<PAGE>
                                                                   Exhibit 10.25

                                                                       EXECUTION

                                    SUBLEASE

     THIS SUBLEASE AGREEMENT ("Sublease") is made as of the 23rd day of July,
2004, by and between Transkaryotic Therapies, Inc. (hereinafter called
"Sublandlord"), a Delaware corporation, and Altus Pharmaceuticals Inc.
(hereinafter called "Subtenant"), a Delaware corporation.

                                    RECITALS:

     A. Pursuant to a Lease dated as of November 28, 1993, as amended by a First
Amendment to Lease dated as of April 13, 1998 and a Second Amendment to Lease
dated as of December 23, 2002 (hereinafter called the "Prime Lease"),
Sublandlord, as tenant, leased from Benjamin L. Wilson, Jr., t/u/w Edward S.
Stimpson, t/u/w Harry F. Stimpson and Harry F. Stimpson, Jr., as landlord
(hereinafter called "Prime Landlord"), certain premises consisting of
approximately 48,000 rentable square feet, together with all rights appurtenant
thereto, including without limitation, such parking as is provided thereunder
(hereinafter, the "Leased Premises"), located at 195 Albany Street, Cambridge,
Middlesex County, Massachusetts (the "Building"), all as more particularly
described in the Prime Lease.

     B. Sublandlord and Subtenant have agreed that Sublandlord will sublet to
Subtenant the portion of the 1st floor of the Leased Premises shown on Exhibit A
attached hereto (hereinafter, the "Subleased Premises") containing approximately
16,000 rentable square feet.

     C. Sublandlord and Subtenant hereby execute and deliver this Sublease
subject to the condition precedent of Sublandlord's obtaining the Prime
Landlord's written consent hereto.

     D. Capitalized terms defined in the Prime Lease and not otherwise defined
herein shall have the same meanings as the Prime Lease.

                                   AGREEMENTS:

     For good and valuable consideration, the receipt and sufficiency of which
are hereby acknowledged and for the mutual covenants contained herein, the
parties agree as follows.

1.   Lease; Term; Early Access. Sublandlord hereby leases to Subtenant, and
     Subtenant hereby leases from Sublandlord, the Subleased Premises, for a
     term (the "Sublease Term") commencing on the date upon which Prime Landlord
     delivers its written consent to this Sublease in the form required in
     Section 22 below to Subtenant (the "Commencement Date"), and expiring on
     December 31, 2008 (the "Expiration Date"). Notwithstanding the foregoing,
     Subtenant shall have access to the Subleased Premises for preparations for
     occupancy, from and after the date of this Sublease, provided that in no
     event shall such preparations require Prime Landlord's consent.

     The "Occupancy Date" shall be the date which is the earlier to occur of (i)
     September 15, 2004, or (ii) the date of substantial completion of
     Subtenant's Work, as defined below, but in no event shall such date be
     earlier than the Commencement Date. Notwithstanding


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     the foregoing, in the event that Prime Landlord has not delivered its
     written consent to this Sublease in the form required in Section 22 below
     by July 1, 2004, then the Occupancy Date shall be one day later for each
     day beyond July 1, 2004 that such consent is not delivered to Subtenant.

2.   Condition of the Subleased Premises. Other than Sublandlord's obligation to
     deliver possession of the Sublease Premises in "broom clean" condition,
     free of all occupants on the Occupancy Date, the Subleased Premises are
     leased to Subtenant in their condition on the date hereof. Sublandlord has
     made no representations, warranties or promises with respect to the
     Subleased Premises or the suitability thereof for the uses contemplated by
     this Sublease. Subtenant agrees to accept possession of the Subleased
     Premises on the Commencement Date "as is," in their same condition as on
     the date hereof.

3.   Subtenant's Work; Allowance. Subtenant shall have the right to make certain
     improvements in and around the Subleased Premises, as more particularly
     described in Exhibit B hereto ("Subtenant's Work") and Sublandlord hereby
     approves the same. Subtenant shall (i) hire the Richmond Group or another
     contractor to perform Subtenant's Work, provided that Sublandlord shall
     have the right to approve Subtenant's choice of contractor if other than
     the Richmond Group, which approval shall not be. unreasonably withheld, and
     subject to the terms of the Prime Lease, and (ii) be responsible for all
     architectural plans, construction drawings and design specifications (the
     "Plans"), provided that Prime Landlord and Sublandlord shall have the right
     to approve the Plans, in accordance with the terms of the Prime Lease.
     Sublandlord shall cooperate with Subtenant in obtaining all permits and
     approvals as are necessary for the Subtenant's Work, including joining such
     applications as are necessary for the Subtenant's Work. Subtenant shall
     complete Subtenant's Work at its sole cost and expense, subject to
     reimbursement of the Allowance as provided below, and in accordance with
     the requirements of the Prime Lease. Sublandlord shall have the reasonable
     right to approve items to be reimbursed by Sublandlord. Sublandlord shall
     reimburse Subtenant for the actual cost of Subtenant's Work, up to Three
     Hundred Eighty-Five Thousand and 00/100 ($385,000.00) Dollars (the
     "Allowance"). Sublandlord shall pay the Allowance to Subtenant within ten
     (10) business days after Sublandlord's receipt of written notice from
     Subtenant, accompanied by a certificate of substantial completion from
     Subtenant's architect and a certificate of occupancy from the City of
     Cambridge, confirming that Subtenant has achieved substantial completion of
     Subtenant's Work (the "Completion Notice"). The Completion Notice shall
     include the itemized cost of Subtenant's Work. Subtenant shall be solely
     responsible for all costs related to Subtenant's Work in excess of the
     Allowance. Subtenant shall be solely responsible for removing any
     alterations installed by Subtenant (other than the Subtenant's Work) upon
     the expiration or earlier termination of this Sublease, to the extent that
     such removal is required by Prime Landlord under the Prime Lease.
     Sublandlord agrees that it shall not require Subtenant to remove any of
     Subtenant's Work at the expiration or earlier termination of the Sublease.

4.   Rent. The annual base rent per year (the "Base Rent"), drawn on a U.S.
     bank, payable in advance in equal monthly installments, commencing on the
     date which is sixty (60) days after the Occupancy Date (the "Rent
     Commencement Date"), and thereafter on the first


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     day of each calendar month in advance, prorated for any partial month at
     the beginning or end of the Sublease Term, shall be paid as follows:

<TABLE>
<CAPTION>
                                    Annual Rental Rate   Monthly Rent
                                    ------------------   ------------
<S>                                 <C>                  <C>
Rent Commencement Date - 12/31/08      $400,000.00        $33,333.33
</TABLE>

     Rent and all other charges due hereunder shall be payable without demand,
     notice, set-off, or counterclaim at Sublandlord's address set forth below
     or at such other place as may be set forth by notice from Sublandlord to
     Subtenant. Any installment of rent due or accruing hereunder and any other
     sum, whether termed rent or otherwise, and payable hereunder by Subtenant
     to Sublandlord, not paid within five (5) days from the date when due, shall
     bear interest from the due date at a rate equal to the prime rate published
     by the Wall Street Journal from time to time plus four percent (4%).

5.   Additional Rent. Subtenant agrees to pay to Sublandlord, commencing on the
     Occupancy Date, its pro rata share, which is agreed to be 33.33%, hereafter
     "Subtenant's Pro Rata Share", of any and all additional rent payable by
     Sublandlord under the Prime Lease during the Sublease Term (exclusive of
     utilities addressed under Section 6 below), including, without limitation,
     interior maintenance, whether paid directly by Sublandlord, as permitted
     under Section 3.3 of the Prime Lease, or by Sublandlord to Prime Landlord.
     Notwithstanding the fact that the same as deemed additional rent under the
     Prime Lease, Subtenant shall not be responsible for (i) late fees, holdover
     payments, default damages, or interest due under the Prime Lease which
     relate to the acts or omissions of Sublandlord under the Prime Lease, (ii)
     costs of maintenance, repair or replacement of portions of the Premises
     (other than the Subleased Premises), (iii) costs of maintaining the
     Building in compliance with laws, (iv) costs of indemnifying Prime Landlord
     for acts of Sublandlord, (iv) share of any profit made by Sublandlord on
     another sublease, (v) costs of Sublandlord's insurance other than the
     insurance required under Sections 6.2(a) of the Prime Lease, (vi) costs
     incurred in restoring the building after a casualty, (vii) costs of Prime
     Landlord obtaining any insurance which Sublandlord fails to obtain, (viii)
     costs of Prime Landlord performing any obligation under the Prime Lease
     which Sublandlord failed to perform, and (ix) attorney's fees charged by
     Prime Landlord in connection with enforcement of the Prime Lease against
     Sublandlord (except to the extent that such enforcement is occasioned by
     the default of Subtenant hereunder). Subtenant acknowledges that Subtenant
     is responsible for the provision of security, janitorial and trash removal
     services to the Subleased Premises.

6.   Utilities. Subtenant hereby acknowledges that the Leased Premises are
     currently vacant, and that Subtenant initially shall be the sole occupant
     of the Leased Premises under the terms of this Sublease. Accordingly,
     commencing on the Occupancy Date, Subtenant shall pay to Sublandlord, as
     additional rent, the amount which is the sum of:

          (i) the "Variable Utility Cost" defined as the difference between (a)
     $9,064.00 (the average monthly utility cost incurred by Sublandlord for the
     Leased Premises in their vacant condition, hereinafter the "Base Utility
     Cost"), and (b) the actual monthly utility cost incurred by Sublandlord for
     the Leased Premises, including, without limitation,


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     electricity, gas and water and sewer, whether paid directly by Sublandlord,
     as permitted under Section 3.3 of the Prime Lease, or by Sublandlord to
     Prime Landlord; and

          (ii) $3,021.00 (Subtenant's Pro Rata Share of the Base Utility Cost).

     ; provided, however, as additional space in the Leased Premises is leased
     to other subtenants or occupied by anyone other than Subtenant, Subtenant,
     shall pay to Sublandlord, as additional rent, the sum of (i) its
     proportionate share (on a pro rata square foot basis based on the total
     square footage then leased and/or occupied) of the Variable Utility Cost,
     and (ii) the amount set forth in Section 6(ii). Commencing on the first
     month after the Leased Premises is ninety-five percent (95%) occupied,
     Subtenant shall pay Subtenant's Pro Rata Share of all utility costs
     incurred by Sublandlord for the Leased Premises. This provision shall apply
     in the event any conflicting provision of the Prime Lease is incorporated
     herein.

7.   Parking. Subtenant shall have the non-exclusive right to use thirty-two
     (32) parking spaces in the lot immediately adjacent to the Building at no
     additional cost. In addition, Subtenant shall have the temporary right to
     use any additional parking spaces located in the same lot, at no additional
     charge, which right shall be revocable at any time by Sublandlord, in its
     sole discretion, upon written notice to Subtenant.

8.   Building Systems and Equipment. Subtenant shall have the exclusive use of
     the House Ro/DI, the PH Neutralization System and House Compressed Air
     systems servicing the Subleased Premises (collectively, the "Systems"). In
     addition, Subtenant shall have exclusive use of one of the back-up
     generators on the roof of the Building. If Sublandlord subleases space in
     the Building to another subtenant, Sublandlord reserves the right to review
     the exclusivity granted to Subtenant for the use of any System, and to make
     the Systems available to other subtenants, provided that sharing the System
     in question is feasible, and that any proposed changes do not materially
     adversely affect the use and cost of the System in question to Subtenant.
     Subtenant shall be responsible for the operation and maintenance of the
     Systems, provided however, that in the event the use of any such Systems
     are shared with another subtenant, such subtenant shall agree in writing
     for the benefit of Subtenant to pay to Subtenant within fifteen (15) days
     of invoice therefor its pro rata share of amounts incurred for the
     operation and maintenance of the Systems. Subtenant shall have use of, and
     access to, all areas of the Leased Premises as are necessary for access to
     the Systems, the back-up generator and the electrical room and boiler in
     the basement of the Building, and a corresponding reservation of such
     rights to Subtenant shall be included in any sublease document to the
     extent any areas containing such systems are subleased to another party.

9.   Expansion. Sublandlord agrees to keep Subtenant informed as to the
     subleasing activity relating to the remaining available space in the
     Building. Sublandlord shall notify Subtenant orally or by email when lease
     proposals to other subtenants are issued and keep Subtenant apprised as
     lease proposal negotiations with other subtenants progress (provided that
     Sublandlord is not obligated to disclose to Subtenant the identity of any
     proposed subtenants or the business terms related thereto). No right of
     first refusal, right of first offer, or similar right is hereby granted.


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10.  Personal Property Taxes. Subtenant agrees to pay to local tax authorities
     and other governmental agencies throughout the term of this Sublease all
     personal property taxes which maybe levied against Subtenant's merchandise,
     trade fixtures and other personal property in and about the Subleased
     Premises.

11.  Use. Subtenant shall use the Subleased Premises solely for the uses
     permitted under the Prime Lease.

12.  Common Areas. Sublandlord and Subtenant hereby agree that Subtenant shall
     have the right, in common with others entitled thereto, to use the entrance
     lobby shown on Exhibit A (the "Entrance Lobby"). Subtenant shall have the
     right to place a sign containing its name and location in the Entrance
     Lobby and on the entrance to the Subleased Premises. Until such time as
     other portions of the Leased Premises are subleased to others, Subtenant
     shall have the right to (i) place personal property of a nature consistent
     with a reception area in the Entrance Lobby, and (ii) have a receptionist
     sit in the Entrance Lobby and direct visitors to the Subleased Premises.
     Sublandlord and Subtenant hereby agree to work cooperatively to facilitate
     the transition of the Leased Premises to use by multiple occupants, the
     first of whom is Subtenant. Accordingly, Sublandlord hereby reserves a
     right of access to and use of the common areas of the Leased Premises,
     including without limitation, the Entrance Lobby, the elevator lobby, and
     the elevator. Such reservation shall include Sublandlord's right to alter
     and improve those areas from time to time to facilitate multiple occupancy,
     and to grant to third parties non-exclusive rights therein. Sublandlord
     agrees to give Subtenant reasonable prior notice of any such alterations,
     and to use reasonable efforts to minimize any interruption of Subtenant's
     use of, or access to, the Subleased Premises occasioned thereby, provided
     that any such work may be undertaken during normal business hours, but in
     no event shall Sublandlord have the right to limit Subtenant's use of, or
     access to, the Subleased Premises, and the elevator shall be operational at
     all times. After notice that another subtenant will occupy a portion of the
     Leased Premises, Subtenant shall remove any personal property from the
     Entrance Lobby at Sublandlord's request and shall cooperate with
     Sublandlord's alterations and conversions of use of those areas for
     multiple occupancy as aforesaid. Sublandlord hereby grants Subtenant a
     right to use the loading docks serving the Subleased Premises subject to
     the remaining terms of this Section. Sublandlord, on its behalf and on
     behalf of any subtenant, assignee or other party claiming by, through or
     under Sublandlord, hereby reserves a right of access to the loading dock on
     the first floor of the Building via the freight elevator and the corridor
     between the loading dock and the freight elevator throughout the term of
     this Sublease (the "Loading Dock Rights"), upon reasonable prior notice to
     Subtenant provided that (i) such party requests such access during regular
     business hours, (ii) such party complies with Subtenant's reasonable safety
     and security requirements, and (iii) such party agrees in writing to
     indemnify, defend and hold harmless Subtenant, its officers, directors and
     employees for any liability, claim, damage, cost or loss (including
     reasonable fees of legal counsel) arising in whole, or in part out of, or
     in any manner connected with any injury, loss, theft or damage to any
     person or property while exercising the Loading Dock Rights. Subtenant
     shall have the right in common with others entitled thereto to use the
     Common Areas as defined in the Prime Lease.


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13.  Prime Lease Terms and Conditions. The terms and conditions of the Prime
     Lease are hereby incorporated by reference and made a part hereof, meaning
     that, as applicable, references to "Tenant" therein shall be deemed to be
     "Subtenant" hereunder, references to "Landlord" therein shall be deemed to
     be "Sublandlord" hereunder, references to "Premises" therein shall be
     deemed to "Subleased Premises" and such other terms and conditions shall be
     deemed modified as may be appropriate in the given context or to the extent
     inconsistent with the other provisions of this Sublease, provided (i) Prime
     Landlord shall continue to have all rights set forth in the Prime Lease
     (notwithstanding the fact that Sublandlord shall also have the same rights
     under this Sublease), and (ii) Sublandlord shall not be deemed to have
     assumed any of the obligations of Prime Landlord as a result of the
     incorporation of the Prime Lease. Sections 3.3 through 3.9 of the Prime
     Lease are incorporated herein but Subtenant shall only be responsible for
     Subtenant's Pro Rata Share of the amounts due thereunder. Notwithstanding
     the foregoing, the following terms of the Prime Lease shall not be
     incorporated herein: the second sentence of Section 4.1; Section 4.7;
     Section 6.2(a); the obligation under Section 6.2(b) to obtain contractual
     liability endorsements as to losses resulting from the failure of Subtenant
     to perform and discharge its covenants and obligations under the Sublease;
     Section 7.1; Section 10.3 (except as to notices to Prime Landlord); Section
     10.5; Section 10.10; and Section 10.14. This Sublease and all of its terms,
     covenants, representations, warranties, agreements and conditions are in
     all respects subject and subordinate to the Prime Lease. Subtenant agrees
     that in no event shall Prime Landlord be (a) liable for any act or omission
     of Sublandlord; (b) liable for the return of any security deposit unless
     Prime Landlord is holding the same; (c) subject to any offsets or defenses
     which Subtenant may have against Sublandlord; or (d) bound by any rent or
     additional rent which Subtenant may have prepaid for more than the current
     month. Sublandlord shall use reasonable efforts to enforce the obligations
     of the Prime Landlord under the Prime Lease, provided that Sublandlord
     shall not be obligated to commence litigation to do so.

14.  Subtenant Obligations Under Prime Lease. To the extent incorporated herein
     and not otherwise modified herein, Subtenant agrees to perform, fulfill,
     and observe, and shall have the benefit of, all of the covenants,
     agreements, obligations, conditions, terms and provisions imposed upon, or
     provided to, Sublandlord as Tenant of the Subleased Premises under the
     Prime Lease arising from and after the Commencement Date. Notwithstanding
     the foregoing, Subtenant shall not be obligated to (i) pay the rent and
     additional rent (except Subtenant's Pro Rata Share thereof as provided
     above) to be paid by Sublandlord under the Prime Lease, (ii) cure any
     default of Sublandlord under the Prime Lease, (iii) perform any obligation
     of Sublandlord under the Prime Lease which arose prior to the Commencement
     Date and Sublandlord failed to perform, (iv) repair any damage to the
     Subleased Premises caused by Sublandlord, (v) remove any alterations or
     additions installed within the Subleased Premises by Sublandlord, (vi)
     indemnify Sublandlord or Landlord with respect to any act, omission,
     negligence or willful misconduct of Sublandlord, its agents employees or
     contractors, or (vii) discharge any liens on the Subleased Premises or the
     Building which arise out of any work performed, or claimed to be performed,
     by or at the direction of Sublandlord. Subtenant agrees to indemnify and
     hold Sublandlord harmless from and against any and all claims, liabilities,
     losses and damages of any kind whatsoever (including, without limitation,
     attorneys' fees and expenses) which Sublandlord may incur by reason of
     Subtenant's failure to perform,


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     fulfill or observe any of the covenants or agreements set forth herein or
     the applicable provisions set forth in the Prime Lease as incorporated
     herein. Sublandlord agrees to indemnify and hold Subtenant harmless from
     and against any and all claims, liabilities, losses and damages of any kind
     whatsoever (including, without limitation, attorneys fees and expenses)
     which Subtenant may incur (i) by reason of Sublandlord's failure to pay
     rent or additional rent when due under the Prime Lease, or any other
     default by Sublandlord (or any of its successors, assigns or sublessees)
     under the Prime Lease or which Subtenant may incur by reason of
     Sublandlord' s failure to perform, fulfill or observe any of the covenants
     or agreements set forth herein, provided that Subtenant has timely paid to
     Sublandlord rent when due hereunder, and (ii) arising out of, or related to
     the Tanks (as defined in Section 6.1 of the Prime Lease) but only to the
     extent of indemnification actually received by Sublandlord from Prime
     Landlord under the Prime Lease. The indemnification obligations of each
     party shall survive the termination or expiration of this Sublease.

15.  Termination. This Sublease shall terminate upon the termination of the
     Prime Lease for any reason whatsoever, without any liability therefor on
     the part of either party to the other (except as expressly set forth in
     Section 14 above), with the same force and effect as if the date of such
     termination had been provided expressly in this Sublease as the Expiration
     Date. Sublandlord agrees not to voluntarily terminate the Prime Lease
     without the consent of Subtenant which may be withheld in its reasonable
     discretion, except in the event of a termination by Sublandlord in
     accordance with the provisions of Article VII of the Prime Lease (Casualty
     and Eminent Domain), which rights of termination Sublandlord may exercise
     in its sole and absolute discretion.

