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                                                                    EXHIBIT 10.5

     THIS INDENTURE OF LEASE (the "LEASE") is hereby made and entered into on
the Execution Date by and between Landlord and Tenant.

Landlord does hereby demise and lease to Tenant, and Tenant does hereby lease
and take from Landlord, the Premises upon and subject to the covenants,
agreements, terms, provisions and conditions of the Lease for the term
hereinafter stated.

1.   REFERENCE DATA; NET LEASE; NON-TERMINABILITY

     1.1    Each reference in the Lease to any of the terms and titles contained
in any Exhibit attached to this Lease shall be deemed and construed to
incorporate the data stated under that term or title in such Exhibit. All
capitalized terms not otherwise defined herein shall have the meanings ascribed
to them as set forth in EXHIBIT 1.

     1.2    The Lease is a net lease, and Rent (hereinafter defined) shall be
paid without notice or demand, and without setoff, counterclaim, defense,
abatement, suspension, deferment, reduction or deduction, except as expressly
provided herein.

     1.3    The Lease shall not terminate, nor shall Tenant have any right to
terminate the Lease, nor shall the obligations and liabilities of Tenant set
forth herein be otherwise affected, except as expressly provided herein.

     1.4    Tenant waives all rights (i) to any abatement, suspension,
deferment, reduction or deduction of or from Rent, and (ii) to quit, terminate
or surrender the Lease or the Premises or any part thereof, except as expressly
provided herein.

     1.5    It is the intention of the parties hereto that the obligations of
Tenant hereunder shall be separate and independent covenants and agreements,
that Rent shall continue to be payable in all events and that the obligations of
Tenant hereunder shall continue unaffected, unless the requirement to pay or
perform the same shall have been terminated pursuant to an express provision of
the Lease.

2.   DESCRIPTION OF PREMISES

     2.1    PREMISES. The Premises are those portions of the Building more
particularly described in EXHIBIT 1, as the same may from time to time be
constituted after changes therein, additions thereto and eliminations therefrom
pursuant to the provisions hereof.

     2.2    ROOFTOP PREMISES. Tenant's use and occupancy of the Rooftop Premises
(as the same shall change during the term of this Lease) shall be subject to the
following additional requirements and restrictions:

            (a)  The Rooftop Premises shall only be used for housing and
operating certain equipment approved by Landlord and to be purchased and
installed by Tenant as part of Tenant's Work (hereinafter defined), including
without limitation an emergency back-up natural gas generator of a type and size
approved by Landlord (the "GENERATOR"), which Generator Tenant shall install,
maintain and operate in compliance with Legal Requirements, and certain other
mechanical equipment serving the laboratory areas of the Premises solely for the
benefit of Tenant and any Successors, Affiliated Entities and permitted
sublessees and licensees occupying the Premises, all as specifically approved in
writing by Landlord (any equipment installed within the Rooftop Premises, as the
same may be modified, altered or replaced during the term hereof, is
collectively referred to herein as "TENANT'S ROOFTOP EQUIPMENT").

                                TOLERRX LEASE / BUILDING 300 / EXECUTION VERSION

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Landlord's approval shall not be unreasonably withheld, conditioned or delayed
provided Tenant demonstrates to Landlord's reasonable satisfaction that the
proposed equipment (x) does not interfere with any base building equipment
operated by Landlord on the roof; (y) will not affect the structural integrity
of the Building or impact the roof or the roof membrane in any manner; and (z)
shall be adequately sound-proofed to meet all requirements of Legal Requirements
and Landlord's specified maximum decibel levels for equipment operations.

            (b)  Tenant shall not install or operate Tenant's Rooftop Equipment
until Tenant has obtained and submitted to Landlord copies of all required
governmental permits, licenses, and authorizations necessary for the
installation and operation thereof. In addition, Tenant shall comply with all
reasonable construction rules and regulations promulgated by Landlord in the
installation, maintenance and operation of Tenant's Rooftop Equipment.

            (c)  All electricity generated by the Generator may only be consumed
by Tenant in the Premises. Other than for periodic testing subject to Section
2.2(h) below, in no event shall Tenant operate the Generator except in cases of
a power outage to the Premises or any portion thereof.

            (d)  Landlord shall have no obligation to provide any services
including, without limitation, electric current, or gas service to the Rooftop
Premises or to Tenant's Rooftop Equipment.

            (e)  Tenant shall be responsible for the cost of repairing and
maintaining Tenant's Rooftop Equipment and the cost of repairing any damage to
the Building, or the cost of any necessary improvements to the Building, caused
by or as a result of the installation, replacement and/or removal of Tenant's
Rooftop Equipment.

            (f)  Landlord makes no warranties or representations to Tenant as to
the suitability of the Rooftop Premises for the installation and operation of
Tenant's Rooftop Equipment.

            (g)  If any of Tenant's Work on the roof of the Building, including
without limitation the installation and maintenance of Tenant's Rooftop
Equipment, damages the roof or invalidates or adversely affects any warranty
provided by Landlord to Tenant, Tenant shall be fully responsible for the cost
of repairs (and any subsequent repairs to the roof to the extent that any
warranty is invalidated or adversely affected).

            (h)  Notwithstanding anything to the contrary contained herein, in
the event that at any time during the term hereof, Landlord determines, in its
sole but bona fide business judgment, that the periodic testing of Tenant's
Rooftop Equipment interferes with the operation of the Building or the business
operations of any of the occupants of the Building, then Tenant shall, upon
notice from Landlord, cause all further testing of Tenant's Rooftop Equipment to
occur after normal business hours (hereinafter defined).

     2.3    APPURTENANT RIGHTS; TENANT'S ACCESS.

            (a)  Tenant shall have, as appurtenant to the Premises, rights to
use in common, with others entitled thereto, subject to the Rules and
Regulations (hereinafter defined) the following areas: (i) the common lobbies,
loading docks, elevators, hallways and stairways of the Building serving the
Premises, (ii) common walkways necessary for access to the Building, (iii)
common rooftop areas within which the Rooftop Premises are located and other
common rooftop areas necessary for access thereto, and (iv) if the Premises
include less than the entire rentable area of any floor, the common toilets and
other common facilities of such floor; and no other appurtenant rights or
easements.

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            (b)  From and after the Term Commencement Date and until the end of
the term hereof, Tenant shall have access to the Building and to the Premises
twenty-four (24) hours a day, seven (7) days a week, subject to the terms of
this Lease. Tenant shall have the right, during the term hereof, to use the
internal stairwells of the Building to provide access for Tenant's employees
between the floors of the Premises provided that such use is permitted by Legal
Requirements. Tenant shall have the right to access the Premises, at Tenant's
sole risk, prior to the Term Commencement Date for purposes reasonably related
to the performance of Tenant's Work (hereinafter defined), provided such access
does not materially interfere with the preparation for or performance of
Landlord's Work (hereinafter defined). Tenant shall, prior to the first entry to
the Premises pursuant to this Section 2.3(b), provide Landlord with certificates
of insurance evidencing that the insurance required in Article 15 hereof is in
full force and effect and covering any person or entity entering the
Condominium. Tenant shall defend, indemnify and hold Landlord, Landlord's
agents, contractors and employees, and any of the officers, trustees, directors,
partners, beneficiaries, joint venturers, members, stockholders or other
principals or representatives and the like, disclosed or undisclosed, thereof
(collectively, the "LANDLORD INDEMNITEES") harmless from and against any and all
claims, damages, losses, penalties, costs, expenses and fees (including without
limitation reasonable legal fees) (collectively, "CLAIMS") for injury to persons
or property resulting from or relating to Tenant's access to and use of the
Premises prior to the Term Commencement Date as provided under this Section
2.3(b). Tenant shall coordinate any access to the Premises prior to the Term
Commencement Date with Landlord's Construction Representative.

     2.4    PARKING. During the term hereof, commencing on the Rent Commencement
Date, Landlord will, subject to the terms hereof, make available up to
fifty-four (54) parking spaces for Tenant's use in the Parking Garage. The
number of parking spaces in the Parking Garage reserved for Tenant pursuant to
the following sentence or as otherwise permitted by Landlord, are hereinafter
referred to as the "PARKING SPACES." Until the date which is twenty-four (24)
months after the Rent Commencement Date (the "PARKING DETERMINATION DATE") and
upon written notice to Landlord, Tenant shall have the right from time to time
to reduce or increase the number of parking spaces to which Tenant is entitled
pursuant to this Section 2.4 (provided, however, that in no event will Tenant be
entitled to more than fifty-four (54) parking spaces at any time). Upon the
Parking Determination Date, Tenant's right to Parking Spaces shall be fixed at
the number last requested by Tenant in writing prior to the Parking
Determination Date (up to a maximum of fifty-four (54) spaces) and may not be
further increased without the express written consent of Landlord. From and
after the Parking Determination Date, Landlord may allocate any of the original
fifty four (54) parking spaces not reserved to Tenant in accordance with the
preceding sentence for use by other tenants of the Condominium free and clear of
Tenant's rights under this Section 2.4. From and after the Parking Determination
Date, Tenant shall have the right once per year to reduce the number of parking
spaces to which Tenant is entitled by written notice to Landlord (a "PARKING
REDUCTION NOTICE") at least thirty (30) days prior to the anniversary of the
Parking Determination Date, which notice shall be effective as of the
anniversary of the Parking Determination Date. From and after the effective date
of any Parking Reduction Notice, Landlord may allocate any of the original fifty
four (54) parking spaces not reserved to Tenant in accordance with the preceding
sentence for use by other tenants of the Condominium free and clear of Tenant's
rights under this Section 2.4. Tenant shall have no right to hypothecate or
encumber the Parking Spaces, and shall not sublet, assign, or otherwise transfer
the Parking Spaces other than to employees of Tenant occupying the Premises or
to a Successor (hereinafter defined), an Affiliated Entity (hereinafter defined)
or a transferee pursuant to an approved Transfer under Article 16 hereof. The
Parking Spaces shall be paid for by Tenant at the then-current prevailing rate
in the Parking Garage, as such rate may vary from time to time, provided that
any such increases are commercially reasonable as determined by the market rate
for comparable parking spaces in the Kendall Square vicinity. As of the Rent
Commencement Date, the monthly charge for parking is One Hundred Ninety Dollars
($190.00) per Parking Space per month. If, for any reason, Tenant shall fail
timely to pay the charge for any of said Parking Spaces, and if such

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default continues for ten (10) days after written notice thereof, Tenant shall
have no further right to the Parking Spaces for which Tenant failed to pay the
charge under this Section 2.4 and Landlord may allocate such Parking Spaces for
use by other tenants of the Condominium free and clear of Tenant's rights under
this Section 2.4. Said Parking Spaces will be on an unassigned, non-reserved
basis, and shall be subject to such reasonable rules and regulations as may be
in effect for the use of the Parking Garage from time to time (including,
without limitation, Landlord's right, without additional charge to Tenant above
the prevailing rate for Parking Spaces, to institute a valet or
attendant-managed parking system).

     2.5    EXCLUSIONS. The following are expressly excluded from the Premises
and reserved to Landlord: all the perimeter walls of the Premises (except the
inner surfaces thereof), any lobbies, balconies (except to the extent same are
shown as part of the Premises on the Lease Plan (EXHIBIT 2)), terraces, decks or
roofs adjacent to the Premises, and any space in or adjacent to the Premises
used for shafts, stacks, pipes, conduits, wires and appurtenant fixtures, fan
rooms, ducts, electric or other utilities, sinks or other Building facilities,
and the use of all of the foregoing.

     2.6    RIGHTS RESERVED TO LANDLORD.

            (a)  ALTERATIONS TO THE BUILDING OR CONDOMINIUM. Landlord reserves
the right, exercisable by Landlord or its nominee, at any time and from time to
time, to make such changes, alterations, additions, improvements, repairs or
replacements in or to the Condominium, the Building (including the Premises but,
with respect to the Premises, only for purposes of repairs, maintenance,
replacements and other rights expressly reserved to Landlord herein) and the
fixtures and equipment therein, as well as in or to the street entrances,
lobbies, halls, passages, elevators, escalators, and stairways thereof, as it
may deem necessary or desirable, and to change the arrangement and/or location
of entrances or passageways, lobbies, doors and doorways, corridors, elevators,
stairs, toilets, and/or other public parts of the Building, provided, however,
that there be no material obstruction of access to, or material interference
with the use and enjoyment of, the Premises by Tenant. Landlord expressly
reserves the right to temporarily close all, or any portion, of the common areas
of the Building and/or the Condominium for the purpose of making repairs or
changes thereto.

            (b)  ADDITIONS TO THE CONDOMINIUM. Landlord may at any time or from
time to time construct additional improvements in all or any part of the
Condominium, including, without limitation, adding additional buildings (Units)
to the Condominium or changing the location or arrangement of any improvement in
the Condominium or all or any part of the common areas thereof, or add or deduct
any land to or from the Condominium; provided that there shall be no material
increase in Tenant's obligations or material interference with Tenant's rights
under the Lease in connection with the exercise of the foregoing reserved
rights.

            (c)  CHANGE NAME OR ADDRESS. Landlord reserves the right at any time
and from time to time to change the name or address of the Building or the
Condominium provided that the name of the Building or Condominium shall not be
changed to the name of any public or private biotechnology or pharmaceutical
company and further provided that Landlord gives Tenant at least six (6) months'
prior written notice thereof. Tenant hereby acknowledges and agrees that certain
tenants and occupants of the Condominium may have the right to install and
maintain signage on the exterior of buildings in the Condominium, and that any
such signage shall not be deemed a violation of this Section 2.6(c).

            (d)  CHANGE IN FORM OF OWNERSHIP. Pursuant to MGL Chapter 183A
Section 19, Landlord reserves the right to remove all or part of the Condominium
from the provisions of MGL Chapter 183A. In the event that the Condominium is
so removed, then (i) Taxes shall thereafter refer to the Taxes

                                TOLERRX LEASE / BUILDING 300 / EXECUTION VERSION

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assessed against the property on which the Building is located (the "PROPERTY");
and (ii) Condominium Operating Costs shall refer to all costs incurred and
expenditures of whatever nature made in the operation, management, repair,
replacement, maintenance and insurance of the Property.

            (e)  ACCESS TO THE PREMISES. (i) Tenant shall (x) permit Landlord to
erect, use and maintain pipes, ducts and conduits in and through the Premises,
provided the same do not materially reduce the floor area or materially
adversely affect the appearance thereof; (y) upon as much advance notice as is
practical under the circumstances (except that no notice shall be required in
emergency situations), permit Landlord and any mortgagee of the Building or the
Condominium or of the interest of Landlord therein (each, a "MORTGAGEE"), and
their agents, employees and contractors, to have free and unrestricted access to
and to enter upon the Premises at all reasonable hours for the purposes of
inspection, making repairs, replacements or improvements in or to the Premises
or the Building or equipment therein (including, without limitation, sanitary,
electrical, heating, air conditioning or other systems), complying with all
applicable laws, ordinances, rules, regulations, statutes, by-laws, court
decisions and orders and requirements of all public authorities (collectively,
"LEGAL REQUIREMENTS"), or exercising any right reserved to Landlord by the Lease
(including without limitation the right to take upon or through, or to keep and
store within the Premises all necessary materials, tools and equipment); and (z)
permit Landlord and its agents and employees, at reasonable times, upon
reasonable advance notice, to show the Premises during ordinary business hours
to any existing or prospective Mortgagee or purchaser of the Building or
Condominium or of the interest of Landlord therein, and during the last twelve
(12) months of the term hereof, prospective tenants.

                 (ii)    If Landlord's access to the Premises for any purposes
permitted under this Lease requires Landlord to go through or work in any
controlled or sensitive laboratory areas within the Premises, then, Tenant shall
have the right to have a representative present during such access and Landlord
shall use reasonable efforts to avoid any interference with Tenant's sensitive
operations in connection therewith. If Tenant or its designated representative
shall not be personally present to open and permit an entry into the Premises at
any time when for any reason an entry therein shall be necessary due to an
emergency, Landlord or Landlord's agents may enter the same by a master key, or
may forcibly enter the same, without rendering Landlord or such agents liable
therefor (if during such entry Landlord or Landlord's agents shall accord
reasonable care to Tenant's property and to the ongoing sensitive operations
areas), and without in any manner affecting the obligations and covenants of
this Lease.

            (f)  TENANT REMAINS OBLIGATED. Nothing contained in this Section 2.6
shall be deemed to relieve Tenant of any duty, obligation or liability of Tenant
with respect to making any repair, replacement or improvement or complying with
any Legal Requirements.

            (g)  RELOCATION OF EQUIPMENT IN 1ST FLOOR PREMISES. Landlord shall
have the right, upon at least fifteen (15) business days' prior written notice
to Tenant (which notice shall not be required in the event of an emergency,
Landlord however agreeing to use reasonable efforts to give Tenant some prior
notice if at all practicable given the emergency situation), to require Tenant
to temporarily relocate any and all equipment located in the 1st Floor Premises
to another location approved by Landlord on the first (1st) floor of the
Building as may be reasonably necessary in connection with the erection,
installation, maintenance, repair and/or replacement of pipes, ducts and
conduits in and through the 1st Floor Premises. Landlord shall notify Tenant
promptly after the completion of any such erection, installation, maintenance,
repair and/or replacement, and Tenant shall, within five (5) business days after
delivery of such notice, move any relocated equipment back to its original
location in the 1st Floor Premises. Upon receipt of a reasonably detailed
invoice, Landlord shall reimburse Tenant for all reasonable third party costs
and expenses actually incurred by Tenant in connection with the exercise of
Landlord's rights under this Section 2.6(g).

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            (h)  MINIMIZE INTERFERENCE. Landlord shall use commercially
reasonable efforts to minimize any interference with Tenant's business
operations and use and occupancy of the Premises in connection with the exercise
any of the foregoing rights under this Section 2.6.

3.   TERM OF LEASE.

     3.1    HABENDUM. TO HAVE AND TO HOLD the Premises for a term of years
commencing on the Term Commencement Date and, unless earlier terminated or
extended pursuant to Article 25 hereof, ending on the Expiration Date.
Notwithstanding the foregoing, if the Expiration Date shall fall on any day
other than the last day of a calendar month, the term hereof shall end on the
last day of the calendar month in which said Expiration Date occurs.

     3.2    DECLARATION FIXING TERM COMMENCEMENT DATE, FULL RENT COMMENCEMENT
DATE, AND EXPIRATION DATE. Each of the parties hereto agrees to join in the
execution, in recordable form, of a statutory notice of lease and/or written
declaration in which shall be stated the Term Commencement Date, the Rent
Commencement Date, and (if need be) the Expiration Date, which notice of lease
may be recorded by Tenant with the Middlesex South Registry of Deeds and the
Registry District of the Land Court (collectively, the "REGISTRY") at Tenant's
sole cost and expense. Upon the expiration or earlier termination of this Lease,
Landlord shall deliver to Tenant a notice of termination of lease acknowledging
the termination of the Lease and Tenant shall promptly execute and deliver the
same to Landlord for Landlord's execution and recordation with the Registry. If
Tenant fails to deliver the executed notice of termination of lease within ten
(10) days of receipt thereof, Landlord may execute same on Tenant's behalf,
Tenant hereby appointing Landlord as Tenant's attorney-in-fact to execute the
same under the foregoing circumstances.

4.   CONSTRUCTION

     4.1    LANDLORD'S WORK.

            (a)  BASE BUILDING. Landlord has completed the base building shell
for the Building as of the date hereof. Accordingly, Landlord shall endeavor to
deliver the base building to Tenant on or about the Estimated Delivery Date.

            (b)  LABORATORY BASE BUILDING. Landlord, at Landlord's sole cost and
expense, shall perform the laboratory base building work specified in Section
4.1(c) below (collectively, "LANDLORD'S WORK"). Subject to delays due to
governmental regulation, unusual scarcity of or inability to obtain labor or
materials, labor difficulties, casualty or other causes reasonably beyond
Landlord's control (collectively "LANDLORD'S FORCE MAJEURE") and subject to any
Tenant Delay (hereinafter defined), Landlord shall use reasonable speed and
diligence in the construction of Landlord's Work so as to have Landlord's Work
Substantially Completed on or before the Outside Delivery Date, but Tenant shall
have no claim against Landlord for failure to complete construction of
Landlord's Work, except as expressly set forth in Section 4.1(f) below.

            (c)  SUBSTANTIAL COMPLETION. The Laboratory Base Building shall be
deemed "SUBSTANTIALLY COMPLETE" upon construction of the following items of
Landlord's Work with respect to each floor delivered:

                 (i)     Additional electrical service to the Building and to
                         the Premises in order to provide 25 watts psf to the
                         Premises;
                 (ii)    Installation of additional water and gas service to the
                         Building;
                 (iii)   Installation of gas-powered heating, ventilation and
                         air conditioning

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                         infrastructure sized to accommodate laboratory use
                         based upon a ratio of 60% laboratory and 40% office
                         use,
                 (iv)    Installation of new water distribution system providing
                         increased volume of cold water to all floors of the
                         Building; and
                 (v)     Other items specified in the column entitled
                         "Shell/Core" in the Responsibilities Matrix attached
                         hereto as EXHIBIT 4 and more particularly specified in
                         the coordinated drawings showing the coordination of
                         shafts to be finalized by Landlord's architect and
                         provided to Tenant's architect subsequent to the
                         signing of this Lease which will be based on Landlord's
                         permit and pricing drawings set entitled "300 Tech
                         Square Penthouse Upgrade Permit Set" dated June 7, 2001
                         prepared by Tsoi/Kobus and Associates and any other
                         items necessary for Landlord to permit use of the
                         Premises as a laboratory facility (collectively, the
                         "LABORATORY BASE BUILDING SPECIFICATIONS").

            (d)  TENANT DELAY. A "TENANT DELAY" shall be defined as any act or
omission by any of the Tenant Parties (hereinafter defined) which causes an
actual delay in the performance of Landlord's Work. Notwithstanding the
foregoing, no event shall be deemed to be a Tenant Delay until and unless
Landlord has given Tenant written notice (the "TENANT DELAY NOTICE") advising
Tenant: (i) that a Tenant Delay is occurring, (ii) of the basis on which
Landlord has determined that a Tenant Delay is occurring, and (iii) the actions
which Landlord believes that Tenant must take to eliminate such Tenant Delay,
and Tenant has failed to correct the Tenant Delay specified in the Tenant Delay
Notice within twenty-four (24) hours following receipt thereof. No period of
time prior to the expiration of such 24-hour period shall be included in the
period of time charged to Tenant pursuant to such Tenant Delay Notice.

            (e)  LANDLORD DELAY. A "LANDLORD DELAY" shall be defined as any act
or omission by Landlord or any agent, employee, consultant, contractor or
subcontractor of Landlord which (i) is not a result of the priority granted to
Landlord's Work as set forth in Section 4.2(d) below, and (ii) causes an actual
delay in the performance of Tenant's Work. Notwithstanding the foregoing, no
event shall be deemed to be a Landlord Delay until and unless Tenant has given
Landlord written notice (the "LANDLORD DELAY NOTICE") advising Landlord (i) that
a Landlord Delay is occurring, (ii) of the basis on which Tenant has determined
that a Landlord Delay is occurring, and (iii) the actions which Tenant believes
that Landlord must take to eliminate such Landlord Delay, and Landlord has
failed to correct the Landlord Delay specified in the Landlord Delay Notice
within twenty-four (24) hours following receipt thereof. No period of time prior
to expiration of such 24-hour period shall be included in the period of time
charged to Landlord pursuant to such Landlord Delay Notice.

            (f)  DELAY IN RENT COMMENCEMENT. If Landlord's Work is not
substantially complete on or before the Outside Delivery Date, the Rent
Commencement Date shall be delayed one day for each day after the Outside
Delivery Date that Landlord's Work is not substantially complete unless such
delay is as a direct result of a Tenant Delay. The remedies set forth in this
Article 4.1(f) are Tenant's sole and exclusive rights and remedies based upon
any delay in the performance of Landlord's Work.

            (g)  FREIGHT ELEVATOR. Landlord, at Landlord's sole cost and
expense, shall install a freight elevator for the sole purpose of lifting
freight, equipment, animals and other deliveries of goods and materials and not
also used for passengers (the "FREIGHT ELEVATOR") for use by all tenants of the
Building, including Tenant. Landlord shall use commercially reasonable efforts
to have the Freight Elevator installed and operational by the Rent Commencement
Date, however Landlord shall not be penalized for failing to do so. Use of the
Freight Elevator by tenants of the Building shall be subject to Landlord's
reasonable rules and restrictions with respect thereto.

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            (h)  LANDLORD'S WARRANTY; SATISFACTION OF LANDLORD'S OBLIGATIONS

                 (i)     LANDLORD'S WARRANTY. Landlord warrants to Tenant that
(A) materials and equipment furnished in the performance of Landlord's Work will
be of good quality and new unless otherwise required or permitted by the
Laboratory Base Building Specifications, and (B) Landlord's Work will be free
from defects not inherent in the quality required or permitted under the
Laboratory Base Building Specifications. Any portion of Landlord's Work not
conforming to the foregoing requirements, including substitutions not properly
approved and authorized, may be considered defective. Landlord's warranty
excludes remedy for damage or defect caused by abuse, modifications not executed
by Landlord, improper or insufficient maintenance (other than by Landlord, where
Landlord is required to perform maintenance on the item or system in question),
improper operation (other than by Landlord, where Landlord operates the item or
system in question), or normal wear and tear and normal usage.

                 (ii)    WARRANTY PERIOD. Landlord shall be deemed to have
satisfied all of its obligations under this Article 4 (including, without
limitation, Landlord's warranty obligations under this Section 4.1(h)) except to
the extent that, on or before the date which is three hundred fifty eight (358)
days after the Rent Commencement Date (the "WARRANTY EXPIRATION DATE"), TIME
BEING OF THE ESSENCE, Tenant gives written notice to Landlord in accordance with
the provisions of Article 27 below setting forth with specificity the manner in
which Tenant believes that Landlord has failed to comply with its obligations
under this Article 4.

                 (iii)   REPAIR OF DEFECTIVE WORK. Landlord agrees that it
shall, without cost to Tenant, correct any portion of Landlord's Work which is
found not to be in accordance with the requirements of the warranties set forth
in this Section 4.1(h), unless Tenant has previously given Landlord express
written acceptance of such condition, provided that Tenant gives Landlord
written notice of such condition in accordance with the provisions of Article 27
below promptly after it becomes aware of such condition, and in any event on or
before the Warranty Expiration Date.

            (i)  PUNCHLIST. Promptly following delivery of the Premises to
Tenant with Landlord's Work with respect thereto substantially complete,
Landlord, Tenant, their respective architects and representatives shall inspect
the Premises and mutually prepare a list (the "PUNCHLIST") of outstanding items
which need to be completed to make Landlord's Work comply with the Laboratory
Base Building Specifications ("PUNCHLIST ITEMS"). Landlord shall use good faith
diligent efforts to complete all Punchlist Items within sixty (60) days of the
date of the Punchlist. If Landlord fails to complete any Punchlist Items as a
result of an event of Landlord's Force Majeure, Landlord shall have such
additional time as is reasonably necessary to procure and/or complete the
delayed Punchlist Items.

            (j)  TENANT'S TERMINATION RIGHT. If Landlord's Work is not
substantially complete on or before NOVEMBER 1, 2002, then Tenant may terminate
this Lease by providing written notice of such intent within thirty (30) days
after such date; provided, however, that if Landlord's Work is substantially
completed within said 30-day period, such termination notice shall be null and
void and the Lease shall continue in full force and effect.

     4.2    TENANT'S WORK.

            (a)  TENANT'S PLANS. (i) In connection with the performance of the
work necessary to prepare the 4th Floor Premises for Tenant's occupancy (the
"4TH FLOOR WORK"), Tenant shall submit to Landlord for Landlord's approval (A)
the name of and other reasonably requested information regarding Tenant's
proposed architect and HVAC and MEP engineers; (B) on or before the 4th Floor
Design/Development Plans Delivery Date, a set of design/development plans
sufficient for Landlord to

                                TOLERRX LEASE / BUILDING 300 / EXECUTION VERSION

                                       -8-
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approve Tenant's proposed design of the 4th Floor Premises (the "4TH FLOOR
DESIGN/DEVELOPMENT PLANS"), (C) on or before the 4th Floor Permit Plans Delivery
Date, an initial set of permit plans sufficient to permit Tenant to commence the
4th Floor Work ("4TH FLOOR PERMIT PLANS"), and (D) on or before the 4th Floor
Final Construction Drawings Delivery Date, a full set of construction drawings
("4TH FLOOR FINAL CONSTRUCTION DRAWINGS") for the 4th Floor Work. The 4th Floor
Design/Development Plans, the 4th Floor Permit Plans and the 4th Floor Final
Construction Drawings are collectively referred to herein as the "4th FLOOR
PLANS." Landlord's approval of the 4th Floor Design/Development Plans and the
4th Floor Permit Plans (and the 4th Floor Final Construction Drawings, provided
that the 4th Floor Final Construction Drawings are consistent with the 4th Floor
Permit Plans), shall not be unreasonably withheld, conditioned or delayed
provided the same comply with the requirements to avoid aesthetic or other
conflicts with the design and function of the balance of the Building and the
Condominium. Landlord's approval is solely given for the benefit of Landlord
under this Section 4.2 and neither Tenant nor any third party shall have the
right to rely upon Landlord's approval of the 4th Floor Plans for any other
purpose whatsoever. Without limiting the foregoing, Tenant shall be responsible
for all elements of the design of the 4th Floor Plans (including, without
limitation, compliance with Legal Requirements, functionality of design, the
structural integrity of the design, the configuration of the 4th Floor Premises
and the placement of Tenant's furniture, appliances and equipment), and
Landlord's approval of the 4th Floor Plans shall in no event relieve Tenant of
the responsibility therefor. Landlord agrees to respond to any request for
approval of the 4th Floor Design/Development Plans within ten (10) days of
receipt thereof, the 4th Floor Permit Plans within fifteen (15) days of receipt
thereof and the 4th Floor Final Construction Drawings within fifteen (15) days
of receipt thereof.

                 (ii)    In connection with the performance of the work
necessary to prepare the 3rd Floor Premises for Tenant's occupancy (the "3RD
FLOOR WORK"), Tenant shall submit to Landlord for Landlord's approval (A) the
name of and other reasonably requested information regarding Tenant's proposed
architect and HVAC and MEP engineers; (B) on or before the 3rd Floor
Design/Development Plans Delivery Date, a set of design/development plans
sufficient for Landlord to approve Tenant's proposed design of the 3rd Floor
Premises (the "3RD FLOOR DESIGN/DEVELOPMENT PLANS"), (C) on or before the 3rd
Floor Permit Plans Delivery Date, an initial set of permit plans sufficient to
permit Tenant to commence the 3rd Floor Work ("3RD FLOOR PERMIT PLANS"), and (D)
on or before the 3rd Floor Final Construction Drawings Delivery Date, a full set
of construction drawings ("3RD FLOOR FINAL CONSTRUCTION DRAWINGS") for the 3rd
Floor Work. The 3rd Floor Design/Development Plans, the 3rd Floor Permit Plans
and the 3rd Floor Final Construction Drawings are collectively referred to
herein as the "3RD FLOOR PLANS." Landlord's approval of the 3rd Floor
Design/Development Plans and the 3rd Floor Permit Plans (and the 3rd Floor Final
Construction Drawings, provided that the 3rd Floor Final Construction Drawings
are consistent with the 3rd Floor Permit Plans), shall not be unreasonably
withheld, conditioned or delayed provided the same (1) comply with the
requirements to avoid aesthetic or other conflicts with the design and function
of the balance of the Building and the Condominium, and (2) are compatible with
the design and function of the 4th Floor Premises. Landlord's approval is solely
given for the benefit of Landlord under this Section 4.2 and neither Tenant nor
any third party shall have the right to rely upon Landlord's approval of the 3rd
Floor Plans for any other purpose whatsoever. Without limiting the foregoing,
Tenant shall be responsible for all elements of the design of the 3rd Floor
Plans (including, without limitation, compliance with Legal Requirements,
functionality of design, the structural integrity of the design, the
configuration of the 3rd Floor Premises and the placement of Tenant's furniture,
appliances and equipment), and Landlord's approval of the 3rd Floor Plans shall
in no event relieve Tenant of the responsibility therefor. Landlord agrees to
respond to any request for approval of the 3rd Floor Design/Development Plans
within ten (10) days of receipt thereof, the 3rd Floor Permit Plans within
fifteen (15) days of receipt thereof and the 3rd Floor Final Construction
Drawings within fifteen (15) days of receipt thereof.

                                TOLERRX LEASE / BUILDING 300 / EXECUTION VERSION

                                       -9-
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                 (iii)   The 4th Floor Work and the 3rd Floor Work are
hereinafter collectively referred to as "TENANT'S WORK."

            (b)  COMMENCEMENT OF TENANT'S WORK. (i) Tenant shall, on or before
the Outside 4th Floor Work Commencement Date, commence the performance of the
4th Floor Work, and Tenant shall thereafter diligently prosecute the 4th Floor
Work to completion. The "OUTSIDE 4TH FLOOR WORK COMMENCEMENT DATE" shall be
defined as the date that is ninety (90) days after the Term Commencement Date,
provided that if Tenant is delayed in the commencement of the 4th Floor Work by
reason of a Landlord Delay or other causes beyond Tenant's reasonable control,
the Outside 4th Floor Work Commencement Date shall be extended by the lesser of
(i) the period of time which Tenant is so delayed, or (ii) ninety (90)
additional days (i.e. in no event shall the Outside 4th Floor Work Commencement
Date occur later than one hundred eighty (180) days after the Term Commencement
Date).

                 (ii)    Tenant shall, on or before the Outside 3rd Floor Work
Commencement Date, commence the performance of the 3rd Floor Work, and Tenant
shall thereafter diligently prosecute the 3rd Floor Work to completion. The
"OUTSIDE 3RD FLOOR WORK COMMENCEMENT DATE" shall be defined as the date that is
two (2) years after the Term Commencement Date, provided that if Tenant is
delayed in the commencement of the 3rd Floor Work by reason of a Landlord Delay
or other causes beyond Tenant's reasonable control, the Outside 3rd Floor Work
Commencement Date shall be extended by the lesser of (i) the period of time
which Tenant is so delayed, or (ii) ninety (90) additional days (i.e. in no
event shall the Outside 3rd Floor Work Commencement Date occur later than
twenty-seven (27) months after the Term Commencement Date).

            (c)  COMPLETION OF TENANT'S WORK. (i)    Tenant shall substantially
complete the 4th Floor Work on or before the date which is six (6) months after
the Rent Commencement Date (the "OUTSIDE 4TH FLOOR WORK COMPLETION DATE"),
provided that if Tenant is delayed in the performance of the 4th Floor Work by
reason of a Landlord Delay or other causes beyond Tenant's reasonable control,
the Outside 4th Floor Work Completion Date shall be extended by the lesser of
(i) the period of time which Tenant is so delayed, or (ii) three (3) additional
months (i.e. in no event shall the Outside 4th Floor Work Completion Date occur
later than the date which is nine (9) months after the Rent Commencement Date).

                 (ii)    Tenant shall substantially complete the 3rd Floor Work
on or before the date which is thirty (30) months after the Rent Commencement
Date (the "OUTSIDE 3RD FLOOR WORK COMPLETION DATE"), provided that if Tenant is
delayed in the performance of the 3rd Floor Work by reason of a Landlord Delay
or other causes beyond Tenant's reasonable control, the Outside 3rd Floor Work
Completion Date shall be extended by the lesser of (i) the period of time which
Tenant is so delayed, or (ii) three (3) additional months (i.e. in no event
shall the Outside 3rd Floor Work Completion Date occur later than the date which
is thirty-three(33) months after the Rent Commencement Date).

