<PAGE>   1
                                                                   EXHIBIT 10.22

                                      LEASE


                                45 Sidney Street

                                       and

                                75 Sidney Street

                            Cambridge, Massachusetts


                                    LANDLORD
                              FC 45/75 SIDNEY, INC.


                                     TENANT
                        MILLENNIUM PHARMACEUTICALS, INC.




                            Dated: November 17, 1997
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                                Table of Contents

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ARTICLE I

         RECITALS AND DEFINITIONS.............................................................................    1
         Section 1.1       Recitals...........................................................................    1
         Section 1.2       Definitions........................................................................    1

ARTICLE II

         PREMISES AND TERM....................................................................................    3
         Section 2.1       Premises...........................................................................    3
         Section 2.2       (a) Appurtenant Rights.............................................................    4
         Section 2.3       Landlord's Reservations............................................................    4
         Section 2.4       Parking; Construction of Garage....................................................    5
         Section 2.5       Commencement Date; Scheduled Rent Commencement Date; Rent
                           Commencement Date..................................................................    6
         Section 2.6       Extension Options..................................................................    7
         Section 2.7       Expansion Options..................................................................    9

ARTICLE III

         RENT AND OTHER PAYMENTS..............................................................................   15
         Section 3.1       Annual Fixed Rent..................................................................   15
         Section 3.2       Real Estate Taxes..................................................................   15
         Section 3.3       Operating Expenses.................................................................   18
         Section 3.4       Other Utility Charges..............................................................   21
         Section 3.5       Above-standard Services............................................................   21
         Section 3.6       No Offsets.........................................................................   22
         Section 3.7       Net Lease..........................................................................   22

ARTICLE IV

         ALTERATIONS..........................................................................................   22
         Section 4.1       Consent Required for Tenant's Alterations..........................................   22
         Section 4.2       Ownership of Alterations...........................................................   23
         Section 4.3       Construction Requirements for Alterations..........................................   24
         Section 4.4       Payment for Tenant Alterations.....................................................   25

ARTICLE V

         RESPONSIBILITY FOR CONDITION OF BUILDING AND PREMISES................................................   25
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                                      (i)
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         Section 5.1       Maintenance of Building and Common Areas by Landlord...............................   25
         Section 5.2       Maintenance of Premises by Tenant..................................................   26
         Section 5.3       Tenant-Provided Services...........................................................   26
         Section 5.4       Delays in Landlord's Services......................................................   27
         Section 5.5       Tenant's Responsibilities Regarding Hazardous Materials............................   27
         Section 5.6       Landlord's Responsibilities Regarding Hazardous Materials..........................   28
         Section 5.7       Cross Indemnification..............................................................   28

ARTICLE VI

         TENANT COVENANTS.....................................................................................   29
         Section 6.1       Permitted Uses.....................................................................   29
         Section 6.2       Laws and Regulations...............................................................   29
         Section 6.3       Rules and Regulations; Signs.......................................................   29
         Section 6.4       Safety Compliance..................................................................   30
         Section 6.5       Landlord's Entry...................................................................   30
         Section 6.6       Floor Load.........................................................................   31
         Section 6.7       Personal Property Tax..............................................................   31
         Section 6.8       Assignment and Subleases...........................................................   31

ARTICLE VII

         INDEMNITY AND INSURANCE..............................................................................   34
         Section 7.1       Indemnity..........................................................................   34
         Section 7.2       Liability Insurance................................................................   35
         Section 7.3       Personal Property at Risk..........................................................   35
         Section 7.4       Landlord's Insurance...............................................................   36
         Section 7.5       Waiver of Subrogation..............................................................   36
         Section 7.6       Policy Requirements................................................................   36

ARTICLE VIII

         CASUALTY AND EMINENT DOMAIN..........................................................................   36
         Section 8.1       Restoration Following Casualties; Termination for Failing to Maintain
                           Parking............................................................................   36
         Section 8.2       Landlord's Termination Election....................................................   37
         Section 8.3       Tenant's Termination Election......................................................   37
         Section 8.4       Casualty at Expiration of Lease....................................................   38
         Section 8.5       Eminent Domain.....................................................................   38
         Section 8.6       Rent After Casualty or Taking......................................................   39
         Section 8.7       Temporary Taking...................................................................   39
         Section 8.8       Taking Award.......................................................................   39
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                                      (ii)
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ARTICLE IX

         DEFAULT..............................................................................................   40
         Section 9.1       Tenant's Default...................................................................   40
         Section 9.2       Damages............................................................................   41
         Section 9.3       Cumulative Rights..................................................................   41
         Section 9.4       Landlord's Self-help...............................................................   42
         Section 9.5       Enforcement Expenses; Litigation...................................................   42
         Section 9.6       Late Charges and Interest on Overdue Payments......................................   42
         Section 9.7       Landlord's Right to Notice and Cure; Tenant's Self-Help Rights.....................   43

ARTICLE X

         MORTGAGEES' AND GROUND LESSORS' RIGHTS...............................................................   43
         Section 10.1      Subordination......................................................................   43
         Section 10.2      Prepayment of Rent not to Bind Mortgagee...........................................   44
         Section 10.3      Tenant's Duty to Notify Mortgagee: Mortgagee's Ability to Cure.....................   44
         Section 10.4      Estoppel Certificates..............................................................   44

ARTICLE XI

         SECURITY DEPOSIT.....................................................................................   46

ARTICLE XII

         MISCELLANEOUS........................................................................................   49
         Section 12.1      Notice of Lease....................................................................   49
         Section 12.2      Notices............................................................................   49
         Section 12.3      Successors and Limitation on Liability.............................................   49
         Section 12.4      Waivers by the Landlord............................................................   50
         Section 12.5      Acceptance of Partial Payments of Rent.............................................   50
         Section 12.6      Interpretation and Partial Invalidity..............................................   50
         Section 12.7      Quiet Enjoyment....................................................................   50
         Section 12.8      Brokerage..........................................................................   51
         Section 12.9      Surrender of Premises and Holding Over.............................................   51
         Section 12.10     Ground Lease.......................................................................   51
         Section 12.11     Financial Reporting................................................................   52
         Section 12.12     Cambridge Employment Plan..........................................................   52
         Section 12.13     Truck Delivery Routes; Traffic Mitigation Measures.................................   52
         Section 12.14     Laboratory Animals.................................................................   52
         Section 12.15     No Consequential Damages...........................................................   52
         Section 12.16     Governing Law......................................................................   53
         Section 12.17     Termination Rights for Failure of Conditions.......................................   53
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                                     (iii)
<PAGE>   5
EXHIBIT A          -  Basic Lease Terms
EXHIBIT B          -  Legal Description
EXHIBIT B-1        -  Depiction of Premises
EXHIBIT B-2        -  Map of University Park
EXHIBIT B-3        -  Preferred Expansion Space
EXHIBIT C          -  Work Letter
EXHIBIT D          -  Standard Services
EXHIBIT D-1        -  Allocation of Maintenance and Repair Services
EXHIBIT E          -  Rules and Regulations
EXHIBIT F          -  Standard Tenant System Allocations and Capacities
EXHIBIT G          -  Measurement Method
EXHIBIT H          -  Form of MIT Non-Disturbance Agreement
EXHIBIT I          -  Form of Lender's SNDA
EXHIBIT J          -  Dispute Resolution Process
EXHIBIT K          -  Construction Lender's SNDA
EXHIBIT L          -  Millennium Completion Guaranty


                                      (iv)
<PAGE>   6
                                      LEASE


                                    ARTICLE I

                            RECITALS AND DEFINITIONS

      Section 1.1 Recitals. This Lease (this "Lease") is entered into this 17th
day of November, 1997 by and between FC 45/75 Sidney, Inc. (the "Landlord"), a
Massachusetts corporation, and Millennium Pharmaceuticals, Inc. (the "Tenant"),
a Delaware corporation.

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

      Section 1.2 Definitions. The following terms shall have the meanings
indicated or referred to below:

      "Additional Rent" means all charges payable by the Tenant pursuant to this
Lease other than Annual Fixed Rent, including without implied limitation the
Tenant's parking charges as provided in Section 2.4; the Tenant's Tax Expense
Allocable to the Premises as provided in Section 3.2; the Tenant's Operating
Expenses Allocable to the Premises in accordance with Section 3.3; amounts
payable to Landlord for separately submetered utilities and services pursuant to
Section 3.4; amounts payable for special services pursuant to Section 3.5; costs
for alterations or additions to the Original Premises exceeding the Tenant's
Allowance (as described in the Work Letter); and the Landlord's share of any
sublease or assignment proceeds pursuant to Section 6.8.

      "Annual Fixed Rent" - See Exhibit A, and Section 3.1.

      "Base Building Improvements" - See the Workletter.

      "Building" means collectively the building located at 45 Sidney Street,
Cambridge, Massachusetts (the "45 Sidney Building") and the building located at
75 Sidney Street, Cambridge, Massachusetts (the "75 Sidney Building"), in which
the Premises are located.

      "Commencement Date" - See Section 2.5.

      "Common Building Areas" means those portions of the Building which are not
part of the Premises and to which the Tenant has appurtenant rights pursuant to
Section 2.2.

      "Consolidated Net Available Cash" - See Section 11.4.

      "Expansion Premises" - See Section 2.7.

      "Extension Term" - See Section 2.6.

      "Excusable Delay" - See the Workletter.
<PAGE>   7
      "External Causes" means, when referring to a party's responsibilities
under this Lease, collectively (i) Acts of God, war, civil commotion, fire,
flood or other casualty, strikes or other extraordinary labor difficulties,
shortages of labor or materials or equipment in the ordinary course of trade,
extraordinary weather conditions, government order or regulations or other cause
not reasonably within the control of such party, and not due to the fault or
neglect of such party, and (ii) any act, failure to act or neglect of the other
party or the other party's servants, agents, employees, licensees or, which in
the case of the Tenant shall include, without limitation, its sublessees,
licensees or other occupants deriving their rights under Tenant, which delays
such party in the performance of any act required to be performed by such party
under this Lease.

      "First Rent Commencement Date" - The earlier of the Rent Commencement Date
with respect to the 75 Sidney Building or the Rent Commencement Date with
respect to the 45 Sidney Building.

      "Initial Term" - See Exhibit A.

      "Land" means the parcels of land situated in Cambridge, Massachusetts,
described in Exhibit B.

      "Landlord's Original Address" - See Exhibit A.

      "Lease Year" means each period of one year during the Term commencing on
the First Rent Commencement Date or on any anniversary thereof.

      "Leasehold Improvements" - See the Workletter.

      "Net Working Capital" - See Section 11.4.

      "Original Premises" - See Exhibit A.

      "Permitted Uses" - See Exhibit A.

      "Premises" means that portion of the Building which the Tenant is leasing
at any given time pursuant to the provisions of this Lease. See Exhibit A and
Section 2.1.

      "Property" means the Land and the Building.

      "Removable Alterations" - See Section 4.2.

      "Rent Commencement Date" - See Section 2.5.

      "Scheduled Rent Commencement Date" - See Exhibit A.

      "Substantial Completion" - See the Workletter.


                                       2
<PAGE>   8
      "Tenant's Original Address" - See Exhibit A.

      "Term" means the Initial Term together with any Extension Term for which
an extension option is timely exercised by the Tenant under Section 2.6.

      "University Park" means the area in Cambridge, Massachusetts, bounded on
the Northside by Massachusetts Avenue, Green and Blanche Streets, on the East
side by Lansdowne, Cross and Purrington Streets, on the South side by Pacific
Street and on the West side by Brookline Street.

      "Work Letter" means the letter agreement of even date herewith between the
Landlord and Tenant relating to the construction of the Building and the
leasehold improvements in the Premises attached hereto and made a part hereof as
Exhibit C.


                                   ARTICLE II

                                PREMISES AND TERM

      Section 2.1 Premises. The Landlord hereby leases to the Tenant, and the
Tenant hereby leases from the Landlord, for the Term, the Original Premises. The
Premises shall exclude the entry and main lobby of the Building, first floor
elevator lobby, first floor mail room, the common stairways and stairwells,
elevators and elevator wells, sprinklers, sprinkler rooms, elevator rooms,
mechanical rooms, loading and receiving areas, electric and telephone closets,
janitor closets, loading docks and bays, rooftop mechanical penthouses to the
extent they house Building equipment, and pipes, ducts, conduits, wires and
appurtenant fixtures and equipment serving exclusively or in common other parts
of the Building. If the Premises at any time includes less than the entire
rentable floor area of any floor of the Building, the Premises shall also
exclude the common corridors, vestibules, elevator lobby and toilets located on
such floor. At any time during which the Premises includes the entire rentable
floor area of the 75 Sidney Building or the 45 Sidney Building or both of such
buildings, then with respect to the building(s) the rentable floor area of which
is fully leased by the Tenant, the Premises shall also include the following
otherwise common areas: the entry and main lobby of such building, first floor
elevator lobby, first floor mailroom, the common stairways and stairwells,
elevators and elevator wells, rooftop mechanical penthouse areas to the extent
they serve the remainder of the Premises exclusively, loading and receiving
areas, loading docks and bays, and pipes, ducts, conduits, wires and appurtenant
fixtures and equipment servicing exclusively such building. The Tenant
acknowledges that, except as expressly set forth in this Lease, there have been
no representations or warranties made by or on behalf of the Landlord with
respect to the Premises, the Building or the Property or with respect to the
suitability of any of them for the conduct of the Tenant's business. Promptly
following the First Rent Commencement Date, the Landlord shall deliver to the
Tenant a statement from the Landlord's architect setting forth the rentable
floor area of the Premises and the total rentable floor area of the Building as
computed in accordance with Exhibit G. The Landlord and the Tenant shall, after
such determination at the request of either party, confirm in writing the
rentable square feet of floor area in the Premises, rentable square


                                       3
<PAGE>   9
feet of floor area in the Building, initial Annual Fixed Rent and the total
number of parking spaces guaranteed to the Tenant hereunder.

      Section 2.2 (a) Appurtenant Rights. Subject to the provisions of Section
2.1, at any time during which the Premises does not include the entire rentable
floor area of either the 75 Sidney Building or the 45 Sidney Building, the
Tenant shall have as to such building as appurtenant to the Premises, the
nonexclusive right to use in common with others, subject to reasonable rules of
general applicability to occupants of the Building from time to time made by the
Landlord of which the Tenant is given notice, the following areas and facilities
in such building: (i) the entry, vestibules and main lobby of the Building,
first floor mailroom, the common stairways, elevators, elevator wells, elevator
rooms, sprinkler rooms, mechanical rooms, electric and telephone closets,
janitor closets, loading docks and bays, and the pipes, sprinklers, ducts,
conduits, wires and appurtenant fixtures and equipment serving the Premises in
common with others, (ii) common walkways and driveways necessary or reasonably
convenient for access to the Building, (iii) access to loading area and freight
elevator subject to rules and regulations then in effect, and (iv) if the
Premises at any time include less than the entire rentable floor area of any
floor, the common toilets, corridors, vestibules, and elevator lobby of such
floor.

      If the Tenant occupies the entire rentable floor area of the 75 Sidney
Building, the entire rentable floor area of the 45 Sidney Building or both, then
with respect to the fully occupied building(s) only, the Tenant shall have the
right to install a controlled access system reasonably approved by the Landlord
controlling access to all elevators, stairwells and roof areas of such building;
provided, however, that the Landlord shall at all times have access to the
Building and the Premises, as contemplated under Section 2.3 and Section 6.5.

      (b) Roof Rights. The Tenant shall have, as appurtenant to the Premises
(and exclusively for use in connection with the occupancy of the Premises), the
nonexclusive right of access to and use of the roof for the purpose of
installing and maintaining mechanical equipment, antennae and dishes which, in
each case, have been pre-approved by the Landlord as part of the initial
construction of the Building or as otherwise approved by the Landlord under
Article IV, subject however, to reasonable rules of general applicability to
occupants of the Building from time to time made by the Landlord of which the
Tenant is given notice, but only to the extent that the Tenant has assumed
responsibility for maintenance and repair of certain Building equipment and
mechanical systems serving exclusively the Premises pursuant to Section 5.2.

      Section 2.3 Landlord's Reservations. The Landlord reserves the right from
time to time, without unreasonable interference with the Tenant's use (including
the specialized needs of Tenant's operations which Landlord hereby
acknowledges): (a) to access, install, use, maintain, repair, replace and
relocate for service to the Premises and other parts of the Building, or either,
pipes, ducts, conduits, wires and appurtenant fixtures and equipment, wherever
located in the Premises or the Building, and (b) to alter or relocate any other
common facility provided that substitutions are substantially equivalent or
better. Any such actions taken by the Landlord shall be without undue
interference by the Tenant so long as such actions are: (i) consistent with the
Tenant's reasonable security requirements, (ii) carried out at times reasonably
satisfactory to the


                                       4
<PAGE>   10
Tenant, (iii) effected in a good and workmanlike manner, and (iv) at no
additional cost to the Tenant.

      Section 2.4 Parking; Construction of Garage. The Landlord shall provide
and the Tenant shall pay for parking privileges for use by the Tenant's
employees and business invitees and visitors in accordance with Exhibit A. The
Landlord shall use diligent, good faith efforts to cause to be constructed on or
before the First Rent Commencement Date, and shall operate, or cause to be
operated, at the location depicted on Exhibit B-2, a first-class parking garage
(the "101 Pacific Street Garage") to serve the Building and other buildings. In
the event the 101 Pacific Street Garage is not completed on or before the First
Rent Commencement Date, the Landlord shall designate alternative temporary
parking at one or more of the locations shown on Exhibit B-2 for the Tenant's
use until the 101 Pacific Street Garage is completed. Such temporary parking
shall include the number of parking spaces guaranteed by the Landlord to the
Tenant in Exhibit A, and shall be maintained in good order and repair together
with security comparable to other parking areas provided in the University Park
development. If such temporary parking includes surface parking spaces, the
charge for each surface space shall be the lesser of: (a) the market rate for
comparable surface parking spaces in the City of Cambridge, or (b) whatever
amount the Landlord charges for comparable surface parking spaces within
University Park. When the 101 Pacific Street Garage is completed, the Landlord
shall relocate any parking spaces contemplated under Exhibit A to be located in
the 101 Pacific Street Garage to such garage. The Tenant's parking privileges
shall be on a nonexclusive basis (i.e., no reserved spaces); provided, however,
the Landlord agrees that the 101 Pacific Street Garage, upon completion, shall
be operated so as to maintain therein sufficient spaces to accommodate the
Tenant's parking privileges described in Exhibit A. The Tenant agrees that it
and all persons claiming by, through and under it, shall at all times abide by
the reasonable rules and regulations promulgated by the Landlord, of which the
Tenant is given written notice, with respect to the use of the parking
facilities provided by the Landlord pursuant to this Lease.

      Charges for the Tenant's parking privileges hereunder shall constitute
Additional Rent and shall be payable monthly to the Landlord, during the Term,
from and after (i) the First Rent Commencement Date with respect to two (2)
parking spaces per 1,000 rsf of floor area in the portion of the Premises
demised as of the First Rent Commencement Date and (ii) from and after the Rent
Commencement Date with respect to the remaining floor area in the Premises with
respect to the remaining parking spaces to which reference is made in Exhibit A,
at the time and in the fashion in which Annual Fixed Rent under this Lease is
payable. At the option of the Landlord, the Tenant shall enter into a separate
lease agreement for such parking rights upon the same terms and conditions
contained in this Lease (and cross-defaulted, both as to the Landlord's and
Tenant's obligations, with this Lease) for a period which shall have the same
expiration date as the Term and which, if this Lease provides for options on the
part of the Tenant to extend, shall be automatically extended upon the exercise
of any of such options.

      At any time during the Term the Landlord shall have the right to assign
the Landlord's obligations to provide parking, as herein set forth, together
with the Landlord's right to receive Additional Rent for such parking spaces as
herein provided, to a separate entity created for the purpose of providing the
parking privileges set forth herein. In such event, the Landlord and the


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<PAGE>   11
Tenant agree to execute and deliver appropriate documentation, including
documentation with the new entity, reasonably necessary to provide for the new
entity to assume the Landlord's obligations to provide the parking privileges to
the Tenant as specified herein and for the Tenant to pay the Additional Rent
attributable to the parking privileges directly to the new entity, provided,
however, the Landlord shall at all times remain obligated to the Tenant for the
Tenant's parking privileges hereunder as an obligation of the Landlord under
this Lease, notwithstanding that a new entity is providing the same to the
Tenant pursuant to separate documentation.

      Section 2.5 Commencement Date; Scheduled Rent Commencement Date; Rent
Commencement Date. "Commencement Date" means the date on which the Tenant is
first provided access to any portion of the Premises for the construction of the
Leasehold Improvements. "Scheduled Rent Commencement Date" for each of the 75
Sidney Building and the 45 Sidney Building shall be the respective dates
specified therefor in Exhibit A hereto. "Rent Commencement Date" for each of the
75 Sidney Building and the 45 Sidney Building shall mean the earlier of (i) the
Scheduled Rent Commencement Date therefor specified in Exhibit A hereto or (ii)
the date upon which the Tenant commences occupancy for the conduct of business
of fifty percent (50%) or more of the rentable square footage of the Premises
located therein ("Commencement of Occupancy"). Notwithstanding the foregoing,
upon the following terms and conditions, but not otherwise, if (i) the Tenant is
delayed beyond the Scheduled Rent Commencement Date set forth in Exhibit A
hereto in its construction of the Leasehold Improvements, or the Landlord is
delayed beyond the Scheduled Rent Commencement Date set forth in Exhibit A
hereto in causing Substantial Completion of the Base Building Improvements, and
(ii) that to the extent of such delay, the Tenant cannot occupy the Premises in
the building in question, there shall be a postponement of the Scheduled Rent
Commencement Date and/or the Rent Commencement Date as follows:

            (a) if the cause of such delay is Excusable Delay other than Tenant
      Delay affecting the Substantial Completion of the Base Building
      Improvements, then the Scheduled Rent Commencement Date shall be postponed
      by the number of days such right to occupancy is so delayed on account of
      such Excusable Delay; and

            (b) if the cause of such delay is Landlord Delay affecting the
      Substantial Completion of the Base Building Improvements or construction
      by the Tenant of the Leasehold Improvements, then (i) the Scheduled Rent
      Commencement Date shall be postponed by the number of days such right to
      occupy is so delayed on account of such Landlord Delay and (ii) the Tenant
      shall be entitled to commence occupancy of the portions of the Premises in
      question for the conduct of its business, without triggering the
      occurrence of the Rent Commencement Date with respect to the building in
      question, for one (1) day for each day the Tenant's right to occupy was so
      delayed on account of such Landlord Delay.


                                       6
<PAGE>   12
Notwithstanding the foregoing, in no event shall the Rent Commencement Date
occur sooner than 225 days following the Tenant Construction Readiness Date
unless the conditions to the Commencement of Occupancy by the Tenant have been
achieved, whereupon the Rent Commencement Date shall occur, subject to clause
(b) above.

Without limitation of the foregoing, there shall be no postponement of the
Scheduled Rent Commencement Date or the Rent Commencement Date to the extent
Substantial Completion of the Base Building Improvements is delayed on account
of Tenant Delay (there would, however, be a postponement of the Scheduled Rent
Commencement Date to the extent Substantial Completion of the Base Building
Improvements is delayed on account of Excusable Delay or Landlord Delay), nor
shall there be any postponement of the Scheduled Rent Commencement Date or the
Rent Commencement Date to the extent Tenant's construction of the Leasehold
Improvements is delayed due to Excusable Delay or Tenant Delay. The postponement
of the Rent Commencement Date, set forth in clause (b) above, shall constitute
the sole and liquidated damages with respect to damages associated with any
delay in the Tenant's ability to occupy the Premises by virtue of Landlord Delay
and, except as expressly otherwise provided in Article 9 of the Workletter, the
Tenant shall have no right to terminate this Lease on account thereof. Nothing
in this paragraph is intended to derogate from Tenant's right to terminate this
Lease under Section 12.17(e).

      Section 2.6 Extension Options. Provided that there has been no Event of
Default which is uncured and continuing on the part of the Tenant and the Tenant
is, as of the date of exercise and as of the commencement date of each Extension
Term, actually occupying at least sixty percent (60%) of the Premises for its
own business purposes, the Tenant shall have the right to extend the Term hereof
for two (2) successive periods of five (5) years each (each such five (5) year
period an "Extension Term") on the following terms and conditions:

            (a) Such right to extend the Term shall be exercised by the giving
      of notice by Tenant to Landlord at least twelve (12) months prior to the
      expiration of the Initial Term or the then current Extension Term, as
      applicable. Upon the giving of such notice, this Lease and the Term hereof
      shall be extended for an additional term of five (5) years without the
      necessity for the execution of any additional documents except a document
      memorializing the Annual Fixed Rent for the Extension Term to be
      determined as set forth below. Time shall be of the essence with respect
      to the Tenant's giving notice to extend the Term. In no event may the
      Tenant extend the Term under this Section 2.6 for more than ten (10) years
      after the expiration of the Initial Term.

            (b) Each Extension Term shall be upon all the terms, conditions and
      provisions of this Lease except the Annual Fixed Rent during each five (5)
      year Extension Term shall be the then Extension Fair Rental Value of the
      Premises for such Extension Term to be determined under Section 2.6(c)
      below, but in no case less than the Annual Fixed Rent that was applicable
      thereto immediately preceding the Extension Term with respect to which the
      Extension Fair Rental Value is to be established (the "Then Applicable
      Annual Fixed Rental Rate"). If the Tenant makes a written request to the
      Landlord for a proposal for the Extension Fair Rental Value for an
      Extension Term,


                                       7
<PAGE>   13
      the Landlord shall make such a written proposal to the Tenant within
      thirty (30) days after receipt of the Tenant's request therefor, but in no
      event shall the Landlord be required to deliver such a proposal sooner
      than fifteen (15) months prior to the date as of which such proposal is to
      become effective. Alternatively, the Landlord may, at its election,
      propose an Extension Fair Rental Value to the Tenant without any request
      having been made.

            (c) For purposes of this Section 2.6, the Extension Fair Rental
      Value of the Premises shall mean the then current fair market annual rent
      for leases of other space similarly improved, taking into account the
      condition to which such premises have been improved (excluding Removable
      Alterations) and the economic terms and conditions specified in this Lease
      that will be applicable thereto, including the savings, if any, due to the
      absence or reduction of brokerage commissions. The Landlord and the Tenant
      shall endeavor to agree upon the Extension Fair Rental Value of the
      Premises within forty five (45) days after the Tenant has exercised an
      option for an Extension Term. If the Extension Fair Rental Value of the
      Premises is not agreed upon by the Landlord and the Tenant within this
      time frame, each of the Landlord and the Tenant shall retain a real estate
      professional with at least ten (10) years continuous experience in the
      business of appraising or marketing similar commercial real estate in the
      Cambridge, Massachusetts area who shall, within thirty (30) days of his or
      her selection, prepare a written report summarizing his or her conclusion
      as to the Extension Fair Rental Value. The Landlord and the Tenant shall
      simultaneously exchange such reports; provided, however, if either party
      has not obtained such a report within ninety (90) days after the last day
      of the forty-five (45) day period referred to above in this Section
      2.6(c), then the determination set forth in the other party's report shall
      be final and binding upon the parties. If both parties receive reports
      within such time and the lower determination is within ten percent (10%)
      of the higher determination, then the average of these determinations
      shall be deemed to be the Extension Fair Rental Value for the Premises. If
      these determinations differ by more than ten percent (10%), then the
      Landlord and the Tenant shall mutually select a person with the
      qualifications stated above (the "Final Professional") to resolve the
      dispute as to the Extension Fair Rental Value for the Premises. If the
      Landlord and the Tenant cannot agree upon the designation of the Final
      Professional within thirty (30) days of the exchange of the first
      valuation reports, either party may apply to the American Arbitration
      Association, the Greater Boston Real Estate Board, or any successor
      thereto, for the designation of a Final Professional. Within ten (10) days
      of the selection of the Final Professional, the Landlord and the Tenant
      shall each submit to the Final Professional a copy of their respective
      real estate professional's determination of the Extension Fair Rental
      Value for the Premises. The Final Professional shall not perform his or
      her own valuation, but rather shall, within thirty (30) days after such
      submissions, select the submission which is closest to the determination
      of the Extension Fair Rental Value for the Premises which the Final
      Professional would have made acting alone. The Final Professional shall
      give notice of his or her selection to the Landlord and the Tenant and
      such decision shall be final and binding upon the Landlord and the Tenant.
      Each party shall pay the fees and expenses of its real estate professional
      and counsel, if any, in connection with any proceeding under this
      paragraph, and one-half of the fees and 


                                       8
<PAGE>   14
      expenses of the Final Professional. In the event that the commencement of
      the Extension Term occurs prior to a final determination of the Extension
      Fair Rental Value therefor (the "Extension Rent Determination Date"), then
      the Tenant shall pay the Annual Fixed Rent at the greater of (i) the rate
      specified by the Landlord in its proposed Extension Fair Rental Value or
      (ii) the Then Applicable Fixed Rental Rate. If the Annual Fixed Rent for
      the Extension Term is determined to be greater than the Annual Fixed Rent
      paid with respect to the Premises prior to the Extension Rent
      Determination Date, then the Tenant shall pay to the Landlord the amount
      of such underpayment within ten (10) days of the Expansion Rent
      Determination Date, and if the Annual Fixed Rent for the Extension Term is
      determined to be less than the Annual Fixed Rent paid with respect to the
      Premises prior to the Extension Rent Determination Date, then the Landlord
      shall credit the amount of such overpayment against the monthly
      installments of Annual Fixed Rent thereafter coming due.

