Document:

<PAGE>

                                                                    Exhibit 10.6

                                      , 1993

Dear :

The Board of Directors (the "Board") of T Cell Sciences, Inc. (the "Company")
has determined that appropriate steps should be taken to reinforce and encourage
the continued attention and dedication of members of the Company's management,
including yourself, to their responsibilities without distraction arising from
the possibility of a Change in Control (as defined in Section 2) of the Company,
although no such change is now contemplated.

In order to induce you to remain in the employ of the Company, the Company
agrees that you shall receive the benefits set forth in this letter agreement
(the "Agreement") in the event your employment with the Company is terminated
subsequent to a "Change in Control" of the Company and under the circumstances
described in Section 3 below.

1. Term of Agreement. This agreement shall commence on January 1, 1993 and each
January 1 thereafter, the term of this Agreement shall automatically be extended
for one additional year unless, not later than the October 31 of the preceding
year, the Company shall have given notice that it does not wish to extend this
Agreement. This Agreement shall cease to be operative and shall be of no further
force and effect if your employment terminates for any reason prior to a Change
in Control. Further, nothing contained herein shall restrict the ability of the
Company to terminate your employment.

2. Change in Control. No benefits shall be payable hereunder if (i) there has
been a Change in Control of the Company and your employment is thereafter
terminated by you for other than Good Reason, or (ii) there has been a Change in
Control of the Company and your employment is thereafter terminated for Cause by
the Company, death, Disability, or Retirement.

      (a)   "Change in Control" of the Company shall have the meaning set forth
            in the Company's Stock Incentive Plan, except that the Board agrees
            not to override the occurrence of a Change in Control.

      (b)   "Disability" shall mean that as a result of your incapacity due to
            physical or mental illness, you are absent from your duties with the
            Company for a consecutive period of more than six (6) months, the
            Company may terminate your employment on account of "Disability".

      (c)   "Retirement" shall mean your voluntary termination of employment at
            age sixty-five (65) or any other early retirement arrangement
            established with your consent with respect to you.

      (d)   "Cause" shall mean the willful and continued engaging by you in
            gross misconduct materially and demonstrably injurious to the
            Company. No termination for Cause shall be effective until you have
            received a copy of a resolution duly adopted by the affirmative vote
            of not less than 75% of the entire membership of the Board at a
            meeting of the Board called and held for the purpose (after
            reasonable notice to you and an opportunity for you, together with
            your counsel, to be heard before the Board), finding that in the
            good faith opinion of the Board you were guilty of conduct set forth
            in the Section 4(a) and specifying the particulars thereof in
            detail.

<PAGE>

      (e)   "Good Reason" shall mean:

            (i)   Change of Position. The assignment to you of any duties
                  inconsistent with your position or status as an officer prior
                  to the Change in Control or any alteration in the nature or
                  status of your responsibilities to a lesser position by you.

            (ii)  Compensation and Benefits. (1) A reduction in your base
                  salary, incentive compensation, or benefits or perquisites, as
                  in effect immediately prior to the Change in Control; or (2)
                  the failure by the Company to continue base salary increases,
                  incentive compensation grants, benefits and perquisites in
                  effect prior to the Change in Control.

            (iii) Relocation. The relocation of the principal place of your
                  employment prior to the Change in Control without your written
                  consent.

            (iv)  Assumption of Agreement. If you elect to terminate your
                  employment because of the failure of the Company to obtain the
                  assumption of this Agreement as provided in Section 7.

3. Benefits Payable. If your employment is terminated following a Change in
Control of the Company by you for Good Reason or by the Company other than for
Cause, death, Disability or Retirement, then your benefits shall be those
described in this Section 3.

      (a)   Your base salary shall be continued for a period of 12 months. These
            special severance payments shall be in lieu of any severance
            payments payable under any severance plan or policy of the Company.

      (b)   During the continuation of your salary payments, the Company shall
            continue health insurance benefits for you at its own expense.
            Thereafter, you shall be afforded the right to continue such
            insurance benefits as provided under the Consolidated Omnibus Budget
            Reconciliation Act of 1985 (COBRA).

      (c)   All stock incentive grants or options under the Company stock option
            plan or stock incentive plan shall be 100% vested.

      (d)   Nothing contained herein shall adversely affect your rights, if any,
            to receive payments under any other bonus, incentive compensation,
            deferred compensation plan or group term life insurance plan, long
            term disability plan or retirement plan of the Company.

6. No Mitigation. You shall not be required to mitigate the amount of any
payment provided for in this Agreement by seeking other employment or otherwise,
nor shall the amount of any payment provided for in this Agreement be reduced by
any compensation earned by you as the result of employment by another employer
after the date of termination, or otherwise.

7. Successors; Binding Agreement.

      (a)   The Company shall require any successor entity (whether direct or
            indirect, by purchase, merger, consolidation or otherwise) to all or
            substantially all of the business and/or assets of the Company to
            expressly assume this Agreement.

      (b)   This Agreement shall inure to the benefit of and be enforceable by
            your personal or legal representatives, executors, administrators,
            successors, heirs, distributees, devisees and legatees.

<PAGE>

8. Notice. Notices and all other communications provided for herein shall be in
writing and shall be deemed to have been duly given when delivered or mailed by
United States registered mail, return receipt requested, postage prepaid,
addressed to the Company at its principal office or to you at your address set
forth on the first page of this Agreement, provided that all notices to the
Company shall be directed to the attention of the President of the Company with
a copy to the Secretary of the Company, or to such other address as either party
may have furnished to the other in writing in accordance herewith, except that
notices of change of address shall be effective only upon receipt.

