<PAGE>   1
                                                                    Exhibit 1.23


                                    SUBLEASE

         This SUBLEASE is made as of August 21, 2000 by and between ANADYS
PHARMACEUTICALS, INC. ("Sublessor"), and ALTAREX US, CORP. ("Sublessee").

                                    RECITALS:

         A.   Pursuant to that certain lease (the "Original Lease") dated
November 29, 1991 (which lease is also dated November 13, 1991 on its cover
page), as amended by (i) that certain First Amendment to Lease (the "First
Amendment") dated May 8, 1992; and (ii) that certain Second Amendment to Lease
(the "Second Amendment") dated July 30, 1999 (the Original Lease, together with
the First Amendment and the Second Amendment, are collectively referred to
herein as the "Main Lease," a copy of which is attached hereto as Exhibit A),
the Trustees of the Lincoln Street Trust, u/d/t dated July 6, 1963 and recorded
with the Middlesex South District Registry of Deeds in Book 10333, Page 194
("Landlord"), are leasing the entire building (the "Main Premises") known and
numbered as 610 Lincoln Street, Waltham, Massachusetts, more specifically
described in the Main Lease, to Sublessor, successor to Immulogic Pharmaceutical
Corporation, as Tenant thereunder.

         B.   Sublessor has agreed to sublease to Sublessee, and Sublessee has
agreed to sublease from Sublessor, for the Sublease Term (as hereinafter
defined), on the terms and conditions stated herein, approximately Sixteen
Thousand Three Hundred Ten (16,310) rentable square feet of space located within
the Main Premises on the first floor of the Main Premises (and also including a
portion of the common areas of the Main Premises located on the first floor
thereof), which space is shown crosshatched on Exhibit B attached hereto (the
"Sublease Premises").

         C.   Capitalized terms not otherwise defined herein shall have the
meaning set forth in the Main Lease.

                                   AGREEMENTS:

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

              1.   Incorporation of Main Lease. Except to the extent
inconsistent with the terms and conditions of this Sublease, all terms and
conditions of the Main Lease are hereby incorporated into this Sublease and
shall govern Sublessee's use and occupancy of the Sublease Premises in the same
manner as if Sublessee were the Tenant under the Main Lease, Sublessor
<PAGE>   2
were the Landlord under the Main Lease, the Sublease Premises were the Premises
under the Main Lease, and the Sublease Term were the Term under the Main Lease.
Notwithstanding the foregoing, whenever the obligations of Sublessor to
Sublessee derive from the obligations of Landlord to Sublessor, as Tenant under
the Main Lease (including, without limitation, any consent or approval of
Landlord), the maximum obligation of Sublessor hereunder shall be to use
reasonable efforts to obtain appropriate action on the part of Landlord. In no
event shall Sublessor be liable to Sublessee for any breach of Sublessor's
obligations under this Sublease, nor shall such breach diminish Sublessor's
rights hereunder, where the same is caused by or attributable to the failure of
Landlord to perform its obligations under the Main Lease. Sublessor and
Sublessee each covenant to comply with the terms and provisions of the Main
Lease, to the extent the same are not inconsistent with the terms and provisions
of this Sublease, and to do nothing which will subject the Main Lease to
termination by Landlord under the provisions of the Main Lease. Notwithstanding
the foregoing, the following provisions of the Main Lease shall NOT be
incorporated into this Sublease:

              a. Section 1.2 of the Main Lease;

              b. Sections 2.1.1, 2.4, 2.4.1, and 2.6.1 of the Main Lease, the
         second sentence of the first paragraph of Section 2.5, and Section 2.7
         of the Main Lease;

              c. Sections 3.1 and 3.2 of the Main Lease;

              d. The second sentence of Section 5.2 and the last sentence of
         Section 5.11 of the Main Lease;

              e. The last sentence of Section 6.1 of the Main Lease;

              f. Section 8.3 and Section 8.6 of the Main Lease;

              g. Section 8.14 of the Main Lease;

              h. The first sentence of Section 9.1 of the Main Lease.

              i. Article X of the Main Lease;

              j. Article XII of the Main Lease; and

              k. The First Amendment to the Main Lease.

Section 8.16 of the Main Lease is modified to provide that Sublessee only, and
not the individual(s) executing this Sublease on behalf of Sublessee, makes the
representations and warranties set forth in Section 8.16 of the Main Lease.


                                      -2-
<PAGE>   3
Sublessor represents to Sublessee that the copy of the Main Lease attached
hereto as Exhibit A is true and accurate, and that except as shown on said
Exhibit A, the Main Lease has not been modified, amended or terminated, and
remains in full force and effect. Sublessor further represents to Sublessee
that, to the best of its knowledge: (a) no default by the Landlord or Sublessor,
as Tenant, currently exists under the Main Lease, and (b) nor does any state of
fact or condition now exist which will become a default under the Main Lease
upon passage of time and/or notice.

Sublessee shall have the same rights and obligations with respect to assignment
and/or subletting of the Sublease Premises as Sublessor has with respect to the
Main Premises, as set forth in Section 5.9 of the Main Lease, incorporated
herein pursuant to Section 1 above.

              2.   Demise of Sublease Premises; Term. Sublessor hereby leases to
Sublessee, and Sublessee hereby leases from Sublessor, on the terms and
conditions set forth herein, the Sublease Premises, TO HAVE AND TO HOLD
commencing on September 1, 2000 (the "Commencement Date"), and expiring at 5:00
p.m. on August 31, 2002, unless sooner terminated as herein provided or as
provided in the Main Lease (the "Sublease Term"). During the Sublease Term,
Sublessee shall have access to the Sublease Premises twenty-four (24) hours a
day, seven (7) days a week (subject to (i) the terms of the Main Lease, and (ii)
such interruptions as are necessary for maintenance to the building or in case
of emergencies).

         Sublessor further grants to Sublessee the right to use, as appurtenant
to the Sublease Premises and in common with Landlord, Sublessor, and all others
now or hereafter entitled thereto: (i) the lockers and the showers located in
the Main Premises; (ii) such lobbies, hallways, and common areas of the Main
Premises located on the first floor of the Main Premises as are necessary for
access to and from the Sublease Premises, but excluding the right to use the
elevators and stairways of the Main Premises; and (iii) on a fee-for-use basis
(as reasonably determined by Landlord from time to time): the animal room and
Sublessor's glass-washing and autoclaving facilities on the first floor of the
Main Premises.

              3.   Annual Fixed Rent. Sublessee covenants and agrees to pay to
Sublessor, with respect to the Sublease Term, Annual Fixed Rent at the per annum
rate of Four Hundred Fifty Six Thousand Six Hundred Eighty Dollars ($456,680.00)
payable in equal monthly installments of Thirty Eight Thousand Fifty-Six Dollars
and Sixty-Seven Cents ($38,056.67) in advance on the first (1st) day of each and
every calendar month during the Sublease Term, without notice, setoff or
deduction, at the Sublessor's address, as set forth herein, or at such other
place or to such other person as Sublessor may from time to time designate in
writing to Sublessee. With respect to any partial month at the beginning or end
of the Sublease Term, the Annual Fixed Rent due under this Sublease shall be
pro-rated accordingly.

              4.   Additional Rent. Sublessee shall pay to Sublessor the
following amounts as "Additional Rent":


                                      -3-
<PAGE>   4
         (a) Landlord's Operating Expenses and Taxes. Sublessee covenants and
agrees to pay to Sublessor as "Additional Rent" Sublessee's Proportionate Share
(as hereinafter defined) of Landlord's Operating Expenses and Landlord's Taxes
over Base Taxes, as defined in Section 2.6 of the Main Lease. "Sublessee's
Proportionate Share" shall be a fraction, the numerator of which is the number
of rentable square feet in the Sublease Premises (which the parties agree is
presently 16,310 rentable square feet) and the denominator of which is the
number of rentable square feet in the Main Premises (which the parties agree is
presently 85,430 rentable square feet). The parties agree that Sublessee's
Proportionate Share is presently 19.09%. Sublessee shall pay such charges to
Sublessor in the time and manner (and subject to adjustment) as set forth for
the payments by Tenant to Landlord in Section 2.6.2 of the Main Lease.

         (b) Electricity. Sublessee acknowledges that the Annual Fixed Rent
payable hereunder does not include the cost of supplying electricity to the
Sublease Premises. During the Sublease Term, Sublessee shall pay to Sublessor a
per annum charge for supplying electricity to the Sublease Premises in the
amount of Thirty Two Thousand Six Hundred Twenty Dollars and 00/100
($32,620.00), payable in advance, together with and upon the same conditions as
Sublessee's installments of Annual Fixed Rent hereunder, in equal monthly
installments of Two Thousand Seven Hundred Eighteen Dollars and 33/100
($2,718.33).

         (c) Sublessor's Building Services Expenses. Sublessee shall also pay to
Sublessor as "Additional Rent" an amount equal to Sublessee's Proportionate
Share (as defined in Section 4(a) above) of all costs or expenses incurred by
Sublessor with respect to the administration, operation, repair, cleaning and
maintenance of the Main Premises, including without limitation expenses in
connection with the security system, security desk personnel, pest control and
cleaning services (collectively "Sublessor's Building Services Expenses"). Such
payments shall be made in the same time, place and manner, and subject to
adjustment, as Sublessee's payment of Sublessee's Proportionate Share of
Landlord's Operating Expenses and Landlord's Taxes over Base Taxes, as set forth
in Section 4(a) above.

         (d) Receptionist. Sublessee shall pay to Sublessor as "Additional Rent"
an amount equal to one-third (1/3) of the reasonable costs of maintaining a
receptionist at the Main Premises until such time, if any, as Sublessee shall
exclusively utilize the services of its own receptionist. Such amount shall be
payable by Sublessee in monthly installments at the time prescribed for monthly
installments of Annual Fixed Rent.

         (e) Special Services. Sublessee shall pay to Sublessor as "Additional
Rent" within thirty (30) days of billing therefor, One Hundred Percent (100%) of
any costs, charges, fines, assessments or other expenses which are incurred by
Sublessor and are either caused by the act or negligence of Sublessee, its
agents, employees, contractors or invitees, are performed as special services
exclusively for Sublessee at Sublessee's request, or are otherwise directly
allocable to the Sublease Premises (excluding charges and/or expenses payable by
Sublessee to Sublessor pursuant to Sections 4(a) through (d) of this Sublease),
including without limitation


                                      -4-
<PAGE>   5
any utilities, services, materials, supplies, or equipment provided by Sublessor
exclusively to Sublessee or the Sublease Premises.

              5.   Use. Sublessee shall not use the Sublease Premises for any
uses other than general office use, and shall not make any use of the Premises
which is prohibited by any applicable law, ordinance, code, regulation, license,
permit, variance or governmental order. Sublessee, at its sole cost and expense,
shall obtain all permits necessary for the conduct of its business in the
Sublease Premises. Notwithstanding the foregoing, Sublessee shall be permitted
to use that portion of the Sublease Premises shown as "Laboratory Room" on
Exhibit B for laboratory use.

              6.   Default by Sublessee. Notwithstanding anything in the Main
Lease to the contrary, for the purposes of determining applicable grace periods
hereunder, Sublessee's grace period hereunder shall be one-half of any such
grace period granted to Sublessor under the Main Lease.

              7.   Condition of the Sublease Premises. By its execution hereof,
Sublessee acknowledges that Sublessee has inspected the Sublease Premises, is
fully satisfied with the condition thereof (structural, mechanical or otherwise)
and accepts the same "AS IS" as of the date of this Sublease. Sublessor shall
have no obligation or duty to Sublessee regarding the condition of the Sublease
Premises or the preparation of the Sublease Premises for occupancy by Sublessee.

              8.   Parking. Sublessee shall be entitled to use, on a
non-exclusive basis together with Sublessor and all others now or hereafter
entitled thereto, fifty-five (55) parking spaces from the parking spaces
allocated to Sublessor under the Main Lease.

              9.   Security Deposit. Within two (2) days after the full
execution of this Sublease by Sublessor, Sublessee and Landlord (and in all
events prior to the date Sublessee occupies any portion of the Sublease Premises
for any purpose), Sublessee shall pay to Sublessor Two Hundred Twenty Eight
Thousand Three Hundred Forty Dollars ($228,340.00) (the "Security Deposit"),
which shall be held by Sublessor to secure Sublessee's performance of its
obligations under this Sublease. The Security Deposit is not an advance payment
of rent or a measure or limit of Sublessor's damages upon a default by
Sublessee. Sublessor may, from time to time and without prejudice to any other
remedy, use all or a part of the Security Deposit to perform any obligation
Sublessee fails to perform hereunder. Following any such application of the
Security Deposit, Sublessee shall pay to Sublessor on demand the amount so
applied in order to restore the Security Deposit to its original amount.
Provided that Sublessee has performed all of its obligations hereunder,
Sublessor shall, within thirty (30) days after the Sublease Term ends, return to
Sublessee the portion of the Security Deposit which was not applied to satisfy
Sublessee's obligations under this Sublease. The Security Deposit shall not be
commingled with other funds of Sublessor and shall be held by Sublessor in an
interest-bearing account. Interest on the Security Deposit shall be paid to
Sublessee at the rate actually received by Sublessor, less


                                      -5-
<PAGE>   6
Sublessor's reasonable third party costs incurred in maintaining the Security
Deposit in a separate interest-bearing account. If Sublessor transfers its
interest in the Sublease Premises and the transferee assumes Sublessor's
obligations under this Sublease, then Sublessor may assign the Security Deposit
to the transferee and Sublessor thereafter shall have no further liability for
the return of the Security Deposit.

              10.  Surrender. Upon the expiration or earlier termination of this
Sublease, Sublessee shall perform all the obligations of Sublessor, as Tenant,
under Section 5.11 of the Main Lease with respect to the Sublease Premises.