            (d)  COST OF TENANT'S WORK; PRIORITY OF WORK. Except for Landlord's
Contribution, as set forth in Section 4.3 below, all of Tenant's Work shall be
performed at Tenant's sole cost and expense, and shall be performed in
accordance with the provisions of this Lease (including, without limitation,
Article 13). Tenant and Landlord shall each take reasonably necessary measures
to maintain harmonious labor relations and to ensure that Tenant's contractors
and Landlord's contractors cooperate in all commercially reasonable ways with
each other to avoid any delay in either Landlord's Work or Tenant's Work or any
conflict with the performance of either Landlord's Work or Tenant's Work, Tenant
acknowledging, however, that in the case of conflict that is not reasonably
avoidable, the performance of Landlord's Work shall have priority. Tenant shall
pay to Landlord, as additional rent,

                                TOLERRX LEASE / BUILDING 300 / EXECUTION VERSION

                                      -10-
<Page>

within ten (10) days after demand therefor, any costs or expenses incurred by
Landlord (which shall be reasonably based on Tenant's usage) for the use of
elevators, including, without limitation, the Freight Elevator, and/or hoisting
in connection with the performance of Tenant's Work. Landlord and Tenant
recognize that to the extent Tenant elects to perform some or all of Tenant's
Work during times other than normal construction hours (i.e., Monday-Friday,
7 a.m. to 3 p.m., excluding holidays), Landlord will need to make arrangements
to have supervisory personnel on site. Accordingly, Landlord and Tenant agree as
follows: Tenant shall give Landlord at least forty-eight (48) hours' notice of
any time outside of normal construction hours when Tenant intends to perform
portions of Tenant's Work (the "AFTER-HOURS WORK"). Tenant shall reimburse
Landlord, within thirty (30) days after demand therefor, for the cost of
Landlord's supervisory personnel overseeing the After Hours Work. Landlord shall
notify Tenant of the hourly rates (which shall be normal and customary) for such
after-hours supervisory personnel from time to time upon written request. In
addition, if construction during normal construction hours unreasonably disturbs
other tenants of the Building or the Condominium, in Landlord's sole discretion,
Landlord may require Tenant to stop performance of Tenant's Work during normal
construction hours and to perform the same after normal construction hours,
subject to the foregoing requirement to pay for the cost of Landlord's
supervisory personnel.

     4.3    LANDLORD'S CONTRIBUTION.

            (a)  AMOUNT. As an inducement to Tenant's entering into the Lease,
Landlord shall provide to Tenant a special tenant improvement allowance equal to
up to Seventy Five and 00/100 Dollars ($75.00) per rentable square foot of the
Premises demised to Tenant (i.e. a maximum of Two Million Eight Hundred
Twenty-Three Thousand Two Hundred Twenty Five and No/100 ($2,823,225.00)
("LANDLORD'S CONTRIBUTION") to be used by Tenant to pay for the cost to
construct Tenant's Work, including all associated wiring and cabling costs. For
the purposes hereof, the cost to be so reimbursed by Landlord shall not include:
(i) the cost of any of Tenant's personal property which will be removed at the
end of the term hereof, telecommunications and computer equipment, any
decorations and artwork, de-mountable partitions, signs, and trade fixtures,
(ii) any fees paid to Tenant, any Affiliated Entity or Successor, or (iii) any
so-called "soft costs." Furthermore, in the event that Tenant does not build out
all of the Premises on or before the Outside Requisition Date (hereinafter
defined), Landlord's Contribution shall be limited to a maximum of Seventy-Five
and 00/100 Dollars ($75.00) per rentable square foot of the Premises actually
built out by Tenant as of the Outside Requisition Date.

            (b)  REQUISITIONS. Landlord shall pay Landlord's Proportion
(hereinafter defined) of the cost shown on each requisition (hereinafter
defined) submitted by Tenant to Landlord within thirty (30) days of submission
thereof by Tenant to Landlord until the entirety of Landlord's Contribution has
been exhausted. "LANDLORD'S PROPORTION" shall be a fraction, the numerator of
which is Landlord's Contribution and the denominator of which is the total
contract price for the applicable portion of Tenant's Work. A "REQUISITION"
shall mean written documentation (including, without limitation, invoices from
Tenant's contractors, vendors, service providers and consultants (collectively,
"CONTRACTORS") and partial lien waivers and subordinations of lien, as specified
in M.G.L. Chapter 254, Section 32 ("LIEN WAIVERS") with respect to the prior
month's requisition, and such other documentation as Landlord or any Mortgagee
may reasonably request) showing in reasonable detail the costs of the item in
question or of the improvements installed to date in the Premises, accompanied
by certifications from Tenant that the amount of the requisition in question
does not exceed the cost of the items, services and work covered by such
requisition. Each requisition shall be accompanied by evidence reasonably
satisfactory to Landlord, including without limitation Lien Waivers, that items,
services and work covered by the prior requisition have been fully paid by
Tenant and that the work has been performed. Notwithstanding the foregoing, with
respect to the first requisition for Landlord's Contribution, Tenant shall not
be required to deliver Lien Waivers at the time of the requisition, but shall
deliver the Lien

                                TOLERRX LEASE / BUILDING 300 / EXECUTION VERSION

                                      -11-
<Page>

Waivers and evidence of payment of the requisition in full within five (5) days
following payment of Landlord's Contribution with respect to such first
requisition. Landlord shall have the right, upon reasonable advance notice to
Tenant, to inspect Tenant's books and records relating to each requisition in
order to verify the amount thereof. Tenant shall submit requisition(s) no more
often than monthly.

            (c)  Notwithstanding anything to the contrary herein contained: (i)
Landlord shall have no obligation to advance funds on account of Landlord's
Contribution more than once per month; (ii) If Tenant fails to pay the amounts
paid by Landlord to Tenant in the prior month's requisition to Tenant's
Contractors, Landlord shall thereafter have the right to have Landlord's
Contribution paid directly to Tenant's Contractors; (iii) Landlord shall have no
obligation to pay any portion of Landlord's Contribution with respect to any
requisition submitted after the date (the "OUTSIDE REQUISITION DATE") which is
the earlier of: (A) three (3) months after the completion of all of Tenant's
Work, or (B) thirty-three (33) months after the Rent Commencement Date;
provided, however, that if Tenant certifies to Landlord that it is engaged in a
good faith dispute with any Contractor, such Outside Requisition Date shall be
extended while such dispute is ongoing, so long as Tenant is diligently
prosecuting the resolution of such dispute; (iv) Landlord's obligation to pay
any portion of Landlord's Contribution shall be conditioned upon there existing
no default by Tenant in its obligations under the Lease at the time that
Landlord would otherwise be required to make such payment; and (v) In addition
to all other requirements hereof, Landlord's obligation to pay the final
requisition of Landlord's Contribution shall be subject to simultaneous delivery
of all Lien Waivers relating to items, services and work performed in connection
with all phases or portions of Tenant's Work.

            (d)  In the event that there remains any unused portion of
Landlord's Contribution after the Outside Requisition Date, Tenant shall receive
a credit against subsequent monthly payments of Yearly Rent in the amount of up
to Ten Dollars ($10) per rentable square foot of such unused portion, amortized
over the term hereof at the rate of ten percent (10%) per annum up to a maximum
of $1.59 per rentable square foot per year.

     4.4    EQUIPMENT ALLOWANCE. (a)    As an inducement to Tenant's entering
into the Lease, Landlord shall provide to Tenant a special tenant equipment
allowance equal to Two Hundred Sixty-Nine Thousand Six Hundred Twenty Seven and
29/100 Dollars ($269,627.29) (the "EQUIPMENT ALLOWANCE") to be used by Tenant to
pay for the reasonable cost of the acquisition of the equipment listed on
EXHIBIT 12 attached hereto (the "EQUIPMENT").

            (b)  Within thirty (30) days of receipt, Landlord shall pay to
Tenant, or at Tenant's written request, directly to the provider thereof, the
reasonable cost of the Equipment as shown on a reasonably detailed invoice
therefor.

            (c)  Tenant hereby grants to Landlord a security interest in all of
the Equipment, and the Equipment shall not be removed from the Premises at any
time during or at the end of the term hereof. Upon the occurrence of an Event of
Default, Landlord may, in addition to all other remedies, without notice or
demand except as provided below, exercise the rights afforded to a secured party
under the Uniform Commercial Code of the state in which the Premises are located
(the "UCC"). To the extent the UCC requires Landlord to give to Tenant notice of
any act or event and such notice cannot be validly waived before a default
occurs, then five (5) days' prior written notice thereof shall be reasonable
notice of the act or event. In order to perfect such security interest, Landlord
may file any financing statement or other instrument necessary at Tenant's
expense at the state and county Uniform Commercial Code filing offices. Within
ten (10) days following written request therefor, Tenant shall execute financing
statements to be filed of record to perfect Landlord's security interest in the
Equipment. Provided that Tenant has paid all sums due to Landlord under this
Section 4.4, and provided further that there is no

                                TOLERRX LEASE / BUILDING 300 / EXECUTION VERSION

                                      -12-
<Page>

Event of Default or event which, with the passage of time and/or the giving of
notice would constitute an Event of Default at the time of Tenant's request
therefor, upon written request by Tenant, Landlord shall file UCC termination
statements.

            (d)  Notwithstanding anything to the contrary contained herein, (i)
Landlord shall have no obligation to advance funds on account of the Equipment
Allowance more than once per month; (ii) Landlord shall have no obligation to
pay any portion of the Equipment Allowance with respect to any invoice submitted
in accordance with Section 4.4(a) above after the date (the "OUTSIDE SUBMISSION
DATE") which is three (3) months after the Outside 4th Floor Completion Date;
and (iii) Landlord's obligation to pay any portion of the Equipment Allowance
shall be conditioned upon there existing no Event of Default or event which with
the giving of notice and/or the passage of time would constitute an Event of
Default at the time that Landlord would otherwise be required to make such
payment.

            (e)  Commencing on the first day of the calendar month following the
Outside Submission Date, Tenant shall pay to Landlord as additional rent the
total amount furnished by Landlord under the Equipment Allowance in equal
monthly installments, calculated by utilizing straight-line amortization over a
three-year term and assuming an interest rate of ten percent (10%) per annum.

     4.5    DISPUTE RESOLUTION. Any dispute between the parties with respect to
the provisions of this Article 4 shall be resolved in accordance with the
procedures set forth in Article 28 hereof.

5.   USE OF PREMISES

     5.1    PERMITTED USE. Tenant shall during the term hereof use the Premises
only for the Permitted Uses and for no other purposes. Service and utility areas
(whether or not a part of the Premises) shall be used only for the particular
purpose for which they designed.

     5.2    PROHIBITED USES.

            (a)  Notwithstanding any other provision of this Lease, Tenant shall
not use, or suffer or permit the use or occupancy of the Premises or the
Building or any part thereof (i) in a manner which would violate any of the
covenants, agreements, terms, provisions and conditions of this Lease or any
other agreement or instrument of record of which Tenant has received notice;
(ii) for any unlawful purposes or in any unlawful manner; (iii) which, in the
reasonable judgment of Landlord (taking into account the use of the Building as
a combination office and laboratory facility and the Permitted Uses) shall (a)
impair, interfere with or otherwise diminish the quality of any of the Building
services or the proper and economic heating, cleaning, ventilating, air
conditioning or other servicing of the Building or Premises, or the use or
occupancy of any of the common areas of the Building or Condominium; or (b)
occasion discomfort, inconvenience or annoyance in any material respect (and
Tenant shall not install or use any electrical or other equipment of any kind,
including without limitation, Tenant's Rooftop Equipment, which, in the
reasonable judgment of Landlord, will cause any such impairment, interference,
discomfort, inconvenience, annoyance or injury), or cause any injury or damage
to any occupants of the Premises or other tenants or occupants of the Building
or their property; (iv) which is inconsistent with the operation of the Building
as a combination office, research, development and laboratory facility of the
first class in the quality of its maintenance, use, or occupancy; (v) for any
fermentation processes whatsoever other than closed vessel or vented
fermentation processes approved by Landlord in writing in advance; (vi) for the
preparation, cooking or serving of any food except for microwaves and toasters
used in a standard employee lunchroom; (vii) in a manner which shall increase
such insurance rates on the Building or the Condominium or on property located
therein over that applicable when Tenant first took occupancy of the Premises
hereunder; or (viii) in violation of any exclusive use granted to any Existing

                                TOLERRX LEASE / BUILDING 300 / EXECUTION VERSION

                                      -13-
<Page>

Tenant (hereinafter defined) as more particularly set forth on EXHIBIT 5
attached hereto.

            (b)  With respect to the use and occupancy of the Premises and the
common areas of the Condominium, Tenant will not: (i) place or maintain any
signage, trash, refuse or other articles in any vestibule or entry of the
Premises, on the footwalks or corridors adjacent thereto or elsewhere on the
exterior of the Premises, nor obstruct any driveway, corridor, footwalk, parking
area, mall or any other common areas of the Building or Condominium; (ii) permit
undue accumulations of or burn garbage, trash, rubbish or other refuse within or
without the Premises; (iii) permit the parking of vehicles so as to interfere
with the use of any driveway, corridor, footwalk, parking area, or other common
areas of the Condominium; (iv) receive or ship articles of any kind outside the
designated loading areas for the Building; (v) conduct or permit to be conducted
any auction, going out of business sale, bankruptcy sale (unless directed by
court order), or other similar type sale in or connected with the Premises; (vi)
use the name of the Building, Landlord, or any of Landlord's affiliates or
subsidiaries or any photograph, film, drawing, or other depiction or
representation of the Building, the Condominium or any part thereof, which
contains signage or distinctive architectural characteristics that cause the
scene photographed, filmed, drawn, depicted, or represented to be identifiable
as being the Building or the Condominium, in any publicity, promotion, trailer,
press release, advertising, printed, or display materials without Landlord's
prior written consent; (vii) cause or permit any hole to be drilled or made in
any part of the Building; and (viii) violate the provision of Section 14.4
below.

     5.3    LICENSES AND PERMITS. If any governmental license or permit shall be
required for the proper and lawful conduct of Tenant's business and/or Tenant's
Rooftop Equipment, Tenant, at Tenant's expense, shall duly procure and
thereafter maintain such license and submit the same to inspection by Landlord.
Tenant, at Tenant's expense, shall at all times comply with the terms and
conditions of each such license or permit. Tenant shall furnish all data and
information to governmental authorities, with a copy to Landlord, as required in
accordance with Legal Requirements as they relate to Tenant's use or occupancy
of the Premises or the Building. Landlord shall cooperate with Tenant, at
Tenant's sole cost and expense, in connection with its application for any
required licenses, permits and approvals for the Permitted Uses.

     5.4    DUE CARE.    Tenant shall use reasonable care in connection with the
use of any materials, appliances or equipment (including, without limitation,
those selected by Tenant for the construction or other preparation of the
Premises and furniture and carpeting) so as not to pose any danger to life,
safety or health or cause damage, injury or death.

6.   RENT

     6.1    YEARLY RENT. During the term hereof, Tenant shall pay to Landlord
the Yearly Rent, additional rent and other charges in equal monthly
installments, in advance and without demand on the first day of each month for
and in respect of such month. Unless otherwise expressly provided herein, the
payment of Yearly Rent, additional rent and other charges reserved and
covenanted to be paid under the Lease in respect of the Premises (collectively,
"RENT") shall commence on the Rent Commencement Date. If the Rent Commencement
Date is on any day other than the first day of a calendar month, Rent for such
calendar month shall be prorated accordingly. Rent shall be payable to Landlord
or, if Landlord shall so direct in writing, to Landlord's agent or nominee, in
lawful money of the United States which shall be legal tender for payment of all
debts and dues, public and private, at the time of payment, at the office of
Landlord set forth in EXHIBIT 1 or such other place as Landlord may designate in
writing, and Rent in all circumstances shall be payable without any setoff or
deduction whatsoever.

     6.2    WARRANTS. Upon execution hereof, Tenant shall deliver to Landlord
warrants in the

                                TOLERRX LEASE / BUILDING 300 / EXECUTION VERSION

                                      -14-
<Page>

form attached hereto as EXHIBIT 6 to purchase 100,000 shares of Tenant stock at
its Series B strike price.

     6.3    LATE PAYMENTS.

            (a)  Any payment of Rent due hereunder not paid within five (5) days
of the date due shall bear interest for each month or fraction thereof from the
6th day after the due date until paid in full at the annual rate of five (5)
percentage points over the so-called prime rate charged from time to time by
Fleet National Bank, or its successor national bank, or at any applicable lesser
maximum legally permissible rate for debts of this nature (the "DEFAULT RATE").

            (b)  Additionally, if Tenant fails to make any payment within ten
(10) days of the date due hereunder, Landlord may charge Tenant a fee equal to
five percent (5%) of the delinquent payment to reimburse Landlord for its cost
and inconvenience incurred as a consequence of Tenant's delinquency.

7.   RENTABLE AREA

     Landlord and Tenant acknowledge the total rentable square footage of the
Building and of the other buildings in the Condominium have been determined by
agreement, and that the figures set forth in EXHIBIT 1 shall be conclusive and
binding on Landlord and Tenant, except for the Premises and Building 100 which
shall be finally measured following construction thereof. The methodology for
measuring the Building and the Premises is set forth in EXHIBIT 7 attached
hereto.

8.   SERVICES FURNISHED BY LANDLORD

     8.1    ELECTRIC CURRENT.

            (a)  PRORATED CHARGES. Landlord shall have the right to charge
Tenant for its use of electricity in the Premises based upon one of two methods,
at Landlord's sole discretion. If Landlord elects to install and can feasibly
install separate checkmeters on a floor by floor basis, Landlord shall charge
Tenant for its share of electricity charges attributable to each floor of the
Building based upon the ratio of the rentable square footage in the portion of
the Premises on each floor to the total non-retail rentable square feet of space
on such floor ("FLOOR PERCENTAGE SHARE"). Tenant shall pay its Floor Percentage
Share of electricity charges attributable to such meter(s), as additional rent
hereunder, within ten (10) days of receipt of Landlord's invoice therefor.

            (b)  METERED CHARGES. Alternatively, Tenant may, at Tenant's
expense, furnish and install in a location approved by Landlord in or near the
Premises any necessary metering equipment approved by Landlord to be used in
connection with measuring Tenant's consumption of electric current in the
Premises, and Tenant, at Tenant's expense, shall maintain and keep in repair
such metering equipment. If the Premises are separately metered, Tenant shall
pay the full amount of any charges attributable to such meter on or before the
due date therefor either to Landlord or directly to the supplier thereof, at
Landlord's election.

            (c)  ROOFTOP ELECTRICITY. Landlord shall install a check meter to
measure the use of electricity by all equipment installed on the roof, including
Tenant's Rooftop Equipment. Landlord shall charge Tenant for its share of the
electricity charges attributable to the roof check meter based upon either (x)
the ratio of the number of hours of usage of Tenant's Rooftop Equipment to the
total hours of use shown on the check meter, or (y) the ratio of cubic feet per
minute ("CFM")'s requested by Tenant to total CFMs requested by other tenants of
the Building, at Landlord's election. Tenant shall pay its share of electricity
charges attributable to the roof check meter, as additional rent hereunder,
within ten (10) days of receipt of Landlord's invoice therefor.

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                                      -15-
<Page>

            (d)  ALLOCATION BY LANDLORD. Landlord shall have the right to
monitor the allocation of electricity charges to all tenants of the Building to
ensure that the allocation method is appropriately related to Tenant's actual
use of electricity within or in connection with the Premises. If the current
method of allocation is inaccurate, Landlord may change the method of
allocation, as necessary, to correct the disproportionate charges. In addition,
if Landlord determines in the course of its audit of the electricity charges
previously allocated that Tenant has underpaid charges properly due for its use
of electricity, Landlord shall invoice Tenant for the amounts due (together with
reasonable back-up documentation regarding the total charges and the method of
allocating the charges to Tenant) and Tenant shall pay such additional amount,
as additional rent hereunder, within ten (10) days of receipt of Landlord's
invoice therefor.

            (e)  ADDITIONAL ELECTRICITY REQUIREMENTS. If Tenant shall
subsequently require electric current for use in the Premises in excess of the
capacity set forth in the Final Construction Drawings and related specifications
approved by Landlord and if in Landlord's reasonable judgment, (i) Landlord's
facilities are inadequate for such excess requirements, or (ii) such excess use
shall result in an additional burden on the Building air conditioning systems
and additional cost to Landlord on account thereof then, as the case may be,
Landlord, upon written request and at the sole cost and expense of Tenant, will
furnish and install such additional wire, conduits, feeders, switchboards and
appurtenances as reasonably may be required to supply such additional
requirements of Tenant if current therefor is available to Landlord, provided
that the same (v) shall be permitted by Legal Requirements and insurance
regulations, (w) shall not cause damage to the Building or the Premises, (x)
shall not cause or create a dangerous or hazardous condition, (y) shall not
entail excessive or unreasonable alterations or repairs, and (z) shall not
interfere with or disturb other tenants or occupants of the Building. Tenant
shall reimburse Landlord for such additional cost within ten (10) days of demand
therefor.

            (f)  REPLACEMENT LAMPS/BULBS. Landlord, at Tenant's sole cost and
expense and upon Tenant's request, shall purchase and install all replacement
lamps of types generally commercially available (including, but not limited to,
incandescent and fluorescent) and used in the Premises. Tenant, at Tenant's sole
cost and expense, shall purchase and install all replacement bulbs used in the
Premises.

            (g)  INTERRUPTION OF ELECTRICAL SERVICE. Subject to Section 8.6(b)
below, Landlord shall not in any way be liable or responsible to Tenant for any
loss, damage or expense which Tenant may sustain or incur if the quantity,
character, or supply of electrical energy which Landlord agrees to furnish
hereunder subsequently becomes no longer available or suitable for Tenant's
requirements.

            (h)  ALTERATIONS TO ELECTRICAL EQUIPMENT. Tenant agrees that it will
not make any material alteration or material addition to the electrical
equipment and/or appliances in the Premises which would adversely affect any
base Building or laboratory base Building systems or equipment without the prior
written consent of Landlord in each instance, which consent will not be
unreasonably withheld, conditioned or delayed, and will promptly advise Landlord
of any other alteration or addition to such electrical equipment and/or
appliances.

     8.2    WATER. Landlord shall furnish hot and cold water for ordinary
cleaning, toilet, lavatory and drinking purposes with respect to the office
areas and ordinary laboratory use with respect to the laboratory areas. Landlord
shall install a separate water meter for the Building and shall allocate the
water meter charges, together with any sewer charges based on said meter
charges, among the tenants of the Building based upon estimated water usage, as
reasonably estimated by Landlord. Landlord shall provide Tenant with reasonable
back-up documentation regarding the total charges and the method of allocating
the charges to Tenant. Tenant shall pay to Landlord, as additional rent
hereunder, its allocated share of water charges within ten (10) days of demand
therefor.

                                TOLERRX LEASE / BUILDING 300 / EXECUTION VERSION

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     8.3    ELEVATORS, HEAT, AIR CONDITIONING, CLEANING.

            (a)  ELEVATORS. Landlord at its expense shall provide necessary
elevator facilities, including the Freight Elevator (which may be manually or
automatically operated, either or both, as Landlord may from time to time
elect), on Mondays through Fridays, excepting legal holidays, from 8:00 a.m. to
6:00 p.m. and on Saturdays, excepting legal holidays, from 8:00 a.m. to 1:00
p.m. (collectively, "BUSINESS HOURS") and have at least one passenger elevator
and one freight elevator in operation available for Tenant's non-exclusive use,
together with others having business in the Building, at all other times.

            (b)  HEAT. Landlord at its expense shall furnish heat (substantially
equivalent to that being furnished in comparably-aged, similarly-equipped
combination office/laboratory buildings in Cambridge, Massachusetts) to the
Premises during the normal heating season twenty-four (24) hours per day, seven
(7) days per week.

            (c)  AIR CONDITIONING. Landlord shall through the air conditioning
equipment of the Building furnish to and distribute in the Premises air
conditioning when air conditioning may reasonably be required for the
comfortable occupancy of the Premises by Tenant. Landlord shall also furnish a
separate but integrated gas-powered air conditioning system for the laboratory
areas of the Building. Whenever the air conditioning systems are in operation,
Tenant agrees to use reasonable efforts to lower and close the blinds or drapes
when necessary because of the sun's position, and to cooperate fully with
Landlord with regard to, and to abide by all the reasonable regulations and
requirements which Landlord may prescribe for the proper functioning and
protection of the air conditioning systems, provided Landlord first delivers a
copy of such regulations and requirements to Tenant.

            (d)  CLEANING. Landlord at its expense shall cause the common areas
of the Building to be cleaned Monday through Friday. Either EXHIBIT 8 (if
annexed hereto) or, otherwise, the cleaning standards generally prevailing in
first-class combination office/laboratory buildings in the City of Cambridge,
shall represent substantially the extent and scope of the cleaning by Landlord
referred to in this Section 8.3(d).

     8.4    ADDITIONAL AIR CONDITIONING EQUIPMENT. In the event Tenant requires
additional air conditioning other than as specified in the 4th Floor Final
Construction Drawings and/or the 3rd Floor Final Construction Drawings for
equipment, business machines, meeting rooms or other special purposes, or
because of occupancy, then any additional air conditioning units, chillers,
condensers, compressors, ducts, piping and other equipment will be installed by
Landlord or, at Landlord's election, by Tenant with Landlord's supervision, in
either case at Tenant's sole cost and expense, but only if, in Landlord's
reasonable judgment, the same will not (i) cause damage or injury to the
Building, (ii) create a dangerous or hazardous condition, or (iii) entail
excessive or unreasonable alterations, repairs or expense. Tenant shall
reimburse Landlord, as additional rent hereunder, for the cost incurred by
Landlord in installing, maintaining and operating such additional air
conditioning equipment and the charges for all utilities consumed thereby.

     8.5    REPAIRS. Except as otherwise provided in Article 18, and subject to
Tenant's obligations in Article 14, Landlord shall keep and maintain the roof,
exterior walls (except the interior surfaces thereof), structural floor slabs,
columns, elevators (including the Freight Elevator), public stairways,
corridors, lavatories, equipment installed by Landlord (including, without
limitation, all base building and laboratory base building systems, sanitary,
electrical, heating, air conditioning, plumbing, security or other systems) and
common facilities of the Building in good condition and repair. In addition,
Landlord shall operate and maintain the common areas of the Building and shall
cause the association of unit

                                TOLERRX LEASE / BUILDING 300 / EXECUTION VERSION

                                      -17-
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owners of the Condominium to operate and maintain the Condominium in
substantially the same manner as other first-class mixed use office/laboratory
facilities in the Kendall Square, Cambridge area.

     8.6    INTERRUPTION OR CURTAILMENT OF SERVICES.

            (a)  LANDLORD RIGHTS. When necessary by reason of accident or
emergency, or for repairs, alterations, replacements or improvements which in
the reasonable judgment of Landlord are desirable or necessary to be made,
Landlord reserves the right, upon as much prior notice to Tenant as is
practicable under the circumstances and no less than twenty-four (24) hours'
notice except in the event of an emergency, to interrupt, curtail, stop or
suspend (i) the furnishing of heating, elevator, air conditioning, and cleaning
services, and (ii) the operation of the plumbing and electric systems. Landlord
shall exercise reasonable diligence to eliminate the cause of any such
interruption, curtailment, stoppage or suspension, but, subject to Section
8.6(b) below, there shall be no diminution or abatement of Rent or other
compensation due from Landlord to Tenant hereunder, nor shall this Lease be
affected or any of Tenant's obligations hereunder reduced, and Landlord shall
have no responsibility or liability for any such interruption, curtailment,
stoppage, or suspension of services or systems.

            (b)  ABATEMENT. Notwithstanding anything to the contrary in this
Lease contained, if the Premises shall lack any service which Landlord is
required to provide hereunder, or if Tenant's use and occupancy of the Premises
shall be disturbed in violation of Article 22 hereof (thereby rendering the
Premises or a portion thereof substantially untenantable) such that, for the
duration of the Landlord Service Interruption Cure Period (hereinafter defined),
the continued operation in the ordinary course of Tenant's business is
materially and adversely affected, and if Tenant ceases to use the affected
portion of the Premises (the "AFFECTED PORTION") during the period of
untenantability as the direct result of such lack of service or disturbance,
then, provided that Tenant ceases to use the Affected Portion during the
entirety of the Landlord Service Interruption Cure Period and that such
untenantability and Landlord's inability to cure such condition is not caused by
the fault or neglect of Tenant, Tenant's agents, servants, employees,
consultants, contractors, subcontractors, licensees and/or subtenants
(collectively, the "TENANT PARTIES"), Yearly Rent, Building Operating Expenses
and Taxes shall thereafter be abated in proportion to such untenantability until
the day such condition is completely corrected. For purposes hereof, the
"LANDLORD SERVICE INTERRUPTION CURE PERIOD" shall be defined as fifteen (15)
consecutive business days after Landlord's receipt of written notice from Tenant
of the condition causing untenantability in the Affected Portion, provided
however, that the Landlord Service Interruption Cure Period shall be twenty five
(25) consecutive business days after Landlord's receipt of written notice from
Tenant of such condition causing untenantability in the Affected Portion if
either the condition was caused by causes beyond Landlord's control or Landlord
is unable to cure such condition as the result of causes beyond Landlord's
control. The provisions of this Section 8.6(b) shall not apply in the event of
untenantability caused by fire or other casualty, or Taking (hereinafter
defined), which shall be governed by Article 18 below.

     8.7    ENERGY CONSERVATION. Notwithstanding anything to the contrary
contained herein, Landlord may institute upon written notice to Tenant such
policies, programs and measures as may be necessary, required, or expedient for
the conservation and/or preservation of energy or energy services (collectively,
the "CONSERVATION PROGRAM"), provided however, subject to Legal Requirements,
that the Conservation Program does not, by reason of such policies, programs and
measures, reduce the level of energy or energy services being provided to the
Premises immediately prior to the institution of such policy, program and/or
measure. Upon receipt of such notice, Tenant shall comply with the Conservation
Program.

     8.8    PREMISES POPULATION. Other than air conditioning, all services
provided by Landlord to

                                TOLERRX LEASE / BUILDING 300 / EXECUTION VERSION

                                      -18-
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Tenant are based upon an assumed maximum Premises population of one person per
one hundred fifty (150) rentable square feet of the Premises, which limit Tenant
shall in no event exceed. Tenant acknowledges that if it exceeds the foregoing
limitation, Landlord may incur costs including, without limitation, additional
costs due to the additional load on building systems. Tenant agrees to reimburse
Landlord for the amount of such costs (if any), as reasonably determined by
Landlord, due to a Premises population in excess of the foregoing maximum.

     8.9    SECURITY. Landlord shall cause security personnel to be present at
the Condominium and the Parking Garage, and to inspect the exterior of the
Condominium buildings and the Common Areas thereof on a twenty-four (24) hour,
seven (7) days per week basis. The Parking Garage shall be equipped with
security cameras and emergency callboxes. As part of Landlord's Work, Landlord
shall install an electronic card access system at the Building entrance doors,
within the elevators and at the entrance to the Parking Garage. Notwithstanding
Landlord's obligation to provide security personnel and an electronic card
access system, Landlord shall not be liable for damage to property of Tenant in
the Premises or for injury to person unless such damage or injury is caused by
the negligence of Landlord, or the agents, employees, contractors,
subcontractors, invitees, licensees or other authorized representatives of
Landlord. Landlord will install a MAC security system for the Building and
Tenant shall have the right, at its sole cost and expense, to install its own
module for the Premises and connect same to the Building's security system.
Tenant shall be fully responsible for the cost of any repairs to the Building's
security system required as a result of the connection of Tenant's security
module thereto. Tenant, at Tenant's sole cost, expense and responsibility, may
install additional electronic card devices and systems within the Premises and
at the access points to the stairwells provided such devices and systems are
compatible with Landlord's electronic card access system.

9.   UTILITIES

     9.1    UTILITY SERVICES. In addition to Tenant's obligations under Sections
8.1 and 8.2 above and unless otherwise expressly provided herein, Tenant shall
obtain and pay for all other utilities and services, including without
limitation heat and air conditioning furnished to the Premises pursuant to
Article 8 above, consumed and/or furnished to the Premises, together with all
taxes, penalties, surcharges and maintenance charges pertaining thereto.
Landlord shall have the right to make any such payment if Tenant fails to do so
prior to delinquency, in which event Tenant shall reimburse Landlord for the
amount so paid upon demand therefor, together with interest at the Default Rate
until paid in full.

     9.2.   TELECOMMUNICATION PROVIDERS. Notwithstanding anything to the
contrary herein or in the Lease contained, Landlord has no obligation to allow
any particular telecommunication service provider to have access to the Building
or to Premises other than Verizon or Level 3 (collectively, the "APPROVED
PROVIDERS"). If Landlord permits such access, Landlord may condition such access
upon the payment to Landlord by Tenant or the service provider of any costs
incurred by Landlord in facilitating such access. Landlord's consent to
providing access to the Building to any service provider other than the Approved
Providers shall not be unreasonably withheld, conditioned or delayed provided
such access does not require any street opening permits or approvals (unless
otherwise agreed to by the City of Cambridge) or would unreasonably interfere
with the use of the common areas of the Condominium.

10.  OPERATING EXPENSES AND TAXES

     10.1   DEFINITIONS. As used in this Article 10, the words and terms which
follow shall have the meanings set forth below:

            (a)  "TAXES" shall mean the real estate taxes and other taxes,
levies and assessments

                                TOLERRX LEASE / BUILDING 300 / EXECUTION VERSION

                                      -19-
<Page>

imposed upon Unit 300 of the Condominium, and upon any personal property of
Landlord used in the operation of Unit 300, or on Landlord's interest in Unit
300 or such personal property (provided that to the extent such taxes, levies,
and assessments are still assessed against the Condominium as a whole, such
amounts shall be allocated among all Units comprising the Condominium based on
the assessor's records or, if the records do not provide a separate allocation,
based on square footage of the buildings in question unless Landlord reasonably
determines that such allocation should be made on another reasonable basis);
charges, fees and assessments for transit, housing, police, fire or other
services or purported benefits to Unit 300; service or user payments in lieu of
taxes; and any and all other taxes, levies, betterments, assessments and charges
arising from the ownership, leasing, operation, use or occupancy of Unit 300 or
based upon rentals derived therefrom, which are or shall be imposed by federal,
state, county, municipal or other governmental authorities. Taxes shall not
include any inheritance, estate, succession, gift, franchise, rental, income or
profit tax, capital stock tax, capital levy or excise, or any income taxes
arising out of or related to the ownership and operation of the Building or
Condominium, provided, however, that any of the same and any other tax, excise,
fee, levy, charge or assessment, however described, that may in the future be
levied or assessed as a substitute for or an addition to, in whole or in part,
any tax, levy or assessment which would otherwise constitute "Taxes," whether or
not now customary or in the contemplation of the parties on the Execution Date
of this Lease, shall constitute "Taxes," but only to the extent calculated as if
the Condominium were the only real estate owned by Landlord. "Taxes" shall also
include reasonable expenses (including without limitation legal and consultant
fees) of tax abatement or other proceedings contesting assessments or levies.

            (b)  "TAX PERIOD" shall be any fiscal/tax period in respect of which
Taxes are due and payable to the appropriate governmental taxing authority
(i.e., as mandated by the governmental taxing authority), any portion of which
period occurs during the term of this Lease, the first such Tax Period being the
one in which the Rent Commencement Date occurs.

            (c)  "OPERATING YEAR": shall mean a fiscal year in which occurs any
part of the term of this Lease.