      Section 2.7 Expansion Options. Provided that there has been no Event of
Default which is uncured and continuing on the part of the Tenant and the Tenant
is, as of the date of exercise of its rights under this Section 2.7, actually
occupying a minimum of seventy-five percent (75%) of the Premises for its own
business purposes, Tenant shall have the following rights with respect to the
remaining space in the Building not included in the Premises at any given time
(hereinafter the "Expansion Space"):

            (a) From time to time following the mutual execution and delivery of
      this Lease, upon the request of the Tenant, the Landlord shall inform the
      Tenant of the progress the Landlord is making regarding the initial
      leasing of the Expansion Space to third parties. Additionally, the
      Landlord shall give the Tenant not less than ten (10) business days'
      advance written notice prior to making any bona fide formal lease proposal
      to a prospective third party tenant for any of the Preferred Expansion
      Space (as defined in Section 2.7(b)) identified on Exhibit B-3 attached
      hereto and not less than five (5) business days' advance written notice
      prior to making any bona fide formal lease proposal to a prospective third
      party tenant for all other space in the 45 Sidney Building not part of
      such Preferred Expansion Space, each such notice being hereinafter
      referred to as a "Landlord's Prospect Notice;" provided, however, the
      Landlord shall not offer any space on the balance of the fourth floor of
      the 45 Sidney Building not included in the Original Premises or the third
      floor of the 45 Sidney Building (such space being hereinafter referred to
      as the "Early Expansion Space") to potential third party tenants until
      after November 1, 1997. Unless and until the Landlord, after expiration of
      the five (5) or ten (10) day advance notice period, as applicable, has
      entered into either a letter of intent (but only if such letter of intent
      is formalized thereafter as a binding lease between the Landlord and the
      other party to such letter of intent) or a lease with a third party for
      any of the Expansion Space ("Third Party Commitment"), but subject to the
      Landlord's right thereafter to enter into a Third Party Commitment during
      the Prospect Negotiation Period specified below in this Section 2.7(a),
      following the mutual execution and delivery of this Lease the Tenant may,
      by written notice to Landlord (the "Initial Expansion Election Notice"),
      elect to lease all or any portion (provided the configuration which the
      Tenant desires is reasonably acceptable to the Landlord) of the Expansion
      Space that has


                                       9
<PAGE>   15
      not earlier been made subject of a Third Party Lease pursuant to this
      Section 2.7(a). Tenant's election to lease any Expansion Space that falls
      within the scope of a Landlord's Prospect Notice must, in order to qualify
      as a validly exercised election, be an election to lease all of the square
      footage specified in such Landlord's Prospect Notice. With respect to any
      Expansion Space that is incorporated into the Premises under this Section
      2.7(a), the terms and conditions applicable to such Expansion Space shall
      be the same terms and conditions set forth in this Lease except for the
      Tenant Allowance and Annual Fixed Rent payable with respect thereto, which
      shall instead be, respectively: (i) $25.00 per square foot for the Tenant
      Allowance and the Expansion Fair Rental Value of such Expansion Space,
      determined in accordance with Section 2.7(f) below for the Annual Fixed
      Rent, with respect to all space not part of the Early Expansion Space or
      any portion of the Early Expansion Space for which the Landlord has not
      received from the Tenant an Initial Expansion Election Notice on or before
      November 1, 1997; or (ii) $50.00 per square foot for the Tenant Allowance
      and $30.00 per rentable square foot for Lease Years one (1) through five
      (5) and $33.00 per rentable square foot for Lease Years six (6) through
      fifteen (15) for the Annual Fixed Rent, with respect to any portion of the
      Early Expansion Space for which the Landlord has received from the Tenant
      an Initial Expansion Election Notice on or before November 1, 1997.
      However, if all or any part of the Expansion Space specified in the
      Initial Expansion Election Notice given by the Tenant includes space
      specified in a Landlord's Prospect Notice with respect to which the Tenant
      did not timely elect to lease, then any Initial Expansion Election Notice
      shall be subject to the Landlord reaching a Third Party Commitment for
      such space with the party (or any affiliate thereof) to whom reference is
      made in Landlord's Prospect Notice until the date which is sixty (60) days
      after the expiration of the Tenant's five (5) or ten (10) day advance
      notice period, as applicable, (such period being hereinafter referred to
      as the "Prospect Negotiation Period"). If the Tenant elects to lease any
      Expansion Space under this Section 2.7(a), the Tenant shall begin to pay
      Annual Fixed Rent and Additional Rent allocable to such Expansion Space on
      the later to occur of: (i) the date which is one hundred twenty (120) days
      after the Landlord receives the Tenant's Initial Expansion Election
      Notice, or (ii) the Rent Commencement Date. At any time prior to the
      Landlord receiving from the Tenant an Initial Expansion Election Notice as
      hereinbefore provided, but always after the five (5) or ten (10) day
      advance notice period, as applicable, the Landlord may lease (the "Initial
      Third Party Lease") all or any part of such Expansion Space to one or more
      third parties (the "Initial Third Party Tenants") without notice to or
      approval from the Tenant, provided, however, that any request for
      information made by the Tenant for information regarding the progress the
      Landlord is making in the initial leasing of the Expansion Space to third
      parties shall specify the expiration date of the term of each such Initial
      Third Party Lease and the part of such Expansion Space which is subject to
      each such Initial Third Party Lease. In the event the Landlord enters into
      any Initial Third Party Lease(s), the remainder of the Expansion Space not
      so leased to Initial Third Party Tenants shall remain subject to the
      Tenant's rights under this Section 2.7(a).

            (b) The Landlord agrees that, in the Landlord's negotiation of any
      Initial Third Party Lease, or any subsequent third party lease
      (collectively a "Third Party Lease"), which relates to approximately
      25,000 rentable square feet of the Expansion 


                                       10
<PAGE>   16
      Space located on the first and fourth floors of the 45 Sidney Building and
      identified on the plan attached hereto as Exhibit B-3 (such space being
      hereinafter referred to as the "Preferred Expansion Space"), the Landlord
      shall not permit the expiration date thereof to extend beyond the last day
      of the seventh Lease Year of this Lease.

            (c) From time to time during the Term of this Lease, upon the
      request of the Tenant, the Landlord shall provide to the Tenant a list of
      all Third Party Leases, including the location of the spaces so leased and
      the date of expiration of each such Third Party Lease. The Tenant shall
      have the right of first opportunity to lease the Expansion Space
      (including, without limitation, the Preferred Expansion Space) which is
      subject to a Third Party Lease effective upon the earlier of the
      expiration or earlier termination of the term of such Third Party Lease.
      With respect to the Preferred Expansion Space only, should any such space
      become available after the last day of the fourth Lease Year of this
      Lease, and Tenant fails to timely exercise its right to incorporate such
      space into the Premises under this Section 2.7(c), then the Tenant shall
      be deemed to have waived its option to incorporate such space into the
      Premises under Section 2.7(d). The Tenant shall exercise its right to
      incorporate into the Premises any Expansion Space which has been earlier
      made subject to a Third Party Lease under this Section 2.7(c) as follows:
      the Tenant shall give the Landlord written notice of its desire to lease
      such Expansion Space not less than twelve (12) months prior to the date of
      expiration of the term of the Third Party Lease. Not later than ten (10)
      business days following such notice from the Tenant, or in the event the
      Third Party Lease is being terminated prior to the expiration of its term,
      the Landlord shall promptly give written notice to the Tenant (the
      "Expansion Opportunity Notice") describing such Expansion Space, the date
      of its expected availability and the Landlord's proposal for the Expansion
      Fair Rental Value therefor. The Tenant shall, by giving written notice to
      Landlord within ten (10) business days after receipt of the Expansion
      Opportunity Notice, either (i) elect by written notice ("Vacancy Expansion
      Election Notice") to lease such Expansion Space under this Section 2.7(c),
      or (ii) waive its right to lease such Expansion Space under this Section
      2.7(c) until the expiration or earlier termination of the next Third Party
      Lease executed with respect thereto, whereupon the Tenant's rights under
      this Section 2.7(c) shall again apply. If the Tenant does not timely elect
      to exercise its right to lease such Expansion Space under this Section
      2.7(c), by timely giving the Landlord a Vacancy Expansion Election Notice,
      then the Tenant will be deemed to have waived its rights to lease such
      Expansion Space under this Section 2.7(c) and the Landlord may lease such
      Expansion Space without restrictions of any kind; provided, however, that
      the Tenant shall at all times during the Term of this Lease have the right
      of first opportunity to lease such Expansion Space under this Section
      2.7(c) effective upon the earlier of the date of expiration or earlier
      termination of the term of the next and any future Third Party Lease for
      such Expansion Space as provided hereunder.

            If the Tenant timely elects to lease any Expansion Space under this
      Section 2.7(c), such Expansion Space shall be included as part of the
      Premises for purposes of this Lease effective as of the date upon which
      the Third Party Lease expires, is earlier terminated, or such later date
      as the Landlord is able to deliver the space for the Tenant's occupancy,


                                       11
<PAGE>   17
      and the terms and conditions applicable to such Expansion Space shall be
      the same terms and conditions set forth in this Lease except for the
      condition of the space, the Tenant Allowance and the Annual Fixed Rent
      payable with respect thereto. Instead, the Expansion Space shall be
      delivered by the Landlord in a then "as is" condition, there shall be no
      Tenant Allowance and the Annual Fixed Rent with respect thereto shall be
      the Expansion Fair Rental Value therefor as determined in accordance with
      Section 2.7(f) below.

            (d) Unless and to the extent the Tenant has earlier incorporated the
      same into the Premises or waived its option to incorporate the same into
      the Premises under Section 2.7(d) pursuant to the terms and conditions of
      Section 2.7(c), the Tenant shall have the option to incorporate into the
      Premises the Preferred Expansion Space as follows: the Landlord shall give
      the Tenant written notice at least twelve (12) months prior to the
      availability of the Preferred Expansion Space (the "Preferred Expansion
      Space Notice") setting forth the date of its expected availability and the
      Landlord's proposal for the Expansion Fair Rental Value therefor. The
      Landlord agrees that the aforesaid date of expected availability shall not
      occur earlier than the first day of the fifth (5th) Lease Year nor later
      than the first day of the eighth (8th) Lease Year. The Tenant shall, by
      giving written notice to the Landlord within ten (10) business days after
      receipt of the Preferred Space Expansion Notice, either (i) elect to lease
      such Preferred Expansion Space under this Section 2.7(d) by giving notice
      to the Landlord to such effect, or (ii) waive its right to lease such
      Preferred Expansion Space under this Section 2.7(d) until the expiration
      or earlier termination of the next Third Party Lease executed with respect
      thereto, whereupon the Tenant's rights under Section 2.7(c) shall apply.
      If the Tenant does not timely elect to exercise its right to lease the
      Preferred Expansion Space under this Section 2.7(d), then the Tenant will
      be deemed to have waived its rights to lease such Preferred Expansion
      Space under this Section 2.7(d) and the Landlord may lease such Preferred
      Expansion Space without restrictions of any kind; provided, however, that
      the Tenant shall at all times during the Term of this Lease have the right
      of first opportunity to lease such Preferred Expansion Space effective
      upon the earlier of the date of expiration or earlier termination of the
      term of the next and any future Third Party Lease for such Preferred
      Expansion Space as provided in Section 2.7(c) above.

            If the Tenant timely elects to lease any Preferred Expansion Space,
      under this Section 2.7(d), such Preferred Expansion Space shall be
      included as part of the Premises for purposes of this Lease effective as
      of the date upon which the Third Party Lease expires, is earlier
      terminated (but in no event shall the effective date occur prior to the
      first day of the fifth Lease Year of this Lease), or such later date as
      the Landlord is able to deliver the space for occupancy by the Tenant, and
      the terms and conditions applicable to such Preferred Expansion Space
      shall be the same terms and conditions set forth in this Lease except for
      the condition of the space, the Tenant Allowance and the Annual Fixed Rent
      payable with respect thereto. Instead, Preferred Expansion Space shall be
      delivered by the Landlord in its then "as is" condition, there shall be no
      Tenant Allowance and the Annual Fixed Rent with respect thereto shall be
      the Expansion Fair Rental Value therefor as determined in accordance with
      Section 2.7(f) below.


                                       12
<PAGE>   18
            (e) Notwithstanding anything to the contrary provided herein, if the
      remaining Term of this Lease would be less than five (5) years at the time
      that any Expansion Space is to be incorporated into the Premises pursuant
      to this Section 2.7, the Tenant shall have no right to lease such space
      unless the Tenant elects pursuant to Section 2.6 to extend the Term for
      the next Extension Term. However, if there are no further such Extension
      Terms available to the Tenant under Section 2.6, then the Tenant shall not
      have the right to lease the Expansion Space in question under this Section
      2.7.

            (f) For purposes of this Section 2.7, the Expansion Fair Rental
      Value of Expansion Space shall mean the then current fair market annual
      rent for leases of space improved to the same level as the Premises and
      taking into account the condition to which such premises have been
      improved (excluding Removable Alterations) and the economic terms and
      conditions specified in this Lease that will be applicable thereto (e.g.
      the amount of the fit-up allowance), including the savings, if any, due to
      the absence of brokerage commissions and the absence of any rent-free
      period for construction of leasehold improvements, determined as provided
      below in this Section 2.7(f). The Landlord and the Tenant shall endeavor
      to agree upon the Expansion Fair Rental Value of Expansion Space within
      forty five (45) days after the Tenant's election to lease such Expansion
      Space by giving the Landlord either its Initial Expansion Election Notice
      or its Vacancy Expansion Election Notice, as the case may be (the "Rental
      Determination Commencement Date"). If the Expansion Fair Rental Value of
      such Expansion Space is not agreed upon by the Landlord and the Tenant
      within this time frame, each of the Landlord and the Tenant shall retain a
      real estate professional with at least ten (10) years continuous
      experience in the business of appraising or marketing similar commercial
      real estate in the Cambridge, Massachusetts area who shall, within thirty
      (30) days of his or her selection, prepare a written report summarizing
      his or her conclusion as to the Expansion Fair Rental Value. The Landlord
      and the Tenant shall simultaneously exchange such reports; provided,
      however, if either party has not obtained such a report within ninety (90)
      days after the Rental Determination Commencement Date, then the
      determination set forth in the other party's report shall be final and
      binding upon the parties. If both parties receive reports within such time
      and the lower determination is within ten percent (10%) of the higher
      determination, then the average of these determinations shall be deemed to
      be the Expansion Fair Rental Value for such Expansion Space. If these
      determinations differ by more than ten percent (10%), then the Landlord
      and the Tenant shall mutually select a person with the qualifications
      stated above (the "Final Professional") to resolve the dispute as to the
      Expansion Fair Rental Value for such Expansion Space. If the Landlord and
      the Tenant cannot agree upon the designation of the Final Professional
      within thirty (30) days of the exchange of the first valuation reports,
      either party may apply to the American Arbitration Association, the
      Greater Boston Real Estate Board, or any successor thereto, for the
      designation of a Final Professional. Within ten (10) days of the selection
      of the Final Professional, the Landlord and the Tenant shall each submit
      to the Final Professional a copy of their respective real estate
      professional's determination of the Expansion Fair Rental Value for such
      Space. The Final Professional shall not perform his or her own valuation,
      but rather shall, within thirty (30) days after such submissions, select
      the submission which is closest to the


                                       13
<PAGE>   19
      determination of the Expansion Fair Rental Value for such Expansion Space
      which the Final Professional would have made acting alone. The Final
      Professional shall give notice of his or her selection to the Landlord and
      the Tenant and such decision shall be final and binding upon the Landlord
      and the Tenant. Each party shall pay the fees and expenses of its real
      estate professional and counsel, if any, in connection with any proceeding
      under this paragraph, and one-half of the fees and expenses of the Final
      Professional. In the event that the Tenant commences occupancy of any
      Expansion Space prior to a final determination of the Expansion Fair
      Rental Value therefor (the "Expansion Rent Determination Date"), then the
      Tenant shall pay the Annual Fixed Rent at the rate specified in the
      Expansion Opportunity Notice until the Expansion Fair Rental Value is
      established. If the Expansion Fair Rental Value is determined to be
      greater than the Annual Fixed Rent paid with respect to the Expansion
      Space prior to the Expansion Rent Determination Date, then the Tenant
      shall pay to the Landlord the amount of such underpayment within ten (10)
      days of the Expansion Rent Determination Date, and if the Expansion Fair
      Rental Value is determined to be less than the Annual Fixed Rent paid with
      respect to the Expansion Space prior to the Expansion Rent Determination
      Date, then the Landlord shall credit the amount of such overpayment
      against the monthly installments of Annual Fixed Rent thereafter coming
      due.

            (g) The Tenant's election to lease any Expansion Space under this
      Section 2.7 shall automatically increase the Premises to include the same
      in accordance herewith. No amendment to this Lease shall be necessary to
      effect the exercise of the Tenant's rights pursuant to this Section 2.7.

            (h) Notwithstanding anything to the contrary contained in this
      Section 2.7, the Landlord may grant to other third party tenants occupying
      space within the Building first priority expansion rights for additional
      space located on the remainder of the first floor of the 45 Sidney
      Building which is not part of the Preferred Expansion Space identified in
      Exhibit B-3 attached hereto, in which case Tenant's right of first
      opportunity to lease such space shall arise only upon the failure of the
      third party tenant to exercise its expansion rights with respect to such
      space prior to the expiration of such third party tenant's lease.

                                   ARTICLE III

                             RENT AND OTHER PAYMENTS

      Section 3.1 Annual Fixed Rent. From and after the First Rent Commencement
Date (as defined in Exhibit A), the Tenant shall pay, without notice or demand,
monthly installments of one-twelfth (1/12th) of the Annual Fixed Rent in effect
and applicable to the Premises in advance for each full calendar month of the
Term following the First Rent Commencement Date and of the corresponding
fraction of said one-twelfth (1/12th) for any fraction of a calendar month at
the First Rent Commencement Date. The Annual Fixed Rent applicable to the
Premises during the Initial Term shall be as set forth in Exhibit A.
Notwithstanding the foregoing, during the period from the First Rent
Commencement Date until the day prior to the


                                       14
<PAGE>   20
occurrence of the Rent Commencement Date with respect to the remaining building
in which the Premises is located, such payments shall be pro rata on the basis
of the portion of the Premises with respect to which the Rent Commencement Date
has occurred.

      Section 3.2 Real Estate Taxes. From and after the First Rent Commencement
Date, during the Term, the Tenant shall pay to the Landlord, as Additional Rent,
the Tenant's Tax Expenses Allocable to the Premises (as such term is hereinafter
defined) in accordance with this Section 3.2. Notwithstanding the foregoing,
during the period from the First Rent Commencement Date until the day prior to
the occurrence of the Rent Commencement Date with respect to the remaining
building in which the Premises is located, such payments shall be pro rata on
the basis of the portion of the Premises with respect to which the Rent
Commencement Date has occurred. The terms used in this Section 3.2 are defined
as follows:

            (a) "Fiscal Year" means the 12-month period beginning February 1
      each year, or such other fiscal period of twelve (12) consecutive months
      hereinafter adopted by Landlord for lease administration purposes.

            (b) "The Tenant's Tax Expense Allocable to the Premises" means (i)
      that portion of the Landlord's Tax Expenses for a Fiscal Year which bears
      the same proportion thereto as the Rentable Floor Area of the Premises
      (from time to time) bears to the Total Rentable Floor Area of the Building
      and (ii) in the event that the Premises are improved to a standard which
      is higher or lower than other portions of the Property, such portion of
      the Real Estate Taxes on the Property with respect to any Fiscal Year as
      is appropriate so that the Tenant bears the portion of the Real Estate
      Taxes which are properly allocable to the Premises, as reasonably
      determined by Landlord based on assessment values and other information
      with respect to the Premises and the Building made available by the
      assessing authorities. If the Tenant disagrees with any adjustment that
      the Landlord has made in its determination of the Tenant's Tax Expense
      Allocable to the Premises by virtue of clause (ii), above, then it shall,
      within sixty (60) days after its receipt of documentation establishing
      Tenant's Tax Expense Allocable to the Premises, send written notice of
      such disagreement to the Landlord. After Landlord's receipt of such
      notice, the Landlord and the Tenant shall have thirty (30) days within
      which to resolve such controversy after which such controversy shall be
      resolved by submittal to the binding Dispute Resolution Process described
      in Exhibit J attached hereto and made a part hereof.

            (c) "The Landlord's Tax Expenses" with respect to any Fiscal Year
      means the aggregate Real Estate Taxes on the Property with respect to that
      Fiscal Year, reduced by any abatement receipts with respect to that Fiscal
      Year.

            (d) "Real Estate Taxes" means (i) all taxes and special assessments
      of every kind and nature assessed by any governmental authority on the
      applicable property; and (ii) reasonable expenses of any proceedings for
      abatement of such taxes or special assessments. Any special assessments to
      be included within the definition of "Real Estate Taxes" shall be limited
      to the amount of the installment (plus any interest thereon) 


                                       15
<PAGE>   21
      of such special tax or special assessment (which shall be payable over the
      longest period permitted by law) required to be paid during the Fiscal
      Year in respect of which such taxes are being determined. The Landlord
      hereby represents and warrants that, as of the date hereof, it has no
      knowledge of any special assessments affecting either the Premises or
      University Park. There shall be excluded from such taxes all income,
      estate, succession, inheritance, excess profit, franchise and transfer
      taxes, all so-called linkage payments and delinquency interest or
      penalties; provided, however, that if at any time during the Term the
      present system of ad valorem taxation of real property shall be changed so
      that in lieu of the whole or any part of the ad valorem tax on real
      property, there shall be assessed on the Landlord a capital levy or other
      tax on the gross rents received with respect to the Property, or a
      federal, state, county, municipal or other local income, franchise, excise
      or similar tax, assessment, levy or charge (distinct from any now in
      effect) based, in whole or in part, upon any such gross rents, then any
      and all of such taxes, assessments, levies or charges, to the extent so
      based, shall be deemed to be included within the term "Real Estate Taxes,"
      based on the Building being the Landlord's only property. There shall also
      be excluded from the definition of "Real Estate Taxes" any taxes on the 75
      Sidney Building or the 45 Sidney Building, to the extent such building is
      occupied entirely by the Tenant as part of the Premises, relating to
      capital improvements not approved by the Tenant; provided, however, that
      Landlord may make any improvements or repairs as it may determine in its
      reasonable discretion are necessary in order to maintain the Building in
      the condition required under Section 5.1, without regard to the tax impact
      of such improvements and repairs.

      Payments by the Tenant on account of the Tenant's Tax Expenses Allocable
to the Premises shall be made monthly at the time and in the fashion herein
provided for the payment of Annual Fixed Rent and shall be in an amount of the
greater of (i) one-twelfth (1/12th) of the Tenant's Tax Expenses Allocable to
the Premises for the current Fiscal Year as reasonably estimated by the
Landlord, or (ii) an amount reasonably estimated by any ground lessor of the
Land or holder of a first mortgage on the Property, to be sufficient, if paid
monthly, to pay the Landlord's Tax Expenses on the dates due to the taxing
authority.

      Not later than ninety (90) days after the Landlord's Tax Expenses are
determinable for the first Fiscal Year of the Term or fraction thereof and for
each succeeding Fiscal Year or fraction thereof during the Term, the Landlord
shall render the Tenant a statement in reasonable detail showing for the
preceding year or fraction thereof, as the case may be, real estate taxes on the
Property, and any abatements or refunds of such taxes. Reasonable expenses
incurred in obtaining any tax abatement or refund not previously charged may be
charged against such tax abatement or refund before the adjustments are made for
the Fiscal Year. If at the time such statement is rendered it is determined with
respect to any Fiscal Year, that the Tenant has paid (i) less than the Tenant's
Tax Expenses Allocable to the Premises or (ii) more than the Tenant's Tax
Expenses Allocable to the Premises, then, in the case of (i) the Tenant shall
pay to the Landlord, as Additional Rent, within fifteen (15) days of such
statement the amount of such underpayment and, in the case of (ii) the Landlord
shall credit the amount of such overpayment against the monthly installments of
the Tenant's Tax Expenses Allocable to the Premises next thereafter 


                                       16
<PAGE>   22
coming due (or refund such overpayment within fifteen (15) days if the Term has
expired and the Tenant has no further obligation to the Landlord).

      To the extent that real estate taxes shall be payable to the taxing
authority in installments with respect to periods less than a Fiscal Year, the
statement to be furnished by the Landlord shall be rendered and payments made on
account of such installments. Notwithstanding the foregoing provisions, no
decrease in Landlord's Tax Expenses with respect to any Fiscal Year shall result
in a reduction of the amount otherwise payable by the Tenant if and to the
extent said decrease is attributable to vacancies in the Building, rather than
to a reduction in the assessed value of the Property as a whole or a reduction
in the tax rate. The Landlord shall so notify the Tenant if a decrease in
Landlord's Tax Expense is attributable to vacancies in the Building as opposed
to a reduction in either the assessed value of the Property or the tax rate. In
such case, the Tenant shall have sixty (60) days after receipt of such notice to
challenge, in writing, the Landlord's contention. Thereafter, the Landlord and
Tenant shall have thirty (30) days within which to resolve the disagreement,
after which such controversy shall be submitted to the binding Dispute
Resolution Process described in Exhibit J. Landlord shall, upon Tenant's request
therefor, provide Tenant with copies of all applicable tax bills, statements,
records and the like, as well as copies of Landlord's calculations and all other
relevant information.

      At the reasonable request of the Tenant, the Landlord shall use reasonable
efforts to contest or seek abatement of any Real Estate Taxes affecting the
Premises. Should the Landlord contest or seek abatement of such taxes, then it
shall do so with diligence and shall keep the Tenant appropriately informed, in
the Landlord's reasonable discretion, as to such action.

      Section 3.3 Operating Expenses. From and after the First Rent Commencement
Date, during the Term the Tenant shall pay to the Landlord, as Additional Rent,
the Tenant's Operating Expenses Allocable to the Premises, as hereinafter
defined, in accordance with this Section 3.3. Notwithstanding the foregoing,
during the period from the First Rent Commencement Date until the day prior to
the occurrence of the Rent Commencement Date with respect to the remaining
building in which the Premises is located, such payments shall be pro rata on
the basis of the portion of the Premises with respect to which the Rent
Commencement Date has occurred. The terms used in this Section 3.3 are defined
as follows:

            (a) "The Tenant's Operating Expenses Allocable to the Premises"
      means that portion of the Operating Expenses for the Property which bears
      the same proportion thereto as the Rentable Floor Area of the Premises
      (from time to time) bears to the Total Rentable Floor Area of the
      Building.