              11.  Notices. All notices required or permitted hereunder shall
be in writing and shall be deemed duly served if and when delivered by hand or
mailed by registered, certified or express mail, postage prepaid, return receipt
requested, and addressed:

         If to Sublessor:     Anadys Pharmaceuticals, Inc.
                              610 Lincoln Street
                              Waltham, Massachusetts 02451
                              Attention: Joseph McPherson
                                         Director of Facilities and
                                         Technical Services

         with a copy to:      Choate, Hall & Stewart
                              Exchange Place
                              53 State Street
                              Boston, Massachusetts  02109
                              Attention: Frank Giso III, Esq.

         If to Sublessee:     After the Commencement Date:

                              AltaRex US, Corp.
                              610 Lincoln Street
                              Waltham, Massachusetts 02451
                              Attention: Edward Fitzgerald
                                         Senior Vice President and Chief
                                         Financial Officer

                              Prior to the Commencement Date:

                              AltaRex US, Corp.
                              303 Wyman Street
                              Waltham, MA 02451
                              Attention: Edward Fitzgerald
                                         Senior Vice President and Chief
                                         Financial Officer


                                      -6-
<PAGE>   7
           with a copy to:    Hale and Dorr LLP
                              60 State Street
                              Boston, MA 02109
                              Attention: Jeffrey Hermanson, Esq.


Any of the persons named in this Section may change the address for notices by
written notice sent to each of the other persons at the addresses as set forth
herein.

              12.  Amendment. This Sublease may not be amended, altered or
modified except by instrument in writing and executed by Sublessor and
Sublessee, with the consent and approval of Landlord.

              13.  Brokerage. Sublessee and Sublessor each warrant and represent
to each other that they have not dealt with any broker or finder in connection
with this Sublease or the Sublease Premises, except Trammell Crow Company (the
"Broker"). Sublessee and Sublessor agree to hold each other harmless and
indemnify each other for any loss, cost, damage and expenses, including
reasonable attorney's fees, incurred by Sublessee, Sublessor or Landlord for any
breach of the foregoing warranty and representation. Sublessor shall be
responsible for any commission due to the Broker pursuant to a separate
agreement.

              14.  Security. All security for the Sublease Premises shall be
Sublessee's sole responsibility and expense. Notwithstanding the foregoing,
Sublessor may from time to time provide security services for the Main Premises,
and a portion of the cost and expense therefor shall be payable by Sublessee
pursuant to Section 4(c) of this Sublease.

              15.  Financial Statements. Sublessee covenants and agrees to
provide financial statements to Sublessor upon request if at any time during the
Sublease Term, or any extension thereof, Sublessee ceases to be a publicly
traded company.

              16.  Indemnification and Insurance. Sublessee acknowledges and
agrees that: (a) Sublessee's indemnification obligations (as set forth in
Section 5.5 of the Main Lease, as incorporated herein by Section 1 above) shall
include the obligation to protect, indemnify and save harmless the Landlord, and
its respective managing agents and mortgagees from time to time, in accordance
with the terms of said Section 5.5; and (b) all insurance required to be carried
by Sublessee (as set forth in Section 5.5 of the Main Lease, as incorporated
herein by Section 1 above) for which Sublessee is required to name Sublessor as
an additional insured, shall also name Landlord and its respective mortgagees
from time to time, if any, as additional insureds.

              17.  Lessor's Approval. This Sublease is conditioned upon and
subject to the consent and approval of Landlord. Sublessor shall use reasonable
efforts to obtain such consent and approval. If Sublessor does not obtain such
consent on or before the Commencement Date and is unable to deliver the Sublease
Premises to Tenant on the Commencement Date, Sublessor


                                      -7-
<PAGE>   8
shall not be liable to Sublessee on account thereof, and Sublessee's sole
remedy, at law or in equity shall be an abatement of Annual Fixed Rent and all
other charges due under this Sublease until such time as Sublessor delivers the
Sublease Premises to Sublessee free of all other occupants, having obtained the
Landlord's consent to this Sublease. If Sublessor fails to obtain such consent
and deliver the Sublease Premises to Sublessee free of all other occupants on or
before October 1, 2000, Sublessee shall have the right to terminate this
Sublease upon five (5) business days prior written notice to Sublessor, and upon
the expiration of said five (5) business day period, this Sublease shall
terminate and become void without recourse to the parties hereto, unless within
such time Sublessor obtains the Landlord's consent and delivers the Sublease
Premises to Sublessee free of all other occupants.

              18.  Entire Agreement. This Sublease constitutes the entire
agreement between Sublessor and Sublessee regarding the subject matter hereof
and supersedes all oral statements and prior writings relating thereto
(including, but not limited to, that certain Letter of Intent dated April 3,
2000). Except for those set forth in this Sublease, no representations,
warranties, or agreements have been made by Sublessor or Sublessee to the other
with respect to this Sublease or the obligations of Sublessor or Sublessee in
connection therewith.

              19.  Casualty and Taking.

         (a) Termination of Main Lease. In the event that during the Term, all
or any part of the Sublease Premises or the Main Premises is destroyed or
damaged by fire or other casualty or taken by eminent domain, and either
Sublessor or Landlord terminates the Main Lease, then this Sublease shall
likewise terminate on the same date that the Main Lease terminates. Sublessor
shall have the same right to terminate this Sublease as Landlord has to
terminate the Main Lease under Section 6.1 thereof. Sublessee shall have the
same right to terminate this Sublease as Sublessor has to terminate the Main
Lease, as Tenant thereunder, pursuant to said Section 6.1, except such
termination election must be made within five (5) days of the expiration of the
twelve (12) month period set forth therein.

         (b) Repair, Restoration and Abatement. In the event any such damage,
destruction or taking of the Sublease Premises or Main Premises occurs and this
Sublease is not terminated pursuant to Section 19(a) above, then Sublessor shall
use reasonable efforts to cause the Landlord to repair and restore the Sublease
Premises or the Main Premises, as the case may be, in accordance with the terms
and provisions contained in the Main Lease. In no event shall Sublessee be
entitled to an abatement of Fixed Rent and Additional Rent pursuant to Section
6.1 or Section 6.2 of the Main Lease, as incorporated herein, unless Sublessor
receives a corresponding abatement of Fixed rent and additional rent from
Landlord pursuant to the Main Lease.


                                      -8-
<PAGE>   9
              20.  Excluded Obligations. Notwithstanding anything to the
contrary contained herein or in the Main Lease, the incorporated provisions of
the Main Lease are amended or qualified as follows:

         (a) Sublessor shall not be liable under any circumstances for a loss of
or injury to property of Sublessee, or interference with Sublessee's business,
however occurring, arising from or in any way related to the interruption or
curtailment of utilities or services to the Sublease Premises, unless the same
is caused by Sublessor's willful misconduct;

         (b) Sublessor shall have no responsibility to perform or construct (or
to pay the cost of performing or constructing) any repair, maintenance or
improvement in or to the Sublease Premises except to the extent required of
Sublessor as Tenant under the Main Lease, or as expressly provided herein, or to
the extent required due to Sublessor's willful misconduct.

         21. Access. Without in any way limiting the rights of Sublessor under
Section 5.7 of the Main Lease, as incorporated herein by Section 1, Sublessor
shall have the right to access the Sublease Premises from time to time in order
to inspect, operate, use, maintain, repair and replace the wastewater storage
tank located in the utility closet in the Sublease Premises as shown on Exhibit
B hereto, and all pipes, wires, conduits and other facilities or appurtenances
thereto. Sublessor agrees to hold harmless and indemnify Sublessee from and
against any claims, demands, causes of action, liabilities, suits, judgments,
damages and expenses, including reasonable attorney's fees, arising from harm to
persons and/or property caused by said wastewater storage tank, or the presence
of Sublessor, its employees, agents or contractors, within the Sublease Premises
pursuant to this Section 21.

         21. No Offer. The submission of this Sublease to Sublessee shall not be
construed as an offer, and this Sublease shall be of no force or effect until
fully executed and delivered by both Sublessor and Sublessee.

EXECUTED under seal as of the day and year first above written.

Sublessor:                                  Sublessee:

ANADYS PHARMACEUTICALS, INC.                ALTAREX US, CORP.



By:  /s/ Kenneth A. Hurley                  By:  /s/ Richard E. Bagley
   ------------------------------------         --------------------------------
     Name:  Kenneth A. Hurley                    Name:  Richard E. Bagley
     Title: CFO                                  Title: President & CEO
            hereunto duly authorized                    hereunto duly authorized


                                      -9-
<PAGE>   10
     The undersigned ___________________, as Trustee of Landlord, the Landlord
under the "Main Lease" described herein, hereby consents to the execution of
this Sublease and the terms and conditions set forth therein. Nothing herein
shall be interpreted to modify Landlord's rights and obligations under the Main
Lease.


                                            Landlord:

                                            LINCOLN STREET TRUST



                                            By:  /s/ Michael Bank
                                                --------------------------------
                                                 Name:   Michael Bank
                                                 Title:  Trustee as aforesaid




                                      -10-
<PAGE>   11
                                    EXHIBIT A

                                   Main Lease






                                      -11-
<PAGE>   12
                                                               November 13, 1991






                            HOBBS BROOK OFFICE PARK

                             Waltham, Massachusetts

                                  OFFICE LEASE

                               610 Lincoln Street

                      IMMULOGIC PHARMACEUTICAL CORPORATION






<PAGE>   13
                         TABLE OF ARTICLES AND SECTIONS

ARTICLE I - Reference Data

1.1       Subjects Referred To..................................... 1
1.2       Exhibits................................................. 2

ARTICLE II - Premises, Term, Rent, Operating Expenses
             Electricity

2.1       The Premises............................................. 2
          2.1.1  Expansion of Premises............................. 3
2.2       Appurtenant Rights....................................... 3
2.3       Omitted.................................................. 3
2.4       Term..................................................... 3
          2.4.1  Extension Option.................................. 3
2.5       Annual Fixed Rent........................................ 5
2.6       Additional Charges - Operating Expenses and Taxes........ 5
          2.6.1  Additional Charges - General Covenant............. 5
          2.6.2  Payment........................................... 6
          2.6.3  Landlord's Operating Expenses - Definition........ 6
          2.6.4  Landlord's Taxes - Definition..................... 7
2.7       Electricity.............................................. 8

<PAGE>   14
ARTICLE III - Construction of Premises

3.1  Plans and Specifications............................................. 8
3.2  Construction of Premises............................................. 8

ARTICLE IV - Landlord's Covenants

4.1  Landlord's Covenants................................................. 9
     4.1.1     Building Services.......................................... 9
     4.1.2     Repairs.................................................... 9
     4.1.3     Quiet Enjoyment............................................10
     4.1.4     Environmental Hazards......................................10
     4.1.5     Landlord's Insurance.......................................10
4.2  Interruption.........................................................10

ARTICLE V - Tenant's Additional Covenants

5.1  Maintenance, Repair, and Cleaning....................................12
5.2  Use, Waste and Nuisance..............................................12
5.3  Rules and Regulations................................................13
5.4  Safety Appliances....................................................13
5.5  Indemnification and Insurance........................................13
5.6  Tenant's Property....................................................14
5.7  Entry for Repairs and Inspections....................................15
5.8  Omitted..............................................................15
5.9  Assignment, Subletting...............................................15
5.10 Alterations..........................................................16

                                      -2-
<PAGE>   15
5.11 Surrender.............................................................17
5.12 Personal Property Taxes...............................................17

ARTICLE VI - Casualty and Taking

6.1  Damage by Fire or Casualty............................................18
6.2  Condemnation - Eminent Domain.........................................19
6.3  Eminent Domain Award..................................................20

ARTICLE VII - Default

7.1  Termination for Default or Insolvency.................................20
7.2  Reimbursement of Landlord's Expenses..................................21
7.3  Damages...............................................................22
7.4  Mitigation............................................................23
7.5  Claims in Bankruptcy..................................................23
7.6  Interest on Unpaid Amounts............................................23
7.7  Vacancy During Last Three Months......................................23

ARTICLE VIII - Miscellaneous

8.1  Holdover..............................................................24
8.2  Estoppel Certificates.................................................24
8.3  Notice................................................................24
8.4  Landlord's Right to Cure..............................................25
8.5  Successors and Assigns................................................25
8.6  Brokerage.............................................................25
8.7  Waiver................................................................26

                                      -3-
<PAGE>   16
8.8       Accord and Satisfaction..........................................26
8.9       Remedies, Cumulative.............................................26
8.10      Partial Invalidity...............................................26
8.11      Waivers of Subrogation...........................................27
8.12      Entire Agreement.................................................27
8.13      No Agreement Until Signed........................................27
8.14      Tenant's Authorized Representative...............................27
8.15      Notice of Lease..................................................27
8.16      Tenant as Business Entity........................................28
8.17      Miscellaneous Provisions.........................................28

ARTICLE IX - Landlord's Liability and Assignment for Financing

9.1       Landlord's Liability.............................................29
9.2       Assignment of Rents..............................................30

ARTICLE X - Security Deposit...............................................31

ARTICLE XI - Subordination and Non-Disturbance.............................31

ARTICLE XII - Parking......................................................32

Exhibit A - Plan of Land

Exhibit B - Construction Costs Disbursement Schedule

                                      -4-
<PAGE>   17
                            HOBBS BROOK OFFICE PARK

                             Waltham, Massachusetts

                         LEASE dated November 29, 1991

                                   ARTICLE I

                                 REFERENCE DATA


     1.1  SUBJECTS REFERRED TO

     Each reference in this Lease to any of the following subjects shall be
construed to incorporate the data stated for that subject in this Article.

LANDLORD:  Lincoln Street Trust

LANDLORD'S ADDRESS:  P. O. Box 9198
                     Waltham, Massachusetts 02254-9198
                     Attention:  Real Estate Manager

TENANT:  Immulogic Pharmaceutical Corporation

TENANT'S ORIGINAL ADDRESS:  One Kendall Square, Building 600
                            Cambridge, MA  02139

TERM COMMENCEMENT DATE:  September 1, 1992

TERM EXPIRATION DATE:  The last day of the one hundred twentieth (120th) full
calendar month after the Term Commencement Date.