            (d)  "BUILDING OPERATING COSTS" shall mean all costs incurred and
expenditures made by Landlord in the operation and management of the Building or
allocated to the Building, including, without limitation, any costs for
utilities supplied to the common areas of the Building, and any costs for repair
and replacements, cleaning and maintenance of the common areas of the Building,
including, without limitation, vehicular and pedestrian passageways serving the
Building, related equipment, facilities and appurtenances and cooling and
heating equipment. For costs and expenditures made by Landlord in connection
with the operation, management, repair, replacement, maintenance and insurance
of the Building as a whole, Landlord shall make a reasonable allocation thereof
between the retail and non-retail portions of the Building. A portion of
Condominium Operating Costs shall be included in Building Operating Costs in
accordance with Section 10.1(e). Building Operating Costs shall not include
Excluded Costs (hereinafter defined).

            (e)  "CONDOMINIUM OPERATING COSTS" shall mean all costs incurred and
expenditures made in the operation and management, repair, replacement,
cleaning, insurance and maintenance of the common areas of the Condominium,
exclusive of the Garage, the Building, and the other buildings in the
Condominium including without limitation a commercially reasonable management
fee paid to Landlord's property manager. To the extent that a cost included in
Condominium Operating Costs is also allocable to property other than the
Condominium, such cost shall be equitably allocated to each parcel of property
which benefits from such cost. The allocation of costs and expenditures among
the various buildings in the Condominium shall be on the basis of the ratio of
the total rentable square feet of each building in the Condominium to the total
rentable square feet of the Condominium, unless

                                TOLERRX LEASE / BUILDING 300 / EXECUTION VERSION

                                      -20-
<Page>

such allocation would result in a disproportionate charge (x) based upon the
manner in which any subsequent building in the Condominium is measured relative
to the manner in which the Building was measured, in which case the allocation
shall be made equitably among the buildings of the Condominium, or (y) based
upon the relative usage of the service on which such cost is based, in which
case such allocation shall be based upon such relative usage. Condominium
Operating Costs shall include, without limitation, the cost of operating any
appropriate amenities in the Condominium available to all tenants of the
Condominium, the costs of Landlord's management office for the Condominium and
any subsidy provided by Landlord for or with respect to any such amenity.

            (f)  "EXCLUDED COSTS" shall be defined as (i) any mortgage charges
(including interest, principal, points and fees); (ii) brokerage commissions;
(iii) salaries of executives, owners and employees above the grade of area
manager not directly employed in the management/operation of the Condominium;
(iv) the cost of work or services done or furnished by Landlord for a particular
tenant; (v) subject to Subsection 10.4 below, any capital expenditures or
capital improvements or such portion of any other expenditures which are not
properly chargeable against income; (vi) the costs of Landlord's Work and any
contributions made by Landlord to any tenant of the Condominium in connection
with the build-out of its premises; (vii) the cost of soil and groundwater
testing attributable to environmental conditions existing as of the date of this
Lease or caused by Landlord, its agents and employees or any tenant or occupant
of the Condominium; (viii) franchise or income taxes imposed on Landlord; (ix)
costs paid or payable directly by individual tenants to suppliers, including
tenant electricity, telephone and other utility costs; (x) the cost of any
repairs made by Landlord pursuant to Article 18 below; (xi) increases in
premiums for insurance when such increase is caused by the use of the Building
by Landlord or any other tenant of the Building; (xii) costs or taxes relating
to the ownership, operation, maintenance or repair of the Parking Garage, other
than as set forth in Section 2.4 of the Lease; (xiii) maintenance and repair of
capital items not a part of the Building or the Condominium; (xiv) depreciation
of the buildings, improvements and the common areas comprising the Condominium;
(xv) costs relating to maintaining Landlord's existence as a corporation,
partnership or other entity; (xvi) advertising and other fees and costs incurred
in procuring tenants; (xvi) the cost of any items for which Landlord is
reimbursed by insurance, condemnation awards, refund, rebate or otherwise, and
any expenses for repairs or maintenance to the extent covered by warranties,
guaranties and service contracts; (xvii) costs incurred in connection with any
disputes between Landlord and its employees, between Landlord and Building
management, or between Landlord and other tenants or occupants; (xv) any cost to
the extent paid by Tenant pursuant to any other provision of this Lease; and
(xvi) any portion of contributions made by Landlord to the so-called WORKING
CAPITAL FUND (as defined in that certain Declaration of Trust and By-Laws of The
Technology Square Condominium Trust dated as of November 30, 2000).

            (g)  "CAPITAL INTEREST RATE" shall be defined as an annual rate of
either one percentage point over the AA Bond rate (Standard & Poor's corporate
composite or, if unavailable, its equivalent) as reported in the financial press
at the time the capital expenditure is made or, if the capital item is acquired
through third-party financing, then the actual (including fluctuating) rate paid
by Landlord in financing the acquisition of such capital item.

            (h)  "ANNUAL CHARGE-OFF" shall be defined as the annual amount of
principal and interest payments which would be required to repay a loan
("CAPITAL LOAN") in equal monthly installments over the Useful Life (hereinafter
defined) of the capital item in question on a direct reduction basis at an
annual interest rate equal to the Capital Interest Rate, where the initial
principal balance is the cost of the capital item in question.

            (i)  "USEFUL LIFE" shall be reasonably determined by Landlord in
accordance with sound accounting principles consistently applied in effect at
the time of acquisition of the capital item.

                                TOLERRX LEASE / BUILDING 300 / EXECUTION VERSION

                                      -21-
<Page>

Notwithstanding the foregoing, if Landlord reasonably concludes on the basis of
engineering estimates that a particular capital expenditure will effect savings
in Building Operating Costs and/or Condominium Operating Costs including,
without limitation, energy-related costs, and that such annual projected savings
will exceed the Annual Charge-Off of Capital Expenditures computed as aforesaid,
then and in such events, the Annual Charge-Off shall be determined based upon a
Useful Life which would cause the principal and interest payments in a full
repayment of the Capital Loan in question to equal the amount of projected
savings of such Useful Life.

     10.2   TAX PAYMENT. (a) Tenant shall pay to Landlord, as additional rent,
Tenant's Percentage Share of Taxes. Landlord may make a good faith estimate of
the Taxes to be due by Tenant for any Tax Period or part thereof during the term
hereof, and Tenant shall pay to Landlord, on the Rent Commencement Date and on
the first (1st) day of each calendar month thereafter, an amount equal to
Tenant's Percentage Share of Taxes for such Tax Period or part thereof divided
by the number of months therein. Landlord may estimate and re-estimate Tenant's
Percentage Share of Taxes and deliver a copy of the estimate or re-estimate to
Tenant. Thereafter, the monthly installments of Tenant's Percentage Share of
Taxes shall be appropriately adjusted in accordance with the estimations so
that, by the end of the calendar year in question, Tenant shall have paid all of
Tenant's Percentage Share of Taxes as reasonably estimated by Landlord. Any
amounts paid based on such an estimate shall be subject to adjustment as herein
provided when actual Taxes are available for each Tax Period. As soon as
practicable after actual Tax bills are available for each Tax Period, Landlord
shall deliver to Tenant a copy of the same. If the total of such monthly
remittances is greater than Tenant's Percentage Share of the actual Taxes due
for such Tax Period, then, provided there is not an Event of Default nor an
event which, with the passage of time and/or the giving of notice would
constitute an Event of Default, Tenant may credit the difference against the
next installment of Yearly Rent due hereunder, except that if such difference is
determined after the end of the term hereof, Landlord shall refund such
difference to Tenant within thirty (30) days after such determination to the
extent that such difference exceeds any amounts then due from Tenant to
Landlord. If the total of such remittances is less than Tenant's Percentage
Share of the actual Taxes due for such Tax Period, Tenant shall pay the
difference to Landlord within ten (10) days of Tenant's receipt of an invoice
therefor. Landlord's estimate for the next Tax Period shall be based upon the
actual Taxes attributable to the Building for the prior Tax Period plus a
reasonable adjustment based upon estimated increases in Taxes. In the event that
Payments in Lieu of Taxes ("PILOT"), instead of or in addition to Taxes, are
separately assessed to certain portions of the Building or the Condominium
including the Premises, Tenant agrees, except as otherwise expressly provided
herein to the contrary, to pay to Landlord, as additional rent, the portion of
such PILOT attributable to the Premises in the same manner as provided above for
the payment of Taxes. In the event that PILOT are separately assessed to certain
portions of the Building or the Condominium including the Premises, Tenant's
payments under this Section 10.2(a) shall not be greater than the amount that
would have been paid if such PILOT was not assessed.

            (b)  EFFECT OF ABATEMENTS. Appropriate credit against Taxes or PILOT
shall be given for any refund obtained by reason of a reduction in any Taxes by
the assessors or the administrative, judicial or other governmental agency
responsible therefor after deduction of Landlord's expenditures for reasonable
legal fees and for other reasonable expenses incurred in obtaining the Tax or
PILOT refund.

     10.3   PAYMENT OF BUILDING OPERATING COSTS.

            (a)  Tenant shall pay to Landlord, as additional rent, Tenant's
Percentage Share of Building Operating Costs. Landlord may make a good faith
estimate of Tenant's Percentage Share of Building Operating Costs for any
Operating Year or part thereof during the term based upon Landlord's pro forma
budget, a copy of which shall be delivered to Tenant when available, and Tenant
shall pay to

                                TOLERRX LEASE / BUILDING 300 / EXECUTION VERSION

                                      -22-
<Page>

Landlord, on the Rent Commencement Date and on the first (1st) day of each
calendar month thereafter, an amount equal to Tenant's Percentage Share of the
estimated Building Operating Costs for such Operating Year and/or part thereof
divided by the number of months therein. Landlord may reasonably estimate and
re-estimate Tenant's Percentage Share of Building Operating Costs and deliver a
copy of the estimate or re-estimate to Tenant. Thereafter, the monthly
installments of Tenant's Percentage Share of Building Operating Costs shall be
appropriately adjusted in accordance with the estimations so that, by the end of
the calendar year in question, Tenant shall have paid all of Tenant's Percentage
Share of Building Operating Costs as reasonably estimated by Landlord. Any
amounts paid based on such an estimate shall be subject to adjustment as herein
provided when actual Building Operating Costs are available for each Operating
Year.

            (b)  ANNUAL RECONCILIATION. Landlord shall, within one hundred
twenty (120) days after the end of each Operating Year, deliver to Tenant a
reasonably detailed statement of the actual amount of Building Operating Costs
for such Operating Year ("YEAR END STATEMENT"). If the total of such monthly
remittances on account of any Operating Year is greater than Tenant's Percentage
Share of the actual Building Operating Costs for such Operating Year, then,
provided there is not an Event of Default nor an event which, with the passage
of time and/or the giving of notice would constitute an Event of Default, Tenant
may credit the difference against the next installment of Yearly Rent due
hereunder, except that if such difference is determined after the end of the
term hereof, Landlord shall refund such difference to Tenant within thirty (30)
days after such determination to the extent that such difference exceeds any
amounts then due from Tenant to Landlord. If the total of such remittances is
less than Tenant's Percentage Share of the actual Building Operating Costs for
such Operating Year, Tenant shall pay the difference to Landlord within thirty
(30) days of Tenant's receipt of an invoice therefor. Landlord's estimate of
Building Operating Costs for the next Operating Year shall be based upon the
actual Building Operating Costs for the prior Operating Year as reflected in the
Year-End Statement plus a reasonable adjustment based upon estimated increases
or decreases in Building Operating Costs.

     10.4   CAPITAL EXPENDITURES.

            (a)  REPLACEMENTS. If, during the term hereof, Landlord shall
replace any capital items (collectively, "CAPITAL EXPENDITURES") the total
amount of which (net of any warranty claims) is not properly includable in
Building Operating Costs for the Operating Year in which they were made, in
accordance with sound accounting principles consistently applied, there shall
nevertheless be included in such Building Operating Costs and in Building
Operating Costs for each succeeding Operating Year the amount, if any, by which
the Annual Charge-Off (determined as hereinafter provided) of such Capital
Expenditure (less insurance proceeds, if any, collected by Landlord by reason of
damage to, or destruction of the capital item being replaced) exceeds the Annual
Charge-Off of the Capital Expenditure for the item being replaced.

            (b)  NEW CAPITAL ITEMS. If a new capital item is acquired which does
not replace another capital item which was worn out, has become obsolete, etc.,
and such new capital item being acquired is either (i) required by any Legal
Requirements enacted after the date of this Lease, or (ii) reasonably projected
to reduce Building Operating Costs, then there shall be included in Building
Operating Costs for each Operating Year in which and after such capital
expenditure is made the Annual Charge-Off of such capital expenditure.

     10.5   PART YEARS. If the Rent Commencement Date or the Expiration Date
occurs in the middle of an Operating Year or Tax Period, Tenant shall be liable
for only that portion of the Building Operating Costs or Taxes, as the case may
be, with respect to such Operating Year or Tax Period within the term hereof.
Any credit pursuant to Section 10.2(b) for the years in which the Rent
Commencement

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Date or the Expiration Date occur shall be similarly pro-rated.

     10.6   DISPUTES, SURVIVAL. Any disputes arising under this Article 10 may,
at the election of either party, be submitted for dispute resolution as provided
in Article 28 below. Any obligations under this Article 10 which shall not have
been paid at the expiration or sooner termination of the term hereof shall
survive such expiration and shall be paid when and as the amount of same shall
be determined and be due.

     10.7   AUDIT RIGHT. After giving Landlord at least sixty (60) days' prior
written notice thereof, Tenant may inspect or audit Landlord's records relating
to Building Operating Costs for any periods of time within the previous fiscal
year before the audit or inspection. However, no audit or inspection shall
extend to periods of time before the Term Commencement Date. If Tenant fails to
object to the calculation of Tenant's Percentage Share of Building Operating
Costs on the Year-End Statement within sixty (60) days after such statement has
been delivered to Tenant, then Tenant shall be deemed to have waived its right
to object to the calculation of Tenant's Percentage Share of Building Operating
Costs for the year in question and the calculation of Tenant's Percentage Share
of Building Operating Costs set forth on such statement shall be final. Tenant's
audit or inspection shall be conducted only at Landlord's offices or the offices
of Landlord's property manager during business hours reasonably designated by
Landlord. Tenant shall pay the cost of such audit or inspection. Tenant may not
conduct an inspection or have an audit performed more than once during any
fiscal year. If such inspection or audit reveals that an error was made in the
calculation of Tenant's Percentage Share of Building Operating Costs previously
charged to Tenant, then, provided there is not an Event of Default nor an event
which, with the passage of time and/or the giving of notice would constitute an
Event of Default, Landlord shall refund to Tenant any overpayment of any such
costs, or Tenant shall pay to Landlord any underpayment of any such costs, as
the case may be, within ten (10) days after notification thereof. If Tenant's
inspection or audit reveals an overcharge of more than five percent (5%), then
Landlord shall reimburse Tenant for up to Five Thousand and No/100 Dollars
($5,000.00) of the reasonable cost of such audit or inspection within thirty
(30) days of receipt of a reasonably detailed invoice therefor. Tenant shall
maintain the results of any such audit or inspection confidential and shall not
be permitted to use any third party to perform such audit or inspection, other
than an independent firm of certified public accountants (A) reasonably
acceptable to Landlord, (B) which is not compensated on a contingency fee basis
or in any other manner which is dependent upon the results of such audit or
inspection, and (C) which agrees with Landlord in writing to maintain the
results of such audit or inspection confidential.

11.  FIXTURES, EQUIPMENT AND IMPROVEMENTS--REMOVAL BY TENANT

     All fixtures (which expressly includes for purposes of this Section 11 fume
hoods, lab sinks and laboratory benches), equipment, improvements and
appurtenances attached to or built into the Premises prior to or during the term
hereof, whether by Landlord at Landlord's expense or at the expense of Tenant
(either or both) or by Tenant (but excluding all items of Tenant's Removable
Property) shall be and remain part of the Premises and shall not be removed by
Tenant during or at the end of the term hereof unless Landlord authorizes such
removal in writing or otherwise elects to require Tenant to remove such
fixtures, equipment, improvements and appurtenances, in accordance with the
terms of Section 12.1 below; provided, however, that Tenant shall have the right
to remove (at Tenant's expense) the items of "TENANT'S REMOVABLE PROPERTY"
listed on EXHIBIT 9, attached hereto (as same may be updated from time to time
by Tenant with the prior approval of Landlord), provided that such removal shall
not materially damage the Premises or the Building and that Tenant shall repair
any damage to the Premises or the Building arising from the installation or
removal thereof. In addition, (i) the Equipment shall not be removed from the
Premises, and (ii) the pure water system and the waste treatment system shall
not be removed from the Premises during or at the end of term hereof except,
upon at least ten (10)

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business days' prior written notice to Landlord, by the holder of a purchase
money security interest therein and then only as a result of Tenant's failure to
pay sums as and when due to such holder and in accordance with the terms of the
loan agreement by and between Tenant and such holder. Nothing in this Lease
shall be construed to permit Tenant to grant any interest whatsoever in (a) any
fixtures within the Premises or (b) any item paid in whole or in part with
Landlord's Contribution or the Equipment Allowance without the consent of
Landlord. All electric, plumbing, heating and sprinkling systems, fixtures and
outlets, vaults, paneling, molding, shelving, radiator enclosures, cork, rubber,
linoleum and composition floors, ventilating, silencing, air conditioning and
cooling equipment, shall be deemed to be included in such fixtures, improvements
and appurtenances, whether or not attached to or built into the Premises. Where
not built into the Premises, all removable electric fixtures, carpets, drinking
or tap water facilities, furniture, or trade fixtures or business or laboratory
equipment or Tenant's inventory or stock in trade shall not be deemed to be
included in such fixtures, improvements and appurtenances and may be, and upon
the request of Landlord will be, removed by Tenant upon the condition that such
removal shall not materially damage the Premises or the Building and that the
cost of repairing any damage to the Premises or the Building arising from
installation or such removal shall be paid by Tenant. Nothing in this Section 11
shall prohibit Tenant from relocating any fume hoods and laboratory benches
installed within the Premises from time to time during the term of this Lease.
Notwithstanding anything to the contrary contained herein, at the end of the
term hereof Tenant shall remove all autoclaves and cage washers from the
Premises.

12.  ALTERATIONS AND IMPROVEMENTS BY TENANT

     12.1   Tenant shall make no alterations, decorations, installations,
removals, additions or improvements (collectively, "ALTERATIONS") in or to the
Premises (other than Tenant's Work which shall be governed by the provisions of
Article 4 above) without Landlord's prior written consent and then only those
made by contractors or mechanics approved by Landlord. Notwithstanding the
foregoing, but provided that no HVAC system serving any portion of the Building
is adversely affected, Tenant may make non-structural Alterations costing less
than $20,000 in any one instance ("PERMITTED ALTERATIONS") without Landlord's
prior written consent but subject to the provisions of this Lease including
without limitation Article 13 below. No Alterations other than Permitted
Alterations shall be undertaken or begun by Tenant until Landlord has approved
written plans and specifications and a time schedule for such work. No
amendments or additions to such plans and specifications shall be made without
the prior written consent of Landlord. Landlord's consent and approval required
under this Article 12 shall not be unreasonably withheld, conditioned or
delayed, except for matters of aesthetics relating to Alterations to or
affecting the Rooftop Premises and/or the exterior of the Building, which shall
be determined in Landlord's sole discretion. Landlord's approval is solely given
for the benefit of Landlord and neither Tenant nor any third party shall have
the right to rely upon Landlord's approval of Tenant's plans for any purpose
whatsoever. Without limiting the foregoing, Tenant shall be responsible for all
elements of the design of Tenant's plans (including, without limitation,
compliance with Legal Requirements, functionality of design, the structural
integrity of the design, the configuration of the Premises and the placement of
Tenant's furniture, appliances and equipment), and Landlord's approval of
Tenant's plans shall in no event relieve Tenant of the responsibility for such
design. Landlord shall have no liability or responsibility for any claim, injury
or damage alleged to have been caused by the particular materials (whether
building standard or non-building standard), appliances or equipment selected by
Tenant in connection with any work performed by or on behalf of Tenant in the
Premises. Any such Alterations shall be done at Tenant's sole cost and expense
and at such times and in such manner as Landlord may from time to time
reasonably designate. If Tenant shall make any Alterations to the Premises other
than the Permitted Alterations, then Landlord may elect to require Tenant at the
expiration or sooner termination of the term hereof to restore the Premises to
substantially the same condition as existed immediately prior to the Alteration.
Upon Tenant's request, Landlord agrees to make such election at the

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time that Landlord approves Tenant's plans for any such Alterations. Tenant
shall provide Landlord with reproducible record drawings of all Alterations
within sixty (60) days after completion thereof.

     12.2   Tenant shall pay to Landlord, as additional rent, within ten (10)
days after demand therefor, any costs or expenses incurred by Landlord (which
shall be reasonably based on Tenant's usage) for the use of elevators (including
without limitation the Freight Elevator) and/or hoisting in connection with the
performance of any Alterations. Landlord and Tenant recognize that to the extent
Tenant elects to perform some or all of the Alterations during times other than
normal construction hours, Landlord will need to make arrangements to have
supervisory personnel on site. Accordingly, Landlord and Tenant agree as
follows: Tenant shall give Landlord at least forty-eight (48) hours' notice of
any time outside of normal construction hours when Tenant intends to perform
portions of the Alterations. Tenant shall reimburse Landlord, within thirty (30)
days after demand therefor, for the cost of Landlord's supervisory personnel
overseeing such after hours work. In addition, if construction during the normal
construction hours unreasonably disturbs other tenants of the Building or the
Condominium, in Landlord's sole discretion, Landlord may require Tenant to stop
the performance of the Alterations during normal construction hours and to
perform the same after hours, subject to the foregoing requirement to pay for
the cost of Landlord's supervisory personnel.

13.  TENANT'S CONTRACTORS--MECHANICS' AND OTHER LIENS--STANDARD OF TENANT'S
PERFORMANCE--COMPLIANCE WITH LAWS

     Whenever Tenant shall make any Alterations (including without limitation,
the performance of Tenant's Work) in or to the Premises, Tenant will observe the
following covenants and agreements:

     13.1   HARMONIOUS RELATIONS. Tenant agrees that it will not, either
directly or indirectly, use any contractors and/or materials if their use will
create any difficulty, whether in the nature of a labor dispute or otherwise,
with other contractors and/or labor engaged by Tenant or Landlord or others in
the construction, maintenance and/or operation of the Building or any part
thereof.

     13.2   LIENS. In no event shall any Encumbered Material (hereinafter
defined) be incorporated in or added to the Premises, so as to become a fixture
or otherwise a part of the Building, in connection with any Alteration. For
purposes hereof, "ENCUMBERED MATERIAL" shall mean any material or equipment
which is subject to any lien, charge, mortgage or other encumbrance of any kind
whatsoever (other than pursuant to Section 4.4 above) or is subject to any
security interest or any form of title retention agreement not approved by
Landlord in advance in writing which approval may be given or withheld in
Landlord's sole discretion. No Alterations shall be undertaken or begun by
Tenant until (i) Tenant has made provision for written waiver of liens from all
Contractors for such Alteration and taken other appropriate protective measures
approved and/or required by Landlord; (ii) Tenant has procured appropriate
surety payment and performance bonds which shall name Landlord as an additional
obligee and has filed lien bond(s) (in jurisdictions where available) on behalf
of such Contractors; and (iii) plans and specifications prepared by and at the
expense of Tenant have been submitted to and approved by Landlord where
Landlord's approval is required hereunder. Any mechanic's lien filed against the
Premises or the Building for work claimed to have been done for, or materials
claimed to have been furnished to, Tenant shall be discharged by Tenant within
ten (10) days after Tenant's receipt of notice of the filing thereof, at
Tenant's expense by filing the bond required by law or otherwise. If Tenant
fails so to discharge any lien, Landlord may do so at Tenant's expense and
Tenant shall reimburse Landlord for any expense or cost incurred by Landlord in
so doing, together with interest at the Default Rate until paid in full, within
ten (10) days after receipt of an invoice therefor.

     13.3   PERMITS. Unless Landlord and Tenant otherwise agree in writing,
Tenant shall procure

                                TOLERRX LEASE / BUILDING 300 / EXECUTION VERSION

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or cause others to procure on its behalf all necessary permits before
undertaking any work in the Premises; do all of such work in a good and
workmanlike manner, employing materials of good quality; and defend, save
harmless, exonerate and indemnify the Landlord Indemnitees from and against any
and all Claims occasioned by or growing out of such work. Tenant shall cause
Contractors employed by Tenant to (a) carry Worker's Compensation Insurance in
accordance with statutory requirements, (b) carry Automobile Liability Insurance
and Commercial General Liability Insurance (i) naming Landlord as an additional
insured and (ii) covering such Contractors on or about the Premises in the
amounts stated in Article 15 hereof or in such other reasonable amounts as
Landlord shall require, and (c) submit certificates evidencing such coverage to
Landlord prior to the commencement of any such work.

     13.4.  QUALITY AND PERFORMANCE. All Alterations shall be done in a good and
workmanlike manner by Contractors approved by Landlord and in compliance with
Landlord's construction rules and regulations for the Condominium attached as an
addendum to the Building Rules and Regulations, all insurance requirements of
the Lease, and Legal Requirements. Each party authorizes the other to rely upon
the written approval or other written authorizations on the other party's behalf
by its Construction Representative(s) in connection with design and
construction.

14. MAINTENANCE AND REPAIRS BY TENANT--LABORATORY CLEANING AND WASTE REMOVAL --
FLOOR LOAD

     14.1   MAINTENANCE AND REPAIRS BY TENANT. Tenant shall keep all and
singular the Premises neat and clean and free of insects, animals (other than
animals used in connection with the Permitted Uses), vermin and other pests and
in such good repair, order and condition as the same are in on the Term
Commencement Date or in such better condition as the Premises may be put in
during the term hereof, reasonable use and wearing thereof and damage by fire or
by other casualty excepted. Tenant shall be solely responsible, at Tenant's sole
cost and expense, (a) for the proper maintenance of all equipment and appliances
operated by Tenant including without limitation the Equipment; (b) repairs and
maintenance of any Tenant's Rooftop Equipment, any heating, ventilating and air
conditioning equipment or security equipment installed by Tenant and any other
building systems installed by Tenant for exclusive use within the Premises; and
(c) for cleaning all areas of the Premises (office and laboratory areas) to a
standard reasonably comparable to other combination laboratory/office buildings
in the greater Cambridge area with a service provider reasonably acceptable to
Landlord. Tenant shall make, as and when needed as a result of misuse by, or
neglect or improper conduct of any of the Tenant Parties or otherwise, all
repairs in and about the Premises necessary to preserve them in such repair,
order and condition, which repairs shall be in quality and class equal to the
original work.

     14.2   LABORATORY CLEANING, WASTE REMOVAL AND ANIMAL CARE. Tenant shall be
responsible, at its sole cost and expense, for routine janitorial and trash
removal services and other biohazard disposal services for the laboratory areas
of the Premises. Such services shall be performed by contractors reasonably
acceptable to Landlord and on a sufficient basis to ensure that the laboratory
areas of the Premises are at all times kept neat, clean and free of trash,
Hazardous Materials and biohazards except in appropriate, specially marked
containers reasonably approved by Landlord. In addition, Tenant shall be
responsible, at Tenant's sole cost and expense, for the care and safe storage of
any animals housed within the Premises, including without limitation all animal
husbandry and custodial services with respect thereto.

     14.3   FLOOR LOAD--HEAVY MACHINERY. Tenant shall not place a load upon any
floor of the Premises exceeding the floor load per square foot of area which
such floor was designed to carry and which is allowed by Legal Requirements.
Landlord reserves the right to prescribe the weight and position of all business
machines and mechanical equipment, including safes, which shall be placed so as

                                TOLERRX LEASE / BUILDING 300 / EXECUTION VERSION

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<Page>

to distribute the weight. Business machines and mechanical equipment shall be
placed and maintained by Tenant at Tenant's expense in settings sufficient in
Landlord's reasonable judgment to absorb and prevent vibration, noise and
annoyance. Tenant shall not move any safe, heavy machinery, heavy equipment,
freight, bulky matter or fixtures (collectively, "HEAVY EQUIPMENT") into or out
of the Building without giving Landlord prior written notice thereof and
observing all of Landlord's Rules and Regulations with respect to the same. If
such Heavy Equipment requires special handling, Tenant agrees to employ only
persons holding a Master Rigger's License to do said work, and that all work in
connection therewith shall comply with Legal Requirements. Any such moving shall
be at the sole risk and hazard of Tenant and Tenant will defend, indemnify and
save the Landlord Indemnitees harmless from and against any and all Claims
resulting directly or indirectly from such moving. Proper placement of all Heavy
Equipment in the Premises shall be Tenant's responsibility.

     14.4   ANIMAL TRANSPORTATION. No animals, animal waste, food or supplies
relating to the animals maintained from time to time in the animal storage areas
of the Premises shall be transported within the Building except as provided in
this Section 14.4. All deliveries of animals or animal food or supplies to
Tenant at the Building shall be made prior to 11:00 a.m. No transportation of
animals, animal waste, food or supplies within the Building shall occur between
the hours of 11:00 a.m. and 1:00 p.m. At all times that animals are transported
within the Condominium common areas or within the Building, they shall be
transported in an appropriate cage or other container. At no time shall any
animals, animal waste, food or supplies relating to the animals be brought into,
transported through, or delivered to the lobby of the Building or be transported
within the Building in elevators other than the Freight Elevator.

     14.5   WASTE REMOVAL; RECYCLING.

            (a)  Throughout the term hereof, Tenant shall, at its sole cost and
expense: (i) keep any garbage, trash, rubbish and refuse (collectively, "TRASH")
in vermin-proof containers within the interior of the Premises until removed;
and (ii) deposit such Trash on a daily basis, in designated receptacles provided
by Landlord.

            (b)  At its option, Landlord may furnish (or authorize others to
furnish) a service for the removal of Trash from receptacles designated by
Landlord for the daily deposit by Tenant of its Trash, and, if it shall do so,
the cost of such service shall be included in Building Operating Costs.
Otherwise, Tenant must contract for trash removal at Tenant's sole cost and
expense.

            (c)  Upon written notice, Landlord may establish policies, programs
and measures for the recycling of paper, products, plastic, tin and other
materials (a "RECYCLING PROGRAM"). Upon receipt of such notice, Tenant will
comply with the Recycling Program at Tenant's sole cost and expense.

15.  INSURANCE, INDEMNIFICATION, EXONERATION AND EXCULPATION

     15.1   GENERAL LIABILITY INSURANCE. Tenant shall procure, pay for and keep
in force throughout the term hereof (and for so long thereafter as Tenant
remains in occupancy) commercial general liability insurance insuring Tenant on
an occurrence basis against all claims and demands for personal injury liability
(including, without limitation, bodily injury, sickness, disease, and death) or
damage to property which may be claimed to have occurred from and after the time
any of the Tenant Parties shall first enter the Premises, of not less than Two
Million Dollars ($2,000,000), and from time to time thereafter shall be not less
than such higher amounts, if procurable, as may be reasonably required by
Landlord. Tenant shall also carry umbrella liability coverage in an amount of no
less than Five Million Dollars ($5,000,000). Such policy shall also include
contractual liability coverage covering Tenant's liability assumed under this
Lease, including without limitation the indemnification obligations

                                TOLERRX LEASE / BUILDING 300 / EXECUTION VERSION

                                      -28-
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contained in Sections 2.3(b), 14.3, 15.5, 17.6(g), 28.6 and 29.3 hereof.

     15.2   PROPERTY INSURANCE. Tenant shall take out and maintain throughout
the term hereof a policy of fire, vandalism, malicious mischief, extended
coverage and so-called "all risk" coverage insurance insuring (i) all items or
components of Tenant's Work or Alterations which Tenant is by this Lease either
entitled to or required to remove upon the expiration or earlier termination of
the term hereof (collectively, the "TENANT-INSURED IMPROVEMENTS"), and (ii)
Tenant's Property (hereinafter defined) for the benefit of Landlord and Tenant,
as their respective interests may appear, in an amount equal to one hundred
percent (100%) of the replacement value thereof. Such insurance shall insure the
interests of both Landlord and Tenant as their respective interests may appear
from time to time.

     15.3   BUSINESS INTERRUPTION INSURANCE. Tenant shall also take out and
maintain a policy of business interruption insurance throughout the term of the
Lease sufficient to cover at least six (6) months of Rent due hereunder and
Tenant's business losses during such 6-month period.

     15.4   FORM OF INSURANCE. The insurance required pursuant to Sections 15.1,
15.2 and 15.3 (collectively, "TENANT'S INSURANCE POLICIES") shall be effected
with insurers approved by Landlord, with a rating of not less than "A-XI" in the
current BEST'S INSURANCE REPORTS, and authorized to do business in the
Commonwealth of Massachusetts under valid and enforceable policies, and with
respect to the insurance required pursuant to Section 15.1 and the property
insurance covering the Tenant-Insured Improvements specified in Section 15.2,
such insurance policy(ies) shall name Landlord, Landlord's managing agent and
persons claiming by, through or under them, if any, as additional insureds.
Tenant's Insurance Policies shall each provide that it shall not be canceled or
modified without at least thirty (30) days' prior written notice to each insured
named therein. On or before the time any of the Tenant Parties shall first enter
the Premises and thereafter not less than fifteen (15) days prior to the
expiration date of each expiring policy, Tenant shall deliver to Landlord either
original copies of Tenant's Insurance Policies issued by the respective
insurers, or binders thereof setting forth in full the provisions thereof and
issued by such insurers together with evidence satisfactory to Landlord of the
payment of all premiums for such policies, and upon request of Landlord, Tenant
shall deliver to any Mortgagee copies of the foregoing documents.

     15.5   INDEMNIFICATION.

            (a)  Tenant will defend, indemnify and save the Landlord Indemnitees
harmless from and against any and all Claims asserted by or on behalf of any
person, firm, corporation or public authority arising from:

                 (i)     Tenant's breach of any covenant or obligation under the
Lease;

                 (ii)    Any injury to or death of any person, or loss of or
damage to property, sustained or occurring in, upon or at the Premises unless
resulting from the negligence or willful misconduct of Landlord or any of the
Landlord Parties;

                 (iii)   Any injury to or death of any person, or loss of or
damage to property, sustained or occurring in or about the Building or
Condominium to the extent arising out of the use or occupancy of the Premises
by, or the negligence or misconduct of, any of the Tenant Parties; and

                 (iv)    On account of or based upon (including monies due on
account of) any work or thing whatsoever done (other than by any of the Landlord
Parties) at the Premises during the term hereof and during the period of time,
if any, prior to the Term Commencement Date that any of the Tenant Parties may
have been given access to the Premises, including without limitation Tenant's
Work

                                TOLERRX LEASE / BUILDING 300 / EXECUTION VERSION

                                      -29-
<Page>

and any Alterations.

            (b)  Landlord will defend, indemnify and save Tenant harmless from
and against any and all Claims asserted by or on behalf of any person, firm,
corporation or public authority arising from any injury to or death of any
person, or loss of or damage to property, sustained or occurring in or about the
Condominium to the extent arising from the negligence of willful misconduct of
Landlord or any of the Landlord Parties.

     15.6   PROPERTY OF TENANT. Tenant covenants and agrees that, to the maximum
extent permitted by Legal Requirements, all of Tenant's Rooftop Equipment and
all of Tenant's animals, furniture, fixtures and property of every kind, nature
and description related or arising out of Tenant's leasehold estate hereunder,
which may be in or upon the Premises, the Building or the Condominium
(collectively, "TENANT'S PROPERTY") shall be at the sole risk and hazard of
Tenant, and that if the whole or any part thereof shall be damaged, destroyed,
stolen or removed from any cause or reason whatsoever, no part of said damage or
loss shall be charged to, or borne by, Landlord, except, subject to Section 15.9
hereof, to the extent such damage or loss is due to the negligence or willful
misconduct of Landlord or Landlord's agents, employees and/or contractors
(collectively, the "LANDLORD PARTIES").