            (b) "Operating Expenses for the Property" means the Landlord's
      reasonable cost of operating, cleaning, maintaining and repairing the
      Property, the roads, driveways and walkways for providing access to the
      Building and shall include without limitation, the cost of fulfilling the
      maintenance and repair obligations required to be performed by Landlord
      under Section 5.1 and the cost of services specified on Exhibit D;
      premiums for insurance carried pursuant to Section 7.4; the reasonable
      amount deductible from any insurance claim of the Landlord; reasonable
      compensation including, without limitation, 


                                       17
<PAGE>   23
      reasonable fringe benefits, worker's compensation insurance premiums and
      payroll taxes paid to, for or with respect to all persons (University
      Park/Building general manager and below) directly engaged in the
      operating, maintaining or cleaning of the Property; interior landscaping
      and maintenance; steam, water, sewer, gas, oil electricity, telephone and
      other utility charges (excluding such utility charges either separately
      metered or separately chargeable to tenants for either measured or
      additional or special services); cost of providing conditioned water for
      HVAC services; cost of building and cleaning supplies; the costs of
      routine environmental management programs operated by Landlord; market
      rental costs for equipment used in the operating, cleaning, maintaining or
      repairing of the Property, or the amortized cost of equipment owned by the
      Landlord; cost of cleaning; cost of maintenance, repairs and replacements
      (other than repairs and replacements reimbursed from contractors under
      guarantees or made by the Landlord pursuant to the Work Letter); cost of
      snow removal; cost of landscape maintenance; security services; payments
      under service contracts with independent contractors; management fees at
      reasonable rates consistent with comparable single-tenant or multi-tenant
      buildings, as applicable, in the Cambridge market with the type of
      occupancy and services rendered; the cost of any capital repair or
      improvement: (i) required by any law or regulation enacted or promulgated
      after the issuance of a building permit for the construction of the
      Building, (ii) which is required in order to maintain the Property in the
      condition it is required to be kept and maintained under Section 5.1
      (excluding those repairs, however, which are necessitated by Landlord's
      negligence or willful misconduct or the errors or omissions by the
      Landlord's base building architect or contractor(s) to the extent such
      errors and omissions are covered by insurance or are otherwise recovered
      by the Landlord), (iii) which reduces the Operating Expenses for the
      Property, or (iv) which improves the management and operation of the
      Property in a manner reasonably acceptable to Tenant (all such capital
      costs to be amortized in accordance with generally accepted accounting
      principles, together with interest on the unamortized balance at the base
      lending rate announced by a major commercial bank designated by the
      Landlord, or such higher rate as may have been paid by the Landlord on
      funds borrowed for the purpose of constructing such capital improvements,
      with only the annual amortization amount being included in Operating
      Expenses with respect to any Fiscal Year); charges equitably and
      reasonably allocated to the Building for the operating, cleaning,
      maintaining, securing and repairing of University Park common areas and
      amenities; and all other reasonable and necessary (in the Landlord's
      reasonable judgment) expenses paid in connection with the operation,
      cleaning, maintenance and repair of the Property. If, for any reason
      portions of the rentable area of the Building not included in the Premises
      were not occupied by tenants or the Landlord was not supplying all tenants
      with the services being supplied under the Lease or any tenants in the
      Building were supplied with a lesser level of standard services than those
      supplied to the Tenant under this Lease, Landlord's Operating Expenses for
      the Property shall include the amounts reasonably determined by Landlord
      which would have been incurred if all of the rentable area in the Building
      were occupied and were supplied with the same level of standard services
      as supplied to the Tenant under this Lease. Likewise, if any tenants in
      the Building were supplied with a higher level of standard services than
      those supplied to the Tenant, Landlord's Operating Expenses for the
      Property shall be reduced to an amount reasonably determined by the


                                       18
<PAGE>   24
      Landlord which would have been incurred if all tenants in the Building
      were supplied with the same level of services as supplied to the Tenant
      under this Lease. Tenant acknowledges that the Building is comprised of
      two (2) distinct buildings, and that one or more of the Operating Expenses
      for the Property may be allocated by Landlord other than based solely on
      the respective square footage in each such building in appropriate
      circumstances if the services with respect to which such Operating
      Expenses relate disproportionally benefit one building or the other (e.g.
      Operating Expenses associated with a lobby attendant located in one
      building but not in the other may be allocated solely to the building in
      which such lobby attendant is located). Any such disproportional
      allocation, however, shall be reasonably determined by the Landlord.

            Operating Expenses for the Property shall not include the following:
      the amortized cost of capital improvements expressly not allowed pursuant
      to the preceding paragraph unless otherwise approved by the Tenant; the
      Landlord's Tax Expense; cost of repairs or replacements (i) resulting from
      eminent domain takings, (ii) to the extent reimbursed by insurance or
      otherwise, (iii) resulting from correcting defects in the work for which
      the Landlord is obligated pursuant to the Work Letter, or (iv) resulting
      from Landlord's negligence or willful misconduct; replacement or
      contingency reserves; ground lease rents or payment of debt obligations;
      legal and other professional fees for matters not relating to the normal
      administration and operation of the Property, such as those fees incurred
      in connection with eviction proceedings and rent collection; promotional,
      advertising, public relations or brokerage fees and commissions paid in
      connection with services rendered for securing or renewing leases; lease
      up and tenant improvement costs for space other than the Premises in the
      Building; interest or penalties for late payments; depreciation and other
      non-cash charges; and separately metered or submetered utilities, which
      will be the subject of separate charges to each of the applicable tenants
      of the Building.

            Notwithstanding anything to the contrary contained in this Section
      3.3(b), the reasonable costs of the Tenant-Provided Services (as defined
      in Section 5.3) shall be excluded from the calculation of the Tenant's
      Operating Expenses Allocable to the Premises.

      Payments by the Tenant for its share of the Operating Expenses for the
Property shall be made monthly at the time and in the fashion herein provided
for the payment of Annual Fixed Rent. The amount so to be paid to the Landlord
shall be an amount from time to time reasonably estimated by the Landlord to be
sufficient to aggregate a sum equal to the Tenant's share of the Operating
Expenses for the Property for each Fiscal Year.

      Not later than one hundred twenty (120) days after the end of each Fiscal
Year or fraction thereof during the Term or fraction thereof at the end of the
Term, the Landlord shall render the Tenant a statement in reasonable detail and
according to usual accounting practices certified by an officer of the Landlord,
showing for the preceding Fiscal Year or fraction thereof, as the case may be,
the Operating Expenses for the Property and the Tenant's Operating Expenses
Allocable to the Premises. Said statement to be rendered to the Tenant also
shall show for the preceding


                                       19
<PAGE>   25
Fiscal Year or fraction thereof, as the case may be, the amounts of Operating
Expenses already paid by the Tenant. If at the time such statement is rendered
it is determined with respect to any Fiscal Year, that the Tenant has paid (i)
less than the Tenant's Operating Expenses Allocable to the Premises or (ii) more
than the Tenant's Operating Expenses Allocable to the Premises, then, in the
case of (i) the Tenant shall pay to the Landlord, as Additional Rent, within
thirty (30) days of such statement the amounts of such underpayment and, in the
case of (ii) the Landlord shall credit the amount of such overpayment against
the monthly installments of the Tenant's Operating Expenses Allocable to the
Premises next thereafter coming due (or refund such overpayment within thirty
(30) days if the Term has expired and the Tenant has no further obligation to
the Landlord).

      The Tenant may examine or audit the accounts and original bills for
Landlord's Operating Expenses upon ten (10) days' prior written notice to the
Landlord, but no more often than one (1) time in any Fiscal Year. The Landlord
agrees that it will make available to the Tenant in the Landlord's office in
University Park, during regular business hours, such information as the Landlord
has available at such office. In similar manner, the Tenant may examine such
further records as the Landlord (or its affiliates) may have, but such matters
will be conducted where the Landlord customarily keeps such records, which may
be at the headquarters of the Landlord's parent company. The Tenant shall bear
the cost of any such audit, unless the same discloses a discrepancy in excess of
three percent (3%) of the Tenant's Operating Expenses Allocable to the Premises,
in which event the Landlord shall reimburse the Tenant for such costs reasonably
incurred. For any given Fiscal Year of the Landlord, the Tenant must make any
such audit within two (2) years after the Tenant's receipt of itemized
statements (and any supporting documentation requested by the Tenant) referred
to in the preceding paragraph. The Tenant must further make any claim for
revision of Tenant's Operating Expenses Allocable to the Premises for such
Fiscal Year by written notice to the Landlord within said two (2) year period.

      Section 3.4 Other Utility Charges. During the Term, the Tenant shall pay
directly to the provider of the service all separately metered charges for
steam, heat, gas, electricity, fuel and other services and utilities furnished
to the Premises, and shall pay to Landlord as Additional Rent its pro rata share
of any utilities or services such as but not limited to water and sewer which
are measured based on submetered usage in the Premises. The Tenant shall cause
all electricity and gas service (specifically serving the Premises and not the
common areas) provided by a public utility to be furnished on a separately
metered basis.

      Section 3.5 Above-standard Services. If the Tenant requests and the
Landlord elects to provide any services to the Tenant in addition to those
described in Exhibit D, the Tenant shall pay to the Landlord, as Additional
Rent, the amount billed by Landlord for such services at Landlord's standard
rates as from time to time in effect, so long as such rates are consistent with
comparable services in comparable buildings within the Cambridge market. If the
Tenant has requested that such services be provided on a regular basis, the
Tenant shall, if requested by the Landlord, pay for such services at their
actual cost to Landlord, including, without limitation, a reasonable overhead
component, at the time and in the fashion in which Annual Fixed Rent under this
Lease is payable. Otherwise, the Tenant shall pay for such additional services
within fifteen (15) days after receipt of an invoice from the Landlord.


                                       20
<PAGE>   26
      Section 3.6 No Offsets. Annual Fixed Rent and Additional Rent shall be
paid by the Tenant without offset, abatement or deduction except as provided
herein.

      Section 3.7 Net Lease. It is understood and agreed that this Lease is a
net lease and that the Annual Fixed Rent is absolutely net to the Landlord
excepting only the Landlord's obligations to pay any debt service or ground rent
on the Property, to provide the Landlord's services, to repair or restore the
Premises after any casualty or condemnation as provided in Article VIII hereof,
and to pay the real estate taxes and operating expenses which the Tenant is not
required to pay under this Lease.


                                   ARTICLE IV

                                   ALTERATIONS

      Section 4.1 Consent Required for Tenant's Alterations. The Tenant shall
not make alterations or additions to the Premises except in accordance with the
Tenant Design and Construction Manual, and with plans and specifications
therefor first approved by the Landlord, which approval shall not be withheld
unreasonably. Notwithstanding the foregoing, the Tenant may, from time to time
without the Landlord's prior consent and at the Tenant's own expense, make
interior non-structural alterations and changes in and to the Premises costing
less than $50,000.00 in each instance, provided that such alterations or changes
(i) do not materially diminish the value of the Building, (ii) are not
incompatible with existing mechanical or electrical, plumbing, HVAC or other
systems in the Building, or use more than the Tenant's pro rata share of
Building capacities as outlined in Exhibit F attached hereto, or (iii) do not
affect the exterior appearance of the Building, in each case, as reasonably
determined by the Landlord. Whether or not the Tenant's changes and/or
alterations require the Landlord's consent pursuant to this paragraph, the
Tenant shall give reasonable prior notice to the Landlord of any alterations and
changes in and to the Premises which the Tenant intends to undertake, together
with a reasonable description of the proposed work and such plans and
specifications, if any, as the Tenant has therefor. Tenant shall furnish
Landlord an "as-built" set of plans and specifications of the Premises annually,
on the first day of each Fiscal Year, in addition to any other plans and
specifications furnished by Tenant to Landlord from time to time. The Landlord
shall not be deemed unreasonable for withholding approval of any alterations or
additions which (i) involve or might affect any structural or exterior element
of the Building, any area or element outside of the Premises (including, without
limitation, interior alterations or additions that affect the exterior
appearance of the Building), or any facility serving any area of the Building
outside of the Premises or any publicly accessible major interior features of
the Building; (ii) will require unusual expense to readapt the Premises to
normal use as a biotechnology office and research and development facility
unless the Tenant first gives assurance acceptable to the Landlord that such
readaptation will be made prior to such termination without expense to the
Landlord; or (iii) would not be compatible with existing mechanical or
electrical, plumbing, HVAC or other systems in the Building, or use more than
the Tenant's pro rata share of Building capacities as outlined in Exhibit F
attached hereto and made a part hereof, in each case, as reasonably determined
by the Landlord; provided, however, with respect to clause (iii), the Landlord
shall


                                       21
<PAGE>   27
not withhold its approval if the Tenant agrees to, at its own cost and expense
and within a reasonable period of time as determined by the Landlord, make such
alterations or additions compatible with all Building systems and equipment.
Neither the Landlord's failure to object to any proposed alterations or
additions, nor the Landlord's approval of any plans and specifications furnished
by Tenant to Landlord, shall be construed as superseding in any respect, or as a
waiver of Landlord's right to enforce, the Tenant's obligation to fulfill all of
the terms and conditions of this Lease applicable to any work contemplated
thereby.

      Notwithstanding anything to the contrary contained in this Section 4.1, if
any of the Tenant's proposed alterations and/or additions affect the roof or the
envelope of the Building, the following additional conditions shall apply:

            (a) Such alterations and changes will not in any way interfere with
      the proper functioning of and Landlord's access to other equipment located
      on the roof of the Building; and

            (b) Adequate measures are taken to screen and otherwise reduce the
      visibility and noise of such mechanical equipment, antennae and dishes
      consistent with the appearance and design scheme required by the City of
      Cambridge and other structures in University Park.

      Section 4.2 Ownership of Alterations. All alterations and additions shall
be part of the Building and owned by the Landlord, except for certain
biotechnology laboratory equipment that is to be installed in the Premises,
which shall be deemed to be independent of the real property, and which have
been identified as Removable Alterations (as defined herein) in accordance with
the terms of this Section 4.2 and by mutual agreement between the Landlord and
Tenant either at the time of the Tenant's initial occupancy of the Premises or
from time to time thereafter; provided, however, that the Landlord may require
removal by Tenant of all or any portion of all other alterations and additions
so long as Landlord advised Tenant of such requirement prior to the installation
of the alteration or addition by Tenant. If the Tenant fails to inform the
Landlord, in writing, at least ten (10) days prior to the installation of the
alteration or addition, thereby preventing the Landlord from making a
determination as to whether it will want such addition or alteration removed
from the Premises prior to its installation, then the Landlord may require such
removal without exception. All movable equipment and furnishings not attached to
the Premises shall remain the property of the Tenant and shall be removed by the
Tenant upon termination or expiration of this Lease. Notwithstanding anything to
the contrary contained in this Section 4.2, any alterations and additions funded
by the Landlord and installed as part of the Leasehold Improvements (as defined
in the Work Letter) (the "Landlord Funded Alterations") shall be part of the
Building and owned by the Landlord; all alterations and additions which are
necessary for the use of the Premises as an operational biotechnology laboratory
(the "Base Laboratory Alterations"), regardless of who funded their acquisition
and installation, shall in no event constitute Removable Alterations; and all
alterations and additions which: (i) are not Landlord Funded Alterations; (ii)
are not Base Laboratory Alterations; and (iii) have been designated as Removable
Alterations by mutual agreement from time to time established between the
Landlord and the Tenant (such items being hereinafter collectively referred to
as the "Removable 


                                       22
<PAGE>   28
Alterations") shall remain the property of the Tenant and shall be removed by
the Tenant upon termination or expiration of this Lease, unless the Landlord
elects to purchase all or a portion of such Removable Alterations from the
Tenant for a price equal to the then depreciated book value thereof established
on the Tenant's books maintained in accordance with generally accepted
accounting principals consistently applied. If the Landlord terminates this
Lease on the basis of a default by the Tenant and, the Landlord elects to
purchase all or a portion of the Removable Alterations as provided above, then
the Landlord will credit such amounts due to the Tenant against any sums owed by
Tenant to Landlord, whether overdue Annual Fixed Rent, Additional Rent, damages
or otherwise. In connection with any removal by the Tenant of the Removable
Alterations, the Tenant shall cap off all utility connections behind the
adjacent interior finish and restore such interior finish to the extent
necessary so that the Premises are left with complete wall, ceiling and floor
finishes.

      The Tenant shall have the right to subject the Removable Alterations to a
prior security interest in connection with the financing of its Leasehold
Improvements (as defined in the Work Letter) so long as the security agreement
evidencing the secured party's interest in such Removable Alterations:

            (a) Requires the secured party to offer the Removable Alterations to
      the Landlord prior to offering them to third parties in the case of a
      default by the Tenant as part of the secured party's remedy under such
      security agreement;

            (b) Prohibits the sale of any Removable Alterations at the Premises;
      and

            (c) Provides that the secured party agrees to fulfill the Tenant's
      restoration and repair obligations as a condition to recovering possession
      of the Removable Alterations.

      Section 4.3 Construction Requirements for Alterations. All construction
work by the Tenant shall be done in a good and workmanlike manner employing only
first-class materials and in compliance with Landlord's construction rules and
regulations and with all applicable laws and all lawful ordinances, regulations
and orders of Governmental authority and insurers of the Building. The Landlord
or Landlord's authorized agent may (but without any implied obligation to do so)
inspect the work of the Tenant at reasonable times and shall give notice of
observed defects. All of the Tenant's alterations and additions and installation
of furnishings shall be coordinated with any work being performed by the
Landlord and in such manner as to maintain harmonious labor relations and not to
damage the Building or interfere with Building construction or operation and,
except for installation of furnishings, shall be performed by the Landlord's
general contractor or by contractors or workmen first approved by the Landlord,
which approval the Landlord agrees not to unreasonably withhold or delay. The
Tenant, before starting any work, shall receive and comply with Landlord's
construction rules and regulations and shall cause Tenant's contractors to
comply therewith, shall secure all licenses and permits necessary therefor and
shall deliver to the Landlord a statement of the names of all its contractors
and subcontractors and the estimated cost of all labor and material to be
furnished by them and security satisfactory to the Landlord in its reasonable
discretion and consistent with the security


                                       23
<PAGE>   29
requirements for comparable work in comparable buildings in the Cambridge market
protecting the Landlord against liens arising out of the furnishing of such
labor and material; and cause each contractor to carry worker's compensation
insurance in statutory amounts covering all the contractors' and subcontractors'
employees and comprehensive general public liability insurance with limits of
$1,000,000 (individual ) and $5,000,000 (occurrence), or in such lesser amounts
as Landlord may accept, covering personal injury and death and property damage
(all such insurance to be written in companies approved reasonably by the
Landlord and insuring the Landlord, such individuals and entities affiliated
with the Landlord as the Landlord may designate, and the Tenant as well as the
contractors and to contain a requirement for at least thirty (30) days' notice
to the Landlord prior to cancellation, nonrenewal or material change), and to
deliver to the Landlord certificates of all such insurance.

      Section 4.4 Payment for Tenant Alterations. The Tenant agrees to pay
promptly when due the entire cost of any work done on the Premises by the
Tenant, its agents, employees or independent contractors, and not to cause or
permit any liens for labor or materials performed or furnished in connection
therewith to attach to the Premises or the Property and promptly to discharge or
bond over any such liens which may so attach. If any such lien shall be filed
against the Premises or the Property and the Tenant shall fail to cause such
lien to be discharged within fifteen (15) days after receipt by the Tenant of
notice of the filing thereof, the Landlord after a further five (5) days'
written notice may cause such lien to be discharged by payment, bond or
otherwise without investigation as to the validity thereof or as to any offsets
or defenses which the Tenant may have with respect to the amount claimed. The
Tenant shall reimburse the Landlord, as additional rent, for any cost so
incurred and shall indemnify and hold harmless the Landlord from and against any
and all claims, costs, damages, liabilities and expenses (including reasonable
attorneys' fees) which may be incurred or suffered by the Landlord by reason of
any such lien or its discharge.

                                    ARTICLE V

              RESPONSIBILITY FOR CONDITION OF BUILDING AND PREMISES

      Section 5.1 Maintenance of Building and Common Areas by Landlord. Except
as otherwise provided in Section 5.3 and Article VIII, the Landlord shall make
such repairs to the major structural elements of the Building, including the
roof, exterior walls and floor slabs as may be necessary to keep and maintain
the same in good condition and maintain and make such repairs to the Common
Building Areas as may be necessary to keep them in good order, condition and
repair, including without limitation, the glass in the exterior walls of the
Building, and all mechanical systems and equipment serving the Building and not
exclusively serving the Premises. The Landlord shall further perform the
services designated as Landlord's Services on Exhibit D. The Landlord shall in
no event be responsible to the Tenant for any condition in the Premises, the
Building or the Land caused by an act or neglect of the Tenant, or any invitee
or contractor or agent of the Tenant. Landlord's costs in performing such
services shall be reimbursed by the Tenant to the extent provided in Section
3.3.


                                       24
<PAGE>   30
      Section 5.2 Maintenance of Premises by Tenant. The Tenant shall keep neat
and clean and maintain in good order, condition and repair the Premises and
every part thereof and all Building and mechanical equipment exclusively serving
the Premises, reasonable wear and tear excepted and further excepting those
repairs for which the Landlord is responsible pursuant to Sections 5.1, 8.1 and
8.5, and shall surrender the Premises and all alterations and additions thereto,
at the end of the Term, in such condition, first removing all goods and effects
of the Tenant and, to the extent specified by the Landlord by notice to the
Tenant, all alterations and additions, including the Removable Alterations, made
by the Tenant, which Tenant has not elected to retain in accordance with the
terms of Sections 4.2 and 5.2, and repairing any damage caused by such removal
and restoring the Premises and leaving them clean and neat. If the Tenant elects
to provide the Tenant-Provided Services, identified as such in Section 5.3, the
Tenant shall perform the Tenant-Provided Services promptly, as necessary and
appropriate, with due diligence and in accordance with the standards therefor
established under Section 5.3. The Tenant shall not permit or commit any damage
(waste), and the Tenant shall be responsible for the cost of repairs which may
be made necessary by reason of damages to common areas in the Building by the
Tenant, or any of the contractors or invitees of the Tenant. Mechanical, HVAC,
and all laboratory systems and equipment shall be maintained in good order,
condition and repair consistent with prevailing standards at comparable
first-class biotechnology facilities.

      Section 5.3 Tenant-Provided Services. Notwithstanding anything to the
contrary contained in this Article V, the Tenant may choose to provide, at its
own cost and expense, in lieu of the Landlord providing the same under this
Lease, any of the building services within the Premises, including the services
specified in Exhibit D and such other services as may be hereafter approved by
the Landlord in its reasonable discretion. Such services which are paid for and
provided by the Tenant are hereinafter referred to as the "Tenant-Provided
Services." The provision by Tenant of Tenant-Provided Services shall be subject
to reasonable standards imposed by Landlord for the purpose of assuring the
fulfillment of the requirements of any ground lessee, mortgagee, tenant,
governmental authority or other third party pertaining to the maintenance and
operation of the Building in good order, condition and repair and in compliance
with all legal requirements.

      With respect to HVAC and certain other Building equipment at both the 45
Sidney Building and the 75 Sidney Building, the Tenant and the Landlord shall
provide maintenance services in accordance with the terms set forth in Exhibit
D-1 attached hereto and made a part hereof. The terms of Exhibit D-1 may be
modified from time to time by mutual reasonable agreement between the parties
hereto. In connection with the maintenance of HVAC and other Building Equipment,
both the Landlord and Tenant agree to provide to each other, within a reasonable
period of time after receipt thereof, access to all inspection records and
reports pertaining to such equipment.

      Section 5.4 Delays in Landlord's Services. The Landlord shall not be
liable to the Tenant for any compensation or reduction of rent by reason or
inconvenience or annoyance or for loss of business arising from the necessity of
the Landlord or its agents entering the Premises for any purposes authorized in
this Lease, or for repairing the Premises or any portion of the Building. In
case the Landlord is prevented or delayed from making any repairs, alterations
or


                                       25
<PAGE>   31
improvements, or furnishing any services or performing any other covenant or
duty to be performed on the Landlord's part, by reason of any External Cause,
the Landlord shall not be liable to the Tenant therefor, nor, except as
expressly otherwise provided in this Lease, shall the Tenant be entitled to any
abatement or reduction of rent by reason thereof, nor shall the same give rise
to a claim in the Tenant's favor that such failure constitutes actual or
constructive, total or partial, eviction from the Premises.

      The Landlord reserves the right to stop any service or utility system the
Landlord provides or causes to be provided under this Lease (i.e. exclusive of
any Tenant-Provided Services or other obligations of the Tenant under this
Lease) when necessary by reason of accident or emergency, until necessary
repairs have been completed; provided, however, that in each instance of
stoppage, the Landlord shall exercise reasonable diligence to eliminate the
cause thereof. Except in case of emergency repairs, the Landlord will schedule
contemplated stoppages at times reasonably approved by the Tenant and will use
reasonable efforts to avoid unnecessary inconvenience to the Tenant by reason
thereof. To the extent that the Landlord is providing or causing to be provided
heat, light or any utility or service, in no event shall the Landlord have any
liability to the Tenant for the unavailability of the same to the extent that
such unavailability is caused by External Causes, provided, however, that the
Landlord is obligated to exercise reasonable efforts to restore such services or
utility systems' operation. The Landlord agrees to carry rent interruption
insurance in commercially reasonable amounts which, to the extent commercially
reasonable, permits recovery within five (5) days after the insured peril. If
the unavailability of heat, light or any utility or service provided or caused
to be provided by the Landlord other than the unavailability of the same due to
the Tenant's acts or omissions renders all or any portion of the Premises
untenantable, and the Tenant ceases to occupy the same for the conduct of its
business, the Tenant shall receive an abatement of rent as reasonably determined
by the Landlord, taking into account the extent of Tenant's loss of use of the
Premises and the loss of use suffered by other tenants of the Building,
commencing with the day following the expiration of the deductible period
provided in Landlord's rent interruption insurance. For all purposes of this
Lease, if Tenant has responsibility for maintenance and repair of any aspect of
the Building or any equipment or system therein, the functioning and performance
of the same shall be the responsibility of the Tenant under this Lease, and
shall in no event constitute a service or utility system that the Landlord
provides or causes to be provided under this Lease.

      Section 5.5 Tenant's Responsibilities Regarding Hazardous Materials. The
Tenant covenants and agrees that the Tenant shall not use, generate, store or
dispose, nor shall the Tenant suffer or permit the use, generation, storing or
disposal in the Premises or otherwise by any of Tenant's contractors, licensees,
invitees, agents or employees, of any oil, toxic substances, hazardous wastes or
hazardous materials (collectively, "Hazardous Materials") in, on or about the
Premises, the Building or the Land, except for Hazardous Materials that are
necessary for Tenant's operation of an office and research facility, and in all
cases which Hazardous Materials must be used, generated, stored and disposed of
in compliance with all applicable law and regulations. The Tenant covenants and
agrees that no dumping, flushing or other introduction of Hazardous Materials
into the septic, sewage or other waste disposal systems serving the Premises
shall occur, except as specifically permitted by law and subject to the
conditions and qualifications imposed by any governmental license or permit. The
Tenant shall provide to the


                                       26
<PAGE>   32
Landlord copies of all licenses and permits that the Tenant has been required to
obtain prior to the handling of any such Hazardous Materials, and the Tenant
must obtain all of such licenses and permits prior to the commencement of
operations in the Premises requiring the same. From time to time during the Term
of this Lease, and thereafter during which the Tenant occupies any portion of
the Premises, the Tenant shall provide the Landlord with such reasonable
substantiation of the Tenant's compliance with the requirements of this Section
5.5 and any additional requirements set forth in Section 6.2 as the Landlord may
reasonably request. The Tenant covenants and agrees that the Tenant shall, at
its sole cost, promptly remove or remediate all Hazardous Materials that are
found upon the Premises, the Building or the Land by virtue of the failure of
the foregoing covenants and agreements to have been fulfilled, or otherwise as
the result of the act or omission of Tenant or its contractors, licensees,
invitees, agents or employees, in a manner complying with all applicable laws
and regulations and the provisions of this Lease. If the Tenant should have any
responsibility under this Section 5.5 to remove or remediate Hazardous
Materials, the Tenant shall keep the Landlord reasonably informed as to the
status of the environmental condition at issue, promptly furnish to the Landlord
copies of all regulatory filings with any governmental regulatory agencies in
connection therewith, and substantiate the performance of its obligations under
this Section 5.5.

      Section 5.6 Landlord's Responsibilities Regarding Hazardous Materials.
During the Term of this Lease, if the removal or remediation of Hazardous
Materials from the Premises, Building or Land is required to be undertaken, then
except to the extent such obligation is the responsibility of the Tenant under
Section 5.5 hereof, the Landlord covenants and agrees to undertake the same.
Without limitation of the foregoing, if necessary to comply with any applicable
legal requirements, should the existing environmental condition of the Land
require the removal or remediation of Hazardous Materials, such removal or
remediation is expressly intended herein to be the Landlord's responsibility
under this Section 5.6. The Landlord shall keep the Tenant reasonably informed
as to the status of the environmental condition at issue, promptly furnish to
the Tenant copies of all regulatory filings with any governmental regulatory
agencies in connection therewith, and substantiate the performance of its
obligations under this Section 5.6.

      Section 5.7 Cross Indemnification. Each of the Landlord and the Tenant
shall defend and indemnify the other and hold the other harmless from and
against any damages, liability or expense associated with claims by governmental
or other third parties arising out of the presence, removal or remediation of
Hazardous Materials for which the indemnifying party is responsible for removal
or remediation under this Lease.