ANNUAL FIXED RENT:  Lease Years 1 and 2:          $1,055,060.50
                    Lease Year 3:                 $1,097,777.50
                    Lease Year 4:                 $1,183,205.50
                    Lease Year 5:                 $1,225,920.50
                    Lease Years 6 through 8:      $1,268,635.50
                    Lease Years 9 and 10:         $1,311,350.60

BASE TAXES:  Landlord's Taxes as defined in Section 2.6.4 for the one year
period beginning with the Term Commencement Date.

LAND:  The land upon which the Premises are situated including parking areas,
       garages, drives, walks, landscaped areas and other common areas serving
       the Premises.

PREMISES:  The entire building known and numbered as 610 Lincoln Street,
           Waltham, Massachusetts.


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RENTABLE FLOOR AREA OF PREMISES:   85,430 square feet.

PERMITTED USES:     Offices, research and development, and the manufacturing,
                    assembly or packaging of products that, (1) do not require
                    any smelting or chemical reduction processes, (2) have a
                    decibel level of fifty-five (55) or below, fifty (50) feet
                    from any portion of any structure on the Land, (3) are
                    non-nuisance in character, and (4) are performed in
                    accordance with reasonable and prudent industry practices;
                    and uses accessory to such assembly or packaging.

SECURITY DEPOSIT:   $750,000.00

PUBLIC LIABILITY INSURANCE:   $3,000,000.00

BROKER:   R. M. Bradley & Co., Inc. and Lynch, Murphy, Walsh and Partners

TENANT'S AUTHORIZED REPRESENTATIVE:     Janet C. Bush

     1.2  EXHIBITS

     The following is a list of Exhibits attached to this Lease.

          Exhibit A.     Plan of Premises.

          Exhibit B.     Construction Costs Disbursement Schedule


                                   ARTICLE II

                        PREMISES; TERM; RENT; OPERATING
                           EXPENSES; AND ELECTRICITY

     2.1  PREMISES

     Landlord hereby leases to Tenant and Tenant hereby leases from Landlord
the Premises.

     This Lease is subject to all easements, restrictions, agreements, and
encumbrances of record to the extent in force and applicable.




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     2.1.1 EXPANSION OF PREMISES. Subject to causes beyond Landlord's reasonable
control, Landlord will build an addition to the Premises, provided that all the
following conditions are met:

     (a) Tenant notifies Landlord prior to the end of the fourth lease year that
         Tenant desires to lease additional space;

     (b) Landlord and Tenant have reached agreement prior to the end of the
         fifth lease year on the terms of a lease for the additional space; and

     (c) The construction of such additional space is permitted by state and
         city laws, ordinances and regulations.

     2.2 APPURTENANT RIGHTS

     Tenant shall have, as appurtenant to the Premises, rights to use in common
(subject to reasonable rules of general applicability to tenants in Hobbs Brook
Office Park made by Landlord of which Tenant is given notice) common driveways
and walkways necessary for access to the Premises, and the parking areas
described in ARTICLE XII.

     2.3 OMITTED

     2.4 TERM

     The Term shall begin at 12:01 a.m. on the Term Commencement Date, and
shall end at 12:00 midnight on the Term Expiration Date set forth in Section
1.1. Tenant may enter onto the Premises prior to the Term Commencement Date for
construction of the Premises as provided in Article III.

     2.4.1 EXTENSION OPTION

     Tenant shall have the option to extend the Term for three additional five
year extension terms (the "Extension Terms") by notice given to Landlord at
least twelve months before the Term Expiration Date or the expiration of any
Extension Term, as the case may be. Tenant's election shall be exercised, and
Annual Fixed Rent for each Extension Term determined, as set forth below. If
Tenant fails timely to exercise its option for any Extension Term, Tenant shall
have no further extension rights hereunder.

     Tenant's option so to extend the Term shall be void, at Landlord's
election, if Tenant is in default (continuing beyond any applicable cure
period) at the time Tenant elects to extend the Term or at the time the Term
would expire but for such extension. Any

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extension of the Term shall be applicable to the entire Premises. During an
Extension Term, if any, all provisions of this Lease shall apply except that
Tenant shall have no further option to extend the Term after the third
Extension Term.

     During each Extension Term, Tenant shall pay Annual Fixed Rent equal to
90% of the then prevailing market rate for a five year lease of office space in
the greater Boston, Massachusetts "Metro-West" area comparable to the Premises
in terms of location, finish, age, building quality and amenities for a tenant
of equal size and financial strength as Tenant.

     Landlord shall notify Tenant of its estimate of the prevailing market rate
within ten (10) days after Tenant exercises its extension option. Tenant shall
have the option to accept or reject Landlord's estimate by written notice to
Landlord within ten (10) days of receipt of Landlord's estimate. If Tenant
rejects such estimate, Tenant may either rescind its election to extend the term
or elect to have the prevailing market rate arbitrated in accordance with the
following procedure. Each of Landlord and Tenant, within twenty days after
notice by Tenant disputing Landlord's estimate of the prevailing market rate,
shall appoint as an arbitrator an MAI appraiser with at least ten years
experience as an appraiser of Boston office buildings, including first class
suburban office buildings, and shall give notice of such appointment to the
other party. If either Landlord or Tenant shall fail timely to appoint an
arbitrator, the other may apply to the Boston Office of the American Arbitration
Association ("AAA") for appointment of such an arbitrator if the arbitrator has
not been appointed within five business days after notice of such failure has
been given to the delinquent party. The two arbitrators shall, within five
business days after appointment of the second arbitrator, appoint a third
arbitrator who shall be similarly qualified. If the two arbitrators are unable
to agree timely on the selection of the third arbitrator, then both arbitrators
together may request such appointment from the Boston office of the AAA. The
arbitration shall be conducted in accordance with the Commercial Arbitration
Rules of the AAA insofar as such rules are not inconsistent with the provisions
of this Lease (in which case the provisions of this Lease shall govern), and the
arbitrators shall reach a majority decision in accordance with the standards
provided in this Lease at least six months before the Term Expiration Date or
the expiration of any Extension Terms, as the case may be. The prevailing market
rent rate shall be in accordance with the arbitrators' decision. Tenant shall
have the option to reject the decision and rescind its election to extend the
Term by notice to Landlord within five (5) days of the date of the decision. The
cost of the arbitration (exclusive of each party's witness and attorneys fees,
which shall be paid by such party) shall be borne equally by the parties. If the
AAA shall cease to provide



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arbitration for commercial disputes in Boston, the second or third arbitrator,
as the case may be, shall be appointed by any successor organization providing
substantially the same services, and in the absence of such an organization, by
a court competent jurisdiction under the arbitration act of The Commonwealth of
Massachusetts.

     For any portion of an Extension Term during which the prevailing market
rent is in dispute hereunder, Tenant shall make payment on account of Annual
Fixed Rent at the rate last in effect and the parties shall adjust for over or
under payments within twenty days after the decision of the arbitrators is
announced.

     Promptly after the Annual Fixed Rent is determined for any Extension Term,
Landlord and Tenant shall enter into an amendment of this Lease confirming the
extension of the Term and the new rate for Annual Fixed Rent.

     2.5  ANNUAL FIXED RENT

     Except as expressly provided herein, tenant covenants and agrees to pay the
Annual Fixed Rent in Section 1.1 to Landlord in advance in equal monthly
installments on the first day of each calendar month during the Term. As an
inducement to Tenant to enter into and perform this Lease, Landlord shall waive
payment of Annual Fixed Rent for the first six months of the Term. All payments
shall be due without billing or demand and without deduction, setoff or
counterclaim. Tenant shall make payment for any portion of a month at the
beginning or end of the Term. All payments shall be payable to Landlord at its
Address, both as specified in Section 1.1, or to such other entities at such
other places as Landlord may from time to time designate.

     Without limiting the foregoing, Tenant's obligation so to pay rent, or to
pay any additional charge hereunder, shall not be discharged or otherwise
affected by any law or regulation now or hereafter applicable to the Premises,
or any other restriction on Tenant's use, or (except as expressly provided
herein) any casualty or taking, or any failure by Landlord to perform any
covenant contained herein, or any other occurrence; and Tenant waives all rights
now or hereafter existing to terminate or cancel this Lease or quit or surrender
the Premises or any part thereof, or to assert any defense in the nature of
constructive eviction to any action seeking to recover rent or additional
charges.

     2.6  ADDITIONAL CHARGES - OPERATING EXPENSES AND TAXES

     2.6.1  ADDITIONAL CHARGES - GENERAL COVENANT. Tenant covenants and agrees
to pay to Landlord, as additional charges, (i) 100% of Landlord's Operating
Expenses and (ii) an amount equal to the excess (if any) of Landlord's Taxes
over Base Taxes.

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          2.6.2  PAYMENT. Additional charges for Operating Expenses and Taxes
under this Section 2.6 shall be paid for any portion of a month at the
beginning of the Term and thereafter in monthly installments on the first day of
each calendar month in amounts reasonably estimated by Landlord for the then
current calendar year. Landlord may from time to time revise such estimates
based on available information relating to Landlord's Operating Expenses and
Taxes or otherwise affecting the calculation hereunder. Within 90 days after the
end of each calendar year, Landlord will provide Tenant with an accounting of
Landlord's Operating Expenses and Taxes and other data necessary to calculate
additional charges hereunder for such calendar year prepared in accordance
herewith and otherwise in accordance with generally accepted accounting
principles. Upon issuance thereof, there shall be an adjustment between Landlord
and Tenant for the calendar year covered by such accounting to the end that
Landlord shall have received the exact amount of additional charges due
hereunder. Any overpayments by Tenant hereunder shall be credited against the
next payments of additional charges due under this Section 2.6, provided there
are no outstanding amounts due Landlord under this Lease at such time. Any
underpayments by Tenant shall be due and payable within ten (10) days of
delivery of Landlord's statement. With respect to the calendar year in which the
Term ends, the adjustment shall be pro rated for the portion of the year
included in the Term, but shall take place nevertheless at the times provided in
the preceding sentences.

          2.6.3  "LANDLORD'S OPERATING EXPENSES" - DEFINITION. "Landlord's
Operating Expenses" means all costs of Landlord in owning, servicing,
operating, managing, maintaining, and repairing the Premises, and providing
services to Tenant including, without limitation, the costs of the following:
(i) supplies, materials and equipment purchased or rented, total wage and
salary costs paid to, and all contract payments made on account of, all persons
engaged in the operation, maintenance, security, cleaning and repair of the
Premises and Land, including Social Security, old age and unemployment taxes
and reasonable so-called "fringe benefits"; (ii) maintenance and repair of and
services provided to or on behalf of the Premises performed by Landlord's
employees or by other persons under contract with Landlord; (iii) utilities
consumed and expenses incurred in the operation, maintenance and repair of the
Premises including, without limitation, oil, gas, electricity, water, sewer and
snow removal; (iv) casualty, liability and other insurance, and unreimbursed
costs incurred by Landlord which are subject to an insurance deductible; (v)
costs of operating any cafeteria or other food service facility on the
Premises; and (vi) management fees. If Landlord, in its sole discretion,
installs a new or replacement capital item for the purpose of reducing
Operating Expenses, the cost of such item amortized over a reasonable period
with interest

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shall be included in Landlord's Operating Expenses. Landlord's Operating
Expenses shall not include expenses for any capital repairs, replacements or
improvements (except as specifically provided above); depreciation; expenses
incurred in leasing or procuring tenants or purchasers of the Building
(including lease or brokerage commissions, advertising expenses and expenses of
renovating or subdividing space or relocating improvements for tenants or
occupants); legal expenses arising out of the construction, use or occupancy of
the Premises or the Land or the enforcement of the provisions of any agreements
affecting the Premises or Land; interest or amortization payments on any
mortgage or mortgages and rental under any ground or underlying lease or leases;
expenses in connection with any restoration or compensation after casualty or
condemnation; expenses in connection with re-surfacing the parking facility
operated by Landlord; the cost of correcting defects (latent or otherwise) in
the construction of the Premises or the appurtenances, except that conditions
(not occasioned by construction defects) resulting from ordinary wear and tear
shall not be deemed defects; and any cost or expense representing an amount paid
to a related or affiliated person or entity which is in excess of the amount
which would be paid in the absence of such relationship. Tenant may from time to
time, with Landlord's consent which consent shall not be unreasonably withheld
or delayed, contract directly with providers of services to the Premises.

     2.6.4     "LANDLORD'S TAXES" - DEFINITION. "Landlord's Taxes" means all
taxes, assessments and similar charges assessed or imposed on the Land for the
then current calendar year by any governmental authority attributable to the
Premises (including personal property associated therewith). The amount of any
special taxes, special assessments and agreed or governmentally imposed "in
lieu of tax" or similar charges shall be included in Landlord's Taxes for any
year but shall be limited to the amount of the installment (plus any interest,
other than penalty interest, payable thereon) of such special tax, special
assessment or such charge required to be paid during or with respect to the
year in question. Landlord's Taxes include expenses, including fees of
attorneys, appraisers and other consultants, incurred in connection with any
efforts to obtain abatements or reduction or to assure maintenance of
Landlord's Taxes for any year wholly or partially included in the Term, whether
or not successful and whether or not such efforts involved filing of actual
abatement applications or initiation of formal proceedings. Landlord's Taxes
exclude income taxes of general application and all estate, succession,
inheritance and transfer taxes. If at any time during the Term there shall be
assessed on Landlord, in addition to or lieu of the whole or any part of the ad
valorem tax on real or personal property, a capital levy or other tax on the
gross rents or other measures of building operations, or a governmental income,

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franchise, excise or similar tax, assessment, levy, charge or fee measured by or
based, in whole or in part, upon Premises valuation, gross rents or other
measures of building operations or benefits of governmental services furnished
to the Premises, then any and all of such taxes, assessments, levies, charges
and fees, to the extent so measured or based, shall be included within the term
Landlord's Taxes, but only to the extent that the same would be payable if the
Premises and Land were the only property of Landlord.