9. Modification; Waiver. No provisions hereof may be modified, waived or
discharged unless such waiver, modification or discharge is agreed to in writing
signed by you and a duly authorized officer of the Company (other than you). No
waiver by either party hereto of any condition or provision hereof to be
performed by such other party shall be deemed a waiver of similar or dissimilar
provisions or conditions at the same or at any other time. No agreements or
representations, oral or otherwise, express or implied, with respect to the
subject matter hereof have been made by either party which are not set forth
expressly herein.

10. Validity. This Agreement shall be governed by and construed in accordance
with the law of the State of Delaware. The invalidity or unenforceability of any
provision hereof shall not affect the validity or enforceability of any other
provision hereof, which shall remain in full force and effect.

11. Counterparts. This Agreement may be executed in one or more counterparts,
each of which shall be deemed to be an original, but all of which together shall
constitute one and the same instrument.

12. Arbitration. Any dispute or controversy arising in connection herewith shall
be settled exclusively by arbitration to be held in New York in accordance with
the rules of the American Arbitration Association then in effect.
Notwithstanding the pendency of any such dispute or controversy, the Company
shall continue to pay you your full compensation in effect when the notice
giving rise to the dispute was given (including, without limitation, base salary
and installments under any incentive plan) and continue you as a participant in
all the employee pension, welfare, incentive, compensation or other similar
plans, programs or policies of the Company in which you were participating when
the notice giving rise to the dispute was given, until the dispute is finally
resolved in accordance with this Section. Amounts paid to you under this
paragraph are in addition to all other amounts due hereunder and shall not be
offset against or reduce any other amounts due hereunder. Each party shall bear
their own costs, including attorneys' fees of the arbitration; provided,
however, that if you prevail on the claim, the Company shall reimburse you for
all reasonable costs and attorneys' fees. Judgement may be entered on the
arbitrator's award in any court of competent jurisdiction.

                                   Sincerely,

                                   T CELL SCIENCES, INC.

                                   by: ___________________________________

Agreed to this _____ day of _______________, 1993

_________________________________________________<PAGE>
                                                                   Exhibit 10.14

                               AMENDMENT TO LEASE
                                     BETWEEN
                             MOULTON REALTY COMPANY
                                       AND
                         VIRUS RESEARCH INSTITUTE, INC.

      The lease ("Lease") dated December 9, 1991 between Michael J. Spinelli,
Trustee of M.R.C. Realty Trust; Carol A. Hickey; Peter A. Spinelli, General
Partner; and Spinelli Family Associates all doing business as Moulton Realty
Company, as Landlord and Lessor, and Virus Research Institute, Inc., as Tenant
and Lessee, demising the premises located at 61 Moulton Street, Cambridge,
notice of which is recorded in the Middlesex South Registry of Deeds in Book
21695, Page 407, is hereby amended as follows:

      1. The number of parking spaces demised to Tenant for its exclusive use is
to be increased from 30 spaces to 43 spaces, effective December 1,1996. The
parking spaces demised to the Tenant effective December 1, 1996 are shown on the
new Schedule A annexed hereto, which the parties agree will substitute for the
current Schedule A to the Lease, effective December 1, 1996.

      2. The parties acknowledge that Tenant has exercised validly and
effectively its right and option to extend the term of the Lease, as set forth
in Article III(b) of the Lease, and that the term of the Lease now expires on
November 30, 2001; provided however, that the base rent due during the five (5)
year period commencing on December 1, 1996 to November 30, 2001 shall be
$293,700.00 per year in monthly installments of $24,475.00.

      3. Article III(b) of the Lease is amended to read as follows:

      OPTION

            "OPTION The Landlord hereby grants to the Tenant and its successors
      and assigns the right and option to extend the term of the Lease for a
      five-year period commencing on December 1, 2001 and ending an November 30,
      2006, in accordance with the following terms and conditions:

            If this Lease shall be in full force and effect at the expiration of
      the first extension term on November 30, 2001, then the Tenant shall have
      the right to extend this Lease for an additional period of five (5) years,
      beginning on December 1, 2001 and expiring November 30, 2006, as
      hereinafter set forth, providing that the Tenant shall give written notice
      to the Landlord at least six (6) months prior to expiration of said first
      extension term of this Lease of its election to exercise the aforesaid
      option. If the aforesaid option is exercised, the terms of this Lease
      shall be the same, except that the base rent hereunder shall be adjusted
      to equal the fair market rental of the demised premises, but in no event
      less than the base rent due in the fifth year of the first extension term
      of the Lease. If the parties are unable to agree on the fair market rental
<PAGE>

      then each shall appoint an arbitrator who shall be a licensed real estate
      broker or appraiser. If the two arbitrators are unable to agree on a fair
      market rental then the two arbitrators shall appoint a third arbitrator
      and a decision of the majority of the arbitrators shall be binding. In
      computing fair market rental for the purposes of this section, any portion
      of the Building which on September 1, 1996 is used and improved as office
      space and subsequently is converted to laboratory or similar use will,
      notwithstanding any such conversion, be treated and valued as office space
      in the condition it was in immediately prior to its conversion to
      laboratory or similar use. Both landlord and Tenant shall have the right,
      prior to conversion, to photograph or otherwise document and memorialize
      the condition of any office space intended to be converted to laboratory
      or similar use."

