in this Agreement.

10.4 Governing Law

. This Agreement shall be governed by and construed in accordance with the laws
of the State of Delaware as applied to contracts entered into and performed
entirely in the State of Delaware by Delaware residents, without regard to
conflicts of law principles.

10.5 Counterparts

. This Agreement may be executed in two or more counterparts, each of which
shall constitute an original, but all of which, when taken together, shall
constitute but one instrument, and shall become effective when one or more
counterparts have been signed by each party hereto and delivered to the other
parties.

10.6 Successors and Assigns

. Except as otherwise expressly provided herein, the provisions hereof shall
inure to the benefit of, and be binding upon, the successors, assigns, heirs,
executors and administrators of the parties hereto, provided that CELL GENESYS
shall not assign its rights or obligations hereunder unless CELL GENESYS assigns
such rights in whole and not in part to an assignee of such rights and
obligations which shall agree in writing with the Company to be bound by this
Agreement. The Company shall not, directly or indirectly, enter into any merger,
consolidation or reorganization in which the Company shall not be the surviving
corporation unless the proposed surviving corporation shall, prior to such
merger, consolidation or reorganization, agree in writing to assume the
obligations of the Company under this Agreement; provided, however, that the
provisions of this Section 10.6 shall not apply in the event of any merger,
consolidation or reorganization in which the Company is not the surviving
corporation if CELL GENESYS is entitled to receive in exchange for their
Registrable Shares consideration consisting solely of (i) cash, or (ii)
securities of the acquiring corporation which may be immediately sold to the
public without registration under the Securities Act.

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10.7 Expenses

. Each party shall pay all costs and expenses that it incurs with respect to the
negotiation, execution, delivery and performance of this Agreement.

10.8 Entire Agreement

. This Agreement, the License Agreements and other documents delivered pursuant
hereto and thereto, including the exhibits, constitute the full and entire
understanding and agreement between the parties with regard to the subjects
hereof and thereof.

10.9 Publicity

. No party shall issue any press releases or otherwise make any public statement
with respect to the transactions contemplated by this Agreement without the
prior written consent of the other party, except as may be required by
applicable law or regulations, in which case such party shall provide the other
parties with reasonable notice of such publicity and/or opportunity to review
such disclosure.

10.10 Waiver of Rule of Construction.

Each Party has had the opportunity to consult with counsel in connection with
the review, drafting and negotiation of this Agreement. Accordingly, the rule of
construction that any ambiguity in this Agreement shall be construed against the
drafting Party shall not apply.

10.11 Termination.

This Agreement shall terminate when the Company's obligation to issue additional
shares under the License Agreement terminates.

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In Witness Whereof

, the parties hereto have caused this Stock Purchase Agreement to be executed by
their duly authorized representatives as of the day and year first above
written.

Transkaryotic Therapies, Inc.

Cell Genesys, Inc.

By:__________________________

By:__________________________

Name:

Name:

Title:

Title:

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