                                   ARTICLE VI

                                TENANT COVENANTS

      The Tenant covenants during the Term and for such further time as the
Tenant occupies any part of the Premises:


                                       27
<PAGE>   33
      Section 6.1 Permitted Uses. The Tenant shall occupy the Premises only for
the Permitted Uses, and shall not injure or deface the Premises or the Property,
nor permit in the Premises any auction sale. The Tenant shall give written
notice to the Landlord, within twenty (20) days after the First Rent
Commencement Date and thereafter once annually within twenty (20) days of each
anniversary of the First Rent Commencement Date, of any materials on OSHA's
right to know list or which are subject to regulation by any other federal,
state, municipal or other governmental authority and which the Tenant intends to
have present at the Premises. The 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 thereof although nothing herein shall
prevent the Tenant from challenging the validity of such requirements. The
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 (above those normally
incurred for Permitted Uses) for any insurance on the Building or its contents
(unless the Tenant pays for any such increase in premiums and provided such
actions do not interfere with the use and enjoyment of the Building by the
Landlord, other tenants, visitors or invitees of University Park) or liable to
render necessary any alteration or addition to the Building, nor commit or
permit any waste in or with respect to the Premises.

      Section 6.2 Laws and Regulations. The Tenant shall comply with all
federal, state and local laws, regulations, ordinances. executive orders,
federal guidelines, and similar requirements in effect from time to time,
including, without limitation, City of Cambridge ordinances numbered 1005 and
1086 and any subsequently adopted ordinance for employment and animal
experimentation with respect to animal experiments and hazardous waste and any
such requirements pertaining to employment opportunity, anti-discrimination and
affirmative action. Tenant shall have the right to contest any notice of
violation for any of the foregoing by appropriate proceedings diligently
conducted in good faith.

      Section 6.3 Rules and Regulations; Signs. The Tenant shall not obstruct in
any manner any portion of the Property not hereby leased; shall not permit the
placing of any signs, curtains, blinds, shades, awnings, aerials or flagpoles,
or the like, visible from outside the Premises; and shall comply with all
reasonable rules and regulations of uniform application to all occupants of the
Building now or hereafter made by the Landlord, of which the Tenant has been
given notice, for the care and use of the Property and the parking facilities
relating thereto. The Landlord shall not enforce rules and regulations in a
discriminatory manner, nor shall the Landlord be liable to the Tenant for the
failure of other occupants of the Building to conform to any such rules and
regulations.

      The Landlord shall provide in any multi-tenant building in which a portion
of the Premises is located a directory in the lobby thereof with the Tenant's
name and floor locations within such building listed thereon. Notwithstanding
anything contained in this Lease (including all exhibits) to the contrary, the
Tenant shall have the right to install a sign with its corporate logo on the
Sidney Street facade of the 75 Sidney Building and signage in such building's
main lobby according to plans agreed to by the parties hereto. Any exterior
sign, however, shall be


                                       28
<PAGE>   34
subject to prior approval by the City of Cambridge and all signs must be
consistent with both the University Park signage guidelines then in effect and
all applicable legal requirements.

      Section 6.4 Safety Compliance. The Tenant shall keep the Premises equipped
with all safety appliances required by law or ordinance or any other regulations
of any public authority because of the manner of use made by the Tenant and to
procure all licenses and permits so required because of such manner of use and,
if requested by the Landlord, do any work so required because of such use, it
being understood that the foregoing provisions shall not be construed to broaden
in any way the Tenant's Permitted Uses. Tenant shall conduct such periodic
tests, evaluations or certifications of safety appliances and laboratory
equipment as are required or recommended in accordance with generally accepted
standards for good laboratory practice to ensure that such safety appliances and
equipment remain in good working order, and shall, upon Landlord's reasonable
request but not more often than two (2) times in any Fiscal Year, provide to
Landlord copies of such reports, evaluations and certifications.

      Section 6.5 Landlord's Entry. The Tenant shall permit the Landlord and it
agents, after reasonable notice except in the case of emergencies, to enter the
Premises at all reasonable hours for the purpose of inspecting or making repairs
to the same, monitoring Tenant's compliance with the requirements and
restrictions set forth in this Lease, and for the purpose of showing the
Premises to prospective purchasers and mortgagees at all reasonable times and to
prospective tenants within twelve (12) months of the end of the Term provided
that in connection with such entry, Tenant may provide procedures reasonably
designed so as not to jeopardize Tenant's trade secrets, proprietary technology
or critical business operations, including accompaniment of all such persons by
an employee of the Tenant. In case of an emergency, the Landlord shall make good
faith efforts to notify the Tenant in person or by telephone prior to such
entry, and in any event, the Landlord shall notify Tenant promptly thereafter
such entry.

      Section 6.6 Floor Load. The Tenant shall not place a load upon any floor
in the Premises exceeding the floor load per square foot of area which such
floor was designed to carry and which is allowed by law as set forth in Exhibit
F attached hereto. The Tenant's machines and mechanical equipment shall be
placed and maintained by the Tenant at the Tenant's expense in settings
sufficient to absorb or prevent vibration or noise that may be transmitted to
the Building structure or to any other space in the Building.

      Section 6.7 Personal Property Tax. The Tenant shall pay promptly when due
all taxes which may be imposed upon personal property (including, without
limitation, fixtures and equipment) in the Premises to whomever assessed. Tenant
shall have the right to contest the validity or amount of any such taxes by
appropriate proceedings diligently conducted in good faith.

      Section 6.8 Assignment and Subleases. The Tenant shall not assign 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 (each
a "Transfer") without, in each instance, having first received the consent of
the Landlord which consent shall not be unreasonably withheld or delayed;
provided, however, that a Transfer shall include an assignment only to the
extent that it 


                                       29
<PAGE>   35
is an assignment of the Lease to a successor tenant and not a collateral
assignment. Tenant shall have no right to transfer its roof rights granted under
Section 2.2(b) other than in connection with a Transfer of the whole or any part
of the Premises for purposes of enabling the transferee to occupy the same for
the conduct of its business therein (provided that the occupancy of part of the
Premises in service of a business the substantial orientation of which is roof
communications shall not qualify as such an occupancy). Except as specifically
permitted herein, any Transfer made without such consent shall be void, and in
no event shall the Tenant have the right to mortgage, pledge, hypothecate or
otherwise transfer this Lease. The Landlord shall not be deemed to be
unreasonable in withholding its consent to any proposed Transfer by the Tenant
based on any of the following factors:

            (a) If the manner in which the proposed occupant conducts its
      business operations is not consistent, in Landlord's reasonable opinion,
      with the image and character of the University Park development as a
      first-class office/research and development park then the Landlord may
      reasonably withhold its consent.

            (b) If at the time of the contemplated consummation of the proposed
      Transfer the Tenant's Consolidated Net Available Cash and Net Working
      Capital are not, in Landlord's reasonable judgment, sufficient to support
      its obligations under this Lease, then: (i) in the event of a proposed
      Transfer constituting an assignment of this Lease, the Landlord may
      reasonably withhold its consent if the proposed assignee is not
      sufficiently creditworthy in the reasonable opinion of the Landlord based
      on a comparison of the creditworthiness of other companies in the same
      industry as the proposed occupant and (ii) in the event of a proposed
      Transfer constituting a sublease, if, as a result of the consummation of
      the proposed sublease, the then Tenant shall no longer be in occupancy of
      at least seventy five percent (75%) of the rentable floor area of the
      Premises (e.g. any sublease that would result in more than twenty five
      percent (25%) of the rentable floor area of the Premises being subject to
      a sublease or subleases), then the Landlord may reasonably withhold its
      consent if the proposed sublessee is not sufficiently creditworthy in the
      reasonable opinion of Landlord based on a comparison of the
      creditworthiness of other companies in the same industry as the proposed
      occupant.

            (c) If the proposed occupant has already initiated discussions with
      either the Landlord or any affiliate of the Landlord regarding space
      within University Park that is or is to become available for lease, then
      the Landlord may reasonably withhold its consent.

If the Tenant desires to contest the Landlord's withholding of consent to any
proposed Transfer based on any of the foregoing factors, then Tenant shall,
within sixty (60) days after receipt of the Landlord's notice withholding
consent, send written notice of such disagreement to the Landlord. After the
Landlord's receipt of such notice, the Landlord and the Tenant shall have thirty
(30) days within which to resolve such controversy after which such controversy
shall be resolved by submittal to the binding Dispute Resolution Process
described in Exhibit J attached hereto and made a part hereof.


                                       30
<PAGE>   36
      Notwithstanding anything to the contrary contained in this Section, Tenant
shall have the right to assign or otherwise transfer this Lease or the Premises,
or part of the Premises, without obtaining the prior consent of Landlord, (a) to
its parent entity or to a majority owned subsidiary or to an entity which is
wholly owned by the same entity which wholly owns Tenant, provided that (i) the
transferee shall, subject to applicable law, regulation or prior binding
agreement, prior to the effective date of the transfer, deliver to Landlord
instruments evidencing such transfer and its agreement to assume and be bound by
all the terms, conditions and covenants of this Lease to be performed by Tenant,
all in form reasonably acceptable to Landlord, and (ii) at the time of such
transfer there shall not be an uncured Event of Default under this Lease; or (b)
to the purchaser of at least fifty percent (50%) of its assets or stock, or to
any entity into which the Tenant may be merged or consolidated (along with all
or substantially all of its assets) (the "Acquiring Company"), provided that (i)
the net worth of the Acquiring Company upon the consummation of the transfer or
merger shall not be less than the net worth of the Tenant at the time
immediately prior to such transfer or merger, (ii) the Acquiring Company
continues to operate the business conducted in the Premises consistent with the
Permitted Uses described in Exhibit A hereto, (iii) the Acquiring Company shall
assume in writing, in form acceptable to Landlord, all of Tenant's obligations
under this Lease, (iv) Tenant shall provide to Landlord such additional
information regarding the Acquiring Company as Landlord shall reasonably
request, and (v) Tenant shall pay Landlord's reasonable out-of-pocket expenses
incurred in connection therewith. Unless Landlord shall have objected to such
assignment or transfer by Tenant within ten (10) business days following
Landlord's receipt of the information or items described in (b)(i) and (iii)
above, Landlord shall be deemed to have waived its right to object thereto. Each
of the transfers described in this paragraph is referred to hereinafter as
"Permitted Transfers." In no event shall any transaction consummated for the
purpose of evading Tenant's obligation to obtain Landlord's consent under this
Section 6.8 be construed as a Permitted Transfer, notwithstanding that such
transaction otherwise qualifies as a Permitted Transfer.


      Whether or not the Landlord consents, or is required to consent, to any
Transfer, the Tenant named herein 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 provided under this
Lease.

      The Tenant shall give the Landlord notice of any proposed Transfer,
whether or not the Landlord's consent is required hereunder, specifying the
provisions thereof, including (i) the name and address of the proposed
subtenant, assignee, mortgagee or other transferee, (ii) a copy of the proposed
subtenant's, assignee's, mortgagee's or other transferee's most recent annual
financial statement, (iii) all of the terms and provisions upon which the
proposed Transfer is to be made including, without limitation, all of the
documentation effectuating such Transfer (which shall be subject to the
Landlord's approval not to be unreasonably withheld) and such other reasonable
information concerning the proposed Transfer or concerning the proposed
subtenant, assignee, mortgagee or other transferee as the Tenant has obtained in
connection with the proposed Transfer. The Tenant shall reimburse the Landlord
promptly for reasonable legal and other expenses incurred by the Landlord in
connection with any request by the Tenant for consent to any Transfer. If this
Lease is assigned, or if the Premises or any part thereof is sublet


                                       31
<PAGE>   37
or occupied by anyone other than the Tenant, or there is otherwise a Transfer
after an event of default the Landlord may, at any time and from time to time,
collect rent and other charges from the assignee, sublessee, occupant, mortgagee
or transferee 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 6.8 or
the acceptance of the assignee, sublessee or occupant as a tenant or a release
of the Tenant from the further performance by the Tenant of covenants on the
part of the Tenant herein contained. The Tenant shall pay to the Landlord fifty
percent (50%) of any amounts the Tenant receives from any subtenant, assignee,
mortgagee or other transferee as rent, additional rent or other forms of
compensation or reimbursement other than those which are less than or equal to
the aggregate of (i) the then due and payable (present valued in a manner
reasonably satisfactory to Landlord in the case of an assignment or similar
Transfer) proportionate monthly share of Annual Fixed Rent, Additional Rent and
all other monies due to Landlord pursuant to this Lease (allocable in the case
of a sublease to that portion of the Premises being subleased), (ii) the
reasonable transaction costs associated with such a transaction, which shall
include brokerage commissions, fees for legal services and any expenses of
preparing the Premises or applicable portion thereof for occupancy by such
subtenant, assignee, mortgagee or other transferee (provided that only the
monthly amortization of the expenses incurred in preparing the space for
occupancy by such transferee, utilizing an interest component reasonably
satisfactory to Landlord, may be included in this calculation in case of a
sublease or similar Transfer) and (iii) any fees the Tenant receives for
services provided to any such transferee, such as glass washing. The preceding
sentence shall not apply to any Permitted Transfers. Neither the fact that the
Landlord's consent may not be required in order for the Tenant to effectuate a
Permitted Transfer, nor the consent by the Landlord to a Transfer for which the
Landlord's consent is required shall be construed to relieve the Tenant from
obtaining the express consent in writing of the Landlord to any further Transfer
whether by the Tenant or by anyone claiming by, through or under the Tenant
including, without limitation, any assignee, subtenant, mortgagee or other
transferee, excluding any Permitted Transfer.

      Landlord may elect, within thirty (30) days of receipt of written notice
from Tenant of any proposed assignment of this Lease, sublease of all of the
Premises or sublease of the remainder of the Premises then occupied by the
Tenant (in the case where the Tenant has theretofore sublet a portion of the
Premises), prior to approving or disapproving any such proposed assignment or
sublease, to repossess the Premises (or in the case where Tenant has theretofore
sublet a portion of the Premises, the portion of the Premises not then subject
to sublease). Landlord may thereafter lease the Premises (or the portion thereof
repossessed) in such a manner as the Landlord may in its sole discretion
determine. In the event Landlord elects to repossess the Premises as provided
above, then all of the Tenant's rights and obligations hereunder with respect to
the portion of the Premises repossessed by the Landlord shall cease and shall be
of no further force and effect. The provisions of this paragraph shall not apply
to Permitted Transfers.


                                       32
<PAGE>   38
                                   ARTICLE VII

                             INDEMNITY AND INSURANCE

         Section 7.1 Indemnity. The Tenant shall indemnify and save harmless the
Landlord and the Landlord's ground lessees, mortgagees and managing agent for
the Building from and against all claims, loss, or damage of whatever nature
arising from (i) any breach by Tenant of any obligation of Tenant under this
Lease, or (ii) from any negligence or misconduct of the Tenant, or the Tenant's
contractors, licensees, invitees, agents, servants or employees, or (iii)
arising from any accident, injury or damage whatsoever caused to any person or
property in or about the Premises, occurring after the date that possession of
the Premises is first delivered to the Tenant and until the end of the Term and
thereafter, so long as the Tenant is in occupancy of any part of the Premises,
provided that the foregoing indemnity shall not include any claims, loss or
damage to the extent arising from any negligence or misconduct of the Landlord,
or the Landlord's contractors, licensees, agents, servants or employees or the
Landlord's ground lessees, mortgagees or managing agent for the Building.

      The Landlord shall indemnify and save harmless the Tenant from and against
all claims, loss, or damage of whatever nature arising from (i) any breach by
Landlord of any obligation of Landlord under this Lease or (ii) from any
negligence or misconduct of the Landlord, or the Landlord's contractors,
licensees, agents, servants or employees, provided that the foregoing indemnity
shall not include any claims, loss or damage to the extent arising from any act,
omission or negligence of the Tenant, or the Tenant's contractors, licensees,
invitees, agents, servants or employees.

      The foregoing indemnity and hold harmless agreements shall include
indemnity against reasonable attorneys' fees and all other costs, expenses and
liabilities incurred in connection with any such claim or proceeding brought
thereon, and the defense thereof, but shall be subject to the limitation
specified in Section 12.15.

      Section 7.2 Liability Insurance. The Tenant agrees to maintain in full
force from the date upon which the Tenant first enters the Premises for any
reason, throughout the Term, and thereafter, so long as the Tenant is in
occupancy of any part of the Premises, a policy of comprehensive general
liability insurance under which the Landlord (and any individuals or entities
affiliated with the Landlord, any ground lessor and any holder of a mortgage on
the Property of whom the Tenant is notified by the Landlord) and the Tenant 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 7.1, in the broadest form of such coverage from time to time available.
Each such policy shall be noncancellable and nonamendable (to the extent that
any proposed amendment reduces the limits or the scope of the insurance required
in this Lease) with respect to the Landlord and such ground lessors and
mortgagees without thirty (30) days' prior notice to the Landlord and such
ground lessors and mortgagees and at the election of the Landlord, either a
certificate of insurance or a duplicate original policy shall be delivered to
the Landlord. The minimum limits of liability of such insurance as of the
Commencement Date


                                       33
<PAGE>   39
shall be Ten Million Dollars ($10,000,000.00) for combined bodily injury (or
death) and damage to property (per occurrence) with an aggregate annual limit of
liability of Ten Million Dollars ($10,000,000.00), and from time to time during
the Term such limits of liability shall be increased to reflect such higher
limits as are customarily required pursuant to new leases of space in the
Boston-Cambridge area with respect to similar properties.

      Section 7.3 Personal Property at Risk. The Tenant agrees that all of the
furnishings, fixtures, equipment, effects and property of every kind, nature and
description of the Tenant and of all persons claiming by, through or under the
Tenant which, during the continuance of this Lease or any occupancy of the
Premises by the Tenant or anyone claiming under the Tenant which, during the
continuance of this Lease or any occupancy of the Premises by the Tenant or
anyone claiming under the Tenant, may be on the Premises or elsewhere in the
Building or on the Lot or parking facilities provided hereby, shall be at the
sole risk and hazard of the 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 water pipes, steam pipes, or other pipes. by theft or from any other
cause, no part of said loss or damage is to be charged to or be borne by the
Landlord, except that the Landlord shall in no event be exonerated from any
liability to the Tenant or to any person, for any injury, loss, damage or
liability to the extent caused by Landlord's or its employees', agents' or
contractors' negligence or willful misconduct.

      Section 7.4 Landlord's Insurance. The Landlord shall carry such all risk
casualty and liability insurance upon and with respect to operations at the
Building as may from time to time be deemed reasonably prudent by the Landlord
with deductibles in amounts carried at comparable buildings with similar uses
within the Cambridge market or required by any mortgagee holding a mortgage
thereon or any ground lessor of the Land, in an amount equal to the replacement
cost of the Building, including all leasehold improvements, exclusive of
foundations, site preparation and other nonrecurring construction costs.

      Section 7.5 Waiver of Subrogation. Any insurance carried by either party
with respect to the Building, Land, Premises, parking facilities 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.

      Section 7.6 Policy Requirements. Any required insurance may be in the form
of blanket coverage, so long as the coverage required herein is maintained. Each
party shall cause a certificate, providing such information as reasonably
requested by the other party, evidencing the existence and limits of its
insurance coverage with respect to the Premises and the Building, as the case
may be, to be delivered to such other party upon the commencement of the Term.
Thereafter, each party shall cause similar certificates evidencing renewal
policies to be delivered


                                       34
<PAGE>   40
to such other party at least thirty (30) days prior to the expiration of the
term of each policy and at such other times as reasonably requested by the other
party. The insurance policies and certificates required by this Article VII
shall contain a provision requiring the insurance company to furnish Landlord
and Tenant, as the case may be, thirty (30) days' prior written notice of any
cancellation or lapse, or the effective date of any reduction in the amounts or
scope of coverage.

                                  ARTICLE VIII

                           CASUALTY AND EMINENT DOMAIN

      Section 8.1 Restoration Following Casualties; Termination for Failing to
Maintain Parking. If, during the Term, the Building, the Premises or the 101
Pacific Street Garage shall be damaged by fire or casualty, subject to
termination rights of the Landlord and the Tenant provided below in this Article
VIII, the Landlord shall proceed promptly to exercise diligent efforts to
restore, or cause to be restored, the Building, the Premises or the 101 Pacific
Street Garage, as the case may be, to substantially the condition thereof just
prior to time of such damage, but the Landlord shall not be responsible for
delay in such restoration which may result from External Causes. The Landlord
shall have no obligation to expend in the reconstruction of the Building, the
Premises or the 101 Pacific Street Garage more than the sum of the amount of any
deductible and the actual amount of insurance proceeds made available to the
Landlord by its insurer. Any restoration of the Building, the Premises or the
101 Pacific Street Garage shall be altered to the extent necessary to comply
with then current and applicable laws and codes. The Landlord shall designate by
notice to the Tenant, as soon as reasonably practicable following any casualty
to the 101 Pacific Street Garage, alternative parking within University Park
that shall be used for the parking of the automobiles of the employees and
invitees of the Tenant during restoration of the 101 Pacific Street Garage. The
Tenant shall pay the market rate from time to time in effect for such
alternative parking facilities. If the Landlord shall reasonably determine that
the amount of insurance proceeds available to the Landlord is insufficient by
more than the amount of any deductible to cover the cost of restoring the 101
Pacific Street Garage, or if the Landlord reasonably determines it will be
unable to restore the 101 Pacific Street Garage within twenty four (24) months
from the date of the casualty, the Landlord shall so notify the Tenant in
writing. In such event, the Tenant shall have the right, as its sole remedy, to
terminate this Lease by notice to the Landlord of its desire to do so, provided
such notice is given not later than thirty (30) days after such notice is given
to the Landlord. Such termination shall be effective thirty (30) days after such
notice is given to the Landlord, or such later date specified by the Tenant in
such notice not exceeding one hundred twenty (120) days after such notice is
given.

      Section 8.2 Landlord's Termination Election. If the Landlord reasonably
determines, based upon certification by its architect or other design
professional, that (a) the amount of insurance proceeds available to the
Landlord is insufficient (by more than the amount of any deductible) to cover
the cost of restoring the Building, or (b) the Landlord will be unable to
restore the Building within twelve (12) months from the date of the casualty,
then the Landlord may terminate this Lease by giving notice to the Tenant. Any
such termination shall be effective on the date designated in such notice from
the Landlord, but in any event not later than sixty (60) days after such notice,
and if no date is specified, effective upon the delivery of such notice. 


                                       35
<PAGE>   41
Failure by the Landlord to give the Tenant notice of termination within ninety
(90) days following the occurrence of the casualty shall constitute the
Landlord's agreement to restore the Building as contemplated in Section 8.1.

      Section 8.3 Tenant's Termination Election. If the Landlord has not
terminated this Lease under Section 8.2, but the Landlord has failed to restore
the Premises, within twelve (12) months from the date of the casualty or taking,
such period to be subject, however, to extension where the delay in completion
of such work is due to External Causes, the Tenant shall have the right to
terminate this Lease at any time after the expiration of such 12-month period
(as extended by delay due to External Causes), as the case may be, until the
restoration is substantially completed, such termination to take effect as of
the date of the Tenant's notice. However, if the Landlord reasonably determines
at any time, and from time to time, during the restoration, based upon
certification by its architect or other design professional, that such
restoration will not be able to be completed before the deadline date after
which the Tenant may terminate this Lease under this Section 8.3, and the
Landlord specifies in a notice to Tenant to such effect a later date that the
Landlord estimates will be the date upon which such restoration will be
completed, then the Tenant may terminate this Lease within ten (10) days of the
Landlord's notice as aforesaid, failing which the deadline date shall be
extended to the date set forth in Landlord's notice (as extended by delay due to
External Causes). The Landlord shall exercise reasonable efforts to keep the
Tenant advised of the status of restoration work from time to time, and promptly
following any request for information during the course of the performance of
the restoration work.

      Section 8.4 Casualty at Expiration of Lease. If the Premises shall be
damaged by fire or casualty in such a manner that the Premises cannot, in the
ordinary course, reasonably be expected to be repaired within one hundred twenty
(120) days from the commencement of repair work and such damage occurs within
the last eighteen (18) months of the Term (as the same may have been extended
prior to such fire or casualty), either party shall have the right, by giving
notice to the other not later than sixty (60) days after such damage, to
terminate this Lease, whereupon this Lease shall terminate as of the date of
such notice. Notwithstanding the foregoing, the Landlord shall not have the
right to terminate this Lease as aforesaid provided that the Tenant shall have
exercised its right to extend the Term of this Lease pursuant to Section 2.6
hereof not later than forty-five (45) days after the date of damage to the
Premises.

      Section 8.5 Eminent Domain. 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 the Tenant's
purposes as contemplated under this Lease, shall be taken by condemnation or
right of eminent domain, the Landlord or the Tenant shall have the right to
terminate this Lease and any separate parking 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 receipt by the Tenant of notice of the effective date of such
taking. If so much of the Building shall be so taken that the Landlord
reasonably determines that it would be reasonably necessary to raze or
substantially alter the Building, the Landlord shall have the right to terminate
this Lease by giving notice to the Tenant of the Landlord's desire to do so not
later than thirty (30) days after the effective date of such taking.


                                       36
<PAGE>   42
      Should any part of the Premises be so taken or condemned during the Term,
and should this Lease be not terminated in accordance with the foregoing
provisions, the Landlord agrees to use reasonable efforts to put what may remain
of the Premises into proper condition for use and occupation as nearly like the
condition of the Premises prior to such taking as shall be practicable, subject,
however, to applicable laws and codes then in existence.

      If the 101 Pacific Street Garage, or such portion thereof as to render the
Tenant's parking privileges therein impossible or impracticable in the
Landlord's reasonable determination, shall be taken by condemnation or right of
eminent domain, then the Landlord shall designate, if available and promptly
following any such taking, alternative parking within University Park that shall
be used for the parking of the automobiles of the employees and invitees of the
Tenant. All such alternative parking shall be allocated proportionately among
all tenants, including the Tenant, then currently leasing parking spaces within
the 101 Pacific Street Garage; provided, however, the number of the Tenant's
parking spaces guaranteed by the Landlord in Exhibit A shall not change. The
Tenant shall pay the market rate from time to time in effect for such
alternative parking facilities. In the event the Landlord is unable to secure
for the Tenant such alterative parking, the Tenant shall have the right, as its
sole remedy, to terminate this Lease and any separate parking lease by notice to
Landlord of its desire to do so, provided such notice is given not later than
the later of thirty (30) days after the effective date of such taking or thirty
(30) days after the Tenant has notice of the effective date of such taking. Such
termination shall be effective thirty (30) days after such notice is given to
the Landlord, or such later date specified by the Tenant in such notice not
exceeding one hundred twenty (120) days after such notice is given.

      Section 8.6 Rent After Casualty or Taking. If the Premises shall be
damaged by fire or other casualty, until the Lease is terminated or the Premises
is restored, 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 the Tenant. In the event of a taking which permanently
reduces the area of the Premises, a just proportion of the Annual Fixed Rent
shall be abated for the remainder of the Term.

      Section 8.7 Temporary Taking. In the event of any taking of the Premises
or any part thereof for a temporary use not in excess of twelve (12) months, (i)
this Lease shall be and remain unaffected thereby and Annual Fixed Rent and
Additional Rent shall not abate, and (ii) the Tenant shall be entitled to
receive for itself such portion or portions of any award made for such use with
respect to the period of the taking which is within the Term.

      Section 8.8 Taking Award. Except as otherwise provided in Section 8.7, the
Landlord shall have and hereby reserves and accepts, and the Tenant hereby
grants and assigns to the Landlord, all rights to recover for damages to the
Building and the Land, and the leasehold interest hereby created, and to
compensation accrued or hereafter to accrue by reason of such taking, damage or
destruction, as aforesaid, and by way of confirming the foregoing, the Tenant
hereby grants and assigns to the Landlord, all rights to such damages or
compensation. Nothing contained herein shall be construed to prevent the Tenant
from prosecuting in any condemnation


                                       37
<PAGE>   43
proceedings a claim for relocation expenses and improvements made by the Tenant
in the Premises that constitute Tenant's personal property, including the
Removable Alterations.


                                   ARTICLE IX

                                     DEFAULT

      Section 9.1 Tenant's Default. Each of the following shall constitute an
Event of Default:

            (a) Failure on the part of the Tenant to pay the Annual Fixed Rent,
      Additional Rent or other charges for which provision is made herein on or
      before the date on which the same become due and payable, if such
      condition continues for five (5) business days after written notice that
      the same are due; provided, however if Tenant shall fail to pay any of the
      foregoing when due two (2) times in any period of twelve (12) consecutive
      months, then Landlord shall not be required to give notice to Tenant of
      any future failure to pay during the remainder of the Term and any
      extension thereof, and such failure shall thereafter constitute an Event
      of Default if not cured within five (5) days after the same are due.

            (b) Failure on the part of the Tenant to perform or observe any
      other term or condition contained in this Lease if the Tenant shall not
      cure such failure within thirty (30) days after written notice from the
      Landlord to the Tenant thereof, provided that in the case of breaches that
      are not reasonably susceptible to cure within thirty (30) days through the
      exercise of due diligence, then so long as the Tenant commences such cure
      within thirty (30) days, and the Tenant diligently pursues such cure to
      completion, such breach shall not be deemed to create an Event of Default.