      4. Landlord agrees to defend, indemnify and hold harmless Tenant, its
officers, employees, agents, successors, and assigns (the "Indemnitees"),
against and in respect of, any and all reasonable damages, losses, liabilities,
expenses, costs, claims, actions, suits, proceedings, assessments, orders,
judgments, fines, and penalties (including without limitation, reasonable legal,
accounting, consulting, engineering, and other expenses), which may be incurred
by any of the Indemnitees, or imposed upon or asserted against any of the
indemnitees by any other party or parties (including, without limitation, a
governmental entity), arising out of, in connection with, or relating to the
subject matter of (a) any actual violation (or any alleged violation which
appears to have a legitimate basis in fact) of any environmental or health and
safety-related law, regulation, rule, ordinance or by-law, whether at the
federal, state or local level, with respect to the demised premises or any
facility or improvement or any operation or activity thereon, occurring or
existing as of and/or prior to December 1, 1991, even if not discovered until
after such date; or (b) the actual presence (or the alleged presence which
appears to have a legitimate basis in fact) of any Hazardous Material, as
defined below, on, in, under, adjacent to, or affecting the premises, occurring
or existing as of and/or prior to December 1, 1991, even if not discovered until
after such date. For purposes of this provision, "Hazardous Material" shall mean
any pollutant, contaminant, toxic substance, hazardous waste, hazardous
material, or hazardous substance, or any oil, petroleum, or petroleum product,
as defined in or pursuant in the Resource Conservation and Recovery Act, as
amended, the Comprehensive Environmental Response, Compensation, and Liability
Act, as amended, the Federal Clean Water Act, as amended, the Massachusetts
Hazardous Waste Management Act, as amended, the Massachusetts Oil and Hazardous
Material Release Prevention and Response Act, as amended, or any other federal,
state, or local environmental law, regulation, ordinance, rule, or by-law.
<PAGE>

      Except as expressly amended by this Amendment, the Lease dated December 9,
1991 continues unmodified and in full force and effect.

      Signed and sealed this ___ day of October, 1996.

                                    MOULTON REALTY COMPANY

                                    /s/ Michael J. Spinelli
                                    -----------------------------
                                    Michael J. Spinelli
                                    Trustee of M.R.C. Realty Trust

                                    /s/ Carol A. Hickey
                                    -----------------------------
                                    Carol A. Hickey

                                    /s/ Peter A. Spinelli
                                    -----------------------------
                                    Peter A. Spinelli, General Partner
                                    Spinelli Family Associates

                                    VIRUS RESEARCH INSTITUTE, INC.

                                    By: /s/ [Illegible]
                                        -------------------------
<PAGE>

                                      LEASE
                                     between
                             MOULTON REALTY COMPANY
                                       and
                         VIRUS RESEARCH INSTITUTE, INC.

THIS INDENTURE OF LEASE, made as of this 9th day of December, 1991, between
MICHAEL J. SPINELLI, TRUSTEE OF M.R.C. REALTY TRUST, CAROL A. HICKEY, PETER A.
SPINELLI, GENERAL PARTNER, SPINELLI FAMILY ASSOCIATES all doing business as
MOULTON REALTY COMPANY having a principal place of business at 25 Moulton
Street, Cambridge, County of Middlesex, Massachusetts, 02139, (hereinafter
called the "Landlord"), and VIRUS RESEARCH INSTITUTE, INC. a corporation duly
organized by law and having an usual place of business in Cambridge, in the
County of Middlesex, Massachusetts (hereinafter called the "Tenant")

                              W I T N E S S E T H:

I. (a) The Landlord hereby leases to the Tenant the entire premises located at
61 Moulton Street, Cambridge, Middlesex County, Massachusetts which Leasehold is
the existing Building shown on plan annexed hereto as Schedule A, said Building
contains 17,800 square feet, together with parking shown on said plan.

            (b) The premises described herein may be used for the purpose of
conducting a research laboratory and uses incidental thereto, including sales,
service, and manufacture of Tenant's products, general office use, as well as
any other use authorized
<PAGE>

under applicable zoning laws and ordinances in connection with its business. The
Landlord's knowledge and belief is that there are no restrictions in the title
to the premises which should prevent the intended use by the Tenant.

            (c) Located on the premises are approximately thirty (30) parking
spaces intended for the exclusive use of the Tenant more particularly described
in Schedule A.

            (d) The Tenant shall have the right of unobstructed access to the
premises by motor vehicle and otherwise for use in connection with its business,
including unobstructed access to the use of the truck dock, driveway and parking
areas, and Tenant may install a movable trash disposal unit outside the building
at a location agreed to by both parties. the premises are however subject to a
right-of-way as shown on Schedule A.

      II. The initial term of this Lease shall be for a period of five (5)
years, commencing December 1, 1991, as hereafter defined.

      III. (a) During the term of this Lease, the Tenant shall pay as base rent
to the Landlord at the Landlord's address first written above, or such other
place as the Landlord, by notice in writing to the Tenant, as follows:

                  (i) During the first year of the term, the sum of $135,000.00,
payable in monthly installments of $11,250.00 per month, due on the first of
each month;

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                  (ii) During the second year of the term, the sum of
$190,000.00, payable in monthly installments of $15,833.33 per month, due on the
first of each month;

                  (iii) During the third year of the term, the sum of
$210,000.00, payable in monthly installments of $17,500.00 per month, due on the
first of each month; and

                  (iv) During the fourth and fifth year of the term, the sum of
$270,000.00, payable in monthly installments of $22,500.00 per month, due on the
first of the each month.