     2.7  ELECTRICITY

     Tenant shall contract with and pay to the local utility company for
electricity used in the Premises.

                                  ARTICLE III

                            CONSTRUCTION OF PREMISES

     3.1  PLANS AND SPECIFICATIONS

     Tenant shall be solely responsible for the preparation of the final
architectural, electrical and mechanical construction drawings, plans and
specifications (called "Plans") necessary to lay out the Premises for Tenant's
occupancy, which Plans shall be subject to Landlord's reasonable approval and
shall comply with its requirements to avoid aesthetic or other conflict with the
design and function of the Building. Landlord shall reimburse Tenant for the
reasonable costs of preparing the Plans, not in excess of $2.00 per rentable
square foot of the Premises. Such reimbursement shall be paid one-half when
Landlord approves the Plans and one-half when the building permit is issued.
Tenant agrees to remain solely responsible for the timely preparation and
submission of all such Plans and any errors or omissions contained therein.
Landlord will cooperate with Tenant in filing applications and obtaining permits
necessary for the construction.

     3.2  CONSTRUCTION OF PREMISES

     All work necessary to prepare the Premises for Tenant's occupancy shall be
performed substantially in accordance with the Plans by contractors approved by
Landlord and employed by Tenant. Landlord shall have the right to approve
construction scheduling, methods and processes, and shall be entitled to have a
representative present at all construction meetings and on the construction site
at all times. Landlord shall bear the cost of construction not in excess of
$23.50 per rentable square foot of the Premises and Tenant shall bear all cost
in excess of $23.50 per

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rentable square foot. Landlord's portion of the construction cost shall be
disbursed in accordance with Exhibit B.

                                   ARTICLE IV

                              LANDLORD'S COVENANTS

     4.1  LANDLORD'S COVENANTS

          4.1.1     BUILDING SERVICES. Landlord shall furnish services,
utilities, facilities and supplies set forth in this Section 4.1.1.

                    4.1.1.1   WATER CHARGES. Landlord shall furnish water for
Tenant's use.

                    4.1.1.2   ELEVATOR SERVICE. Landlord shall provide elevator
facilities on the Premises.

                    4.1.1.3   OMITTED.

                    4.1.1.4   HEAT AND AIR-CONDITIONING. Landlord shall,
through the Building heating and air-conditioning system, furnish to and
distribute in the Premises heat during the normal heating season and
air-conditioning when air-conditioning may reasonably be required for the
comfortable occupancy of the Premises by Tenant. Landlord shall not be required
to furnish heat and air-conditioning in the Premises in excess of the capacity
of the equipment presently installed in the Building.

                    4.1.1.5   ENERGY CONSERVATION. Tenant agrees to cooperate
with Landlord and to abide by all reasonable Building regulations which
Landlord may, from time to time, prescribe for the proper functioning and
protection of the heating and air-conditioning systems and in order to maximize
the effect thereof and to conserve heat and air-conditioning. Notwithstanding
anything to the contrary in this Section 4.1.1 or otherwise in this Lease,
Landlord may institute such policies, programs and measures as may be in
Landlord's judgment necessary, required or expedient for the conservation or
preservation of energy or energy services, or as may be necessary to comply
with applicable codes, rules, regulations or standards, provided such policies,
programs or measures do not interfere with the operation of Tenant's business
in the Premises.

          4.1.2     REPAIRS. Except as otherwise provided in this Lease, and
except for repairs to items referred to below necessitated by Tenant's act or
neglect (which shall be Tenant's repair obligation under Section 5.1), Landlord
shall make such

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repairs to the roofs, exterior walls, exterior windows, floor slabs, core
walls, parking area and landscaping as may be necessary to keep them in good
condition.

          4.1.3     QUIET ENJOYMENT.     Landlord covenants that Tenant, on
paying the rent and performing the tenant obligations in this Lease, shall
peacefully and quietly have, hold and enjoy the Premises, free from any claim by
Landlord or persons claiming under Landlord, but subject to all of the terms and
provisions hereof, provisions of law and rights of record to which this Lease is
or may become subordinate. This covenant is in lieu of any other so-called quiet
enjoyment covenant, either express or implied.

          4.1.4     ENVIRONMENTAL HAZARDS.   Landlord represents that to the
best of its knowledge there are no hazardous substances as defined in Section
5.2 in the Premises or on the Land. If any hazardous substance as defined in
Section 5.2 is discovered in or on the premises or the Land during the term,
Landlord shall, unless the presence of such hazardous substance is the result of
a release caused by Tenant or persons acting under Tenant, at its sole cost and
expense, promptly cause all of such hazardous substances to be removed or
remediated strictly in accordance with all laws and shall provide Tenant with
reasonably satisfactory evidence that such hazardous substances have been
removed in accordance with applicable law. If either the presence, removal or
remediation of any hazardous substance actually prevents Tenant from carrying on
its normal business operation for a period of more than 90 consecutive days in
any twelve-month period, then Tenant may terminate this Lease by giving notice
to Landlord. The rent shall abate equitably based on the practical
nonavailability of any portion of the Premises for the purposes permitted by
this Lease due to the presence or removal of the hazardous substance.

     Landlord shall indemnify Tenant and hold it harmless against any claims,
damages, losses or liabilities (including reasonable attorneys' fees) incurred
by Tenant and arising from the presence or removal of hazardous substances.

          4.1.5     LANDLORD'S INSURANCE.    Landlord shall maintain in force
throughout the term of the Lease Comprehensive all risk insurance for the full
replacement value of the Premises and leasehold improvements, with a deductible
not to exceed $5000.00.

     4.2  INTERRUPTION

     Except as hereinafter provided, Landlord shall not be liable to Tenant for
any compensation or reduction of rent by reason of inconvenience or annoyance
or for loss of business arising from the



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necessity of Landlord or its agents entering the Premises for any of the
purposes authorized in this Lease or for repairing the Premises or from repairs
by Landlord of any portion of the Building however the necessity may occur. In
case Landlord is prevented or delayed from diligent construction of
improvements, making any repairs, alterations or improvements, or furnishing
any services or performing any other covenant or duty to be performed on
Landlord's part, by reason of any cause reasonably beyond Landlord's control,
Landlord shall not be liable to Tenant therefor, nor, except as otherwise
provided in this Section and Section 6.1 hereof, shall Tenant be entitled to
any abatement or reduction of rent by reason thereof, nor shall the same give
rise to a claim in Tenant's favor that such failure constitutes actual or
constructive, total or partial, eviction from the Premises. In no event shall
Landlord be liable for indirect or consequential damages arising out of any
default by Landlord.

     Notwithstanding any contrary provision of this Lease, in the event (i)
Landlord fails to perform any act or provide any service required hereunder or
Landlord undertakes activities which interfere with Tenant's normal activities
and such failure or interference occurs for reasons other than events that are
beyond Landlord's reasonable control, and (ii) such interference continues
(other than for causes which are beyond Landlord's reasonable control) after
notice from Tenant to Landlord more than ten (10) consecutive days, rent and
additional rent payable under Section 2.5 and 2.6 hereof shall be equitably
abated according to the nature and extent of the interference with Tenant's
business for the period from the date of commencement of such interference to
the date on which such interference no longer exists.

     Notwithstanding any contrary provision of this Lease, in the event that
Landlord, for reasons beyond Landlord's reasonable control (i) fails to perform
any act or provide any service required hereunder or Landlord undertakes
activities, and (ii) such interference continues after notice from Tenant to
Landlord for more than twenty (20) consecutive days, rent and additional rent
payable under Section 2.6 hereof shall be equitably abated according to the
nature and extent of the interference with Tenant's business beginning on the
21st consecutive day of such interference and continuing until the date on
which such interference no longer exists.

     Landlord reserves the right to stop any service or utility system, when
necessary by reason of accident or emergency, or until necessary repairs have
been completed; provided, however, that in each instance of stoppage, Landlord
shall exercise reasonable diligence to eliminate the cause thereof. Except in
case of emergency repairs, Landlord will give Tenant reasonable advance

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<PAGE>   28
notice of any contemplated stoppage and will use reasonable efforts to avoid
unnecessary interruption of Tenant's use of the Premises by reason thereof.


                                   ARTICLE V

                         TENANT'S ADDITIONAL COVENANTS

     5.1  MAINTENANCE, REPAIR AND CLEANING

     Except for damage by fire or casualty and reasonable wear, Tenant shall at
all times keep the Premises clean, neat and in as good repair, order and
condition as the same are at the beginning of the Term or may be put in
thereafter. The foregoing shall include without limitation Tenant's obligation
to maintain floors and floor coverings, to paint and repair walls and doors, to
replace and repair ceiling tiles, lights and light fixtures, drains and the
like, and clean the Premises.

     5.2  USE, WASTE AND NUISANCE

     Throughout the Term, Tenant shall occupy the Premises, shall use the
Premises for the Permitted Uses only, and shall not use the Premises for any
other purpose. Tenant shall, at Tenant's sole cost, use diligent efforts to
obtain all permits necessary for the conduct of its business in the Premises,
but if Tenant is unable to obtain all such permits by March 1, 1992, either
Landlord or Tenant may terminate this lease by notice within ten (10) days after
March 1, 1992, except that if Tenant is still pursuring such permits on March 1,
1992, Tenant or Landlord may extend such deadline to April 1, 1992. Tenant shall
not injure, overload, deface or commit waste in the Premises or any part of the
improvement on the Land, nor permit the emission therefrom of any objectionable
noise, light or odor, nor use or permit any use of the Premises which is
improper, offensive, contrary to law or ordinance or which is liable to
invalidate or increase the premium for any insurance on the Premises or its
contents or which is liable to render necessary any alterations or additions in
the Premises, nor obstruct in any manner any portion of the Premises. If
Tenant's use of the Premises results in an increase in the premium for any
insurance on the Premises or the contents thereof, Landlord shall notify Tenant
of such increase and Tenant shall pay same as additional charges.

     Tenant shall not (either with or without negligence) cause or permit the
escape, disposal or release of any biologically or chemically active or other
hazardous substances, or materials. Tenant shall not allow the storage or use of
such substances or materials in any manner not sanctioned by law or by the
highest

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<PAGE>   29
standards prevailing in the industry for the storage and use of such substances
or materials, nor allow to be brought into the Premises any such materials or
substances except to use in the ordinary course of Tenant's business. Upon
request by Landlord from time to time, Tenant shall provide Landlord with an
inventory of all chemicals on the Premises and copies of all specialized waste
disposal and removal contracts. Without limitation, hazardous substances and
materials shall include those described in the Comprehensive Environmental
Response, Compensation and Liability Act of 1980, as amended, 42 U.S.C. Section
9601 et seq., the Resource Conservation and Recovery Act, as amended, 42 U.S.C.
Section 6901 et seq., the Massachusetts Hazardous Waste Management Act, as
amended, M.G.L. Chapter 21C, and the Massachusetts Oil and Hazardous Material
Release Prevention Act, as amended, M.G.L. Chapter 21E, and the regulations
adopted under these acts. If any lender or governmental agency shall ever
require testing to ascertain whether or not there has been any release of
hazardous materials, then the reasonable costs thereof shall be reimbursed by
Tenant to Landlord upon demand as additional charges. In addition, Tenant shall
execute affidavits, representations and the like from time to time at Landlord's
request concerning Tenant's best knowledge and belief regarding the presence of
hazardous substances or materials on the Premises. In all events, Tenant shall
indemnify Landlord in the manner elsewhere provided from any release of
hazardous materials on the Premises occurring while Tenant is in possession, or
elsewhere if caused by Tenant or persons acting under Tenant.

     5.3  RULES AND REGULATIONS

     Tenant shall conform to all reasonable rules and regulations now or
hereafter promulgated by Landlord for the care and use of the Premises.

     5.4  SAFETY APPLIANCES

     Tenant shall keep the Premises equipped with all safety appliances and
permits which, as a result of Tenant's particular activities, are required by
law or ordinance or any order or regulation of any public authority, shall keep
the Premises equipped at all times with adequate fire extinguishers and other
such equipment reasonably required by Landlord, and, subject to Section 5.10,
shall make all repairs, alterations, replacements, or additions so required as a
result of Tenant's particular activities.

     5.5  INDEMNIFICATION AND INSURANCE

     Tenant shall save Landlord, its mortgagees, agents, employees, independent
contractors, invitees, and any other parties designated by Landlord from time to
time (collectively, the "Indemnitees")


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<PAGE>   30
harmless and indemnified (and shall defend the Indemnitees with counsel
reasonably approved by the Indemnitees) against any claim, loss or cost arising
in whole or in part out of any injury, loss, theft or damage to any person or
property while on or in the Premises, if not due solely to negligence or
willful misconduct of the Indemnitees, and to any person or property anywhere
occasioned by any act, omission, neglect or default of Tenant or of employees,
agents, independent contractors or invitees of Tenant or any person acting
under Tenant. In addition to the foregoing, Landlord may make all repairs and
replacements to the improvements on the Land resulting from acts or omissions
of Tenant's employees, agents, independent contractors or invitees or any other
persons acting under Tenant and Landlord may recover all costs and expenses
thereof from tenant as additional charges. Throughout the Term (and such
further time as Tenant or any person claiming through Tenant occupies any part
of the Premises) Tenant shall maintain in a responsible company or companies
approved by Landlord, liability insurance in form satisfactory to Landlord,
written on an occurrence basis, insuring the Indemnitees and other parties
designated by Landlord, and Tenant, as their respective interests may appear,
against all claims, demands or actions for injury, death, and property damage
in amounts not less than those specified in Section 1.1 (as such amounts may,
from time to time, be reasonably increased by Landlord). All insurance to be
maintained by Tenant under this Section 5.5 shall provide that it will not be
subject to cancellation, termination, or change except after at least 30 days'
prior written notice to the Indemnitees and other parties designated by
Landlord. The policy or policies or a duly executed certificate or certificates
for the same (together with satisfactory evidence of the payment of the premium
thereon if requested by Landlord) shall be deposited with Landlord and other
parties designated by Landlord at the beginning of the Term and, upon renewals
of such policies, not less than 30 days prior to the expiration of the term of
such coverage. If Tenant fails to comply with any of the foregoing
requirements, Landlord may obtain such insurance on behalf of Tenant and may
keep the same in effect, and Tenant shall pay Landlord, as additional charges,
the premium cost thereof upon demand. The covenants of this Section 5.5 shall
survive the expiration of the Term or earlier termination of this Lease.