            (c) The taking of the estate hereby created on execution or by other
      process of law; or a judicial declaration that the Tenant is bankrupt or
      insolvent according to law; or any assignment of the property of the
      Tenant for the benefit of creditors; or the appointment of a receiver,
      guardian, conservator, trustee in bankruptcy or other similar officer to
      take charge of all or any substantial part of the Tenant's property by a
      court of competent jurisdiction, which officer is not dismissed or removed
      within ninety (90) days; or the filing of an involuntary petition against
      the Tenant under any provisions of the bankruptcy act now or hereafter
      enacted if the same is not dismissed within ninety (90) days; the filing
      by the Tenant of any voluntary petition for relief under provisions of any
      bankruptcy law now or hereafter enacted.

      If an Event of Default shall occur, then, in any such case, whether or not
the Term shall have begun, the Landlord lawfully may, immediately or at any time
thereafter, give notice to the Tenant specifying the Event of Default and this
Lease shall come to an end on the date specified therein as fully and completely
as if such date were the date herein originally fixed for the


                                       38
<PAGE>   44
expiration of the Lease Term, and the Tenant will then quit and surrender the
Premises to the Landlord, but the Tenant shall remain liable as hereinafter
provided.

      Section 9.2 Damages. In the event that this Lease is terminated, the
Tenant covenants to pay to the Landlord forthwith on the Landlord's demand, as
compensation, an amount (the "Lump Sum Payment") equal to the excess, if any, of
the discounted present value of the total rent reserved for the remainder of the
Term over the then discounted present fair rental value of the Premises for the
remainder of the Term. The discount rate for calculating such sum shall be the
then current rate of United States Treasury securities having a maturity date as
close as possible to the end of the Term (had the Lease not been terminated). 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 the Tenant over the remainder of the Term. In
addition, the Tenant shall pay punctually to the Landlord all the sums
("Periodic Payments") and perform all the obligations which the 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 until such time as
the entire Premises has been relet and the term under the new lease has
commenced. In calculating the amounts to be paid by the Tenant under the
foregoing covenant, the Tenant shall be credited with the net proceeds of any
rent obtained by reletting the Premises, after deducting all the 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. The Tenant shall also be entitled
to credit against the last periodic payments which would otherwise become due
the amount, if any, paid to the Landlord as a Lump Sum Payment. The Landlord may
(i) relet the Premises, or any part or parts thereof, for a term or terms which
may, at the Landlord's option, exceed or be equal to or less than the period
which would otherwise have constituted the balance of the Term, and may grant
such concessions and free rent as the Landlord in its reasonable commercial
judgment considers advisable or necessary to relet the same and (ii) make such
alterations, repairs and improvements in the Premises as the Landlord in its
reasonable commercial judgment considers advisable or necessary to relet the
same. No action of the Landlord in accordance with foregoing or failure to relet
or to collect rent under-reletting shall operate to release or reduce the
Tenant's liability. The Landlord shall be entitled to seek to rent other
properties of the Landlord prior to reletting the Premises. Notwithstanding the
foregoing, the Landlord shall offer such Premises to lease in the same manner as
the Landlord offers other vacant space for lease in University Park.

      Section 9.3 Cumulative Rights. The specific remedies to which the Landlord
may resort under the terms of this Lease are cumulative and are not intended to
be exclusive of any other remedies or means of redress to which it may be
lawfully entitled in case of any breach or threatened breach by the Tenant of
any provisions of this Lease. In addition to the other remedies provided ir this
Lease, the Landlord shall be entitled to seek 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. Nothing contained
in this Lease shall limit or prejudice the right of the 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 


                                       39
<PAGE>   45
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.

      Section 9.4 Landlord's Self-help. If there shall be an Event of Default or
circumstances which, upon the giving of notice or passage of time would
constitute an Event of Default by the Tenant in the performance of any
obligation under this Lease, then the Landlord shall have the right, but not the
obligation, after the giving by the Landlord of notice thereof to the Tenant and
the expiration of any applicable cure period (except in case of emergency in
which case no notice need be given nor must any applicable cure period expire)
and upon reasonable, but in no event more than ten (10) days' notice to the
Tenant (except in case of emergency in which case no such additional notice need
be given), to perform such obligation (including, without limitation, stopping
any service or utility system until necessary repairs have been completed). In
the event the Landlord exercises its rights under this Section 9.4 in case of
emergency, the Landlord shall notify the Tenant as soon as reasonably possible
after the taking of such action. The Landlord may exercise its rights under this
Section without waiving any other of its rights or releasing the Tenant from any
of its obligations under this Lease. The Tenant shall be liable to the Landlord
for all of the Landlord's reasonable costs associated with effecting such cure.

      Section 9.5 Enforcement Expenses; Litigation. Each party hereto shall
promptly reimburse the other for all costs and expenses, including without
limitation legal fees, incurred by such party in exercising and enforcing its
rights under this Lease following the other party's failure to comply with its
obligations hereunder, whether or not such failure constitutes an Event of
Default pursuant to Sections 9.1 or 9.7 hereof.

      If either party hereto be made or becomes a party to any litigation
commenced by or against the other party by or against a third party, or incurs
costs or expenses related to such litigation, involving any part of the Property
and the enforcement of any of the rights, obligations or remedies of such party,
then the party becoming involved in any such litigation because of a claim
against such other party hereto shall receive from such other party hereto all
costs and reasonable attorneys' fees incurred by such party in such litigation.

      Section 9.6 Late Charges and Interest on Overdue Payments. In the event
that any payment of Annual Fixed Rent or Additional Rent shall remain unpaid for
a period of five (5) days following notice by the Landlord to the Tenant that
such payment is overdue, there shall become due to the Landlord from the Tenant,
as Additional Rent and as compensation for the Landlord's extra administrative
costs in investigating the circumstances of late rent, a late charge of two
percent (2%) of the amount overdue. In addition, any Annual Fixed Rent and
Additional Rent not paid when due shall bear interest from the date due to the
Landlord until paid at the variable rate (the "Default Interest Rate") equal to
the higher of (i) the rate at which interest accrues on amounts not paid when
due under the terms of the Landlord's financing for the Building, as from time
to time in effect, and (ii) one hundred and twenty-five percent (125%) of the
rate from time to time announced by BankBoston N.A. as its base rate, or if such
rate can no longer be determined, one hundred and twenty-five percent (125%) of
the rate from time to time


                                       40
<PAGE>   46
announced by a major commercial bank selected by the Landlord as the rate
charged to creditworthy commercial clients for short-term unsecured borrowings.

      Section 9.7 Landlord's Right to Notice and Cure; Tenant's Self-Help
Rights. The Landlord shall in no event be in default in the performance of any
of the Landlord's obligations hereunder unless and until the Landlord shall have
failed to perform such obligations within thirty (30) days, or such additional
time as is reasonably required to correct any such default, after notice by the
Tenant to the Landlord expressly specifying wherein the Landlord has failed to
perform any such obligation. If Landlord has failed to make any repair which
results in a material risk of damage or injury to persons or property within the
Premises within thirty (30) days or such additional time as is required to make
such repair, then the Tenant shall have the right, after providing an additional
ten (10) days' written notice to the Landlord, to perform such obligation so
long as the same may be done solely on the Property or within the common areas
of the Building. Notwithstanding the foregoing, in the case of an emergency, the
Tenant shall have the right to perform any such obligation without regard to the
thirty (30) day notice period, so long as (a) the Tenant makes a good faith
attempt to notify the Landlord prior to taking such action and (b) notifies the
Tenant as soon as possible thereafter. The Landlord shall be liable to the
Tenant for all of the Tenant's reasonable costs associated with effecting such
cure, provided that in no event shall the Tenant be entitled to abate any Annual
Fixed Rent or Additional Rent or otherwise offset such costs against sums due
the Landlord under this Lease.


                                    ARTICLE X

                     MORTGAGEES' AND GROUND LESSORS' RIGHTS

      Section 10.1 Subordination. This Lease shall, at the election of the
holder of any mortgage or ground lease on the Property, be subject and
subordinate to any and all mortgages or ground leases on the Property, so that
the lien of any such mortgage or ground lease shall be superior to all rights
hereby or hereafter vested in the Tenant, provided that such mortgagee or ground
lessor shall have entered into a subordination non-disturbance and attornment
agreement with Tenant, the form of which shall be furnished by the mortgagee or
ground lessor, as the case may be, with such reasonable modifications as Tenant
shall request within a reasonable time period. The form of non-disturbance and
attornment agreement attached hereto as Exhibit H is acceptable to Tenant in
connection with the Ground Lease held by MIT (as such terms are defined in
Section 12.10). The form of subordination, non-disturbance and attornment
agreement attached hereto as Exhibit I is acceptable to the Tenant with respect
to any such agreement to be entered into during the period following Substantial
Completion of the Premises, and the form of subordination, non-disturbance and
attornment agreement attached hereto as Exhibit K is acceptable to the Tenant
with respect to any such agreement to be entered into during the period prior
thereto, in connection with any mortgage to which this Lease shall be
subordinated.

      Section 10.2 Prepayment of Rent not to Bind Mortgagee. No Annual Fixed
Rent, Additional Rent, or any other charge payable to the Landlord shall be paid
more than thirty (30) 


                                       41
<PAGE>   47
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 or ground lessor) be a nullity as
against such mortgagee or ground lessor and the Tenant shall be liable for the
amount of such payments to such mortgagee or ground lessor.

      Section 10.3 Tenant's Duty to Notify Mortgagee: Mortgagee's Ability to
Cure. No act or failure to act on the part of the Landlord which would entitle
the Tenant under the terms of this Lease, or by law, to be relieved of the
Tenant's obligations to pay Annual Fixed Rent or Additional Rent hereunder or to
terminate this Lease, shall result in a release or termination of such
obligations of the Tenant or a termination of this Lease unless (i) the Tenant
shall have first given written notice of the Landlord's act or failure to act to
the Landlord's mortgagees or ground lessors of record, if any, of whose identity
and address the Tenant shall have been given notice, specifying the act or
failure to act on the part of the Landlord which would give basis to the
Tenant's rights; and (ii) such mortgagees or ground lessors, after receipt of
such notice, have failed or refused to correct or cure the condition complained
of within a reasonable time thereafter; which shall include a reasonable time
for such mortgagee or ground lessors, but in no event more than thirty (30) days
after receipt of such notice, to obtain possession of the Property if possession
is necessary for the mortgagee or ground lessor to correct or cure the condition
and if the mortgagee or ground lessor notifies the Tenant of its intention to
take possession of the Property and correct or cure such condition; provided,
however, nothing contained in this Section 10.3 shall affect Tenant's right (a)
to terminate this Lease under Sections 8.3, 8.4 or 8.5 or (b) to exercise its
self-help rights under Section 9.7.

      Section 10.4 Estoppel Certificates. The Tenant shall from time to time,
upon not less than fifteen (15) days' prior written request by the Landlord,
execute, acknowledge and deliver to the Landlord a statement in writing
certifying to the Landlord or an independent third party, with a true and
correct copy of this Lease attached thereto, to the extent such statements
continue to be true and accurate, (i) 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); (ii) that the
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); (iii) that there are no
known uncured defaults of the Landlord or the Tenant under this Lease (or if
there are known defaults, setting them forth in reasonable detail); (iv) the
dates to which the Annual Fixed Rent, Additional Rent and other charges have
been paid; (v) that the Tenant has accepted, is satisfied with, and is in full
possession of the Premises, including all improvements, additions and
alterations thereto required to be made by Landlord under the Lease; (vi) that
the Landlord has satisfactorily complied with all of the requirements and
conditions precedent to the occurrence of the Rent Commencement Date with
respect to the entire Building; (vii) that the Tenant has been in occupancy
since the First Rent Commencement Date and paying rent since the specified
dates; (viii) that no monetary or other considerations, including, but not
limited to, rental concessions for Landlord, special tenant improvements or
Landlord's assumption of prior lease obligations of Tenant have been granted to
Tenant by Landlord for entering into Lease, except as specified; (ix) that
Tenant has no notice of a prior assignment, hypothecation, or pledge of rents or
of the Lease; (x) that the Lease represents the


                                       42
<PAGE>   48
entire agreement between Landlord and Tenant; (xi) that no prepayment or
reduction of rent and no modification, termination or acceptance of Lease will
be valid as to the party to whom such certificate is addressed without the
consent of such party; (xii) that any notice to Tenant may be given it by
certified or registered mail, return receipt requested, or delivered, at the
Premises, or at another address specified; and (xiii) such other matters with
respect to the Tenant and this Lease as the Landlord may reasonably request. On
or following each Rent Commencement Date to occur hereunder, the Tenant shall,
within ten (10) days after receipt of Landlord's request therefor, promptly
execute, acknowledge and deliver to the Landlord a statement in writing that the
Rent Commencement Date has occurred with respect to a portion of the Premises,
that the Annual Fixed Rent has begun to accrue with respect thereto, and that
the Tenant has taken occupancy of such portion of the Premises. Any statement
delivered pursuant to this Section may be relied upon by any prospective
purchaser, mortgagee or ground lessor of the Premises and shall be binding on
the Tenant.

      Landlord shall from time to time, upon not less than fifteen (15) days'
prior written request by the Tenant, execute, acknowledge and deliver to the
Tenant a statement in writing certifying to the Tenant or an independent third
party, with a true and correct copy of this Lease attached thereto, to the
extent such statements continue to be true and accurate (i) 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); (ii) that the Landlord has no knowledge of any defenses,
offsets or counterclaims against its obligations to perform its covenants under
this Lease (or if there are any defenses, offsets, or counterclaims, setting
them forth in reasonable detail); (iii) that there are no known uncured defaults
of the Tenant or the Landlord under this Lease (or if there are known defaults,
setting them forth in reasonable detail); (iv) the dates to which the Annual
Fixed Rent, Additional Rent and other charges have been paid; (v) that the
Tenant is in full possession of the Premises; (vi) that Landlord has no notice
of a prior assignment of the Lease or sublease of space therein; (vii) that the
Lease represents the entire agreement between Landlord and Tenant; (viii) that
any notice to Landlord may be given if by certified or registered mail, return
receipt requested, or delivered to the Landlord's address listed on Exhibit A,
or at another address specified; and (xii) such other matters with respect to
the Tenant and this Lease as the Tenant may reasonably request. Any statement
delivered pursuant to this Section may be relied upon by any prospective
assignee or sublessee of Tenant and shall be binding on the Landlord.


                                   ARTICLE XI

                                SECURITY DEPOSIT

      Section 11.1 Concurrently with the mutual execution and delivery of this
Lease by the Landlord and the Tenant, the Tenant has deposited with the
Landlord, and thereafter throughout the Term, the Tenant shall maintain with the
Landlord, a security deposit (the "Lease Security Deposit") equal to the product
of (i) six (6) times (ii) the aggregate of (a) the then applicable monthly
installment of Annual Fixed Rent payable by the Landlord to the Tenant under
this Lease and (b) the then applicable monthly installment of the Tenant's Tax
Expenses Allocable to


                                       43
<PAGE>   49
the Premises. The Landlord may draw upon any letter of credit (if deposited as a
letter of credit) and apply such deposit, including all interest thereon accrued
but not yet paid to the Tenant, as provided in this Article XI, upon any Event
of Default by the Tenant hereunder or any default of the Tenant with respect to
which the Landlord may exercise its self-help rights under Section 9.4. Provided
there is no then subsisting default by the Tenant under this Lease with respect
to which the Landlord has given the Tenant notice, and thereafter only at such
time as there is no such default by the Tenant then subsisting: (i) on each
anniversary of the date upon which the Rent Commencement Date has occurred with
respect to the entire Original Premises, all interest which shall have
theretofore accrued on the Lease Security Deposit shall be disbursed to Tenant
and (ii) within thirty (30) days after the expiration of this Lease, any
remaining portion of the Lease Security Deposit not theretofore applied shall be
disbursed to Tenant. However, upon any termination of this Lease the Lease
Security Deposit may first be applied by the Landlord to any amounts for which
the Tenant is liable under this Lease. In the event the Landlord draws down on
any letter of credit or applies any funds constituting the Lease Security
Deposit, the Tenant shall deliver to the Landlord as Additional Rent, within ten
(10) days after invoice therefor, either a replacement or supplemental letter of
credit, or the amount of the Lease Security Deposit applied by the Landlord,
such that the balance of the Lease Security Deposit shall be restored to the
appropriate amount specified herein. Failure by the Tenant to timely make the
Lease Security Deposit shall constitute a condition to the effectiveness of this
Lease, failure of which to be timely satisfied by the Tenant shall entitle the
Landlord to terminate this Lease.

      Section 11.2 On or before the respective dates specified below in this
Section 11.2, the Tenant shall deposit an additional amount (collectively, the
"TI Security Deposit") that, in the aggregate, equals fifty-seven percent (57%)
of the lesser of (i) fifty percent (50%) of Tenant's Allowance or (ii)
$7,437,500, as follows:

            (a) One Million Three Hundred Thousand Dollars ($1,300,000) upon the
      Architect's notice to the Tenant that construction of the Building has
      commenced ("Construction Commencement Date"); plus

            (b) One Million Dollars ($1,000,000) on or before the date which is
      three (3) months following the Construction Commencement Date; plus

            (c) One Million Dollars ($1,000,000) on or before the date which is
      ten (10) months following the Construction Commencement Date; plus

            (d) the balance of the TI Security Deposit upon the occurrence of
      the First Rent Commencement Date.

      Additionally, the TI Security Deposit shall be increased to the amount by
which (x) fifty percent (50%) of Tenant's Allowance exceeds (y) the aggregate of
the amounts set forth in clauses (a), (b), (c) and (d) above, if the
circumstances contemplated under Section 11.4 should occur. Once deposited by
the Tenant in accordance with the aforesaid schedule, the TI Security Deposit
shall be maintained by the Tenant and held by the Landlord, whether in cash or
by letter


                                       44
<PAGE>   50
of credit, on the same terms and conditions, and subject to being applied by the
Landlord in accordance with such terms and conditions, as pertain to the Lease
Security Deposit.

      Section 11.3 The Lease Security Deposit and TI Security Deposit
(collectively, the "Security Deposits") may be made and maintained by the
Tenant, at its election, either in the form of a clean, unconditional and
irrevocable letter of credit in form and substance satisfactory in all respects
to the Landlord, and from a commercial bank having an AA rating by Standard and
Poors or from an institution that is a wholly owned subsidiary of a bank having
an AA rating by Standard and Poors or in cash. If and to the extent the Security
Deposits are held in the form of a letter of credit, the Landlord may pledge its
right, title and interest in and to such letter of credit to any mortgagee or
ground lessor and, in order to perfect such pledge, have such letter of credit
held in escrow by such mortgagee or ground lessee. If and to the extent the
Security Deposits are held in the form of cash, the Landlord may pledge its
right and interest in and to such cash to any mortgagee or ground lessor and, in
order to perfect such pledge, have such cash held in escrow by such mortgagee or
ground lessee or grant such mortgagee or ground lessee a security interest
therein. In connection with any such pledge or grant of security interest by the
Landlord to a mortgagee or ground lessee ("Security Deposit Pledgee"), Tenant
covenants and agrees to cooperate as reasonably requested by the Landlord, in
order to permit the Landlord to implement the same on terms and conditions
reasonably required by such mortgagee or ground lessee including, without
limitation, providing in any letter of credit that the Tenant elects to give
under this Article XI any necessary and appropriate language that will permit
the implementation of such pledge. If and to the extent the Security Deposits
are or are hereafter held in the form of cash, and whether or not a Security
Deposit Pledgee shall have a security interest therein, such cash shall be
deposited in a separately maintained and accounted escrow account established
with a bank or other financial institution reasonably acceptable to the Tenant
(the "Escrow Holder"), and all monies held therein shall be invested and
reinvested by the Escrow Holder in the name of the Escrow Holder or its nominee
in cash equivalents or other investments approved by the Landlord and the Escrow
Holder. The Tenant agrees that any Security Deposit Pledgee may be the Escrow
Holder so long as the Security Deposit Pledgee is a bank or other financial
institution. The Landlord and the Tenant agree that a separate three-party
escrow agreement, in form and substance satisfactory to the Landlord, the Tenant
and the Escrow Holder, will be entered into prior to the date upon which the
Tenant may deposit any such sums in cash, and the Tenant agrees to reasonably
cooperate from time to time as requested by the Landlord in order to effectuate
the holding of any cash amount comprising a portion of the Security Deposits (as
defined below) by the Escrow Holder in accordance with terms and conditions
reasonably required by such Escrow Holder. Notwithstanding anything in this
Lease to the contrary, the Security Deposits shall at all times constitute the
property of the Tenant and title to the Security Deposits shall remain with the
Tenant. To the extent, if any, the Security Deposits are deemed to be held by
the Landlord they shall be deemed to be held in trust for the benefit of the
Tenant, in all cases, subject however to the Landlord's rights pursuant to this
Article XI. None of the Security Deposits shall be available for the use of the
Landlord for any reason other than in accordance with the exercise of the
Landlord's rights pursuant to this Article XI.

      Section 11.4 The TI Security Deposit shall be immediately increased by the
Tenant by the additional amount specified in Section 11.2 (the "Security Deposit
Covenant Amount") in the 


                                       45
<PAGE>   51
event that either (i) the Tenant's Consolidated Net Available Cash falls below
Thirty Million Dollars ($30,000,000) or (ii) the Tenant's Net Working Capital
falls below an amount equal to one hundred fifty percent (150%) of the Security
Deposit Covenant Amount; provided, however, if the Tenant's Consolidated Net
Available Cash thereafter rises to a level above Thirty Million Dollars
($30,000,000.00) or the Tenant's Net Working Capital rises to a level above an
amount equal to one hundred fifty percent (150%) of the Security Deposit
Covenant Amount for six (6) consecutive months, the Tenant shall be entitled to
a refund of the Security Deposit Covenant Amount within thirty (30) days after
the end of such six (6) month period. For purposes of this Lease, the Tenant's
"Consolidated Net Available Cash" shall be the sum of the Tenant's (A) cash and
cash equivalents and (B) marketable securities as reported on the consolidated
balance sheets contained in the Tenant's quarterly reports on Form 10-Q and
Annual Report on Form 10-K. For purposes of this Lease, the Tenant's "Net
Working Capital" shall mean current assets minus current liabilities, as
reported on the consolidated balance sheets contained in the Tenant's quarterly
reports on Form 10-Q and the Annual Report on Form 10-K. The Tenant shall
provide the Landlord with such reports as soon as practicable but in no case
later than five (5) business days following the filing of same with the
Securities and Exchange Commission. The Tenant shall promptly notify the
Landlord in the event that (A) the Tenant's Consolidated Net Available Cash
falls below Thirty Million Dollars ($30,000,000.00) or (B) the Tenant's Net
Working Capital falls below an amount equal to one hundred fifty percent (150%)
of the Security Deposit Covenant Amount. The Tenant shall be required to provide
monthly reporting of its Consolidated Net Available Cash during any quarterly
period following a quarter in which Tenant's Consolidated Net Available Cash is
less than Thirty Five Million Dollars ($35,000,000.00) or Tenant's Net Working
Capital is less than an amount equal to one hundred fifty percent (150%) of the
Security Deposit Covenant Amount.

      Section 11.5 Provided there is no then subsisting default by the Tenant
under this Lease with respect to which the Landlord has given the Tenant notice,
and thereafter only at such time as there is no such default by the Tenant then
subsisting, the required TI Security Deposit under this Section 11 shall be
reduced on the first anniversary of the date upon which the Rent Commencement
Date has occurred with respect to the entire Original Premises, and on each
following anniversary of the Commencement Date, by One Million Dollars
($1,000,000). However, if the Security Deposit Covenant Amount has been
required, but has not theretofore been deposited by the Tenant as part of the TI
Security Deposit held by the Landlord, then the retirement of the TI Security
Deposit obligation contemplated under this Section 11.4 shall first be applied
to the Security Deposit Covenant Amount until fully retired, and thereafter to
the TI Security Deposit held by the Landlord under this Section 11.5


                                   ARTICLE XII

                                  MISCELLANEOUS

      Section 12.1 Notice of Lease. The Tenant agrees not to record this Lease,
but upon request of either party, both parties shall execute and deliver a
memorandum of this Lease in form appropriate for recording or registration, an
instrument acknowledging the Commencement 


                                       46
<PAGE>   52
Date of the Term, and if this Lease is terminated before the Term expires, an
instrument in such form acknowledging the date of termination.

      Section 12.2 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 the
Landlord, at the Landlord's Address for Notices as set forth in Exhibit A or at
such other address as may have been specified by prior notice to the Tenant; and
if to the Tenant, at the Tenant's Original Address or at such other place as may
have been specified by prior notice to the Landlord. Any communication so
addressed shall be deemed duly given on the earlier of (i) the date received,
(ii) on the third business day following the day of mailing if mailed by
registered or certified mail, return receipt requested, or (iii) on the next
business day if sent by a nationally recognized overnight courier service. If
the Landlord by notice to the Tenant at any time designates some other person to
receive payments or notices, all payments or notices thereafter by the Tenant
shall be paid or given to the agent designated until notice to the contrary is
received by the Tenant from the Landlord.


      Section 12.3 Successors and Limitation on Liability. The obligations of
this Lease shall run with the land, and 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 successor
Landlord shall be liable only for obligations accruing during the period of its
ownership. The obligations of the Landlord under this Lease shall be binding
upon the assets of the Landlord consisting of an equity ownership of the
Property (and including any proceeds realized from the sale of such Property)
but not upon other assets of the Landlord and neither the Tenant, nor anyone
claiming by, under or through the Tenant, shall be entitled to obtain any
judgment in enforcing the terms and conditions of this Lease creating personal
liability on the part of the Landlord or enforcing any obligations of the
Landlord against any assets of the Landlord other than an equity ownership of
the Property. The obligations of the Tenant under this Lease shall be binding
upon the assets of the Tenant and neither the Landlord, nor anyone claiming by,
under or through the Landlord, shall be entitled to obtain any judgment in
enforcing the terms and conditions of this Lease creating personal liability on
the part of any of Tenant's, officers, employees, directors or shareholders.

      Section 12.4 Waivers by the Landlord. The failure of the Landlord or the
Tenant to seek redress for violation of, or to insist upon 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 the Landlord of Annual Fixed Rent or Additional Rent
with knowledge of the breach of any covenant of this Lease shall not be deemed a
waiver of such breach. No provision of this Lease shall be deemed to have been
waived by the Landlord or the Tenant, as the case may be, unless such waiver be
in writing signed by the Landlord or the Tenant, as the case may be. No consent
or waiver, express or implied, by the Landlord or Tenant 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.


                                       47
<PAGE>   53
      Section 12.5 Acceptance of Partial Payments of Rent. No acceptance by the
Landlord of a lesser sum than the Annual Fixed Rent and Additional Rent then due
shall be deemed to be other than a partial installment of such rent due, nor
shall any endorsement or statement on any check or any letter accompanying any
check or payment as rent be deemed an accord and satisfaction, and the Landlord
may accept such check or payment without prejudice to the Landlord's right to
recover the balance of such installment or pursue any other remedy in this Lease
provided. The delivery of keys to any employee of the Landlord or to the
Landlord's agent or any employee thereof shall not operate as a termination of
this Lease or a surrender of the Premises.

      Section 12.6 Interpretation and Partial Invalidity. 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. The titles of the Articles are for convenience only and not to
be considered in construing this Lease. This Lease contains all of the
agreements of the parties with respect to the subject matter thereof and
supersedes all prior dealings between them with respect to such subject matter.

      Section 12.7 Quiet Enjoyment. So long as the Tenant pays Annual Fixed Rent
and Additional Rent, performs all other Tenant covenants of this Lease and
observes all conditions hereof, the Tenant shall peaceably and quietly have,
hold and enjoy the Premises free of any claims by, through or under the
Landlord.

      Section 12.8 Brokerage. Each party represents and warrants to the other
that it has had no dealings with any broker or agent other than Meredith & Grew,
Incorporated and Lynch, Murphy, Walsh & Partners (collectively, the "Broker") in
connection with this Lease and shall indemnify and hold harmless the other from
claims for any brokerage commission (other than by the Broker) arising out a
breach of the foregoing representations. Landlord shall be responsible for any
commission due to the Broker pursuant to the terms of a separate agreement.