16.  Compliance with Law. Subtenant shall comply with all statutes, ordinances,
     rules, orders, regulations or requirements, including environmental
     regulations applicable to its particular use of the Subleased Premises, and
     shall obtain all government permits and approvals required in connection
     with Subtenant's activities in the Subleased Premises. Nothing contained
     herein or any provision of the Prime Lease incorporated herein shall be
     deemed to impose any obligation on the Subtenant to bring the Sublease
     Premises or any other area of the Building into compliance with statutes,
     ordinances, rules, orders, regulations or requirements with which the same
     do not comply as of the date of this Sublease.

17.  Insurance. Prior to the Commencement Date, and at least twenty (20) days
     prior to the expiration thereof during the Sublease Term, Subtenant shall
     provide to Sublandlord certificates which evidence the insurance coverages
     required under the Prime Lease, which insurance shall name both Prime
     Landlord and Sublandlord as additional insureds thereunder.

18.  Holding Over. If Subtenant remains on the Subleased Premises after the
     Expiration Date or after any earlier termination provided for herein, then
     such holding over shall not be deemed to extend or renew the term of this
     Sublease or to create any tenancy at will, but such holding over shall be
     as a tenancy-at-sufferance only subject to all the terms and provisions of
     this Sublease; provided, however, Subtenant shall be liable for two hundred
     percent (200%) of all rent and other charges related to occupancy of the
     Subleased


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     Premises pro rated at a daily rate during such holdover. In addition,
     Subtenant shall indemnify and hold harmless Sublandlord from and against
     all liability, damages, losses and claims (including, without limitation,
     attorneys' fees and expenses) incurred by Sublandlord in connection with
     the holding over of Subtenant, including, without limitation, any liability
     of Sublandlord to Prime Landlord under the Prime Lease. Notwithstanding the
     foregoing, Sublandlord may, at its option, regain possession of the
     Subleased Premises or any part thereof by any and all means available to
     Sublandlord under this Sublease, the Prime Lease, or at law.

19.  Brokerage Representations. Sublandlord and Subtenant each represent that it
     has not dealt with any broker in connection with this Sublease except
     Meredith & Grew and CRESA Partners (the "Brokers"). Each party hereby
     agrees to defend, indemnify and hold harmless the other party from and
     against any loss, cost or expense (including reasonable attorneys fees)
     incurred as a result of its breach of the foregoing representation.
     Sublandlord shall pay all fees due to the Brokers in connection with the
     Subleased Premises.

20.  Security Deposit. Subtenant agrees to deliver to Sublandlord, upon the
     execution and delivery of this Sublease, a security deposit in the amount
     of One Hundred Sixty-Six Thousand Six Hundred Sixty-Seven and 00/100
     ($166,667.00) Dollars in the form of cash or an irrevocable, unconditional,
     absolutely "clean" letter of credit, in the face amount equal to the
     security deposit, running to Sublandlord as the sole beneficiary, which
     letter of credit shall in all ways be satisfactory to Sublandlord in its
     reasonable discretion (the "Letter of Credit").

     If Subtenant elects to deliver the security deposit in the form of a letter
     of credit, the Letter of Credit shall have a stated duration of and shall
     be effective for at least one (1) year with provision for automatic
     successive annual one-year extensions during the Sublease Term. Subtenant
     shall keep the Letter of Credit in force throughout the Sublease Term.
     Subtenant shall deliver to Sublandlord a renewal Letter of Credit no later
     than thirty (30) days prior to the expiration date of any Letter of Credit
     issued under this paragraph, and if Subtenant fails to do so, Sublandlord
     may draw the entire amount of the expiring Letter of Credit and hold the
     proceeds in cash as the Security Deposit. Any cash security deposit shall
     not be held by Sublandlord in a separate interest bearing account nor shall
     interest accrue or be payable thereon. The Letter of Credit shall be issued
     by a financially sound major regional or national financial institution
     satisfactory to and approved by Sublandlord in its reasonable discretion.
     If the issuer of the Letter of Credit shall admit in writing its inability
     to pay its debts generally as they become due, shall file a petition in
     bankruptcy or a petition to take advantage of any insolvency act, shall
     consent to the appointment of a receiver or conservator of itself or the
     whole or any substantial part of its property, shall file a petition or
     answer seeking reorganization or arrangement under the United States
     Bankruptcy Code, shall have a receiver or conservator appointed or shall
     become subject to operational supervision by any Federal or State
     regulatory authority, then Subtenant within thirty (30) days after written
     demand by Sublandlord shall obtain a replacement Letter of Credit from
     another financial institution satisfactory to Sublandlord, in its
     reasonable judgment.


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     The security deposit is given as security for the faithful performance by
     Subtenant of all the terms, covenants and conditions of this Sublease to be
     kept and performed by Subtenant, and not as an advance rental deposit or as
     a measure of Sublandlord's damage in case of Subtenant's default. If
     Subtenant defaults after the expiration of any applicable grace periods,
     Sublandlord may draw upon the security deposit in whole or in part for the
     payment of any rent and/or any other sum in default, and/or for the payment
     of any amount which Sublandlord may spend or become obligated to spend by
     reason of such default, and/or to compensate Sublandlord for any other loss
     or amount which Sublandlord may suffer by reason of Subtenant's default to
     which Sublandlord may be entitled under this Sublease. If any portion is so
     used, Subtenant shall within five (5) business days after written demand
     therefor, increase the security deposit to the amount required hereunder,
     and Subtenant's failure to do so shall be deemed to be a default under this
     Sublease. Sublandlord shall not be required to indemnify itself from the
     security deposit, or any portion therefore with respect to any particular
     violation or default of the Subtenant, and the appropriation of such money
     from the security deposit shall be discretionary with Sublandlord.

21.  Assignment and Subletting. Subtenant shall not assign this Sublease or
     sublease all or part of the Subleased Premises without the prior written
     consent of Sublandlord, which consent shall not be unreasonably withheld or
     delayed, and the prior written consent of Prime Landlord, as provided in
     the Prime Lease. It is agreed that as between Sublandlord and Subtenant,
     the phrase "transfer in control" as contained in Section 5.5(a) of the
     Prime Lease shall mean a transfer of more than 50% of the stock interests
     in Subtenant.

22.  Prime Landlord's Consent Contingency. This Sublease is conditioned upon
     obtaining Prime Landlord's written consent to this Sublease by August 1,
     2004. Sublandlord agrees to diligently pursue Prime Landlord's written
     consent to this Sublease promptly after execution of this Sublease. In the
     event Prime Landlord's consent, in form satisfying the foregoing
     conditions, to the extent not waived by Subtenant, is not delivered to
     Subtenant by August 1, 2004, either party shall have the right to rescind
     its execution of this Sublease by written notice to the other party, and
     upon receipt of such notice, this Sublease shall terminate and all sums
     paid by Subtenant hereunder shall be immediately returned to Subtenant.

23.  Notices. Any notice required or permitted hereunder shall be deemed to have
     been given when deposited with the U.S. Mail (certified mail, postage
     prepaid, return receipt requested), when deposited with a recognized
     overnight courier, or when delivered in hand by a direct courier who
     obtains a receipt for such delivery. Such notices shall be sent to the
     following addresses:

     If to Sublandlord:   Transkaryotic Therapies, Inc.
                          700 Main Street
                          Cambridge, Massachusetts 02139
                          Attention: General Counsel

     With a copy to:      Wilmer Cutler Pickering Hale and Dorr LLP
                          60 State Street


                                       -9-
<PAGE>
                          Boston, Massachusetts 02109
                          Attention: Katharine E. Bachman, Esq.

     If to Subtenant:     Altus Pharmaceuticals Inc.
                          195 Albany Street
                          Cambridge, Massachusetts 02139
                          Attention: Mr. Richard Forrest

     With a copy to:      Torpy & Garner, LLC
                          One Washington Mall, 15th floor
                          Boston, MA 02109
                          Attention: Joseph R. Torpy, Esq.

     Any party may change its address for notice by notifying the other parties
     as aforesaid.

24.  No Partnership. Sublandlord shall not be held to be a partner, joint
     venturer, or associate of Subtenant in the conduct of its business, it
     being expressly understood and agreed that the relationship between the
     parties hereto is and at all times shall remain that of Sublandlord and
     Subtenant.

25.  Entire Agreement. All prior understandings and agreements between the
     parties are merged within this Sublease, which alone fully and completely
     sets forth the understanding of the parties, and this Sublease may not be
     changed or terminated orally or in any manner other than by an agreement in
     writing and signed by the party against whom enforcement of the change or
     termination is sought.

26.  Binding Effect. The covenants and agreements herein contained shall bind
     and inure to the benefit of Sublandlord and Subtenant and their permitted
     successors and assigns.

27.  Governing Law. The Sublease and all rights and remedies thereunder shall be
     governed by the law of the Commonwealth of Massachusetts.

28.  Consequential Damages. Notwithstanding anything herein to the contrary, in
     no event shall Sublandlord or Subtenant be liable to the other hereunder
     for indirect or special damages (including, without limitation, damages for
     lost profits).

29.  Casualty. In addition to the abatement rights provided under Section 7.3 of
     the Prime Lease as incorporated herein, in the event the Subleased
     Premises, access thereto or the Systems or any other systems serving the
     same are damaged or interrupted by fire or other casualty and such damage
     is not repaired and such interruption is not removed within 180 days from
     the date of such fire or other casualty, Subtenant shall have the right to
     terminate this Sublease by written notice to Sublandlord. Sublandlord
     acknowledges that it retains the obligations contained in Section 7.1 of
     the Prime Lease.

30.  Materials License. Sublandlord shall, at its expense, take all action
     necessary to amend their Materials License #28-3701 to reflect the removal
     of 195 Albany Street from such license.


                                      -10-
<PAGE>
31.  Sublandlord's Representations and Warranties. Sublandlord warrants and
     represents that:

          (i) the copy of the Prime Lease attached to this Sublease as Exhibit C
     is a complete and accurate copy of the Lease, which is in effect and has
     not been amended except as set forth in Exhibit C;

          (ii) To the best of Sublandlord's knowledge, Prime Landlord is not in
     default under the Prime Lease, nor has any event occurred which, after any
     applicable notice and/or the expiration of any grace period, shall
     constitute a default by Prime Landlord under the Prime Lease;

          (iii) To the best of Sublandlord's knowledge, Sublandlord is not in
     default under the Prime Lease, nor has any event occurred which, after any
     applicable notice and/or the expiration of any grace period, shall
     constitute a material default by Sublandlord under the Prime Lease; and

          (iv) All rent, additional rent and other charges due under the Prime
     Lease have been paid as billed or required in the normal course through
     June 30, 2004.

                  [Remainder of page intentionally left blank]


                                      -11-
<PAGE>
IN WITNESS WHEREOF the parties hereto set their hands and seals as of the day
and year first above written.

                                        SUBLANDLORD:

                                        TRANSKARYOTIC THERAPIES, INC.


                                        By: /s/ Gregory Perry
                                            ------------------------------------
                                        Name: Gregory Perry
                                        Title: VP Finance & CFO


                                        SUBTENANT:

                                        ALTUS PHARMACEUTICALS INC.


                                        By: /s/ Jonathan Lieber
                                            ------------------------------------
                                        Name: Jonathan Lieber
                                        Title: VP Finance


                                      -12-
<PAGE>
                                    EXHIBIT A

                               SUBLEASED PREMISES


                                        1
<PAGE>
                               [INSERT FLOOR PLAN]


                                        2
<PAGE>
                                    EXHIBIT B

                                SUBTENANT'S WORK


                                        3
<PAGE>
                                    EXHIBIT C

                                   PRIME LEASE


                                        4
<PAGE>
                     LEASE BETWEEN BENJAMIN L. WILSON, JR.,
              T/U/W EDWARD S. STIMPSON, T/U/W HARRY F. STIMPSON AND
                             HARRY F. STIMPSON, JR.
                                   AS LANDLORD
                        AND TRANSKARYOTIC THERAPIES, INC.
                                    AS TENANT

                                TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                                            Page
                                                                            ----
<S>                                                                         <C>
ARTICLE I    Reference Data..............................................     1

   1.1       Subjects Referred To........................................     1
   1.2       Exhibits....................................................     3

ARTICLE II   Premises and Term...........................................     3

   2.1       Premises....................................................     3
   2.2       Term........................................................     5
   2.3       Option to Extend............................................     5
   2.4       Right to Negotiate Purchase of Premises and Adjacent
                Building.................................................     5
   2.5       Right to Negotiate Lease....................................     6

ARTICLE III  Rent........................................................     7

   3.1       Annual Fixed Rent...........................................     7
   3.2       Adjustments to Annual Fixed Rent............................     7
   3.3       Additional Rent.............................................     9
   3.4       Real Estate Taxes...........................................    10
   3.5       Betterment Assessments......................................    10
   3.6       Tax Fund Payments...........................................    11
   3.7       Insurance...................................................    11
   3.8       Utilities and Services......................................    11
   3.9       Additional Expenses.........................................    11
   3.10      Late Charge.................................................    12
   3.11      Net Lease...................................................    12
   3.12      No Offsets..................................................    12

ARTICLE IV   MAINTENANCE AND REPAIR, ALTERATIONS; SURRENDER; HOLDING
OVER.....................................................................    12

   4.1       Tenant's Maintenance and Repair.............................    12
   4.2       Landlord's Maintenance and Repair...........................    12
   4.3       Alterations.................................................    13
   4.4       Alterations Requirements....................................    13
   4.5       Entry by Landlord...........................................    14
   4.6       Surrender...................................................    14
</TABLE>


                                       (i)
<PAGE>
<TABLE>
<S>                                                                         <C>
   4.7       Holding Over................................................    15

ARTICLE V    ADDITIONAL TENANT COVENANTS.................................    15

   5.1       Payment-and Performance.....................................    15
   5.2       Use.........................................................    15
   5.3       Compliance with Law.........................................    16
   5.4       Personal Property Taxes.....................................    16
   5.5       Assignment and Subletting...................................    16

ARTICLE VI   ARTICLE VI INDEMNITY AND INSURANCE..........................    17

   6.1       Indemnity...................................................    17
   6.2       Tenant's Insurance..........................................    18
   6.3       Tenant's Risk...............................................    20
   6.4       Subrogation.................................................    20

ARTICLE VII  CASUALTY AND EMINENT DOMAIN.................................    20

   7.1       Casualty During Term........................................    20
   7.2       Condemnation................................................    21
   7.3       Abatement of Rent...........................................    21
   7.4       Condemnation Award..........................................    21

ARTICLE VIII DEFAULT.....................................................    22

   8.1       Tenant's Default............................................    22
   8.2       Damages.....................................................    23
   8.3       Remedies Cumulative.........................................    23
   8.4       Landlord's Election.........................................    23
   8.5       Effect of Waivers of Default................................    24
   8.6       No Waiver...................................................    24
   8.7       No Accord and Satisfaction..................................    24
   8.8       Delivery of Keys............................................    24
   8.9       Attorneys' Fees.............................................    24

ARTICLE IX   MORTGAGEES' AND GROUND LESSORS' RIGHTS......................    24

   9.1       Superiority of Lease........................................    25
   9.2       Subordination...............................................    25
   9.3       Limitation on Tenant's Rights...............................    25
   9.4       Exercise of Mortgagee's Remedies............................    25
   9.5       Further Assurances..........................................    25
   9.6       No Prepaid Rent.............................................    26

ARTICLE X    MISCELLANEOUS...............................................    26

   10.1      Estoppel Certificates.......................................    26
</TABLE>


                                      (ii)
<PAGE>
<TABLE>
<S>                                                                         <C>
   10.2      No Recordation..............................................    26
   10.3      Notices.....................................................    26
   10.4      Successors and Assigns......................................    27
   10.5      Limitation of Liability.....................................    27
   10.6      Covenants and Conditions....................................    27
   10.7      Severability................................................    27
   10.8      Quiet Enjoyment.............................................    27
   10.9      Entire Agreement............................................    27
   10.10     Brokers.....................................................    27
   10.11     Applicable Law and Construction.............................    28
   10.12     Time of Essence.............................................    28
   10.13     Authorization...............................................    28
   10.14     Security Deposit............................................    28
</TABLE>


                                      (iii)
<PAGE>
     THIS LEASE is made and entered into as of the 28th day of November, 1993 by
and between Benjamin L. Wilson, Jr.; Margaret W. Stimpson, Edward S. Stimpson,
III, Harry F. Stimpson, III, and Nicholas U. Sommerfeld, trustees under the will
of Edward S. Stimpson; Harry F. Stimpson, III, trustee under the will of Harry
F. Stimpson; and Harry F. Stimpson, Jr.; as tenants in common (collectively, the
"Landlord"), and TRANSKARYOTIC THERAPIES, INC., a Delaware corporation
("Tenant").

     In consideration of the mutual covenants herein set forth, Landlord and
Tenant do hereby agree to the terms and conditions set forth in this Lease.

                                    ARTICLE I

                                 Reference Data

     1.1 Subjects Referred To. Each reference in this Lease to any of the
following shall be construed to incorporate the following data:

<TABLE>
<S>                        <C>
Annual Fixed Rent:         [Illegible], as that amount may be increased pursuant
                           to the terms of this Lease, which amount reflects the
                           sum of (i) [Illegible] per square foot of Premises
                           located on the second floor of the Building and (ii)
                           [Illegible] per square foot of Premises located on
                           the first floor and lower level of the Building.

Building:                  The building known as and numbered 195 Albany Street,
                           Cambridge., Massachusetts

Common Area:               See Section 2.1.2

Extension Term:            Two (2) periods of five (5) years each as provided in
                           Section 2.3.

External Causes:           See Section 7.1

Initial Public Liability
Insurance Limits:          Bodily Injury:     $1,000,000
                           Property Damage:   $1,000,000
                           Umbrella Coverage: $5,000,000

Land:                      A parcel of land located at 195 Albany Street,
                           Cambridge, Massachusetts, as more particularly
                           described on Exhibit A attached hereto

Landlord's Address:        c/o Meredith &Grew, Incorporated
                           160 Federal Street
                           Boston, MA 02110-1701
</TABLE>
<PAGE>
<TABLE>
<S>                        <C>
Lease Commencement Date:   January 1, 1994

Lease Year:                Any period of one year during the Term commencing on
                           the Lease Commencement Date or on any anniversary
                           thereof.

Original Term:             Five (5) years starting on the Lease Commencement
                           Date and expiring on December 31, 1998, unless
                           extended pursuant to Section 2.3.

Permitted Uses:            See Section 5.2

Premises:                  (i) 16,000 square feet on the second floor of the
                           Building (the "Second Floor");

                           (ii) 16,000 square feet on each of the first floor
                           (the "First Floor") and lower level ("Lower Level")
                           of the Building (total of 32,000 square feet on the
                           First Floor and Lower Level);

                           (iii) 64 parking spaces in the parking lot located at
                           the corner of Albany and Pacific Streets, Cambridge,
                           Massachusetts; and

                           (iv) Access to and the periodic use of the Common
                           Areas, as defined in Section 2.1.2

Rent Commencement Date:    January 1, 1994

Tenant's Address:          195 Albany Street
                           Cambridge, MA 02139
                           Attn: Director of Operations

Term:                      The Original Term and any Extension Term as to which
                           Tenant properly exercises its option to extend as set
                           forth in Section 2.3.
</TABLE>


                                        2
<PAGE>
     1.2 Exhibits. The exhibits listed below are attached hereto and
incorporated in this Lease by reference and are to be construed as a part of
this Lease:

     Exhibit A - Legal Description of Land
     Exhibit B - Encumbrances
     Exhibit C - Equipment Remaining
     Exhibit D - Insurance

                                   ARTICLE II

                                Premises and Term

     2.1 Premises. Landlord hereby leases to Tenant and Tenant hereby leases
from Landlord, to have and to hold for the Term provided for by Section 2.2
below, subject to and with the benefit of the terms, covenants, conditions and
provisions of this lease, the Premises. Tenant is currently in possession of the
portion of the Premises located on the Second Floor of the Building under a
sublease arrangement which terminates on the Lease Commencement Date and Tenant
is fully aware of the existing conditions of the Premises and the Building and
agrees to take the same on a strictly "as is" basis without warranty or
representation express or implied and without any further obligation whatsoever
on the part of Landlord with respect thereto except as follows:

     Landlord hereby represents and warrants to Tenant:

          (i) that it has good and clear record title to the Building free from
     all encumbrances other than those listed on Exhibit B attached hereto and
     that the execution of this Lease by the undersigned on behalf of the
     Landlord has been duly authorized and consented to by all required parties;
     and

          (ii) that the Landlord shall deliver the Premises to Tenant on January
     1, 1994, free of all prior tenants and occupants thereof, including without
     limitation, all equipment and other personal property of such parties other
     than those items listed on Exhibit C attached hereto.