     5.6  TENANT'S PROPERTY

     All furnishings, fixtures, equipment, effects and property of Tenant and
of all persons claiming through Tenant which from time to time may be on the
Premises or in transit thereto or therefrom shall be at the sole risk of Tenant
and shall be kept insured by Tenant throughout the term at Tenant's expense and
in prudent amounts, and throughout the term at Tenant's expense and in prudent
amounts, 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

                                                                              14
<PAGE>   31
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 Landlord, unless
caused by the negligence or misconduct of Landlord.

     5.7  ENTRY FOR REPAIRS AND INSPECTIONS

     Upon reasonable advance notice, Tenant shall permit Landlord and its agents
to enter and examine the Premises at reasonable times and, if Landlord shall so
elect, to make any repairs or replacements Landlord may deem necessary or
desirable, to remove at Tenant's expense any alterations, additions, signs,
curtains, blinds, shades, awnings, aerials, flagpoles, or the like not consented
to in writing, and to show the Premises to prospective tenants during the twelve
months preceding expiration of the Term and to prospective purchasers and
mortgagees at all times. In case of an emergency in the Premises, Landlord or
its representative may enter the Premises (forcibly, if necessary) at any time
to take such measures as may be needed to deal with such emergency. Tenant shall
have the right to accompany Landlord and its agents with respect to entry on
restricted areas. Certain areas of the premises may be used as "sterile areas"
and Landlord and its agents shall not have the right to enter "sterile areas",
in any event.

     5.8  OMITTED

     5.9  ASSIGNMENT, SUBLETTING

     Tenant shall not assign this Lease, or sublet or license the Premises or
any portion thereof, or permit the occupancy of all or any portion of the
Premises by anybody other than Tenant (all or any of the foregoing actions
are referred to as "Subleases" and all or any of assignees, subtenants,
licensees, and other such parties are referred to as "Subtenants") without
obtaining, on each occasion, the prior consent of the Landlord, which consent
shall not be unreasonably withheld or delayed. A Sublease shall not include any
transfer of Tenant's interest in this Lease by operation of law, merger or
consolidation of Tenant into any other firm or corporation, and the transfer or
sale of a controlling interest in Tenant, whether by sale of its capital stock
or otherwise. Unless Landlord's consent specifically provides otherwise with
respect to a particular proposed Subtenant, Tenant shall not offer to make or
enter into negotiations with respect to a Sublease to any of the following: (i)
a tenant in the Hobbs Brook Office Park; (ii) any party with whom Landlord or
any affiliate of Landlord is then negotiating with respect to space in the Hobbs
Brook Office Park; or (iii) any party which would be of such type, character or
condition as to be inappropriate, in Landlord's judgment, as a tenant for a
first class office building. Tenant's request for consent to a

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<PAGE>   32
Sublease shall include a copy of the proposed Sublease instrument, if available,
or else a statement of the proposed Sublease in detail satisfactory to Landlord,
together with reasonably detailed financial, business and other information
about the proposed Subtenant. If Tenant does make a Sublease hereunder, and if
the aggregate rent and other charges payable to Tenant under and in connection
with such Sublease (including without limitation any amounts paid for leasehold
improvements or on account of Tenant's costs associated with such Sublease but
deducting Tenant's costs such as architect's fees, brokerage fees, Tenant
improvements and the like) exceed the rent and other charges paid hereunder with
respect to the space in question, Tenant shall pay to Landlord, as an additional
charge, one-half the amount of such excess.

     Notwithstanding any such Sublease, the original Tenant named herein shall
remain directly and primarily obligated under this Lease.

     If Tenant enters into any Sublease with respect to the Premises (or any
part thereof), Landlord may, at any time and from time to time, require that
such Subtenant agree directly with Landlord to be liable, jointly and severally
with Tenant, to the extent of the obligation undertaken by or attributable to
such Subtenant, for the performance of Tenant's agreements under this Lease
(including payment of rent and other charges under the Sublease), and every
Sublease shall so provide. Landlord may collect rent and other charges from the
Subtenant and apply the net amount collected to the rent and other charges
hereunder, but no such assignment or collection shall be deemed a waiver of the
provisions of Section 5.9, or the acceptance of the Subtenant, as a tenant, or
a release of Tenant from direct and primary liability for the further
performance of Tenant's covenants hereunder. The consent by Landlord to a
particular Sublease shall not relieve Tenant from the requirement of obtaining
the consent of Landlord to any further Sublease.

     5.10 ALTERATIONS

     Tenant shall make no alterations, additions or improvements to the
Premises exceeding a cost of $1000.00 without the prior written consent of
Landlord and only in accordance with complete construction documents approved
in advance by Landlord, which approval shall not be unreasonably withheld or
delayed. All such alterations, additions and improvements shall be done only by
contractors approved in advance by Landlord. Tenant shall obtain all necessary
permits before undertaking any such alterations, additions or improvements and
shall carry such insurance and obtain such payment, performance and lien bonds
as Landlord shall reasonably require. Any alterations, additions and
improvements to


                                                                              16

<PAGE>   33
the premises, except movable furniture and trade fixtures, shall belong to
Landlord. All alterations, additions and improvements to the Premises shall be
at Tenant's sole cost. If any mechanic's lien (which term shall include all
similar liens relating to the furnishing of labor and materials) is filed
against the Building which is claimed to be attributable to Tenant, its agents,
employees or contractors, Tenant shall give immediate notice of such lien to
Landlord and shall discharge the same by payment or filing any necessary bond
within 10 days after Tenant has notice (from any source) of such lien.
Landlord's approval of the construction documents shall signify Landlord's
consent to the work shown thereon only and Tenant shall be solely responsible
for any errors or omissions contained therein.

     5.11 SURRENDER

     At the expiration of the Term or earlier termination of this Lease,
without the requirement of any notice, Tenant shall peaceably surrender the
Premises including all alterations and additions except such alterations and
additions as Landlord and Tenant have agreed shall or may be left on the
Premises, the Premises and improvements to be in the condition in which the
same are required to be maintained under Section 5.1. Tenant shall, at the time
of termination, remove the goods, effects and fixtures which Tenant is directed
or permitted to remove in accordance with the provisions of this Section,
making any repairs to the Premises and other areas necessitated by such removal
and leaving the Premises clean and tenantable. Should Tenant fail to remove any
of such goods, effects, and fixtures, Landlord may have them removed forcibly,
if necessary, and store any of Tenant's property in a public warehouse at the
risk of Tenant. If such items are not removed from storage within thirty (30)
days, such items may be sold by any customary methods in order to pay storage
costs and other expenses of Landlord. The expense of such removal, storage and
reasonable repairs necessitated by such removal shall be borne by Tenant or
reimbursed by Tenant to Landlord. Upon approval of the Plans by Landlord as
provided in Section 3.1, Landlord and Tenant shall enter into an agreement as
to which items (i) must be removed by tenant, (ii) may be removed by Tenant and
(iii) may not be removed by Tenant at the expiration of the Term of the Lease,
which agreement may be modified from time to time by mutual agreement.

     5.12 PERSONAL PROPERTY TAXES

     Tenant shall pay promptly when due all taxes (and charges in lieu thereof)
imposed upon personal property in the Premises, no matter to whom assessed
(including, without limitation, fixtures and equipment), subject to the right
of Tenant to attempt to obtain an abatement or reduction in said taxes.



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<PAGE>   34
                                   ARTICLE VI

                              CASUALTY AND TAKING

     6.1  DAMAGE BY FIRE OR CASUALTY

     If the Premises or any part thereof shall be damaged by fire or other
insured casualty, then, subject to the last paragraph of this Section 6.1,
Landlord shall proceed with diligence, subject to then, applicable statutes,
building codes, zoning ordinances and regulations of any governmental
authority, and at the expense of Landlord (but only to the extent of insurance
proceeds available to Landlord) to repair or cause to be repaired such damage.
Landlord shall commence such repairs within three (3) months of such damage and
proceed with diligence to complete such repairs, but if Landlord has not
completed such repairs within twelve (12) months of such damage Tenant may
terminate this Lease by notice to Landlord within ten (10) days of the
expiration of such twelve month period. All such repairs made necessary by any
act or omission of Tenant shall be made at the Tenant's expense to the extent
that the cost of such repairs are less than the deductible amount in Landlord's
insurance policy. All repairs to and replacements of property which Tenant is
entitled to remove shall be made by and at the expense of Tenant. If the
Premises or any part thereof shall have been rendered unfit for use and
occupation hereunder by reason of such damage the Annual Fixed Rent and
additional rent or a just and proportionate part thereof, according to the
nature and extent to which the Premises shall have been so rendered unfit,
shall be abated until the Premises (except as to the property which is to be
repaired by or at the expense of Tenant) shall have been restored as nearly as
practicable to the condition in which they were immediately prior to such fire
or other casualty, provided, however, that if Landlord or any mortgagee shall
be unable to collect the insurance proceeds (including rent insurance proceeds)
applicable to such damage because of some action or inaction on the part of
Tenant, or the employees, licensees or invitees of Tenant, the cost of
repairing such damage shall be paid by Tenant and there shall be no abatement
of rent. Landlord shall not be liable for delays in the making of any such
repairs which are due to government regulation, casualties and strikes,
unavailability of labor and materials, delays in obtaining insurance proceeds,
and other causes beyond the reasonable control of Landlord, nor shall Landlord
be liable for any inconvenience or annoyance to Tenant or injury to the
business of Tenant resulting from delays in repairing such damage.

     If (i) the Premises are so damaged by fire or other casualty (whether or
not insured) at any time during the last thirty months


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<PAGE>   35
of the Term that the cost to repair such damage is reasonably estimated to
exceed one-third of the total Annual Fixed Rent payable hereunder for the
period from the estimated completion date of repair until the end of the Term,
(ii) at any time the Premises (or any portion thereof) are so damaged by fire
or other casualty (whether or not insured) that substantial alteration or
reconstruction or demolition of the Premises (or a portion thereof) shall in
Landlord's judgment by required, or (iii) at any time damage to the Premises
occurs by fire or other insured casualty and any mortgagee shall refuse to
permit insurance proceeds to be utilized for the repair or replacement of such
property and Landlord determines not to repair such damage, then and in any of
such events, this Lease and the term hereof may be terminated at the election
of Landlord by a notice from Landlord to Tenant within sixty (60) days, or such
longer period as is required to complete arrangements with any mortgagee
regarding such situation, following such fire or other casualty; the effective
termination date pursuant to such notice shall be not less than thirty (30)
days after the day on which such termination notice is received by Tenant. In
the event of any termination, the Term shall expire as though such effective
termination date were the date originally stipulated in Section 1.1 for the end
of the Term and the Fixed Rent and additional charges for Operating Expenses
shall be apportioned as of such date. Notwithstanding the foregoing, in the
event Landlord elects to terminate this Lease pursuant to this paragraph,
Landlord shall reimburse Tenant for the unamortized amount of Tenant's share
of the construction costs referred to in Article III.

     6.2  CONDEMNATION - EMINENT DOMAIN

     In case during the Term all or any substantial part of the Premises are
taken by eminent domain or Landlord receives compensable damage by reason of
anything lawfully done in pursuance of public or other authority, this Lease
shall terminate at Landlord's election, which may be made (notwithstanding that
Landlord's entire interest may have been divested) by notice given to Tenant
within 90 days after the election to terminate arises, specifying the effective
date of termination. The effective date of termination specified by Landlord
shall not be less than 15 nor more than 30 days after the date of notice of
such termination. Unless terminated pursuant to the foregoing provisions, this
Lease shall remain in full force and effect following any such taking, subject,
however, to the following provisions. If in any such case the Premises are
rendered unfit for use and occupation and this Lease is not terminated,
Landlord shall use due diligence (following the expiration of the period in
which Landlord may terminate this Lease pursuant to the foregoing provisions of
this Section) to put the Premises, or what may remain thereof (excluding any
items installed or paid for by Tenant which Tenant may be required to remove



                                                                              19
<PAGE>   36
pursuant to Section 5.12), into proper condition for use and occupation and a
just proportion of the Fixed Rent and additional charges for Operating Expenses
according to the nature and extent of the injury shall be abated until the
Premises or such remainder shall have been put by Landlord in such condition;
and in case of a taking which permanently reduces the area of the Premises, a
just proportion of the Fixed Rent and additional charges for Operating Expenses
shall be abated for the remainder of the Term.

     6.3  EMINENT DOMAIN AWARD

     Except for Tenant's relocation expenses (specifically so designated by the
court or authority having jurisdiction over the matter) Landlord reserves to
itself any and all rights to receive awards made for damages to the Premises, or
the leasehold hereby created, or any one or more of them, accruing by reason of
exercise of eminent domain or by reason of anything lawfully done in pursuance
of public of other authority. Tenant hereby releases and assigns to Landlord all
Tenant's rights to such awards, and covenants to deliver such further
assignments and assurances thereof as Landlord may from time to time request,
hereby irrevocably designating and appointing Landlord as its attorney-in-fact
to execute and deliver in Tenant's name and behalf all such further assignments
thereof.