     15.7   BURSTING OF PIPES, ETC. Landlord shall not be liable for any injury
or damage to persons, animals or property resulting from fire, explosion,
falling plaster, steam, gas, air contaminants or emissions, electricity,
electrical or electronic emanations or disturbance, water, rain or snow or leaks
from any part of the Building or from the pipes, appliances, equipment or
plumbing works or from the roof, street or sub-surface or from any other place
or caused by dampness, vandalism, malicious mischief or by any other cause of
whatever nature, unless caused by or due to the negligence or willful misconduct
of any of the Landlord Parties, and then, where notice and an opportunity to
cure are appropriate (i.e., where Tenant has an opportunity to know or should
have known of such condition sufficiently in advance of the occurrence of any
such injury or damage resulting therefrom as would have enabled Landlord to
prevent such damage or loss had Tenant notified Landlord of such condition) only
after (i) notice to Landlord of the condition claimed to constitute negligence
and (ii) the expiration of a reasonable time after such notice has been received
by Landlord without Landlord having taken all reasonable and practicable means
to cure or correct such condition; and pending such cure or correction by
Landlord, Tenant shall take all reasonably prudent temporary measures and
safeguards to prevent any injury, loss or damage to persons or property. In no
event shall any of the Landlord Indemnitees be liable for any loss which is
covered by Tenant's insurance or is required to be so covered by this Lease; nor
shall any of the Landlord Indemnitees be liable for any such damage caused by
other tenants or persons in the Building or caused by operations in construction
of any private, public, or quasi-public work; nor shall any of the Landlord
Indemnitees be liable for any latent defect in the Premises or in the Building.

     15.8   LANDLORD'S INSURANCE. Landlord shall take out and maintain in force
throughout the term hereof, in a company or companies authorized to do business
in the Commonwealth of Massachusetts: (a) property insurance on the Building
(exclusive of Tenant's Property and the Tenant-Insured Improvements) in an
amount equal to the full replacement value of the Building (exclusive of
foundations and those items set forth in the preceding parenthetical in this
sentence), covering all risks of direct physical loss or damage and so-called
"extended coverage" risks; and (b) commercial general liability insurance
against claims of bodily injury, personal injury and property damage arising out
of Landlord's operation of the Building, in such amount as a prudent owner of
similar property would carry or as otherwise required by any Mortgagee. The
foregoing insurance may be maintained in the form of a blanket policy covering
the Building and/or the other Condominium units as well as other properties
owned by Landlord. Notwithstanding the foregoing provisions of this Section
15.8, Landlord shall have the right, at any time during the term hereof, to
self-insure all or any portion of the coverages required by

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                                      -30-
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this Section 15.8.

     15.9   WAIVER OF SUBROGATION; MUTUAL RELEASE. Landlord and Tenant each
hereby waives on behalf of itself and its property insurers (none of which shall
ever be assigned any such claim or be entitled thereto due to subrogation or
otherwise) any and all rights of recovery, claim, action, or cause of action
against the other and its agents, officers, servants, partners, shareholders, or
employees (collectively, the "RELATED PARTIES") for any loss or damage that may
occur to or within the Premises, the Building or the Condominium or any
improvements thereto, or any personal property of such party therein, by reason
of fire, the elements, or any other cause of origin, which is insured against
under any property insurance policy actually being maintained from time to time,
even if not required hereunder, or which would be insured against under the
terms of any insurance policy required to be carried or maintained hereunder,
whether or not such insurance coverage is actually being maintained and
regardless of the cause or origin, including, in every instance, negligence by
the other party hereto and/or its Related Parties. With respect to such portion
of the term during which Landlord elects to self-insure under Section 15.8
above, then for purposes of this Section 15.9 and Article 18 hereof, Landlord
shall be deemed to have maintained fire and all-risk coverage in an amount equal
to the full insurable value of the Building. The foregoing waiver shall apply to
the extent of any amount that would have been recoverable under such deemed
coverage. Landlord and Tenant each agree to cause appropriate clauses to be
included in their property insurance policies necessary to implement the
foregoing provisions.

16.  ASSIGNMENT, MORTGAGING AND SUBLETTING

     16.1   Except as otherwise set forth herein, Tenant shall not, without
Landlord's prior written consent, which consent may be withheld in Landlord's
sole discretion, assign, sublet, mortgage, license, transfer or encumber the
Lease or the Premises in whole or in part whether by changes in the ownership or
control of Tenant, or any direct or indirect owner of Tenant, whether at one
time or at intervals, by sale or transfer of stock, partnership or beneficial
interests, operation of law or otherwise (each of the foregoing, a "TRANSFER").
Any purported Transfer made without Landlord's approval, if required hereunder,
shall be void and confer no rights upon any third person, provided that if there
is a Transfer, after the occurrence of an Event of Default, Landlord may collect
rent from the transferee without waiving the prohibition against Transfers,
accepting the transferee, or releasing Tenant from full performance under the
Lease. In the event of any Transfer in violation of this Article 16, Landlord
shall have the right to terminate the Lease upon thirty (30) days' written
notice to Tenant within sixty (60) days after written notice from Tenant to
Landlord of any Transfer, or within one (1) year after Landlord first learns of
the Transfer if no notice is given. No Transfer shall relieve Tenant of its
primary obligation as party-Tenant hereunder, nor shall it reduce or increase
Landlord's obligations under the Lease.

     16.2   LANDLORD'S RECAPTURE RIGHT

            (a)  Subject to Sections 16.2(c) and 16.5 below, Tenant shall, prior
to offering or advertising the Premises or any portion thereof for a Transfer,
give a written notice (the "RECAPTURE NOTICE") to Landlord which: (i) states
that Tenant desires to make a Transfer, (ii) identifies the affected portion of
the Premises (the "RECAPTURE PREMISES"), (iii) identifies the period of time
(the "RECAPTURE PERIOD") during which Tenant proposes to sublet the Recapture
Premises or to assign its interest in the Lease, and (iv) offers to Landlord to
terminate the Lease with respect to the Recapture Premises (in the case of a
proposed assignment of Tenant's interest in the Lease or a subletting for the
remainder of the term of the Lease) or to suspend the term of the Lease for the
same period of time as the Recapture Period (i.e. the term of the Lease in
respect of the Recapture Premises shall be terminated during the Recapture
Period and Tenant's rental obligations shall be reduced in proportion to the
ratio of the total rentable area of the Recapture Premises to the total rentable
area of the Premises then demised to

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Tenant). Landlord shall have fifteen (15) business days within which to respond
to the Recapture Notice.

            (b)  If Tenant does not enter into a Transfer on the terms and
conditions contained in the Recapture Notice on or before the date which is one
hundred eighty (180) days after the earlier of: (x) the expiration of the
15-business day period specified in Section 16.2(a) above or (y) the date that
Landlord notifies Tenant that Landlord will not accept Tenant's offer contained
in the Recapture Notice, then prior to entering into any Transfer after such
180-day period, Tenant must deliver to Landlord a new Recapture Notice in
accordance with Section 16.2(a) above

            (c)  Notwithstanding the foregoing, Tenant shall not be obligated to
give Landlord a Recapture Notice if: (i) Tenant occupies at least fifty-one
percent (51%) of the Premises both before and after the proposed Transfer; or
(ii) the total term of the proposed Transfer is equal to or less than two (2)
years and will commence on or before the date which is two (2) years prior to
the expiration of the then- current term.

            (d)  In the event that Landlord notifies Tenant that it accepts the
offer contained in any Recapture Notice delivered by Tenant to Landlord on or
before the date which is five (5) years after the Rent Commencement Date, and
provided that (i) there is not an Event of Default nor an event which with the
giving of notice and/or the passage of time would constitute an Event of Default
on the date of such notification and on the date on which such reimbursement is
due, and (ii) Tenant has submitted to Landlord a reasonably detailed invoice
satisfactory to Landlord indicating the cost of such improvements and the
amortization thereof, Landlord shall reimburse Tenant for the unamortized cost
of improvements made by Tenant to the Recapture Premises at Tenant's sole cost
and expense (i.e. not reimbursed by Landlord pursuant to the terms hereof).

            (e)  Notwithstanding anything to the contrary contained herein, if
Landlord notifies Tenant that it accepts the offer contained in the Recapture
Notice, Tenant shall have the right, for a period of fifteen (15) days following
receipt of such notice from Landlord, to notify Landlord in writing that it
wishes to withdraw such offer and this Lease shall continue in full force and
effect.

     16.3   STANDARD OF CONSENT TO TRANSFER. If Landlord does not timely give
written notice to Tenant accepting a Recapture Offer or declines to accept the
same, then Landlord agrees that, subject to the provisions of this Article 16,
it will not unreasonably withhold, condition or delay its consent to a Transfer
on the terms contained in the Recapture Notice, to an entity which, in
Landlord's reasonable opinion: (i) has a net worth and other financial
indicators sufficient to meet Tenant's obligations hereunder; (ii) has a
business reputation compatible with the operation of a first class office,
research, development, laboratory and retail building; and (iii) whose intended
use is consistent with the Permitted Uses hereunder and does not violate any
exclusive or restrictive use provisions of any leases then in effect with
respect to space in the Condominium.

     16.4   LOCKOUT PERIOD. Notwithstanding anything to the contrary herein
contained, Tenant shall have not have the right to deliver a Recapture Notice
nor to make any Transfer with respect to any portion of the 4th Floor Premises
prior to the date ("LOCKOUT EXPIRATION DATE") that is the earlier of (i) one (1)
year after the Rent Commencement Date, and (ii) the date when Buildings 100,
300, 600 and 700 are one hundred percent (100%) leased.

     16.5   EXCEPTIONS TO REQUIREMENT FOR CONSENT. Notwithstanding anything to
the contrary herein contained, Tenant shall have the right, without obtaining
Landlord's consent and without giving Landlord a Recapture Offer or to wait
until the Lockout Expiration Date, to make a Transfer to (a) an

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Affiliated Entity (hereinafter defined) so long as such entity remains in such
relationship to Tenant, and (b) a Successor, provided that prior to or
simultaneously with any such Transfer, such Affiliated Entity or Successor, as
the case may be, and Tenant execute and deliver to Landlord an assignment and
assumption agreement in form and substance satisfactory to Landlord whereby such
Affiliated Entity or Successor, as the case may be, shall agree to be
independently bound by and upon all the covenants, agreements, terms, provisions
and conditions set forth in the Lease on the part of Tenant to be performed, and
whereby such Affiliated Entity or Successor, as the case may be, shall expressly
agree that the provisions of this Article 16 shall, notwithstanding such
Transfer, continue to be binding upon it with respect to all future Transfers
(an "ASSUMPTION AGREEMENT"). For the purposes hereof, an "AFFILIATED ENTITY"
shall be defined as any entity (a) that has a net worth at least equal to the
greater of the net worth of Tenant (i) on the Execution Date and (ii)
immediately prior to the Transfer; and (b) which is controlled by, is under
common control with, or which controls Tenant. For the purposes hereof, a
"SUCCESSOR" shall be defined as any entity into which Tenant is merged or with
which Tenant is consolidated or which acquires all or substantially all of
Tenant's stock or assets, provided that the surviving entity shall have a net
worth at least equal to the greater of the net worth of Tenant (x) on the
Execution Date and (y) immediately prior to the Transfer.

     16.6   TENANT AS PARTNERSHIP. If Tenant is an individual who uses and/or
occupies the Premises with partners, or if Tenant is a partnership, then: (a)
each present and future partner shall be personally bound by and upon all of the
covenants, agreements, terms, provisions and conditions set forth in the Lease
on the part of Tenant to be performed; and (b) in confirmation of the foregoing,
Landlord may (but without being required to do so) request (and Tenant shall
duly comply) that Tenant, at the time that Tenant admits any new partner to its
partnership, shall require each such new partner to execute an agreement in form
and substance satisfactory to Landlord whereby such new partner shall agree to
be personally bound by and upon all of the covenants, agreements, terms,
provisions and conditions of the Lease on the part of Tenant to be performed,
without regard to the time when such new partner is admitted to partnership or
when any obligations under any such covenants, etc., accrue.

     16.7   LISTING CONFERS NO RIGHTS. The listing of any name other than that
of Tenant, whether on the doors of the Premises or on the Building directory, or
otherwise, shall not operate to vest in any such other person, firm or
corporation any right or interest in the Lease or in the Premises or be deemed
to effect or evidence any consent of Landlord, it being expressly understood
that any such listing is a privilege extended by Landlord revocable at will by
written notice to Tenant.

     16.8   PROFITS IN CONNECTION WITH TRANSFERS. Tenant shall, within thirty
(30) days of receipt thereof, pay to Landlord fifty percent (50%) of any rent,
sum or other consideration to be paid or given in connection with any Transfer
to any entity other than an Affiliated Entity, either initially or over time,
after deducting reasonable actual out-of-pocket legal and brokerage expenses
incurred by Tenant in connection therewith, in excess of Rent hereunder as if
such amount were originally called for by the terms of this Lease as additional
rent.

     16.9   PROHIBITED TRANSFERS. Notwithstanding any contrary provision of this
Lease, Tenant shall have no right to make a Transfer unless on both (i) the date
on which Tenant notifies Landlord of its intention to enter into a Transfer and
(ii) the date on which such Transfer is to take effect, no Event of Default
exists. Notwithstanding anything to the contrary contained herein, Tenant agrees
that in no event shall Tenant make a Transfer to any of the following entities:
(a) any tenant, subtenant or occupant of other premises in the Building or the
Condominium unless the tenant, subtenant or occupant is seeking expansion space
and Landlord has stated in writing that it cannot supply such space; (b)
government agencies; or (c) any tenants with whom Landlord shall have negotiated
for any space in the Condominium in the six (6) months immediately preceding
such proposed Transfer.

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17.  MISCELLANEOUS COVENANTS

     Tenant covenants and agrees as follows:

     17.1   RULES AND REGULATIONS. Tenant will faithfully observe and comply
with the all rules and regulations promulgated by Landlord from time to time
with respect to the Building, the Condominium, the Parking Garage and relating
to construction within the Condominium (collectively, the "RULES AND
REGULATIONS"). The current version of the Rules and Regulations is attached
hereto as EXHIBIT 10. In the case of any conflict or inconsistency between the
provisions of the Lease and any future rules and regulations, the provisions of
the Lease shall control. Nothing contained in the Lease shall be construed to
impose upon Landlord any duty or obligation to enforce the Rules and Regulations
or the terms, covenants or conditions in any other lease as against any other
tenant and Landlord shall not be liable to Tenant for violation of the same by
any other tenant, its servants, employees, agents, contractors, visitors,
invitees or licensees.

     17.2   ACCESS TO PREMISES-SHORING. If an excavation shall be made upon
land adjacent to the Premises or shall be authorized to be made, Tenant shall
afford to the person or entity causing or authorized to cause such excavation,
license to enter upon the Premises for the purpose of doing such work as said
person or entity shall deem necessary to preserve the Building from injury or
damage and to support the same by proper foundations without any claims for
damages or indemnity against Landlord, or diminution or abatement of rent.

     17.3   ACCIDENTS TO SANITARY AND OTHER SYSTEMS. Tenant shall give to
Landlord prompt notice of any fire or accident in the Premises or in the
Building and of any damage to, or defective condition in, any part or
appurtenance of the Building including, without limitation, acid waste
neutralization systems, sanitary, electrical, ventilation, heating and air
conditioning or other systems located in, or passing through, the Premises.
Except as otherwise provided in Article 18, and subject to Tenant's obligations
in Article 14, such damage or defective condition shall be remedied by Landlord
with reasonable diligence, but subject to Section 15.9 above, if such damage or
defective condition was caused by any of the Tenant Parties, the cost to remedy
the same shall be paid by Tenant.

     17.4   SIGNS, BLINDS AND DRAPES. Tenant will not place or suffer to be
placed or maintained on the exterior of the Premises, or any part of the
interior visible from the exterior thereof, any sign, banner, advertising matter
or any other thing of any kind (including, without limitation, any hand-lettered
advertising), and will not place or maintain any decoration, letter or
advertising matter on the glass of any window or door of the Premises without
first obtaining Landlord's written approval. No signs or blinds may be put on or
in any window or elsewhere if visible from the exterior of the Building.
Landlord shall provide Tenant with the building standard blinds for each window
within the Premises and Tenant shall install the same at Tenant's sole cost and
expense. Tenant may not remove the building standard blinds without Landlord's
prior written consent. Tenant may hang its own drapes, provided that they shall
not in any way interfere with the building standard drapery or blinds or be
visible from the exterior of the Building and that such drapes are so hung and
installed such that when drawn, the building standard drapery or blinds are
automatically also drawn.

     17.5   ESTOPPEL CERTIFICATE. Tenant shall at any time and from time to time
upon not less than fifteen (15) days' prior notice from Landlord, execute,
acknowledge and deliver to Landlord a statement in writing certifying that the
Lease is unmodified and in full force and effect (or if there have been
modifications, that the same is in full force and effect as modified and stating
the modifications), and the dates to which Rent has been paid in advance, if
any, stating whether or not Landlord is in default in performance of any
covenant, agreement, term, provision or condition contained in the Lease and, if
so,

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specifying each such default, and such other facts as Landlord may reasonably
request, it being intended that any such statement delivered pursuant hereto may
be relied upon by any prospective purchaser of the Building or of any interest
of Landlord therein, any Mortgagee or prospective Mortgagee thereof, any lessor
or prospective lessor thereof, any lessee or prospective lessee thereof, or any
prospective assignee of any mortgage thereof. TIME IS OF THE ESSENCE WITH
RESPECT TO ANY SUCH REQUESTED CERTIFICATE, Tenant hereby acknowledging the
importance of such certificates in mortgage financing arrangements, prospective
sales and the like.

     17.6   PROHIBITED MATERIALS AND PROPERTY; ENVIRONMENTAL PROVISIONS.

            (a)  Tenant shall not, without the prior written consent of
Landlord, bring or permit to be brought or kept in or on the Premises or
elsewhere in the Building or the Condominium (i) any inflammable, combustible or
explosive fluid, material, chemical or substance (except for standard office
supplies stored in proper containers); and (ii) any Hazardous Material
(hereinafter defined) other than the types of Hazardous Materials listed on
EXHIBIT 13 attached hereto ("TENANT'S HAZARDOUS MATERIALS"), provided that the
same shall at all times be brought upon, kept or used in so-called 'control
rooms' and in accordance with all applicable Environmental Laws (hereinafter
defined) and prudent environmental practice and (with respect to medical waste
and so-called "biohazard" materials) good medical practice. Tenant shall be
responsible for assuring that all laboratory uses are adequately and properly
vented. On or before each anniversary of the Rent Commencement Date, and on any
earlier date during the 12-month period on which Tenant intends to add a new
Hazardous Material to the list of Tenant's Hazardous Materials, Tenant shall
submit to Landlord an updated list of Tenant's Hazardous Materials for
Landlord's review and approval, which approval shall not be unreasonably
withheld, conditioned or delayed. Tenant shall have no more than one (1) control
room on each floor of the Premises. In no event shall the quantity of any of
Tenant's Hazardous Materials on any floor of the Premises exceed Tenant's
Proportionate Share of Hazardous Materials for such floor at any one time
without Landlord's prior written consent. For purposes hereof, "TENANT'S
PROPORTIONATE SHARE OF HAZARDOUS MATERIALS" shall mean Tenant's proportionate
share (calculated by dividing the number of rentable square feet on each floor
of the Premises by the total number of rentable square feet on such floor) of
the amount of each of Tenant's Hazardous Materials allowed to be brought or kept
on such floor (as constructed and configured pursuant to the provisions hereof
and without the construction of a so-called 'explosion room', the parties hereby
acknowledging that the Building was not designed to allow for the construction
of any explosion rooms) by Environmental Laws. Landlord shall have the right,
from time to time, upon twenty four (24) hours' advance written notice (except
that no notice shall be required in an emergency), to inspect the Premises for
compliance with the terms of this Section 17.6 at Tenant's sole cost and
expense. Notwithstanding the foregoing, with respect to any of Tenant's
Hazardous Materials which Tenant does not properly handle, store or dispose of
in compliance with all applicable Environmental Laws (hereinafter defined),
prudent environmental practice and (with respect to medical waste and so-called
"biohazard materials) good medical practice, Tenant shall, upon written notice
from Landlord, no longer have the right to bring such material into the Building
or the Condominium until Tenant has demonstrated, to Landlord's reasonable
satisfaction, that Tenant has implemented programs to thereafter properly
handle, store or dispose of such material.

            (b)  Tenant, at its sole cost and expense, shall comply with (i) all
laws, statutes, ordinances, rules and regulations of any local, state or federal
governmental authority having jurisdiction concerning environmental, health and
safety matters, including, without limitation, the laws listed in Section
17.6(c) below (collectively, "ENVIRONMENTAL LAWS"), including but not limited to
any discharge into the air, surface, water, sewers, soil or groundwater of any
Hazardous Material, whether within or outside the Premises, Building,
Condominium or Parking Garage, and (ii) any rules, requirements and safety
procedures of the Massachusetts Department of Environmental Protection, the City
of Cambridge

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Fire Marshall and any insurer of the Condominium, Building or the Premises with
respect to the use, storage and disposal of any Hazardous Materials at or from
the Premises.

            (c)  As used herein, the term "HAZARDOUS MATERIAL" means (x) medical
waste or "biohazard" materials, and (y) any hazardous, radioactive or toxic
substance, material or waste or petroleum derivative which is or becomes
regulated by any Environmental Law. The term "HAZARDOUS MATERIAL" includes,
without limitation, any material or substance which is (i) designated as a
"hazardous substance" pursuant to Section 1311 of the Federal Water Pollution
Control Act (33 U.S.C. Section 1317), (ii) defined as a "hazardous waste"
pursuant to Section 1004 of the Federal Resource Conservation and Recovery Act,
42 U.S.C. Section 6901 et seq. (42 U.S.C. Section 6903), or (iii) defined as a
"hazardous substance" pursuant to Section 101 of the Comprehensive Environmental
Response, Compensation and Liability Act, 42 U.S.C. Section 9601 et seq. (42
U.S.C. Section 9601), or (iv) defined as "hazardous substance" or "oil" under
Chapter 21E of the General Laws of Massachusetts.

            (d)  Tenant shall procure and maintain at its sole expense such
additional insurance as may be necessary to comply with any Legal Requirements
and will deliver certificates of such insurance to Landlord evidencing the
foregoing.

            (e)  Any increase in the premium for necessary insurance on the
Premises or the Condominium, to the extent such increase arises from Tenant's
use and/or storage of Tenant's Hazardous Materials, shall be at Tenant's
expense. Tenant shall procure and maintain at its sole expense such additional
insurance as may be necessary to comply with any requirement of any Federal,
State or local government agency with jurisdiction.

            (f)  If any Mortgagee or governmental authority requires testing to
determine whether there has been any release of Hazardous Materials and such
testing is required as a result of the acts or omissions of any of the Tenant
Parties, then Tenant shall reimburse Landlord upon demand, as additional rent,
for the reasonable costs thereof, together with interest at the Default Rate
until paid in full. Tenant shall execute affidavits, certifications and the
like, as may be reasonably requested by Landlord from time to time concerning
Tenant's best knowledge and belief concerning the presence of Hazardous
Materials in or on the Premises, the Building or the Condominium.

            (g)  Tenant hereby covenants and agrees to indemnify, defend and
hold the Landlord Indemnitees harmless from and against any and all Claims
against any of the Landlord Indemnitees arising out of contamination of any part
of the Condominium or the Parking Garage or other adjacent property, which
contamination arises as a result of: (i) the presence of Hazardous Material in
the Premises, the presence of which is caused by any act or omission of any of
the Tenant Parties, or (ii) from a breach by Tenant of its obligations under
this Section 17.6. This indemnification of the Landlord Indemnitees by Tenant
includes, without limitation, reasonable costs incurred in connection with any
investigation of site conditions or any cleanup, remedial, removal or
restoration work required by any federal, state or local governmental agency or
political subdivision because of Hazardous Material present in the soil or
ground water on or under the Building based upon the circumstances identified in
the first sentence of this Section 17.6(g). The indemnification and hold
harmless obligations of Tenant under this Section 17.6(g) shall survive the
expiration or any earlier termination of this Lease. Without limiting the
foregoing, if the presence of any Hazardous Material in the Building or
otherwise in the Condominium is caused by any of the Tenant Parties and results
in any contamination of any part of the Condominium or the Parking Garage or any
adjacent property, Tenant shall promptly take all actions at Tenant's sole cost
and expense as are necessary to return the Condominium, Building and/or the
Parking Garage or any adjacent property to their condition immediately prior
thereto, provided that Tenant shall first obtain Landlord's approval of such
actions, which approval shall not be unreasonably withheld,

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conditioned or delayed so long as such actions, in Landlord's reasonable
discretion, would not potentially have any adverse effect on the Condominium,
and, in any event, Landlord shall not withhold its approval of any proposed
actions which are required by applicable Environmental Laws.

            (h)  Prior to bringing any Hazardous Material into any part of the
Condominium, Tenant shall deliver to Landlord the following information with
respect thereto: (a) a description of handling, storage, use and disposal
procedures; (b) all plans or disclosures and/or emergency response plans which
Tenant has prepared, including without limitation Tenant's Spill Response Plan,
and all plans which Tenant is required to supply to any governmental agency or
authority pursuant to any Environmental Laws; and (c) other information
reasonably requested by Landlord.

     17.7   LEGAL REQUIREMENTS. Tenant shall be responsible at its sole cost and
expense for complying with (and keeping the Building and the Premises in
compliance with) all Legal Requirements which are applicable to Tenant's
particular use or occupancy of, or Tenant's Work or Alterations made by Tenant
to, the Premises. In addition, Tenant shall, at Tenant's sole expense, for so
long as the Parking and Traffic Demand Management Plan dated May 9, 1999 as
approved by the City of Cambridge on July 9, 1999 (and subject to the conditions
set forth in such approval) remains applicable to the Condominium, offer to
subsidize mass transit monthly passes for all of its employees and otherwise
cooperate with Landlord in encouraging employees to seek alternate modes of
transportation. If Tenant receives notice of any violation of Legal Requirements
applicable to the Premises, it shall give prompt notice thereof to Landlord.
Nothing contained in this Section 17.7 shall be construed to expand the uses
permitted hereunder beyond the Permitted Uses. Landlord shall comply with any
Legal Requirements and with any direction of any public office or officer
relating to the maintenance or operation of the Building as a combination
office/laboratory building, and the costs so incurred by Landlord shall be
included in Building Operating Costs in accordance with the provisions of
Article 10.

     17.8   TENANT'S ACTS--EFFECT ON INSURANCE. Tenant shall not do or permit to
be done any act or thing upon the Premises or elsewhere in the Building which
will invalidate or be in conflict with any insurance policies covering the
Building, any other building within the Condominium and the fixtures and
property therein; and shall not do, or permit to be done, any act or thing upon
the Premises which shall subject Landlord to any liability or responsibility for
injury to any person or persons or to property by reason of any business or
operation being carried on upon said Premises or for any other reason. If by
reason of the failure of Tenant to comply with the provisions hereof the
insurance rate applicable to any policy of insurance shall at any time
thereafter be higher than it otherwise would be, Tenant shall reimburse Landlord
for that part of any insurance premiums which shall have been charged because of
such failure by Tenant.

18.  CASUALTY; TAKING

     18.1   DAMAGE. If the Premises become untenantable in whole or part because
of fire or other casualty covered by insurance required under the Lease or
actually carried ("CASUALTY"), or as the result of a taking of, or damage to,
the Building, thereon in connection with the exercise of any power of eminent
domain, condemnation, or purchase under threat or in lieu thereof (any of the
foregoing, a "TAKING"), then unless the Lease is terminated in accordance with
Section 18.2 below, Landlord, with reasonable dispatch shall restore the
Building and/or the Premises as applicable in the manner set forth herein. In
the event of a Casualty or Taking, Landlord shall repair the Building and the
Premises so that the Building and the Premises are in substantially the same
condition as following completion of Landlord's Work as set forth in Section
4.1, or in the event of a partial Taking which affects the Building and the
Premises, restore the remainder of the Building and the Premises not so Taken to
substantially the same condition as is reasonably feasible. If, in Landlord's
reasonable judgment, any element of the

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                                      -37-
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Tenant-Insured Improvements can more effectively be repaired as an integral part
of Landlord's repair work to the Building or the Premises, such repair shall
also be made by Landlord, but at Tenant's sole cost and expense. Landlord shall
substantially complete such repair within one (1) year with respect to
substantial reconstruction of at least 50% of the Building, or, within one
hundred eighty (180) days in the case of restoration of less than 50% of the
Building from the date of said Casualty or Taking. Landlord's obligation to
repair shall be subject to rights of Mortgagees, Legal Requirements, zoning
laws, and building codes then in existence and to delays for adjustment of
insurance proceeds or Taking awards, as the case may be, and instances of
Landlord's Force Majeure. Tenant agrees to cooperate with Landlord in such
manner as Landlord may reasonably request to assist Landlord in collecting
insurance proceeds due in connection with any Casualty which affects the
Premises or the Building. In no event shall Landlord be required to expend more
than the Net (hereinafter defined) insurance proceeds Landlord receives for
damage to the Premises and/or the Building or the Net Taking award attributable
to the Premises and/or the Building. "NET" means the insurance proceeds or
Taking award actually paid to Landlord (and not paid over to a Mortgagee) less
all costs and expenses, including adjusters and attorney's fees, of obtaining
the same. Tenant also shall be required to pay to Landlord Tenant's Percentage
Share of any deductible under any property insurance policy maintained by
Landlord (but only to the extent not already accounted for in Building Operating
Costs). Under no circumstances shall Landlord be required to repair any damage
to, or make any repairs to or replacements of, Tenant's Property.

     18.2   TERMINATION RIGHTS.

            (a)  LANDLORD'S TERMINATION RIGHTS. Landlord may terminate the Lease
upon thirty (30) days' prior written notice to Tenant:

                 (i)     if the cost to repair the Premises or Building in the
event of a Casualty or Taking exceeds $750,000 or the same is not covered by
insurance maintained by Landlord;

                 (ii)    if any material portion of the Building or any material
means of access thereto is subject to a Taking; or

                 (iii)   if more than twenty-five percent (25%) of the Building
is damaged by any Casualty.

            (b)  TENANT'S TERMINATION RIGHT. If Landlord is so required but
fails to complete restoration of the Premises within the time frames set forth
in Section 18.1 above, subject to Landlord's Force Majeure and Tenant Delay,
then Tenant may terminate the Lease upon thirty (30) days' written notice to
Landlord; provided, however, that if Landlord completes such restoration within
said 30-day period, such termination notice shall be null and void and the Lease
shall continue in full force and effect.

            (c)  EITHER PARTY MAY TERMINATE. In the case of any Casualty or
Taking affecting the Premises and occurring during the last twelve (12) months
of the term hereof, then (i) if such Casualty or Taking to the Premises results
in more than twenty-five percent (25%) of the floor area of the Premises being
unsuitable for the Permitted Uses, or (ii) the damage to the Premises costs more
than $50,000 to repair, then either Landlord or Tenant shall have the option to
terminate the Lease upon thirty (30) days' written notice to the other;
provided, however, that Tenant shall have the right to nullify Landlord's
termination notice under this Section 18.2(c) by sending written notice to
Landlord exercising its right to extend the term hereof, if any, pursuant to
Article 25 below.

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            (d)  AUTOMATIC TERMINATION. In the case of a Taking of the entire
Premises, then this Lease shall automatically terminate as of the date of
possession by the Taking authority.

     18.3   ABATEMENT. If the Premises are untenantable in whole or in part as a
result of Casualty or Taking, the Yearly Rent and payments of Building Operating
Costs and Taxes payable hereunder during the period in which they are
untenantable shall be equitably reduced or abated.

     18.4   TAKING FOR TEMPORARY USE. Subject to Section 18.3 above, if the
Premises are Taken for temporary use, the Lease and Tenant's obligations,
including without limitation the payment of Rent, shall continue. For purposes
hereof, a "Taking for temporary use" shall mean a Taking of ninety (90) days or
less.

     18.5   DISPOSITION OF AWARDS. Except for any separate award for Tenant's
movable trade fixtures, relocation expenses, and unamortized leasehold
improvements (provided that the same may not reduce Landlord's award), all
Taking awards to Landlord or Tenant shall be Landlord's property without
Tenant's participation. Tenant may pursue its own claim against the Taking
authority.

19.  DEFAULT

     19.1   EVENTS OF DEFAULT; REMEDIES. The occurrence of any one or more of
the following events shall constitute an "EVENT OF DEFAULT" hereunder by Tenant:

            (a)  The failure by Tenant to make any payment of Rent or any other
payment required hereunder, as and when due, where such failure shall continue
for a period often (10) days after notice thereof from Landlord to Tenant;
provided, however, an Event of Default shall occur hereunder without any
obligation of Landlord to give any notice if Landlord has given Tenant written
notice under this Section 19.1(a) on more than one (1) occasion during the
twelve (12) month interval preceding such failure by Tenant;

            (b)  If Tenant shall abandon the Premises (whether or not the keys
shall have been surrendered or the rent shall have been paid);

            (c)  If Tenant shall fail to maintain any insurance required
hereunder;

            (d)  If Tenant shall fail to deliver a replacement Letter of Credit
as required under Article 24 below;

            (e)  If Tenant causes or suffers any release of Hazardous Materials
in or near the Condominium;

            (f)  If Tenant shall make a Transfer in violation of the provisions
of Article 16 above, or if any event shall occur or any contingency shall arise
whereby the Lease, or the term and estate thereby created, would (by operation
of law or otherwise) devolve upon or pass to any person, firm or corporation
other than Tenant, except as expressly permitted under Article 16 hereof;

            (g)  If Tenant shall fail to deliver an estoppel certificate as
required pursuant to Section 17.5 above;

            (h)  The failure by Tenant to observe or perform any of the
covenants or provisions of this Lease to be observed or performed by Tenant,
other than as specified above, and such failure continues for more than thirty
(30) days after notice thereof from Landlord; provided, further, that if the

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nature of Tenant's default is such that more than thirty (30) days are
reasonably required for its cure, then Tenant shall not be deemed to be in
default if Tenant shall commence such cure within said thirty (30) day period
and thereafter diligently prosecute such cure to completion, which completion
shall occur not later than ninety (90) days from the date of such notice from
Landlord;

            (i)  Tenant shall be involved in financial difficulties as evidenced
by an admission in writing by Tenant of Tenant's inability to pay its debts
generally as they become due, or by the making or offering to make a composition
of its debts with its creditors;

            (j)  an attachment on mesne process, on execution or otherwise, or
other legal process shall issue against Tenant or its property and a sale of any
of its assets shall be held thereunder;

            (k)  any judgment, attachment or the like in excess of $75,000 shall
be entered, recorded or filed against Tenant in any court, registry, etc. and
Tenant shall fail to pay such judgment within forty five (45) days after the
judgment shall have become final beyond appeal or to discharge or secure by
surety bond such lien, attachment, etc. within forty five (45) days of such
entry, recording or filing, as the case may be;

            (l)  the leasehold hereby created shall be taken on execution or by
other process of law and shall not be revested in Tenant within thirty (30) days
thereafter;

            (m)  a receiver, sequesterer, trustee 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 shall not be vacated within thirty
(30) days; or

            (n)  any proceeding shall be instituted by or against Tenant
pursuant to any of the provisions of any Act of Congress or State law relating
to bankruptcy, reorganizations, arrangements, compositions or other relief from
creditors, and, in the case of any proceeding instituted against it, if Tenant
shall fail to have such proceedings dismissed within thirty (30) days or if
Tenant is adjudged bankrupt or insolvent as a result of any such proceeding.