          2.1.1 Parking. Landlord. shall provide sixty-four (64) parking spaces
for use by Tenant and Tenant's employees in the parking lot located on the
corner of Albany Street and Pacific Street, Cambridge, Massachusetts currently
consisting of one hundred sixteen (116) parking spaces (the "Parking Lot") at no
additional cost to Tenant other than Annual Fixed Rent and additional rent.
Landlord shall also grant Tenant a monthly license to use up to thirty-two (32)
additional parking spaces (the "Additional Parking Spaces") for a fee equal to
the then current fair market value for such parking spaces, which on the
Commencement Date shall equal fifty dollars ($50) per space, payable monthly in
advance. In the event Landlord requires use of any of the Additional Parking
Spaces, Landlord shall provide Tenant with thirty (30) days advance written
notice and Landlord shall thereafter be under no obligation to continue to
license the Additional Parking Spaces to the Tenant. Tenant agrees that it and
all persons claiming by, through and under it shall at times cooperate with the
manager of the Parking Lot which


                                        3
<PAGE>
Landlord may designate from time to time, as to use of said Parking Lot and
shall abide by the reasonable rules and regulations imposed on the use of the
Parking Lot, from time to-time. Landlord shall have the right to designate, from
time to time, and to change, from time to time, the designation of managers,
parking spaces and total number of parking spaces within the Parking Lot. Tenant
shall use the designated parking spaces only for parking of vehicles, which
parking shall be available to Tenant at all hours.

          2.1.2 Common Areas. The term "Common Areas" is defined as all areas
and facilities outside the Premises which Common Areas may be used in common by
lessees of the Building and the building located at 185 Albany Street (the
"Adjacent Building") and each of their employees and invitees, including, but
not limited to, the entranceway, courtyard, lobby, emergency exits, driveway and
corridors.

          Tenant, its employees and invitees agree to abide by and conform to
the reasonable rules and regulations governing the Common Areas. Landlord or
such other person(s) as Landlord may appoint shall have the exclusive control
and management of the Common Areas and shall have the right to modify, amend and
enforce said rules and regulations. Landlord shall not be responsible to Tenant
for the non-compliance of said rules and regulations by other tenants or their
invitees, but shall uniformly enforce all such rules and regulations against all
such parties.

     Landlord shall have the right:

          (a) to make changes, at its sole cost and expense (unless otherwise
properly allocable to the Tenant under the terms of this Lease), to the Building
exterior and the Common Areas, including, without limitation, changes in the
location, size, shape, number and appearance thereof, including, but not limited
to, the lobbies, windows, stairways, air-shafts, elevators, driveways,
entranceways, parking spaces, parking areas (but not off of the Parking Lot),
loading and unloading areas, loading bays, trash areas, ingress, egress,
decorative walls, signs, landscaped areas and walkways with reasonable notice to
Tenant (except in the case of an emergency) provided, however, that any such
relocation of Parking Spaces shall not be off of the Parking Lot or the
Premises; and provided further that the implementation of such changes will not
(i) materially interfere with the Tenant's conduct of its business at the
Premises; or (ii) alter the number of parking spaces leased to Tenant pursuant
to the terms of this Lease; or (iii) materially alter the percentage of Tenant's
share of operating and tax expenses applicable to the Parking Lot; provided that
if such changes are made to the Parking Lot Tenant shall only be responsible for
its share of operating and tax expenses prior to such change.

          (b) for maintenance, repair or construction purposes, to use or to
close temporarily any of the Common Areas so long as reasonable access to the
Premises remains available.


                                        4
<PAGE>
          2.1.3 Landlord's Reservations. Landlord reserves the right, from time
to time, with reasonable notice to Tenant (except in the case of an emergency)
and without unreasonable interference with Tenant's use to gain access to the
Premises for any purpose permitted under this Lease as provided in Section 4.5
below.

     2.2 Term. The Term of this Lease shall begin on the Lease Commencement Date
and continue for the Term, unless sooner terminated or extended as provided in
this Lease.

     2.3 Option to Extend. Provided that (i) this Lease remains in full force
and effect; (ii) Tenant is not in default hereunder beyond any applicable period
of notice and grace, if any; and (iii) Tenant is in actual occupancy of at least
thirty-three percent (33%) of the Premises, Tenant shall have the option, to be
exercised as hereinafter provided, to extend the Original Term of this Lease for
two (2) periods of five (5) years each following the expiration of the Original
Term (each, an "Extension Term"). Each Extension Term shall be upon the same
terms and conditions as provided in this Lease, except for the Annual Fixed
Rent, which shall be determined in accordance with Section 3.2.1 below and
except that Tenant shall have no further option to extend the Term. Tenant shall
exercise this option to extend for an Extension Term by notifying Landlord in
writing at least one year prior to the expiration of the Original Term or the
first Extension Term, as the case may be. In the event Tenant does not exercise
the first option to extend the Term there shall be no second option to extend.

     2.4 Right to Negotiate Purchase of Premises and Adjacent Building. Provided
that (i) this Lease remains in full force and effect; (ii) Tenant is not in
default hereunder beyond any applicable period of notice and grace, if any, and
(iii) Tenant is in actual occupancy of at least sixty-seven percent (67%) of the
Premises, Tenant shall have the right to negotiate for the acquisition of the
Premises, Land and Building and the Adjacent Building (the "Right to Negotiate")
during the Original Term and the Extension Terms on the following terms and
conditions. If Landlord determines to sell the Premises, Land and Building or
any part thereof or the Adjacent Building, or any part thereof, at any time
during the Original Term or the Extension Term, Landlord shall notify Tenant of
the terms on which Landlord will be willing to sell after the expiration of time
for performance by Massachusetts Institute of Technology (together with its
successors and assigns, "MIT") under its right of first refusal with respect to
the Adjacent Building and after first offering the Premises, Land and Building
to MIT and MIT declining to so purchase the Premises, Land and Building. If
Tenant, within fifteen (15) days after receipt of Landlord's notice, indicates
in writing its desire to acquire the Premises, Land, Building or the Adjacent
Building, or any part thereof, as the case may be, Landlord and Tenant shall,
for a period of thirty (30) days after receipt of said notice, negotiate the
necessary documentation regarding Tenant's agreement 'to so purchase the
Premises, Land and Building or the Adjacent Building or such part thereof, as
the case may be, subject to and in accordance with the principal terms stated in
Landlord's notice. If written agreement is reached between Landlord and Tenant,
Landlord shall sell and convey the Premises, Land and Building or the Adjacent
Building or the part thereof, as the case may be, to Tenant on the terms in the
signed written agreement. If Landlord and Tenant so enter into a written
agreement regarding the Tenant's purchase of the Premises, Land and Building or
the Adjacent Building or part thereof, as they case may be, and thereafter
Tenant defaults in its obligation, the Right to Negotiate shall expire and
terminate for all purposes. If Tenant does not indicate its interest within the
initial fifteen (15) day period, or if Landlord and Tenant fail to enter into a
signed written agreement regarding Tenant's acquisition


                                        5
<PAGE>
of the Premises, Land and Building or the Adjacent Building, or a part thereof,
as they case may be, within the additional thirty (30) day period which begins
upon receipt of Tenant's notice of intent, Landlord thereafter shall have the
right to sell and convey the Premises, Land and Building, or the Adjacent
Building or such part thereof, as the case may be, to any third party, and upon
the closing of such sale, the Right to Negotiate shall expire and terminate for
all purposes. If Landlord does not so sell and convey the Premises, Land and
Building or the Adjacent Building or such part thereof, as the case may be,
within one year, any further transaction shall be deemed a new determination by
Landlord to sell and convey the Premises, Land and Building or the Adjacent
Building or such part thereof, as the case may be, and the provisions of this
Section 2.4 shall be applicable. If Tenant purchases all of the Premises, Land
and Building this Lease shall terminate on the date title vests in Tenant, and
Landlord shall remit to Tenant all prepaid and unearned rent. If Tenant
purchases a part thereof, this Lease as to the part purchased shall terminate on
the date title vests in Tenant, and the Annual Fixed Rent and additional rent
shall be reduced so that Tenant continues to pay $8.25 per square foot, triple
net, for the Second Floor of the Building, and $28.00 per square foot, triple
net, for the First Floor and Lower Level of the Building as the same may be
adjusted pursuant to Section 3.2 below during the Original Term, or the
corresponding rent per square foot during the Extension Terms based on the
adjustment(s) contained in Section 3.2 below. The Right to Negotiate shall not
apply to a transfer (either outright or in trust) between any of those persons
who constitute the beneficial owners or principals of Landlord, the relatives by
blood or marriage of any of those persons, or to a legal entity (i.e.,
partnership, corporation, trust, or like entity) when the majority interest is
owned by all or some of. such persons, or any transfer by gift or for nominal
consideration, so long as the Premises continue to be subject to this Lease,
including this Section 2.4. An affidavit of an officer, trustee or principal of
Landlord recorded with the Middlesex South District Registry of Deeds stating
that the provisions of. this Section 2.4 have been complied with or met as to
any conveyance of all or any portion of the Premises shall conclusively
establish compliance therewith as to any third party or parties.

     2.5 Right to Negotiate Lease. Provided that (i) this Lease remains in full
force and effect; (ii) Tenant is not in default hereunder beyond any applicable
period of notice and. grace, if any; and (iii) Tenant is in actual occupancy of
at least sixty-seven percent (67%) of the Premises, Tenant shall have the right
to negotiate for any space which becomes available and is under Landlord's
exclusive control in the Adjacent Building. Tenant acknowledges and recognizes
that the Adjacent Building is currently leased to MIT and Landlord does not have
control over MIT's sublet rights. If Landlord determines to lease all or any
portion of the Adjacent Building at anytime during the Original Term or the
Extension Terms, Landlord shall so notify Tenant. If Tenant, within fifteen (15)
days after the receipt of Landlord's notice indicates in writing its agreement
to enter into lease negotiations for such space in the Adjacent Building,
Landlord and Tenant shall each thereafter negotiate in good faith and attempt to
reach mutually acceptable lease terms within fifteen (15) days from the date of
such notice from Tenant to Landlord regarding the Tenant' s. desire to so lease
the Adjacent Building and if such terms are reached within said fifteen (15)
days, thereafter enter into a lease within thirty (30) days from the date of
such agreement for such Adjacent Building substantially in the form of this
Lease but on the terms reached by mutual agreement. If Landlord and Tenant enter
into a written lease agreement pursuant to which Tenant agrees to lease the
Adjacent Building and Tenant thereafter defaults in its obligation to so lease
space, the negotiation right contained in this Section 2.5 shall expire and
terminate for all purposes. If Tenant does not indicate its agreement


                                        6
<PAGE>
within said fifteen (15) days or if Landlord and Tenant do not enter into a
written lease agreement within the time frame provided in this Section 2.5,
Landlord thereafter shall have the right to lease the Adjacent Building to any
third party and Tenant's rights under this Section 2.5 shall expire and
terminate for all purposes.

                                   ARTICLE III

                                      Rent

     3.1 Annual Fixed Rent. Tenant covenants and agrees to pay rent to Landlord,
at the Original Address of Landlord or such other place as Landlord may by
notice in writing to Tenant from time to time direct during the Term, in the
amount of the Annual Fixed Rent as set forth in Section 1.1 above and as
adjusted pursuant to this Article III, in equal monthly installments in advance
on the first day of each calendar month during the Term, commencing on the Rent
Commencement Date. Annual Fixed Rent for any portion of a calendar month at the
beginning or the end of such period shall be prorated accordingly.
Notwithstanding any provision of this Section 3.1 to the contrary, Annual Fixed
Rent for the period from the Lease Commencement Date throughout December 31,
1994 shall be $580,000 (the "First Year Fixed Rent"). First Year Fixed Rent is a
base rent for calendar year 1994 and Tenant remains liable and responsible for
all additional rent or parking license fees otherwise due under the terms and
conditions of this Lease.

     3.2 Adjustments to Annual Fixed Rent. The Annual Fixed Rent provided for in
Section 1.1 shall be subject to adjustment as provided in Section 3.2.1 and
Section 3.2.2 below. On adjustment of the Annual Fixed Rent as provided in
Section 3.2.1 and Section 3.2.2, the parties hereto shall immediately execute an
amendment to this Lease stating the new Annual Fixed Rent.

          3.2.1 Adjustment to Annual Fixed Rent For Extension Term. Not less
than eighteen (18) months nor more than twenty (20) months prior to the
commencement of the Extension Terms, Tenant may notify Landlord that it desires
to establish Annual Fixed Rent for the applicable Extension Term; whereupon
Landlord shall immediately enter into negotiations with Tenant to set such
Annual Fixed Rent. If within thirty (30) days after said notification Landlord
and Tenant have not reached agreement on the Annual Fixed Rent for the
applicable Extension Term, then within ten (10) days after said thirty (30) day
period, Landlord and Tenant shall each name an appraiser and the Annual Fixed
Rent for the Extension Term shall be determined by appraisal in the following
manner: The two appraisers thus named shall promptly name a third appraiser. If
the two appraisers shall not have agreement upon a third appraiser within ten
(10) days after the end of the previous ten (10) day period, either Landlord or
Tenant may request the then President of the Greater Boston Real Estate Board or
the successor of such Board to appoint the third appraiser. The third appraiser
shall be a member of the Appraiser's Institute or otherwise qualify as an expert
in the appraisal of commercial real estate. The three appraisers thus selected
shall promptly proceed to determine:

     A. with respect to the first Extension Term:


                                        7
<PAGE>
          (i) with respect to the Second Floor of the Building the fair and
equitable Annual Fixed Rent for the Extension Term, such determination to be
based on the fair rental value of the leasehold interest demised hereby on
January 1, 1997. In determining such rental value the appraisers shall consider
commercial real estate in Cambridge, Massachusetts in general and specifically
those properties which have been renovated to office, research and development,
laboratory and manufacturing use, provided, however that the appraisers shall
not consider the value of any improvements which have been installed in or added
to the Second Floor which have been paid for by Tenant, whether during or prior
to the term of this Lease; and (ii) with respect to the First Floor and Lower
Level of the Building the fair and equitable Annual Fixed Rent for the extension
term, such determination to be based on 95% of the then current fair market rent
for first-class laboratory, research and development space in Cambridge,
Massachusetts leased for similar periods and upon substantially similar terms
and conditions as provided in this Lease, excluding the value of any additional
improvements to the First Floor and Lower Level of the Building paid for by
Tenant but specifically including replacements of all improvements existing on
the Lease Commencement Date (including, but not limited to. the equipment.
listed on Exhibit C). The appraisers shall make such a determination in writing
to Landlord and Tenant no later than sixty (60) days prior to January 1, 1998.

     B. with respect to the Second Extension Term:

          (i) with respect to the Second Floor of the Building the fair and
equitable Annual Fixed Rent for the Extension Term, such determination to be
based on the fair rental value of the leasehold interest demised hereby on
January 1, 2002.

In determining such rental value the appraisers shall consider commercial real
estate in Cambridge, Massachusetts in general and specifically those properties
which have been renovated to first class research and development, laboratory
and-manufacturing use, in comparable condition and equipped comparably to the
Second Floor of the Building on January 1, 2002 leased for similar periods and
upon substantially similar terms and conditions as provided in this Lease; and
(ii) with respect to the First Floor and Lower Level of the Building the fair
and equitable Annual Fixed Rent for the extension term, such determination to be
based on 95% of the then current fair market rent for first-class laboratory,
research and development space in Cambridge, Massachusetts leased for similar
periods and upon substantially similar terms and conditions as provided in this
Lease, excluding the value of any additional improvements to the First Floor and
Lower Level of the Building paid for by Tenant but specifically including
replacements of all improvements existing on the Lease Commencement Date
(including, but not limited to the equipment listed on Exhibit C). The
appraisers shall make such a determination in writing to Landlord and Tenant no
later than sixty (60) days prior to January 1, 2003.

          The parties agree to provide appropriate relevant information and
otherwise to assist the appraisers in arriving in a prompt determination. The
expenses of appraisal shall be shared equally between Landlord and Tenant but
each party shall pay its own counsel fees. The appraisers shall determine a fair
and equitable annual base rent which may be greater but not less than Annual
Fixed Rent for the Original Term, as adjusted by Section 3.2.2. below with
respect to the First Extension Term and not less than Annual Fixed Rent for the
first Extension Term, as adjusted by Section 3.2.2 below with respect to the
second Extension Term. If, following the


                                        8
<PAGE>
determination of Annual Fixed Rent for the extended term whether by agreement of
the parties or by appraisal. hereunder, Tenant exercises its option to extend
the Term granted under Section 2.3 above, the fair and equitable Annual Fixed
Rent so determined shall be and become the Annual Fixed Rent hereunder in effect
beginning with the first day of the Extension Term.

          3.2.2 Adjustment to Annual Fixed Rent Based Upon Consumer Price Index.
Beginning on January 1, 1996 and at the commencement of every second calendar
year thereafter during the Term and the first Extension Term (specifically
excluding the second Extension Term) the Annual Fixed Rent provided for in
Section 1.1 applicable to the Second Floor of the Building shall be adjusted as
follows:

          The base for computing the-adjustment is the Consumer Price Index for
All Urban Consumers - All Items for the Boston metropolitan area, published by
the United States Department of Labor, Bureau of Labor Statistics ("Index"),
which is in effect on November 1, 1993 ("Beginning Index"). The Index published
most immediately preceding the Adjustment Date ("Extension Index") is to be used
in determining the amount of the adjustment. If the Extension Index has
increased over the Beginning Index, the Annual Fixed Rent for the Extension Term
shall be set as follows:

          (a) the Annual Fixed Rent set forth in Section 1.1 applicable to the
Second Floor of the Building shall be multiplied by the figure obtained by
dividing the Extension Index by the Beginning Index (the total of which shall be
the "CPI Rent"); and

          (b) the difference between the CPI Rent and the Annual Fixed Rent set
forth in Section 1.1 applicable to the Second Floor of the Building shall be
multiplied by seventy percent (70%), the product of which shall be added to
Annual Fixed Rent set forth in Section 1.1 applicable to the Second Floor of the
Building to determine Annual Fixed Rent and the total Annual Fixed Rent shall be
adjusted accordingly.

     In no event whatsoever shall the Annual Fixed Rent by way of a CPI
adjustment be less than the Annual Fixed Rent set forth in Section 1.1, as
adjusted pursuant to this Section 3.2.2. If the Index is discontinued or revised
during the Term, such other government index or computation with which it is
replaced shall be used in order to obtain substantially the same result as would
be obtained if the Index had not been discontinued or revised.

     3.3 Additional Rent. In order that the Annual Fixed Rent shall be
absolutely net to Landlord, Tenant covenants and agrees to pay either directly
or to Landlord, as additional rent, all real estate taxes, betterment
assessments, insurance costs, and charges for utilities and other services with
respect to the Building as hereinafter provided in this Lease. All amounts
payable by Tenant to Landlord under this Lease shall be deemed to be additional
rent and shall be paid within twenty (20) days after Tenant's receipt of
Landlord's statement itemizing such charges together with invoices therefor. In
the event Tenant. pays such real estate taxes betterment assessments insurance
costs and charges for utilities and other services with respect to the building.
directly to the authority charged with the collection thereof, Tenant shall
provide Landlord written evidence of the payment thereof within ten (10)
business days after receipt of Landlord's request for such evidence with respect
to all items other than real estate taxes and


                                        9
<PAGE>
municipal betterments, which Tenant shall provide to Landlord within ten (10)
days of the payment thereof.

     3.4 Real Estate Taxes.

          3.4.1 Building. Tenant shall pay, subject to Tenant's right to contest
any such tax in good faith, all taxes levied or assessed by or becoming payable
to any municipality or any other governmental authority having jurisdiction of
the Land and Building, for or in respect of the ownership, leasing or operation
of the Land and Building or which may become a lien on the Land and Building,
for each tax period wholly included in the Term, all such payments to be made at
least ten (10) days before the last date on which the same may be paid without
interest or penalty; provided that for any fraction of a tax period included in
the Term at the beginning (beginning on the Lease Commencement Date) or end
thereof, Tenant shall pay to Landlord, within twenty (20) days after receipt of
Landlord's invoice therefor, the fraction of taxes so levied or assessed or
becoming payable which is allocable to such included period. Nothing contained
in this Lease shall, however, require Tenant to pay any franchise, corporate,
estate, inheritance, succession, capital levy or transfer tax of Landlord, or
any net income, profits or revenue tax or charge upon the rent payable by Tenant
under this Lease.

          3.4.2 Parking Lot. Tenant shall pay to Landlord as additional rent,
Tenant's proportionate share of real estate taxes applicable to the Parking Lot.
For purposes of this. section, Tenant's proportionate share of taxes for the
Parking Lot shall equal the total number of parking spaces which Tenant is
leasing under the terms of this Lease and any Additional Parking Spaces licensed
by Tenant for the applicable period over the total number of parking spaces in
the Parking Lot. If the number of Additional. Parking Spaces licensed by Tenant
during a tax year fluctuates, the proportionate share shall be calculated on a
pro rata basis.