            (b) OPTION. If this Lease shall be in full force and effect at the
expiration of the initial term, then the LESSEE shall have the right to extend
this Lease for an additional period of five (5) years, as hereinafter set forth,
providing that the LESSEE shall give written notice to the Landlord at least six
(6) months prior to expiration of the original term of this Lease of its
election to exercise the aforesaid option. If the aforesaid option is exercised,
the terms of this Lease shall be the same, except that the rent hereunder shall
be adjusted to equal the fair market rental of the demised premises, but in no
event less than the fifth year of the original Lease term. If the parties are
unable to agree on the fair market rental then each shall appoint an arbitrator
who shall be a licensed real estate broker or appraiser. If the two arbitrators
are unable to agree on a fair market rental then the two arbitrators shall
appoint a third arbitrator and a decision of the majority of the arbitrators
shall be binding. However, in the event that the

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<PAGE>

fair market rental is not determined within sixty (60) days of the election to
exercise the option, then the said option shall thereupon terminate

            (c) The Landlord shall promptly pay and discharge all real estate
taxes and betterment assessments levied or assessed upon the premises during the
term of the Lease, except that the Landlord may elect to have such betterment
assessments payable over the longest period permitted by law.

            (d) The Tenant shall pay as additional rent to Landlord, 100% of the
real estate taxes levied against the premises. The Tenant shall make payment
within thirty (30) days after receiving a copy of the paid tax bill together
with appropriate proof of payment, prorated on a 365-day year per diem basis for
any partial calendar year during the term of the Lease. Landlord represents and
warrants to Tenant that as of the date of this Lease, the premises are assessed
and maintained as a single and separate tax parcel or lot by the City of
Cambridge. Throughout the term of this Lease, Landlord shall cause the premises
to be assessed and maintained as such a separate tax parcel or lot so that bills
for real estate taxes shall issue solely with respect to real estate taxes
applicable to the premises.

            (e) The Landlord shall promptly pay and discharge all real estate
taxes and betterment assessments levied or assessed upon the premises during the
term of the Lease, except that the Landlord may elect to have such betterment
assessments payable

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<PAGE>

over the longest period permitted by law. Tenant shall not be required to pay
any portion of any increases in said taxes which are attributable to an increase
in the assessed valuation of the land or buildings, of which the demised
premises are a part, arising out of improvements (including new construction)
made to premises or adjacent Landlord land or buildings unless such improvements
are made by Tenant during the term of the Lease.

            (f) If any abatement refund or rebate shall be received for any tax
year, an appropriate adjustment shall thereafter be made in the amount paid by
the Tenant. If Landlord undertakes such abatement process, the cost of such
proceedings, and of any appeal therefrom, shall be charged first against any
abatement received, and the net proceeds credited to the Tenant.

      IV. (a) On or after the effective Commencement Date of the Lease, the
Tenant shall have the right and may install at its own expense alterations to
the interior of the building as may be reasonably desirable or necessary for the
conduct of its business. Such work shall be done in a good and workmanlike
manner, after submission of plans and specifications to the Landlord for
approval in writing, which approval shall not be unreasonably withheld or
delayed. At the time of the approval of the Landlord, the parties shall
determine whether or not said improvements shall be considered as an integral
part of Landlord's building and become part of Landlord's property, whereupon
Tenant shall have no obligation to remove same upon

                                        5
<PAGE>

termination of this Lease.

            (b) Promptly following the Commencement Date, Tenant shall perform
the following work with the premises: all working electrical outlets, a fresh
coat of paint to all wall surfaces in this space, 26 new gas and vacuum lines to
the benches in the main laboratory and tissue culture facility (the "Work").
Such work shall be done by contractor(s) selected by Tenant, subject to
Landlord's reasonable approval. As a Tenant allowance (the "Allowance"),
Landlord will reimburse Tenant for up to $16,000.00 of all reasonable documented
costs incurred by Tenant in connection with the Work, by giving Tenant a rental
credit or paying Tenant the amount of the Allowance promptly after substantial
completion of the Work.

      V. The Landlord agrees that during said term and so long as Tenant's
occupancy continues:

            (a) to be responsible for keeping the buildings presently on the
premises structurally sound and, without limiting the generality of the
foregoing, the Landlord will keep the roof and outside walls weather and
watertight and free from leaks and make all structural repairs and replacements
reasonably necessary to the Tenant's occupancy of the building and to its
foundation, roof, structural parts and utility connections from exterior wall to
street; and

            (b) to maintain parking lot and driveways.

            (c) to be responsible for delivering the premises to

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<PAGE>

Tenant in good order, condition and repair at the commencement of the term.

            (d) To the Landlord's best knowledge all activities at the premises
by Landlord and prior tenants and occupants thereof have been undertaken in full
compliance with all applicable environmental and hazardous substance laws.

            (e) Landlord has disclosed to Tenant all threatened or pending
litigation or administrative actions relating to the use or disposal of
hazardous substances at the premises.

            (f) Landlord has delivered to Tenant true and complete copies of all
reports, analyses, studies and other written materials which are in the
possession, custody or control of Landlord concerning the presence or possible
presence of hazardous substances at the premises.

            (g) To the Landlord's best knowledge there are no underground
storage tanks at the premises.

            (h) To the Landlord's best knowledge there are no transformers,
capacitors, switches, or other equipment at the premises which contain PCBs.

            (i) Landlord shall indemnify, defend and save harmless Tenant, its
officers, directors, employees, contractors, servants and agents, from and
against all loss, costs, damages, claims, proceedings, demands, liabilities,
penalties, fines and expenses, including without limitation reasonable
attorney's fees, consultant's fees, litigation costs, and cleanup costs,
asserted against or incurred by Tenant, its officers, directors,

                                        7
<PAGE>

employees, contractors, servants and agents at any time and from time to time by
reason or arising out of the presence of any hazardous substances at the
premises caused by the Landlord, its servants, agents or employees.