Upon an Event of Default, Landlord may, by notice to Tenant, elect to terminate
the Lease; and thereupon (and without prejudice to any remedies which might
otherwise be available for arrears of Rent or preceding breach of covenant or
agreement and without prejudice to Tenant's liability for damages as hereinafter
stated), upon the giving of such notice, the Lease shall terminate as of the
date specified therein as though that were the Expiration Date. Without being
taken or deemed to be guilty of any manner of trespass or conversion, and
without being liable to indictment, prosecution or damages therefor, Landlord
may, forcibly if necessary, enter into and upon the Premises (or any part
thereof in the name of the whole); repossess the same, as of its former estate;
and expel Tenant and those claiming under Tenant. Wherever "Tenant" is used in
subsections (h), (i), (j), (k), (l), (m), and (n) of this Section 19.1, it shall
be deemed to include any parent entity of Tenant and any guarantor of any of
Tenant's obligations under the Lease. The words "re-entry" and "re-enter" as
used in the Lease are not restricted to their technical legal meanings.

     19.2   DAMAGES - TERMINATION.

            (a)  Upon the termination of the Lease under the provisions of this
Article 19, Tenant shall pay to Landlord Rent up to the time of such
termination, shall continue to be liable for any preceding breach of covenant,
and in addition, shall pay to Landlord as damages, at the election of Landlord,
either:

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                 (i)     the amount by which, at the time of the termination of
the Lease (or at any time thereafter if Landlord shall have initially elected
damages under Section 19.2(a)(ii), below), (x) the aggregate of Rent projected
over the period commencing with such termination and ending on the Expiration
Date, exceeds (y) the aggregate projected rental value of the Premises for such
period; or

                 (ii)    amounts equal to Rent which would have been payable by
Tenant had the Lease not been so terminated, payable upon the due dates therefor
specified herein following such termination and until the Expiration Date,
PROVIDED, HOWEVER, if Landlord shall re-let the Premises during such period,
that Landlord shall credit Tenant with the net rents received by Landlord from
such re-letting, such net rents to be determined by first deducting from the
gross rents as and when received by Landlord from such re-letting the expenses
incurred or paid by Landlord in terminating the Lease, as well as the expenses
of re-letting, including altering and preparing the Premises for new tenants,
brokers' commissions, and all other similar and dissimilar expenses properly
chargeable against the Premises and the rental therefrom, it being understood
that any such re-letting may be for a period equal to or shorter or longer than
the remaining term of the Lease; and PROVIDED, FURTHER, that (x) in no event
shall Tenant be entitled to receive any excess of such net rents over the sums
payable by Tenant to Landlord hereunder and (y) in no event shall Tenant be
entitled in any suit for the collection of damages pursuant to this Section
19.2(a)(ii) to a credit in respect of any net rents from a re-letting except to
the extent that such net rents are actually received by Landlord prior to the
commencement of such suit. If the Premises or any part thereof should be re-let
in combination with other space, then proper apportionment on a square foot area
basis shall be made of the rent received from such re-letting and of the
expenses of re-letting.

            (b)  In calculating the amount due under Section 19.2(a)(i), above,
there shall be included, in addition to the Yearly Rent, Tenant's Percentage
Share of Taxes and Building Operating Costs and all other considerations agreed
to be paid or performed by Tenant, on the assumption that all such amounts and
considerations would have remained constant (except as herein otherwise
provided) for the balance of the full term hereby granted.

            (c)  Suit or suits for the recovery of such damages, or any
installments thereof, may be brought by Landlord from time to time at its
election, and nothing contained herein shall be deemed to require Landlord to
postpone suit until the date when the term of the Lease would have expired if it
had not been terminated hereunder.

            (d)  Nothing herein contained shall be construed as limiting or
precluding the recovery by Landlord against Tenant of any sums or damages to
which, in addition to the damages particularly provided above, Landlord may
lawfully be entitled by reason of any Event of Default hereunder.

            (e)  In lieu of any other damages or indemnity and in lieu of full
recovery by Landlord of all sums payable under all the foregoing provisions of
this Section 19.2, Landlord may, by written notice to Tenant, at any time after
the Lease is terminated under any of the provisions herein contained or is
otherwise terminated for breach of any obligation of Tenant and before such full
recovery, elect to recover, and Tenant shall thereupon pay, as liquidated
damages, an amount equal to the aggregate of (x) an amount equal to the lesser
of (1) Rent accrued under the Lease in the nine (9) months immediately prior to
such termination, or (2) Rent payable during the remaining months of the term if
the Lease had not been terminated, plus (y) the amount of Rent accrued and
unpaid at the time of termination, less (z) the amount of any recovery by
Landlord under the foregoing provisions of this Section 19.2 up to the time of
payment of such liquidated damages.

            (f)  Landlord shall use reasonable efforts to mitigate any damages
hereunder

                                TOLERRX LEASE / BUILDING 300 / EXECUTION VERSION

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following the termination of this Lease under this Article 19. The obligation of
Landlord to use reasonable efforts to mitigate damages shall not be construed to
require Landlord to rent all or any portion of the Premises for a use which, or
to a tenant who, would not meet the requirements of Article 16 with respect to a
proposed transferee, or to prioritize the renting of the Premises over other
space which Landlord may have available in the Building, the Condominium or in
other properties owned by Landlord.

     19.3   LANDLORD'S SELF-HELP; FEES AND EXPENSES.

            (a)  LANDLORD'S SELF-HELP. If Tenant shall default in the
performance of any covenant on Tenant's part to be performed in the Lease
contained, including without limitation the obligation to maintain the Premises
in the required condition pursuant to Section 14.1 above, Landlord may, after
the expiration of the applicable grace period provided in Section 19.1 above, if
any (except that no notice and/or grace period shall be required in an
emergency), immediately, or at any time thereafter, without notice, perform the
same for the account of Tenant. Tenant shall pay to Landlord upon demand
therefor any costs incurred by Landlord in connection therewith, together with
interest at the Default Rate until paid in full.

            (b)  REIMBURSEMENT OF FEES AND EXPENSES. If Landlord at any time is
compelled to pay or elects to pay any sum of money, or do any act which will
require the payment of any sum of money, by reason of the failure of Tenant to
comply with any provision hereof after expiration of the applicable notice and
cure periods, if any, or if Landlord is compelled to or does incur any expense,
including reasonable attorneys' fees, in instituting, prosecuting, and/or
defending any action or proceeding instituted by reason of any default of Tenant
hereunder, Tenant shall on demand pay to Landlord by way of reimbursement the
sum or sums so paid by Landlord with all costs and damages, plus interest at the
Default Rate until paid in full. In addition, Tenant shall pay all of Landlord's
costs and expenses, including without limitation reasonable attorneys' fees,
incurred (i) in enforcing any obligation of Tenant under the Lease or (ii) as a
result of Landlord or any of the Landlord Indemnitees, without its fault, being
made party to any litigation pending by or against any of the Tenant Parties.

     19.4   WAIVER OF REDEMPTION, STATUTORY NOTICE AND GRACE PERIODS. Tenant
does hereby waive and surrender all rights and privileges which it might have
under or by reason of any present or future Legal Requirements to redeem the
Premises or to have a continuance of the Lease for the term hereby demised after
being dispossessed or ejected therefrom by process of law or under the terms of
the Lease or after the termination of the Lease as herein provided. Except to
the extent prohibited by Legal Requirements, any statutory notice and grace
periods provided to Tenant by law are hereby expressly waived by Tenant.

     19.5   LANDLORD'S REMEDIES NOT EXCLUSIVE. The specified remedies to which
Landlord may resort hereunder are cumulative and are not intended to be
exclusive of any remedies or means of redress to which Landlord may at any time
be lawfully entitled, and Landlord may invoke any remedy (including the remedy
of specific performance) allowed at law or in equity as if specific remedies
were not herein provided for.

     19.6   NO WAIVER. Landlord's failure to seek redress for violation, or to
insist upon the strict performance, of any covenant or condition of the Lease,
or any of the Rules and Regulations promulgated hereunder, shall not prevent a
subsequent act, which would have originally constituted a violation, from having
all the force and effect of an original violation. The receipt by Landlord of
Rent with knowledge of the breach of any covenant of the Lease shall not be
deemed a waiver of such breach. The failure of Landlord to enforce any of such
Rules and Regulations against Tenant and/or any other tenant in the

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Building shall not be deemed a waiver of any such Rules and Regulations. No
provisions of the Lease shall be deemed to have been waived by either party
unless such waiver be in writing signed by such party. No payment by Tenant or
receipt by Landlord of a lesser amount than the Rent herein stipulated shall be
deemed to be other than on account of the stipulated Rent, 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 Rent or pursue any other remedy in the Lease provided.

20.  SURRENDER; ABANDONED PROPERTY; HOLD-OVER

     20.1   SURRENDER.

            (a)  Upon the expiration or other termination of the term hereof,
Tenant shall (i) peaceably quit and surrender to Landlord the Premises and all
Tenant's Work and Alterations thereto, broom clean, in good order, repair and
condition (except as provided herein and in Section 8.5 and Article 18)
excepting only ordinary wear and tear and damage by fire or other Casualty; (ii)
remove any and all Hazardous Materials, all of Tenant's Property and, to the
extent specified by Landlord but subject to the terms of Article 12 above, all
Alterations made by Tenant and Tenant's Removable Property, and (iii) repair any
damages to the Premises or the Building caused by the installation or removal
thereof. Tenant's obligations under this Section 20.1 (a) shall survive the
expiration or other termination of the Lease.

            (b)  No act or thing done by Landlord during the term hereby demised
shall be deemed an acceptance of a surrender of the Premises, and no agreement
to accept such surrender shall be valid, unless in writing signed by Landlord.
Unless otherwise agreed by the parties in writing, no employee of Landlord or of
Landlord's agents shall have any power to accept the keys of the Premises prior
to the termination of the Lease. The delivery of keys to any employee of
Landlord or of Landlord's agents shall not operate as a termination of the Lease
or a surrender of the Premises.

     20.2   ABANDONED PROPERTY. After the expiration or earlier termination
hereof, if Tenant fails to remove any property from the Building or the Premises
which Tenant is obligated by the terms of this Lease to remove within fifteen
(15) days after written notice from Landlord, such property (the "ABANDONED
PROPERTY") shall be conclusively deemed to have been abandoned, and may either
be retained by Landlord as its property or sold or otherwise disposed of in such
manner as Landlord may see fit. If any item of Abandoned Property shall be sold,
Tenant hereby agrees that Landlord may receive and retain the proceeds of such
sale and apply the same, at its option, to the expenses of the sale, the cost of
moving and storage, any damages to which Landlord may be entitled under Article
19 hereof or pursuant to law, and to any arrears of Rent.

     20.3   HOLDOVER. If any of the Tenant Parties holds over after the end of
the term hereof, such party shall, prior to Landlord's acceptance of Rent, be a
tenant-at-sufferance, and, after Landlord's acceptance of Rent, be a
tenant-at-will subject to the provisions of this Lease insofar as the same may
be made applicable to a tenancy-at-will; provided that whether or not Landlord
has accepted Rent, (i) Tenant shall pay Yearly Rent at 150% of the highest rate
of Yearly Rent payable during the term hereof. In addition, in the event Tenant
holds over for a period in excess of thirty (30) days, provided that Landlord
notifies Tenant in writing that it has entered into a lease for the Premises (or
a portion thereof), which notice shall specify a period of not less than
forty-five (45) days after which consequential damages shall commence to accrue
if such holdover continues by Tenant and which notice by Landlord to Tenant may
be given prior to the expiration of said 30-day period, then, Tenant shall be
liable for all actual damages, including without limitation consequential
damages, incurred by Landlord as a result of

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such holding over.

21.  MORTGAGEE RIGHTS

     21.1   SUBORDINATION. Tenant's rights and interests under this Lease shall
be (i) subject and subordinate to any future mortgages, deeds of trust,
overleases, or similar instruments covering the Premises and to all advances,
modifications, renewals, replacements, and extensions thereof (each of the
foregoing, a "MORTGAGE"), or (ii) if any Mortgagee elects, prior to the lien of
any present or future Mortgage. Tenant further shall attorn to and recognize any
successor landlord, whether through foreclosure or otherwise, as if the
successor landlord were the originally named landlord, provided such successor
assumes all obligations under the Lease. Notwithstanding anything to the
contrary in this Article 21 contained, as to any future Mortgage, the herein
provided subordination and attornment shall be effective only if the Mortgagee
agrees, by a written commercially reasonable instrument in recordable form
("NONDISTURBANCE AGREEMENT") that, as long as Tenant shall not be in default of
the obligations on its part to be kept and performed under the terms of this
Lease, this Lease will not be affected and Tenant's possession and rights
hereunder will not be disturbed by any default in, termination, and/or
foreclosure of, such Mortgage. In no event shall such Mortgagee (i) have any
liability for any act, omission, negligence or default of any prior landlord
(other than to cure defaults of a continuing nature with respect to the
maintenance or repair of the Premises, the Building or the Condominium); (ii) be
bound by any rents paid more than one month in advance to any prior landlord,
(iii) be subject to any offsets or defenses which Tenant might have against any
prior landlord under the Lease; (iv) be bound by any modification, amendment,
extension or cancellation of the Lease not consented to in writing by the
Mortgagee; (v) have any liability for indirect or consequential damages; or (vi)
be liable for the Letter of Credit (hereinafter defined) not delivered to
Mortgagee. Furthermore, as to any Event of Default by Tenant under the Lease
existing at the time of foreclosure, such foreclosure shall not operate to waive
or abate any action initiated by any prior landlord under the Lease to terminate
the same on account of such Event of Default. In no event shall the Mortgagee
have any personal liability as successor to Landlord, and Tenant shall look only
to the estate and property of the Mortgagee in the Building and the Condominium
for the satisfaction of Tenant's remedies for the collection of a judgment (or
other judicial process) requiring the payment of money in the event of any
default by Mortgagee as Landlord under the Lease, and no other property or
assets of the Mortgagee shall be subject to levy, execution or other enforcement
procedure for the satisfaction of Tenant's remedies under or with respect to the
Lease.

     21.2   NOTICES. Tenant shall give each Mortgagee of which Tenant has
received written notice the same notices given to Landlord concurrently with the
notice to Landlord, and each Mortgagee shall have a reasonable opportunity
thereafter to cure a Landlord default, and Mortgagee's curing of any of
Landlord's default shall be treated as performance by Landlord.

     21.3   MORTGAGEE CONSENT. Tenant acknowledges that, where applicable, any
consent or approval hereafter given by Landlord may be subject to the further
consent or approval of a Mortgagee; and the failure or refusal of such Mortgagee
to give such consent or approval shall, notwithstanding anything to the contrary
in the Lease contained, constitute reasonable justification for Landlord's
withholding its consent or approval.

22.  QUIET ENJOYMENT

     Landlord covenants that so long as Tenant keeps and performs each and every
covenant, agreement, term, provision and condition herein contained on the part
and on behalf of Tenant to be kept and performed, Tenant shall peaceably and
quietly hold, occupy and enjoy the Premises during the Term hereof from and
against the claims of all persons lawfully claiming by, through or under
Landlord

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subject, nevertheless, to the covenants, agreements, terms, provisions and
conditions of the Lease, any matters of record or of which Tenant has knowledge
and to any Mortgage to which the Lease is subject and subordinate, as
hereinabove set forth.

23.  INTENTIONALLY DELETED

24.  LETTER OF CREDIT

     24.1   AMOUNT OF LETTER OF CREDIT. Contemporaneously with the execution of
the Lease, Tenant shall deliver an irrevocable letter of credit to Landlord
which shall (i) be in the form attached hereto as EXHIBIT 11; (ii) issued by a
bank reasonably acceptable to Landlord upon which presentment may be made in
Boston, Massachusetts (if Landlord so requires at the time of its approval
thereof); and (iii) be for a term of one (1) year, subject to extension in
accordance with the terms hereof (the "LETTER OF CREDIT"). The Letter of Credit
shall be held by Landlord, without liability for interest, as security for the
faithful performance by Tenant of all of the terms, covenants and conditions of
the Lease by the Tenant to be kept and performed during the Term. In no event
shall the Letter of Credit be deemed to be a prepayment of Rent nor shall it be
considered a measure of liquidated damages. At least thirty (30) days prior to
the maturity date of the Letter of Credit (or any replacement Letter of Credit),
Tenant shall deliver to Landlord a replacement Letter of Credit which shall have
a maturity date no earlier than the next anniversary of the Term Commencement
Date or one (1) year from its date of delivery to Landlord, whichever is later.

     24.2   If no Event of Default has occurred and no event has occurred which,
with the passage of time and/or the giving of notice, would constitute an Event
of Default at the commencement of such Lease Year, then the face amount of the
Letter of Credit shall be reduced to (a) $1,552,500.00 at the commencement of
the Second Lease Year, and (b) $1,035,000.00 at the commencement of the Third
Lease Year. Upon receipt of a replacement Letter of Credit in the reduced face
amount, Landlord shall return the original Letter of Credit to the issuer
thereof, with a copy to Tenant.

     24.3   APPLICATION OF PROCEEDS OF LETTER OF CREDIT. Upon an Event of
Default, then Landlord at its sole option may draw down all or a part of the
Letter of Credit to compensate Landlord for loss or damage sustained or suffered
by Landlord due to such breach on the part of Tenant. Should the entire Letter
of Credit, or any portion thereof, be appropriated and applied by Landlord,
Tenant shall, upon the written demand of Landlord, deliver to Landlord a
replacement Letter of Credit in the full original amount, and Tenant's failure
to do so within five (5) days after receipt of such demand shall constitute an
Event of Default hereunder. The application of all or any part of the cash
proceeds of the Letter of Credit to any obligation or default of Tenant under
the Lease shall not deprive Landlord of any other rights or remedies Landlord
may have nor shall such application by Landlord constitute a waiver by Landlord.

     24.4   TRANSFER OF LETTER OF CREDIT. In the event that Landlord transfers
its interest in the Premises, Tenant shall, at Tenant's cost subject to
reimbursement by Landlord in accordance with the following sentence, upon notice
from Landlord deliver to Landlord an amendment to the Letter of Credit or a
replacement Letter of Credit naming Landlord's successor as the beneficiary
thereof. Upon receipt of a reasonably detailed invoice therefor, Landlord shall
reimburse Tenant for the cost of the transfer fee charged by the issuer of such
amendment or replacement Letter of Credit up to a maximum of one-quarter (1/4)
of one percent (1%) of the transferred amount thereof. Tenant hereby agrees that
upon any such delivery, Landlord shall be released from any and all liability
with respect to the Letter of Credit, its application and return, and Tenant
shall look solely to Landlord's successor for same. If Tenant fails to deliver
such amendment or replacement within fifteen (15) days after notice from
Landlord, Landlord shall have the right to draw down the entire amount of the
Letter of Credit and hold the proceeds thereof

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                                      -45-
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in accordance with this Article 24.

     24.5   CREDIT OF ISSUER OF LETTER OF CREDIT. In the event of a material
adverse change in the financial position of any bank or institution which has
issued the Letter of Credit or any replacement Letter of Credit hereunder,
Landlord reserves the right to require that Tenant change the issuing bank or
institution to another bank or institution reasonably approved by Landlord. If
the bank or institution on which the original Letter of Credit or any
replacement Letter of Credit is drawn is declared insolvent or placed into
conservatorship or receivership, Tenant shall, within ten (10) days thereafter,
replace the then-outstanding letter of credit with a like letter of credit from
another bank or institution acceptable to Landlord.

     24.6   RETURN OF LETTER OF CREDIT. Should Tenant comply with all of such
terms, covenants and conditions and promptly pay all sums payable by Tenant to
Landlord hereunder, the Letter of Credit shall be returned to Tenant within
thirty-one (31) days following the end of the term of the Lease, less any
portion thereof which may have been utilized by Landlord to cure any default or
applied to any damage suffered by Landlord.

25.  TENANT'S OPTION TO EXTEND THE TERM OF THE LEASE

     25.1   Provided (a) Tenant, an Affiliated Entity and/or a Successor is/are
then occupying at least fifty one percent (51%) of the Premises; and (b) no
Event of Default has occurred (i) at the time of Tenant's exercise of such
option, and (ii) at the commencement of the Extension Term (hereinafter
defined), Tenant shall have the option to extend the term of the Lease for one
(1) additional five (5) year term (the "EXTENSION TERM"), commencing as of the
expiration of the initial term of the Lease. Tenant may exercise such option to
extend by giving Landlord written notice on or before the date twelve (12)
months prior to the expiration date of the initial term of the Lease, TIME BEING
OF THE ESSENCE. Upon the timely giving of such notice, the term of the Lease
shall be deemed extended upon all of the terms and conditions of the Lease,
except that Yearly Rent shall be calculated in accordance with Section 25.2
below, Landlord shall have no obligation to construct or renovate the Premises
and Tenant shall have no option to further extend the term hereof. If Tenant
fails to give timely notice, as aforesaid, Tenant shall have no further right to
extend the term of the Lease. Notwithstanding the fact that Tenant's exercise of
the herein option to extend the term hereof shall be self-executing, the parties
shall promptly execute a lease amendment reflecting such Extension Term after
Tenant exercises such option. The execution of such lease amendment shall not be
deemed to waive any of the conditions to Tenant's exercise of its rights under
this Article 25.

     25.2   (a)  The Yearly Rent during the Extension Term (the "EXTENSION TERM
YEARLY RENT") shall be based upon the fair market rental value of the Premises
then demised to Tenant as of the commencement of the Extension Term as
determined in accordance with the process described below, for renewals of space
in the Building of equivalent quality, size, utility and location, with the
length of the Extension Term and the credit standing of Tenant to be taken into
account, provided however, that in no event (including the arbitration procedure
set forth below) shall the sum of Yearly Rent, Tenant's Percentage Share of
Building Operating Costs and Taxes payable by Tenant for any twelve (12) month
period during the Extension Term be less than the sum of Yearly Rent, Tenant's
Percentage Share of Building Operating Costs and Taxes payable by Tenant with
respect to the twelve (12) month period immediately preceding the commencement
of the Extension Term. Within thirty (30) days after receipt of Tenant's notice
to extend the term hereof, Landlord shall deliver to Tenant written notice of
its determination of the Extension Term Yearly Rent. Tenant shall, within thirty
(30) days after receipt of such notice, notify Landlord in writing whether
Tenant accepts or rejects Landlord's determination of the Extension Term Yearly
Rent ("TENANT'S RESPONSE NOTICE"). If Tenant fails timely to deliver Tenant's

                                TOLERRX LEASE / BUILDING 300 / EXECUTION VERSION

                                      -46-
<Page>

Response Notice, Landlord's determination of the Extension Term Yearly Rent
shall be binding on Tenant.

            (b)  If and only if Tenant's Response Notice is timely delivered to
Landlord and indicates both that Tenant rejects Landlord's determination of the
Extension Term Yearly Rent, and Tenant's submission of the matter to
arbitration, then the Extension Term Yearly Rent shall be determined in
accordance with the procedure set forth in this Section 25.2(b). In such event,
within five (5) days after receipt by Landlord of Tenant's Response Notice
indicating Tenant's desire to submit the determination of the Extension Term
Yearly Rent to arbitration, Tenant and Landlord shall each notify the other, in
writing, of their respective selections of an appraiser (respectively,
"LANDLORD'S APPRAISER" and "TENANT'S APPRAISER"). Landlord's Appraiser and
Tenant's Appraiser shall then jointly select a third appraiser (the "THIRD
APPRAISER"). All of the appraisers selected shall be individuals with at least
five (5) years' commercial appraisal experience in the area in which the
Premises are located, shall be members of the Appraisal Institute (M.A.I.), and,
in the case of the Third Appraiser, shall not have acted in any capacity for
either Landlord or Tenant within five (5) years of his or her selection. The
three appraisers shall determine the Extension Term Yearly Rent in accordance
with the requirements and criteria set forth in Section 25.2(a) above, employing
the method commonly known as BASEBALL ARBITRATION, whereby Landlord's Appraiser
and Tenant's Appraiser each sets forth its determination of the Extension Term
Yearly Rent as defined above, and the Third Appraiser must select between the
two (it being understood that the Third Appraiser shall be expressly prohibited
from selecting a compromise figure). Landlord's Appraiser and Tenant's Appraiser
shall deliver their determinations of the Extension Term Yearly Rent to the
Third Appraiser within ten (10) days of their respective appointments and the
Third Appraiser shall render his or her decision within ten (10) days after
receipt of both of the other two determinations of the Extension Term Yearly
Rent. The Third Appraiser's decision shall be binding on both Landlord and
Tenant. Each party shall bear the cost of its own appraiser and shall share
equally in the cost of the Third Appraiser.

            (c)  If Tenant's Response Notice indicates Tenant's acceptance of
Landlord's determination of the Extension Term Yearly Rent, or if Tenant fails
to timely send Tenant's Response Notice, Tenant shall be deemed to have duly
exercised its extension option and, on or before the commencement date of the
Extension Term, Landlord and Tenant shall execute an amendment to this Lease
extending the term on the same terms provided in this Lease, except as follows:

                 (i)     Yearly Rent shall be adjusted to the Extension Term
Yearly Rent (as determined in accordance with this Section 25.2);

                 (ii)    Tenant shall have no right to further extend the term
hereof unless expressly granted by Landlord in writing; and

                 (iii)   Landlord shall lease to Tenant the Premises in their
then-current condition, and Landlord shall not provide to Tenant any allowances
(e.g., moving allowance, construction allowance, and the like) or other tenant
inducements.

26.  SIGNAGE

     26.1   DIRECTORY SIGNAGE. Landlord shall supply Building standard signage
for Tenant within the directory in the Building lobby at Landlord's sole cost
and expense. The cost to add any names of any approved subtenants or licensees
occupying any portion of the Premises shall be subject to reasonable limits on
the number of lines on the directory Landlord can provide and all such
additional

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signage in the lobby directory shall be at Tenant's sole cost and expense.

     26.2   MONUMENT SIGNAGE. In the event that Landlord installs and/or erects
a so-called monument sign outside of the Building, which sign identifies other
tenants of the Building, Tenant shall have the right, during the term hereof, to
be listed thereon.

27.  BILLS AND NOTICES

     Any notice, consent, request, bill, demand or statement hereunder (each, a
"NOTICE") by either party to the other party shall be in writing and, shall be
deemed to have been duly given when either delivered or served personally with
receipt of delivery, delivered via nationally recognized overnight courier with
receipt of delivery, or sent via certified mail, postage prepaid with receipt
requested addressed to Landlord at its address as stated in EXHIBIT 1, with a
copy to Brown, Rudnick, Freed & Gesmer, One Financial Center, Boston, MA 02111,
Attention: Daniel D. Sullivan, Esq., and to Tenant at the Premises (or at
Tenant's address as stated in EXHIBIT 1, if mailed prior to Tenant's occupancy
of the Premises) with a copy to Bingham Dana LLP, 150 Federal Street, Boston, MA
02110, Attention: Julio Vega, Esquire. Either party may at any time change the
address or specify an additional address for such Notices by delivering or
mailing, as aforesaid, to the other party a notice stating the change and
setting forth the changed or additional address, provided such changed or
additional address is within the United States. Notices shall be effective upon
the date of receipt or refusal thereof.

28.  DISPUTE RESOLUTION. Any disputes relating to provisions or obligations in
the Lease shall be resolved in accordance with the following procedures:

     28.1   NEGOTIATION. Either party may give the other party written notice of
the dispute. Within ten (10) days after receipt of such notice, the receiving
party shall submit to the other a written response. The notice and response
shall include (a) a statement of each party's position and a summary of the
evidence and arguments supporting its position and (b) the name and title of the
officer or executive who will act for that party. Officers or executives shall
be selected to act for the parties in negotiations only if they (x) are among
the senior executive personnel for the party in question, (y) have authority to
settle the controversy and (z) do not have direct responsibility for
administration of the Lease. The executives shall meet at a mutually acceptable
time and place within twenty (20) days of the date of the originating party's
notice (and as often thereafter as they reasonably deem necessary) to exchange
relevant information and to attempt to resolve the dispute.

     28.2   MEDIATION. If the matter has not been resolved within thirty (30)
days of the originating party's notice, either party may initiate mediation of
the controversy or claim.

            (a)  SELECTION OF MEDIATOR. The parties shall seek to identify
within ten (10) day after initiation of mediation a mutually acceptable
mediator, who shall mediate the dispute in accordance with the now current
American Arbitration Association ("AAA") Commercial Mediation Rules, except that
the mediator selected pursuant to this Article shall act as the administrator of
the mediation and shall have all of the powers and duties conferred on the AAA
pursuant to said Rules. Any conflicts between said rules and this Article shall
be resolved in favor of this Article. If the parties are unable or fail timely
to agree upon the mediator, upon request of either party, the dispute shall be
submitted for mediation to ENDISPUTE, Inc. or any successor entity. If neither
ENDISPUTE Inc. nor any successor entity exists at the time of the dispute, the
dispute shall be submitted for mediation to the AAA or any successor entity. If
neither the AAA nor any successor entity exists at the time of the dispute, the
dispute shall be submitted for mediation to the largest private provider of
dispute resolution services then doing business in the greater Boston area.

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            (b)  PROCEEDINGS. Attendance at the mediation shall be limited to
the parties and their counsel. All information exchanged or presented to the
mediator in these proceedings, whether in oral, written or other form, and the
results of the proceedings, shall be confidential and except as required by
Legal Requirements shall not be disclosed to any person or entity, including but
not limited to any arbitrator(s) in a subsequent proceeding, without prior
written permission from both parties. A party offering evidence or information
in mediation shall not be precluded thereby from offering that evidence or
information in any other proceeding.

     28.3   ARBITRATION. If the matter has not been resolved pursuant to the
aforesaid mediation procedure within twenty (20) days of the selection of the
mediator, or if either party does not participate in mediation, and the amount
in controversy does not exceed $100,000, either party may initiate binding
arbitration in accordance with the new current ENDISPUTE Comprehensive
Arbitration Rules and Procedures. Any conflicts between said rules and this
Article shall be resolved in favor of this Article 28. If the amount in
controversy exceeds $100,000, the parties may initiate binding arbitration, or
if the parties do not so agree to submit the matter for binding arbitration,
either party may initiate litigation.

            (a)  SELECTION OF ARBITRATOR(S). Each party shall within ten (10)
days select one impartial and neutral person (a "QUALIFIED NEUTRAL") to act as
an arbitrator. The two selected arbitrators (or either acting singly if a party
has failed timely to appoint a Qualified Neutral) shall, within ten (10) days of
the appointment of the second arbitrator, select a third Qualified Neutral with
at least ten (10) years' experience as an arbitrator, shall not have been
engaged by either party within the previous five (5) years (the "THIRD
ARBITRATOR"), and who shall be the chairperson of the panel. If the arbitrators
selected by the parties are unable or fail to agree upon the Third Arbitrator
within ten (10) days of the appointment of the second arbitrator, the Third
Arbitrator shall be selected by ENDISPUTE, Inc. or any successor entity. If
neither ENDISPUTE, Inc. nor any successor entity exists at the time of the
dispute, the Third Arbitrator shall be selected by the AAA or any successor
entity. If neither the AAA nor any successor entity exists at the time of the
dispute, the Third Arbitrator shall be selected by the largest private provide
of dispute resolution services then doing business in the greater Boston Area.

            (b)  PROCEEDINGS. The arbitration shall take place in Cambridge,
Massachusetts, and shall be governed by and conducted in accordance with, the
Federal Arbitration Act, 9 U.S.C. SS 1 ET SEQ. No arbitration conducted pursuant
to this Article shall be consolidated with any other proceeding. Attendance at
the arbitration proceedings shall be limited to the parties, their counsel and
any witnesses. The arbitration hearing shall not last more than three days,
unless both parties agree otherwise. All information exchanged or presented to
the arbitrator(s) in these proceedings, whether in oral, written or other form,
and the results of the proceedings, shall be confidential and except as required
by Legal Requirements shall not be disclosed to any person or entity without
prior written permission from both parties to these proceedings. Either party
may, without first obtaining the other party's consent, file dispositive motions
to resolve the dispute prior to a factual hearing, including but not limited to
motions to dismiss, motions to strike, motions for judgment on the pleadings and
motions for summary judgment. Such motions shall be filed and decided in
accordance with the ENDISPUTE Comprehensive Arbitration Rules. A party offering
evidence or information in this arbitration shall not be precluded thereby from
offering that evidence or information in any other proceeding.

            (c)  AWARD. The arbitrator(s) shall issue a written decision,
stating the reasons for the decision, within twenty-one (21) days of the
termination of the arbitration proceedings. Any such award shall be binding and
shall have the same force and effect as a judgment made in a court of competent
jurisdiction, and either parry shall have the right to apply to a court of
competent jurisdiction for a decree, judgment or order upon such award. The
arbitrator(s) shall award to the prevailing party reasonable attorneys' fees and
costs associated with the mediation and arbitration proceedings except as

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                                      -49-
<Page>

otherwise specifically provided in the Lease.

     28.4   INTERIM RELIEF. In any dispute covered by this Article 28, either
party may, notwithstanding the other provisions of this Article 28, request at
any time a temporary restraining order or preliminary injunction from any court
of competent jurisdiction without thereby waiving its other rights under this
Article 28.

     28.5   COSTS. For any dispute resolved without the issuance of an arbitral
award, all costs incurred for the services of neutrals under this Article shall
be borne equally by the parties. For any dispute resolved by arbitral award,
such costs shall be borne by the non-prevailing party. If an arbitral award is
issued and the non-prevailing party does not comply with its terms within thirty
(30) days of its issuance or if the non-prevailing party in the arbitration
unsuccessfully challenges the award in court, the prevailing party shall be
entitled to recover reasonable attorneys' fees and costs incurred in connection
with the enforcement and/or challenge of the award.

     28.6   INDEMNIFICATION. Except as otherwise provided in the Lease, the
parties shall rely solely on the procedures set forth in this Article to resolve
any dispute subject to this Article 28. If either party files an action in
court, or proceeds with litigation that has already been filed, in violation of
the Lease, that party shall indemnify the other party for its costs and
attorneys' fees incurred as a result of such violation.

29.  MISCELLANEOUS

     29.1   SEPARABILITY. If any provision of the Lease or portion of such
provision or the application thereof to any person or circumstance is for any
reason held invalid or unenforceable, the remainder of the Lease (or the
remainder of such provision) and the application thereof to other persons or
circumstances shall not be affected thereby.

     29.2   CAPTIONS. The captions are inserted only as a matter of convenience
and for reference, and in no way define, limit or describe the scope of the
Lease nor the intent of any provisions thereof.

     29.3   BROKER. Tenant and Landlord each warrants and represents that it has
dealt with no broker in connection with the consummation of this Lease other
than Broker. Tenant and Landlord each agrees to defend, indemnify and save the
other harmless from and against any Claims arising in breach of the
representation and warranty set forth in the immediately preceding sentence,
provided that Landlord shall be solely responsible for the payment of any
brokerage commissions to Broker.

     29.4   ENTIRE AGREEMENT. The Lease and EXHIBITS 1-13 attached hereto
contain the entire and only agreement between the parties and any and all
statements and representations, written and oral, including previous
correspondence and agreements between the parties hereto, are merged herein.
Tenant acknowledges that all representations and statements upon which it relied
in executing the Lease are contained herein and that Tenant in no way relied
upon any other statements or representations, written or oral. This Lease may
not be modified orally or in any manner other than by written agreement signed
by the parties hereto.

     29.5   GOVERNING LAW.    The Lease is made pursuant to, and shall be
governed by, and construed in accordance with, the laws of the Commonwealth of
Massachusetts and any applicable local municipal rules, regulations, by-laws,
ordinances and the like.

     29.6   REPRESENTATION OF AUTHORITY. By his or her execution hereof, each of
the signatories on

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                                      -50-
<Page>

behalf of the respective parties hereby warrants and represents to the other
that he or she is duly authorized to execute the Lease on behalf of such party.
Upon Landlord's request, Tenant shall provide Landlord with evidence that any
requisite resolution, corporate authority and any other necessary consents have
been duly adopted and obtained.