     3.5 Betterment Assessments.

          3.5.1 Premises. Tenant shall pay, 100% of each installment of any
public, special or municipal betterment assessment levied or assessed by or
becoming payable to any municipality or other governmental authority having
jurisdiction of the Land and Building, for or in respect of the ownership,
leasing or operation of the Land and Building or which may become a lien on the
Land and Building, for each installment period wholly included in the Term, all
such payments-to be made at least ten (10) days before the last date on which
the same may be made without interest or penalty; provided that for any fraction
of an installment period included in the Term at the beginning (beginning on the
Rent Commencement Date) or end thereof, Tenant shall pay to Landlord, within
twenty (20) days after receipt of Landlord's invoice therefor, the fraction of
such installment which is allocable to such included period. Landlord shall
elect to pay any such assessment in installments over the longest period
permitted by law.

          3.5.2 Parking Lot. Tenant shall pay to Landlord as additional rent,
Tenant's proportionate share of such installments of municipal betterment
assessments applicable to the Parking Lot for each installment period wholly
within the Term or with respect to periods at the beginning or end of the Term,
apportioned accordingly for the applicable installment period. For purposes of
this Section, Tenant's proportionate share of betterment assessments applicable
to the Parking Lot shall equal the total number of parking spaces which Tenant
is leasing under the


                                       10
<PAGE>
terms of this Lease and any Additional Parking Spaces licensed by Tenant for the
applicable period over the total number of parking spaces in the Parking Lot. If
the number of Additional Parking Spaces licensed by Tenant during an applicable
assessment period fluctuates, the proportionate share shall be calculated on a
pro rata basis. Landlord shall elect to pay any such installment over the
longest period permitted by law.

     3.6 Tax Fund Payments. If any holder of a first mortgage on the Land,
Building or Parking Lot requires Landlord to make tax fund payments to it,
Tenant shall, as additional rent, on the first day of each month of the Term,
make Tax Fund Payments to Landlord in lieu of making such payment directly as
provided under Section 3.4 above. "Tax Fund Payments" refer to such payments as
the holder of such first Mortgage shall reasonably determine to be sufficient to
provide in the aggregate a fund adequate to pay all taxes and assessments
referred to in Sections 3.4 and 3.5 when they become due and payable. If the
aggregate of said Tax Fund Payments is not adequate to pay all said taxes and
assessments, Tenant shall pay to Landlord the amount by which such aggregate is
less than the amount equal to all said taxes and assessments, such payment to be
made on or before the later of (a) twenty (20) days after receipt by Tenant of
written notice from Landlord of such amount, or (b) the 30th day prior to the
last day on which such taxes and assessments may be paid without interest or
penalty. If Tenant shall have made the foresaid payments, Landlord shall on or
before the last day on which the same may be paid without interest or penalty,
pay or cause to be paid to the proper authority charged with the collection
thereof all taxes and assessments referred to in said Sections 3.4 and 3.5 and
furnish Tenant, upon request, with reasonable evidence of such payment. Any
balance remaining after such payment by Landlord shall be accounted for to
Tenant annually. All payments made by Tenant pursuant to this Section 3.6 shall
to the extent thereof-relieve Tenant of its obligations under said sections 3.4
and 3.5.

     3.7 Insurance. Tenant shall obtain insurance for the Premises and the
Parking Lot as provided for by Section 6.2.

     3.8 Utilities and Services. Tenant shall pay directly to the proper
authorities charged with the collection thereof all charges for water, sewer,
gas, electricity, telephone and other utilities or services used or consumed on
the Premises during the Term.

     3.9 Additional Expenses. Tenant shall pay to Landlord as additional rent:

          (a) One half of all operating and maintenance expenses attributable to
the Common Areas including, without limitation, landscape, snowplowing and any
and all other costs and expenses attributable to the maintenance of said Common
Areas.

          (b) Tenant's proportionate share of operating and maintenance expenses
attributable to the Parking Lot. For purposes of this Section, Tenant's
proportionate share of maintenance expenses applicable to the Parking Lot shall
equal the total number of parking spaces which Tenant is leasing under the terms
of this Lease and any Additional Parking Spaces licensed by Tenant for the
applicable period over the total number of parking spaces in the Parking Lot. If
the number of Additional Parking Spaces licensed by Tenant during an applicable
operating year fluctuates, the proportionate share shall be calculated on a pro
rata basis.


                                       11
<PAGE>
     3.10 Late Charge. In the event that any payment of Annual Fixed Rent or
additional rent shall remain unpaid for a period of five (5) business days after
due, there shall become due to Landlord from Tenant, as additional rent and as
compensation for Landlord's extra administrative costs in investigating the
circumstances of late rent, a late charge of three percent (3%) of the amount
overdue. Payment of any late charge shall not constitute a cure of any default
with respect to the amount as to which such late charge is paid.

     3.11 Net Lease. It is understood and agreed that this Lease is a net lease
and that the Annual Fixed Rent is absolutely net to Landlord, excepting only
those matters which Landlord is required to pay under this Lease.

     3.12 No Offsets. All payments to be made by Tenant to Landlord in
accordance with the terms of this Lease, including, but not limited to, Annual
Fixed Rent and additional rent, shall be. paid by Tenant without offset,
abatement or deduction other than as expressly provided for in Section 3.1 above
and in Article VII below.

                                   ARTICLE IV

          MAINTENANCE AND REPAIR, ALTERATIONS; SURRENDER; HOLDING OVER

     4.1 Tenant's Maintenance and Repair. Except as otherwise, provided in
Section 4.2 or Article VII below, Tenant, at Tenant's expense, shall keep neat
and clean and maintain and repair in good order, condition and repair the
Premises and every part thereof (including, without limitation, maintenance of
the electrical, plumbing and HVAC systems and equipment serving the Premises and
the other fixtures and equipment therein and the cleaning of and trash removal
from the Premises), reasonable wear and tear excepted. Without limiting the
generality of the foregoing, Tenant, at Tenant's expense, shall provide or cause
to be provided landscape care to and maintenance of the portion of the Land not
included in the Common Areas and used exclusively by Tenant, and maintenance
(including snow plowing and removal of ice) of the walkways on the Premises not
included in the Common Areas and used exclusively by Tenant. Tenant hereby
covenants and agrees to remove all trash from the Premises in compliance with
all federal, state, and local laws, rules, ordinances and regulations. If
maintenance or repairs are required to be done or made by Tenant pursuant to the
terms hereof, Landlord may demand that Tenant do or make the same forthwith,
and, if Tenant refuses or neglects to commence such repairs and complete the
same with reasonable dispatch after such demand, Landlord may (but shall not be
required to do so) make or cause such repairs to be made and shall not be
responsible to Tenant for any loss or damage that may accrue to Tenant's
property or business by reason thereof, so long as Landlord makes or causes such
repairs to be made in a reasonable manner. If Landlord makes or causes such
repairs to be made, Tenant agrees that Tenant will forthwith on demand pay to
Landlord the cost thereof as additional rent pursuant to Section 8.4. Tenant
shall receive the benefit of all warranties and guaranties with respect to those
portions of the Premises that Tenant is obligated to maintain, as well as, at
Tenant's election and Tenant's expense, any options to extend or similar rights
with respect to the warranties and guaranties.

     4.2 Landlord's Maintenance and Repair. Except as otherwise provided in
Article VII below, Landlord, at Landlord's expense, shall keep, maintain and
repair in good order, condition and repair the structural-parts of the Building,
which structural parts include only the


                                       12
<PAGE>
foundations, bearing and exterior walls(excluding glass and doors), subflooring,
support columns, support beams and roof (excluding skylights), except for (i)
any damage caused to any of the foregoing by the negligence or neglect of
Tenant, its agents, contractors, employees or invitees or (ii) any maintenance
or repair required as a result of damage caused to any of the foregoing by any
alterations or other work performed by or on behalf of the Tenant. Except as set
forth in this Section 4.2 and in Article VII below, Tenant shall be responsible
for the cost of all replacements and repairs to the Premises, including any
maintenance or repair required as a result of damage caused to any structural
element or system of the Building by any alterations or other work performed by
or on behalf of the Tenant.

     4.3 Alterations. Tenant shall not make alterations and additions to the
Premises except in accordance with plans and specifications therefor first
approved by Landlord, which approval shall be requested in writing and shall not
be unreasonably withheld or delayed, provided, however, no such approval shall
be required for alterations or additions costing less than fifteen thousand
dollars ($15,000) individually or seventy-five thousand dollars ($75,000) in the
aggregate in any calendar year. Landlord shall not be deemed unreasonable for
withholding approval of any alterations or additions that (a) might adversely
affect any structural or exterior element of the Building, or any area or
element outside of the Premises, or (b) will require unusual expense to readapt
the Premises to normal office or laboratory use on expiration or earlier
termination of the Term, unless Tenant first provides assurances acceptable to
Landlord that such readaptation will be made prior to such expiration or
termination without expense to Landlord. All alterations and additions other
than Tenant's moveable equipment shall become part of the Building and shall
become the property of Landlord upon expiration or earlier termination of the
Term unless (i) Tenant shall remove the same prior to such expiration or earlier
termination and replace,-repair and restore any such alterations or additions,
or (ii) Landlord shall notify Tenant in writing that the same must be removed.
Such notice by Landlord shall be given no later than in response to Tenant's
written request for Landlord's approval of the alterations or additions prior to
their installation, and in such event Tenant shall remove such alterations or
additions and any damage caused by removal shall be repaired by Tenant at
Tenant's expense upon expiration or earlier termination of this Lease.

     4.4 Alterations Requirements. Landlord may (but shall not be obligated to)
inspect any construction work of Tenant under this Lease at reasonable times
after notice to Tenant (other than in the case of an emergency). Tenant, before
its work is started, shall secure all licenses and permits necessary therefor;
deliver to Landlord a statement of the names of all its contractors and
subcontractors; and shall cause each contractor to carry such workmen's
compensation insurance and comprehensive general public liability insurance as
Landlord may reasonably require insuring Landlord and Tenant as well as the
contractors, and to deliver to Landlord certificates of all such insurance.
Tenant agrees to pay promptly when due the entire cost of any work done on or
about the Premises by or on behalf of Tenant, its agents, employees or
independent contractors, not to cause or permit any liens for labor or materials
performed or furnished in connection therewith to attach to the Premises and
promptly to discharge or bond off in form and substance satisfactory to Landlord
in Landlord's sole and absolute discretion any such liens which may so attach.
Tenant shall hold Landlord harmless and indemnify Landlord from and against all
injury, loss, claims or damage to any person or property ("Claims") occasioned
by or growing out of any such work other than with respect to Claims arising
from the gross negligence or willful misconduct of Landlord, its agents,
contractors or employees.


                                       13
<PAGE>
     4.5 Entry by Landlord. Tenant shall permit Landlord and its agents, after
reasonable notice (except in the case of emergencies in which case no notice is
required), to enter the Premises (other than the Manufacturing Facility Clean
Room, as hereinafter defined, as provided in the immediately succeeding
sentence) at all reasonable hours for the purpose of inspecting, testing, or of
making repairs to the same, or otherwise carrying out Landlord's rights or
obligations under this Lease, and to show the Premises to prospective tenants
during the year preceding expiration of the Term and to prospective purchasers
and mortgagees at all reasonable times. In case of emergency, or if Landlord
reasonably suspects that there is any violation of law, rule, ordinance or
regulation in connection with the Manufacturing Facility Clean Room, as
hereinafter defined, or the use and/or operation thereof, Tenant shall permit
Landlord and its agents to enter the Manufacturing Facility Clean Room without
prior notice after taking reasonable precautions (if appropriate under the
circumstances) requested by. Tenant. In the event Landlord requires access to
the Manufacturing Facility Clean Room, as hereinafter defined, for the purpose
of making repairs which Landlord is required or permitted to make under the
terms and conditions of this Lease, Tenant shall permit Landlord and its agents,
after 72 hours advance written notice, to enter the Manufacturing Facility Clean
Room after taking all reasonable precautions which Tenant may require. The
phrase Manufacturing Facility Clean Room. shall mean the 25' x 40' class 1.00
clean room facility to be located on the second floor of the Premises. Landlord
shall not be liable to Tenant for any compensation or reduction of rent by
reason of inconvenience or annoyance or for loss of business arising from
Landlord or its agents entering the Premises (including the Manufacturing
Facility Clean Room) for any purposes authorized in this Lease. Notwithstanding
Landlord's right to enter the Premises or other rights reserved by Landlord
pursuant to any other provision of this Lease, Landlord hereby covenants and
agrees in the exercise of any such rights not to disclose, photograph or
otherwise reveal to any party information related to Tenant's business operation
at the Premises, including in particular Tenant's manufacturing processes,
provided, however, that Landlord may disclose any such information to its
counsel and as directed by a court of competent jurisdiction or by subpoena.

     4.6 Surrender. Tenant shall surrender the Premises, and all alterations and
additions thereto as hereinabove provided, at the expiration or earlier
termination of the Term, in the condition described in Section 4.1, first
removing all personal property and trade fixtures of Tenant and, to the extent
specified by Landlord by notice to Tenant as hereinabove provided or as
otherwise agreed by Landlord and Tenant, alterations and additions made by
Tenant, and repairing any damage caused by such removal and restoring the
Premises and leaving them clean and neat. Tenant waives all claims against
Landlord for any damage to Tenant resulting from Landlord's retention or
disposition of any of Tenant's personal property or trade fixtures remaining on
the Premises on expiration or earlier termination of the Term. Tenant shall be
liable to Landlord for Landlord's costs for storing, removing, and disposing of
any alterations or additions that Tenant is obligated to remove but fails to
remove or Tenant's personal property or trade fixtures. If Tenant fails to
surrender the Premises to Landlord on expiration or earlier termination of the
Term in the condition and otherwise as required by this Section, Tenant shall
hold Landlord harmless from all damages resulting from Tenant's failure to
surrender the Premises, including, without limitation, claims made by succeeding
tenants resulting from Tenant's failure to surrender the Premises.


                                       14
<PAGE>
     4.7 Holding Over. If Tenant, without Landlord's consent remains in
possession of the Premises after expiration or earlier termination of Term, such
possession by Tenant shall be deemed to be a month-to-month tenancy terminable
on thirty days' notice given at any time by either party. During any such
month-to-month tenancy, Tenant shall pay all rent and other sums required by
this Lease, and all provisions of this Lease, except those pertaining to Term,
option to extend and rights of refusal shall apply to the month-to-month
tenancy, and the monthly base rent (excluding additional rent) shall be
$40,000.00 for the Second Floor of the Building and shall be one hundred fifty
percent (150%) of the Annual Fixed Rent applicable to the First Floor and Lower
Level of the Building then in effect at the expiration or earlier termination of
the Term. This provision shall not be construed as a consent by Landlord to any
such holding over.

                                    ARTICLE V

                           ADDITIONAL TENANT COVENANTS

     5.1 Payment-and Performance. Tenant agrees to pay when due all Annual Fixed
Rent and additional rent, all charges for utility and other services rendered to
the Premises, and all other monies required to be paid by Tenant pursuant to
this Lease and to promptly perform all obligations of Tenant pursuant to this
Lease. Annual Fixed Rent and additional rent payments required under this Lease
shall be deemed sufficiently paid if made by check collected on first
presentation.

     5.2 Use. Tenant agrees, from the Commencement Date to the end of the Term,
to use and occupy the Premises for general office, research and development,
laboratory and manufacturing or other purposes permitted by federal, state and
local laws and ordinances. Tenant agrees not to injure, overload or deface the
Premises, nor to permit on the Premises any auction sale. Tenant shall comply
with all requirements of public authorities and of the Board of Fire
Underwriters in connection with methods of storage, use and disposal. Tenant
shall not permit in the Premises any nuisance, or the emission from the Premises
of any objectionable noise, odor or vibration, nor use or devote the Premises or
any part thereof for any purpose which is contrary-to law or ordinance or liable
to invalidate or increase premiums for any insurance on the Building or its
contents or liable to render necessary any unpermitted alteration or addition to
the Building, nor commit or. permit any waste in or with respect to the
Premises, nor generate, store or dispose of any oil, toxic substances, hazardous
wastes, or hazardous materials (each a "Hazardous Material"), or permit the same
in or on the Premises provided for under this Lease, except in compliance
with-applicable law. Tenant shall not dump, flush or in any way introduce any
Hazardous Material into septic, sewage or other waste disposal systems serving
the Premises provided for under this Lease. Tenant shall permit Landlord to
enter the Premises for the purpose of testing and to determine Tenant's
compliance with the covenants herein contained, each such entry shall be made in
accordance with Section 4.5 above. Tenant will indemnify the Landlord and its
successors and assigns against all claims, loss, cost, and expenses, including,
without limitation, attorneys' fees, incurred as a result of any contamination
of the Building or any portion of the Land with Hazardous Materials by the
Tenant or Tenant's contractors, licensees, invitees, agents, servants or
employees, and this indemnity shall survive the expiration of the Term or any
other termination of this Lease.


                                       15
<PAGE>
     5.3 Compliance with Law. Tenant agrees to comply with all federal, state
and local laws, regulations, ordinances, executive orders and similar
requirements applicable to the Premises or the Parking Lot or Tenant's use
thereof in effect from time to time during the Term, including, without
limitation, City of Cambridge ordinances with respect to zoning, smoking, animal
experiments and hazardous waste and any such requirements pertaining to
employment opportunity, anti-discrimination and affirmative action. Tenant
agrees, at its sole cost, to comply with the aforesaid laws regulations and
ordinances, and to keep the Premises equipped with all safety appliances
required by law or ordinance or any other regulations of any public authority,
and to procure all licenses and permits required for the Premises or Tenant's
use thereof, it being understood that the foregoing provisions shall not be
construed to broaden in any way the Permitted Uses.

     5.4 Personal Property Taxes. Tenant agrees to pay promptly when due all
taxes which may be imposed upon personal property (including, without
limitation, fixtures and equipment) on the Premises.

     5.5 Assignment and Subletting. Any assignment, mortgage, pledge,
hypothecation or transfer of all or any portion of Tenant's interest under this
Lease or any subletting of all or any portion of the Premises shall be subject
to the provisions of this Section.

          (a) Except in the cases of Permitted Transfers (as defined below)
Tenant agrees not to assign, mortgage, pledge, hypothecate or otherwise transfer
this Lease, or sublet (which term, without limitation, shall include granting of
concessions, licenses and the like) the whole or any part of the Premises
without, in each instance, having first received the consent of Landlord, which
shall not be unreasonably withheld or delayed. Any assignment or sublease made
without such consent shall be void, and in any case where Landlord consents to
such assignment or subletting or such assignment is permitted by this Lease,
Tenant shall remain fully and primarily liable for the obligations of the tenant
hereunder, including, without limitation, the obligation to pay Annual Fixed
Rent and additional rent as provided under this Lease. Except as otherwise
permitted by Permitted Transfers, any transfer of control of Tenant by means of
one or more transfers of stock or partnership interests shall be deemed an
assignment for purposes of this Section.

          (b) In the event that any sublease or assignment of the Second Floor
is permitted under this Lease (other than with respect to Permitted Transfers
and the sublease described in subsection (e) below), Tenant shall pay to
Landlord as additional rent one half of the amount Tenant receives from any
subtenant or assignee as rent, additional rent or other form of compensation or
reimbursement in excess of (i) the Annual Fixed Rent applicable to the space so
sublet or assigned, additional rent and other monies otherwise due to Landlord
pursuant to this Lease (allocable in the case of a sublease to that portion of
the Premises being subleased), and (ii) any reasonable expenses incurred and
paid by Tenant in connection with such sublease or assignment such as brokerage
commissions, fees for legal services and expenses of preparing the Premises for
occupancy by such subtenant or assignee and specifically including Tenant's
recovery of the unamortized value of the improvements to the second floor made
by Tenant based on a ten-year useful life utilizing the so-called "straight
line" method of cost recovery.


                                       16
<PAGE>
          (c) If this Lease is assigned, or if the Premises or any part thereof
is sublet or occupied by anyone other than Tenant (other than as a result of a
Permitted Transfer), Landlord may, at any time and from time to time, collect
rent and other charges from the assignee, sublessee or occupant and apply the
net amount collected to the rent and other charges herein reserved, but no such
assignment, subletting, occupancy or collection shall be deemed a waiver of the
prohibitions contained in this Section 5.5, or the acceptance of the assignee,
sublessee or occupant as a tenant, or a release of Tenant from the further
performance by Tenant of the covenants herein contained to be performed by
Tenant. The consent by Landlord to one assignment or subletting shall not be
construed to relieve Tenant from obtaining the express consent in writing of
Landlord to any further assignment or subletting.

          (d) Notwithstanding any provision of this Section 5.5 to the contrary,
in the event that (i) all of the Premises is to be sublet, or (ii) all of the
Second Floor of the Building is to be sublet, Landlord may elect to terminate
this Lease with respect to either the entire Premises or the entire Second Floor
of the Building being sublet, as the case may be, by giving Tenant 30 days'
prior written notice.