             (j) The Landlord represents that there is handicap access to the
building from the street and handicap bathroom facilities. In the event that
either Federal or State law requires that an elevator be installed on the
premises then the parties agree that the cost for installation for said elevator
will be born equally by said parties.

      VI. Tenant agrees during said term and so long as Tenant's occupancy
continues:

            (a) to be responsible for all maintenance and repairs of the heating
system, plumbing system, electrical system, central air conditioning system (if
any), interior mains and conduits for utilities, stairways and stairwells.
Landlord will repair, as required, all of above prior to Commencement date and
warrants that the existing systems and utilities will be in good repair and
working order on such date.

            (b) to pay when due all charges by public authority or utility for
heat, water, electricity, telephone, gas and other services rendered to the
premises;

            (c) to remove promptly snow, ice and foreign substances from the
stairs, parking lot areas designated for Tenant's use, and to maintain
landscaping adjacent to the within Leasehold;

                                        8
<PAGE>

            (d) will be responsible for replacing any glass which may be damaged
or broken with glass of the same quality;

            (e) to save the Landlord harmless from all loss and damage
occasioned by any nuisance made or suffered on the premises caused by the
omission, fault, negligence, or other misconduct of the Tenant as well as from
any claim or damage arising from neglect in not removing snow and ice from
stairs or parking lots assigned for Tenant's exclusive use on the premises, and
from any other injury, loss or damage to any person or property on said premises
caused by the omission, fault, negligence or other misconduct of the Tenant;
provided, however, that the above obligations do not apply when the injury or
damage was caused or contributed to by the negligent acts or omissions of the
Landlord, its agents, employees or contractors.

            (f) Tenant will not generate, store, dispose of, or otherwise handle
any hazardous substances on the premises in violation of any applicable
environmental or hazardous substance law.

            (g) Tenant will promptly inform Landlord of any environmental
releases of hazardous substances that are reportable to governmental authorities
under applicable environmental or hazardous substances laws. Tenant covenants
and agrees that no asbestos, asbestos-containing materials, or PCB compounds
will be used in the development of, or any alteration or additions to, any
portion of the premises.

            (h) Tenant shall indemnify, defend and save harmless

                                        9
<PAGE>

Landlord, its officers, directors, employees, contractors, servants and agents,
from and against all loss, costs, damages, claims, proceedings, demands,
liabilities, penalties, fines and expenses, including without limitation
reasonable attorney's fees, consultants' fees, litigation costs, and cleanup
costs, asserted against or incurred by Landlord, its officers, directors,
employees, contractors, servants and agents at any time and from time to time
resulting from the presence of any hazardous substances on the premises during
the term of this Lease arising after Tenant's taking possession of the premises
and resulting solely from (i) the action or inaction of the Tenant, its
officers, directors, employees, contractors, servants and agents, or (ii)
Tenant's generation, storage, treatment, handling, transportation, disposal or
release of any hazardous substance at or near the premises, or (iii) the
violation of any applicable law governing hazardous substances by tenant, its
officers, directors, employees, contractors, servants or agents. the indemnities
and duties to defend set forth in this Paragraph shall survive the termination
of this Lease. Parties agree to undertake to update the previous 21E Report to
establish that the presence of any hazardous waste is within the acceptable
limits determined by the Commonwealth of Massachusetts. If as a result of said
updated study any remedial action is required by the Commonwealth of
Massachusetts, said work will be taken at the expense of the prior Tenant and/or
Landlord.

            (i) not to overload or deface the premises or the

                                       10
<PAGE>

building or commit or suffer any strip or waste thereon, and not to conduct any
trade or occupation or to make any use of the premises or to do any act or thing
thereon or in the buildings that shall create a nuisance or be contrary to any
law of the Commonwealth of Massachusetts or ordinance or by-law for the time
being in force in the City of Cambridge, or which shall be injurious to any
person or property, or that shall make void or voidable any fire insurance
thereon or on the buildings, but proper conduct of Tenant's business shall not
be deemed a violation of this covenant; nor make any alterations, additions or
improvements without the consent of the Landlord, providing however, the
Landlord may set forth in its consent conditions or criteria to be complied with
by the Lessee;

            (j) not to assign this lease or to make any sublease for the whole
or any part of the demised premises without the prior written approval of the
Landlord which approval shall not be unreasonably withheld or delayed. In the
event of any assignment or sublease of the demises premises, any and all rents
payable under such assignment or sublease shall be payable directly to the
Landlord as payment toward the rent and other sums do hereunder; provided,
however, that if the rents and other sums payable or such sub-lease shall
exceed those rents and other sums due hereunder, then the Landlord shall be
entitled to retain such overage. For purposes of calculating any excess rent or
other consideration payable by Tenant to Landlord in connection with any
subletting or assignment, tenant shall be entitled to

                                       11
<PAGE>

"net out" (i.e., retain) the value of any improvements to the premises made by
Tenant at its expense allocable over the remaining term of the Lease. If any
consideration is paid to the Lessee hereunder for any assignment or sublease,
such consideration shall be paid to the Lessor hereunder. Notwithstanding
anything in this Paragraph to the contrary, the prior approval of the of the
Landlord shall not be required for the assignment of the Lease to any
corporation or business entity into or with which the Tenant is merged or
consolidated or to which substantially all of the Tenant's assets or corporate
stock are transferred provided that in any of such events (i) following any such
transfer Tenant has, (or in the case of a merger or consolidation the successor
to Tenant has) a creditworthiness adequate to meet its obligations hereunder;
(ii) proof reasonably satisfactory to Landlord of such creditworthiness shall
have been delivered to Landlord prior to the effective date of any such transfer
or transaction; and (iii) in the case of a merger or consolidation, the
successor agrees directly with Landlord, by written instrument in form
reasonably satisfactory to Landlord, to be bound by all the obligations of
Tenant hereunder, including, without limitation, the covenant against further
assignment and subletting.