     29.7   EXPENSES INCURRED BY LANDLORD UPON TENANT REQUESTS. Tenant shall,
upon demand, reimburse Landlord for all reasonable expenses, including, without
limitation, legal fees, incurred by Landlord in connection with all requests by
Tenant for consents, approvals or execution of collateral documentation related
to the Lease, including, without limitation, costs incurred by Landlord in the
review and approval of Tenant's plans and specifications in connection with
proposed Alterations to be made by Tenant to the Premises or requests by Tenant
for Landlord's consent to make a Transfer. Such costs shall be deemed to be
additional rent under the Lease.

     29.8   SURVIVAL. Without limiting any other obligation of Tenant which may
survive the expiration or prior termination of the term of the Lease, all
obligations on the part of Tenant to indemnify, defend, or hold Landlord
harmless, as set forth in the Lease shall survive the expiration or prior
termination of the term of the Lease.

     29.9   LIMITATION OF LIABILITY. Tenant shall neither assert nor seek to
enforce any claim against Landlord or any of the Landlord Indemnitees, or the
assets of Landlord or any of the Landlord Indemnitees, for breach of the Lease
or otherwise, other than against Landlord's interest in the Building and the
Condominium and in the uncollected rents, issues and profits thereof, and Tenant
agrees to look solely to such interest for the satisfaction of any liability of
Landlord under the Lease. This Section 29.9 shall not limit any right that
Tenant might otherwise have to obtain injunctive relief against Landlord.
Landlord and Tenant specifically agree that in no event shall Landlord or any of
the Landlord Indemnitees ever be personally liable for any obligation under the
Lease. In no event shall Landlord or any of the Landlord Indemnitees ever be
liable for consequential or incidental damages or for lost profits. If by reason
of Landlord's failure to complete construction of the Building or Premises,
Landlord shall be held to be in breach of the Lease, Tenant's sole and exclusive
remedy shall be as set forth in Article 4 hereof.

     29.10  BINDING EFFECT. The covenants, agreements, terms, provisions and
conditions of the Lease shall bind and benefit the successors and assigns of the
parties hereto with the same effect as if mentioned in each instance where a
party hereto is named or referred to, except that no violation of the provisions
of Article 16 hereof shall operate to vest any rights in any successor or
assignee of Tenant.

     29.11  SEIZIN OF TITLE. Upon any sale, transfer or other disposition of the
Building, Landlord shall be entirely freed and relieved from the performance and
observance thereafter of all covenants and obligations hereunder on the part of
Landlord to be performed and observed, it being understood and agreed in such
event (and it shall be deemed and construed as a covenant running with the land)
that the person succeeding to Landlord's ownership of said reversionary interest
shall thereupon and thereafter assume, and perform and observe, any and all of
such covenants and obligations of Landlord.

                         [SIGNATURES ON FOLLOWING PAGE]

                                TOLERRX LEASE / BUILDING 300 / EXECUTION VERSION

                                      -51-
<Page>

     IN WITNESS WHEREOF the parties hereto have executed this Indenture of Lease
in multiple copies, each to be considered an original hereof, as a sealed
instrument on the day and year noted in Exhibit 1 as of the Execution Date.

LANDLORD                                        TENANT
MASSACHUSETTS INSTITUTE                         TOLERRX, INC.
OF TECHNOLOGY

By: /s/ Steven C. Marsh                         By: /s/ D. J. Ringler
    -----------------------------------             ------------------------
Name: Steven C. Marsh                           Name: D. J. Ringler
Title: Managing Director of Real Estate         Title: CEO

                                TOLERRX LEASE / BUILDING 300 / EXECUTION VERSION

                                      -52-
<Page>

                               EXHIBIT 1, SHEET i
                                Building No. 300
                               TECHNOLOGY SQUARE
                         Cambridge, Massachusetts 02139
                                   LEASE DATA

<Table>
<S>                    <C>
EXECUTION DATE:        November 20, 2001

TENANT:                TolerRx, Inc. a Delaware corporation

MAILING ADDRESS
PRIOR TO OCCUPANCY:    TolerRx, Inc.
                       675 Massachusetts Avenue
                       14th Floor
                       Cambridge, MA 02139

LANDLORD:              Massachusetts Institute of Technology, a Massachusetts
                       charitable corporation

LANDLORD'S
MAILING ADDRESS:       238 Main Street, Suite 200
                       Cambridge, MA 02142

CONDOMINIUM:           Technology Square Condominium, including all of the land,
                       buildings and other improvements comprising the same,
                       from time to time located off Main Street in the City of
                       Cambridge, Middlesex County, Commonwealth of
                       Massachusetts known as "Technology Square". The
                       Condominium is initially substantially as shown on
                       EXHIBIT 2-1, and the legal description of the Condominium
                       and the Building is set forth on EXHIBIT 3; however, the
                       Condominium may change from time to time as set forth
                       herein. Without limiting the foregoing, the parties
                       acknowledge that the Condominium presently consists of
                       Units 200, 400 and 500 (also known as Buildings 200, 400
                       and 500). The Building (hereinafter defined) and Units
                       100, 600 and 700 (also known as Buildings 100, 600 and
                       700), consisting of approximately 609,867 rentable square
                       feet of space in the aggregate, are currently under
                       construction and will be added to the Condominium in the
                       coming months. The parking garage for Technology Square
                       is located at and known as 595 Technology Square and is
                       included within the common areas of the Condominium (the
                       "PARKING GARAGE").

BUILDING:              300 Technology Square, Cambridge, Massachusetts,
                       comprising Unit 300 of the Condominium and also known as
                       "Building 300."

PREMISES:              Approximately 37,643 rentable square feet of space
                       (subject to remeasurement by Landlord in accordance with
                       EXHIBIT 7 prior to the Rent Commencement Date),
                       consisting of the entire fourth floor of the Building
                       (which contains approximately 24,145 rentable square
                       feet; the "4TH FLOOR PREMISES"). approximately 12,642
                       rentable square feet of the third floor of the Building
                       (the "3RD FLOOR PREMISES"), and approximately 856
                       rentable square feet of space within the non-retail space
                       on the first floor of the Building (the "1ST FLOOR
                       PREMISES"), all as more particularly shown as hatched,
                       highlighted or outlined on the Lease Plan (EXHIBIT 2)
                       attached hereto and made a part hereof, together with the
                       Rooftop Premises (hereinafter defined).
</Table>

                                TOLERRX LEASE / BUILDING 300 / EXECUTION VERSION

                                       -i-
<Page>

<Table>
<S>                    <C>
ROOFTOP PREMISES:      The portion of the rooftop space designated by Landlord
                       which Tenant may utilize for the installation of Tenant's
                       Rooftop Equipment.

ART. 3                 TERM COMMENCEMENT DATE:         the Execution Date

                       ESTIMATED DELIVERY DATE:        the Execution Date

                       OUTSIDE DELIVERY DATE:          January 31, 2002

                       RENT COMMENCEMENT DATE:         One hundred eighty (180) days
                                                       after the Term Commencement Date
                                                       (subject to Section 4.1(f) below)

                       EXPIRATION DATE:                Ten (10) years after the last day
                                                       of the month in which the Rent
                                                       Commencement Date occurs, unless
                                                       earlier terminated or extended as
                                                       set forth in Article 25.

ART. 4                 4TH FLOOR DESIGN DEVELOPMENT
                       PLANS DELIVERY DATE:            Thirty (30) days after the Term
                                                       Commencement Date

                       4TH FLOOR PERMIT PLANS
                       DELIVERY DATE:                  Forty-five (45) days after the
                                                       Term Commencement Date

                       4TH FLOOR FINAL CONSTRUCTION
                       DRAWINGS DELIVERY DATE:         Sixty (60) days after the Term
                                                       Commencement Date

                       3RD FLOOR DESIGN DEVELOPMENT
                       PLANS DELIVERY DATE:            Twenty-one (21) months after the
                                                       Term Commencement Date

                       3RD FLOOR PERMIT PLANS
                       DELIVERY DATE:                  Twenty-two (22) months after the
                                                       Term Commencement Date

                       3RD FLOOR FINAL CONSTRUCTION
                       DRAWINGS DELIVERY DATE:         Twenty-three (23) months after the
                                                       Term Commencement Date

                       LANDLORD'S CONTRIBUTION:        Tenant improvement allowance of up
                                                       to $75.00 per rentable square foot
                                                       of the Premises, to be paid by
                                                       Landlord as provided in Section 4.3.

ART.5                  PERMITTED USES: General office, research, development and
                       laboratory use, including so-called "wet laboratory" with
                       fume hoods and multiple sinks, live animal storage for
                       small animals (not larger than a rabbit) only (not to
                       exceed
</Table>

                                TOLERRX LEASE / BUILDING 300 / EXECUTION VERSION

                                      -ii-
<Page>

<Table>
<S>                    <C>
                       4,000 rentable square feet of the Premises), and other
                       ancillary uses related to the foregoing.

ART. 6                 YEARLY RENT (subject to remeasurement of the Premises by
                       Landlord in accordance with EXHIBIT 7 prior to the Rent
                       Commencement Date):

<Caption>
                       Rent         Yearly         Monthly
                       Year(1)       Rent          Payment      PSF (NNN)
                       -------      ------         -------      ---------
                       <S>      <C>              <C>             <C>
                       1-5:     $ 2,164,472.50   $ 180,372.71    $ 57.50

                       6-10:    $ 2,315,044.50   $ 192,920.38    $ 61.50

ART. 7                 Total rentable square feet of the Premises:   37,643 (subject to
                                                                     remeasurement by
                                                                     Landlord in accordance
                                                                     with EXHIBIT 7 prior to
                                                                     the Rent Commencement
                                                                     Date)

                       Total rentable square feet of the Building:   175,609

                       Initial total rentable square feet of the Condominium: 1,130,276

                           Buildings 200, 400 and 500                520,409 rentable square feet
                           Building 100                              258,178 rentable square feet
                           Building 300                              175,609 rentable square feet
                           Building 600                              127,150 rentable square feet
                           Building 700                               48,930 rentable square feet

                           NOTE: The rentable square footage listed above for Building 100 is an
                           estimate only. Building 100 will be remeasured when fully constructed
                           and Landlord shall notify Tenant in writing as to the final
                           measurement therefor.

ART. 10                TENANT'S PERCENTAGE SHARE:                    21.44% (subject to
                                                                     remeasurement of the
                                                                     Premises by Landlord in
                                                                     accordance with EXHIBIT 7
                                                                     prior to the Rent
                                                                     Commencement Date)

ART. 12                LANDLORD'S CONSTRUCTION REPRESENTATIVE:       John L. Myers

                       TENANT'S CONSTRUCTION REPRESENTATIVE:         John Doherty

ART. 24
</Table>

----------
(1) For the purposes of this Lease, "Rent Year 1" shall be defined as the
twelve-(12)-month period commencing as of the Rent Commencement Date and ending
on the last day of the month in which the first (1st) anniversary of the Rent
Commencement Date occurs. Thereafter, "Rent Year" shall be defined as any twelve
(12) month period during the term of the Lease commencing as of the first (1st)
day of the month following the month in which any anniversary of the Rent
Commencement Date occurs.

                                TOLERRX LEASE / BUILDING 300 / EXECUTION VERSION

                                     -iii-
<Page>

<Table>
<S>                    <C>                                           <C>
                       LETTER OF CREDIT:                             $2,070,000.00

ART. 28                ARBITRATION:                                  Superior Court; Middlesex County

ART. 29                BROKER:                                       Insignia/ESG and Richards Barry Joyce &
                                                                     Partners
</Table>

                                TOLERRX LEASE / BUILDING 300 / EXECUTION VERSION

                                      -iv-<Page>

                                                                   EXHIBIT 10.6

GENENTECH CONFIDENTIAL

[***] INDICATES MATERIAL THAT HAS BEEN OMITTED AND FOR WHICH CONFIDENTIAL
TREATMENT HAS BEEN REQUESTED. ALL SUCH OMITTED MATERIAL HAS BEEN FILED WITH THE
SECURITIES AND EXCHANGE COMMISSION PURSUANT TO RULE 406 PROMULGATED UNDER THE
SECURITIES ACT OF 1933, AS AMENDED.

                             COLLABORATION AGREEMENT

                               GENENTECH, INC. AND

                                  TOLERRX, INC.

          This Collaboration Agreement (this "AGREEMENT") is made effective as
of December 23, 2002 (the "EFFECTIVE DATE") by and between GENENTECH, INC.
("GENENTECH"), a corporation organized under Delaware law, with its principal
office at 1 DNA Way, South San Francisco, California 94080, and TolerRx, Inc.
("TOLERRX"), a corporation organized under Delaware law, with its principal
office at 300 Technology Square, Cambridge, MA 02139.

                                    RECITALS

          WHEREAS, TolerRx is engaged in the development of therapies related to
immunological tolerance;

          WHEREAS, TolerRx owns or controls certain intellectual property
related to Licensed Product (as defined below);

          WHEREAS, the Parties desire to collaborate and wish to set out their
rights and obligations with respect to development and commercialization of
Licensed Products as set forth below;

          NOW, THEREFORE, for good and valuable consideration, the receipt and
sufficiency of which is hereby acknowledged, Genentech and TolerRx agree as
follows:

                                    ARTICLE 1

                                   DEFINITIONS

          1.1.   "AFFILIATE" of a Party means any corporation or other business
entity that, directly or indirectly, through one or more intermediaries,
controls, is controlled by, or is under common control with a Party. As used
herein, the term "control" will mean the direct or indirect ownership of fifty
percent (50%) or more of the stock having the right to vote for directors
thereof or the ability to otherwise control the management thereof.

                                  * Confidential treatment requested:
                                    material has been omitted and filed
                                    separately with the Commission.

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          1.2.   "AGREEMENT" means this Collaboration Agreement, including any
exhibits attached hereto which are hereby incorporated herein by reference. In
the event of any inconsistency between the terms of this Agreement and the terms
of any exhibits incorporated herein, the terms of this Agreement shall govern
unless the Parties otherwise expressly agree in writing.

          1.3.   "ANTIBODY" or "ANTIBODIES" means any and all antibodies that
target, bind to or recognize CD4, and shall include, without limitation, full
length antibodies, variants (including, without limitation, chimeric and
humanized antibodies), fragments (including, without limitation, single-chain,
Fab and F(ab)'2 fragments), analogues or derivatives (including, without
limitation, conjugates thereof with radionuclides, immunoadhesins, toxins or
other compounds) thereof, as well as the DNA encoding any of the above.
"Antibody" shall include, but is not limited to, TRX1.

          1.4.   "BLA" means a biologics license application (as that term is
used in Title 21 of the United States Code of Federal Regulations) filed with
the FDA seeking Regulatory Approval to market and sell any Licensed Product in
the United States for a particular Indication.

          1.5.   "COMMERCIAL INTRODUCTION" of Licensed Product(s) means, on a
country-by-country and Licensed Product-by-Licensed Product basis in the
Territory, the date of first commercial sale (other than for purposes of
obtaining Regulatory Approval) of a Licensed Product by Genentech, or any of its
third party sublicensees in an arms'-length transaction to an independent Third
Party in such country after obtaining all necessary Regulatory Approvals;
provided that such Licensed Product(s) are neither units provided for evaluation
purposes nor free units for indigent persons.

          1.6.   "COMMERCIALLY REASONABLE AND DILIGENT EFFORTS" has the meaning
set forth in Section 3.2.

          1.7.   "CONFIDENTIAL INFORMATION" has the meaning set forth in Section
8.1.

          1.8.   "CONTROL" or "CONTROLLED" means possession of the ability to
grant access to or a license or sublicense as provided for herein without
violating the terms of any agreement or other arrangement with any third party.

          1.9.   "DEVELOPMENT PLAN" means a written plan, developed by Genentech
and approved by the JSC pursuant to Section 3 below, for research and/or
development work covered by this Agreement to be performed by the Parties
relating to the Product(s) selected by the JSC, and any modifications to such
plan made by Genentech from time to time in accordance with Section 3 below. Any
and all Development Plan(s) are hereby incorporated by reference into this
Agreement.

          1.10.  "DOLLAR" OR "DOLLAR" means United States dollars.

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          1.11.  "DRUG APPROVAL APPLICATION" means an application for Regulatory
Approval required for commercial sale or use of a Licensed Product as a drug or
biologic in the Field in a regulatory jurisdiction.

          1.12.  "EMEA" means the European Agency for the Evaluation of
Medicinal Products and any successor agency or authority thereto.

          1.13.  "FDA" means the United States Food and Drug Administration and
any successor agency or authority thereto.

          1.14.  "FIELD" means any human use.

          1.15.  "FOREIGN REGULATORY AUTHORITY" means any applicable regulatory
agency, or other governmental entity or authority of any country or regulatory
jurisdiction in the Territory including but not limited to the EMEA (other than
the FDA in the United States), having responsibility in such country or
regulatory jurisdiction for any Regulatory Approvals of any kind necessary for
the development, pre-clinical and/or human clinical testing, manufacture,
supply, marketing and/or sale of Licensed Products in such country or regulatory
jurisdiction.

          1.16.  "FTE" shall mean an exempt or non-exempt employee who works one
person year's worth of effort.

          1.17.  "FTE COST" shall mean the fully burdened cost of an FTE.

          1.18.  "FULLY BURDENED MANUFACTURING COSTS" has the meaning set forth
in Exhibit A.

          1.19.  "GENENTECH PATENTS" means any and all patents and patent
applications that are owned by Genentech and solely based upon inventions
conceived and reduced to practice by Genentech employees in the course of
performing Genentech's development obligations under this Agreement under the
Development Plan to the extent that would be infringed by the use, manufacture
or sale of an existing Licensed Product that Genentech was developing or
manufacturing, if any, prior to termination. For clarity, "Genentech Patents"
shall not include (X) general patents that cover inventions that could be used
for products other than such existing Licensed Product, including without
limitation patents covering manufacturing or process inventions, (Y) any patents
arising from or related to other work (i.e. activities other than Genentech's
development obligations expressly set forth under this Agreement under the
Development Plan), nor (Z) any patents and patent applications that are (i)
owned by Genentech on or before the Effective Date or (ii) Controlled by
Genentech.

          1.20.  "IND" means an Investigational New Drug Application filed or to
be filed with the FDA with regard to a Licensed Product prior to beginning
clinical trials of any Licensed Product.

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          1.21.  "INDEPENDENT PRODUCT" has the meaning set forth in Section
4.2(a).

          1.22.  "INDICATION" means an illness, sickness, interruption,
cessation or disorder of a particular bodily function, system or organ
regardless of the severity, frequency or route of any treatment and regardless
of the patient class. For purposes of this definition, all instances of the same
disease in different patient groups shall be deemed one Indication. For example,
juvenile rheumatoid arthritis and rheumatoid arthritis shall be considered one
Indication. Also, rheumatoid arthritis shall be considered one Indication
regardless of whether such condition is mild, moderate, or severe.

          1.23.  "JSC" OR "JOINT STEERING COMMITTEE" has the meaning set forth
in Section 2.1(a).

          1.24.  "LICENSED PRODUCT" means any Product (i) the manufacture, use,
sale, offer for sale or importation of which in the Territory, but for the
licenses granted herein, would infringe a Valid Claim; or (ii) that relies on or
incorporates TolerRx Know-how including, but not limited to, Antibodies provided
by TolerRx to Genentech pursuant to this Agreement; or (iii) that was or is
being developed pursuant to the Development Plan. It is expressly understood
that TRX1 is a Licensed Product.

          1.25.  "LICENSED PRODUCT MANUFACTURING KNOW-HOW" has the meaning set
forth in Section 9.5(c)(iii).

          1.26.  "MAA" means an application filed with the EMEA seeking final
Regulatory Approval to market and sell a Licensed Product for a particular
Indication in the regulatory jurisdictions for which the EMEA is responsible.
For the purposes of this Agreement, "MAA" only refers to the EMEA equivalent of
a BLA.

          1.27.  "MARKETING PLAN" means a plan developed by Genentech for
marketing and promotional work relating to Licensed Products, and any
modifications thereto made by Genentech from time to time.

          1.28.  "MINIMUM ROYALTY RATE" means with respect to Net Sales of the
applicable Licensed Products described in Section 6.3(c) or 6.4:

                         (i)    Genentech shall pay a royalty of [***] for the
portion of Aggregate Annual Worldwide Net Sales of all such Licensed Products of
the same type that is less than or equal to $[***].

                         (ii)   Genentech shall pay a royalty of [***] for the
portion of Aggregate Annual Worldwide Net Sales of all such Licensed Products of
the same type that is greater than $[***] and less than or equal to $[***].

                                  * Confidential treatment requested:
                                    material has been omitted and filed
                                    separately with the Commission.

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                         (iii)  Genentech shall pay a royalty of [***] for the
portion of Aggregate Annual Worldwide Net Sales of all such Licensed Products of
the same type that is greater than $[***].

"Aggregate Annual Worldwide Net Sales" means the Patented Product Aggregate
Annual Worldwide Net Sales (as defined in Section 6.3(a)) or Non-Patented
Product Aggregate Annual Worldwide Net Sales (as defined in Section 6.3(b)), as
applicable. Aggregate Annual Worldwide Net Sales consists of aggregating such
Net Sales of only such Licensed Products of the same type as described in
Section 6.3(d) below.

          1.29.  "NDA" means a New Drug Application (as that term is used in
Title 21 of the United States Code of Federal Regulations) filed with the FDA
seeking Regulatory Approval to market and sell any Licensed Product in the
United States for a particular Indication.

          1.30.  "NET SALES" shall have the meaning set forth in Exhibit A.

          1.31.  "PARTY" means Genentech or TolerRx, and, when used in the
plural, shall mean both of them.

          1.32.  "PHASE I CLINICAL TRIAL" means, as to a specific Licensed
Product, a lawful study in humans, the principal purpose of which is a
preliminary determination of safety of the Licensed Product for its intended use
in healthy individuals or patients to support its continued testing in similar
clinical trials prescribed by the FDA or any relevant Foreign Regulatory
Authority.

          1.33.  "PHASE II CLINICAL TRIAL" means, as to a specific Licensed
Product, a controlled and lawful study in humans of the safety, dose ranging and
efficacy of such Licensed Product, which is prospectively designed to generate
sufficient data (if successful) to commence a Phase III Clinical Trial (or
foreign equivalent) of such product.

          1.34.  "PHASE III CLINICAL TRIAL" means, as to a specific Licensed
Product, a controlled and lawful study in humans of the efficacy and safety of
such Licensed Product, which is prospectively designed to demonstrate
statistically whether such Licensed Product is effective and safe for use in a
particular Indication in a manner sufficient to file a BLA or NDA (or foreign
equivalent) to obtain Regulatory Approval to market and sell that Licensed
Product in the Territory for the Indication being investigated by the study.

          1.35.  "PRODUCT(S)" means any product and any formulation thereof
containing an agent targeting, binding to or recognizing CD4, either alone or
together with or incorporated into any other substance or product or material or
device, whether active or not. Product shall include Antibody.

          1.36.  "REGULATORY APPROVAL" means any and all approvals (including
pricing and reimbursement approvals), licenses, registrations or authorizations
of any kind of the FDA or

                                  * Confidential treatment requested:
                                    material has been omitted and filed
                                    separately with the Commission.

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any Foreign Regulatory Authority necessary for the development, pre-clinical
and/or human clinical testing, manufacture, supply, marketing and sale of a
Licensed Product in any country or other regulatory jurisdiction in the
Territory. "Regulatory Approval" shall include, without limitation, approval
granted with respect to any BLA, NDA or foreign equivalent. However, with
respect to Sections 4.1 and 6.2 of the Agreement, and Section A.7.3 of Exhibit A
herein, the term "Regulatory Approval" means governmental approvals, of the FDA
or Foreign Regulatory Authority as the context indicates, only for the sale of
the applicable Licensed Product. With respect to Section 4.2(a) of the
Agreement, "Regulatory Approval" means governmental approvals of the FDA, only
for the sale of the Third Party pharmaceutical stand-alone product described in
Section 4.2(a). With respect to Section 6.3(c) of the Agreement, "Regulatory
Approval" means governmental approvals, of the FDA or Foreign Regulatory
Authority, only for the sale of the applicable Licensed Product or Another
Anti-CD4 Product, as the context indicates.

          1.37.  "ROYALTY TERM" means, with respect to each Licensed Product in
each country in the Territory on a Licensed Product-by-Licensed Product and
country-by-country basis, the period of time commencing on the Commercial
Introduction and ending [***] years from the date of the Commercial Introduction
of such Licensed Product in such country.

          1.38.  "TERM" has the meaning set forth in Section 9.1.

          1.39.  "TERRITORY" means the world.

          1.40.  "THIRD PARTY" shall mean any entity other than TolerRx,
Genentech, their Affiliates and their sublicensees.

          1.41.  "THIRD PARTY AGREEMENTS" means only the following agreements as
they exist as of the Effective Date: (A) the License of Certain Improvements to
anti-CD4 and anti-CD8 Antibodies by and among Isis Innovation Limited, The
Chancellor Masters and Scholars of the University of Oxford, and TolerRx, Inc.
dated December 5, 2000 (the "ISIS AGREEMENT"); and (B) the License Agreement by
and between Cambridge University Technical Services Limited and TolerRx dated
December 8, 2000 (the "CUTS AGREEMENT"). The term "Third Party Agreements" shall
include amendments thereto only if such amendments were made in compliance with
Section 5.4.

          1.42.  "TOLERRX KNOW-HOW" means any and all proprietary materials and
information that are (i) owned by TolerRx or its Affiliates as of the Effective
Date or thereafter during the Term; or (ii) licensed to TolerRx under the Third
Party Agreements; or (iii) Controlled by TolerRx or its Affiliates during the
Term but only to the extent that it is directed to a Product or the manufacture
or use thereof, in each case only to the extent that any of the foregoing under
(i)-(iii) is necessary or useful for the manufacture, use, import, offer for
sale, or sale of any Product in the Field in the Territory. "TolerRx Know-how"
excludes TolerRx's proprietary materials and information with respect to an
anti-CD8 antibody or fragment thereof. It is expressly understood that TRX1 is
included in TolerRx Know-how. TolerRx Know-how

                                  * Confidential treatment requested:
                                    material has been omitted and filed
                                    separately with the Commission.

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shall not include anything that is generally ascertainable from publicly
available information or that was known to Genentech prior to disclosure to
Genentech by TolerRx or which Genentech developed independently or obtained not
in violation of any obligation of confidentiality owed to TolerRx or any third
party.

          1.43.  "TOLERRX PATENT RIGHTS" means any and all patents and patent
applications (including inventor's certificates and utility models) throughout
the Territory, including any substitutions, extensions, reissues,
reexaminations, renewals, divisions, continuations and continuation-in-parts of
any of the foregoing, that are (i) owned by TolerRx or its Affiliates as of the
Effective Date or thereafter during the Term; or (ii) those licensed to TolerRx
under the Third Party Agreements; or (iii) Controlled by TolerRx or its
Affiliates during the Term but only to the extent that they are directed to a
Product or the manufacture or use (including but not limited to diagnostic use)
thereof, in each case only to the extent that any of the foregoing under
(i)-(iii) is necessary or useful for manufacture, use, sale, offer for sale or
import of any Product in the Field in the Territory. The TolerRx Patent Rights
do not include patents and patent applications that are directed to an anti-CD8
antibody or fragment thereof. The TolerRx Patent Rights shall include, without
limitation, the patents and patent applications listed on EXHIBIT B attached
hereto in their entirety.

          1.44.  "TRX1" means anti-CD4 monoclonal antibodies as described in the
U.S. Patent Application Serial No.10/171,452 (filed June 13, 2002).

          1.45.  "VALID CLAIM" means a claim within the TolerRx Patent Rights
(a) in an unexpired and issued patent that has not been revoked, held invalid,
declared unpatentable or unenforceable in a decision of a court or other body of
competent jurisdiction, in a decision that is unappealable or unappealed within
the time allowed for appeal, (b) that has not been rendered unenforceable
through disclaimer or otherwise and (c) is otherwise not subject to an
interference claim. Notwithstanding the foregoing, in the event that an issued
claim within the TolerRx Patent Rights that has been subject to an interference
claim is later resolved in TolerRx's favor, then such claim shall be considered
a "Valid Claim" under this Agreement and (i) Genentech shall promptly pay to
TolerRx back applicable royalties that it would have owed under this Agreement
if such claim had not been subject to the interference claim, and (ii) Genentech
shall continue to pay the applicable royalties for the remaining life of such
Valid Claim.

          1.46.  "UNITED STATES" means the fifty States of the United States of
America.

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                                    ARTICLE 2
                            MANAGEMENT OF DEVELOPMENT

          2.1.   (a)     JOINT STEERING COMMITTEE. The Parties will establish a
Joint Steering Committee (the "JSC"). The purpose of the JSC is to facilitate
the exchange of information relating to the development, marketing and sale of
Licensed Products and the coordination between the Parties relating to the
development of Licensed Products. The JSC will be composed of up to three
representatives of each Party, who are all employees of such Party and who may
be replaced from time to time with other employees of such Party. Such
representatives shall include individuals with expertise in biopharmaceutical
drug development. The JSC will meet at least twice a year during the Term, which
meeting may be in person or by telephone. The quorum for a meeting shall require
at least one representative of Genentech and at least one representative of
TolerRx. The JSC shall meet within thirty (30) days of the Effective Date.

                 (b)     JOINT PROJECT TEAM

                         (i)    ESTABLISHMENT OF A JOINT PROJECT TEAM. The
Parties shall establish a Joint Project Team ("JPT") promptly after the
Effective Date. The JPT shall coordinate all applicable activities for the
Development Plan for Licensed Products, including post-Regulatory Approval
development studies. Each Party shall appoint representatives who are employees
of such Party to the JPT and the JPT shall consist of an equal number of
representatives of each Party as are reasonably necessary to accomplish the
goals of the JPT hereunder. The number of representatives may change from time
to time. Such representatives will include, without limitation, individuals with
expertise and responsibilities in the areas of research, clinical development,
process sciences, regulatory affairs, product development and marketing, as
applicable to the stage of development of the Licensed Product. One such
representative from each Party shall be designated as that Party's "Project Team
Leader" to act as the primary JPT contact for that Party. Each Party may replace
any or all of its representatives with other employees of such Party at any
time. Any member of the JPT may designate a substitute employee of such Party to
attend and perform the functions of that member at any meeting of the JPT. The
JPT will meet in person or by conference call on a regular basis, not fewer than
one time per quarter.

                         (ii)   JOINT PROJECT TEAM RESPONSIBILITIES: The JPT
will be responsible for:

                         a.     Discussing the overall pre-clinical and clinical
                         development program and the initial and subsequent
                         annual Development Plans (if TolerRx has exercised and
                         continues to participate in the US Profit/Loss Sharing
                         Option in accordance with Section 6.5 and

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                         Exhibit A, then the Development Plan shall include the
                         annual budget and an estimate of FTE resources for
                         developing the Licensed Products in the United States);

                         b.     Developing the priority and design of all
                         clinical trials for new Indications;

                         c.     Developing a publication strategy and a calendar
                         of key scientific and clinical meetings and other
                         similar events for the Licensed Products;

                         d.     Exchanging information and facilitating
                         cooperation and coordination between the Parties as
                         they exercise their respective rights and respective
                         obligations related to development of Licensed Products
                         under this Agreement;

                         e.     Determining the priority with respect to seeking
                         Regulatory Approval of Licensed Products; and

                         f.     Implementing all development activities approved
                         by the JSC.

                         (c)    JOINT PROJECT TEAM DECISION MAKING: As a general
          principle, the JPT will operate by consensus. In the event that the
          JPT members do not reach consensus with respect to a matter that is
          within the purview of the JPT, such matter shall be resolved by the
          JSC.

          2.2.   DECISION MAKING RESPONSIBILITY. The Parties intend and agree
that development of Licensed Products in the Field in the Territory, including
but not limited to pre-clinical and clinical testing, and, if applicable as set
forth in Section 6.5, calculation of costs and Operating Profits or Losses as
set forth in Section 6.5 and Exhibit A, and the Development Plan shall be
subject to JSC approval (in the manner set forth in this Section 2.2). If
TolerRx has exercised and continues to participate in the US Profit/Loss Sharing
Option in accordance with Section 6.5 and Exhibit A, then the JSC shall receive
a copy of the budget as described in Section A.3 of the attached Exhibit A.
Subject to the next three sentences, the JSC shall operate by consensus. The JSC
representatives of each Party shall collectively have one vote for purposes of
decision-making hereunder. In the event that the JSC representatives do not
reach consensus, [*******] shall have the authority to make the final decision
and the Parties and JSC shall abide by such decision. With respect to all
decisions contemplated to be made by the JSC, notwithstanding anything else in
this Agreement, [*******] shall have the authority to make the final decision
and the Parties and JSC shall abide by such decision.

                                  * Confidential treatment requested:
                                    material has been omitted and filed
                                    separately with the Commission.

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                                    ARTICLE 3

GENENTECH CONFIDENTIAL

          3.1.   DEVELOPMENT PLAN. Genentech shall use Commercially Reasonable
and Diligent Efforts to create a Development Plan (which shall be attached as
Exhibit E hereto) within sixty (60) days and no later than ninety (90) days from
the Effective Date, which may be modified by the JSC (as provided above) from
time to time. TolerRx understands that Genentech's performance is dependent in
part on the TolerRx's actions, including but not limited to TolerRx providing
the detailed description of the studies set forth in Section 3.4(b)(i) in a
timely manner. TolerRx shall have the opportunity to provide input and
suggestions with regard to the Development Plan. The Parties initially agree to
develop a Licensed Product related to immune tolerance. Only upon the JSC's
written approval shall the Parties perform any activities other than work
related to immune tolerance. The Development Plan shall be updated by Genentech
for each calendar year and submitted to the JSC for consideration and approval
at least three months prior to the beginning of the next calendar year. The
Development Plan will include specific tasks, milestones, and estimated
timelines. As set forth in Section 3.4(b) and 3.4(f), it is anticipated that the
Development Plan may assign specific tasks to TolerRx. TolerRx shall hold in
confidence, not use (except to perform its obligations under the Development
Plan), and not disclose to anyone any and all information arising out of TolerRx
Development Plan Work (as defined in Exhibit A attached hereto), except that
TolerRx may disclose such information to Isis only to the extent required under
the Isis Agreement and only pursuant to Section 5.3(a)(iii). The foregoing
confidentiality obligations shall survive any termination of this Agreement by
Genentech under Sections 9.3 or 9.4 or expiration of this Agreement. In all
events, Genentech shall have final authority regarding the Development Plan and
the content thereof. For avoidance of doubt, the Development Plan shall exclude
marketing and other commercialization activities. The Development Plan and any
modifications thereto shall be approved by the JSC in the written minutes of the
applicable JSC meeting; anything not approved by the JSC in such written minutes
shall be deemed to be excluded from the Development Plan.

          3.2.   DEVELOPMENT EFFORTS. Subject to the terms and conditions of
this Agreement, Genentech agrees to use Commercially Reasonable and Diligent
Efforts to research, develop and obtain Regulatory Approval of a Genentech
selected Licensed Product in at least the United States and Europe. As used in
this Agreement, the term "Commercially Reasonable and Diligent Efforts" will
mean those efforts and resources consistent with the exercise of prudent
scientific and business judgment, as applied to other pharmaceutical products of
similar market potential and market size, probability of technical success, risk
of failure, and at a similar stage in the development or life of such product.
Genentech shall have full responsibility for the conduct of all research and
development activities related to Licensed Products set forth in the Development
Plan, except that TolerRx is responsible for TolerRx's obligations set forth in
Section 3.4. Genentech and TolerRx shall provide written progress reports to the
JSC every twelve (12) months with respect to the research, development and
Regulatory Approval of Licensed Product.