          (e) As used in this Lease, the term "Permitted Transfers" shall mean
any of the following transactions:

               (i) any transaction pursuant to which Tenant is merged or
consolidated with any other entity or pursuant to which all or substantially all
of Tenant's assets, including without limitation, Tenant's interest under the
Lease (the "Tenant Interest") are sold or transferred, provided in each case
that the resulting entity assumes all of Tenant's obligations and agrees to be
bound by all of the terms and conditions of this Lease and provided further that
the Landlord is reasonably satisfied with the financial status of each such
entity; or

               (ii) the sublease or assignment of the Tenant Interest to any
entity which controls, is controlled by or is under common control with Tenant,
provided in each case that the resulting entity assumes all of Tenant's
obligations and agrees to be bound by all of the terms and conditions of this
Lease and provided further that the Landlord is reasonably satisfied with the
financial status of each such entity; or

               (iii) a collateral assignment of this Lease by Tenant to an
institutional lender; provided, that in such collateral assignment said Lender
agrees that upon exercise of its rights thereunder it shall assume and be bound
by all the terms and conditions of this Lease.

                                   ARTICLE VI

                       ARTICLE VI INDEMNITY AND INSURANCE

     6.1 Indemnity. To the maximum extent this agreement may be made effective
according to law, Tenant agrees to defend with counsel, save harmless, and
indemnify Landlord and any manager of the Premises, from time to time, from any
liability or injury, loss, accident or damage to any person or property, and
from any claims, actions, proceedings and expenses and costs in connection
therewith (including without limitation reasonable attorneys' fees and costs),
(i) caused by Tenant, its contractors, agents, employees or invitees, or arising
or claimed to arise


                                       17
<PAGE>
from any use made or thing done or occurring on the Premises during the Term, or
the Extension Term, or during Tenant's possession of any part of the Premises
not due to the willful act, active negligence or other misconduct of Landlord or
any manager or (ii) caused by Tenant, its contractors, agents, employees or
invitees, and arising or claimed to arise from any use made or thing done or
occurring on the Parking Lot during the Term or the Extension Term, or during
Tenant's possession of any part of the Premises or Parking Lot not due to the
willful act, active negligence or other misconduct of Landlord or any manager or
the negligence of any co-tenant of the Parking Lot and their respective
contractors, agents and employees or (iii) resulting from the failure of Tenant
to perform and discharge its covenants and obligations under this Lease,
including, without limitation, the violation of any environmental law or other
governmental requirement by Tenant. This indemnity and hold harmless agreement
shall include indemnity against all costs, expenses and liabilities incurred in
connection with any such claim or proceeding brought thereon for which Tenant is
responsible, and the defense thereof, and shall survive expiration or
termination of the Term for a period of five (5) years. Landlord acknowledges
that as between Landlord and Tenant, Landlord shall be responsible for the two
underground oil storage tanks (the "Tanks") located in the. Courtyard of the
Building. Landlord agrees, to defend with counsel, save harmless and indemnify
Tenant from any liability or injury, loss, accident or damage to any person or
property from any claims, actions, proceedings and expenses and costs in
connection therewith (including, without limitation attorneys' fees and costs)
caused by any leaks in the Tanks or removal of the Tanks.

     6.2 Tenant's Insurance. Tenant shall, as additional rent, take out and
maintain in full force from the date upon which Tenant or its contractors or
agents first enter the Premises for any reason and continuing throughout the
Term and the Extension Term, if so exercised, unless earlier terminated, and
thereafter so long as Tenant is in occupancy of any part of the Premises, the
following insurance protecting Landlord:

          (a) "All Risk" insurance on the Building, expressly including rental
interruption coverage in amounts sufficient to prevent Landlord or Tenant from
becoming a co-insurer of any loss, but in any event, in amounts not less than
the actual replacement value determined from time to time of the improvements on
the Premises exclusive of foundations, site preparation and other non-recurring
construction costs all as more particularly described in Exhibit D attached
hereto.

          (b) A policy of comprehensive public liability and property damage
insurance with broad form comprehensive general liability endorsement attached
under which Landlord and Tenant (and, at Landlord's request, any mortgagee of
the Premises and any manager of the Parking Lot) are named as insureds, and
under which the insurer provides a contractual liability endorsement insuring
against all cost, expense and liability arising out of or based upon any and all
claims, accidents, injuries and damages described in Section 6.1, in the
broadest form of such coverage from time to time available. Each such policy
shall be non-cancelable and non-amendable (to the extent that any proposed
amendment reduces the limits or the scope of the insurance required in this
Lease) with respect to Landlord without thirty (30) days' prior written notice
to Landlord, and a duplicate certificate thereof shall be delivered to Landlord.
As of the Commencement Date hereof, the minimum limits of liability of such
insurance for each year shall be as set forth in Section 1.1, and from time to
time during the Term for such higher limits as may be designated by Landlord, if
any, as are carried customarily in the Boston area with


                                       18
<PAGE>
respect to similar properties. Tenant shall deliver a certificate evidencing
such coverage to Landlord, and at Landlord's request any mortgagee of the
premises or any manager of the Parking Lot, which certificate shall state that
the coverage may not be amended or cancelled without at least thirty (30) days'
prior written notice to Landlord, any mortgagee, or any manager of the Parking
Lot, as the case may be.

          (c) At any time when Tenant is performing construction work in or on
the Premises, Tenant shall carry builder's risk insurance reasonably
satisfactory to Landlord. Tenant shall provide Landlord and at Landlord's
request any mortgagee, with a certificate evidencing such coverage, which shall
state that the coverage cannot be canceled or amended without thirty (30) days'
prior written notice to Landlord and any mortgagee.

          (d) Tenant shall maintain on all its personal property, tenant
improvements, and alterations, in, on, or about the Premises, a policy of
physical hazard insurance on an "all risks" basis covering the perils of fire
and extended coverage, with vandalism and malicious mischief endorsements, to
the extent of their full replacement cost. In the event of casualty causing
damage to the Premises, the proceeds from any such policy shall be used by
Tenant for the replacement of personal property or the restoration of tenant
improvements or alterations, unless this Lease is terminated as a result of the
casualty as hereinafter provided Tenant shall deliver a certificate evidencing
such coverage to Landlord and at Landlord's request any mortgagee, which shall
state that the coverage may not be amended or canceled without at least thirty
(30) days' prior written notice to Landlord and any mortgagee.

          (e) All insurance required to be maintained by Tenant shall be
effected by valid and enforceable policies insured by insurers of recognized
responsibility qualified to do business in The Commonwealth of Massachusetts,
and reasonably satisfactory to Landlord and any mortgagee. Upon the Lease
Commencement Date and thereafter, not less than thirty (30) days prior to the
expiration dates of the existing policies theretofore furnished pursuant to this
paragraph, certificates of insurance shall be delivered by Tenant to Landlord
and at Landlord's request any mortgagee. All such policies shall provide at
least thirty (30) days written notice to Landlord and any mortgagee prior to any
termination thereof.

          (f) All policies of insurance required to be maintained by Tenant
shall name Tenant and Landlord as the insured as their respective interests may
appear. If Landlord so requires', the proceeds of insurance covering damage to
the Building (excluding Tenant's trade fixtures and equipment) shall be payable
to the holder of any mortgage as the interests of such holder may appear
pursuant to the standard mortgagee clause. All such policies shall provide that
any loss shall be payable to Landlord or to the holder of any mortgage
notwithstanding any act or negligence of Tenant which might otherwise result in
forfeiture of such insurance. All such policies shall contain an agreement by
the insurers that such policies shall not be cancelled without at least thirty
(30) days prior written notice to the Landlord and to the holder. of any
mortgage to whom loss hereunder may be payable.

          (g) Landlord may from time to time request Tenant to obtain additional
or alternative insurance. So long as said coverage is reasonable and customary
Tenant shall obtain such insurance.


                                       19
<PAGE>
In the event Tenant breaches any covenant or condition set forth in this Section
6.2, then without limiting any other right or remedy and not withstanding any
other provision herein concerning notice or cure of defaults, Landlord may,
after ten (10) days written notice to Tenant, obtain such insurance as Tenant is
required to obtain and maintain, and Tenant shall pay the cost thereof and
Landlord's reasonable expenses thereto to Landlord as additional rent.

     6.3 Tenant's Risk. Tenant agrees that all of the furnishings, fixtures,
equipment, effects and property of every kind, nature and description of Tenant
and of all persons claiming by, through or under Tenant which, during the
continuance of this Lease or any occupancy of the Premises by Tenant or anyone
claiming under Tenant, may be on the Premises or the Parking Lot, shall be at
the sole risk and hazard of Tenant, and if the whole or any part thereof shall
be destroyed or damaged by fire, water or otherwise, or by the leakage or
bursting of pipes or by theft or from any other cause, no part of said loss or
damage is to be charged to or be borne by Landlord, except that Landlord shall
in no event be exonerated from any liability to Tenant or to any person, for any
injury, loss, damage or liability to the extent such exoneration is prohibited
by law.

     6.4 Subrogation. Any insurance carried by either party with respect to the
Premises, or any property therein or occurrences thereon, shall, without further
request by either party, if it can be so written without additional premium, or
with an additional premium which the other party elects to pay, include a clause
or endorsement denying to the insurer rights of subrogation. against the other
party to the extent rights have been waived by the insured prior to occurrence
of injury or loss. Each party, notwithstanding any provisions of this Lease to
the contrary, hereby waives any rights of recovery against the other for injury
or loss, including, without limitation, injury or loss caused by negligence of
such other party, due to hazards covered by insurance containing such clause or
endorsement to the extent of the indemnification received thereunder.

                                   ARTICLE VII

                           CASUALTY AND EMINENT DOMAIN

     7.1 Casualty During Term. If, during the Term, the Building shall be
damaged as a result of casualty, the following provisions shall apply.

          (a) The term "Substantially Damaged," as used in this Article VII,
shall refer to damage of such a character that the same cannot, in ordinary
course, reasonably be expected to be repaired within 180 days from the time that
repair work would commence or which would cost in excess of seventy-five
thousand dollars ($75,000) to repair.

          (b) If the Building shall be damaged, Tenant shall, subject to the
matters described in subparagraph (c) below and except as otherwise provided in
this Article VII, proceed promptly to restore the Building (consistent, however,
with governmental laws and codes then in existence) to substantially the
condition thereof at the time of such damage, but Tenant shall not be
responsible for delay in such restoration which may result from External Causes,
as hereinafter defined. For purposes of this Lease, External Causes shall mean
(i) Acts of God, war, civil commotion, fire, flood or other casualty, strikes or
other extraordinary and unforeseeable labor difficulties, extraordinary and
unforeseeable shortages of labor or materials


                                       20
<PAGE>
or equipment, government order or regulations or other cause not reasonably
within Tenant's control and not due to the fault or neglect of Tenant, and (ii)
any act, failure to act or neglect of Landlord or Landlord's servants, agents,
employees, licensees or any person claiming by, through or under Landlord, which
actually delays Tenant in the performance of any act required to be performed by
Tenant under this Lease.

          (c) Tenant's restoration obligations described in subparagraph (b)
above are conditioned upon Tenant receiving sufficient proceeds from insurance
covering the Building to .repair the same (less any applicable deductible for
which Tenant shall be solely responsible) unless (i) insurance proceeds are
unavailable as a result of Tenant's failure to insure the Building as required
by the terms and conditions of this Lease or (ii) insurance proceeds are
unavailable as a result of Tenant's acts or omissions, in which cases Tenant
shall be obligated to either (x) restore the Building in accordance with the
terms and conditions hereof or (y) pay to or for the account of the Landlord the
full amount of insurance which would have been payable under the last policies
of insurance approved by Landlord. If the Building is not restored or is unable
to be restored, any insurance proceeds which are not on account of Tenant's
removable personal property shall be paid to or for the account of Landlord.

          (d) If the Building shall be Substantially Damaged within the last
twelve (12) months of the Term (as the same may have been extended hereunder),
either party shall have the right, by giving notice to the other not later than.
90 days after such damage, to terminate this Lease, whereupon this Lease shall
terminate as of the date of such notice.

     7.2 Condemnation. Except as hereinafter provided, if the Premises, or such
portion thereof as to render the balance (if reconstructed to the maximum
extent-practicable in the circumstances) unsuitable for Tenant's purposes, shall
be taken by eminent domain, Landlord and Tenant each shall have the right to
terminate this Lease by notice to the other of its desire to do so, provided
that such notice is given not later than thirty (30) days after the effective
date of such taking. Should any part of the Premises be so taken, and should
this Lease be not terminated in accordance with the foregoing provisions,
Landlord agrees to use due diligence to put what may remain of the Premises
(consistent, however, with governmental laws and codes then in existence) into
proper condition for use and occupation as nearly like the condition of the
Premises prior to such taking as shall be practicable, but Landlord shall not be
required to expend funds in excess of the damages recovered by Landlord as a
result of such taking.

     7.3 Abatement of Rent. If the Premises shall-be damaged by casualty, the
Annual Fixed Rent and additional rent shall be justly and equitably abated and
reduced according to the nature and extent of the loss of use thereof suffered
by Tenant; and in case of a taking which permanently reduces the area of the
Premises, a just proportion of the Annual Fixed Rent and additional rent shall
be so abated and reduced for the remainder of the Term.

     7.4 Condemnation Award. Landlord shall have and hereby reserves and
excepts, and Tenant hereby grants and assigns to Landlord, all rights to recover
for damages to the Premises, and the leasehold interest hereby created, and all
rights to compensation accrued or hereafter to accrue by reason of such taking,
damage or destruction, as aforesaid, and by way of confirming the foregoing,
Tenant hereby grants and assigns to Landlord all rights to such damages or
compensation. Nothing contained herein shall be construed to prevent Tenant from
prosecuting


                                       21
<PAGE>
in any condemnation proceedings a claim for relocation expenses, provided that
such action shall not affect the amount of compensation otherwise recoverable by
Landlord from the taking authority pursuant to the preceding sentence.

                                  ARTICLE VIII

                                     DEFAULT

     8.1 Tenant's Default. In the event that:

          (a) Tenant shall fail to pay the Annual Fixed Rent, additional rent or
any other charges for which provision is made herein on or before the date on
which the same become due and payable, and such condition continues for five (5)
days after notice from Landlord to Tenant that the same are due, unless the
failure to pay the foregoing items when due occurs in any year during which
Landlord has previously given Tenant notice of default twice, in which event the
failure to pay when due shall constitute an event of default without notice; or

          (b) Tenant shall fail to perform or observe any other term or
condition contained in this Lease and Tenant shall not cure such failure within
thirty (30) days after notice from Landlord to Tenant thereof or, if such
failure cannot be cured within such thirty (30) days, if Tenant shall fail to
commence to cure such failure within such thirty (30) days and promptly and
diligently complete the curing of the same, and shall in any event complete the
cure within ninety (90) days; or

          (c) The estate hereby created shall be taken on execution or by other
process of law, or if Tenant shall be judicially declared bankrupt or insolvent
according to law, or if any assignment or trust mortgage arrangement, so-called,
shall be made of the property of Tenant for the benefit of creditors, or if a
receiver, guardian, conservator, trustee in bankruptcy or other similar officer
shall be appointed to take charge of all or any substantial part of Tenant's
property by a court of competent jurisdiction, or if a petition shall be filed
by Tenant under any provisions of the federal Bankruptcy Code or any similar
federal or state law now or hereafter enacted or if a petition shall be filed
against Tenant thereunder and the same is not dismissed within ninety (90) days,
or if Tenant shall file such a petition, then, in any such case, Landlord and
the agents and servants of Landlord lawfully may, in addition to and not in
derogation of any remedies for any preceding breach of covenant, immediately or
at any time thereafter and without demand or notice and with or without due
process of. law, (forcibly if necessary) enter into and upon the Premises or any
part thereof by any lawful means or mail a notice of termination addressed to
Tenant at the Premises, and repossess the same as of Landlord's former estate,
and expel Tenant and those claiming by, through or under Tenant and remove its
and their effects by any lawful means (forcibly if necessary) without being
deemed guilty of any manner of trespass and without prejudice to any remedies
that might otherwise be used for arrears of rent (or prior breach of covenant),
and upon such entry or mailing as aforesaid this Lease shall terminate, as fully
and completely as if such date were the date herein originally fixed for the
expiration of the Term (Tenant hereby waiving any rights of redemption), and
Tenant will then quit and surrender the Premises to Landlord, but Tenant shall
remain liable as hereinafter provided.


                                       22
<PAGE>
     8.2 Damages. In the event that this Lease is terminated under any of the
provisions contained in Section 8.1 or shall be otherwise terminated for breach
of any obligation of Tenant, Tenant covenants to pay to Landlord forthwith on
Landlord's demand, as compensation, in addition to any other amounts to which
Landlord may be entitled, an amount equal to the excess, if any, of the
discounted present value of the total rent reserved for the residue of the Term
or the Extension Term if so exercised, over the then discounted present fair
rental value of the Premises for the residue of the Term. In calculating the
rent reserved, there shall be included, in addition to the Annual Fixed Rent and
all additional rent, the value of all other considerations agreed to be paid or
performed by Tenant for said residue. Tenant further covenants as an additional
and cumulative obligation after any such termination to pay punctually to
Landlord all the sums and perform. all the obligations which Tenant covenants in
this Lease to pay and to perform in the same manner and to the same extent and
at the same time as if this Lease had not been terminated. In calculating the
amounts to be paid by Tenant under the next foregoing covenant, Tenant shall be
credited with (a) any amount received from Tenant under the first sentence of
this Section 8.2; and (b) the net proceeds of any rent obtained by reletting the
Premises, after deducting all Landlord's expenses in connection with such
reletting, including, without limitation, all repossession costs, brokerage
commissions, fees for legal services and expenses of preparing the Premises for
such reletting, it being agreed that Landlord may (i) relet the Premises, or any
part or parts thereof, for a term or terms which may, at Landlord's option, be
equal to or less than or exceed the period which would otherwise have
constituted the balance of the Term, and may grant such concessions and free
rent as Landlord in its reasonable commercial judgment considers advisable or
necessary to relet the same and (ii) make such alterations, repairs and
decorations in the Premises as Landlord in its reasonable commercial judgment
considers advisable or necessary to relet the same, and no action of Landlord in
accordance with the foregoing or failure to relet or to collect rent under
reletting shall operate or be construed to release or. reduce Tenant's liability
as aforesaid Landlord agrees to use reasonable efforts to attempt to relet the
Premises, but shall be entitled to seek to rent other properties of Landlord
prior to reletting the Premises.

     8.3 Remedies Cumulative. The specific remedies to which Landlord may resort
under the terms of this Lease are cumulative and are not intended to be
exclusive of each other or of any other remedies or means of redress to which
Landlord maybe lawfully entitled in case of any breach or threatened breach by
Tenant of any provisions of this Lease. In addition to the other remedies
provided in this Lease, Landlord shall be entitled to the restraint by
injunction of the violation or attempted or threatened violation of any of the
covenants, conditions or provisions of this Lease or to a decree compelling
specific performance of any such covenants, conditions or provisions in the
event a legal remedy will be insufficient. Nothing contained in this Lease shall
limit or prejudice the right of Landlord to prove for and obtain in proceedings
for bankruptcy, insolvency or like proceedings, by reason of the termination of
this Lease, an amount equal to the maximum allowed by any statute or rule of law
in effect at the time when, and governing the proceedings in which, the damages
are to be proved, whether or not the amount be greater, equal to, or less than
the amount of the loss or damages referred to above.

     8.4 Landlord's Election. If Tenant shall at any time default in the
performance of any obligation under this Lease, Landlord shall have the right,
but not the obligation, upon fifteen (15) days' notice to Tenant (except in case
of emergency in which case no notice need be given), to perform such obligation,
notwithstanding the fact that no specific provision for such


                                       23
<PAGE>
substituted performance is made in this Lease with. respect to such default. In
performing such obligation, Landlord may (but shall not be required to) make any
payment of money or perform any other act, and all sums so paid by Landlord and
all necessary incidental costs and expenses thereof, including, without
limitation, reasonable legal fees in connection with enforcement of its rights
under this Section incurred by Landlord, together with interest on all such
amounts at two percent (2%) above the First National Bank of Boston's large
business prime rate from time to time in effect, shall be deemed to be
additional rent under this Lease and shall be payable to Landlord immediately on
demand. Landlord may exercise its rights under this Section without waiving any
other of its rights or releasing Tenant from any of its obligations under this
Lease.

     8.5 Effect of Waivers of Default. Any consent or permission by Landlord to
any act or omission which otherwise would be a breach of any covenant or
condition herein, or any waiver by Landlord of the breach of any covenant or
condition herein, shall not in any way be held or construed (unless expressly so
declared) to operate so as to impair the continuing obligation of any covenant
or condition herein, or otherwise, except as to the specific instance, or to
operate to permit similar acts of omission.