                                  ARTICLE VII

                                    DEFAULT

     7.1  TERMINATION FOR DEFAULT OR INSOLVENCY

     This Lease is upon the condition that (1) if Tenant shall fail to perform
or observe any of Tenant's covenants, and if such failure shall continue, (a) in
the case of rent or payment of additional charges or any sum due Landlord
hereunder, for more than ten (10) days after notice, or (b) in any other case,
after notice, for more than thirty (30) days (provided that if correction of any
such matter reasonably requires longer than 30 days and Tenant so notifies
Landlord within 20 days after Landlord's notice is given together with an
estimate of time required for such cure, Tenant shall be allowed such longer
period, but only if cure is begun within such 30-day period and such delay does
not cause increased risk of damage to person or property), or (2) if three or
more notices under clause (1) hereof are given in any twelve month period or (3)
if a receiver, guardian, conservator, trustee in bankruptcy or similar officer
shall be appointed by a court of competent jurisdiction to take charge of all or
any part of Tenant's property and such appointment is not discharged within 90
days thereafter or


                                                                              20

<PAGE>   37
if a petition including, without limitation, a petition for reorganization or
arrangement is filed by Tenant under any bankruptcy law or is filed against
Tenant and, in the case of a filing against Tenant only, the same shall not be
dismissed within 90 days from the date upon which it is filed, then, and in any
of said cases, Landlord may, immediately or at any time thereafter, elect to
terminate this Lease by notice of termination, by entry, or by any other means
available under law and may recover possession of the Premises as provided
herein. Upon termination by notice, by entry, or by any other means available
under law, Landlord shall be entitled immediately, in the case of termination
by notice or entry, and otherwise in accordance with the provisions of law to
recover possession of the Premises from Tenant and those claiming through or
under the Tenant. Such termination of this Lease and repossession of the
Premises shall be without prejudice to any remedies which Landlord might
otherwise have for arrears of rent or for a prior breach of the provisions of
this Lease. Tenant waives any statutory notice to quit and equitable rights in
the nature of further cure or redemption, and Tenant agrees that upon
Landlord's termination of this Lease Landlord shall be entitled to re-entry and
possession in accordance with the terms hereof. Landlord may, without notice,
store Tenant's personal property (and those of any person claiming under
Tenant) at the expense and risk of Tenant or, if Landlord so elects, Landlord
may sell such personal property at public auction or auctions or at private
sale or sales after seven days notice to Tenant and apply the net proceeds to
the earliest of installments of rent or other charges owing Landlord. Tenant
agrees that a notice by Landlord alleging any default shall, at Landlord's
option (the exercise of such option shall be indicated by the inclusion of the
words "notice to quit" in such notice), constitute a statutory notice to quit.
If Landlord exercises its option to designate a notice of default hereunder as
a statutory notice to quit, any  grace periods provided for herein shall run
concurrently with any statutory notice periods. Landlord and Tenant waive trial
by jury in any action to which they are parties. Tenant further agrees that it
shall not interpose any counterclaim or set-off in any summary proceeding or in
any action based in whole or in part on non-payment of rent.

     7.2  REIMBURSEMENT OF LANDLORD'S EXPENSES

     In the case of termination of this Lease pursuant to Section 7.1, Tenant
shall reimburse Landlord for all expenses arising out of such termination,
including without limitation, all costs incurred in collecting amounts due from
Tenant under this Lease (including attorneys' fees, costs of litigation and the
like); all expenses incurred by Landlord in attempting to relet the Premises or
parts thereof (including advertisements, brokerage commissions, Tenant's
allowances, costs of preparing space, and the like); all of


                                                                              21
<PAGE>   38
Landlord's then unamortized costs of special inducements provided to Tenant
(including without limitation rent holidays, rent waivers, above building
standard leasehold improvements paid for by Landlord, and the like) and all
Landlord's other reasonable expenditures necessitated by the termination. The
reimbursement from Tenant shall be due and payable immediately from time to
time upon notice from Landlord that an expense has been incurred, without
regard to whether the expense was incurred before or after the termination.

     7.3  DAMAGES

     Landlord may elect by written notice to Tenant within one year following
such termination to be indemnified for loss of rent by a lump sum payment
representing the then present value of the amount of rent and additional
charges which would have been paid in accordance with this Lease for the
remainder of the Term minus the then present value of the aggregate fair
market rent and additional charges payable for the Premises for the remainder
of the Term (if less than the rent and additional charges payable hereunder),
estimated as of the date of the termination, and taking into account reasonable
projections of vacancy and time required to re-lease the Premises. (For the
purposes of calculating the rent which would have been paid hereunder for the
lump sum payment calculation described herein, the last full year's additional
charges under Section 2.6 is to be deemed constant for each year thereafter.
The Federal Reserve discount rate (or equivalent) shall be used in calculating
present values.) Should the parties be unable to agree on a fair market rent,
the matter shall be submitted, upon the demand of either party, to the Boston,
Massachusetts office of the American Arbitration Association, with a request
for arbitration in accordance with the rules of the Association by a single
arbitrator who shall be an MAI appraiser with at least ten years experience as
an appraiser of major office buildings in the Greater Boston area. The parties
agree that a decision of the arbitrator shall be conclusive and binding upon
them. If, at the end of the Term, the rent which Landlord has actually received
from the Premises is less than the aggregate fair market rent estimated as
aforesaid, Tenant shall thereupon pay Landlord the amount of such difference.
Should Landlord fail to make the election provided for in this Section 7.3,
Tenant shall indemnify Landlord for the loss of rent by a payment at the end of
each month which would have been included in the Term, representing the
difference between the rent which would have been paid in accordance with this
Lease (Annual Fixed Rent under Section 2.5, and additional charges which would
have been payable under Section 2.6 to be ascertained monthly) and the rent
actually derived from the Premises by Landlord for such month (the amount of
rent deemed derived shall be the actual amount less any portion thereof
attributable to Landlord's reletting expenses described in Section 7.2 which
have not been reimbursed by Tenant thereunder).



                                                                              22

<PAGE>   39

     7.4  MITIGATION

     Any obligation imposed by law upon Landlord to relet the Premises shall be
subject to the reasonable requirements of Landlord to lease to high quality
tenants and to develop the Building in a harmonious manner with an appropriate
mix of uses, tenants, floor areas and terms of tenancies, and the like.

     7.5  CLAIMS IN BANKRUPTCY

     Nothing herein shall limit or prejudice the right of Landlord to prove and
obtain in a proceeding for bankruptcy, insolvency, arrangement or
reorganization, by reason of the termination, an amount equal to the maximum
allowed by a statute or law in effect at the time when, and governing the
proceedings in which, the damages are to be proved, whether or not the amount is
greater to, equal to, or less than the amount of the loss or damage which
Landlord has suffered.

     7.6  INTEREST ON UNPAID AMOUNTS

     If any payment of Annual Fixed Rent, additional charges, or other payment
due from Tenant to Landlord is not paid when due following applicable grace
periods, then without notice and in addition to all other remedies hereunder,
Tenant shall pay to Landlord interest on such unpaid amount at an annual rate of
3% above the Bank of Boston prime rate for each month and for each part thereof
during which said delinquency continues; provided, however, in no event shall
such interest exceed the maximum amount permitted to be charged by applicable
law.

     7.7  VACANCY DURING LAST THREE MONTHS

     If Tenant vacates all of the Premises at any time within the last 3 months
of the Term, Landlord may enter the Premises (or such portion) and commence
demolition work or construction of leasehold improvements for future tenants.
The exercise of such right by Landlord will not affect Tenant's obligations to
pay Annual Fixed Rent or additional charges with respect to the Premises (or
such portion), which obligations shall continue without abatement until the end
of the Term.



                                                                              23


<PAGE>   40
                                  ARTICLE VIII

                                 MISCELLANEOUS

     8.1  HOLDOVER

     If Tenant remains in the Premises after the termination or expiration of
the Term, such holding over shall be, except as Landlord may elect pursuant to
the next sentence, as a tenant at will or tenant by the month (requiring 30
days notice of termination by either party to the other) at a monthly fixed
rent equal to twice the Fixed Rent due hereunder for the last month of the
Term, and otherwise subject to all the covenants and conditions (including
obligations to pay additional charges under Section 2.6) of this Lease as
though it had originally been a monthly tenancy. Notwithstanding the foregoing,
if Landlord desires to regain possession of the Premises promptly after the
termination or expiration hereof and prior to acceptance of rent for any period
thereafter, Landlord may, at its option, forthwith re-enter and take possession
of the Premises or any part thereof without process or by any legal process in
force in The Commonwealth of Massachusetts.

     Notwithstanding the establishment of any holdover tenancy following the
expiration or earlier termination of the Term, if Tenant fails promptly to
vacate the Premises at the expiration or earlier termination of the Term,
Tenant shall save Landlord harmless and indemnified against any claim, loss,
cost or expense (including reasonable attorneys' fees) arising out of Tenant's
failure promptly to vacate the Premises (or any portion thereof).

     8.2  ESTOPPEL CERTIFICATES

     At the request of either party, from time to time, the other party agrees
to execute and deliver, within ten (10) days after such request, a certificate
which acknowledges the dates on which the Term begins and ends, tenancy and
possession of the Premises and recites such other facts concerning any
provision of the Lease or payments made under the Lease which such party or a
mortgagee or lender or a purchaser or prospective purchaser of the Building or
any interest therein or any other party may from time to time reasonably
request.

     8.3  NOTICE

     Any notice, approval, consent and other like communication hereunder from
Landlord to Tenant or from Tenant to Landlord shall be effective only if given
in writing and shall be deemed duly served if and when hand delivered or if and
when mailed prepaid certified mail (in either case, whether or not accepted for



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<PAGE>   41

delivery). Communications to Tenant shall be addressed to Tenant's Authorized
Representative at the Original Address of Tenant set forth in Section 1.1 prior
to the Term Commencement Date and thereafter at the Premises, with a copy to
Steven D. Singer, Esq., Hale & Dorr, 60 State Street, Boston, Massachusetts.
Communications to Landlord shall be addressed to the Address of Landlord set
forth in Section 1.1. Either party may from time to time designate other
addresses within the continental United States by notice to the other.

     8.4  LANDLORD'S RIGHT TO CURE

     At any time and without notice, Landlord may, but need not, cure any
failure by Tenant to perform its obligations under this Lease after applicable
grace periods. Whenever Landlord chooses to do so, Tenant shall pay all costs
and expenses incurred by Landlord in curing any such failure, including,
without limitation, reasonable attorneys' fees together with an administrative
charge equal to 7% of such costs and expenses (or such higher percentage as may
then be customary with respect to first-class office buildings in the Greater
Boston area) and interest as provided in Section 7.6.

     8.5  SUCCESSORS AND ASSIGNS

     This Lease and the covenants and conditions herein contained shall inure
to the benefit of and be binding upon Landlord, its successors and assigns, and
shall be binding upon Tenant, its successors and assigns, and shall inure to
the benefit of Tenant and only such Subtenants of Tenant as are permitted
hereunder. The term "Landlord" means the original Landlord named herein, its
successors and assigns. The term "Tenant" means the original Tenant named
herein and its permitted successors and assigns.

     8.6  BROKERAGE

     Each party warrants to the other that it has had no dealings with any
broker or agent in connection with this Lease or any other space in the Hobbs
Brook Office Park except for any broker designated in Section 1.1. Each party
covenants to pay, hold harmless and indemnify the other from and against any
and all costs, expense or liability for any compensation, commissions and
charges claimed by any broker or agent other than any such broker designated in
Section 1.1 with respect to this Lease or the negotiation thereof arising from
a breach of the foregoing warranty. Landlord shall be responsible for payment
of any brokerage commission to any broker designated in Section 1.1.


                                                                              25


<PAGE>   42
     8.7  WAIVER

     The failure of Landlord or of Tenant to seek redress for violation of, or
to insist upon strict performance of, any covenant or condition of this Lease,
or, with respect to such failure of Landlord, any of the Rules and Regulations
referred to in Section 5.3, whether heretofore or hereafter adopted by
Landlord, shall not be deemed a waiver of such violation or prevent a
subsequent act, which would have originally constituted a violation, from
having all the effect of an original violation. The receipt by Landlord of
Fixed Rent or additional charges with knowledge of the breach of any covenant
of this Lease shall not be deemed waiver of such breach. No provision of this
Lease shall be deemed to have been waived by Landlord, or by Tenant, unless
such waiver be in writing signed by the party to be charged. No consent or
waiver, express or implied, by 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.

     8.8  ACCORD AND SATISFACTION

     No acceptance by Landlord of a lesser sum than the Fixed Rent and
additional charges then due shall be deemed to be other than on account of the
earliest installment of such rent and charges 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 Landlord may accept such check or
payment without prejudice to Landlord's right to recover the balance of such
installment or pursue any other remedy provided in this Lease. The delivery of
keys to Landlord shall not operate as a termination of this Lease or a surrender
of the Premises.

     8.9  REMEDIES CUMULATIVE

     The specific remedies to which either party may resort under the terms of
this Lease are cumulative and are not intended to be exclusive of any other
remedies to which it may be lawfully entitled in case of any breach or
threatened breach by of any provisions of this Lease. In addition to the other
remedies provided in this Lease, each party shall be entitled to the restraint
by injunction of the violation or attempted or threatened violation of any of
the covenants or conditions of this Lease or to a decree compelling specific
performance of any such covenants or conditions.

     8.10 PARTIAL INVALIDITY

     If any term of this Lease, or the application thereof to any person or
circumstance, shall to any extent be invalid or unenforceable, the remainder of
this Lease, or the application of




                                                                              26


<PAGE>   43
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.

        8.11 WAIVERS OF SUBROGATION

        Any insurance carried by either party with respect to the Premises or
property therein or occurrences thereon shall, if it can be so written without
additional premium or with an additional premium which the other party agrees
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 hereunder 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 due to hazards covered
by such insurance to the extent of the indemnification received thereunder.

        8.2     ENTIRE AGREEMENT

        This Lease contains all of the agreements between Landlord and Tenant
with respect to the Premises and supersedes all prior writings and dealings
between them with respect thereto.