            (k) to permit the Landlord or its agents to examine said premises at
reasonable times, subject to reasonable notice and Tenant's reasonable security
precaution and subject to applicable governmental regulations, if any, and
during the six

                                       12
<PAGE>

months prior to the expiration of said term to show said premises to prospective
purchasers and tenants, and keep affixed in suitable places, not obstructing the
Tenant's signs or displays, notices for letting or selling; and

            (l) at the expiration or earlier termination of said term promptly
to remove Tenant's personal property, and, if the Landlord reasonably so
requests or the Tenant so elects, to remove any movable trade fixtures or Tenant
installed equipment; to repair any damage caused by such removal; and, to
peaceably yield up said premises clean and neat and in repair as aforesaid,
damage by reasonable wear and tear and damage by fire and casualties only
excepted. Any such personal property, fixtures or equipment not so removed shall
at the expiration of thirty (30) days from such expiration or termination and
ten (10) days notice to Tenant become the property of the Landlord.

      VII. (a) In case of taking by eminent domain of ten (10%) percent or more
of the total floor area of the building or buildings at the time on the premises
the Tenant may by notice to the Landlord within thirty (30) days thereafter
terminate this Lease as of the date when the Tenant is required to vacate the
portions taken. In case of taking by eminent domain of said premises or any
portion thereof, if this Lease is not so terminated, the Landlord shall repair
or rebuild any building presently on said premises so as to restore the same or
what may remain thereof in case of partial taking, as nearly as possible

                                       13
<PAGE>

to its condition prior to the taking, the work to be commenced within four (4)
weeks after the date when the Tenant is required to vacate the portions taken
and to be completed with due diligence, except for delays due to governmental
regulations, unusual scarcity of or inability to obtain labor or materials, or
any other cause beyond Landlord's control. The Landlord reserves and excepts all
rights to damages to said premises and buildings and the leasehold hereby
created accruing in case of taking or act of public or other authority, and the
Tenant hereby grants to the Landlord all of the Tenant's rights to such damages
and agrees to deliver such further instruments of assignment thereof as the
Landlord from time to time may reasonably request. Tenant, however, reserves its
rights to damages for trade fixtures and relocation expenses. The Landlord
shall, however, pay to the Tenant from such damages when received the amounts,
if any, by which the same were increased by reason of inclusion therein of any
award for fixtures and equipment which Tenant is entitled to remove.

      During such repair or rebuilding, a just proportion of the rent shall be
abated until what remains of the premises shall have been restored to proper
condition for use and occupation and thereafter a just proportion of the rent
according to the nature and extent of the taking shall be permanently abated.
The Landlord and Tenant hereby agree that if they are unable to agree upon the
amount of reduction in rent because of such taking, a board of three appraisers
shall be appointed, one by each party

                                       14
<PAGE>

and the third by the two so chosen and the findings of such board of appraisers
shall bind each party. The expense of such appraisal, including counsel fees,
shall be shared equally by each party.

            (b) In case said building is damaged by fire or other casualty or
action of public authority in consequence thereof or incidents of war,
earthquake, action of the elements, explosion or otherwise, the Tenant shall
promptly notify the Landlord. If the premises are so badly damaged that they
cannot be restored and made tenantable by the exercise of reasonable diligence
within ninety (90) days after the commencement of work, or if they are damaged
to the extent of twenty-five (25%) percent or more of the insurable value, then
the Tenant may terminate this Lease upon ten (10) days' notice in writing given
to the Landlord within thirty (30) days after such damage occurs or, at Tenant's
option, thirty (30) days after advice from Landlord regarding cost and time of
repair, whereupon the Tenant shall surrender the premises, and the Landlord, if
the Tenant is not at the time in default hereunder, shall refund to the Tenant
any unearned rent paid in advance by the Tenant, calculated from the date of the
damage. If the Lease is not so terminated or if the premises are damaged to a
lesser extent, the Landlord will repair the damaged premises and the buildings
thereon as nearly as reasonably possible to its or their condition prior to such
damage, the work to be commenced within thirty (30) days and completed with due
diligence, except for delays due to governmental regulation or

                                       15
<PAGE>

unusual scarcity of or inability to obtain labor or materials, and thereupon
shall be entitled, to the extent of the cost of repairs, to the proceeds of any
insurance against such damage. In case the premises or the buildings thereon are
rendered untenantable by such damage, a just proportion of the rent hereinbefore
reserved according to the nature and extent of the injury shall be abated until
the repair or rebuilding is completed, and the premises shall have been put in
proper condition for use and occupation. The Landlord and Tenant hereby agree
that if they are unable to agree upon the amount of reduction in rent because of
such damage a board of three appraisers shall be appointed, one by each party
and the third by the two so chosen, and the findings of such board of appraisers
shall bind each party. The expense of such appraisal shall be shared equally by
each party.

      Notwithstanding the foregoing provisions of this Lease, if the premises
shall be substantially damaged by fire or other casualty or action of public
authority in consequence thereof or incidents of war, earthquake, action of the
elements, explosion or otherwise, within twelve (12) months of the expiration of
the term or any extension hereof, either party may terminate this Lease as of
the date of such damage, by written notice to the other within ten (10) days of
the occurrence of such damage, except that if, prior to or within thirty (30)
days after such damage during the original term of this Lease the Tenant, having
the right do so, shall have elected to extend, pursuant to

                                       16
<PAGE>

paragraph IV above, the provisions of this paragraph shall not apply.