     8.6 No Waiver. No waiver by Landlord shall be valid unless in writing and
signed by Landlord, and the failure of Landlord to seek redress for violation
of, or to insist upon the strict performance of, any covenant or condition of
this Lease shall not be deemed a waiver of such violation nor prevent a
subsequent act, which would have originally constituted a violation, from having
all the force and effect of an original violation. The receipt by Landlord of
rent with knowledge of the breach of any covenant of this Lease shall not be
deemed to have been waiver of such breach by Landlord unless such waiver be in
writing signed by the party to be charged. No consent or waiver, express or
implied, by Landlord to or of any breach of any agreement or duty shall be
construed as a waiver or consent to or of any other breach of the same or any
other agreement or duty.

     8.7 No Accord and Satisfaction. No acceptance by Landlord of a lesser sum
than the Annual Rent, additional rent or any other charge then due shall be
deemed to be other than on account of the earliest installment of such rent or
charge due, nor shall any endorsement or statement on any check or any letter
accompanying any check or payment as rent or other charge be deemed an accord
and satisfaction, and Landlord may accept such check or payment without
prejudice to Landlord's right to recover the balance of such installment or
pursue any other remedy in this Lease provided.

     8.8 Delivery of Keys. The delivery of keys to any employee of Landlord or
to Landlord's agent or any employee thereof shall not operate as a termination
of this Lease or a surrender of the Premises.

     8.9 Attorneys' Fees. Tenant agrees, as additional rent, to pay all
reasonable costs, counsel and other fees incurred by Landlord in connection with
the successful enforcement by Landlord of any obligations of Tenant under this
Lease.

                                   ARTICLE IX

                     MORTGAGEES' AND GROUND LESSORS' RIGHTS


                                       24
<PAGE>
     9.1 Superiority of Lease. Except as provided in Section 9.2 below, this
Lease shall be superior to and shall not be subordinated to any future mortgage,
lien or other encumbrance on the Premises. Upon entry and taking possession of
the Premises for the purpose of foreclosure the holder thereof shall have all
the rights of Landlord. No such holder shall be liable, either as mortgagee or
as assignee, to perform, or be liable in damages for failure to perform, any of
the obligations of Landlord unless and until such holder shall enter and take
possession of the Premises for the purpose of foreclosure. Upon entry for the
purpose of foreclosure, such holder shall be liable to perform all of the
obligations of Landlord accruing from and after such entry, but not before,
provided that a discontinuance of any foreclosure proceeding shall operate as a
transfer of all such liability to the owner of the equity of the Premises.

     9.2 Subordination. Tenant shall, at the request of Landlord, subordinate
this Lease and all rights and options granted hereunder to any mortgage, lien or
other encumbrance now or hereafter on the Premises, so that the lien thereof
shall be superior to all rights hereby or hereafter vested in Tenant, provided
that the holder thereof enters into an agreement with Tenant by the terms of
which the holder will agree to recognize the rights of Tenant under this Lease
and to accept Tenant as tenant of the Premises under the terms and conditions of
this Lease in the event of acquisition of title by such holder through
foreclosure proceedings or otherwise and Tenant will agree to recognize such
holder as Landlord in such event, which agreement shall be made to expressly
bind and inure to the benefit of the successors and assigns of Tenant and of the
holder and upon anyone purchasing said Premises at any foreclosure sale and upon
the further condition that any such mortgagee agrees in its recognition
agreement to make insurance proceeds available to Tenant provided that Tenant
shall be obligated to use such proceeds solely to repair and restore the
Building and provided further that Tenant agrees to commence repair and
restoration as soon as practical after the event of casualty and to diligently
pursue said repair and restoration until completion.

     9.3 Limitation on Tenant's Rights. Notwithstanding Sections 9.1 or 9.2
above, unless the holder of such a mortgage, lien or other encumbrance of the
Premises otherwise agrees in writing, no such holder shall be obligated to
recognize or accept any of Tenant's rights under Section 2.4 of this Lease.
Further, any such holder whose mortgage, or other encumbrance is superior to
this Lease pursuant to the terms of Section 9.1 may elect to subordinate only
those rights of Tenant under this Lease to purchase all or any portion of the
Premises, including, without limitation, the rights of Tenant under Sections 2.4
of this Lease, to such mortgage, or other encumbrance.

     9.4 Exercise of Mortgagee's Remedies. Notwithstanding any other provision
of this Lease, in no event shall Tenant's rights under Section 2.4 apply to any
exercise of remedies by any mortgagee, or holder of a similar interest in the
Premises, including, without limitation, any foreclosure sale or any conveyance
by deed in lieu of foreclosure.

     9.5 Further Assurances. Tenant agrees, upon Landlord's request, promptly
(but in any event within fifteen (15) days after Landlord's request) to execute
and deliver such documents and instruments as Landlord may reasonably request to
carry out the agreements contained in this Article IX.


                                       25
<PAGE>
     9.6 No Prepaid Rent. No Annual Fixed Rent, additional rent, or any other
charge payable to Landlord shall be paid more than thirty (30) days prior to-the
due date thereof under the terms of this Lease, and payments made in violation
of this provision shall (except to the extent that such payments are actually
received by a mortgagee) be a nullity as against such mortgagee, and Tenant
shall be liable for the amount of such payments to such mortgagee.

                                    ARTICLE X

                                  MISCELLANEOUS

     10.1 Estoppel Certificates. Tenant shall, from time to time, within fifteen
(15) days after a written request by Landlord, execute, acknowledge and deliver
to Landlord a statement in writing certifying to Landlord or an independent
third party designated by Landlord that this Lease is unmodified and in full
force and effect (or, if there have been any modifications, that the same is in
full force and effect as modified and stating the modifications); that Tenant
has no knowledge of any defenses, offsets or counterclaims against its
obligations to pay the Annual Fixed Rent and additional rent and to perform its
other covenants under this Lease (or if there are any defenses, offsets, or
counterclaims, setting them forth in reasonable detail); that there are no known
uncured defaults of Landlord or Tenant under this Lease (or if there are known
uncured defaults, setting them forth in reasonable detail); the dates to which
the Annual Fixed Rent, additional rent and other charges payable hereunder have
been paid; and such other matters as Landlord may reasonably request. On the
Commencement Date, Tenant shall, at the request of Landlord, promptly execute,
acknowledge and deliver to Landlord a statement in writing that the Commencement
Date has occurred, stating the date that the Annual Fixed Rent will begin to
accrue, and that Tenant has taken occupancy of the Premises. Any such statement
delivered pursuant to this Section may be relied upon by any mortgagee or
purchaser of the Premises and shall be binding on Tenant.

     10.2 No Recordation. Tenant agrees not to record this Lease, but both
parties shall execute and deliver a memorandum of this Lease in form appropriate
for recording, an instrument in such form acknowledging the Commencement Date of
the Term, and if this Lease is terminated before the Term expires, an instrument
in such form acknowledging the date of termination.

     10.3 Notices. Whenever any notice, approval, consent, request, election,
offer or acceptance is given or made pursuant to this Lease, it shall be in
writing. Communications and payments shall be addressed, if to Landlord, at
Landlord's Original Address or at such other address as may have been specified
by prior notice to Tenant; and if to Tenant, at Tenant's Original Address or at
such other address as may have been specified by prior notice to Landlord. Any
communication so addressed shall be deemed duly served on the earlier of (i) the
date received, or (ii) the date of delivery, refusal or non-delivery indicated
on the return receipt, if deposited in a United States Postal Service
Depository, postage prepaid, sent by registered or certified mail, return
receipt requested or if sent by a recognized overnight delivery service
providing for a receipt. If Landlord by notice to Tenant at any time designates
some other person to receive payments or notices, all payments or notices
thereafter by Tenant shall be paid or given to the agent designated until notice
to the contrary is received by Tenant from Landlord.


                                       26
<PAGE>
     10.4 Successors and Assigns. Subject to Section 6.5 regarding Tenant's
right to assign and sublet, this Lease shall be binding upon and inure to the
benefit of the parties hereto and their respective successors and assigns,
except that the original Landlord named herein and each successive landlord
shall be liable only for obligations accruing during the period of its
ownership.

     10.5 Limitation of Liability. The obligations of Landlord shall be binding
upon the assets of Landlord consisting of an equity ownership interest in the
Land and Building, but not upon any other assets of Landlord, and neither
Tenant, nor anyone claiming by, under or through Tenant, shall be entitled to
obtain any judgment creating personal liability on the part of Landlord or
enforcing any obligations of Landlord against any assets of Landlord other than
an equity ownership in the Premises.

     10.6 Covenants and Conditions. All provisions, whether covenants or
conditions, on the part of Tenant to be performed under this Lease shall be
deemed to. be both covenants and conditions.

     10.7 Severability. If any term of this Lease, or the application thereof to
any person or circumstances, shall to any extent be invalid or unenforceable,
the remainder of this Lease, or the application of such term to persons or
circumstances other than those as to which it is invalid or unenforceable, shall
not be affected thereby, and each term of this Lease shall be valid and
enforceable to the fullest extent permitted by law.

     10.8 Quiet Enjoyment. So long as Tenant pays the Annual Fixed Rent and
additional rent and other charges provided for under this Lease, performs all
other covenants of this Lease to be performed by Tenant and observes all
conditions of this Lease to be observed by Tenant, Tenant shall peaceably and
quietly have, hold and enjoy the Premises for the Term in accordance with the
terms of this Lease against all those claiming by, under or through Landlord.

     10.9 Entire Agreement. This Lease contains all of the agreements of the
parties with respect to the subject matter hereof and supersedes all prior
dealings between them with respect to such subject matter, including, without
limitation, any letters of intent.

     10.10 Brokers. Tenant represents and warrants that it has had no dealings
with any broker or agent other than Joseph Flaherty of Meredith & Grew and
Robert Richards of Fallon, Hines & O'Connor (collectively, the "Brokers") in
connection with this Lease and shall indemnify and hold harmless Landlord from
any claims for any brokerage commission as a result of the failure of this
warranty. Landlord. represents and warrants that it has had no dealings with any
broker or agent other than the Brokers in connection with this Lease and shall
indemnify and hold harmless Tenant from any claims for any brokerage commission
as a result of the failure of this warranty. Tenant acknowledges that the fees
of Robert Richards of Fallon, Hines & O'Connor are its exclusive obligation and
agrees to indemnity and hold Landlord harmless from any claims for brokerage
commission from said broker. Landlord acknowledges that the fees of Joseph
Flaherty of Meredith & Grew are its exclusive obligation and agrees to indemnify
and hold Tenant harmless from any claims for a brokerage commission from said
broker.


                                       27
<PAGE>
     10.11 Applicable Law and Construction. This Lease shall be governed by and
construed in accordance with the laws of the Commonwealth of Massachusetts. This
Lease may be amended, and the provisions hereof may be waived or modified, only
by instruments in writing executed by Landlord and Tenant. The titles of the
several Articles and Sections contained herein are for convenience only and
shall not be considered in construing this Lease.

     10.12 Time of Essence. Time is of the essence of each provision of this
Lease.

     10.13 Authorization. If either party is a corporation, that party shall
deliver to the other party on execution of this Lease a certified copy of a
resolution of its Board of Directors authorizing the execution of this Lease and
naming the officers that are authorized to execute this Lease on behalf of the
corporation.

     10.14 Security Deposit. Landlord acknowledges receipt of a security deposit
in the amount of _________ as additional security for the full and faithful
performance of Tenant's obligations under this Lease, which security deposit was
tendered by Tenant in connection with its original Sublease of the second floor
on March 1, 1989. Landlord shall pay to Tenant, within ten (10) days after the
execution and delivery of this Lease by all of the parties hereto, interest
accrued on such security deposit in accordance with the terms of the sublease
described above. Such security deposit may be retained by Landlord during the
Term of the Lease and any extensions thereof and may (among Landlord's other
remedies allowed under this Lease and applicable law or equity) be applied by
Landlord toward payment of any damages which result in the event Tenant fails to
perform any of its obligations under this Lease. Provided Tenant is not in
default under the Lease, upon expiration of the Term or in the event the Term is
extended pursuant to Section 2.3 at the expiration of the Extended Term,
Landlord shall pay to Tenant an amount of interest on the security deposit
equivalent to the rate on the United States Treasury Note (as such rate is
reported in the Wall Street Journal) and invest in such Treasury Note in an
amount equal to the security deposit commencing five (5) business days after the
Commencement Date and maturing upon the expiration of the Term for the initial
term of this Lease (or, if no such rate is reported for such period or amount,
for the period an amount nearest thereto). Such rate shall be readjusted in the
event Tenant exercises its option to extend pursuant to Section 2.3.

                                        TENANT:

                                        Transkaryotic Therapies, Inc.


                                        By: /s/ K. Michael Forrest
                                            ------------------------------------
                                        Name: K. Michael Forrest
                                        Title: President and CEO


                                       28
<PAGE>
     EXECUTED as a sealed instrument on the day and year first above written.

                                        LANDLORD:


                                        /s/ Benjamin L. Wilson
                                        ----------------------------------------
                                        Benjamin L. Wilson, Jr.,
                                        individually


                                        Trust Under the Will of
                                        Edward S. Stimpson


                                        ----------------------------------------
                                        Trustee as aforesaid and
                                        not individually


                                        ----------------------------------------
                                        Trustee as aforesaid and
                                        not individually


                                        ----------------------------------------
                                        Trustee as aforesaid and
                                        not individually


                                        ----------------------------------------
                                        Trustee as aforesaid and
                                        not individually


                                        Trust Under the Will of
                                        Harry F. Stimpson


                                        ----------------------------------------
                                        Harry F. Stimpson, III,
                                        Trustee as aforesaid and
                                        not individually


                                        ----------------------------------------
                                        Harry F. Stimpson, Jr.,
                                        individually


                                        TENANT:

                                        Transkaryotic Therapies, Inc.


                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Title:
                                               ---------------------------------
<PAGE>
     EXECUTED as a sealed instrument on the day and year first above written.

                                        LANDLORD:


                                        ----------------------------------------
                                        Benjamin L. Wilson, Jr., individually


                                        Trust Under the Will of
                                        Edward S. Stimpson


                                        ----------------------------------------
                                        Trustee as aforesaid and
                                        not individually


                                        ----------------------------------------
                                        Trustee as aforesaid and
                                        not individually


                                        ----------------------------------------
                                        Trustee as aforesaid and
                                        not individually


                                        /s/ Edward J. Stimpson
                                        ----------------------------------------
                                        Trustee as aforesaid and
                                        not individually


                                        Trust Under the Will of
                                        Harry F. Stimpson


                                        ----------------------------------------
                                        Harry F. Stimpson, III,
                                        Trustee as aforesaid and
                                        not individually


                                        --------------------------------------
                                        Harry F. Stimpson, Jr.,
                                        individually


                                        TENANT:

                                        Transkaryotic Therapies, Inc.


                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Title:
                                               ---------------------------------
<PAGE>
     EXECUTED as a sealed instrument on the day and year first above written.

                                        LANDLORD:


                                        ----------------------------------------
                                        Benjamin L. Wilson, Jr., individually


                                        Trust Under the Will of
                                        Edward S. Stimpson


                                        /s/ Harry F. Stimpson
                                        ----------------------------------------
                                        Trustee as aforesaid and
                                        not individually


                                        ----------------------------------------
                                        Trustee as aforesaid and
                                        not individually


                                        ----------------------------------------
                                        Trustee as aforesaid and
                                        not individually


                                        ----------------------------------------
                                        Trustee as aforesaid and
                                        not individually


                                        Trust Under the Will of
                                        Harry F. Stimpson


                                        /s/ Harry F. Stimpson
                                        ----------------------------------------
                                        Harry F. Stimpson, III,
                                        Trustee as aforesaid and
                                        not individually


                                        /s/ Harry F. Stimpson
                                        ----------------------------------------
                                        Harry F. Stimpson, Jr., individually


                                        TENANT:

                                        Transkaryotic Therapies, Inc.


                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Title:
                                               ---------------------------------
<PAGE>
     EXECUTED as a sealed instrument on the day and year first above written.

                                        LANDLORD:


                                        ----------------------------------------
                                        Benjamin L. Wilson, Jr., individually


                                        Trust Under the Will of
                                        Edward S. Stimpson


                                        /s/ [Illegible]
                                        ----------------------------------------
                                        Trustee as aforesaid and
                                        not individually


                                        ----------------------------------------
                                        Trustee as aforesaid and
                                        not individually


                                        ----------------------------------------
                                        Trustee as aforesaid and
                                        not individually


                                        ----------------------------------------
                                        Trustee as aforesaid and
                                        not individually


                                        Trust Under the Will of
                                        Harry F. Stimpson


                                        ----------------------------------------
                                        Harry F. Stimpson, III,
                                        Trustee as aforesaid and
                                        not individually


                                        ----------------------------------------
                                        Harry F. Stimpson, Jr.,
                                        individually


                                        TENANT:

                                        Transkaryotic Therapies, Inc.


                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Title:
                                               ---------------------------------
<PAGE>
     EXECUTED as a sealed instrument on the day and year first above written.

                                        LANDLORD:


                                        ----------------------------------------
                                        Benjamin L. Wilson, Jr., individually


                                        Trust Under the Will of
                                        Edward S. Stimpson


                                        /s/ Margaret W. Stimpson
                                        ----------------------------------------
                                        Trustee as aforesaid and
                                        not individually


                                        ----------------------------------------
                                        Trustee as aforesaid and
                                        not individually


                                        ----------------------------------------
                                        Trustee as aforesaid and
                                        not individually


                                        ----------------------------------------
                                        Trustee as aforesaid and
                                        not individually


                                        Trust Under the Will of
                                        Harry F. Stimpson


                                        ----------------------------------------
                                        Harry F. Stimpson, III,
                                        Trustee as aforesaid and
                                        not individually


                                        ----------------------------------------
                                        Harry F. Stimpson, Jr.,
                                        individually


                                        TENANT:

                                        Transkaryotic Therapies, Inc.


                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Title:
                                               ---------------------------------
<PAGE>
                                    EXHIBIT A

     The land and the building at 195 Albany Street, Cambridge, Massachusetts
assessed by the City of Cambridge as Block 68 - Lot 59 with a land area of
24,477 square feet, being the same property shown as parcel "B" on a plan
entitled "Plan of Land in Cambridge, Mass.", scale 1"=40', prepared by Robert E.
Anderson Inc., dated November 5, 1981 and the land at the corner of Albany and
Pacific Street, Cambridge, Massachusetts assessed by the City of Cambridge as
Block 68 - Lot 60 with a land area of 30,007 square feet, being the same
property shown as parcel "A" on the above mentioned plan, being further
described in a Notice of Lease recorded with Middlesex South District Registry
of Deeds in Book 14841, Page 555, as follows:

     A parcel of land in Cambridge, Massachusetts, with the building thereon
known as 195 Albany Street, containing about 24,519 square feet of land and
shown as Lot B on "Plan of Land in Cambridge, Mass. surveyed for Stimpson
Investment Corp." dated October 22, 1947, by W.A. Mason & Son Co., Surveyors,
recorded with Middlesex South District Deeds as Plan No. 1566 of 1947 at the end
of Book 7206, bounded and described as follows:

<TABLE>
<S>             <C>
SOUTHERLY       on said Albany Street, One Hundred Nine and 4/100 (109.04) feet;

SOUTHWESTERLY   on land formerly of said Stimpson Investment Corp. shown as Lot
                A on said plan, by a line running through the middle of the
                common way forth-five (45) feet wide shown on said plan, Two
                Hundred Thirty and 69/100 (230.69) feet;

NORTHWESTERLY   on Purrington Street by the Southeasterly side-line thereof, One
                Hundred Nineteen and 73/100 (119.73) feet;

NORTHEASTERLY   on land formerly of said Stimpson Investment Corp. shown as Lot
                C on said plan, by a line running through the middle of a twelve
                inch brick wall, which shall be and remain a common party wall,
                One Hundred Fifteen and 70/100 (115.70) feet;

SOUTHEASTERLY   on the same, Seven and 2/100 (7.02) feet; and

NORTHEASTERLY   on the same, by a line running through the middle of the common
                area shown on said plan, One Hundred Five and 64/100 (105.64)
                feet
</TABLE>

The fee in Purrington Street is specifically excluded.

     Together with rights and easements as reserved in deed from Harry S.
Stimpson, III Trustee under the Will of Harry S. Stimpson to Massachusetts
Institute of Technology dated July 31, 1992 and recorded at Book 22453, Page
425.