        8.13    NO AGREEMENT UNTIL SIGNED

        The submission of this Lease or a summary of some or all of its
provisions for examination does not constitute a reservation of or option for
the Premises or an offer to lease and no legal obligations shall arise with
respect to the Premises or other matters herein until this Lease is executed
and delivered by Landlord and Tenant.

        8.14    TENANT'S AUTHORIZED REPRESENTATIVE

        Tenant designates the person named form time to time as Tenant's
Authorized Representative to take all acts of Tenant hereunder. Landlord may
rely on the acts of such Authorized Representative without further inquiry or
evidence of authority. Tenant's Authorized Representative shall be the person
so designated in Section 1.1 and such successors as may be named from time to
time by the then current Tenant's Authorized Representatives or by Tenant's
president.

        8.15    NOTICE OF LEASE

        Landlord and Tenant agree not to record this Lease. If appropriate,
both parties will, at the request of either, execute,



                                                                              27
<PAGE>   44
acknowledge and deliver a Notice of Lease and a Notice of Termination of Lease
Term, each in recordable form. Such notices shall contain only the information
required by law for recording. Tenant hereby irrevocably appoints Landlord as
Tenant's attorney-in-fact (which appointment shall survive termination of the
Term) with full power of substitution to execute, acknowledge and deliver a
notice of termination of lease on Tenant's name if Tenant fails to do so
within 10 days after request therefor.

     8.16  TENANT AS BUSINESS ENTITY

     If Tenant is a business entity, then the person or persons executing this
Lease on behalf of Tenant jointly and severally warrant and represent that (a)
Tenant is duly organized, validly existing and in good standing under the laws
of the jurisdiction in which such entity was organized; (b) Tenant has the
authority to own its property and to carry on its business as contemplated under
this Lease; (c) Tenant is in compliance with all laws and orders of public
authorities applicable to Tenant; (d) Tenant has duly executed and delivered
this lease; (e) the execution, delivery and performance by Tenant of this Lease
(i) are within the powers of Tenant, (ii) have been duly authorized by all
requisite action, (iii) will not violate any provision of law or any order of
any court or agency of government, or any agreement or other instrument to which
Tenant is a party or by which it or any of its property is bound, and (iv) will
not result in the imposition of any lien or charge on any of Tenant's property,
except by the provisions of this Lease; and (v) the Lease is a valid and binding
obligation of Tenant in accordance with its terms. Tenant, if a business entity,
agrees that breach of the foregoing warranty and representation shall at
Landlord's election be a default under this Lease for which there shall be no
cure. This warranty and representation shall survive the termination of the
Term.

     8.17  MISCELLANEOUS PROVISIONS

     This Lease may be executed in counterparts and shall constitute the
agreement of Landlord and Tenant whether or not their signatures appear in a
single copy hereof. This Lease shall be construed as a sealed instrument and
shall be governed exclusively by the provisions hereof and by the laws of The
Commonwealth of Massachusetts as the same may from time to time exist. The
titles are for convenience only and shall not be considered a part of the
Lease. Where the phrases "persons acting under Tenant" or "persons claiming
under Tenant" or similar phrases are used, the persons included shall be all
employees, agents, independent contractors and invitees of Tenant or of any
Subtenant of Tenant. The enumeration of specific examples of or inclusions in a
general provision shall not be construed as a limitation of the general
provision. If



                                                                              28


<PAGE>   45
Tenant is granted any extension option, expansion option or other right or
option, the exercise of such right or option (and notice thereof) must be
unconditional to be effective, time always being of the essence to the
exercise of such right or option; and if Tenant purports to condition the
exercise of any option or to vary its term in any manner, then the option
granted shall be void and the purported exercise shall be ineffective. Unless
otherwise stated herein, any consent or approval required hereunder may be
given or withheld in the sole absolute discretion of the party whose consent or
approval is required. Nothing herein shall be construed as creating the
relationship between Landlord and Tenant of principal and agent, or of partners
or joint ventures or any relationship other than landlord and tenant. This
Lease and all consents, notices, approvals and all other documents relating
hereto may be reproduced by any party by photographic, microfilm, microfiche or
other reproduction process and the originals thereof may be destroyed; and each
party agrees that any reproductions shall be admissible in evidence as the
original itself in any judicial or administrative proceeding (whether or not
the original is in existence and whether or not reproduction was made in the
regular course of business) and that any further reproduction of such
reproduction shall likewise be admissible in evidence. This Lease may be
amended only by a writing signed by all of the parties hereto.


                                   ARTICLE IX

               LANDLORD'S LIABILITY AND ASSIGNMENT, FOR FINANCING

     9.1  LANDLORD'S LIABILITY

     Tenant agrees from time to time to lock only to Landlord's interest in the
Land and Premises for satisfaction of any claim against Landlord hereunder or
under any other instrument related to the Lease (including any separate
agreements among the parties and any notices or certificates delivered by
Landlord) and not to any other property or assets of Landlord. If Landlord from
time to time transfers its interest in the Land and Premises, then from and
after each such transfer Tenant shall look solely to the interests in the
Land and Premises of each Landlord's transferees for the performance of all of
the obligations of Landlord hereunder (or under any related instrument). The
obligations of Landlord shall not be binding on any partners (or trustees or
beneficiaries) of Landlord or of any successor, individually, but only upon
Landlord's or such successor's interest described above.

     In no event shall Landlord ever be liable for any indirect or
consequential damages.



                                                                              29


<PAGE>   46
     9.2  ASSIGNMENT OF RENTS

     If, at any time and from time to time, Landlord assigns this Lease or the
rents payable hereunder to the holder of any mortgage on the Building, or to
any other party for the purpose of securing financing (the holder of any such
mortgage and any other such financing party are referred to herein as the
"Financing Party"), whether such assignment is conditional in nature or
otherwise, the following provisions shall apply:

          (i)   Such assignment to the Financing Party shall not be deemed an
assumption by the Financing Party of any obligations of Landlord hereunder
unless such Financing Party shall, by written notice to Tenant, specifically
otherwise elect;

          (ii)  Except as provided in (i) above and (iii) below, the Financing
Party shall be treated as having assumed Landlord's obligations hereunder
(subject to Section 9.1) only upon foreclosure of its mortgage (or voluntary
conveyance by deed in lieu thereof) and the taking of possession of the
Premises from and after foreclosure;

          (iii) Subject to Section 9.1, the Financing Party shall be
responsible for only such breaches under the Lease by Landlord which occur
during the period of ownership by the Financing Party after such foreclosure
(or voluntary conveyance by deed in lieu thereof) and taking of possession, as
aforesaid;

          (iv)  In the event Tenant alleges that Landlord is in default under
any of Landlord's obligations under this Lease, Tenant agrees to give the
holder of any mortgage, by registered mail, a copy of any notice of default
which is served upon the Landlord, provided that prior to such notice, Tenant
has been notified, in writing, (whether by way of notice of an assignment of
lease, request to execute an estoppel letter, or otherwise) of the address of
any such holder. Subject to the provisions of Section 4.2, Tenant further
agrees that if Landlord shall have failed to cure such default within the time
provided by law or such additional time as may be provided in such notice to
Landlord, such holder shall have sixty (60) days after the last date on which
Landlord could have cured such default within which such holder will be
permitted to cure such default. If such default cannot be cured within such
sixty day period,then such holder shall have such additional time as may be
necessary to cure such default, if within such sixty day period such holder has
commenced and is diligently pursuing the remedies necessary to effect such cure
(including, but not limited


                                                                              30


<PAGE>   47
to, commencement of foreclosure proceedings, if necessary, to effect such cure),
in which event Tenant shall have no right with respect to such default while
such remedies are being diligently pursued by such holder.

        In all events, any liability of a Financing Party shall be limited to
the interest of such Financing Party in the Land and Building, and in no event
shall a Financing Party ever be liable for any indirect or consequential
damages.

        Tenant hereby agrees to enter into such agreements or instruments as
may, from time to time, be reasonably requested in confirmation of the
foregoing.

                                   ARTICLE X

                                SECURITY DEPOSIT

        Tenant shall pay to Landlord as a security deposit for the performance
of the obligations of Tenant hereunder the amount specified therefor in Section
1.1, such amount to be paid $250,000.00 upon the execution of this Lease and
$500,000.00 upon receipt of the permits referred to in Section 5.2. Said
security deposit shall be held in an escrow separate from other funds of
Landlord and no fiduciary relationship shall be created with respect to such
deposit. Landlord shall invest said security deposit in an investment acceptable
to Tenant and Tenant shall be paid the earned interest or dividend
semi-annually. If Tenant shall fail to perform any of its obligations under this
Lease, Landlord may, but shall not be obliged to, apply the security deposit to
the extent necessary to cure the default, and Tenant shall be obliged to
reinstate such security deposit to the original amount thereof upon demand.
Within thirty (30) days after the expiration of the third Lease Year or sooner
termination of the Term the security deposit, to the extent not applied, shall
be returned to the Tenant, with accrued interest. If the Lease is terminated
because Tenant is unable to obtain the permits referred to in Section 5.2, the
security deposit with all interest shall be returned to Tenant.

                                   ARTICLE XI

                       SUBORDINATION AND NON-DISTURBANCE

        Provided that the holders of any such mortgages agree to recognize this
Lease, this Lease shall be subject and subordinate to any mortgages that may
hereafter be placed upon the Premises and/or the Land and to any and all
advances to be made under such mortgages


                                                                              31

<PAGE>   48
and to the interest thereon, and all renewals, extensions and consolidations
thereof. Tenant shall execute and deliver whatever instruments may be
reasonably required by the mortgagee (or mortgagees) to acknowledge such
subordination in recordable form, and if Tenant fails to do so within ten (10)
days after demand, Tenant hereby irrevocably appoints Landlord as Tenant's
attorney in fact, in its name, place and stead to do so. Landlord agrees to use
its best efforts to obtain a nondisturbance and attornment agreement from its
present mortgages.


                                  ARTICLE XII

                                    PARKING

     Landlord agrees to provide an automobile parking area containing at least
351 parking spaces during the term of this Lease for the benefit and use of the
customers and employees of Tenant. Wherever the words "automobile parking area"
are used in this Lease, it is intended that the same shall include, whether in
a surface parking area or a parking structure, the automobile parking stalls,
driveways, entrances, exits, sidewalks, landscaped areas, pedestrian
passageways in conjunction therewith and other areas designated for parking.
Landlord shall keep the automobile parking area neat, clean and in good repair,
properly lighted and landscaped. Nothing contained herein shall be deemed to
create liability upon Landlord for any damage to motor vehicles of customers or
employees or from loss of property from within such motor vehicles, unless
caused by the negligence of Landlord, its agents, servants and employees.
Landlord shall have the right to establish and enforce against all users of the
automobile parking area, such reasonable rules and regulations as may be deemed
necessary and advisable for the proper and efficient operation and maintenance
of the automobile parking area, including the hours during which the automobile
parking area shall be open for use.

     Landlord may establish for the automobile parking area, a system or systems
of charged validation or other operation including, but not limited to, a system
of charges against nonvalidated parking checks of users. Tenant shall comply
with such system, and all rules and regulations established by Landlord in
conjunction with such system, and shall cause its customers and employees to
comply therewith; provided, however, that such system and such rules and
regulations shall apply equally and without discrimination to all persons
entitled to the use of the automobile parking area.

                                                                              32

<PAGE>   49


      Landlord shall at all times during the term thereof have the sole and
exclusive control of the automobile parking area, and may at any time during the
term hereof exclude and restrain any person from use thereof; excepting,
however, Tenant and its employees, bona fide customers, patrons and service
suppliers of Tenant and other tenants of Landlord who make use of said area in
accordance with any rules and regulations established by Landlord from time to
time with respect thereto. Landlord shall also have the right to designate
certain automobile parking areas as being for the exclusive use of one or more
of the Tenants of Landlord. The rights of Tenant referred to in this Article
shall at all times be subject to the rights of Landlord and the other tenants of
Landlord to use the same in common with Tenant, and it shall be the duty of
Tenant to keep all of said area free and clear of any obstructions created or
permitted by Tenant or resulting from Tenant's operations and to permit the use
of any of said customers, patrons and service suppliers to and from the
Building.

      Landlord shall at all times have the right and privilege of determining
the nature and extent of the automobile parking area, whether the same shall be
surface, underground or other structure, and of making such changes therein
from time to time which in its opinion are deemed to be desirable and for the
best interests of all persons using the automobile parking area.

      Executed to take effect as a sealed instrument.


                                    Lincoln Street Trust,
                                    Landlord


                                    By:  /s/ [Signature Illegible]
                                        ----------------------------------
                                        Agent for the Trustees



                                    Immulogic Pharmaceutical Corporation,

                                    By:  /s/ [Signature Illegible]
                                        ----------------------------------




                                                                              33
<PAGE>   50





                                   EXHIBIT A




                         MAP OF HOBBS BROOK OFFICE PARK
<PAGE>   51
                                   EXHIBIT B

                    Construction Costs Disbursement Schedule

     Landlord's share of construction cost as described in Section 3.2 shall be
disbursed in five (5) equal payments of $401,521.00 each at the times set forth
below:

          1.   Commencement of construction.

          2.   Six weeks after commencement of construction.

          3.   Architect's certification of 60% completion.

          4.   Architect's certification of 80% completion.

          5.   Architect's certification of substantial completion.


WA9

<PAGE>   52
                            FIRST AMENDMENT TO LEASE

                            DATED NOVEMBER 29, 1991

                                    BETWEEN

                              LINCOLN STREET TRUST

                                      AND

                      IMMULOGIC PHARMACEUTICAL CORPORATION

     Agreement made this 8th day of May 1992 by and between Lincoln Street
Trust (hereinafter called "Lessor") and ImmuLogic Pharmaceutical Corporation
(hereinafter called "Tenant").

                                   BACKGROUND

     1.   WHEREAS, in November of 1991, the parties entered into a Lease of
space in the building at 610 Lincoln Street, Waltham, Massachusetts (hereinafter
called the "Lease").