      VIII. The Landlord and Tenant hereby further agree that:

            (a) if any sum or sums due as rent as herein provided shall be
unpaid when due and shall remain unpaid for a period of ten (10) days after
notice in writing of such default has been given by the Landlord to the Tenant;
provided, however, if the Landlord has on three (3) separate occasions during
the term of the Lease been required to give Tenant such written notice of
failure to pay rent and is thereafter again required to give such notice to
Tenant, then Tenant shall be given no further opportunity to cure such default
and this Lease shall immediately terminate and Landlord may thereafter enter in
and upon said Leasehold and repossess the same; or

            (b) if the Tenant or Landlord shall violate or be in default in its
observance or performance of any covenant, condition and agreement herein
contained other than default in the payment of rent, and shall have failed to
remedy such violation or default within thirty (30) days after notice in writing
of such breach or default has been given by one to the other (or, if the nature
of such breach or default is such that it cannot be remedied within such thirty
(30) day period, if the defaulting party has failed to commence remedial action
within said thirty (30) days and thereafter continued such action with

                                       17
<PAGE>

due diligence); or

            (c) if the estate hereby created shall be taken on execution or by
other process of law in any action against the Tenant; or

            (d) if the Tenant shall be declared a bankrupt or insolvent
according to law (or if the Tenant makes any assignment for the benefit of
creditors); or

            (e) if a receiver shall be appointed of the Tenant's property and
not be removed within sixty (60) days; then, and in any such case
(notwithstanding any license of any former breach or waiver of the benefit
hereof or consent in a former instance):

      Then the non-defaulting party, may, as applicable, at its option,
terminate this Lease or, as the case may be, the Landlord shall have the right
thereafter, while Tenant's default continues, to enter into and upon the
premises or any part thereof in the name of the whole, and repossess the same as
of its former estate (after notice and in accordance with applicable law), and
expel the Tenant and those claiming through or under it and remove its or their
effects without being deemed guilty of any manner of trespass, without prejudice
to any other remedies, and thereupon this Lease shall terminate.

      In case of such termination or termination by legal proceeding by Landlord
for default, the Tenant will pay to the Landlord sums equal to the rent reserved
hereunder (as hereinabove defined) at the same time and in the same installments
as herein provided, or if the premises hereby

                                       18
<PAGE>

demised shall have been relet, for which the Landlord will use its reasonable
efforts to accomplish, sums equal to the excess of said rent reserved hereunder
over the sums actually received by the Landlord, except that there shall be
first credited against the obligations of Tenant under this subdivision any sum
actually paid by Tenant to Landlord.

      If the Tenant or Landlord shall default under provision VIII(b) above, the
Landlord or Tenant, as applicable, without being under any obligation to do so
and without thereby waiving such default or any of its other remedies hereunder,
at its sole option, may remedy such default for the account and at the expense
of the Tenant or Landlord, as applicable. Any such sums shall be paid to the
Landlord by the Tenant as additional rent, or in the event of Tenant payments to
cure a Landlord default, the Tenant may deduct same from rental due and owing by
way of set-off to the extent of such payments.

      IX. Tenant shall be responsible, with respect to the demised premises of
which the within Leasehold is a part for the cost of:

            (a) comprehensive general liability insurance covering all Tenant's
general liability obligations under this lease, with limits of
$3,000,000/$5,000,000 on personal injury or death and limits of $500,000.00 on
property damage in a company qualified to do business in Massachusetts, insuring
Landlord as well as Tenant against injury to persons or property.

            (b) insurance upon the premises against fire and loss

                                       19
<PAGE>

or damage by other risks embraced by Extended Coverage Endorsement, so called,
naming Landlord as insured, in an amount equal to the full insurable value of
the premises with insurance companies authorized to do business in
Massachusetts. Such policies may contain an eighty (80%) percent co-insurance
clause.

            (c) Landlord shall be named in all insurance policies.

            (d) The cost of said insurance shall be paid by the Tenant within
ten (10) days after presentation of bill from Landlord to Tenant setting forth
the cost of the aforesaid insurance, whether such insurance shall be paid
annually or in monthly installments.

            (e) Each of the parties hereto hereby waives any and all rights of
recovery against the other or against any other tenant or occupant of the
building, or against the officers, employees, agents, representatives, customers
and business visitors of such other party of such other tenant or occupant of
the building, for loss of or damage to such waiving party of its property or the
property of others under its control, arising from any cause insured against
under the standard form of fire insurance policy with all permissible extensions
and endorsements covering additional periods or under any other policy of
insurance carried by such waiving party in lien thereof. Such waivers shall be
effective only so long as the same is permitted by each party's insurance
carrier without the payment of additional premium.

                                       20
<PAGE>

      X. (a) No consent or waiver, express or implied, by the Landlord or the
Tenant to or of any breach of any agreement or duty of the other shall be
construed as a consent or waiver of any other breach of the same or any other
agreement or duty. This agreement is the entire agreement between the parties
and modification or alteration of this Lease shall be binding unless signed by
both parties. This Lease shall be governed and construed in accordance with the
laws of the Commonwealth of Massachusetts, and if any provisions shall to any
extent be invalid, the remainder shall not be affected.