      Section 12.9 Surrender of Premises and Holding Over. The Tenant shall
surrender possession of the Premises on the last day of the Term and the Tenant
waives the right to any notice of termination or notice to quit. The Tenant
covenants that upon the expiration or sooner termination of this Lease, it
shall, without notice, deliver up and surrender possession of the Premises in
the same condition in which the Tenant has agreed to keep the same during the
continuance of this Lease and in accordance with the terms hereof, normal wear
and tear and damage by fire or other casualty excepted, first removing therefrom
all goods and effects of the Tenant and any leasehold improvements Landlord
specified for removal pursuant to Section 4.2, and repairing all damage caused
by such removal. Upon the expiration of this Lease or if the Premises should be
abandoned by the Tenant, or this Lease should terminate for any cause, and at
the time of such expiration, vacation, abandonment or termination, the Tenant or
Tenant's agents, subtenants or any other person should leave any property of any
kind or character on or in the Premises, the fact of such leaving of property on
or in the Premises shall be conclusive


                                       48
<PAGE>   54
evidence of intent by the Tenant, and individuals and entities deriving their
rights through the Tenant, to abandon such property so left in or upon the
Premises, and such leaving shall constitute abandonment of the property.
Landlord shall have the right and authority without notice to the Tenant or
anyone else, to remove and destroy, or to sell or authorize disposal of such
property, or any part thereof, without being in any way liable to the Tenant
therefor and the proceeds thereof shall belong to the Landlord as compensation
for the removal and disposition of such property.

      If the Tenant fails to surrender possession of the Premises upon the
expiration or sooner termination of this Lease, the Tenant shall pay to
Landlord, as rent for any period after the expiration or sooner termination of
this Lease an amount equal to one hundred fifty percent (150%) of the Annual
Fixed Rent and the Additional Rent required to be paid under this Lease as
applied to any period in which the Tenant shall remain in possession. Acceptance
by the Landlord of such payments shall not constitute a consent to a holdover
hereunder or result in a renewal or extension of the Tenant's rights of
occupancy. Such payments shall be in addition to and shall not affect or limit
the Landlord's right of re-entry, Landlord's right to collect such damages as
may be available at law, or any other rights of the Landlord under this Lease or
as provided by law.

      Section 12.10 Ground Lease. The Land is owned by the Massachusetts
Institute of Technology ("MIT"). MIT as lessor and the Landlord as lessee (or a
limited partnership of which the Landlord would be the general partner (the
"Limited Partnership") and to whom all of the Landlord's rights and obligations
under this Lease may be assigned in the Landlord's sole discretion) shall enter
into a ground lease (the "Ground Lease") of the Land, and this Lease shall in
all respects be subject to such Ground Lease. If the Ground Lease shall
terminate during the Term for any reason whatsoever, except as may otherwise be
agreed between MIT and the Tenant, this Lease shall terminate with the same
force and effect as if such termination date had been named herein as the date
of expiration hereof. However, this Lease is subject to the execution by MIT,
the Tenant and the Landlord of a non-disturbance agreement in the form attached
hereto as Exhibit H. Each party shall pay its own expenses related to such
non-disturbance agreement. The Landlord represents and warrants to the Tenant
that, upon execution of the Ground Lease by the Landlord, or upon assignment of
this Lease to the Limited Partnership and the execution of the Ground Lease by
the Limited Partnership, the Landlord or the Limited Partnership, as the case
may be, shall have the full right and authority to grant the estate demised
herein and the appurtenant rights granted herein.

      Section 12.11 Financial Reporting. Tenant shall from time to time (but not
less frequently than quarterly) provide Landlord with financial statements of
Tenant, together with related statements of Tenant's operations for Tenant's
most recent fiscal year then ended, certified by an independent certified public
accounting firm. Tenant's financial statements shall, in any event, specify the
Tenant's Consolidated Net Available Cash and Net Working Capital.
Notwithstanding the foregoing, so long as the Tenant is a public company, it
shall be in compliance with its financial reporting obligations provided that it
submits all 10-Q and 10- K reports to the Landlord within ten (10) business days
of filing the same with the Securities and Exchange Commission.


                                       49
<PAGE>   55
      Section 12.12 Cambridge Employment Plan. The Tenant agrees to sign an
agreement with the Employment and Training Agency designated by the City Manager
of the City of Cambridge as provided in subsections (a)-(g) of Section 24-4 of
Ordinance Number 1005 of the City of Cambridge, adopted April 23, 1984.

      Section 12.13 Truck Delivery Routes; Traffic Mitigation Measures. Tenant
agrees to exercise good faith efforts to cooperate with any efforts by the City
of Cambridge to direct truck traffic to certain streets and away from certain
other streets, in connection with the making of deliveries to the Premises, and
to comply with any traffic mitigation measures of the City of Cambridge, and
Tenant shall otherwise comply with all legal requirements of the City of
Cambridge pertaining thereto.

      Section 12.14 Laboratory Animals. The Landlord acknowledges that the
Tenant will be conducting biotechnology research and development at the Premises
and as such may require the use of certain laboratory animals at the Premises in
order to carry out such research and development.

      Section 12.15 No Consequential Damages. In no event shall either Landlord
or Tenant be liable to the other for consequential damages, provided that
damages incurred by the Landlord in connection with any holding over by Tenant
in the Premises, including without limitation those associated with loss, cost,
liability or expense arising by virtue of the existence of aggrieved third
parties (e.g. lenders and prospective tenants), shall not constitute
consequential damages.

      Section 12.16 Governing Law. This Lease shall be governed by and construed
in accordance with the laws of the Commonwealth of Massachusetts.

      Section 12.17 Termination Rights for Failure of Conditions. The
effectiveness of this Lease shall be subject to the timely satisfaction of each
of the conditions specified below, unless the satisfaction of a condition is
waived or deemed waived, on or before the deadline date specified below for the
satisfaction thereof:

            (a) Tenant's Title Due Diligence: That the Tenant is reasonably
      satisfied, on or before November 21, 1997, that any matters specified in
      that certain ALTA leasehold title insurance commitment with respect to
      this Lease and a boundary survey of the Land specifying the location of
      any easements or restrictions, which have been heretofore furnished by the
      Landlord to the Tenant, will not materially and adversely interfere with
      Tenant's use of the Premises, and the timely occupancy thereof as
      contemplated under this Lease, for the Permitted Uses. The Tenant's
      failure to terminate this Lease under this clause (a) on the basis of the
      condition herein described, on or before November 24, 1997, shall
      constitute a waiver by the Tenant of such condition.

            (b) Lender's Zoning Opinion: that the Tenant has been furnished with
      a copy of the zoning opinion given by the Landlord's counsel to the lender


                                       50
<PAGE>   56
      making the construction loan to which reference is made in clause (c)
      below on or before the closing of such construction loan, which opinion
      does not reveal, in the Tenant's reasonable judgment, any issues that will
      materially and adversely interfere with Tenant's use of the Premises and
      the timely occupancy thereof as contemplated in this Lease for the
      Permitted Uses.

            (c) Closing of Construction Loan: that a loan financing construction
      of the Building shall have closed on or before March 1, 1998, which
      condition shall be for the benefit of both the Landlord and the Tenant,
      and cannot be waived as a condition unless waived by both the Landlord and
      the Tenant. If the construction loan is not closed on or before March 1,
      1998, this Lease may be terminated by either the Landlord or the Tenant
      upon notice to such effect to the other.

            (d) Subordination, Non-Disturbance and Attornment Agreement: that
      the Tenant has been furnished with a subordination, non-disturbance and
      attornment agreement, substantially in the form attached hereto as Exhibit
      K on or before the closing of the construction loan to which reference is
      made in clause (c) above.

            (e) Commencement of Construction: that the commencement of
      construction of the Building will be able to be, and is, commenced on or
      before March 1, 1998, which condition shall be for the benefit of both the
      Landlord and the Tenant, and cannot be waived as a condition unless waived
      by both the Landlord and the Tenant. If the construction of the Building
      is not commenced on or before March 1, 1998, this Lease may be terminated
      by either the Landlord or the Tenant upon notice to such effect to the
      other.

            (f) Forest City Enterprises Guaranty of Completion: that a guaranty
      of completion for the benefit of the Tenant, in the form attached hereto
      as Exhibit L (the "Millennium Completion Guaranty") is furnished to the
      Tenant on or before the closing of the construction loan to which
      reference is made in clause (c) above, provided that paragraph 2(c)(ii) of
      Exhibit A thereto may be further modified so long as such modification
      does not adversely affect the rights of Tenant under the Millennium
      Completion Guaranty.


                                       51
<PAGE>   57
Upon any termination of this Lease under this Section 12.17, neither party shall
have any further rights or obligations under this Lease, which shall have no
further force or effect.

      IN WITNESS WHEREOF, this Lease has been executed and delivered as of the
date first above written as a sealed instrument.

                                                    LANDLORD:

                                                    FC 45/75 SIDNEY, INC.


                                                    By:
                                                       -------------------------
                                                       Gayle W. Friedland
                                                       Vice President

                                                    TENANT:

                                                    MILLENNIUM PHARMACEUTICALS,
                                                    INC.


                                                    By:
                                                       -------------------------

                                                    Title:
                                                          ----------------------



                                       52
<PAGE>   58
                                    EXHIBIT A

                                Basic Lease Terms


Annual Fixed Rent
for the Initial Term:               Lease Years One (1) through Five (5): $35.00
                                    per rentable square foot.

                                    Lease Years Six (6) through Fifteen (15):
                                    $38.00 per rentable square foot.

Security Deposit:                   See Section 11.

Initial                             Term: Approximately fifteen (15) years,
                                    commencing on the First Rent Commencement
                                    Date, and expiring on the last day of the
                                    month during which the fifteenth (15th)
                                    anniversary of the First Rent Commencement
                                    Date occurs.

Extension Options:                  Tenant shall have two (2) options to extend
                                    the term of this Lease for an additional
                                    five (5) years each, all as described in
                                    Section 2.6 of the Lease.

Landlord's Original
Address:                            FC 45/75 Sidney, Inc.
                                    10800 Brookpark Road
                                    Cleveland, Ohio  44130
                                    Attention:  James Ratner

Landlord's Address for
Notices:                            FC 45/75 Sidney, Inc.
                                    38 Sidney Street
                                    Cambridge, Massachusetts 02139-4234
                                    Attention: Gayle Friedland

                                    With a copy to:

                                    Forest City Commercial Management
                                    38 Sidney Street
                                    Cambridge, Massachusetts 02139-4234
                                    Attention: General Manager


Original Premises:                  Approximately 175,000 total rentable square
                                    feet ("rsf") of space as depicted on Exhibit
                                    B-1, as such calculation may be adjusted in
                                    accordance with Section 2.1 of the Lease.



                                      A-1
<PAGE>   59
Parking Privileges:                 During the Term, Landlord shall provide in
                                    parking garages located in University Park
                                    the aggregate of (i) two (2) parking spaces
                                    per 1,000 rsf of floor area of the Premises
                                    and (ii) an additional seventy (70) parking
                                    spaces; provided that at least two (2)
                                    parking spaces per 1,000 rsf of floor area
                                    contained in the Original Premises shall be
                                    located in the 101 Pacific Street Garage,
                                    subject to the terms and conditions of this
                                    Lease pertaining to alternative temporary
                                    parking spaces. However, with respect to the
                                    seventy (70) parking spaces to which
                                    reference is made in clause (ii) above, and
                                    any additional parking spaces that Tenant
                                    shall be entitled to by virtue of its
                                    expansion beyond 175,000 rentable square
                                    feet of floor area (the "Expansion Parking
                                    Spaces"), such parking spaces shall be
                                    located in the 101 Pacific Street Garage
                                    unless and until construction of a building
                                    on parcel #8 as shown on the Map of
                                    University Park at Exhibit B-2 hereto is
                                    complete, at which time the Landlord may
                                    designate other comparable spaces within
                                    University Park as some or all of such
                                    parking spaces. The Tenant shall pay the
                                    market rate from time to time in effect for
                                    all of the parking spaces provided by
                                    Landlord. The market rate for the first
                                    Lease Year is established to be $140.00 per
                                    month per parking space. Tenant shall have
                                    the right to lease additional spaces, as
                                    available, on a month to month basis. Tenant
                                    shall have 24-hour access, by security card
                                    or other similar means, to the 101 Pacific
                                    Street Garage and any other parking facility
                                    in which it has designated spaces. With
                                    respect to the 101 Pacific Street Garage,
                                    the Landlord shall not provide to other
                                    tenants of the Building more than two (2)
                                    parking spaces per 1,000 rsf of floor area
                                    unless such tenant occupies less than 10,000
                                    rsf of floor area in the Building.

Permitted Uses:                     General business and administrative offices,
                                    pharmaceutical research and manufacturing,
                                    and customary accessory uses supporting the
                                    foregoing, all as permitted by law.

Commencement Date:                  See Section 2.5.

Scheduled Rent
Commencement Date:                  February 15, 1999 with respect to the 75
                                    Sidney Building and March 15, 1999 with
                                    respect to the 45 Sidney Building.

Rent Commencement Date:             See Section 2.5.



                                      A-2
<PAGE>   60
Tenant's Original
Address:                            Millennium Pharmaceuticals, Inc.
                                    238 Main Street
                                    Cambridge, Massachusetts 02142

Tenant's Address for
Notices:                            Millennium Pharmaceuticals, Inc.
                                    75 Sidney Street
                                    Cambridge, Massachusetts 02139-4211
                                    Attention:  Mark Levin

                                    With a copy to:

                                    Joel R. Bloom, Esq.
                                    Mintz, Levin, Cohn, Ferris,
                                      Glovsky and Popeo, P.C.
                                    One Financial Center
                                    Boston, Massachusetts 02111

Total Rentable Floor
Area of Building:                   Approximately 175,000 rsf of which 137,712
                                    rsf is contained in the 45 Sidney Street
                                    building and 37,288 rsf is contained in the
                                    75 Sidney Street building, as such 
                                    calculations may be adjusted in accordance 
                                    with Section 2.1 of this Lease.


                                      A-3
<PAGE>   61
                                    EXHIBIT B

                                Legal Description



                                       B-1
<PAGE>   62
                                   EXHIBIT B-1

                              Depiction of Premises


                                      B-1-1
<PAGE>   63
                                   EXHIBIT B-2

                             Map of University Park

                                      B-2-1
<PAGE>   64
                                    EXHIBIT C

                                   Workletter

         All capitalized terms used herein and not otherwise defined shall have
the meaning ascribed to said terms in the Lease to which this Work Letter is
attached as EXHIBIT C. This Work Letter is expressly subject to the provisions
of the Lease and supplements the Lease. The provisions herein should be read
consistently with the Lease, provided, however, in the event of any
inconsistency between this Work Letter and the Lease, the terms and conditions
of the Lease shall, in all instances, and for all purposes, control.

                                  ARTICLE XIII

                                   Definitions

         Section 13.1 Definitions. The following terms shall have the meanings
indicated or referred to below:

                  "Architect" -- means Tsoi Kobus Associates (or replacement
therefor in accordance with Section 2.1).

                  "Base Building Plans and Specs" -- See Section 3.1.

                  "Base Building Schematic Plans and Specs" means the schematic
plans and outline specifications prepared by the Architect for the Base Building
Improvements identified on SCHEDULE C1 attached hereto.

                  "Base Building Improvements" means the base building shell and
core and base building mechanical systems contemplated by the Project Work
Allocation and the Base Building Plans and Specs.

                  "Building Standards" means the essential qualities associated
with the Base Building Improvements specified in the Project Work Allocation and
the Mechanical Systems Capacities Exhibit.

                  "Construction Progress Schedule" -- See Section 4.7.

                  "Contractor" -- means JMA/Siena Joint Venture (or replacement
therefor in accordance with Section 4.1).

                  "Design and Construction Commencement Schedule" -- See Section
3.1.

                  "Developer's Administrative Fee" means a fee of Fifty Five
Thousand Dollars ($55,000.00), to be charged against the Leasehold Improvement
Allowance by Forest City Development for construction administration services,
in eleven (11) equal monthly installments



                                      C-1
<PAGE>   65
of Five Thousand Dollars ($5,000.00) each, commencing on the first day of the
month following the date upon which Landlord commences construction of the
Building.

                  "Eligible Leasehold Improvement Expenses" -- See Section 6.2.

                  "Excusable Delay" means any delay in the satisfaction of the
conditions in question to the extent the same is a consequence of External
Causes including, without limitation, any governmental embargo restrictions, or
actions or inactions of local, state or federal governments (such as, without
limitation, any delays in issuing building permits, certificates of occupancy or
other similar permits or certificates).

                  "Landlord Delay" -- See Section 7.4.

                  "Leasehold Improvement Allowance" -- See Section 6.1

                  "Leasehold Improvements" means the build-out of the Premises
(and, if applicable, work performed by Tenant in areas not part of the Premises)
into a first class biotechnology research and development laboratory and office
facility as contemplated by the Project Work Allocation and the Tenant's Plans
and Specs.

                  "Mechanical Systems Capacities Exhibit" -- See Section 3.2.

                  "Millennium Project" means, collectively, the Base Building
Improvements and the Leasehold Improvements.

                  "Project Work Allocation" means the schedule denoting aspects
of the Millennium Project and the allocation thereof to either Landlord or
Tenant (or partially to Landlord and the balance to Tenant) attached hereto as
SCHEDULE C2.

                  "Substantial Completion" -- See Section 7.1.

                  "Tenant Base Building Change Order" -- See Section 5.1.

                  "Tenant Leasehold Improvement Change Order" -- See Section
5.5.

                  "Tenant Construction Readiness Date"-- See Section 4.6.

                  "Tenant Delay" -- See Section 7.3.

                  "Tenant's Plans and Specs" -- See Section 3.1.

                  "Tenant's Schematic Plans and Specs" means the schematic plans
and outline specifications prepared by the Architect for the Leasehold
Improvements identified on SCHEDULE C3 attached hereto.



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<PAGE>   66
                  "Tenant's Representative" -- See Section 2.2.

                  "Termination Notice" -- See Section 9.1.


                                   ARTICLE XIV

               Engagement of Architect and Tenant's Representative

         Section 14.1 Landlord and Tenant have, under separate arrangements with
the Architect, engaged the Architect to develop schematic plans, drawings and
specifications for the Base Building Improvements and the Leasehold
Improvements, respectively. Landlord and Tenant shall hereafter enter into
separate formal architect's contracts with the Architect pursuant to which the
Architect will be engaged separately by Landlord and Tenant to prepare more
fully developed plans, drawings and specifications, work with Landlord and
Tenant through the bid process and supervise the construction of the Base
Building Improvements and Leasehold Improvements, respectively. Landlord and
Tenant agree to work together to engage the Architect's services under contracts
that properly allocate the responsibility of the Architect to each of Landlord
and Tenant, and to assure that the construction of the Millennium Project is
well coordinated. In order to assure such coordination, Landlord shall furnish a
copy of its architect's contract to Tenant, and it is intended by the parties
that Landlord's architect's contract shall serve as a guide for the preparation
of Tenant's architect's contract. Tenant shall furnish a copy of its proposed
architect's contract with the Architect to Landlord prior to its execution for
Landlord's review and approval, which shall not be unreasonably withheld or
delayed. In either case, purely economic terms that a party may reasonably
believe is appropriately confidential may be redacted. If either Landlord or
Tenant should elect to replace the Architect and engage a replacement Architect
to fulfill the responsibilities contemplated to be undertaken by the Architect
on behalf of such party, and the parties agree that such a replacement of the
Architect will not be implemented without good cause, the identity of the
replacement shall be subject to the other party's approval, which shall not be
unreasonably withheld or delayed.

         Section 14.2 Tenant has entered into an agreement with The Carlisle
Consulting Group, Inc. ("Tenant's Representative") pursuant to which Tenant's
Representative will perform certain services for and on behalf of Tenant during
the design and construction phases of the Leasehold Improvements. Tenant shall,
at its sole cost and expense, and in accordance with the terms and conditions of
its agreement with Tenant's Representative, compensate Tenant's Representative
for providing such services. Landlord hereby agrees that Tenant's Representative
shall receive copies of all notices to which reference is made in this EXHIBIT C
given by Landlord to Tenant. Tenant hereby agrees that Tenant's Representative
shall have authority to act as Tenant's representative in connection with its
participation in meetings and otherwise, and that except to the extent Landlord
has been given contrary instructions in writing from Tenant with respect to any
matter with which Tenant's Representative has been involved, Landlord is
entitled to rely on Tenant's Representative as the party having authority to
make decisions and establish schedules for the performance of work. Tenant
agrees further to continue to engage Tenant's Representative to render the
services contemplated hereunder, or a qualified successor subject to



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<PAGE>   67
Landlord approval, which shall not be unreasonably withheld, until such time as
final completion of the Leasehold Improvements and occupancy by Tenant in the
Premises has been achieved.


                                   ARTICLE XV

                            Plans and Specifications

         Section 15.1 Landlord shall, at its sole cost and expense (except as
provided in Section 3.4 and Article 5), as soon as reasonably possible, but in
any event in substantial conformity with the Design and Construction
Commencement Schedule, cause the completion of the Base Building Schematic Plans
and Specs as necessary to permit construction of the Base Building Improvements
to commence on or before the date contemplated therefor, and thereafter finally
complete the Base Building Plans and Specs as necessary to permit construction
of the Base Building Improvements to proceed expeditiously. For all purposes
hereof, the "Base Building Plans and Specs" means the plans, specifications and
working drawings for the completion of the Base Building Improvements, as the
same may be modified consistently with the terms and conditions hereof. Tenant
shall at its sole cost and expense (except as provided in Section 3.4 and
Article 5), as soon as reasonably possible, but in any event in substantial
conformity with the "Design and Construction Commencement Schedule" attached
hereto as SCHEDULE C4, cause the completion of the Tenant's Schematic Plans and
Specs as necessary to permit construction of the Leasehold Improvements to
commence on the Tenant Construction Readiness Date for each of the 75 Sidney
Building and the 45 Sidney Building, and thereafter to finally complete the
Tenant's Plans and Specs as necessary to permit construction of the Leasehold
Improvements to proceed expeditiously. For all purposes hereof, the "Tenant's
Plans and Specs" means the plans, specifications and working drawings for the
completion of the Leasehold Improvements approved by Landlord as herein
provided, as the same may be modified consistently with the terms and conditions
hereof.

         Section 15.2 Landlord, Tenant, and Architect have been working together
to create design concepts, plans and specifications for the Millennium Project
that will be mutually satisfactory to Landlord and Tenant. The results of such
efforts as of the date of this Lease are the Project Work Allocation, the
standard tenant system allocations and capacities specified in Exhibit F to this
Lease (the "Mechanical Systems Capacities Exhibit"), the designs for the Base
Building Improvements set forth in the Base Building Schematic Plans and Specs,
the designs for the Leasehold Improvements set forth in Tenant's Schematic Plans
and Specs and the inventory of standard installed laboratory equipment
identified on SCHEDULE C5 attached hereto. The parties agree diligently and in
good faith to work together with the Architect and any other retained design
professionals to finalize the Base Building Plans and Specs and Tenant's Plans
and Specs in the manner contemplated by the Design and Construction Commencement
Schedule. Landlord and Tenant agree to furnish in timely fashion to each other
such information as may be requested by the other party, to promptly "sign off"
or specify objections or concerns as to matters where a "sign off" is requested
by one party or the other and to otherwise undertake all such actions as are
reasonably necessary in order to assure the timely commencement of the



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<PAGE>   68
construction of the Base Building Improvements and, upon the Tenant Construction
Readiness Date, the Leasehold Improvements.

         Section 15.3 Tenant's Plans and Specs, including without limitation
each iteration thereof, and each change proposal with respect thereto, through
and including the "as-built" version thereof, and the work contemplated to be
performed in accordance therewith, shall be subject to Landlord's prior
approval, which approval shall not be unreasonably withheld or delayed. Without
limitation of the foregoing, Landlord shall not be deemed to be unreasonable for
requiring that the standards provided in Article IV of this Lease are being
fulfilled, for withholding approval to any material variance of the Tenant's
Plans and Specs with Tenant's Schematic Plans and Specs, or for withholding
approval with respect to any aspect of Tenant's Plans and Specs that are
inconsistent or incompatible with the Base Building Plans and Specs, unless
Tenant proposes a Tenant Base Building Change Order to remedy such inconsistency
or incompatibility, to which Landlord has no objection under Section 5.1.
Neither the requirement that Tenant's Plans and Specifications be submitted to
Landlord nor Landlord's or Landlord's agents actual or implied review of
Tenant's Plans and Specs on changes thereto shall in any way be deemed to be an
agreement by Landlord that (i) the work contemplated thereby or any other aspect
thereof complies with legal or other requirements, (ii) that the Tenant's Plans
and Specs will be approved by any governmental agency having jurisdiction
thereover, (iii) that Tenant's Plans and Specs are free from errors, omissions
or inconsistencies or are coordinated with the Base Building Plans and Specs or
within Tenant's Plans and Specs, and without limitation, any delay associated
with any of the foregoing (i), (ii) and (iii) shall constitute Tenant's Delay.

         Section 15.4 The Base Building Plans and Specs developed by Landlord
under Section 3.1 shall always remain consistent with the Building Standards
and, if during the development and completion of the Base Building Plans and
Specs, Landlord desires to make any change that would not be so consistent (a
"Major Change"), such Major Change shall be subject to Tenant's consent, which
shall not be unreasonably withheld or delayed. If, during the development and
completion of the Base Building Plans and Specs, Tenant desires to propose a
Major Change, Tenant shall undertake responsibility for having the Architect
prepare any necessary modifications to the Base Building Plans and Specs, and
any such Major Change shall be subject to Landlord's approval, which Landlord
shall not unreasonably withhold or delay. Without limitation of the foregoing,
Landlord shall not be deemed to be unreasonable for withholding consent to any
Major Change which would diminish the quality of the Base Building Improvements,
would cause any delay in the Substantial Completion of the Base Building
Improvements, or which Landlord would be entitled to reject under Article IV of
this Lease. Landlord may, in any event, condition its approval to a Major Change
proposed by Tenant upon Tenant's expressly acknowledging its responsibility for
any increase in the costs associated with the Base Building Improvements
resulting from such Major Change and depositing Landlord's estimate thereof,
based on input from the Contractor, with Landlord for application by Landlord to
the cost thereof as contemplated in Section 6.3. If Landlord should approve
Tenant's proposed Major Change, Tenant shall cause all plans and specifications
associated therewith to be furnished to Landlord for approval. Neither the
requirement that Tenant submit such plans and specifications to Landlord nor
Landlord's or Landlord's agents' actual or implied review thereof shall in any
way be an agreement by Landlord that (i) the work contemplated thereby or


                                      C-5
<PAGE>   69
any other aspect thereof complies with legal or other requirements, (ii) that
such plans and specifications will be approved by any governmental authority
having jurisdiction thereover, (iii) that the plans and specifications are free
from errors, omissions or inconsistencies, or are coordinated with the Base
Building Plans and Specs or within themselves, and without limitation, any delay
associated with any of the foregoing (i), (ii) or (iii) or any delay in
Landlord's ability to cause the Tenant Construction Readiness Date or the date
upon which Substantial Completion of the Base Building Improvements occurs shall
constitute Tenant's Delay. Tenant acknowledges that Landlord has made no
representation or warranty with respect to the Base Building Improvements being
suitable for any particular use or purpose, Tenant having the responsibility to
make such determination.


                                   ARTICLE XVI

                           Construction of the Project


         Section 16.1 Landlord and Tenant shall, under separate contracts,
engage the Contractor, and enter into such other arrangements as are
appropriate, to cause the Base Building Improvements and Leasehold Improvements,
respectively, to be timely constructed, installed and completed. Tenant shall
furnish a copy of its proposed construction contract with the Contractor, prior
to its execution for Landlord's review and approval, which shall not be
unreasonably withheld or delayed. It is contemplated that Tenant's construction
contract with the Contractor be consistent with the terms and conditions set
forth in Landlord's contract with the Contractor, and due to the fact that the
construction of the Base Building Improvements and Leasehold Improvements are to
be performed contemporaneously in significant respects, the coordination of the
construction process and the proper undertaking of responsibility by the
Contractor on behalf of Landlord and Tenant is critically important. In
furtherance of such coordination, Landlord shall furnish Tenant a copy of
Landlord's construction contract, and it is intended by the parties that
Landlord's construction contract shall serve as a guide for the preparation of
Tenant's construction contract. In the case of both Landlord's and Tenant's
delivery of their respective construction contracts to the other, purely
economic terms that a party may reasonably believe is appropriately confidential
may be redacted. However, in no event shall the economic terms associated with
the pricing of change orders be considered appropriately confidential, as under
certain circumstances each party may be responsible for increases in cost
incurred by the other party in connection with change orders. If either Landlord
or Tenant should elect to replace the Contractor to fulfill the responsibilities
contemplated to be undertaken by the Contractor on behalf of such party, and the
parties agree that such a replacement of the Contractor will not be implemented
without good cause, the identity of the replacement shall be subject to the
other party's approval, which shall not be unreasonably withheld or delayed.
Each of Landlord and Tenant agree to notify the other party in the event such
party or the Contractor should seek to terminate, or terminates, a construction
contract entered into by such party and the Contractor.