     Together with rights and easements as set forth in a deed from Edward S.
Stimpson et al, dated October 4, 1948 and recorded at Book 7370, Page 304.
<PAGE>
                                    EXHIBIT B

                                  ENCUMBRANCES

1.   Mortgage and Security Agreement from Benjamin L. Wilson Jr.; Harry F.
     Stimpson Jr.; Edward S. Stimpson III, Margaret W. Stimpson, Harry F.
     Stimpson Jr., and Nicholas U. Sommerfeld trustees of the Edward S. Stimpson
     Trust under declaration of trust dated January 24, 1985 and recorded with
     the Middlesex County Registry of Deeds in Book 18515, Page 407; and Harry
     F. Stimpson III trustee under the will of Harry F. Stimpson to BayBank
     Boston, N.A. dated December ___, 1993 and recorded with said registry in
     Book ____, Page _____.

2.   Collateral Assignment of Leases and Rents from Benjamin L. Wilson Jr.;
     Harry F. Stimpson Jr.; Edward S. Stimpson III, Margaret W. Stimpson, Harry
     F. Stimpson Jr., and Nicholas U. Sommerfeld trustees of the Edward S.
     Stimpson Trust under declaration of trust dated January 24, 1985 and
     recorded with the Middlesex County Registry of Deeds in Book 18515, Page
     407; and Harry F. Sampson III trustee under the will of Harry F. Sampson to
     BayBank Boston, N.A. dated December 1993 and recorded with said registry in
     Book ____, Page ____.

3.   Deed of Rights in Purrington Street subject to reservation of rights from
     Landlord to Massachusetts Institute of Technology recorded at Book 22453,
     Page 423 and as shown on plan entitled "Plan of Land, owned by
     Massachusetts Institute of Technology dated March 18, 1992 prepared by
     Cullinan Engineering Co., Inc." and recorded at Book 22453, Page 418.

4.   Rights of others in common way as shown on plan entitled Plan of Land in
     Cambridge, Mass., surveyed for Sampson Investment Corp., dated October 22,
     1947 and recorded at Book 7206 END

5.   Rights and Easements set forth in a Deed recorded at Book-7370, Page 304 as
     disclosed on plan entitled Plan of Land in Cambridge, Mass., surveyed for
     Sampson Investment Corp., dated October 22, 1947 and recorded at Book 7206
     END

6.   Taxes subsequent to the Commencement Date are a lien but are not yet due
     and payable.

7.   Rights of others in and to Purrington Street.

8.   Terms and provisions of an agreement between Sampson Terminal Company and
     Stimpson Investment Corporation dated October 1, 1948, recorded with said
     Deeds in Book 7344, Page 581.

9.   Common law party wall right.
<PAGE>
                                    EXHIBIT C

            Equipment and Other Items to Remain in Former BASF Space

     All fixtures and equipment existing physically attached to the First Floor
or Lower Level of the Premises (collectively, the "BASF Space") on October 14,
1993 when the BASF space was viewed by the Tenant and representatives of the
Landlord, all as more particularly described on Schedule 1 hereto, which items
where situated, as of October 14, 1993, in the BASF Space in the various
locations identified on the floor plans included in Schedule 1.

     To the extent that the BASF Space is not substantially equipped as
described above on the Commencement Date, the Tenant and the Landlord agree that
if the Landlord does not replace missing equipment with substantially similar
equipment, there will be an equitable adjustment in the Annual Fixed Rent
allocable to the BASF Space based on the fair market value of replacing any
missing fixtures or equipment.
<PAGE>
                               [INSERT EXHIBIT C]
<PAGE>
                                    EXHIBIT D

<TABLE>
<S>                    <C>
NAMED INSURED:         "Landlord" and Transkaryotic Therapies, Inc. (any
                       mortgagee of which tenant is given notice shall be listed
                       as mortgagee and loss payee)

PROPERTY ADDRESS:      195 Albany Street
                       Cambridge, MA 02139

COVERAGE:              Real Property

LIMIT OF INSURANCE:    $5,000,000

COVERAGE TO INCLUDE:   -    Agreed. Amount

                       -    Guaranteed Replacement Cost

                       -    Contingent Liability from Operating of Building Laws

                       -    Demolition

                       -    Debris Removal

                       -    Increased Cost of Insurance

                       -    30 Day Cancellation
</TABLE>
<PAGE>
FIRST AMENDMENT                                                   April 13, 1998

     The lease dated November 28, 1993 between Benjamin L. Wilson, Jr.; Margaret
W. Stimpson, Edward S. Stimpson, III, Harry F. Stimpson, III, and Nicholas U.
Sommerfeld, trustees under the will of Edward S. Stimpson; Harry F. Stimpson,
III, trustee under the will of Harry F. Stimpson; and Harry F. Stimpson, Jr.; as
tenants in common (collectively, the "Landlord"), and TRANSKARYOTIC THERAPIES,
INC., a Delaware corporation ("Tenant") is hereby amended as follows.

1.   Paragraph 1.1

     The annual fixed rent period January 1, 1999 through December 31, 2003
     shall be [Illegible] which reflects the sum of [Illegible] psf of premises
     located on the 2nd floor of the building and [Illegible] of the premises
     located on the first floor and lower level of the building.

2.   All other terms and conditions of said lease remain unchanged.

                                        LANDLORD:


                                        ----------------------------------------
                                        Benjamin L. Wilson, Jr.,
                                        individually


                                        Trust Under the Will of
                                        Edward S. Stimpson


                                        /s/ Wallace J. Stimpson
                                        ----------------------------------------
                                        Trustee as aforesaid and
                                        not individually


                                        /s/ Edward S. Stimpson
                                        ----------------------------------------
                                        Trustee as aforesaid and
                                        not individually


                                        /s/ John Stimpson
                                        ----------------------------------------
                                        Trustee as aforesaid and
                                        not individually
<PAGE>
First Amendment - Cont'd
April 13, 1998
Page 2


                                        Trust Under the Will of
                                        Harry F. Stimpson


                                        /s/ [Illegible]
                                        ----------------------------------------
                                        Trustee as aforesaid and
                                        not individually


                                        /s/ Harry F. Stimpson, Jr.
                                        ----------------------------------------
                                        Harry F. Stimpson, Jr.
                                        individually


                                        TENANT:

                                        Transkaryotic Therapies, Inc.


                                        By: /s/ Andrea T. Jeffrey
                                            ------------------------------------
                                        Name: Andrea T. Jeffrey
                                        Title: Senior Director of Operations
<PAGE>
                            SECOND AMENDMENT TO LEASE

     This Second Amendment to Lease (this "Amendment") is dated as of December
23, 2002, by and between Benjamin L. Wilson Jr., individually; Harry F. Stimpson
Jr., individually; John W. Sampson, Wallace I. Stimpson, and Anne G. Sampson,
each individually, as successors in interest to the Edward S. Stimpson Trust;
and John W. Sampson and J. Louis Newell, as trustees under the will of Harry F.
Sampson ("Landlord"), with an address c/o Meredith & Grew, 160 Federal Street,
Boston, Massachusetts 02110, and Transkaryotic Therapies, Inc., a Delaware
corporation ("Tenant"), with an address of 195 Albany Street, Cambridge,
Massachusetts 02142.

                                    RECITALS

     A. Reference is made to that certain Lease by and between Landlord and
Tenant dated November 28, 1993, as amended by that certain First Amendment to
Lease dated April 13, 1998 (as so amended, the "Original Lease"), pursuant to
which Tenant leased the 48,000 square feet of space (the "Premises") in the
building located at and commonly known as 195 Albany Street, Cambridge,
Massachusetts (the "Building"), as more fully set forth in the Original Lease.

     B. Landlord and Tenant desire to amend the Original Lease to (i) extend the
Term thereof and (ii) amend the Fixed Rent due for the extended Term.

     NOW, THEREFORE, for good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, Landlord and Tenant hereby agree
as follows:

     1. Recitals; Capitalized Terms. All of the foregoing recitals are true and
correct. All capitalized terms not otherwise modified or defined herein shall
have the respective same meanings ascribed to them in the Lease. The term
"Lease" is hereby amended to mean and refer to the Original Lease as amended by
this Amendment.

     2. Extension of Term. The Term of the Lease is hereby extended for an
additional period of five (5) years, commencing on January 1, 2004 and expiring
on December 31, 2008. Tenant shall have no further option to extend the Term of
this Lease. Without limiting the generality of the foregoing, upon the extension
of the Term as described above in this paragraph, Section 2.3 of the Original
Lease shall be deemed to be deleted and of no further force or effect. Landlord
and Tenant acknowledge that Tenant is currently in possession and occupancy of
the Premises. Tenant hereby accepts the Premises, as-is, in the condition
existing as of the date of this Amendment, and Landlord shall have no obligation
to perform any work to prepare the Premises for Tenant's occupancy for the
extended Term.

     3. Annual Fixed Rent: From the date of this Amendment through December 31,
2003, the Annual Fixed Rent shall be as set forth in the First Amendment to
Lease. From January 1, 2004 through December 31, 2008, the Annual Fixed Rent
shall equal [Illegible] per year, payable in monthly installments of
[Illegible].

     4. Rights of Negotiation. Tenant acknowledges and confirms that its Right
to Negotiate under Section 2.4 of the Original Lease remains subject and
subordinate to the existing rights of MIT. Tenant further acknowledges and
confirms that its right to negotiate to lease


                                        1
<PAGE>
additional space in the Adjacent Building under Section 2.5 of the Original
Lease remains subject and subordinate to the existing rights of MIT.

     5. Brokerage. Landlord and Tenant each represent and warrant to the other
that neither of them has employed or dealt with any broker, agent or finder in
carrying on the negotiations relating to this Amendment to the Lease other than
Meredith & Grew/Oncor Incorporated (the "Broker"). Tenant shall indemnify and
hold Landlord harmless from and against any claim or claims for brokerage or
other commissions asserted by any broker, agent or finder engaged by Tenant or
with whom Tenant has dealt, other than the Broker. Landlord shall indemnify and
hold Tenant harmless from and against any claim or claims for brokerage or other
commissions asserted by the Broker engaged by Landlord.

     6. Miscellaneous. Tenant hereby acknowledges that (i) Landlord has no
undischarged obligations under the Lease to perform any work or improvements to
the Premises, or, to Tenant's actual knowledge, otherwise; (ii) there are no
offsets or defenses that Tenant has against the full enforcement of the Lease by
Landlord; (iii) neither Landlord nor Tenant is in any respect in default under
the Lease; and (iv) Tenant has not assigned, transferred or hypothecated the
Lease or any interest therein or subleased all or any portion of the Premises.

     7. Ratification. Except as expressly modified by this Amendment, the
Original Lease shall remain in full force and effect, and as further modified by
this Amendment, is expressly ratified and confirmed by the parties hereto.

     8. Governing Law; Interpretation and Partial Invalidity. This Amendment
shall be governed and construed in accordance with the Laws of the Commonwealth
of Massachusetts, without reference to principles of conflicts of laws. If any
term of this Amendment, or the application thereof to any person or
circumstances, shall to any extent be invalid or unenforceable, the remainder of
this Amendment, or the application of such term to persons or circumstances
other than those as to which it is invalid or unenforceable, shall not be
affected thereby, and each term of this Amendment shall be valid and enforceable
to the fullest extent permitted by law. The titles for the paragraphs are for
convenience only and not to be considered in construing this Amendment. This
Amendment contains all of the agreements of the parties with respect to the
subject matter hereof, and supersedes all prior dealings between them with
respect to such subject matter. No delay or omission on the part of either party
to this Amendment in requiring performance by the other party or exercising any
right hereunder shall operate as a waiver of any provision hereof or any rights
hereunder, and no waiver, omission or delay in requiring performance or
exercising any right hereunder on any one occasion shall be construed as a bar
to or waiver of such performance or right on any future occasion.

     9. Successors. This Amendment shall he binding upon and inure to the
benefit of the parties hereto and their respective successors and assigns,
subject to the provisions of the Lease regarding assignment and subletting.

     10. Counterparts and Authority. This Amendment may be executed in multiple
counterparts, each of which shall be deemed an original and all of which
together shall constitute one and the same document, Tenant warrants that the
person or persons executing this


                                        2
<PAGE>
Amendment on its behalf has or have authority to do so and that such execution
has fully obligated and bound such party to all terms and provisions of this
Amendment.

                    [SIGNATURES BEGIN ON THE FOLLOWING PAGE]


                                        3
<PAGE>
IN WITNESS WHEREOF, the undersigned executed this Amendment as of the date and
year first written above.

                                        LANDLORD:


                                        ----------------------------------------
                                        BENJAMIN L. WILSON, JR., INDIVIDUALLY


                                        /s/ John W. Stimpson
                                        ----------------------------------------
                                        JOHN W. STIMPSON, INDIVIDUALLY


                                        ----------------------------------------
                                        WALLACE I. STIMPSON, INDIVIDUALLY


                                        ----------------------------------------
                                        ANNE G. STIMPSON, INDIVIDUALLY


                                        ----------------------------------------
                                        HARRY F. STIMPSON, JR., INDIVIDUALLY


                                        /s/ John W. Stimpson, Trustee
                                        ----------------------------------------
                                        JOHN W. STIMSON, ASW TRSUTEE UNDER THE
                                        WILL OF HARRY F. STIMPSON, AND NOT
                                        INDIVIDUALLY


                                        ----------------------------------------
                                        J. LOUIS NEWELL, AS TRUSTEE UNDER THE
                                        WILL OF HARRY F. STIMPSON, AND NOT
                                        INDIVIDUALLY


                                        TENANT:

                                        TRANSKARYOTIC THERAPIES, INC.,
                                        a Delaware Corporation


                                        By: /s/ [Illegible]
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Title:
                                               ---------------------------------


                                        4
<PAGE>
                               CONSENT TO SUBLEASE

     THIS CONSENT TO SUBLEASE (this "Consent") dated as of July 23, 2004, is
made with reference to that certain sublease (the "Sublease") dated July 23,
2004, by and between Transkaryotic Therapies, Inc. ("Tenant") and Altus
Pharmaceuticals, Inc. ("Sublessee"), and is entered into between the foregoing
parties and Benjamin L. Wilson Jr., individually; Harry F. Stimpson Jr.,
individually; John W. Stimpson, Wallace I. Stimpson, and Anne G. Stimpson, each
individually, as successors in interest to the Edward S. Stimpson Trust; and
John W. Stimpson and J. Louis Newell, as trustees under the will of Harry F.
Stimpson (collectively, "Landlord"), having an address c/o Meredith & Grew, 160
Federal Street, Boston, MA 02110 with reference to the following facts:

     A. Landlord and Tenant are the parties to that certain Lease dated November
28, 1993, as amended by that certain First Amendment to Lease dated April 13,
1998 and that certain Second Amendment to Lease, dated December 23, 2002 (as so
amended, the "Master Lease"), pursuant to which Tenant leased 48,000 square feet
of space (the "Premises") in the building located at and commonly known as 195
Albany Street, Cambridge, Massachusetts (the "Building"), as more fully set
forth in the Master Lease.

     B. Tenant is not currently in occupancy of any portion of the Premises.

     C. Tenant and Sublessee wish to enter into the Sublease respecting
approximately 16,000 rentable square feet on the first floor of the Building as
more particularly described in the Sublease ("Sublease Premises") for a term
which will expire on December 31, 2008.

     D. The Master Lease provides that Tenant may not enter into any sublease
without Landlord's prior written approval.

     E. Tenant and Sublessee have presented the fully-executed Sublease to
Landlord for Landlord's approval, a copy of which is attached hereto and made a
part hereof as Exhibit A, and Landlord hereby approves such Sublease, subject to
all of the terms and conditions hereinafter appearing.

     NOW, THEREFORE, for good and valuable consideration, the parties hereto
agree as follows:

     1. Neither the Master Lease, the Sublease nor this Consent shall be deemed
to grant Sublessee any rights whatsoever against Landlord. Sublessee hereby
acknowledges and agrees that its sole remedy for any alleged or actual breach of
its rights in connection with the Sublease Premises shall be solely against
Sublandlord.

     2. This Consent shall not release Tenant from any existing or future duty,
obligation or liability to Landlord pursuant to the Master Lease, nor shall this
Consent change, modify or amend the Master Lease in any manner. This Consent
shall not be deemed Landlord's consent to any further subleases.

     3.

          (a) In the event of Master Lease Termination (as hereinafter defined)
prior to the termination of the Sublease, and on condition that (i) Sublessee is
not then in default beyond any


                                        5
<PAGE>
applicable notice and cure period under the Sublease, (ii) Sublessee is then in
occupancy of the entire Sublease Premises, and (iii) Sublessee cures any then
outstanding obligations of Tenant under the Master Lease (any of which
conditions may be waived by Landlord in its sole discretion), Sublessee, at its
option (which shall be in accordance with the provisions of this Section 3(a)),
shall attorn to Landlord and recognize Landlord as Sublessee's landlord, and
Landlord shall accept Sublessee as its tenant, upon all of the executory terms
and conditions of the Master Lease, including without limitation the rental and
all other payment and performance obligations stated therein, and for the then
remaining term of the Master Lease (the "Master Lease Attornment"). Landlord
shall promptly notify Sublessee of any Master Lease Termination (the
"Termination Notice"), and the Termination Notice shall identify all outstanding
obligations of Tenant under the Master Lease which Landlord requests Sublessee
to cure (the "Outstanding Defaults"). Sublessee shall notify Landlord within ten
(10) days of receipt of the Termination Notice if Sublessee shall (i) elect to
accept the Master Lease Attornment as provided above and (ii) cure the
Outstanding Defaults.

          (b) If Sublessee either (i) notifies Landlord it will not accept the
Master Lease Attornment, or (ii) fails to respond to the Termination Notice
within the period specified above, then Landlord may elect to require that
Sublessee attorn to Landlord and to recognize Landlord as Sublessee's landlord
under the Sublease, upon the terms and conditions and at the rental rate
specified in the Sublease, and for the then remaining term of the Sublease (the
"Sublease Attornment"). Landlord shall elect such Sublease Attornment by written
notice to Sublessee given within ten (10) days after (A) receipt of Tenant's
notice that it will not accept the Master Lease Attornment, or (B) the
expiration of the ten (10) day period under clause (a) above upon Sublessee's
failure to so respond. If Landlord either (i) notifies Sublessee it will not
require the Sublease Attornment, or (ii) fails to respond to the notice from
Sublessee within the ten (10) day period specified above, then Sublessee shall
vacate the Premises within thirty (30) days after (A) receipt of Landlord's
notice that it will not require the Sublease Attornment, or (B) the expiration
of the ten (10) day period under this clause (b) if Landlord shall fail to
deliver such notice within such period.

          (c) Sublessee agrees to execute and deliver at any time and from time
to time, upon request of Landlord, any instruments which may be necessary or
appropriate to evidence either the Master Lease Attornment or Sublease
Attornment, as applicable (as applicable, the "Attornment"), provided the same
are in form and substance reasonably acceptable to Sublessee. In the event of
such Attornment, Landlord shall not (i) be liable to Sublessee for any act,
omission or breach of the Master Lease or Sublease by Tenant, (ii) be subject to
any offsets or defenses which Sublessee might have against Tenant, (iii) be
bound by any rent or additional rent which Sublessee might have paid more than
one month in advance to Tenant, or (iv) be bound to honor any rights of
Sublessee in any security deposit made with Tenant except to the extent Tenant
has turned over such security deposit to Landlord. Tenant shall immediately pay
or transfer to Landlord any security deposit required under the terms of the
Sublease. Sublessee hereby agrees that Tenant's option to elect the Master Lease
Attornment in the event of Master Lease Termination shall be subject to and
conditioned upon Sublessee paying to Landlord any amount of the security deposit
under the Master Lease that is not then held by Landlord provided Sublessee is
notified as such as an Outstanding Default in the Termination Notice, but
Sublessee shall be credited against such amount for any portion of the security
deposit paid under the Sublease and delivered by Tenant to the Landlord.

          (d) "Master Lease Termination" means any termination, cancellation,
foreclosure or other event, which by voluntary or involuntary act or by
operation of law, causes the Master Lease to


                                        6
<PAGE>
be terminated, canceled, foreclosed against, or otherwise come to an end,
including but not limited to (1) a default by Tenant under the Master Lease of
any of the terms or provisions thereof; (2) the rejection of the Master Lease in
bankruptcy by Tenant; or (3) the termination of Tenant's leasehold estate by
dispossession proceeding or otherwise.

          (e) In the event of Attornment hereunder, Landlord's liability shall
be limited to matters arising from and after such Attornment, and in the event
that Landlord (or any successor owner) shall convey or dispose of the Building
to another party, such party shall thereupon be and become landlord hereunder
and shall be deemed to have fully assumed and be liable for all obligations of
this Consent or the Sublease or Master Lease, as applicable, to be performed by
Landlord which first arise after the date of conveyance, including the return of
any security deposit, and Tenant shall attorn to such other party, and Landlord
(or such successor owner) shall, from and after the date of conveyance, be free
of all liabilities and obligations hereunder not then incurred. The liability of
Landlord to Sublessee for any default by Landlord under this Consent or the
Sublease or Master Lease, as applicable, after such attornment, or arising in
connection with Landlord's operation, management, leasing, repair, renovation,
alteration, or any other matter relating to the Building or the Sublease
Premises, shall be limited to the interest of the Landlord in the Building (and
proceeds thereof). Under no circumstances shall any present or future trustee,
beneficiary, or general partner of Landlord (if Landlord is a partnership) have
any liability for the performance of Landlord's obligations under this Consent
or the Sublease.