     2.   WHEREAS, the parties hereto desire to amend the Lease by deleting
Article X - Security Deposit.

                                   AGREEMENTS

     In consideration of the mutual agreements herein contained, the parties
hereby agree to amend the lease in the following respects:

     1.   Article X - Security Deposit is hereby deleted in its entirety. The
Tenant acknowledges receipt from Landlord of $252,677.92 representing return of
the security deposit advanced upon execution of the lease, plus all interest
earned payable thereon.

     2.   Except as herein amended, the Agreement shall remain in full force
and effect as originally written and is hereby ratified and confirmed.

     Executed under seal.

                                        Lincoln Street Trust

                                        By: /s/ [Signature Illegible]
                                            ----------------------------------


                                        ImmuLogic Pharmaceutical Corporation

                                        By: /s/ [Signature Illegible]
                                            -------------------------------
                                            VP Finance Administrator


<PAGE>   53
                           SECOND AMENDMENT TO LEASE

     This Second Amendment to Lease ("Amendment") dated as of July 30, 1999 and
effective as of August 1, 1999 and is made by and among Lincoln Street Trust,
as Landlord ("Landlord"), Immulogic Pharmaceutical Corporation ("Immulogic")
and Scriptgen Pharmaceuticals, Inc. ("Scriptgen").

                                    RECITAL

     WHEREAS,  Immulogic entered into that certain Lease dated November 29,
1991, and an Amendment thereto dated May 8, 1992 (as amended, the "Lease") for
the entire building located at 610 Lincoln Street, Waltham, Massachusetts (the
"Premises"):

     WHEREAS, subsequently Immulogic sublet the Premises pursuant to a Sublease
dated January 22, 1998 by and between Immulogic and Scriptgen whereby Scriptgen
subleased substantially all of the Premises (the "Sublease");

     WHEREAS, Immulogic, Scriptgen and Landlord entered into that certain
letter agreement dated February 16, 1998 whereby Scriptgen agreed to certain
covenants in connection with the Sublease (the "Letter Agreement");

     WHEREAS, Immulogic desires to be released of its obligations under the
Lease;

     WHEREAS, Scriptgen desires to become the Tenant under the Lease; and

     WHEREAS, Landlord has agreed to relieve Immulogic of its obligations under
the Lease and recognize Scriptgen as Tenant by amending the Lease and
substituting Scriptgen as the tenant thereunder subject to the following terms
and conditions contained herein.

     NOW, THEREFORE FOR GOOD AND VALUABLE CONSIDERATION, the receipt and
sufficiency of which is hereby acknowledged, the parties agree as follows:

     1.   Immulogic's interest in the Lease is hereby assigned to Scriptgen.
Scriptgen hereby assumes all liability and obligations of Immulogic as Tenant
under the Lease on and after the date of this Amendment, and Immulogic is
hereby released from all liability and obligations under the Lease which shall
accrue after the date of this Amendment. Notwithstanding the foregoing,
Scriptgen shall be liable as if Scriptgen was the original tenant named in the
Lease for any and all claims relating to hazardous substances as defined in
Section 5.2 of the Lease caused by Scriptgen, its agents, employees, invitees,
licensees and for any acts or omissions of Scriptgen, its agents, employees,
invitees, licensees and contractors during Scriptgen's occupancy of the
Premises under the Sublease. The Sublease is hereby terminated. However, the
covenants set forth in the Letter

<PAGE>   54
     Agreement shall survive termination of the Sublease and are hereby
     incorporated in the Lease and be binding on Landlord and Scriptgen.

2.   The following shall be deleted following the term "TENANT" in Section 1.1,
     "Immulogic Pharmaceutical Corporation" and "SCRIPTGEN Pharmaceuticals,
     Inc." shall be substituted in lieu thereof.

3.   The following shall be deleted following the term "TENANT'S ORIGINAL
     ADDRESS" in Section 1.1 "One Kendall Square, Building 600, Cambridge, MA
     02130" and "610 Lincoln Street, Waltham MA 02254" shall be substituted in
     lieu thereof.

4.   The following shall be deleted after the term "ANNUAL FIXED RENT" in
     Section 1.1:

          Lease Years 1 and 2:          $1,055,060.50
          Lease Year 3:                 $1,097,777.50
          Lease Year 4:                 $1,183,205.50
          Lease Year 5:                 $1,225,920.50
          Lease Year 6 through 8:       $1,268,635.50
          Lease Years 9 and 10:         $1,311,350.60

     and "Annual Fixed Rent through August 31, 2002 is $2,392,040.04 annually"
     shall be inserted in lieu thereof. The Annual Fixed Rent includes all
     tenant improvements, fixtures and other property owned by Landlord (or
     transferred to Landlord hereunder) currently used by Scriptgen at the
     Premises.

5.   The following shall be deleted in Section 1.1 of the Lease: "Security
     Deposit: $750,000," "Broker: R.M. Bradley & Co., Inc. and Lynch, Murphy,
     Walsh and Partners," and "Tenant's Authorized Representative: Janet C.
     Bush."

6.   The following shall be deleted from Section 1.2 of the Lease: "Exhibit B.
     Construction Costs Disbursement Schedule."

7.   Article III of the Lease, entitled "Construction of Premises," shall be
     deleted in its entirety.

8.   The second sentence in Section 5.2 shall be deleted in its entirety and
     replaced with the following: "Tenant shall obtain and maintain all permits
     necessary for all operations conducted in the Premises, and shall comply
     with the terms thereof."

9.   Section 8.6 of the Lease shall be deleted in its entirety and the following
     shall be substituted in lieu thereof:

     "Each party warrants to the other that it has had no dealings with any
     broker or agent in connection with this Lease. Each party covenants to
     pay, hold harmless


                                      -2-
<PAGE>   55
        and indemnify the other from and against any and all cost, expense or
        liability for any compensation, commissions and charges claimed by any
        broker or agent with respect to this Lease or the negotiation thereof,
        or arising from a breach of the foregoing warranty."

10.     The following is hereby added as a new section, 8.18:

        8.18    CONSTRUCTION OF ADDITION

                        Landlord shall have the right to construct an addition
                to the Premises (the "Addition") and, in connection with the
                development of the Addition, Landlord shall have the right to
                make alterations to the exterior of the Premises and building
                systems located therein; to utilize the Premises for access and
                egress to and from the Addition or utilities serving the
                Addition; to alter or expand the loading facilities at the
                Premises and to utilize the loading facilities for the Addition
                in common with Premises; to shore up the foundations and/or
                walls of the Premises; to erect scaffolding and protective
                barricades around, within or adjacent to the Premises; and to do
                any other act necessary for the safety of the Premises or the
                development of the Addition. Landlord shall not be liable to
                Tenant for any compensation or reduction of rent by reason of
                inconvenience or annoyance or for loss of business resulting
                from any act by Landlord pursuant to this Section 8.18, provided
                that Landlord shall not materially interfere with Tenant's use
                of the Premises and shall use reasonably efforts to minimize the
                extent and duration of any inconvenience, annoyance or loss of
                business to Tenant resulting from any work pursuant to this
                Section in or about the Premises, consistent with accepted
                construction practice.

11.     The Lease is hereby amended by adding a new Article X thereto, to read
        in its entirety as follows, and simultaneously with the execution of
        this Amendment Immulogic shall pay over to Landlord the Security Deposit
        currently held by Immulogic under the Sublease, which shall become the
        Security Deposit under the Lease:

        The Security Deposit will be held by Landlord in an interest-bearing
        account for and during the Term, which deposit shall be returned to
        Tenant within thirty (30) days after the expiration or termination of
        the Lease, provided there exists no breach of any undertaking of Tenant.
        Provided Tenant is not in default of this Lease, all interest on the
        Security Deposit shall be paid to Tenant on an annual basis on each
        anniversary of the Commencement Date. If all or any part of the Security
        Deposit is applied to an obligation of Tenant hereunder, Tenant shall
        immediately, upon request by Landlord, restore the Security Deposit to
        its original amount. Tenant shall no have the right to call upon
        Landlord to apply all or any part of the Security Deposit to cure any
        default or fulfill any obligation of Tenant, but such use shall solely
        be in the discretion of the Landlord. Provided Tenant is


                                      -3-
<PAGE>   56
      not in default of any of its obligations hereunder, the Security Deposit
      shall be reduced to $250,000.00 and $250,000.00 returned to the Tenant
      within ten (10) days after Tenant provides evidence reasonably
      satisfactory to Landlord that Tenant has successfully completed a public
      offering of Tenant's common stock, which raised not less than
      $30,000,000.00.

12.   Exhibit B to the Lease shall be deleted in its entirety.

13.   Each of Landlord and Immulogic covenants, warrants and represents that:
      (i) the copy of the Lease and the Letter Agreement attached hereto as
      Exhibit A is a true and correct copy of the Lease and the Letter Agreement
      and there are no amendments or modifications thereto except as included in
      said Exhibit A; (ii) the Lease and the Letter Agreement are a complete
      statement of the agreement of the parties thereto with respect to the use
      and occupancy of the Premises; (iii) the Lease and the Letter Agreement
      are in full force and effect; (iv) it has not given or received any notice
      of default or notice of termination of the Lease or the Letter Agreement,
      and is not in default of any monetary obligations or, to the best of its
      knowledge, in the performance of or compliance with any material
      provisions of the Lease and the Letter Agreement, and to the best of its
      knowledge no facts or circumstances exist which, with the giving of notice
      or the passage of time or both, would constitute such a default thereunder
      (Landlord waives its rights in connection with any nonmonetary defaults
      under the Lease of which it is not now aware except for defaults arising
      from the acts or omissions of Scriptgen, its agents, employees, invitees,
      licensees and contractors during Scriptgen's occupancy of the Premises
      under the Sublease), and (v) to the best of its knowledge, each other
      party to the Lease and the Letter Agreement is not in default in the
      performance of or compliance with any material provisions of the Lease and
      the Letter Agreement, and to the best of its knowledge no facts or
      circumstances exist which, with the given of notice or the passage of time
      or both, would constitute such a default thereunder.

14.   Scriptgen covenants, warrants and represents that (i) it has not given or
      received any notice of default or notice of termination of the Sublease or
      the Letter Agreement and it is not in material default in the performance
      or compliance of any of the material provisions of the Sublease or the
      Letter Agreement and no facts or circumstances exist which would, with the
      giving of notice or the passage of time or both would constitute a default
      thereunder; and (ii) to the best of its knowledge, Landlord is not in
      default in the performance of or compliance with any material provisions
      of the Lease or the Letter Agreement, and no facts or circumstances exist
      which, with the given of notice or the passage of time or both, would
      constitute such a default thereunder. Scriptgen hereby agrees that (i) the
      copy of the Lease and the Letter Agreement attached hereto as Exhibit A is
      a true and correct copy of the Lease and the Letter Agreement and there
      are no amendments or modifications thereto except as included in said
      Exhibit A; (ii) the Lease and the Letter Agreement are a complete
      statement of the agreement of the



                                      -4-



<PAGE>   57
     parties thereto with respect to the use and occupancy of the Premises;
     (iii) to the best of Scriptgen's knowledge, the Lease and the Letter
     Agreement are in full force and effect.

15.  Immulogic hereby transfers, assigns and conveys to Landlord all of its
     right, title and interest in all tenant improvements, fixtures or any
     other personal property of any kind on, under, over or about the Premises
     and hereby warrants and represents that all such property is owned by
     Immulogic free and clear of any liens, security interests, or adverse
     claims (other than rights of Scriptgen under the Sublease).

16.  All other terms and provisions of the Lease are hereby ratified and
     confirmed.

17.  Notwithstanding anything contained in this Amendment to the contrary, this
     Amendment shall not be effective and bind the parties until the Landlord's
     lender has consented to this Amendment, it being understood that the
     consent of Landlord's lender is a condition to this Amendment.

18.  This Amendment may be signed in counterparts, all of which taken together
     shall constitute one agreement, provided that it shall not be binding upon
     any party hereto unless and until at least one counterpart shall have been
     executed and delivered by the party hereto.



                            SIGNATURE PAGE TO FOLLOW









                                      -5-



<PAGE>   58
     IN WITNESS WHEREOF, the parties have executed this First Amendment to
Lease as of the date first written above as a sealed instrument.

LINCOLN STREET TRUST               SCRIPTGEN PHARMACEUTICALS, INC.
Landlord

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

   Name:                              Name:
        ------------------                 --------------------------

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


                                   IMMULOGIC PHARMACEUTICAL
                                   CORPORATION

                                   By:  /s/ J. RICHARD CROWLEY
                                      -------------------------------

                                      Name: J. Richard Crowley
                                           --------------------------

                                      Title: President
                                            -------------------------





                                      -6-
<PAGE>   59
     IN WITNESS WHEREOF, the parties have executed this First Amendment to
Lease as of the date first written above as a sealed instrument.

LINCOLN STREET TRUST               SCRIPTGEN PHARMACEUTICALS, INC.
Landlord

By:                                By:  /s/ JOHN M. BARBERICH
   -----------------------            -------------------------------

   Name:                              Name: John M. Barberich
        ------------------                 --------------------------

   Title:                             Title: Vice President & CFO
         -----------------                  -------------------------


                                   IMMULOGIC PHARMACEUTICAL
                                   CORPORATION

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

                                      Name:
                                           --------------------------

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





                                      -6-

<PAGE>   60
     IN WITNESS WHEREOF, the parties have executed this First Amendment to
Lease as of the date first written above as a sealed instrument.

LINCOLN STREET TRUST                         SCRIPTGEN PHARMACEUTICALS, INC.
Landlord


By: /s/ MICHAEL D. BANK                      By:
    ---------------------------------            -------------------------------
    Name: Michael D. Bank                        Name:
          ---------------------------                  -------------------------
    Title: Managing Trustee                      Title:
           --------------------------                   ------------------------


                                             IMMULOGIC PHARMACEUTICAL
                                             CORPORATION

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


                                      -6-
<PAGE>   61









                                   EXHIBIT B

                           Plan of Sublease Premises