         Section 16.2 Landlord shall install, furnish and perform, as the case
may be, with reasonable diligence and in a good and workmanlike manner and at
its sole cost and expense


                                      C-6
<PAGE>   70
(except as otherwise expressly provided herein to the contrary), the facilities,
materials, labor, supplies and work required for the construction of the Base
Building Improvements in accordance with the Base Building Plans and Specs.

         Section 16.3 Tenant shall install, furnish, and perform, as the case
may be, with reasonable diligence and in a good and workmanlike manner and at
its own cost and expense (except as otherwise expressly provided to the contrary
herein) the facilities, materials, labor, supplies and work required for the
construction of the Leasehold Improvements in accordance with the Tenant's Final
Plans and Specs or otherwise as approved by Landlord. The Leasehold Improvements
shall commence to be constructed promptly following the Tenant Construction
Readiness Date, and be constructed, installed and performed in accordance with
the Rules and Regulations for Tenant Construction which are set forth as
SCHEDULE C6 and with any and all reasonable requirements of Landlord's lender in
connection with the loan documents, including without limitation, inspection
procedures, funding payment procedures, and retainage. As construction of the
Base Building Improvements and the Leasehold Improvements will, to a certain
extent, be conducted contemporaneously, each of Landlord and Tenant expressly
acknowledge that in conducting their respective work, due care must be exercised
to avert interference in the conduct by the other party of its work, and each
party covenants and agrees to exercise reasonable efforts to avert such
interference.

         Section 16.4 All building permits, certificates of occupancy and other
governmental approvals required to construct the Base Building Improvements
shall be obtained by Landlord at Landlord's sole cost and expense (except as
expressly otherwise provided herein). All building permits, certificates of
occupancy, and other governmental approvals required to construct the Leasehold
Improvements and to occupy and operate Tenant's business in the Premises shall
be obtained by Tenant at Tenant's sole cost and expense.

         Section 16.5 Landlord and Tenant agree to work together cooperatively
so as to coordinate the management, administration, and scheduling of the Base
Building Improvements and the Leasehold Improvements. Such cooperation shall
include without limitation, regular meetings during the construction period with
the Contractor, the attendance at such meetings to include authorized
representatives of Landlord and Tenant's Representative. Landlord and Tenant
each agree that they shall respectively assure the availability of such
representatives at reasonable times after reasonable notice. For the foregoing
purposes, Landlord has initially designated Allison Nichols as Landlord's
representative.

         Section 16.6 The Base Building Improvements shall for all purposes
hereof be deemed at the stage of completion sufficient to permit Landlord to
establish that the "Tenant Construction Readiness Date" has occurred on such
date as the Base Building Improvements are in such condition, with floor slab
concrete poured and fireproofing installed, that Tenant can reasonably commence
construction of the mechanical, electrical, and plumbing rough-in portions of
the Leasehold Improvements on at least two (2) contiguous floors of the
Premises. Landlord shall diligently proceed with the construction of the Base
Building Improvements and endeavor to achieve the stage of completion sufficient
to permit Landlord to cause the Tenant Construction


                                      C-7
<PAGE>   71
Readiness Date to occur (i) on or before July 5, 1998, for the 75 Sidney
Building; and (ii) on or before August 2, 1998 for the 45 Sidney Building.

         Section 16.7 Landlord and Tenant have jointly prepared a construction
progress schedule (the "Construction Progress Schedule") for construction and
completion of the Millennium Project, which specifies the material activities
and events that will occur during each phase of the Millennium Project and sets
forth key dates and certain aspects of construction that are anticipated to be
substantially completed thereby in order that the Millennium Project is timely
completed. The Construction Progress Schedule will be updated mutually by
Landlord and Tenant as necessary to reflect the then expectations of the parties
including, without limitation, following the occurrence of circumstances
reasonably anticipated to affect the progress of construction. The Construction
Progress Schedule will indicate, without limitation, the anticipated Tenant
Construction Readiness Date. No modification of the Construction Progress
Schedule as hereinabove contemplated, or otherwise as permitted hereunder, shall
necessarily result in a postponement of the Scheduled Rent Commencement Date or
the Rent Commencement Date. The only circumstances resulting in a postponement
of either of such dates shall be the circumstances contemplated in Section 2.5
of the Lease.

                                  ARTICLE XVII

                               Changes in the Work

         Section 17.1 Tenant may request changes, subject to the Landlord's
approval as hereinafter provided, in the Base Building Improvements consisting
of additions or deletions to, or other revisions in, the Base Building Plans and
Specs, with an appropriate adjustment, if any, to the Construction Progress
Schedule and with appropriate provisions for payments by Tenant as herein
provided. Any such changes in the Base Building Plans and Specs which are
approved by Landlord and authorized by Tenant by written change order are herein
referred to as a "Tenant Base Building Change Order". Landlord's rights with
respect to approving or withholding approval to a proposed Tenant Base Building
Change Order, and the allocation of responsibility in paying any increase in the
cost of the Base Building Improvements resulting therefrom, shall be governed by
the same criteria as are applicable to requested change to the Base Building
Plans and Specs under Section 3.4.

         Section 17.2 If Landlord determines that a Tenant Base Building Change
Order will result in an increase in the cost of the Base Building Improvements,
as calculated below, Landlord shall advise Tenant of Landlord's estimate thereof
and permit Tenant, in accordance with Section 5.3 below, to decide whether or
not to give Landlord notice that Tenant desires that Landlord proceed with such
Tenant Base Building Change Order. Such increase in the cost of the Base
Building Improvements ("Tenant Base Building Change Order Cost") shall be equal
to the sum of (a) all so-called "hard costs" as specified in Landlord's contract
with Contractor reasonably and necessarily incurred with the subject change,
plus (b) all reasonable, actually incurred so-called third party "soft costs" in
connection with the subject change (including, without limitation, interest and
other carrying costs), plus (c) reasonable, actually incurred so-called "general
conditions", plus (d) Contractor's overhead and profit, and (e) all reasonable,



                                      C-8
<PAGE>   72
actually incurred design and engineering costs in connection with the design of
such change. Landlord shall provide Tenant with an estimate accompanied by
reasonable substantiation of all costs attributed to Tenant Base Building Change
Orders, including, without limitation, material and labor quantity estimates,
unit costs and contractor and subcontractor quotations. Such costs charged to
Tenant should not exceed the actual cost to be incurred by Landlord.
Additionally, Landlord shall give Tenant notice of its estimate of any effect
that Tenant's Base Building Change Order will have on the Construction Progress
Schedule.

         Section 17.3 Within five (5) business days after such notification,
Tenant shall, in turn, notify Landlord as to whether Tenant wishes to proceed
with the Tenant Base Building Change Order in question and, if the decision is
to proceed, accompanied by payment equal to Landlord's estimated Tenant Base
Building Change Order Cost. In the event that Tenant fails to notify Landlord
within such five (5) business day period, Tenant shall automatically be deemed
not to desire the Tenant Base Building Change Order, and Landlord shall not be
obligated to implement the same. If Tenant timely gives Landlord notice to
implement the Tenant Base Building Change Order, then Tenant shall be
responsible for the full Tenant Base Building Change Order Cost (whether greater
or less than the amount of Landlord's estimate which Tenant shall have paid to
Landlord as a condition to landlord's having implemented the same) and any delay
in the occurrence of the Tenant Construction Readiness Date and/or Substantial
Completion of the Base Building Improvements caused thereby, whether greater or
less than the delay estimated by Landlord, shall be deemed Tenant Delay for all
purposes hereof.

         Section 17.4 Notwithstanding anything to the contrary otherwise
provided in this Article 5, if Tenant should propose a Tenant Base Building
Change Order that is approved by Landlord in accordance with this Article 5 and
approved by Tenant to be implemented by Landlord, and if the calculation of the
Tenant Base Building Change Order Cost with respect thereto results in a
decrease in the cost to the Owner to construct the Base Building Improvements
("Base Building Change Order Savings"), then such Base Building Change Order
Savings, until fully applied, may be applied by Tenant to any future Tenant Base
Building Change Order Costs thereafter incurred by Tenant hereunder. However,
Tenant shall not be entitled to any credit whatsoever for unapplied Base
Building Change Order Savings, as Base Building Change Order Savings may not be
applied other than to Tenant Base Building Change Order Costs.

         Section 17.5 Tenant may, subject to obtaining the Landlord's approval
as hereinafter provided, make changes to the Leasehold Improvements consisting
of additions or deletions to, or other revisions in the Tenant Plans and Specs,
with an appropriate adjustment, if any, to the cost of the Leasehold
Improvements and to the Construction Progress Schedule ("Tenant Leasehold
Improvement Change Order"). Landlord's rights with respect to approving or
withholding approval to a proposed Tenant Leasehold Improvement Change Order
shall be governed by the same criteria as are applicable to the approval of
Tenant's Plans and Specs under Section 3.3.

         5.6 If Landlord elects to make a discretionary change (e.g. not changes
dictated by legal requirements or agreements with municipal authorities, changes
which Landlord is advised




                                      C-9
<PAGE>   73
should be adopted in order to serve good construction practice or other changes
that otherwise are required to serve some other non-discretionary purpose) to
the Base Building Plans and Specs that would have the effect of requiring that
Tenant modify Tenant's Plans and Specs, and increase the cost to Tenant of
constructing the Leasehold Improvements, then Landlord agrees that the Leasehold
Improvement Allowance shall be increased by the amount of such increase. Nothing
in the preceding sentence is intended to impose the burden upon Tenant of any
violation by Landlord in its preparation of the Base Building Plans and Specs of
any applicable legal requirements in effect at the time Landlord obtained the
building permit therefor, or any breach by Landlord of any existing agreements
with municipal authorities. Tenant shall specify based on input from the
Contractor whether the cost of constructing the Leasehold Improvements would be
increased by virtue of such change in the Base Building Plans and Specs promptly
after Landlord's inquiry to such effect, specifying the amount of such increase.
If any such change constitutes a Major Change, Tenant shall not be deemed
unreasonable for withholding approval thereto on the condition that Landlord
agrees to such an increase in the Leasehold Improvement Allowance.
Notwithstanding the foregoing, if Landlord should implement a change in the Base
Building Plans and Specs, but such change has the effect of reducing the cost to
Tenant of constructing the Leasehold Improvements ("Leasehold Improvement Change
Order Savings"), then such Leasehold Improvement Change Order Savings, until
fully applied, may be applied by Landlord to any future increases in the cost of
the Leasehold Improvements resulting from discretionary changes by Landlord in
the Base Building Plans and Specs as aforesaid. However, Landlord shall not be
entitled to any credit whatsoever for unapplied Leasehold Improvement Change
Order Savings.

                                  ARTICLE XVIII

                Payment of Costs; Leasehold Improvement Allowance

         Section 18.1 Landlord has established an allowance (the "Leasehold
Improvements Allowance") equal to the product of Eighty Five and 00/100 Dollars
($85.00) times the rentable square footage of the Original Premises, but limited
to a maximum of $14,875,000, for purposes of being applied to certain costs and
expenses, more particularly set forth below, incurred by or on behalf of Tenant
in connection with the performance of the Leasehold Improvements. If Tenant
incurs costs in connection with the construction of the Leasehold Improvements
in excess of the Leasehold Improvement Allowance, then except as otherwise
expressly provided in Section 5.6 and Section 7.6, all costs shall be borne by
Tenant, and shall be deposited with Landlord in accordance with the terms and
conditions specified in Section 6.3 below.

         Section 18.2 The application of the Leasehold Improvement Allowance by
Landlord shall be limited to payment of the following costs and expenses
incurred by or on behalf of Tenant in connection with the Leasehold Improvements
(collectively "Eligible Leasehold Improvement Expenses"): (i) the actual
documented and verified cost of the labor and materials, together with the
associated contractor's overhead and profit and general conditions and the
Developer's Administrative Fee, incurred in the construction of the Leasehold
Improvements contemplated by Tenant's Plans and Specs, except for the making of
Removable Alterations or other improvements, installation of fixtures or
incorporation of other items which (x) by virtue of


                                      C-10
<PAGE>   74
their quantity or quality (whether greater or less) would not be of general
utility to other laboratory tenants that might later occupy the Premises,
whether at the expiration of the Term or by virtue of the earlier termination of
this Lease, (y) otherwise are not of a nature, scope or capacity consistent with
a first class office and laboratory facility or (z) are moveable rather than
permanent improvements, examples of which are furniture, telephone and security
systems and bench-top laboratory equipment items such as microscopes. In the
event that, upon Substantial Completion of the Millennium Project, there remains
unapplied funds from the Leasehold Improvement Allowance, then architectural and
engineering design fees, up to an aggregate of the product of Five Dollars
($5.00) times the rentable square footage of the Premises, but limited to a
maximum of $875,000, shall be deemed Eligible Leasehold Improvement Expenses.

         Section 18.3 Upon the execution by Tenant of the construction contract
with the Contractor for performance of the Leasehold Improvements, the
anticipated cost and expense of performing the Leasehold Improvements shall be
established by Landlord and Tenant (the "Leasehold Improvement Cost Budget"). If
the anticipated cost and expense established in the Leasehold Improvement Cost
Budget for the Leasehold Improvements exceeds the lesser of (i) so much of such
costs that will constitute Eligible Leasehold Improvement Expenses or (ii) the
Leasehold Improvement Allowance ("Excess Leasehold Improvement Costs"), such
amount shall be deposited in escrow (the "Tenant Construction Escrow") with
Landlord pursuant to the escrow requirements set forth in Article XI of this
Lease. If for any reason the anticipated cost and expense of performing the
Leasehold Improvements should change, the Tenant's Leasehold Improvement Cost
Budget shall be changed accordingly and Tenant shall deposit into the Tenant
Construction Escrow consistent with such reasonable requirements as may be
imposed upon Landlord by Landlord's construction lender with respect to the Base
Building Improvements any increase in the Excess Leasehold Improvement Costs so
that the amount which is so held in escrow shall always equal the amount by
which the then cost of completing the Leasehold Improvements exceeds the
aggregate of (x) the unadvanced Leasehold Improvement Allowance available to pay
the then budgeted Eligible Leasehold Improvement Expenses and (y) the then
amount held in the Tenant Construction Escrow.

         Section 18.4 During the construction of the Leasehold Improvements and
in accordance with the terms and conditions imposed upon the Landlord pursuant
to the loan agreement with Landlord's lender pertaining to the construction of
the Base Building Improvements, Tenant shall, on a monthly basis (as the
Contractor submits to Tenant its application for payment less retainage of not
less than five percent (5%) together with lien waivers), deliver to Landlord a
requisition for payment showing the cost of the Leasehold Improvements and the
amount of the current payment requested from Landlord. Each of the requisitions
for payment shall also show the amounts paid to date and the percent complete of
the total Leasehold Improvements scope. It is Landlord's expectation that
Landlord will deliver such requisition to the Lender together with its own
requisition for payment of costs associated with Base Building Improvements, and
shall promptly, but in any event within (30) days, pay directly to the
Contractor the amount specified in such Contractor's requisition. Following the
completion of the Leasehold Improvements, Tenant shall deliver to the Landlord,
within fifteen (15) days of completion, a statement showing the final costs of
the Leasehold Improvements, the total of Tenant's excess costs, the amounts paid
to date to, or on behalf of the Tenant, and any amounts available for release of
retainage.


                                      C-11
<PAGE>   75
Landlord shall endeavor, in good faith, to ensure that its construction lender
advances monies properly and duly owed to Contractor for the Leasehold
Improvements.

         Section 18.5 Payments made to Contractor on account of Tenant's
requisitions shall be made from the Leasehold Improvement Allowance and the
Tenant Construction Escrow account on a proportionate basis consistent with the
ratio of (i) the lesser of (x) the Eligible Leasehold Improvement Expenses set
forth in the Leasehold Improvement Cost Budget established as of the Tenant
Construction Readiness Date and (y) the Leasehold Improvement Allowance to (ii)
the total Leasehold Improvement Cost Budget established as of the Tenant
Construction Readiness Date. If Tenant should increase the Leasehold Improvement
Cost Budget by authorizing Leasehold Improvement Change Orders, then the
increased costs shall be deposited by Tenant in the Tenant Construction Escrow
account when due, and such increased costs shall be paid exclusively from the
Tenant Construction Escrow account, in order to maintain the same ratio of
Landlord's advances from the Leasehold Improvement Allowance to the total of
Tenant's requisition as the ratio of the Eligible Leasehold Improvement Expenses
to the total Leasehold Improvement Cost Budget.

         6.6 All of the payments to be made by Landlord and Tenant described in
this Article 6, shall be made based upon the rentable floor area of the Premises
calculated by the Architect in accordance with EXHIBIT A to the Lease on the
basis of the Tenant's Plans and Specs as of the Tenant Construction Readiness
Date. After a final determination of such rentable floor area pursuant to
Section 2.1 of the Lease, the aforesaid payments shall be adjusted between the
parties within thirty (30) days of such final determination.

                                   ARTICLE XIX

                         Substantial Completion; Delays

         Section 19.1 For all purposes hereof, "Substantial Completion" of the
Base Building Improvements shall be deemed to have taken place once the Base
Building Improvements have been substantially completed in substantial
accordance with the Base Building Plans and Specs, notwithstanding that minor or
insubstantial details of construction, mechanical adjustment, balancing or
decorating remain to be performed, and notwithstanding that any other work upon
which a temporary certificate of occupancy for the Premises is not contingent,
and the failure of which to complete by Landlord will not materially and
adversely affect Tenant in occupying and conducting business therein remains to
be performed. Once Substantial Completion of the Base Building Improvements has
occurred, upon the completion of the Leasehold Improvements, the "Substantial
Completion" of the Millennium Project will be deemed to have been achieved.

         Section 19.2 It is contemplated by Landlord and Tenant that Landlord
and Tenant shall respectively complete final iterations of Landlord's Plans and
Specs and Tenant's Plans and Specs, and respectively execute construction
contracts with the Contractor, permitting construction of the Base Building
Improvements to occur on or before the date contemplated therefor in the
Construction Progress Schedule. Assuming the foregoing is achieved, Landlord
contemplates the Tenant Construction Readiness Date for each of the 75 Sidney
Building and the


                                      C-12
<PAGE>   76
45 Sidney Building occurring on or before the dates respectively projected
therefor, and that Landlord shall cause Substantial Completion of the Base
Building Improvements with respect to the 75 Sidney Building and the 45 Sidney
Building on the dates set forth as the respective Scheduled Rent Commencement
Dates in the Lease. Tenant shall have the period commencing on the Tenant
Construction Readiness Date until the Scheduled Rent Commencement Date for each
of the aforesaid buildings during which Tenant may cause the Leasehold
Improvements to be constructed prior to the commencement of the rental and other
obligations that accrue thereafter.

         Section 19.3 As used herein, "Tenant Delay" shall mean any delay in the
satisfaction of the condition in question (e.g. the Tenant Construction
Readiness Date or the date upon which Substantial Completion of the Base
Building Improvements is achieved) to the extent the same is a consequence of
any act, omission or neglect of Tenant, of Architect (in connection with
Tenant's Plans and Specs or Tenant Base Building Change Orders), or of any other
employee, agent, Contractor (in its performance of the Leasehold Improvements),
subcontractor, sub-subcontractor, agent or representative of Tenant, including
without limitation, any errors, omissions or inconsistencies in Tenant's Plans
and Specs or the lack of coordination of Tenant's Plans and Specs with the Base
Building Plans and Specs, delays attributable to any Tenant Base Building Change
Orders, or otherwise from interference that could reasonably have been averted
in the manner by which Tenant's construction of the Leasehold Improvements is
conducted.

         Section 19.4 As used in this Work Letter, "Landlord Delay" shall mean
any delay in the satisfaction of the condition in question (e.g. the Tenant
Construction Readiness Date or the date upon which Substantial Completion of the
Base Building Improvements is achieved) to the extent the same is a consequence
of any act, omission or neglect of Landlord, of Architect (in connection with
Base Building Plans and Specs or discretionary Base Building change orders made
by Landlord), or of any other employee, agent, Contractor (in its performance of
the Base Building Improvements), subcontractor, sub-subcontractor, agent or
representative of Landlord, including without limitation from interference that
could reasonably have been averted in the manner in which Landlord's
construction of the Base Building Improvements is conducted.

         Section 19.5 In the event of a condition causing delay as set forth in
this Article 7, the party affected by such condition shall give written notice
to the other party within five (5) days following the commencement of such
condition indicating the cause of delay and the probable duration thereof.

         Section 19.6 If Landlord must incur change order costs under its
construction contract with the Contractor with respect to the Base Building
Improvements by virtue of Tenant Delay, such costs shall be payable by Tenant as
an additional cost of its Leasehold Improvements. If Tenant must incur change
order costs under its construction contract with the Contractor with respect to
the Leasehold Improvements by virtue of Landlord Delay, the Leasehold
Improvement Allowance shall be increased by the amount of such costs.

                                   ARTICLE XX



                                      C-13
<PAGE>   77
              Completion of Basic Building Improvements; Punch List

         Section 20.1 Notwithstanding that Substantial Completion of the Base
Building Improvements shall be deemed to have occurred with respect to one or
both of the 75 Sidney Building and the 45 Sidney Building, subject to the
provisions of this Section 8, Landlord shall with reasonable diligence cause the
remaining Base Building Improvements to be completed.

         Section 20.2 During the five (5) business days immediately preceding
the occupancy of all or any portion of each of the 75 Sidney Building or the 45
Sidney Building by Tenant, Tenant shall conduct an inspection of the Base
Building Improvements with respect thereto, giving Landlord prior notice and an
opportunity to attend the same, and furnish to Landlord a notice ("Punch List
Notice") specifying any aspect of Base Building Improvements which remains to be
completed or which, if completed, is not substantially in accordance with the
Base Building Plans and Specs. Landlord shall cause any incomplete work to be
completed and/or remedy any such work not substantially in accordance with the
Base Building Plans and Specs promptly following the establishment of the
punchlist. In no event shall Landlord be obligated to repair or cause the repair
of any damage to the Base Building Improvements caused by Tenant, its employees,
agents or contractors. Nothing in this Section 8.2 shall limit any of Tenant's
rights or Landlord's obligations under the Lease with respect to the maintenance
or operation of the Building.

         Section 20.3 If Tenant shall fail to conduct an inspection of Base
Building Improvements and timely give to Landlord a Punch List Notice as
provided in Section 8.1 above, then it shall be deemed that, except for latent
defects, and work which cannot be inspected or tested due to seasonal factors,
the Base Building Improvements with respect to the building in question has been
fully completed in accordance with the Base Building Plans and Specs. If Tenant
shall conduct an inspection and give Landlord a Punch List Notice as provided in
Section 8.1, then except for the items specified in the Punch List Notice,
latent defects and work which cannot be inspected due to seasonal factors, the
Base Building Improvements with respect to the building in question has been
fully completed in accordance with the Base Building Plans and Specs. Nothing in
this Section 8.3 shall limit any of Tenant's rights or Landlord's obligations
under the Lease with respect to the maintenance of operation of the Building.

         Section 20.4 Tenant shall furnish Landlord, promptly after the
Substantial Completion of the Millennium Project, an "as built" iteration of
Tenant's Plans and Specs.


                                   ARTICLE XXI

  Right to Terminate for Failure to Achieve Tenant Construction Readiness Date

         Section 21.1 Notwithstanding anything to the contrary provided in this
Lease, Tenant shall have the right, in accordance with the terms of this Section
9.1, to terminate this Lease in the event that the Tenant Construction Readiness
Date has not been achieved, with respect to either the 75 Sidney Building or the
45 Sidney Building by October 15, 1998, as such date may


                                      C-14
<PAGE>   78
be extended by Landlord, but not beyond December 31, 1998, by virtue of
Excusable Delay, or extended without limitation as to the duration of such
extension, by virtue of Tenant Delay (the "Deadline Date"). Any termination as
set forth herein shall become effective immediately upon receipt of the
Termination Notice; provided, however, that if Tenant has not given the
Termination Notice to Landlord on or before the tenth (10th) day following the
occurrence of the Deadline Date, then Tenant's right to terminate the Lease
under this Section 9.1 shall automatically expire and be of no further force and
effect.



                                      C-15
<PAGE>   79
                                    EXHIBIT D

                                Standard Services


         The building standard services shall be defined by the Landlord and its
Management Agent. A listing of services shall be as promulgated from time to
time by the Landlord and shall be further described in the Tenant Handbook.

         The following services are provided by the Landlord:

         A.       Regular maintenance of interior, exterior and parking lot
                  landscaping and University Park common areas.

         B.       Regular maintenance, sweeping and snow removal of building
                  exterior areas such as roadways, driveways, sidewalks, parking
                  areas and courtyard paving.

         C.       Complete interior and exterior cleaning of all windows two
                  times per year.

         D.       Daily, weekday maintenance of hallways, passenger elevators,
                  common area bathrooms, lobby areas and vestibules.

         E.       Periodic cleaning of stairwells, freight elevators, and back
                  of house areas.

         F.       Daily, weekday rubbish removal of all tenant trash
                  receptacles.

         G.       Daily, weekday cleaning of Tenant space to building standard.

         H.       Maintenance and repair of base building surveillance and alarm
                  equipment, elevators, mechanical, electrical, plumbing and
                  life safety systems.

         I.       Building surveillance and alarm system operation and live
                  monitoring service to building standard specifications.

         J.       Chilled water and ventilation air for HVAC purposes shall be
                  provided to the Premises from central mechanical equipment at
                  all times during the appropriate seasons. The Tenant's usage
                  shall be measured and allocated appropriately.

         K.       Utilities for all interior Common areas and exterior building
                  and parking lighting.




                                       D-1
<PAGE>   80
                                   EXHIBIT D-1

                    Terms of Maintenance and Repair Services




                                      D-1-1
<PAGE>   81
                                    EXHIBIT E

                              Rules and Regulations


DEFINITIONS

         Wherever in these Rules and Regulations the word "Tenant" is used, it
shall be taken to apply to and include the Tenant and its agents, employees,
invitees, licensees, contractors, any subtenants and is to be deemed of such
number and gender as the circumstances require. The word "Premises" is to be
taken to include the space covered by the Lease. The word "Landlord" shall be
taken to include the employees and agents of Landlord. Other capitalized terms
used but not defined herein shall have the meanings set forth in the Lease.

GENERAL USE OF BUILDING

         A.       Space for admitting natural light into any public area or
                  tenanted space of the Building shall not be covered or
                  obstructed by Tenant except in a manner approved by Landlord.

         B.       Toilets, showers and other like apparatus shall be used only
                  for the purpose for which they were constructed. Any and all
                  damage from misuse shall be borne by Tenant.

         C.       Except as otherwise permitted in the Lease, Landlord reserves
                  the right to determine the number of letters allowed Lessee on
                  any directory it maintains.

         D.       No sign, advertisement, notice or the like, shall be used in
                  the Building by Tenant (other than at its office and then only
                  as approved by Landlord in accordance with building
                  standards). If Tenant violates the foregoing, Landlord may
                  remove the violation without liability and may charge all
                  costs and expenses incurred in so doing to Tenant.

         E.       Tenant shall not throw or permit to be thrown anything out of
                  windows or doors or down passages or elsewhere in the
                  Building, or bring or keep any pets therein, or commit or make
                  any indecent or improper acts or noises. In addition, Tenant
                  shall not do or permit anything which will obstruct, injure or
                  interfere with other tenants or those having business with
                  them.

         F.       Unless expressly permitted by the Landlord in writing:

                  (1)      No locks or similar devices shall be attached to any
                           door or window which are not on the master key system
                           maintained by the Landlord. If more than two keys for
                           one lock are desired by the Tenant, the Landlord may
                           provide the same upon payment by the Tenant, or the
                           Tenant may have additional



                                      E-1
<PAGE>   82
                           keys made so long as it uses the Landlord's
                           designated locksmith. Upon termination of this lease
                           or of the Tenant's possession, the Lessee hall
                           surrender all keys to tie Premises and shall explain
                           to the Landlord all combination locks on safes,
                           cabinets and vaults.

                  (2)      In order to insure proper use and care of the
                           Premises Tenant shall not install any shades, blinds,
                           or awnings or any interior window treatment without
                           consent of Landlord. Blinds must be building
                           standard.

                  (3)      All doors to the Premises are to be kept closed at
                           all times except when in actual use for entrance to
                           or exit from such Premises. The Tenant shall be
                           responsible for the locking of doors to the Premises.
                           Any damage or loss resulting from violation of this
                           rule shall be paid for by the Tenant.

                  (4)      All equipment of any electrical or mechanical nature
                           shall be placed in settings which absorb and prevent
                           any vibration, noise or annoyance.