          3.3.   DEVELOPMENT COSTS. Genentech shall be responsible for the costs
of all activities performed by it with regard to the research and development of
Licensed Products in

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the Field in the Territory, except for US Costs (as defined in Exhibit A) if
TolerRx exercises the US Profit/Loss Sharing Option (as defined in Section 6.5).
If TolerRx exercises the US Profit/Loss Sharing Option, then all US Costs shall
be shared between Genentech and TolerRx, as provided below and in accordance
with the Financial Planning, Accounting and Reporting Procedures attached hereto
as EXHIBIT A, so that Genentech bears [***] of such costs and TolerRx bears
[***] of such costs. There shall be a reconciliation of such costs which are to
be shared and which are incurred during the prior reporting period by each
Party, in accordance with EXHIBIT A, with a payment by one Party to the other to
the extent necessary so that each Party bears its appropriate percentage of such
shared US Costs.

          3.4.   TOLERRX'S DEVELOPMENT RESPONSIBILITIES

                 (a) TRANSFER OF MATERIALS AND INFORMATION. TolerRx agrees to
provide to Genentech, promptly after execution of this Agreement and at
TolerRx's cost, all materials and information related to TolerRx Patent Rights
and/or TolerRx Know-how including, but not limited to, Antibodies and
information obtained under the Third Party Agreements.

                 (b) TOLERRX STUDIES UNDER THE DEVELOPMENT PLAN.

                         (i)    The Parties anticipate that TolerRx may perform
certain pre-clinical and clinical studies set forth in the Development Plan for
Licensed Products, designed to assess clear performance against pre-defined
decision criteria set forth in the Development Plan. If the JSC approves of
TolerRx's request to perform such studies on the Licensed Product, TolerRx will
receive a milestone payment of $[***] in the aggregate promptly after the
commencement of both the (A) preclinical study entitled "Preclinical Factor VIII
Study" and the (B) clinical study entitled "Human United Kingdom Phase I Study"
to the extent approved by the JSC and set forth in the Development Plan. For the
avoidance of doubt, TolerRx shall receive only one aggregate payment of $[***]
promptly after commencement of both of the foregoing studies. The Parties
anticipate that TolerRx shall begin both of such studies in 2003. TolerRx will
receive a milestone payment of $[***] upon completion of the clinical study
entitled "Factor VIII Clinical Study" only as approved by the JSC and set forth
in the Development Plan. The Parties anticipate that TolerRx shall begin such
study entitled "Factor VIII Clinical Study" in 2004. TolerRx shall provide a
detailed description of the foregoing studies to Genentech promptly after the
Effective Date so that such description of such studies, to the extent approved
by the JSC, shall be included in the Development Plan. For the avoidance of
doubt, the aggregate total of such milestone payments set forth in this Section
3.4(b) shall not exceed $[***]. For clarity, in no event shall Genentech have
any other payment obligations for any costs incurred by TolerRx except as
otherwise decided by the JSC and except as expressly provided herein. If
Genentech elects to use the results of the foregoing studies to develop and/or
commercialize the Licensed Product, and if TolerRx has exercised and continues
to participate in the US Profit/Loss Sharing Option in accordance with Section
6.5 and Exhibit A, then the total reasonable cost of such studies shall be
included in the calculation of "Development Costs" set forth in Exhibit A and
shall be shared in accordance with Exhibit A,

                                  * Confidential treatment requested:
                                    material has been omitted and filed
                                    separately with the Commission.

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provided that any balancing payments owed by one Party to the other Party shall
be adjusted so that the milestone payments of $[***] are deducted from
Genentech's balancing payment (if any). For example, if the total reasonable
cost of all of the above studies is $[***], and Genentech has paid the $[***] as
set forth above, then, if Genentech elects to use the results of the foregoing
studies to develop and/or commercialize the Licensed Product, and if TolerRx has
exercised and continues to participate in the US Profit/Loss Sharing Option in
accordance with Section 6.5 and Exhibit A, then the balancing payment for the
foregoing by Genentech shall be $[***].

                         (ii)   Except for the rights granted to TolerRx
hereunder to perform its obligations under this Section 3.4(b), TolerRx shall
not use and, except to the minimum extent required by applicable law, rule or
regulation and subject to Section 5.3(a)(iii), shall not disclose to anyone
(except to Genentech) any and all results arising out of such studies, except
with prior written approval of Genentech. TolerRx shall use commercially
reasonable efforts to report all results of such studies to Genentech; TolerRx
shall report such results no later than thirty (30) days from the date such
results become available.

                 (c) Pre-Clinical and Clinical Development Outside of the
Development Plan.

                         (i)    At its sole expense, TolerRx may perform
pre-clinical and clinical studies related to Licensed Products not described in
the Development Plan ("TolerRx PreClinical and Clinical Development"), only if
TolerRx submits such study plans to the JSC and only if Genentech approves of
such TolerRx PreClinical and Clinical Development and determines that such
TolerRx PreClinical and Clinical Development is not detrimental to the safety,
prospects, or reputation of any Licensed Product, Genentech, or any other
Genentech product. TolerRx shall not perform any activities related to any
Product unless approved by the JSC. Except for the rights granted to TolerRx
hereunder to perform its obligations under this Section 3.4(c), TolerRx shall
not use and, except to the minimum extent required by applicable law, rule or
regulation, and subject to Section 5.3(a)(iii), TolerRx shall not disclose to
anyone (except to Genentech) any and all results arising out of TolerRx
PreClinical and Clinical Development, except with prior written approval of
Genentech. TolerRx shall promptly report all such results to Genentech. TolerRx
shall use commercially reasonable efforts to report such results; TolerRx shall
report such results no later than thirty (30) days from the date such results
become available.

                         (ii)   If Genentech elects to use any results or data
related to TolerRx PreClinical and Clinical Development to develop or
commercialize the Licensed Product, Genentech shall reimburse TolerRx for the
reasonable costs of such TolerRx PreClinical and Clinical Development.

                 (d) ASSISTANCE IN REGULATORY FILINGS. During the Term, TolerRx
shall assist Genentech in the preparation and filing for any Regulatory Approval
with respect to

                                  * Confidential treatment requested:
                                    material has been omitted and filed
                                    separately with the Commission.

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GENENTECH CONFIDENTIAL

Licensed Products in the Territory, by delivering, at Genentech's request and
TolerRx's expense, all information in TolerRx's possession (in a complete and
accurate form) necessary or useful for completing and filing any Regulatory
Approval for a Licensed Product.

                 (e) ADVERSE EVENTS. During the Term, TolerRx shall report
promptly to Genentech the occurrence of any adverse events that it is aware of
relating to any Licensed Product or component thereof as necessary to comply
with the adverse events reporting regulations of the FDA (as provided in Title
21 of the Code of Federal Regulations) and Foreign Regulatory Authorities.
Notwithstanding the foregoing, if such adverse event is serious or
life-threatening, TolerRx shall report such adverse event within five (5) days
of such awareness.

                 (f) TOLERRX MEDICAL SCIENCE LIAISONS IN UNITED STATES. If
TolerRx has exercised and continues to participate in the US Profit/Loss Sharing
Option in accordance with Section 6.5 and Exhibit A, then TolerRx shall have the
right to provide MSLs (as defined below) to provide expert information to the
medical community on the subject matter of immunological tolerance only in
accordance with the Development Plan. TolerRx shall have the right to provide
such MSLs only if all of the following conditions are true: (A) Genentech
determines that TolerRx, at its sole expense, has established the proper
infrastructure to support and employ such MSLs and has hired sufficient numbers
of MSLs; (B) TolerRx pays for [***] of all TolerRx MSL Costs for a period of
[***] from the date the first MSL is hired; (C) Genentech determines that the
MSLs are not duplicating or performing any work performed by Genentech's or its
sublicensees' personnel or agents (Genentech medical science liaisons will be
solely responsible for any work related to physician advocacy development or
clinical trials (including but not limited to oversight of clinical trials));
(D) MSLs shall strictly follow any and all instructions provided by Genentech
and decisions made by Genentech and shall attend all training and other
activities required by Genentech; (E) MSLs do not adversely affect Genentech's
medical science liaisons (including but not limited to Genentech's medical
science liaison infrastructure and hiring) for such Licensed Product; and (F)
the total number of MSLs shall not exceed [***], unless otherwise agreed upon by
the Parties. "MSLS" or "TOLERRX MSLS" means medical science liaisons employed by
TolerRx who are fully qualified to provide expert information to the medical
community on the subject matter of immunological tolerance. For clarity, MSLs
shall not participate in the sales, marketing, or other commercialization of the
Licensed Product. "TOLERRX MSL COSTS" means fully burdened FTE Costs
pre-approved by Genentech and incurred by TolerRx for TolerRx MSLs, provided
that all of the conditions set forth in Sections 3.4(f)(A) to (F) above are true
and TolerRx complies fully with this Section 3.4(f). Genentech shall pay for
[***] of TolerRx MSL Costs incurred by TolerRx during the [***] period set forth
in Section 3.4(f)(B) above. Such payments shall be made within sixty (60) days
from the end of the calendar quarter in which such TolerRx MSL Costs were
incurred, provided that Genentech receives an invoice for such TolerRx MSL Costs
on or before the end of such calendar quarter. If TolerRx has properly provided
MSLs for the [***] period set forth in clause (B) immediately above, then to the
extent (X) TolerRx continues to comply fully with this Section 3.4(f), and (Y)
all of the foregoing conditions set forth in Sections 3.4(f)(A) to (F) above are
all true, TolerRx MSL Costs incurred after such [***] period shall be included
in the

                                  * Confidential treatment requested:
                                    material has been omitted and filed
                                    separately with the Commission.

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GENENTECH CONFIDENTIAL

calculation of "Development Costs" set forth in Exhibit A and shall be shared in
accordance with Exhibit A.

                 (g) DISCUSSIONS WITH FDA. Other than clinical studies hereunder
for which TolerRx will have primary responsibility, if any, Genentech will be
responsible for conducting meetings and discussions, and routine telephone
communications with the FDA related to clinical trials hereunder. To the extent
practical, during the Term, a reasonable number of representatives of the Party
not primarily responsible for a clinical trial will be given the opportunity to
participate in substantive discussions and meetings with the FDA which relate to
such clinical trial. The Party primarily responsible will have decision making
authority regarding the number of, and which, representatives of the other Party
may attend such meetings, but in any case at least one representative of the
other Party may participate. TolerRx will not have the right to participate,
however, in discussions or meetings with Regulatory Agencies regarding Licensed
Product being developed or sold by or for Genentech in the Territory outside the
United States. Notwithstanding the foregoing, the primarily responsible Party
will not be obligated to permit representatives of the other Party to attend any
Regulatory Agency meetings related specifically to an inspection at such Party's
premises by any Regulatory Agency.

          3.5.   CLINICAL DATA OWNERSHIP AND DRUG APPROVAL APPLICATIONS

                 (a) All data produced as a result of clinical trials conducted
by Genentech under this Agreement shall be owned by Genentech, and all such data
shall be considered Confidential Information of Genentech, regardless of whether
the foregoing has been marked confidential or not.

                 (b) During the Term, Genentech shall be responsible for, and
will use Commercially Reasonable and Diligent Efforts in, filing Drug Approval
Applications for Licensed Products in the Territory. If TolerRx submits to the
JSC a request to file IND(s) in certain Indications then only if the JSC
approves of such filings, TolerRx may file such IND(s). TolerRx shall hold in
confidence, not use (except to perform its obligations under this Section
3.5(b)), and not disclose to anyone any and all information and data related to
such INDs filed by TolerRx. If TolerRx exercises and participates in the US
Profit/Loss Sharing Option in accordance with Exhibit A and Section 6.5, such
costs shall be included in "Development Costs" as set forth in Exhibit A and
shall be shared as set forth therein, otherwise, such costs shall be paid for by
Genentech. Genentech shall own all regulatory submissions including all Drug
Approval Applications for Licensed Products in the Territory and shall be the
holder of all Regulatory Approvals. Genentech shall have the right to own all
INDs filed by TolerRx as set forth above, and at Genentech's request, TolerRx
shall assign such INDs to Genentech. TolerRx agrees to take all additional
actions necessary to effect the foregoing assignment. Except as expressly
provided in Section 9.5(c)(iii),such ownership and status as applicant and
holder shall survive any expiration or termination of this Agreement. The
foregoing confidentiality obligations shall survive any termination of this
Agreement by Genentech under Sections 9.3 or 9.4 or expiration of this
Agreement.

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GENENTECH CONFIDENTIAL

          3.6.   SUPPLY OF LICENSED PRODUCT. During the Term, if TolerRx wants
Genentech to supply Licensed Products to TolerRx so that TolerRx may fulfill its
development obligations under Section 3.4(c) of this Agreement, the Parties
agree to negotiate in good faith regarding Genentech supplying a reasonable
amount of Licensed Products to TolerRx at Fully Burdened Manufacturing Cost (as
defined in Exhibit A). For clarity, Genentech shall not be obligated to supply
Licensed Products to TolerRx with respect to Section 3.4(b) unless approved by
the JSC in the manner set forth in Section 2.2. As a condition of the foregoing,
Genentech shall be obligated to negotiate only if Genentech determines that
supplying such Licensed Products does not adversely affect the Licensed Product
(including but not limited to supply of Licensed Product for clinical testing)
or Genentech's other products. In no event shall Genentech be obligated to
manufacture any Licensed Products for TolerRx, except to the limited extent
expressly set forth in Section 9.5(c)(iii).

          3.7.   RIGHT OF FIRST NEGOTIATION FOR RIGHTS RELATING TO ANTI-CD8
ANTIBODY. To the extent that TolerRx owns or Controls rights solely relating to
anti-CD8 antibodies or fragments thereof, TolerRx hereby grants to Genentech the
exclusive option during the Term to be the first party to negotiate (for a
ninety (90) day period) an exclusive, worldwide license to such rights.

                  ARTICLE 4 COMMERCIALIZATION IN THE TERRITORY

          4.1.   COMMERCIALIZATION EFFORTS; COSTS. During the Term, Genentech
shall use its Commercially Reasonable and Diligent Efforts to commercialize each
Licensed Product in each country in which Regulatory Approval is received.
Genentech shall have the full responsibility and sole right to make all
decisions regarding all commercialization activities, including without
limitation all manufacturing, sales, marketing and product launch activities
related to Licensed Products. Genentech shall bear all costs related to the
commercialization of the Licensed Products by Genentech in the Territory, except
for US Costs if TolerRx exercises the US Profit/Loss Sharing Option set forth in
Section 6.5.

          4.2.   DEVELOPMENT OR MARKETING WITH INDEPENDENT PRODUCTS.

                 (a) Without limiting Genentech's rights, if TolerRx reasonably
believes that marketing a Licensed Product in conjunction with an Independent
Product will maximize the profits for such Licensed Product, at TolerRx's
written request, Genentech agrees to use Commercially Reasonable and Diligent
Efforts to negotiate (for a period of sixty (60) days) in good faith an
arrangement with the Third Party that owns or Controls such Independent Product
whereby Licensed Product will be marketed in conjunction with the Independent
Product, provided that Genentech shall be obligated to do so only if it
determines in its sole discretion that (a) such development or marketing would
not adversely affect any Licensed Product, other Genentech product, or
Genentech; (b) such development or marketing would be desirable and financially
profitable and would significantly increase the Net Sales of such Licensed
Product; and (c) such Third Party is reasonably acceptable to Genentech. This
Section 4.2 shall apply

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GENENTECH CONFIDENTIAL

only after Licensed Product for Phase III Clinical Trials manufactured by
Genentech or its third party sublicensees on Genentech's behalf is available
(and Genentech shall not have any obligations under this Section 4.2 (a) to so
negotiate until such time). "INDEPENDENT PRODUCT" means a Third Party's
pharmaceutical, stand-alone product that (A) has received Regulatory Approval in
the United States; (B) has been fully developed and commercialized as a
stand-alone product by such Third Party, and Genentech is not involved in and
has no rights or obligations with respect to current or future involvement in
researching, developing or commercializing or any other aspect of such product;
and (C) Genentech determines would be desirable to market or develop with the
Licensed Product.

                 (b) If Genentech executes an agreement with such Third Party
for marketing or developing the Licensed Product in conjunction with an
Independent Product, and if (and only if) Genentech is not obligated to provide
any consideration to such Third Party, then during the Term, Genentech shall
share (in accordance with the percentages below) with TolerRx the portion of
upfront, milestone, or royalty payments, if any, actually received by Genentech
from such Third Party that would constitute Independent Product Profit for
Genentech. Such Independent Product Profit shall be shared between the Parties:
with TolerRx receiving [***] of such amounts and Genentech receiving [***] of
such amounts. "INDEPENDENT PRODUCT PROFIT" means the upfront, milestone, royalty
payments received by Genentech from such Third Party and less Reimbursements.
"REIMBURSEMENTS" means reimbursements of all fully burdened costs incurred by
Genentech related to developing, manufacturing, distribution, marketing, and/or
sales of such Licensed Product in conjunction with such Independent Product.
Independent Product Profit shall only consist of such payments received by
Genentech from such Third Party that are solely attributable to Genentech's
marketing and development activities (and not attributable to any other action
or inaction of Genentech or other reasons) for the Licensed Product in
conjunction with such Independent Product. All payments received by Genentech
from such Third Party relating to any of Genentech's intellectual property or
any other Genentech activity shall be excluded from Independent Product Profit.

                                ARTICLE 5 LICENSE

          5.1.   GRANT OF THE RIGHTS TO GENENTECH. Subject to the terms and
conditions of this Agreement, TolerRx hereby grants to Genentech an exclusive
(even as to TolerRx), sublicensable license under TolerRx Patent Rights, TolerRx
Know-how and TolerRx's joint ownership rights in Joint Patents (as defined in
Section 7 herein), to make (and have made), use, sell, offer for sale and/or
import Licensed Product, within the Field in the Territory.

          5.2.   Genentech shall have the right to grant sublicenses under the
license granted pursuant to Section 5.1 provided that: (i) Genentech shall be
responsible for the making of all payments due by reason of milestones achieved
with respect to any Licensed Product and Net Sales of any Licensed Products by
its third party sublicensees, and the making of reports as required under this
Agreement, and their compliance with all applicable licensing terms of this
Agreement to the extent that they are applicable to a sublicensee; and (ii) each
sublicensee agrees

                                  * Confidential treatment requested:
                                    material has been omitted and filed
                                    separately with the Commission.

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GENENTECH CONFIDENTIAL

in writing to comply with the record keeping obligations set forth in Section
6.7, of this Agreement and Genentech shall use reasonable commercial efforts to
enforce the foregoing terms to the extent that such sublicensee's lack of
performance of such terms would constitute a material breach of this Agreement.
Genentech shall notify TolerRx promptly in writing of the name and address of
each sublicensee.

          5.3.   RIGHTS OF TOLERRX UNDER THIRD PARTY AGREEMENT. To the extent
the rights granted herein under Sections 5.1 and 5.2 are rights obtained by
TolerRx under the Third Party Agreements, the Parties understand and agree as
follows:

                 (a) THE ISIS AGREEMENT.

                         (i)    Isis Innovation Ltd. ("Isis") has reserved the
right to grant to the University of Oxford (the "University") a license for the
University and every employee, student, agent and appointee of the University to
use and publish the technologies licensed by Isis to TolerRx under the Isis
Agreement, only to the minimum extent expressly set forth therein ("Isis
Retained Rights") for academic and research purposes; and this will include the
right for the University to use the Isis Retained Rights as enabling technology
in other research projects (including projects which benefit from third-party
funding received from commercial entities).

                         (ii)   The University and every employee, student,
agent and appointee of the University have reserved the right to transfer
antibody owned by Isis and licensed to TolerRx under the Isis Agreement to any
academic collaborator to use solely for academic and research purposes (not
including commercially funded research purposes) for in vitro research, only to
the minimum extent expressly set forth in the Isis Agreement.

                         (iii)  In the event that TolerRx, pursuant to the
relevant term expressly set forth in the Isis Agreement, communicates to Isis
any improvements which TolerRx makes to the technology licensed to TolerRx by
Isis ("TolerRx's Improvement"), TolerRx shall ensure that: (1) the TolerRx's
Improvement is made solely by TolerRx and does not contain or incorporate any of
Genentech's proprietary material or information; (2) any communication to Isis
regarding TolerRx's Improvement is properly identified as TolerRx's confidential
information as to Isis; (3) the communication is made only after proper actions
have been taken (including, but not limited to, filing of patent applications)
to protect any intellectual property related to the TolerRx's Improvement; (4)
prior to making such communication, TolerRx notifies Genentech and discloses to
Genentech the content of such communication and (5) the communication regarding
the TolerRx's Improvement is made by TolerRx to Isis solely for the purpose of
Isis's evaluation of the TolerRx's Improvement for a potential license thereto
by Isis, pursuant to the relevant term expressly set forth in the Isis
Agreement.

                 (b) THE CUTS AGREEMENT. Cambridge University Technical Services
Limited ("CUTS") and the University of Cambridge ("UC") have reserved the
non-exclusive right to use antibodies, patents and patent applications licensed
by CUTS to TolerRx under the CUTS Agreement ("CUTS Retained Rights"), only to
the minimum extent expressly set forth

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GENENTECH CONFIDENTIAL

therein for the purposes of academic research and teaching and to publish the
general scientific findings from research related to the CUTS Retained Rights,
provided that no commercial entity has rights to the results of such research in
the Field.

          5.4.   Without the express written permission of Genentech, TolerRx
shall not amend any of the Third Party Agreements or grant any rights to any
third party in a manner that would adversely affect the rights granted to
Genentech under this Agreement, including but not limited to Sections 5.1 and
5.2. Without limiting TolerRx's obligations above, TolerRx shall not enter into
any agreement with any third party in a manner that would materially adversely
affect the rights granted to Genentech under this Agreement, without the express
written permission of Genentech. This Section 5.4 shall survive any expiration
of the Agreement or termination of the Agreement by Genentech under Sections 9.3
or 9.4.

                       ARTICLE 6 MILESTONES AND ROYALTIES

          6.1.   UPFRONT PAYMENT.

                 (a) Genentech will pay TolerRx an upfront non-refundable,
non-creditable fee of two million five hundred thousand dollars ($2,500,000)
("Upfront Payment") within ten (10) business days after the Effective Date.

                 (b) Genentech shall purchase shares of TolerRx Preferred Stock
for an aggregate purchase price of three million five hundred thousand dollars
($3,500,000) on the terms and conditions set forth in the Stock Purchase
Agreement of even date herewith attached hereto as Exhibit C.

          6.2.   DEVELOPMENT MILESTONES.

                 (a) PAYMENTS FOR THE FIRST OCCURRENCE OF MILESTONES. As
consideration to TolerRx for the licenses and other rights granted to Genentech
under this Agreement, during the Term, Genentech shall pay to TolerRx the
following milestone payments upon the first occurrence of each event set forth
below with respect to only the first Licensed Product for which the milestone is
achieved by or on behalf of Genentech. For purposes of clarification, each
milestone in this Section 6.2(a) shall be payable only once. Such milestone
shall be payable within forty-five (45) days of when the first Licensed Product
that is manufactured by or on behalf of Genentech fully satisfies such milestone
requirement. For the purposes of this Section 6.2 and 6.5 only, any reference to
achieving a milestone or manufacturing "by or on behalf of Genentech" or "by or
for Genentech" refers only to achievement of such milestone or manufacturing by
Genentech or by Genentech's third party sublicensees on Genentech's behalf, and
excludes TolerRx unless otherwise agreed to expressly in writing by the parties.

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GENENTECH CONFIDENTIAL

<Table>
<Caption>
                 Milestone                                                    Payment
                 ---------                                                    -------
                 <S>     <C>                                                  <C>
                 (i)     Genentech's portfolio planning committee (or
                         future equivalent)'s decision to place Licensed
                         Product into formal development for the first time   $[***]

                 (ii)    First filing of IND by Genentech for Licensed
                         Product manufactured by or for Genentech             $[***]

                 (iii)   Administration of Licensed Product manufactured by
                         or for Genentech to first patient in first Phase I
                         Clinical Trial in the United States                  $[***]

                 (iv)    Administration of Licensed Product manufactured by
                         or for Genentech to first patient in first Phase
                         II Clinical Trial in the United States               $[***]

                 (v)     Administration of Licensed Product to first
                         patient in first Phase III Clinical Trial in the
                         United States                                        $[***]

                 (vi)    Filing of first BLA for Licensed Product in United
                         States                                               $[***]

                 (vii)   First Regulatory Approval for Licensed Product in
                         United States                                        $[***]

                 (viii)  Filing of first MAA with the EMEA for Licensed
                         Product                                              $[***]

                 (ix)    First Regulatory Approval by EMEA for Licensed
                         Product                                              $[***]
</Table>

                 (b) ADDITIONAL MILESTONES FOR DIFFERENT INDICATIONS. This
Section 6.2(b) applies only after the corresponding milestone has been paid
under Section 6.2(a). As consideration to TolerRx for the licenses and other
rights granted to Genentech under this Agreement, during the Term, Genentech
shall pay to TolerRx the following milestone payments upon the first occurrence
of each event set forth below with respect to each of two Different Indications
for which the milestone is achieved by or on behalf of Genentech. "Different
Indication" means an Indication that is different from any other Indication for
which the

                                  * Confidential treatment requested:
                                    material has been omitted and filed
                                    separately with the Commission.

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GENENTECH CONFIDENTIAL

corresponding milestone was paid under Section 6.2(a) or 6.2(b). Each milestone
in this Section 6.2(b) shall be payable only once for each Different Indication,
up to a maximum of two Different Indications. Such milestone shall be payable
within forty-five (45) days of when such Indication for a Licensed Product that
is manufactured by or on behalf of Genentech fully satisfies such milestone
requirement. For avoidance of doubt, each milestone in this Section 6.2(b) shall
be paid at most twice only: (R) the first such milestone payment for the first
Different Indication to satisfy that milestone, and (S) the second payment for a
second Different Indication to satisfy that milestone. Genentech shall not make
any payments under Section 6.2(b) with regard to any other Indications or
Licensed Products.

<Table>
<Caption>
                 Milestone                                                    Payment
                 ---------                                                    -------
                 <S>     <C>                                                  <C>
                 (i)     Genentech's portfolio planning committee (or         $[***]
                         future equivalent)'s decision to place
                         Licensed Product into formal development
                         for first or second Different Indication
                         for the first time

                 (ii)    Administration of Licensed Product  to first
                         patient in first Phase III Clinical Trial in the
                         United States for first or second Different
                         Indication                                           $[***]

                 (iii)   Filing of first BLA for Licensed Product for first
                         or second Different Indication in United States      $[***]

                 (iv)    First Regulatory Approval for Licensed Product for
                         first or second Different Indication in United
                         States                                               $[***]

                 (v)     Filing of first MAA with the EMEA for Licensed
                         Product for first or second Indication in European
                         Union                                                $[***]

                 (vi)    First Regulatory Approval by EMEA for Licensed
                         Product for first or second Different Indication
                         in European Union                                    $[***]
</Table>

                 (c) EXAMPLE. The milestone payments above shall be calculated
in accordance with the following example. There are Licensed Product(s) for
three Different Indications. Licensed Product for one Indication ("LP1") is
placed into development by

                                  * Confidential treatment requested:
                                    material has been omitted and filed
                                    separately with the Commission.

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Genentech's portfolio planning committee, continues to develop, and fails to
proceed beyond Phase III Clinical Trials. The Licensed Product for a second
Indication ("LP2") is placed into development by Genentech's portfolio planning
committee, continues to develop, and completes all possible milestones,
including receiving Regulatory Approval in the United States and from the EMEA.
The Licensed Product for a third Indication ("LP3") is placed into development
by Genentech's portfolio planning committee, continues to develop, receives
Regulatory Approval in the United States, and files MAA with the EMEA but fails
to receive Regulatory Approval by EMEA. For LP1, the applicable milestone
payments would be Section 6.2(a)(i) through 6.2(a)(v). For LP2, the applicable
milestone payments would be Section 6.2(b)(i), 6.2(b)(ii) and 6.2(a)(vi) through
6.2(a)(ix). For LP3, the applicable milestone payments would be Section
6.2(b)(i) through 6.2(b)(v). In this example, no further payments shall be made
under Section 6.2(a) and 6.2(b)(i) and 6.2(b)(ii).

          6.3.   ROYALTIES. The royalties set forth in this Section 6.3 shall
apply to Net Sales in each country within the Territory, unless TolerRx properly
exercises and participates in the US Profit/Loss Sharing Option, in which case
(P) the royalties set forth in this Section 6.3 shall apply only to Net Sales in
countries in the Territory other than the United States and (Q) Section 6.5
applies to the United States. Subject to the foregoing, royalties payable by
Genentech under this Section 6.3 shall be determined and payable on a
country-by-country and Licensed Product-by-Licensed Product basis as follows
(depending on the type of Licensed Product sold in such country): (A) with
respect to such Licensed Product that, but for the licenses granted herein,
would infringe a Valid Claim in such country, the royalties as set forth in
Section 6.3(a); or (B) with respect to such Licensed Product that would not
infringe a Valid Claim in such country, but (X) relies on or incorporates
TolerRx Know-how, including but not limited to, Antibodies provided by TolerRx
to Genentech pursuant to this Agreement or (Y) was developed pursuant to the
Development Plan, the royalties set forth in Section 6.3(b). All such royalties
shall be further reduced by one or more of the following Sections, to the extent
applicable: Sections 6.3(c) and 6.4. For clarity, no royalties for a Licensed
Product in a country shall be owed by Genentech under Sections 6.3 or 6.4 until
the date of Commercial Introduction of such Licensed Product in such country.
All references in this Agreement to "royalties under Sections 6.3 and 6.4"
"royalties set forth in Sections 6.3 and 6.4" or the like shall mean royalties
set forth in Sections 6.3, reduced by Section 6.4 if applicable.

                 (a) ROYALTIES OWED BY GENENTECH FOR LICENSED PRODUCTS COVERED
BY VALID CLAIM. As consideration to TolerRx for the licenses and other rights
granted to Genentech under this Agreement, during the Term, Genentech shall make
royalty payments to TolerRx (for each Licensed Product sold in the country(ies)
where the sale of such Licensed Product, but for the licenses granted herein,
would infringe a Valid Claim) as follows and such payments shall be reduced by
Sections 6.3(c), and/or 6.4 to the extent applicable.

                         (i)    Genentech shall pay a royalty of [***] for the
portion of Patented Product Aggregate Annual Worldwide Net Sales that is less
than or equal to $[***].

                                  * Confidential treatment requested:
                                    material has been omitted and filed
                                    separately with the Commission.

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GENENTECH CONFIDENTIAL

                         (ii)   Genentech shall pay a royalty of [***] for the
portion of Patented Product Aggregate Annual Worldwide Net Sales that is greater
than $[***] and less than or equal to $[***].

                         (iii)  Genentech shall pay a royalty of [***] for the
portion of Patented Product Aggregate Annual Worldwide Net Sales that is greater
than $[***] and less than or equal to $[***].

                         (iv)   Genentech shall pay a royalty of [***] for the
portion of Patented Product Aggregate Annual Worldwide Net Sales that is greater
than $[***].

"Patented Product Aggregate Annual Worldwide Net Sales" means aggregating the
Net Sales amounts (occurring in the applicable calendar year) of all such
Licensed Products the sales of which, but for the licenses granted herein, would
infringe a Valid Claim in the country where such sales occur. Patented Product
Aggregate Annual Worldwide Net Sales consists of aggregating such Net Sales of
only such Licensed Products of the same type as described in Section 6.3(d)
below.

For example, if Patented Product Aggregate Annual Worldwide Net Sales of Type A
Licensed Products (as defined in Section 6.3(d) below) in the Territory totaled
$[***], then the applicable royalties that Genentech would pay is ([***] X
$[***]) + ([***] X $[***]) + ([***] X $[***]) + ([***] X [***]) = $[***].

                 (b) ROYALTIES OWED BY GENENTECH FOR LICENSED PRODUCTS COVERED
BY TOLERRX KNOW-HOW. During the Royalty Term, with respect to Licensed Product
sold in the country(ies) where the sale of such Licensed Product, but for the
licenses granted herein, would not infringe a Valid Claim, but such Licensed
Product in the country where sold (A) relies on or incorporates TolerRx
Know-how, including but not limited to, Antibodies provided by TolerRx to
Genentech pursuant to this Agreement, or (B) was developed pursuant to the
Development Plan, Genentech shall make royalty payments to TolerRx for such
Licensed Products as follows and such payments shall be reduced by Sections
6.3(c), and/or 6.4 to the extent applicable.

                         (i)    Genentech shall pay a royalty of [***] for the
portion of Non-Patented Product Aggregate Annual Worldwide Net Sales that is
less than or equal to $[***].

                         (ii)   Genentech shall pay a royalty of [***]for the
portion of Non-Patented Product Aggregate Annual Worldwide Net Sales that is
greater than $[***] and less than or equal to $[***].

                         (iii)  Genentech shall pay a royalty of [***] for the
portion of Non-Patented Product Aggregate Annual Worldwide Net Sales that is
greater than $[***] and less than or equal to $[***].

                                  * Confidential treatment requested:
                                    material has been omitted and filed
                                    separately with the Commission.

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GENENTECH CONFIDENTIAL

                         (iv)   Genentech shall pay a royalty of [***] for the
portion of Non-Patented Product Aggregate Annual Worldwide Net Sales that is
greater than $[***].

"Non-Patented Product Aggregate Annual Worldwide Net Sales" means aggregating
the Net Sales amounts (occurring in the applicable calendar year) of all such
Licensed Products the sales of which, but for the licenses granted herein, would
not infringe a Valid Claim in the country where such sales occur but which
Licensed Products in the country where such sales occur (A) rely on or
incorporate TolerRx Know-how, including but not limited to, Antibodies provided
by TolerRx to Genentech pursuant to this Agreement, or (B) were developed
pursuant to the Development Plan. Non-Patented Product Aggregate Annual
Worldwide Net Sales consists of aggregating such Net Sales of only such Licensed
Products of the same type as described in Section 6.3(d) below.

                 (c) ROYALTIES OWED BY GENENTECH IF ANOTHER ANTI-CD4 PRODUCT
EXISTS. Genentech's royalty payment obligations as set forth in Sections 6.3(a)
or 6.3(b) above shall not apply in those countries for a Licensed Product during
the period that any of the following is true in such countries: (A) Another
Anti-CD4 Product has received Regulatory Approval for an Indication that is the
same as an Indication for which the Licensed Product has received Regulatory
Approval or (B) the total volume of Other Anti-CD4 Products (commercialized,
used or sold for an Indication that is the same as any Indication for which the
Licensed Product has received Regulatory Approval) equals [***] or more of the
total volume of products containing an Antibody or Antibodies or any formulation
thereof commercialized, used, or sold for such Indication. Instead, Genentech
shall only pay a royalty of (i) during the Term, with respect to those Licensed
Products described in Section 6.3(a), [***] for annual Net Sales of such
Licensed Products in such countries where sold; or (B) during the Royalty Term,
with respect to those Licensed Products described in Section 6.3(b), [***] on
all Net Sales amounts of such Licensed Product in such countries where sold
(except that such royalty payments shall not be reduced by this Section 6.3(c)
below the Minimum Royalty Rate). For the purpose of this Agreement, "ANOTHER
ANTI-CD4 PRODUCT" means any third party product containing an Antibody or
Antibodies or any formulation thereof, including, without limitation, any
lyophilized liquid, sustained release or aerosolized formulation. "OTHER
ANTI-CD4 PRODUCTS" means all of the third party products in such countries that
are Another Anti-CD4 Product.