     4. In addition to Landlord's, rights under Section 3 hereof, in the event
Tenant is in default under any of the terms and provisions of the Master Lease,
Landlord may elect to receive directly from Sublessee all sums due or payable to
Tenant by Sublessee pursuant to the Sublease, and upon receipt of Landlord's
notice, Sublessee shall thereafter pay to Landlord any and all sums becoming due
or payable under the Sublease and Tenant shall receive from Landlord a
corresponding credit for such sums against any payments then due or thereafter
becoming due from Tenant. Tenant hereby acknowledges and agrees that Sublessee
shall be entitled to rely upon such notice from Landlord and any payment by
Sublessee to Landlord pursuant to such notice shall satisfy Sublessee's
obligations under the Sublease. Neither the service of such written notice nor
the receipt of such direct payments shall cause Landlord to assume any of
Tenant's duties, obligations and/or liabilities under the Sublease, nor shall
such event impose upon Landlord the duty or obligation to honor the Sublease.

     5.

          (a) Sublandlord and Sublessee acknowledge and agree that Landlord
shall have no obligations whatsoever, whether under the Master Lease or this
Consent, to perform any work to prepare the Sublease Premises for Sublessee's
occupancy, nor shall Landlord have any obligations with respect to the condition
of the Premises during the term of the Sublease except as required under the
Master Lease. In no event shall Landlord have any obligation to perform any
alterations, repairs or improvements of any nature arising as a result of any
work or thing done or performed by Sublessee in, on, under or to the Premises or
the Property, including, without limitation, any obligation that Landlord may
otherwise be required to perform under the Master Lease.

          (b) Except as otherwise expressly provided herein, this Consent shall
not be deemed Landlord's consent to any improvements or alterations that
Sublessee may propose to perform in or to the Premises, either prior to its
initial occupancy or thereafter during the term of the Sublease, and


                                        7
<PAGE>
Sublessee acknowledges and agrees that any alterations or modifications to the
Property that may be necessary for any reason in connection with Sublessee's
improvements or alterations, whether structural or non-structural, and no matter
where located on the Property, shall be performed by Sublessee at Sublessee's
sole cost and expense, subject to Landlord's prior consent, such consent not to
be unreasonably withheld or delayed for nonstructural improvements or
nonstructural alterations, so long as the same do not, in Landlord's reasonable
judgment, diminish the value of the Premises or require unusual expense to
readapt the existing office areas to normal office use and/or to readapt the
existing laboratory areas to normal laboratory use, and Landlord shall have no
obligations to perform any such alterations or modifications, notwithstanding
anything to the contrary contained in the Master Lease.

          (c) Without limiting the generality of the foregoing, Landlord hereby
approves the Subtenant's Work (as defined in the Sublease) as and to the extent
such Subtenant's Work is set forth and described in Exhibit B to the Sublease.
To the extent that any portion of Subtenant's Work is not adequately set forth
in the general scope of work and floor plan layout attached as Exhibit B to the
Sublease, or to the extent more detail is later provided or any changes or
modifications to such Exhibit B are proposed, such detail, and changes shall
require Landlord's prior consent as and to the extent set forth in this Consent
and the Master Lease. Subtenant's Work shall be performed subject to and in
accordance with all of the terms and conditions of the Master Lease, including,
without limitation, the provisions of Sections 4.3 and 4.4. Without limiting
anything contained in the Lease, Sublessee agrees that it will not remove any
Subtenant's Work and will surrender such Subtenant's Work to Landlord upon the
expiration or earlier termination of the Sublease.

     6. Landlord, shall endeavor to provide Sublessee with a concurrent copy of
any notice of default to Tenant under the Master Lease, and to the extent that
such default is capable of cure by Sublessee, Sublessee shall have the right,
but not the obligation, to cure such default on behalf of Tenant. Tenant hereby
acknowledges such right of Sublessee to perform such obligations of Tenant and
agrees that Landlord may accept such cure in respect of such default of Tenant.

     7. Without limiting anything contained in the Master Lease as incorporated
into the Sublease, regarding Sublessee's obligations upon surrender of the
Sublease Premises, to the extent applicable to Sublessee's use of the Premises,
Sublessee agrees with Landlord and Tenant that it shall complete (i) the
Radioactive Material Decontamination in accordance with Exhibit B-l, (ii) the
Hazardous Chemicals removal in accordance with Exhibit B-2; and (iii) the
Hazardous Biologicals removal in accordance with Exhibit B-3. Landlord and
Sublandlord acknowledge and agree that Sublessee does not currently plan to use
radioactive materials within the Sublease Premises and until such time as
Sublessee utilizes such materials in all or any portion of the Sublease
Premises, the requirements of subsection (i) shall be inapplicable to Sublessee.
To the extent applicable, Sublessee shall perform the foregoing obligations at
Sublessee's sole cost and expense, and in compliance with all federal state and
local laws, rules, regulations and ordinances, any decommissioning or
decontamination requirements imposed by any licenses or permits maintained by
Sublessee in connection with the conduct of its business in the Sublease
Premises, and the terms and conditions of the Master Lease as affected by this
Consent. Prior to the expiration or earlier termination, Sublessee shall deliver
to Landlord copies of all applicable closure certifications from governmental
authorities with jurisdiction over such decommissioning, including, without
limitation, Agency Form 120.100-3 from the Radiation Control Program of the
Massachusetts Department of Public Health (or equivalent information
satisfactory to the Massachusetts Department of Public Health) with respect to
any


                                        8
<PAGE>
portions of the Sublease Premises that have been contaminated with radioactive
materials. If Sublessee shall fail to deliver the Sublease Premises to Landlord
in the condition required by this paragraph, such failure shall constitute a
holding over by Tenant under the Master Lease.

     8. Sublessee hereby acknowledges that it has read and has knowledge of all
of the terms, provisions, rules and regulations of the Master Lease and agrees
not to door omit to do anything which would cause Tenant to be in breach of the
Master Lease. Any such act or omission shall also constitute a breach of this
Consent and shall entitle Landlord to recover any damage, loss, cost or expense
which it thereby suffers, from Sublessee, whether or not Landlord proceeds
against Tenant.

     9. Landlord acknowledges that Tenant intends to designate certain areas of
the Premises in common between the Sublessee and Tenant and any future
subtenants of the Premises. Tenant acknowledges that such areas remain the sole
obligation of Tenant as a part of the Premises demised under the Master Lease.
Notwithstanding the foregoing, Landlord reserves the right, but shall have no
obligation, to establish and enforce reasonable rules and regulations from time
to time for the safe and proper use of such common areas of the Building.
Landlord agrees to use reasonable efforts to insure that any such rules and
regulations are uniformly enforced, but Landlord shall not be liable to Tenant
or Sublessee for violation of the same by any occupant of the Premises, or
persons having business with them. Any additional incremental costs and expenses
incurred by Landlord, including, without limitation, any management costs, with
respect to the regulation of such common areas and enforcement of such rules and
regulations shall be paid by Tenant as additional rent under the Master Lease.
In the event that there shall be a conflict between such rules and regulations
and the provisions of the Master Lease or this Consent, the provisions of the
Lease, as modified by this Consent, shall control.

     10. Sublessee agrees to maintain the same insurance required to be carried
by Tenant under the Master Lease, naming the Landlord as an additional insured
under Sublessee's general liability policies of insurance, and Sublessee further
agrees to waive subrogation in favor of Landlord to the same extent required of
Tenant under said Master Lease, and Landlord hereby agrees to waive subrogation
in favor of Sublessee to the same extent required by Landlord under the Master
Lease.

     11. In the event of any litigation between the parties hereto with respect
to the subject matter hereof; the unsuccessful party agrees to pay the
successful party all costs, expenses and reasonable attorney's fees incurred
therein by the successful party, which shall be included as a part of the
judgment therein rendered.

     12. This Consent shall be binding upon and inure to the benefit of the
parties' respective successors and assigns, subject to all agreements and
restrictions contained in the Master Lease, the Sublease and herein with respect
to subleasing, assignment, or other transfer. The agreements contained herein
constitute the entire understanding between the parties with respect to the
subject matter hereof, and supersede all prior agreements, written or oral,
inconsistent herewith. No amendment, modification or change therein will be
effective unless Landlord shall have given its prior written consent thereto.
This Consent may be amended only in writing, signed by all parties hereto. This
Consent may be executed in multiple counterparts, each of which shall be deemed
an original and all of which together shall constitute one and the same
document.


                                        9
<PAGE>
     13. Notices required or desired to be given hereunder shall be effective
either upon personal delivery or three (3) days after deposit in the United
States mail, by certified mail, return receipt requested, addressed to the
Landlord at the address set forth above, or to Tenant or Sublessee at the
address of the Premises or of the. Sublease Premises, respectively. Any party
may change its address for notice by giving notice in the manner hereinabove
provided.

     14. As a condition to the effectiveness of Landlord's consent to the
Sublease, Tenant agrees to pay Landlord concurrently with Tenant's delivery of
an executed counterpart hereof, Three Thousand Two Hundred Fifty Dollars
($3,250.00) in reimbursement of Landlord's reasonable attorneys' fees and
administrative expenses incurred in connection with this Consent, as additional
rent. Landlord's acceptance of such fee shall impose no duty on Landlord to
approve to execute the Sublease.

     15. Tenant and Sublessee agree to indemnify and hold Landlord harmless from
and against any loss, cost, expense, damage or liability, including reasonable
attorneys' fees, incurred as a result of a claim by any third party (i) that it
is entitled to a commission, finder's fee or like payment in connection with the
Sublease or (ii) relating to or arising out of the Sublease or any related
agreements or dealings.


                                       10
<PAGE>
     IN WITNESS WHEREOF, the following parties have executed this Consent to
Sublease as of the date first above written.

                                        TENANT:

                                        TRANSKARYOTIC THERAPIES, INC.


                                        By: /s/ Gregory Perry
                                            ------------------------------------
                                        Name: Gregory Perry
                                        Title: VP Finance & CFO


                                        SUBLESSEE:

                                        ALTUS PHARMACEUTICALS, INC.


                                        By: /s/ Jonathan Lieber
                                            ------------------------------------
                                        Name: Jonathan Lieber
                                        Title: VP Finance


                                        LANDLORD:


                                        /s/ Benjamin L. Wilson, Jr.
                                        ----------------------------------------
                                        BENJAMIN L. WILSON, JR., INDIVIDUALLY


                                        /s/ John W. Stimpson
                                        ----------------------------------------
                                        JOHN W. STIMPSON, INDIVIDUALLY


                                        /s/ Wallace I Stimpson
                                        ----------------------------------------
                                        WALLACE I. STIMPSON, INDIVIDUALLY


                                        /s/ Anne G. Stimpson
                                        ----------------------------------------
                                        ANNE G. STIMPSON, INDIVIDUALLY


                                        /s/ Harry F. Stimpson
                                        ----------------------------------------
                                        HARRY F. STIMPSON, JR., INDIVIDUALLY


                                        /s/ John W. Stimpson
                                        ----------------------------------------
                                        JOHN W. STIMPSON, AS TRUSTEE UNDER THE
                                        WILL OF HARRY F. STIMPSON, AND NOT
                                        INDIVIDUALLY


                                        /s/ J. Louis Newell
                                        ----------------------------------------
                                        J. LOUIS NEWELL, AS TRUSTEE UNDER THE
                                        WILL OF HARRY F. STIMPSON, AND NOT
                                        INDIVIDUALLY


                                       11
<PAGE>
                                    EXHIBIT A
                                    SUBLEASE


                                       12
<PAGE>
                                   Exhibit B-1

                      Radioactive Material Decontamination

Sublessee shall submit the required application for removal of the Sublease
Premises from Sublessee's license from the Radiation Control Program and
undertake the necessary decommissioning activities to be entitled to obtain such
removal, including, without limitation:

(a)  Prepare documentation for presentation to the Radiation Control Program,
     Mass. Department of Public Health to obtain certificate of removal of the
     Sublease Premises from Sublessee's license from the Radiation Control
     Program;

(b)  Report on the activities of Sublessee in removing all radioactive materials
     from the Sublease Premises, and conduct wipe tests in accordance with the
     applicable regulations of the Commonwealth of Massachusetts to confirm
     compliance with item (c) below;

(c)  Confirm that no area of the Sublease Premises contains radiation as a
     result of activities by Sublessee in excess of the applicable regulations
     of the Commonwealth of Massachusetts and that the closeout of the Sublease
     Premises complies with regulations of the Commonwealth of Massachusetts;
     and

Sublessee shall obtain and furnish notice of such removal to Landlord, all as a
condition to having fulfilled its obligations under this Exhibit B-1.


                                       13
<PAGE>
                                   Exhibit B-2

                               Hazardous Chemicals

Sublessee will take the following actions:

(a)  Arrange for and cause the removal of all waste materials and hazardous
     substances generated, acquired or otherwise handled by Sublessee during the
     Term from the Sublease Premises, including without limitation wiping down
     bench tops, sinks, and other horizontal surfaces with water and appropriate
     soaps or cleansers.

(b)  Retain a qualified environmental contractor to collect waste materials and
     hazardous substances and to provide Sublessee with a receipt for said
     materials, and, as appropriate, manifests for shipment and proper disposal.

(c)  Provide Landlord with copies of receipts and/or manifests for removal and
     disposal of such waste materials and hazardous substances removed pursuant
     to this Exhibit B-2.


                                       14
<PAGE>
                                   Exhibit B-3

                              Hazardous Biologicals

Sublessee will take the following actions:

(a)  Remove all biological laboratory material from the Sublease Premises to the
     extent brought thereon by Sublessee.

(b)  Decontaminate each bench top, sink, and any equipment bearing the universal
     biohazard symbol using a 10% sodium hypochlorite solution or similar
     disinfectant, and otherwise undertake the necessary steps to fulfill the
     requirements of the Cambridge Biosafety Committee, Public Health
     Department, City of Cambridge (the "Biosafety Committee").

(c)  Retain a qualified environmental contractor to prepare a Decontamination
     Report and file same with the Biosafety Committee and provide copies of
     such Decontamination Report to Landlord and Sublessee.


                                       15
<PAGE>
     IN WITNESS WHEREOF, the following parties have executed this Consent to
Sublease. as of the date first above written.

                                        TENANT:

                                        TRANSKARYOTIC THERAPIES, INC.


                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Title:
                                               ---------------------------------


                                        SUBLESSEE:

                                        ALTUS PHARMACEUTICALS, INC.


                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Title:
                                               ---------------------------------


                                        LANDLORD:


                                        ----------------------------------------
                                        BENJAMIN L. WILSON, JR., INDIVIDUALLY


                                        ----------------------------------------
                                        JOHN W. STIMPSON, INDIVIDUALLY


                                        ----------------------------------------
                                        WALLACE I. STIMPSON, INDIVIDUALLY


                                        ----------------------------------------
                                        ANNE G. STIMPSON, INDIVIDUALLY


                                        ----------------------------------------
                                        HARRY F. STIMPSON, JR., INDIVIDUALLY


                                        ----------------------------------------
                                        JOHN W. STIMPSON, AS TRUSTEE UNDER THE
                                        WILL OF HARRY F. STIMPSON, AND NOT
                                        INDIVIDUALLY


                                        ----------------------------------------
                                        J. LOUIS NEWELL, AS TRUSTEE UNDER THE
                                        WILL OF HARRY F. STIMPSON, AND NOT
                                        INDIVIDUALLY


                                       16
<PAGE>
     IN WITNESS WHEREOF, the following parties have executed this Consent to
Sublease. as of the date first above written.

                                        TENANT:

                                        TRANSKARYOTIC THERAPIES, INC.


                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Title:
                                               ---------------------------------


                                        SUBLESSEE:

                                        ALTUS PHARMACEUTICALS, INC.


                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Title:
                                               ---------------------------------


                                        LANDLORD:


                                        ----------------------------------------
                                        BENJAMIN L. WILSON, JR., INDIVIDUALLY


                                        ----------------------------------------
                                        JOHN W. STIMPSON, INDIVIDUALLY


                                        ----------------------------------------
                                        WALLACE I. STIMPSON, INDIVIDUALLY


                                        ----------------------------------------
                                        ANNE G. STIMPSON, INDIVIDUALLY


                                        ----------------------------------------
                                        HARRY F. STIMPSON, JR., INDIVIDUALLY


                                        ----------------------------------------
                                        JOHN W. STIMPSON, AS TRUSTEE UNDER THE
                                        WILL OF HARRY F. STIMPSON, AND NOT
                                        INDIVIDUALLY


                                        ----------------------------------------
                                        J. LOUIS NEWELL, AS TRUSTEE UNDER THE
                                        WILL OF HARRY F. STIMPSON, AND NOT
                                        INDIVIDUALLY


                                       17
<PAGE>
     IN WITNESS WHEREOF, the following parties have executed this Consent to
Sublease. as of the date first above written.

                                        TENANT:

                                        TRANSKARYOTIC THERAPIES, INC.


                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Title:
                                               ---------------------------------


                                        SUBLESSEE:

                                        ALTUS PHARMACEUTICALS, INC.


                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Title:
                                               ---------------------------------


                                        LANDLORD:


                                        ----------------------------------------
                                        BENJAMIN L. WILSON, JR., INDIVIDUALLY


                                        ----------------------------------------
                                        JOHN W. STIMPSON, INDIVIDUALLY


                                        ----------------------------------------
                                        WALLACE I. STIMPSON, INDIVIDUALLY


                                        ----------------------------------------
                                        ANNE G. STIMPSON, INDIVIDUALLY


                                        ----------------------------------------
                                        HARRY F. STIMPSON, JR., INDIVIDUALLY


                                        ----------------------------------------
                                        JOHN W. STIMPSON, AS TRUSTEE UNDER THE
                                        WILL OF HARRY F. STIMPSON, AND NOT
                                        INDIVIDUALLY


                                        ----------------------------------------
                                        J. LOUIS NEWELL, AS TRUSTEE UNDER THE
                                        WILL OF HARRY F. STIMPSON, AND NOT
                                        INDIVIDUALLY


                                       18
<PAGE>
     IN WITNESS WHEREOF, the following parties have executed this Consent to
Sublease. as of the date first above written.

                                        TENANT:

                                        TRANSKARYOTIC THERAPIES, INC.


                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Title:
                                               ---------------------------------


                                        SUBLESSEE:

                                        ALTUS PHARMACEUTICALS, INC.


                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Title:
                                               ---------------------------------


                                        LANDLORD:


                                        ----------------------------------------
                                        BENJAMIN L. WILSON, JR., INDIVIDUALLY


                                        ----------------------------------------
                                        JOHN W. STIMPSON, INDIVIDUALLY


                                        ----------------------------------------
                                        WALLACE I. STIMPSON, INDIVIDUALLY


                                        ----------------------------------------
                                        ANNE G. STIMPSON, INDIVIDUALLY


                                        ----------------------------------------
                                        HARRY F. STIMPSON, JR., INDIVIDUALLY


                                        ----------------------------------------
                                        JOHN W. STIMPSON, AS TRUSTEE UNDER THE
                                        WILL OF HARRY F. STIMPSON, AND NOT
                                        INDIVIDUALLY


                                        ----------------------------------------
                                        J. LOUIS NEWELL, AS TRUSTEE UNDER THE
                                        WILL OF HARRY F. STIMPSON, AND NOT
                                        INDIVIDUALLY


                                       19
<PAGE>
     IN WITNESS WHEREOF, the following parties have executed this Consent to
Sublease. as of the date first above written.

                                        TENANT:

                                        TRANSKARYOTIC THERAPIES, INC.


                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Title:
                                               ---------------------------------


                                        SUBLESSEE:

                                        ALTUS PHARMACEUTICALS, INC.


                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Title:
                                               ---------------------------------


                                        LANDLORD:


                                        ----------------------------------------
                                        BENJAMIN L. WILSON, JR., INDIVIDUALLY


                                        ----------------------------------------
                                        JOHN W. STIMPSON, INDIVIDUALLY


                                        ----------------------------------------
                                        WALLACE I. STIMPSON, INDIVIDUALLY


                                        ----------------------------------------
                                        ANNE G. STIMPSON, INDIVIDUALLY


                                        ----------------------------------------
                                        HARRY F. STIMPSON, JR., INDIVIDUALLY


                                        ----------------------------------------
                                        JOHN W. STIMPSON, AS TRUSTEE UNDER THE
                                        WILL OF HARRY F. STIMPSON, AND NOT
                                        INDIVIDUALLY


                                        ----------------------------------------
                                        J. LOUIS NEWELL, AS TRUSTEE UNDER THE
                                        WILL OF HARRY F. STIMPSON, AND NOT
                                        INDIVIDUALLY


                                       20