         G.       Landlord shall designate the time when and the method whereby
                  freight, small office equipment, furniture, safes and other
                  like articles may be brought into, moved or removed through
                  any common lobbies or loading docks shared with other tenants
                  of the Building.

         H.       In order to insure proper use and care of the Premises, Tenant
                  shall not allow anyone other than Landlord's employees or
                  contractors to clean the Premises without Landlord's
                  permission, which shall not be unreasonably withheld or
                  delayed.

         I.       The Premises shall not be defaced in any way. No material
                  changes in the HVAC, electrical or plumbing systems or other
                  appurtenances of said Premises shall be made without the prior
                  approval of Landlord and in accordance with Landlord's
                  construction rules and regulations, except in accordance with
                  the Lease.

         J.       For the general welfare of all tenants and the security of the
                  Building, Landlord may require all persons entering and/or
                  leaving the Building through common entries and/or lobbies
                  shared with other tenants on weekends and holidays and between
                  the hours of 6:00 p.m. and 8:00 a.m. to register with the
                  Building attendant or custodian by signing his name and
                  writing his destination in the Building, and the time of entry
                  and actual or anticipated departure, or other procedures
                  deemed necessary by Lessor. Landlord may deny entry during
                  such hours to any person who fails to provide satisfactory
                  identification.

         K.       No animals (other than those used for research purposes),
                  birds, pets, and no bicycles or vehicles of any kind shall be
                  brought into or kept in or about said Premises or the lobby or
                  halls of the Building. Tenant shall not cause or permit


                                      E-2
<PAGE>   83
                  any unusual or objectionable odors, noises or vibrations to be
                  produced upon or emanate from said Premises.

         L.       Unless specifically authorized by Landlord, employees or
                  agents of Landlord shall not perform for nor be asked by
                  Tenant to perform work other than their regularly assigned
                  duties.

         M.       Landlord shall have the right to prohibit any advertising by
                  Tenant which, in Landlord's opinion, tends to impair the
                  reputation of the Building or its desirability as an office
                  and research and development building and, upon written notice
                  from Landlord, Tenant shall promptly discontinue such
                  advertising.

         N.       Canvassing, soliciting and peddling in the Building is
                  prohibited and Tenant shall cooperate to prevent the same from
                  occurring.

         O.       All parking, Building operation, or construction rules and
                  regulations which may be established from time to time by
                  Landlord on a uniform basis shall be obeyed.

         P.       Intentionally omitted.

         Q.       Intentionally omitted.

         R.       Landlord shall have the right to make such other and further
                  reasonable rules and regulations as in the judgment of
                  Landlord, may from time to time be needful for the safety,
                  appearance, care and cleanliness of the Building and for the
                  preservation of good order therein. Landlord shall not be
                  responsible to Tenant for any violation of rules and
                  regulations by other tenants except that Landlord shall use
                  good faith efforts to uniformly enforce such rules and
                  regulations.

         S.       The access road and loading areas, parking areas, sidewalks,
                  entrances, lobbies, halls, walkways, elevators, stairways and
                  other common area provided by Landlord shall not be obstructed
                  by Tenant, or used for other purpose than for ingress and
                  egress.

         T.       In order to insure proper use and care of the Premises Tenant
                  shall not install any call boxes or communications systems or
                  wiring of any kind (except within the Premises and within
                  those lobby or service areas which it solely controls) without
                  Landlord's permission and direction.

         U.       In order to insure proper use and care of the Premises Tenant
                  shall not prepare or dispense for sales any foods or
                  beverages, tobacco, flowers, or other commodities or articles,
                  except vending machines for the benefit of employees and
                  invitees of Tenant, without the written consent of Landlord.



                                      E-3
<PAGE>   84
         V.       In order to insure use and care of the Premises, except with
                  respect to any building occupied entirely by the Tenant,
                  Tenant shall not enter any janitors' closets, mechanical or
                  electrical areas, telephone closets, loading areas, roof or
                  Building storage areas without the written consent of
                  Landlord, which shall not be unreasonably withheld.

         W.       In order to insure proper use and care of the Premises Tenant
                  shall not place door mats in public corridors without consent
                  of Landlord.

         Notwithstanding anything to the contrary contained herein. Landlord
acknowledges that Tenant maintains animal care facilities on the Premises as
part of its operations, and the presence of animals utilized in the operations
of Tenant shall not constitute a violation of the Lease or the aforesaid
regulations; provided, however, Tenant shall at all times comply with all
applicable local, state and federal codes, regulations and laws relating to such
facilities.





                                      E-4
<PAGE>   85
                                    EXHIBIT F

                             45 and 75 Sidney Street
                Standard Tenant System Allocations and Capacities




                                       F-1
<PAGE>   86
                                    EXHIBIT G

                               Measurement Method



                                       G-1
<PAGE>   87
                                    EXHIBIT H

                      Form of MIT Non-Disturbance Agreement


         Agreement dated as of October __, 1997, by and between MASSACHUSETTS
INSTITUTE OF TECHNOLOGY, a Massachusetts educational corporation chartered by
Massachusetts law (the "Ground Lessor"), FC 45/75 SIDNEY, INC., a Massachusetts
corporation ("Landlord") and MILLENNIUM PHARMACEUTICALS, INC., a Delaware
corporation ("Tenant").

                                   BACKGROUND

         Ground Lessor and Landlord are parties, as landlord and tenant
respectively, to a Construction and Lease Agreement ("Ground Lease") dated
________________, 1997, for certain real property located at 45/75 Sidney Street
in Cambridge, Massachusetts, as more particularly described on Exhibit A
attached hereto ("Land"). A Notice of Lease pertaining to the Ground Lease has
been recorded at the Middlesex South District Registry of Deeds and filed for
registration in the Middlesex South Registry District of the Land Court.
Landlord intends to construct two (2) buildings (collectively, the "Building")
on the Land. Tenant has entered into a lease dated as of _______________, 1997
("Lease") with Landlord for certain premises in the Building ("Premises"), the
Premises being more particularly described in the Lease.

                                   AGREEMENTS

         1. Non-Disturbance. If the Ground Lease is terminated, for any reason,
Ground Lessor shall not disturb Tenant in Tenant's possession of the Premises
and without any hindrance or interference from the Ground Lessor, shall permit
Tenant peaceably to hold and enjoy the Premises for the remainder of the
unexpired term of the Lease, together with any extension periods provided for
therein, upon and subject to the same terms, covenants and conditions as are
contained in the Lease, and shall recognize the Lease as modified hereby. The
foregoing is on the condition that Tenant is not in default under the Lease
beyond any applicable notice and grace periods contained in the Lease.

         2. Attornment. Tenant hereby agrees that if the Ground Lease is
terminated for any reason, Tenant shall attorn to Ground Lessor and shall be
liable to and recognize Ground Lessor as Landlord under the Lease for the
balance of the term of the Lease upon and subject to all of the terms and
conditions thereof. In such case, upon receipt of notice from Ground Lessor
setting forth the effective date of the termination of the Ground Lease, Tenant
shall pay to the Ground Lessor all obligations required to be paid and performed
by Tenant under the Lease arising after the date of termination. The Lease shall
continue in full force and effect as a direct lease between Ground Lessor and
Tenant.


         3. Additional Conditions. Tenant agrees that Ground Lessor shall not
be: (i) liable for any act or omission of any person or party who may be
landlord under the Lease prior to any


                                      H-1
<PAGE>   88
termination of the Ground Lease ("Prior Landlord"); (ii) subject to any offsets
or defenses which Tenant might have against Prior Landlord; (iii) bound by any
prepayment of rent or additional rent, or any other charge which Tenant might
have paid to Prior Landlord for more than the then current month (other than a
bona fide security deposit paid by Tenant to Landlord under the Lease or other
rent, additional rent or charge which has been received by Ground Lessor); and
(iv) bound by any amendment, modification or termination of the Lease made
without Ground Lessor's express agreement when such agreement is required under
the Ground Lease. Tenant additionally agrees with Ground Lessor that Tenant
shall not enter into any assignment of the Lease or sublease of all or any part
of the Premises in cases where Landlord's consent is required thereto, unless
Ground Lessor shall have also given its consent thereto, which consent shall not
be unreasonably withheld or delayed. Nothing herein, however, shall constitute a
waiver of tenant's rights as against such individual or entity which is the
landlord under the Lease as of the time of any event or circumstances which may
give rise to a claim of the Tenant against such individual or entity. In
addition, nothing herein shall relieve any successor landlord under the Lease
from its obligation to comply with those obligations of a Landlord under the
Lease during the period for which it is the owner of the Landlord's interest in
the Lease.

         4. Landlord's Defaults. Tenant hereby agrees that, if Tenant provides
Landlord with any notice of default or claimed default on the part of Landlord
under the Lease, Tenant shall concurrently therewith send a copy of such notice
to Ground Lessor. In such event, Ground Lessor shall be permitted (but not
obligated) to cure any such default within the period of time allotted thereto
in the Lease. If Landlord shall fail to cure such default within the period of
time allocated thereto in the Lease (or, if Landlord shall not within such time
period have commenced diligent efforts to remedy a default that cannot be fully
cured within such time period) then Tenant shall provide Ground Lessor with
notice of such failure. Upon receipt of such notice of Landlord's failure to
cure, Ground Lessor shall be granted an additional thirty (30) days during which
it shall be permitted (but not obligated) to cure such default. In the case of a
default, which cannot with diligence be remedied by Ground Lessor within thirty
(30) days, Ground Lessor shall have such additional period of time as may be
reasonably necessary in order for Ground Lessor to remedy such default with
diligence and continuity of effort, provided that Ground Lessor has commenced to
cure such default within such thirty (30) day period.

         5. Notices. Duplicates of all notices delivered by any party to another
party and required by this Agreement shall be delivered concurrently to all
other parties to this Agreement. All notices shall be written, delivered by
certified or registered mail, and sent, if to Ground Lessor, to 238 Main Street,
Suite 200, Cambridge, Massachusetts 02142, Attention: Director of Real Estate,
if to Tenant to 238 Main Street, Cambridge, Massachusetts 02142, Attention: Mr.
Mark Levin, before the commencement of Tenant's occupancy in the Premises, and
to the Premises after the Rent Commencement Date shall have occurred with
respect to the entire Original Premises, and if to Landlord to 38 Sidney Street,
Cambridge, MA 02139-4234, Attention: Ms. Gayle W. Friedland, or such addresses
as may, from time to time, be set forth in notices to the other parties
hereunder.



                                      H-2
<PAGE>   89
         6. Exculpation of Ground Lessor. Ground Lessor shall not be personally
liable hereunder. Tenant agrees to look to Ground Lessor's interest in the Land
and Building only for satisfaction of any claim against Ground Lessor hereunder.

         7. Successors and Assigns. This Agreement shall bind Tenant, its
successors and assigns, and shall benefit Tenant and only such successor and
assigns of Tenant as are permitted by the Lease and shall bind and benefit
Ground Lessor and its successors and assigns (provided that after transfer of
Ground Lessor's entire interest in the Land to another party, Ground Lessor
shall have no liability for any act or omission of such party) and shall bind
and benefit Landlord and its successors and assigns.

EXECUTED as an instrument under seal as of the date set forth above.

                                       MASSACHUSETTS INSTITUTE OF
                                       TECHNOLOGY
                                       Ground Lessor


                                       By:
                                          --------------------------------------
                                           Philip A. Trussell, Director of
                                           Real Estate and Associate Treasurer


                                       MILLENNIUM PHARMACEUTICALS, INC.
                                       Tenant


                                       By:
                                          --------------------------------------


                                       FC 45/75 SIDNEY, INC.
                                       Landlord


                                       By:
                                          --------------------------------------





                                      H-3
<PAGE>   90
COMMONWEALTH OF MASSACHUSETTS    )
                                 )        ss:
COUNTY OF MIDDLESEX           )

         BEFORE ME, a Notary Public in and for said County and State, personally
appeared the MASSACHUSETTS INSTITUTE OF TECHNOLOGY, by Philip A. Trussell, its
Director of Real Estate and Associate Treasurer, who acknowledged that he did
sign the foregoing instrument and that the same is his free act and deed and the
free act and deed of said corporation.

         IN TESTIMONY HEREOF, I set my hand and official seal at
__________________, this _____ day of _______________, ____.


                                     ___________________________________________
                                     Notary Public
                                     My Commission Expires:_____________________



COMMONWEALTH OF MASSACHUSETTS    )
                                 )        ss:
COUNTY OF MIDDLESEX           )

         BEFORE ME, a Notary Public in and for said County and State, personally
appeared the above-named MILLENNIUM PHARMACEUTICALS, INC., by
______________________ who acknowledged that he/she did sign the foregoing
instrument and that the same is his/her free act and deed and the free act and
deed of said corporation.

         IN TESTIMONY HEREOF, I set my hand and official seal at
__________________, this _____ day of _______________, ____.


                                     ___________________________________________
                                     Notary Public
                                     My Commission Expires:_____________________






                                      H-4
<PAGE>   91
COMMONWEALTH OF MASSACHUSETTS    )
                                 )        ss:
COUNTY OF MIDDLESEX           )

         BEFORE ME, a Notary Public in and for said County and State, personally
appeared the above-named FC 45/75 SIDNEY, INC., by _______________________ who
acknowledged that he/she did sign the foregoing instrument and that the same is
his/her free act and deed and the free act and deed of said corporation.

         IN TESTIMONY HEREOF, I set my hand and official seal at
__________________, this _____ day of _______________, ____.


                                     ___________________________________________
                                     Notary Public
                                     My Commission Expires:_____________________






                                      H-5
<PAGE>   92
                                    EXHIBIT I

                              Form of Lender's SNDA

             SUBORDINATION, NONDISTURBANCE AND ATTORNMENT AGREEMENT


                  THIS AGREEMENT made as of the ____ day of ___________, 1997
between ____________________________________, a
_________________________________, having an office at
________________________________________________________ ("Mortgagee"), FC 45/75
SIDNEY, INC., a Massachusetts corporation, having an office at 1100 Terminal
Tower, 50 Public Square, Cleveland, Ohio 44113 ("Landlord"), and MILLENNIUM
PHARMACEUTICALS, INC., a Delaware corporation, having an office at 238 Main
Street, Cambridge, Massachusetts ("Tenant").

                              W I T N E S S E T H:

                  WHEREAS, Tenant has entered into a lease dated _____________,
1997 between Landlord, as landlord, and Tenant, as tenant, with respect to
certain space (the "Demised Premises") in the buildings located at 45 and 75
Sidney Street, Cambridge, Massachusetts (said lease, as hereafter amended and
supplemented, subject to Paragraph 7 hereof, is hereinafter called the "Lease");
capitalized terms used herein and not otherwise defined herein shall have the
same meanings set forth in the Lease; and

                  WHEREAS, Mortgagee is the holder of the Leasehold Mortgage
with Assignments of Rents, Security Agreement and Fixture Filing dated
____________, 1997 from Landlord to Mortgagee (the "Mortgagee"), which encumbers
the land and improvements more particularly described in Exhibit A hereto (the
"Premises"), of which the Demised Premises are a part, and Landlord's interest
in the Lease; and

                  WHEREAS, Mortgagee, Landlord and Tenant desire to enter into
this Agreement upon the terms, covenants and conditions contained herein.

                  NOW, THEREFORE, in consideration of the premises and the
agreements of the parties contained herein, the parties agree as follows:

                  1. The Lease and all of Tenant's rights thereunder are and
shall be at all times and in all respects subject and subordinate to the lien of
the Mortgage, and to all advances now or hereafter made under or secured by the
Mortgage, and all renewals, modifications, consolidations, replacements,
substitutions, additions and extensions of the Mortgage and to any subsequent
mortgages or assignments with which the Mortgage may be spread and/or
consolidated.

                  2. Provided Tenant complies with this Agreement and if Tenant
shall not be in default under the Lease beyond the applicable period of grace,
if any, provided therein with


                                      I-1
<PAGE>   93
respect to the default in question as of the date Mortgagee commences a
foreclosure action, (i) Tenant shall not be named as a party in any action or
proceeding to enforce the Mortgage, unless such joinder shall be required under
applicable law, and in which case Mortgagee shall not seek affirmative relief
from Tenant in such action or proceeding, nor shall the Lease be cut off or
terminated nor Tenant's possession thereunder be disturbed in any such action or
proceeding, and (ii) subject to the provisions of Paragraph 4 of this Agreement,
Mortgagee will recognize the Lease and Tenant's rights thereunder.

                  3. Upon any foreclosure of the Mortgage or other acquisition
of the leasehold estate in the Premises, Tenant shall attorn to Mortgagee or any
other party acquiring the leasehold estate in the Premises or so succeeding to
Landlord's rights (collectively, the "Successor Landlord") and shall recognize
the Successor Landlord as its landlord under the Lease and Tenant shall promptly
execute and deliver any instrument that the Successor Landlord may reasonably
request in writing to evidence further said attornment.

                  4. Upon such attornment or other acquisition of the leasehold
estate in the Premises, the Lease shall continue as a direct lease between the
Successor Landlord and Tenant upon all terms, covenants and conditions thereof
as are then applicable except that the Successor Landlord shall not be (i)
liable for any previous act or omission of Landlord under the Lease, (ii)
subject to any offsets, defenses, claims or counterclaims that Tenant may have
against Landlord, (iii) bound by any covenant to perform or complete any
construction in connection with the Demised Premises or the Premises or to pay
any sums to Tenant in connection therewith, (iv) bound by any prepayment of more
than one (1) month's rent or other charges under the Lease unless such payment
shall have been expressly approved in writing by Mortgagee, (v) bound by any
amendment, modification, extension, expansion, termination, cancellation or
surrender of the Lease unless approved in writing by Mortgagee, or (vi) liable
for any security deposit given by Tenant under the Lease, unless and to the
extent in Mortgagee's possession on or after the date that Successor Landlord
succeeds to the interest of Landlord under the Lease.

                  5. The attornment provided for in Paragraph 3 of this
Agreement shall inure to the benefit of Mortgagee or any Successor Landlord,
shall be self-operative, and no further instrument shall be required to give
effect to the attornment. Tenant, however, upon demand of Mortgagee or any
Successor Landlord, as the case may be, agrees to execute, from time to time,
instruments in confirmation thereof, reasonably satisfactory to Mortgagee or any
such Successor Landlord, acknowledging such attornment and setting forth the
terms and conditions of its tenancy. Nothing contained in this Paragraph shall
be construed to impair any right otherwise exercisable by Mortgagee or any such
Successor Landlord.

                  6. Tenant from and after the date hereof shall send a copy of
any notice of default or notice in connection with the commencement of any
action to terminate the Lease or similar statement under the Lease to Mortgagee
at the same time such notice or statement is sent to Landlord under the Lease
and agrees that, notwithstanding any provisions of the Lease to the contrary,
such notice shall not be effective unless Mortgagee shall have been given such
notice and shall have failed to cure such default as hereinafter provided. Such
notices shall be sent by


                                      I-2
<PAGE>   94
certified or registered mail, postage prepaid, return receipt requested, or
shall be delivered to Mortgagee at the following address (or at such other
address as Mortgagee shall specify in a written notice to Tenant at the address
specified above for Tenant):

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

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

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

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

Any such notice of default shall be deemed to be given to Mortgagee on the
earlier to occur of (a) the day of receipt (as evidenced by a receipt signed by
Mortgagee or the refusal to accept delivery by Mortgagee) or (b) three (3) days
after deposit in the mail. With respect to the commencement by Tenant of any
action to terminate the Lease, Mortgagee shall have the right, but not the
obligation, to cure any default on the part of Landlord which is the basis for
such action within a reasonable time (including the time required for Mortgagee
to foreclose the Mortgage and obtain possession of the Premises if such
possession is necessary to effect such cure) after receipt of the notice by
Tenant with respect to such action, so long as Mortgagee is diligently
prosecuting such cure and/or the foreclosure of the Mortgagee if possession of
the Premises is necessary to effect such cure. Mortgagee's right to cure shall
not apply to the exercise by Tenant of its right to terminate the Lease pursuant
to Section 12.17 thereof or Article 9 of the Workletter, and shall not affect
Tenant's rights under Section 2.5 of the Lease.

                  7. Tenant shall not change, or consent to a change in, the
terms, covenants, conditions and agreements of the Lease in any manner which
would be binding on Mortgagee without the express consent in writing of
Mortgagee. No exercise by Landlord of any right to terminate the Lease, and no
acceptance of any termination, surrender or cancellation of the Lease (except as
otherwise expressly referred to in Paragraph 6 above), shall be effective unless
Mortgagee shall have expressly consented thereto in writing.

                  8. Anything herein or in the Lease to the contrary
notwithstanding, in the event that Successor Landlord shall acquire title to the
Premises, Successor Landlord shall have no obligation, nor incur any liability,
beyond Successor Landlord's then interest, if any, in the Premises and Tenant
shall look exclusively to such interest of Successor Landlord, if any, in the
Premises for the payment and discharge of any obligations imposed upon Successor
Landlord hereunder or under the Lease and Successor Landlord is hereby released
or relieved of any other liability hereunder and under the Lease. Tenant agrees
that with respect to any money judgment which may be obtained or secured by
Tenant against Successor Landlord, Tenant shall look solely to the estate or
interest owned by Successor Landlord in the Premises and Tenant will not collect
or attempt to collect any such judgment (i) from any officer, director,
shareholder, partner, employee, agent or representative of Successor Landlord or
(ii) out of any assets of Successor Landlord other than Successor Landlord's
estate or interest in the Premises.

                  9. (a) Tenant acknowledges that it has notice that Landlord's
interest under the Lease and the rent and all other sums due thereunder have
been assigned to Mortgagee, pursuant to the Mortgage as part of the security for
the obligations secured by the Mortgage. In


                                      I-3
<PAGE>   95
the event that Mortgagee notifies Tenant of a default under the Mortgage and
demands that Tenant pay its rent and all other sums due under the Lease to
Mortgagee, Tenant agrees that it shall pay its rent and all other sums due under
the Lease to Mortgagee or as Mortgagee shall direct in writing to Tenant at its
address for notices set forth in Section 12.2 of the Lease.

                           (b) Tenant hereby acknowledges receipt of a notice
from Landlord directing Tenant to pay, inter alia, all Annual Fixed Rent and
Additional Rent directly to account #__________ at
______________________________. Tenant shall not make any payment under the
Lease contrary to the aforementioned direction without the written consent of
Mortgagee.

                           (c) Landlord hereby indemnifies and holds Tenant
harmless from and against all claims, loss or damage of whatever nature arising
from Tenant's compliance with Paragraphs 9(a) and (b) above.

                  10. Landlord hereby consents to the terms and provisions of
this Agreement, including, without limitation, Paragraph 9 hereof.

                  11. This Agreement may not be modified, amended or terminated
unless in writing and duly executed by the party against whom the same is sought
to be asserted and constitutes the entire agreement between the parties with
respect to the subject matter hereof.

                  12. This Agreement shall bind and inure to the benefit of the
parties hereto and their respective successors and assigns.

                  13. Notwithstanding anything to the contrary contained in
Section 12.10 of the Lease, the Lease shall not terminate upon or as a result of
the termination of the Ground Lease if Mortgagee exercises its rights under the
Ground Lease to request that MIT (or its successors and assigns) enter into a
"new lease" for the Premises. The entering into of any such "new lease" shall
have the same effect as the acquisition of the leasehold estate in the Premises
for purposes of Paragraphs 3 and 4 hereunder.

                  14. Tenant agrees that Tenant shall from time to time, upon
not less than fifteen (15) days' prior written request by Mortgagee, execute,
acknowledge, deliver and certify to Mortgagee a statement in the form set forth
in Section 10.4 of the Lease.

                  IN WITNESS WHEREOF, the parties hereto have duly executed this
Agreement as of the day and year first above written.

                                     MORTGAGEE:


                                     ___________________________________________


                                     By:________________________________________


                                      I-4
<PAGE>   96
                                        Name:
                                        Title:


                                     TENANT:

                                     MILLENNIUM PHARMACEUTICALS, INC.


                                     By:________________________________________
                                        Name:
                                        Title:


                                     LANDLORD:

                                     FC 45/75 SIDNEY, INC.

                                     By:


                                        By:_____________________________________
                                           Name:
                                           Title:



                         [ACKNOWLEDGEMENTS TO BE ADDED]





                                      I-5
<PAGE>   97
                                    Exhibit A

                           Description of the Premises




                                       A-1
<PAGE>   98
                                    EXHIBIT J

                           Dispute Resolution Process


         Any dispute or determination by a party hereto which, pursuant to the
terms of this Lease, may be resolved by the "Dispute Resolution Process," shall
be undertaken in accordance with the following provisions:

         (a) In the event of any such dispute, the complaining party (the
"Claimant") shall serve upon the other party (the "Respondent") by registered
mail or hand delivery a written demand for arbitration (the "Dispute Notice"),
setting forth with particularity the nature of the dispute. The Claimant shall
simultaneously serve any request (the "Document Request") for production of
relevant documents from the Respondent. The service of such Dispute Notice and
Document Request shall be effective upon receipt thereof. Failure to serve a
Document Request shall constitute a waiver by the Claimant of any right to
demand documents from the Respondent, except as provided in Subparagraph (c)
below. The Dispute Notice shall also be delivered to J.A.M.S./Endispute, 73
Tremont Street, 4th floor, Boston, Massachusetts 02108, for mediation as part of
that firm's national mediation services expertise. J.A.M.S./Endispute shall
select a member of the company to conduct the arbitration (hereinafter the
"Arbitrator"), the choice of which shall be binding on the parties. If
J.A.M.S./Endispute believes it has a material conflict of interest with any of
the parties, it shall select an alternative nationally recognized firm to
conduct the arbitration, within ten (10) business days of receipt of the Dispute
Notice. If J.A.M.S./Endispute shall cease to exist and/or shall decline to serve
under this Lease as to all or any particular dispute submitted thereto for
arbitration, and within ten (10) business days of receipt of a Dispute Notice,
shall fail to select an alternative nationally recognized firm, then, and in any
such event, the parties shall mutually select an alternative arbitrator for
their dispute(s) and, in the absence of agreement within a period of ten (10)
days, either party shall have the right, on notice to the other, to apply to the
President of the Boston Bar Association for selection of an independent
arbitrator.

         (b) Response by Respondent. Within ten (10) business days of receipt of
a Dispute Notice and Document Request, the Respondent shall serve a detailed
written response to the Dispute Notice, including any arbitrable counterclaims,
and shall produce all non-privileged documents called for in the Document
Request. At the same time, Respondent shall serve any Document Request on
Claimant, failing which Respondent shall be deemed to have waived any right to
demand documents from Claimant. Within two (2) business days of delivery of the
response, all undisputed amounts shall be paid by Respondent by wire transfer.

         (c) Response by Claimant. Within ten (10) business days of receipt of
such written response, the Claimant shall serve a reply to any counterclaims
asserted by Respondent and shall produce all non-privileged documents requested
by Respondent. At the same time, the Claimant may serve a second Document
Request limited to documents relevant to Respondent's counterclaim. Within two
(2) business days of delivery of the reply to any counterclaims, all undisputed
amounts shall be paid by the Claimant by wire transfer.



                                      J-1
<PAGE>   99
         (d) Response by Respondent. Respondent shall produce all non-privileged
documents called for in any such second Document Request within ten (10)
business days of service thereof.

         (e) Appearance Before Arbitrator. Within thirty-five (35) business days
of service of the Dispute Notice, any arbitrable dispute shall be submitted to
the Arbitrator, whose decision shall be final, binding and non-appealable, and
may be entered and enforced as a judgment by any court of competent
jurisdiction. The Arbitrator shall consider and determine only matters properly
subject to arbitration pursuant to this Lease.

         The Arbitrator shall, in consultation with the parties, establish such
further procedures, including hearings, as he or she deems appropriate,
provided, however, that a decision of the dispute (including counterclaims)
shall be rendered no later than sixty (60) business days after service of the
Dispute Notice.

         (f) Final Decision; Fees and Expenses. The Arbitrator's decision shall
be in writing, and shall include findings of fact and a concise explanation of
the reasons for the decision. The decision shall be delivered to the parties
immediately. The Arbitrator's fees and expenses shall be borne by one or both of
the parties in accordance with the direction of the Arbitrator, who shall be
guided in such determination by the results of the arbitration. If any party
refuses to appear before the Arbitrator or to respond as required in
subparagraphs (a) through (e) above, the Arbitrator shall decide the matter as
by default against the non-appearing party, and such decision shall be final,
binding and non-appealable to the same extent as a decision rendered with the
full participation of such party.





                                      J-2
<PAGE>   100
                                    EXHIBIT K

                           Construction Lender's SNDA




                                       K-1
<PAGE>   101
                                    EXHIBIT L

                         Millennium Completion Guaranty



                                       L-1