            (b) The following addresses for communications and payments, unless
otherwise specified, by one party addressed to the other shall be sufficient:
for the Landlord - 25 Moulton Street, Cambridge, Massachusetts; and for the
Tenant - 61 Moulton Street, Cambridge, Massachusetts. Any communication, except
payment of rent, which is not delivered personally and receipted, shall be
deemed duly served if in writing, mailed by certified mail so addressed, postage
prepaid, return receipt requested and such notices shall be deemed given when
posted by the U.S. Postal Service.

            (c) The obligations and benefits of this Lease shall run with the
land and this Lease shall be binding upon and inure to the benefit of the
parties hereto and their respective successors and assigns; except that the
Landlord shall be liable hereunder only for obligations and liabilities accruing
or

                                       21
<PAGE>

arising while, or out of facts or situations occurring while, the Landlord is
the owner of the premises, and for indemnifications, obligations and liabilities
incurred by the Landlord under or pursuant to the Lease provisions.

            (d) The Landlord agrees that the Tenant, upon paying rents and all
other charges herein provided and performing the Tenant's agreements hereunder,
shall lawfully and quietly hold, occupy and enjoy said demised premises during
the term of this Lease or until the same is terminated as herein provided, and
neither the Lease nor Tenant's right to remain in exclusive possession shall be
affected or disturbed by reason of transfer of title to premises through
foreclosure or otherwise or by reason of any Landlord default under any mortgage
or deed of trust.

            (e) This Lease, and all rights of Tenant hereunder, are and shall be
subject and subordinate to all mortgages which now or hereafter affect the
premises, whether or not such mortgages shall also cover other lands and/or
buildings and/or leases, to each and every advance made hereafter to be made
under such mortgages, and to all renewals, modifications, replacements and
extensions of such leases and such mortgages and all consolidations of such
mortgages, Landlord agrees to use reasonable efforts to obtain and deliver to
Tenant following the execution of this Lease a so called non-disturbance and
attornment agreement from the existing mortgages.

                  Landlord hereby represents and warrants to Tenant,

                                       22
<PAGE>

as of the date of this Lease and as of the Commencement Date, that (i) Landlord
is not in default under any mortgage which encumbers the premises, (ii) this
Lease and the permitted uses hereunder do not and will not constitute a
violation of any such mortgage, and (iii) all consents or approvals required by
the terms of any such mortgage for this Lease have been duly obtained by the
Landlord.

      XI. The Tenant shall have the right, at its expense, to install a sign or
signs on the demised premises at such locations as may be reasonably necessary
to make known the location of its business. Tenant shall obtain written consent
of Landlord before erecting any sign, which consent shall not be unreasonably
withheld. Upon termination of this Lease, Tenant shall promptly remove the said
signs at its own expense and repair any damage to premises caused by the signs.

      XII. Landlord and Tenant represent and warrant to each other that the only
brokers in this transaction are Spaulding & Slye Colliers and Peter Elliot Co.,
Inc. and that Landlord will pay the brokerage commission due said brokers as per
the agreement between the Landlord and said brokers. Landlord and Tenant agree
to defend and indemnify each other against any claims, losses, damages.
liabilities or expenses (including reasonable attorney's fees) arising out of
the breach of any of their respective foregoing representations.

                                       23
<PAGE>

      XIII. Landlord represents that in 1986 it engaged the services of a
professional environmental engineering firm to conduct a so-called hazardous
waste site assessment of the Premises. A copy has been provided to the Tenant.
Landlord further represents, and Tenant acknowledges, that Landlord is engaging
the services of a professional environmental engineering firm to update such
1986 site assessment. Since such update will require both a physical inspection
of the premises as well as the testing and analysis of samples to be taken from
some test well borings on the Premises, if necessary. Landlord estimates that it
may take four to six weeks for such update to be completed. Upon Landlord's
receipt of such update, Landlord shall deliver a copy thereof to Tenant. If such
update shows no material change in condition of the premises, Landlord and
Tenant agrees to rely on such update. If, however, such update discloses any
material change in the condition of the premises the Landlord agrees to
Indemnify Tenant with material change in condition as provided in Article V,
Section I. Said Indemnification shall apply only to any change in the condition
of the premises up to December 9, 1991.

      XIV. The Tenant shall deliver to the Landlord within the time of the
execution of the within Lease the sum of $11,250.00 as a deposit to secure
perform of all covenants and payment of all sums due under the terms of the
within Lease or the extensions or renewals thereof. At the conclusion of the
Lease

                                       24
<PAGE>

term or any extension thereof, Landlord shall be accountable to the Tenant
regarding said security deposit and Landlord further agrees to pay interest on
said sum at the rate of five percent (5%) per annum payable at the conclusion of
the initial term of the Lease and if the within Lease is extended, interest
shall be computed during such extended period and shall be paid at the end of
said extended period.

WITNESS the execution hereof, in duplicate, under seal, all as of the day and
year first above written.

                                    MOULTON REALTY COMPANY

                                    /s/ Michael J. Spinelli
                                    -----------------------------
                                    Michael J. Spinelli
                                    Trustee of M.R.C. Realty Trust

                                    /s/ Carol Ann Hickey
                                    -----------------------------
                                    Carol Ann Hickey

                                    /s/ Peter A. Spinelli
                                    -----------------------------
                                    Peter A. Spinelli, General Partner
                                    Spinelli Family Associates

                                    VIRUS RESEARCH INSTITUTE, INC.

                                    By: /s/ John W. Littlechild
                                        -------------------------
                                        John W. Littlechild
                                        Its President

                                       25
<PAGE>

                                   SCHEDULE A

                              [GRAPHIC: Plot Plan]

                                PLOT PLAN OF LAND
                                       IN
                                 CAMBRIDGE, MASS

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