                 (d) CALCULATIONS AND EXAMPLE. The royalties in Section 6.3 and
6.4 herein shall be calculated on a country-by-country and Licensed
Product-by-Licensed Product basis, by aggregating Net Sales for all applicable
countries with Licensed Products of the same type, as in the following example:
In France and Germany, only Licensed Products described in Section 6.3(a), but
to which Sections 6.3(c) and 6.4 do not apply ("Type A Licensed Products") are
sold. In Spain and Portugal, only Licensed Products described in Section 6.3(a)
to which Section 6.3(c) does apply (but to which Section 6.4 does not apply,
because no amounts described in Section 6.4 are paid to a third party) ("Type B
Licensed Products") are sold. In the above example, the Net Sales for France and
Germany for Type A Licensed Products shall be aggregated and the applicable
royalty for the portions of Net Sales of such Licensed Products

                                  * Confidential treatment requested:
                                    material has been omitted and filed
                                    separately with the Commission.

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GENENTECH CONFIDENTIAL

shall be as set forth in Section 6.3(a). The Net Sales for Spain and Portugal
for Type B Licensed Products shall be aggregated and the applicable royalty for
the portions of Net Sales of such Licensed Products shall be as set forth in
Section 6.3(c). For clarity, the Net Sales amounts for countries with Licensed
Product of one type shall not be aggregated with Net Sales amounts for countries
with Licensed Product of a different type. In the above example, in calculating
royalties, the Net Sales amounts of Type A Licensed Products shall not be
aggregated with the Net Sales amounts of Type B Licensed Products.

          6.4.   THIRD PARTY ROYALTIES. On a country-by-country basis and
Licensed Product-by Licensed Product basis, the royalties otherwise due and
payable by Genentech to TolerRx hereunder, with respect to a Licensed Product in
a country, shall be reduced by an amount equal to [***] of the amounts Genentech
or its third party sublicensee(s) pays to any third party with respect to the
development, manufacture, import or export, use, offer for sale or sale with
respect to such Licensed Product in such country; PROVIDED, HOWEVER, that in no
event shall the royalty payments due and payable to TolerRx with respect to such
Licensed Product in such country be reduced by this Section 6.4 by more than
[***] of Net Sales with respect to such Licensed Product in such country and the
royalty payments shall not be reduced by this Section 6.4 below the Minimum
Royalty Rate. For example, if the Net Sales amount for a Licensed Product
described in Section 6.3(a) (assuming that no other reductions in Section 6.3(c)
apply) for a country is $[***] and if Genentech owes royalties to a third party
of [***] of Net Sales, then Genentech may reduce such royalty owed to TolerRx by
[***] of such Net Sales, so that the resulting royalty rate is lowered in the
foregoing example from [***] to [***] (in other words, lowered by $[***]). If
the royalty rate to the third party is [***], the royalty reduction is still
$[***].

          6.5.   OPTION TO SHARE OPERATING PROFITS OR LOSSES IN UNITED STATES.

                 (a) Subject to the terms and conditions of this Agreement, in
lieu of the royalties set forth in Sections 6.3 and 6.4 for Net Sales in the
United States, on a Licensed Product-by-Licensed Product basis, subject to
Section 6.5(b), TolerRx shall have an option to share in Operating Profits or
Losses (as defined in Exhibit A) from sales of Licensed Products in the United
States, PROVIDED THAT, TolerRx: (A) makes the US Cost Sharing Payments within
the time period set forth below and (B) during the time period set forth below,
continues to make the applicable balancing payments, if any, relating to sharing
Operating Loss, on a timely basis in accordance with Section 6.5(c) below and
Exhibit A attached hereto (including but not limited to Section A.4 of Exhibit
A) ("US Profit/Loss Sharing Option"). "US COST SHARING PAYMENTS" means the
portion of US Costs owed by TolerRx to Genentech under this Agreement as set
forth in Exhibit A for Development Costs (as defined in Exhibit A) to the date
of the Phase II Go Decision Notice, which amount shall be identified in a
written notice to TolerRx. Upon Genentech providing written notice of its
decision to commence the first Phase II Clinical Trial for the first Indication
of the first such Licensed Product manufactured by or on behalf of Genentech by
third parties and providing TolerRx written notice of the U.S. Cost Sharing
Payments ("Phase II Go Decision Notice"), TolerRx shall have (X) thirty (30)
days from the date

                                  * Confidential treatment requested:
                                    material has been omitted and filed
                                    separately with the Commission.

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GENENTECH CONFIDENTIAL

of such Phase II Go Decision Notice to exercise the US Profit/Loss Sharing
Option by delivering proper written notice to Genentech and (Y) forty-five (45)
days from the date of such Phase II Go Decision Notice to make such US Cost
Sharing Payments.

                 (b) On a Licensed Product-by-Licensed Product basis, TolerRx
shall share in Operating Losses (as defined in Exhibit A), if any, commencing
from the date TolerRx exercises such US Profit/Loss Sharing Option and ending on
the date when Genentech terminates sales of such Licensed Product in the United
States, subject to earlier termination as set forth in Section 6.5(c) below.
Subject to the last two sentences of this Section 6.5(b), TolerRx shall share in
Operating Profits (as defined in Exhibit A), if any, commencing from the first
date that an Operating Profit exists (and TolerRx shall not have such right to
share in Operating Profits until such date) and ending on the date when
Genentech terminates sales of such Licensed Product in the United States,
subject to earlier termination as set forth in Section 6.5(c) below. For the
avoidance of doubt, the Operating Losses shall include costs incurred from the
date of filing of the first IND by Genentech (including but not limited to the
FTE Cost(s) and filing fees for filing such IND). Without limiting any of
Genentech's rights or remedies, TolerRx shall have the right to receive its
share of Operating Profits as set forth in Exhibit A and this Section 6.5 only
after Genentech has recouped all of TolerRx's share of the Operating Losses. At
Genentech's election in its sole discretion, Genentech may recoup all of such
Operating Losses either through (P) direct payment by TolerRx of all applicable
balancing payment amounts in accordance with Exhibit A and this Section 6.5 or
(Q) deducting all of such Operating Losses from TolerRx's share of Operating
Profits.

                 (c) Genentech shall only be obligated to pay the royalties set
forth in Section 6.3 and 6.4, if any, and shall not be obligated at any time to
share Operating Profits or Losses under Exhibit A, if TolerRx: (A) fails to make
US Cost Sharing Payments within forty-five (45) days from the date of such Phase
II Go Decision Notice or (B) fails to notify Genentech of its exercise of the US
Profit/Loss Sharing Option within thirty (30) days from the date of the Phase II
Go Decision Notice for the applicable Licensed Product. If TolerRx fails to make
the applicable balancing payments relating to sharing Operating Profit or Loss,
if any, on a timely basis in accordance with Exhibit A, and does not do so
within thirty (30) days of written notice of such failure from Genentech,
effective as of the beginning of the calendar quarter in which such failure to
pay by TolerRx occurs then Genentech shall not be obligated to share Operating
Profits or Losses under Exhibit A and Genentech shall only be obligated to pay
the royalties set forth in Section 6.3 and 6.4, if any. Nothing herein relieves
TolerRx of its obligation to make such delinquent payment.

                 (d) If TolerRx has exercised and continues to participate in
the US Profit/Loss Sharing Option in accordance with Section 6.5 and Exhibit A,
upon completion of Phase III Clinical Trial for a Licensed Product, Genentech
shall prepare and provide to the JSC a copy of Marketing Plan for such Licensed
Product. Thereafter, for each calendar year, at least three months prior to the
beginning thereof, Genentech shall provide the JSC an updated copy of such
Marketing Plan. The JSC may review such Marketing Plan but Genentech has sole

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GENENTECH CONFIDENTIAL

authority regarding the content of such Marketing Plan and may make
modifications thereto, from time to time. Such Marketing Plan will include a
budget.

          6.6.   PAYMENT OF ROYALTIES AND OTHER AMOUNTS.

                 (a) MODE OF PAYMENTS. Net Sales described in Sections 6.3, 6.4,
9.5(c)(iii) (to the extent applicable) will be calculated on a calendar quarter
basis. For purposes of determining when a sale of any Licensed Product occurs
under this Agreement, the sale shall be deemed to occur on the date the Licensed
Product is shipped. The obligation to pay royalties under this Agreement shall
be imposed only once with respect to the same unit of Licensed Product,
regardless of the number of patents within TolerRx Patent Rights pertaining
thereto and regardless of whether such unit of Licensed Product is based on one
or more than one of the following: TolerRx Know-how, patents within TolerRx
Patent Rights, and/or was developed pursuant to the Development Plan. After the
date of Commercial Introduction of each Licensed Product, all royalty payments
for such Licensed Product shall be made within sixty (60) days after the end of
each calendar quarter in which such sales were deemed to occur. All payments
hereunder shall be made free and clear of any taxes, duties, levies, fees or
charges, except for withholding taxes (to the extent applicable). Genentech
shall make any applicable withholding payments due on behalf of TolerRx and
shall promptly provide TolerRx with written documentation of any such payment
sufficient to satisfy the requirements of the United States Internal Revenue
Service related to an application by TolerRx for a foreign tax credit for such
payment. All payments hereunder due to TolerRx shall be made in U.S. Dollars by
bank wire transfer to: [***], except as provided below. TolerRx may modify such
bank wire transfer information upon providing written notice to Genentech.

                 (b) FOREIGN CURRENCY CONVERSION. For the purpose of calculating
royalty payments to TolerRx under Sections 6.3 and 6.4 above and calculating
royalty payments to Genentech under Section 9.5(c)(iii) (to the extent
applicable), if Licensed Products are sold in a currency other than U.S.
dollars, such non-U.S. currencies shall be converted to U.S. dollars at the
daily Reuters exchange rate for the last business day of such calendar quarter
in which the relevant financial transactions are recorded.

                 (c) RESTRICTIONS ON PAYMENT. If by law, regulations or fiscal
policy of a particular country in the Territory, remittance of royalties in U.S.
Dollars is restricted or forbidden, written notice thereof will promptly be
given to TolerRx, and payment of the royalty shall be made by the deposit
thereof in local currency to the credit of TolerRx in a recognized banking
institution in such country selected by Genentech and reasonably acceptable to
TolerRx. When, in any country in the Territory, the law or regulations prohibit
both the transmittal and deposit of royalties on sales in such country, royalty
payments shall be suspended for as long as such prohibition is in effect and as
soon as such prohibition ceases to be in effect, all royalties that Genentech
would have been under an obligation to transmit or deposit but for the
prohibition shall forthwith be deposited or transmitted to the extent allowable.

                                  * Confidential treatment requested:
                                    material has been omitted and filed
                                    separately with the Commission.

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GENENTECH CONFIDENTIAL

                 (d) REPORTS. Each royalty payment shall be accompanied by a
report, Licensed Product-by- Licensed Product and country-by-country, of the
amount of Gross Sales, the calculation of Net Sales and the units of Licensed
Product sold during such quarter, the amount of royalties due on such Net Sales,
and the conversion rates used in converting to United States Dollars.

          6.7.   RECORDS. Genentech shall keep complete and accurate records
pertaining to the sale of Licensed Products in the Territory and covering all
transactions from which Net Sales and payments to be made to TolerRx and amounts
to be charged to TolerRx are derived for a period of three calendar years after
the year in which such sales occur and such costs are incurred. TolerRx shall
keep complete and accurate records pertaining to the following, if applicable:
TolerRx MSL Costs, costs related to Sections 3.4(b) and 3.4(c) herein, TolerRx
Development Plan Work Costs, and, if Section 9.5(c)(iii) applies, the sale of
Licensed Products in the Territory and covering all transactions from which Net
Sales and payments to be made to Genentech under Section 9.5(c)(iii) are derived
for a period of three calendar years after the year in which such sales occur
and such costs are incurred.

          6.8.   AUDIT. At the request and expense (except as provided below) of
TolerRx, not more than once per year, Genentech shall permit an independent,
certified public accountant appointed by TolerRx and reasonably acceptable to
Genentech, at reasonable times during normal business hours and upon thirty (30)
days' notice, to examine those financial records of Genentech directly used in
Genentech's calculations of (A) royalties under Sections 6.3 and 6.4 herein for
a period of three years after such royalties have accrued, to determine or
verify the appropriate royalties owed to TolerRx, and (B) Direct Costs and Net
Sales (only if TolerRx has exercised and continues to participate in the US
Profit/Loss Sharing Option in accordance with Section 6.5 and Exhibit A), to
determine or verify the Direct Costs and Net Sales. The term "royalties" as
referred to in this Section 6.8 only, shall only refer to the royalties set
forth in Sections 6.3 and 6.4 of this Agreement. "Direct Costs" means (A) direct
costs of labor and materials related to Development Costs, Marketing Costs, and
Sales Costs (as defined in Exhibit A) and (B) Third Party Royalty Expense (as
defined in Exhibit A). For clarity, Direct Costs excludes indirect costs and
Allocable Overhead. For the avoidance of doubt, TolerRx shall not have such
accountant examine financial records related to other items in Exhibit A (ie. US
Costs other than Direct Costs), and shall only have the right to confirm that
Genentech's costing and accounting methodology related to such other items is
consistent with GAAP. Said accountant shall not disclose to TolerRx any
information other than information necessary to verify such royalties or Direct
Costs and Net Sales (if applicable). Subject to the foregoing, results of any
such examination shall be made available to both Parties. If, as a result of
such inspection of the books and records of Genentech to verify (X) royalties or
(Y) Direct Costs and Net Sales (if applicable), it is shown that Genentech's
royalty payments under this Agreement or balancing payments under Sections 6.5
and Exhibit A were less than the amount which should have been paid to TolerRx,
then Genentech shall make all payments required to be made to eliminate any
discrepancy revealed by said inspection within sixty (60) days after TolerRx's
demand therefor. Furthermore, if the aggregate of royalties or balancing
payments under Sections 6.5 and Exhibit A

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GENENTECH CONFIDENTIAL

(if applicable) were less than the amount which should have been paid to TolerRx
by an amount in excess of five percent (5%) of the respective payments actually
made during the period in question, Genentech shall also reimburse TolerRx for
the cost of such inspection. As a condition to such examination, such
independent public accountant shall execute a written agreement, reasonably
satisfactory in form and substance to Genentech, to maintain in confidence all
information obtained during the course of any such examination except for
disclosure to TolerRx as necessary for the above purpose. A Dispute (as defined
in Section 12.13) on the conclusions of such audit by such public accountant
shall be resolved in accordance with Section 12.13.

                       ARTICLE 7 PATENT RIGHTS; TRADEMARKS

          7.1.   OWNERSHIP OF INTELLECTUAL PROPERTY. TolerRx shall own all
inventions, whether or not patentable, made during the course of, or resulting
in whole or in part from, activities carried out under this Agreement solely by
employees of or agents of TolerRx or others obligated to assign inventions to
TolerRx. Genentech shall own all inventions, whether or not patentable, made
during the course of, or resulting in whole or in part from, activities carried
out under this Agreement solely by employees of or agents of Genentech or others
obligated to assign inventions to Genentech. Inventions made during the course
of, or resulting in whole or in part from, activities carried out under this
Agreement jointly by employees of or agents of or others obligated to assign
inventions to TolerRx and Genentech shall be jointly owned by TolerRx and
Genentech.

          7.2.   JOINT PATENTS. "JOINT PATENTS" shall mean any and all patents
and patent applications claiming inventions jointly owned by the Parties which
relate to any and all Licensed Products, their manufacture or their uses. For
the purpose of this Agreement, TolerRx Patent Rights and Genentech Patents shall
not include Joint Patents.

          7.3.   INVENTORSHIP. The determination of inventorship for inventions
made during the course of, or resulting in whole or in part from, activities
carried out under this Agreement shall be made in accordance with applicable
laws relating to inventorship set forth in the patent laws of the United States
(Title 35, United States Code). All such determinations shall be documented to
ensure that any divisional or continuation patent applications reflect
appropriate inventorship and that inventions and patent rights are assigned to
the appropriate Party.

          7.4.   DISCLOSURE OF INVENTIONS. TolerRx shall notify Genentech of any
invention made during the course of, or resulting in whole or in part from,
activities carried out under this Agreement within thirty (30) days after
TolerRx receives disclosure of such invention from its employees, agents or
others obligated to assign inventions to TolerRx.

          7.5.   PROSECUTION OF NEW PATENTS

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GENENTECH CONFIDENTIAL

                 (a) Genentech is solely responsible, in its sole discretion, to
conduct all the filings and prosecutions of Genentech Patents. Genentech shall
have the first right, using in-house or outside legal counsel selected at
Genentech's sole discretion, to prepare, file, prosecute, maintain and obtain
extensions of Joint Patents in countries of Genentech's choice throughout the
Territory. Subject to Section 6.5 and Exhibit A regarding TolerRx's US
Profit/Loss Sharing Option, Genentech shall bear the costs relating to
preparation, filing, prosecution and maintenance of Genentech Patents and Joint
Patents in the Territory. Genentech shall use reasonable efforts to solicit
TolerRx's advice and review of Joint Patents and material prosecution matters
related thereto in reasonable time prior to filing thereof, and Genentech shall
consider in good faith TolerRx's reasonable comments related thereto.

                 (b) If Genentech, prior or subsequent to filing Joint Patents,
elects not to file, prosecute or maintain such patents or certain claims
encompassed thereby, Genentech shall give TolerRx notice thereof within a
reasonable period prior to allowing such patents or claims to lapse or become
abandoned or unenforceable. TolerRx shall thereafter have the right, at its sole
expense, to prepare, file, prosecute and maintain such patents or claims in
countries of its choice throughout the world.

                 (c) TolerRx shall have the first right, using in-house or
outside legal counsel selected by TolerRx and acceptable to Genentech, to
prepare, file, prosecute, maintain and obtain extensions of TolerRx Patent
Rights claiming inventions made during the course of, or resulting in whole or
in part from, activities carried out under this Agreement in the Territory.
TolerRx shall bear the costs relating to such filing, prosecution, and
maintenance activities in the Territory. TolerRx shall keep Genentech promptly
and fully informed of the course of patent preparation, filing, prosecution or
other proceeding of such TolerRx Patent Rights including, but not limited to,
providing Genentech with copies of draft applications, applications and
substantive communications by or with a domestic or foreign patent office.
TolerRx shall use reasonable efforts to solicit Genentech's advice and review of
such TolerRx Patent Rights and material prosecution matters related thereto in
reasonable time prior to filing thereof, and TolerRx shall consider in good
faith Genentech's reasonable comments and suggestions related thereto.

                 (d) If TolerRx, prior or subsequent to filing TolerRx Patent
Rights pursuant to Section 7.5(c) above, elects not to file, prosecute or
maintain such patents or certain claims encompassed thereby, TolerRx shall give
Genentech notice thereof within a reasonable period prior to allowing such
patents or claims to lapse or become abandoned or unenforceable. Genentech shall
thereafter have the right, at its sole expense (subject to Section 6.5 and
Exhibit A regarding TolerRx's US Profit/Loss Sharing Option), to prepare, file,
prosecute and maintain such patents or claims in countries of its choice
throughout the world.

          7.6.   PROSECUTION OF EXISTING TOLERRX PATENT RIGHTS.

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                 (a) TolerRx shall disclose to Genentech all information
relating to TolerRx Patent Rights claiming inventions conceived and reduced to
practice prior to the Effective Date which cover the manufacture, use, or sale
of Licensed Products including but not limited to compositions, processes and
methods of use of TRX1 ("EXISTING TOLERRX PATENT RIGHTS"). TolerRx agrees to
keep Genentech promptly and fully informed of the course of preparation, filing,
prosecution or other proceeding of Existing TolerRx Patent Rights including, but
not limited to, providing Genentech with copies of draft applications,
applications and substantive communications by or with a domestic or foreign
patent office, as well as disclosing all information received by TolerRx
concerning the institution or possible institution of any interference,
opposition, re-examination, reissue, revocation, nullification or any official
proceeding involving any Existing TolerRx Patent Rights anywhere in the
Territory. TolerRx shall use reasonable efforts to solicit Genentech's advice
and review of such Existing TolerRx Patent Rights and material prosecution
matters related thereto in reasonable time prior to filing thereof, and TolerRx
shall consider, or cause other participating party to consider, in good faith
Genentech's reasonable comments and suggestions related thereto.

                 (b) In the event that TolerRx (or TolerRx licensors in the case
of TolerRx Patent Rights in-licensed to TolerRx) intends to finally abandon or
otherwise cause or allow to be forfeited any Existing TolerRx Patent Rights,
Genentech shall have the right to assume, at its own costs (subject to Section
6.5 and Exhibit A regarding TolerRx's US Profit/Loss Sharing Option),
responsibility for preparation, filing, prosecution and maintenance of such
Existing TolerRx Patent Rights. TolerRx shall give Genentech notice thereof
within a reasonable period prior to allowing such patents to become abandoned or
otherwise forfeited.

                 (c) At Genentech's request, TolerRx shall file an application
for a Supplementary Protection Certificate for any TolerRx Patent Rights.
Genentech shall provide relevant marketing authorizations as appropriate.

          7.7.   PATENT INFRINGEMENT.

                 (a) NOTICE. If either Party learns of any infringement or
threatened infringement by a third party of any Genentech Patents, TolerRx
Patent Rights or Joint Patents ("PATENT INFRINGEMENT"), it shall promptly notify
the other Party thereof including available evidence of infringement.

                 (b) ENFORCEMENT ACTIONS.

                         (1) JOINT PATENTS. Genentech shall have the first right
(but not the obligation) to take the appropriate steps to remove the Patent
Infringement or alleged Patent Infringement of Joint Patents, including, without
limitation, by initiation, prosecution and control, at its own expense (subject
to Section 6.5 and Exhibit A regarding TolerRx's US Profit/Loss Sharing Option)
of any suit, proceeding or other legal action by counsel of its own choice.
TolerRx shall have the right, at its own expense, to be represented in any such
action by counsel of its own choice. TolerRx agrees to cooperate reasonably in
any such action Genentech

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initiates or wishes to initiate hereunder, including, without limitation,
supplying essential documentary evidence and making essential witnesses then in
TolerRx's employment available. As part of such cooperation, Genentech may join
or include TolerRx as a party, if the need arises. Genentech shall notify
TolerRx of its decision to exercise its right to enforce Joint Patents not later
than ninety (90) days following its discovery or receipt of notice of the
alleged Patent Infringement. TolerRx has no right to bring any such action or
proceeding relating to Genentech Patents. With respect to Joint Patents, if (i)
Genentech notifies TolerRx that Genentech elects not to bring a suit, action or
proceeding to enforce the Joint Patents in accordance with this Section
7.7(b)(1); or (ii) Genentech has not provided TolerRx with evidence of bona fide
negotiations with the alleged infringer, then TolerRx shall have the right (but
not the obligation), at is own expense, to bring any such suit, action or
proceeding relating to Joint Patents by counsel of its own choice, and Genentech
shall have the right, at its own expense (subject to Section 6.5 and Exhibit A
regarding TolerRx's US Profit/Loss Sharing Option), to be represented in any
such action by counsel of its own choice. In the case of infringement or alleged
infringement of a Joint Patent, Genentech in its sole discretion, may elect to
assign such Joint Patent to TolerRx so that TolerRx may maintain such suit,
proceeding or legal action in its own name. In such event, the licenses to
Genentech under such a Joint Patent shall remain unaffected. Neither Party shall
settle a dispute regarding the Joint Patents without the consent of the other
Party, which consent shall not be unreasonably withheld.

                         (2) TOLERRX PATENT RIGHTS. TolerRx shall have the first
right (but not the obligation) to take the appropriate steps to remove the
Patent Infringement or alleged Patent Infringement of TolerRx Patent Rights,
including, without limitation, by initiation, prosecution and control, at its
own expense of any suit, proceeding or other legal action by counsel of its own
choice. Genentech shall have the right, at its own expense (subject to Section
6.5 and Exhibit A regarding TolerRx's US Profit/Loss Sharing Option), to be
represented in any such action by counsel of its own choice. TolerRx shall
notify Genentech of its decision to exercise its right to enforce TolerRx Patent
Rights not later than ninety (90) days following its discovery or receipt of
notice of the alleged Patent Infringement. If (i) TolerRx notifies Genentech
that TolerRx elects not to bring a suit, action or proceeding to enforce the
TolerRx Patent Rights with respect to the Patent Infringement in accordance with
this Section 7.7(b)(2); or (ii) TolerRx has not provided Genentech with evidence
of bona fide negotiations with the alleged infringer, then Genentech shall have
the right (but not the obligation) to bring any such suit, action or proceeding
relating to TolerRx Patent Rights with respect to the Patent Infringement by
counsel of its own choice, and TolerRx shall have the right, at its own expense,
to be represented in any such action by counsel of its own choice. TolerRx
agrees to cooperate reasonably in any such action Genentech initiates or wishes
to initiate hereunder, including, without limitation, supplying essential
documentary evidence and making essential witnesses then in TolerRx's employment
available. As part of such cooperation, Genentech may join or include TolerRx as
a party, if the need arises. At Genentech's request, TolerRx shall use all
reasonable efforts to join all necessary parties to the extent that TolerRx has
rights to do so. Neither Party shall settle a dispute regarding the TolerRx
Patent Rights without the consent of the other Party, which consent shall not be
unreasonably withheld.

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                         (3) Any damages or other monetary awards recovered
pursuant to any suit, proceeding or other legal action taken under this Section
7.7(b) shall be allocated first to the costs and expenses of the Party bringing
suit, and second to the costs and expenses (if any) of the other Party. The
balance of any recovery shall be allocated between the Parties as follows: (i)
to Genentech in an amount equal to its lost profits or a reasonable royalty on
the sales of the infringer (whichever measure of damages shall have been
applied), and (ii) to TolerRx in an amount equal to the royalties due TolerRx
based on such sales (if sales of the infringer or a reasonable royalty measure
of damages is applied) or a reasonable approximation of the royalties that
Genentech would have owed to TolerRx on sales of Licensed Products that
Genentech lost to the infringer (if a lost profits measure of damages is
applied). With respect to royalties due to TolerRx, the previous sentence shall
not apply to royalties related to the United States if TolerRx is participating
in the US Profit/Loss Sharing Option in accordance with Section 6.5 and Exhibit
A. Instead, in such circumstance, such balance related to damages for lost
profits or reasonable royalty in the United States shall be added to the
calculation of Other Operating Income/Expense (as defined in Exhibit A). The
balance, if any, remaining after Genentech and TolerRx have been compensated as
provided herein shall be allocated to the Party bringing suit.

          7.8.   THIRD PARTY PATENTS. If any notice of infringement is received
by, or a suit is initiated against, either Party with respect to any Licensed
Product, the Parties shall consult in good faith regarding the best response. If
Genentech is required to pay any third party to obtain a license under patents
owned by such third party to avoid infringement of such third party's
patent-protected technology with respect to a Licensed Product or that is
necessary or used in its manufacture, use, sale, or import, Genentech shall be
entitled to (A) offset such payments against the royalties otherwise due and
payable by Genentech under this Agreement to TolerRx as provided in Section 6
and (B) include such payments in the calculation of "US Costs" (as defined in
Exhibit A), if TolerRx is participating in the US Profit/Loss Sharing Option in
accordance with Section 6.5 and Exhibit A.

          7.9.   TRADEMARKS. Genentech shall sell all Licensed Products in the
Territory under trademarks selected and owned by Genentech worldwide. Genentech,
at its sole discretion, shall control the preparation, filing, prosecution and
maintenance of applications and/or registrations related to such trademarks in
the Territory, and shall be responsible for the costs of the foregoing (subject
to Section 6.5 and Exhibit A regarding TolerRx's US Profit/Loss Sharing Option).
Each Party shall notify the JSC promptly upon learning of any actual, alleged or
threatened infringement of a trademark applicable to a Licensed Product in the
Territory, any practice of unfair trade, trade dress imitation, passing off of
counterfeit goods, any claim conflicting with Genentech's exclusive ownership of
such trademarks or like offenses in the Territory. Genentech will have the sole
right to determine whether any action shall be taken on account of any such
infringement, practice, claim or offense with respect to any such trademarks and
TolerRx shall not take any action on account of any such infringement, practice,
claim or offense with respect to any such trademarks without the prior written
consent of Genentech. All of the costs, expenses and legal fees in bringing,
maintaining and prosecuting any action to

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GENENTECH CONFIDENTIAL

maintain, protect or defend a trademark in the Territory, and any recovery,
shall be Genentech's sole responsibility, except for costs in the United States
as set forth in Exhibit A. TolerRx agrees to cooperate with and assist Genentech
in protecting and defending any such trademarks at Genentech's expense (subject
to Section 6.5 and Exhibit A regarding TolerRx's US Profit/Loss Sharing Option).
Genentech, at its sole discretion, shall be responsible for obtaining and
maintaining any domain names corresponding to such trademarks worldwide and
shall own such domain names.

                            ARTICLE 8 CONFIDENTIALITY

          8.1.   CONFIDENTIAL INFORMATION.

                 (a) As used in this Agreement, "Confidential Information" means
nonpublic information that may be disclosed by one Party (the "Disclosing
Party") to the other Party (the "Receiving Party") in connection with this
Agreement, provided that such information is clearly marked as confidential.
Information disclosed other than in written or other tangible form will be
deemed Confidential Information only if the Disclosing Party provides the
Receiving Party with a written statement within thirty (30) days of the initial
disclosure that identifies which portion of such information is to be deemed
Confidential Information. The Receiving Party agrees (i) to use such
Confidential Information of the Disclosing Party solely in accordance with this
Agreement; and (ii) except as otherwise expressly permitted herein, to not
disclose such Confidential Information of the Disclosing Party to any third
party without prior written permission. All Development Plans, Marketing Plans,
and Genentech's reports and information related to Section 6 and/or Exhibit A,
are deemed Confidential Information of Genentech, regardless of whether the
foregoing has been marked confidential or not.

                 (b) The foregoing confidentiality obligations do not pertain to
any Confidential Information that a Receiving Party establishes: (i) was known
to the Receiving Party without restriction prior to receipt from the Disclosing
Party; (ii) is now or becomes public knowledge, other than through acts or
omissions of the Receiving Party in breach of this Agreement; (iii) is disclosed
at any time without restriction to the Receiving Party by a third party with a
lawful right to disclose such information; (iv) was independently developed by
or on behalf of the Receiving Party without use of the Confidential Information
of the Disclosing Party; or (v) is disclosed by the Receiving Party to comply
with any applicable law, court order or governmental regulation, only to the
minimum extent required to comply with such law, order, or regulation. The
confidentiality provisions of this Section will continue with respect to given
Confidential Information during the Term of this Agreement and for a period of
ten (10) years thereafter. Without limiting the Parties' obligations, the
Parties shall hold in confidence and not disclose the terms and conditions of
this Agreement, except as mutually agreed upon in writing and except to the
minimum extent required by applicable law, court order, or regulation.

          8.2.   PERMITTED DISCLOSURE. Each Party shall be entitled to disclose
Confidential Information of the other Party to consultants and other third
parties for exercising

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the rights and performing the obligations of a Party under this Agreement,
provided that the third party agrees in writing to confidentiality obligations
no less protective of the Disclosing Party`s rights as those under this
Agreement. For clarity, Genentech may provide to third party(ies) all materials
and information received from TolerRx hereunder (including but not limited to
TolerRx Know-how), provided that such third party agrees in writing to
confidentiality obligations no less protective of the TolerRx's rights as those
under this Agreement. Notwithstanding the foregoing, TolerRx shall not disclose
any Genentech Confidential Information (including but not limited to any
information and reports under Section 6, and Licensed Product Manufacturing
Know-how (except that TolerRx may disclose Licensed Product Manufacturing
Know-how to the designated contract manufacturer set forth in Section
9.5(c)(iii) in accordance therewith for the purposes set forth therein) to any
third party, unless TolerRx has obtained prior written consent from Genentech
for such disclosure. With respect to information that TolerRx is required under
the Third Party Agreements to disclose in reports to Isis, CUTS or University,
the Parties shall discuss the appropriate content of such disclosure and TolerRx
shall disclose only the content that is mutually agreed upon by the Parties and
such information shall be used by Isis, CUTS, or University only for a purpose
mutually agreed upon by the Parties, taking into account the limited disclosure
required by the Third Party Agreements.

          8.3.   SURVIVAL. This Section 8 shall survive termination or
expiration of this Agreement.

                     ARTICLE 9 TERM; EXPIRATION; TERMINATION

          9.1.   TERM; EXPIRATION. The term of this Agreement shall commence as
of the Effective Date and, unless sooner terminated as provided hereunder, shall
expire on the later of: (A) the date when Genentech has made all the royalty
payments that Genentech is obligated to make under Sections 6.3 and 6.4; or (B)
if (and only if) TolerRx has exercised and continues to participate in the US
Profit/Loss Sharing Option for a Licensed Product in accordance with Section 6.5
and Exhibit A, the date when Genentech terminates sales of Licensed Products in
the United States ("Term"). With respect to each Licensed Product in each
country, at the time that Genentech has no further royalty obligations under
Sections 6.3 and 6.4, Genentech shall have a fully paid up, perpetual,
non-cancelable, exclusive license under Section 5.1 with respect to such
Licensed Product in such country. The foregoing sentence shall survive any
expiration of this Agreement. Upon expiration of this Agreement, all obligations
and restrictions on Genentech and TolerRx shall terminate except those that
survive under Section 9.5(a), Section 9.5(b), and other sections which are
expressly indicated to survive termination.

          9.2.   UNILATERAL TERMINATION. Genentech shall have the right to
terminate this Agreement at any time, with or without cause, ninety (90) days
after written notice to TolerRx.

          9.3.   BREACH.

                 (a) In the event that a party materially breaches this
Agreement (the "Defaulting Party"), the other party (the "Non-Defaulting Party")
may provide written notice to

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the Defaulting Party describing the breach. If the Defaulting Party in good
faith disputes such breach and provides the Non-Defaulting Party in writing the
grounds for disputing the breach within thirty (30) days after receipt of the
notice of material breach from the Non-Defaulting Party, then the Non-Defaulting
may not terminate this Agreement under this Section 9.3 and the Parties shall
submit the dispute to arbitration in accordance with Section 12.13(b), and as
provided in Section 9.3(b), hereinafter such dispute is a "Dispute" as defined
in Section 12.13. In the event that the Defaulting Party does not provide a
written notice of Dispute, and fails to cure such breach within ninety (90) days
(thirty (30) days for a payment breach) of the written notice describing the
breach, then the Non Defaulting Party shall have the right to terminate this
Agreement by written notice to the Defaulting Party unless such breach is not
capable of being cured within such ninety (90) day period. If the Defaulting
Party does not provide a written notice of Dispute and if such breach is not
capable of being cured within such ninety (90) day period (thirty (30) day
period for a payment breach where no Dispute exists), then so long as the
Defaulting Party is making diligent efforts to cure such breach within such
amount of time as may be reasonably necessary to cure such breach, the
Non-Defaulting Party may not terminate this Agreement under this Section 9.3(a)
unless such breach is not cured within one-hundred and twenty (120) days of such
notice.

                 (b) In the event of a Dispute between the Parties as to whether
one Party has materially breached its material obligations, the Parties shall
resolve such Dispute in accordance with Section 12.13. With respect to a payment
Dispute, the Defaulting Party shall pay to the Non-Defaulting Party all amounts
that are due except the amount that is in Dispute. If the decision of the
arbitration tribunal (described in Section 12.13) ("Arbitration Panel" or
"arbitration tribunal") is that the Defaulting Party is in material breach of
its material obligations (an "ADVERSE JUDGMENT"), then the arbitration tribunal
shall specify the manner in which such breach could be cured. If the decision of
the arbitration tribunal is an Adverse Judgment, then the Defaulting Party shall
have thirty (30) days to cure such breach in accordance with the arbitration
tribunal's decision or as otherwise agreed by the Parties. If the Defaulting
Party fails to cure such breach within such thirty (30) day period or as
otherwise agreed, only then shall the Non-Defaulting Party have the right to
terminate this Agreement under this Section 9.3. The time table for such
arbitration proceeding for such Dispute shall be no more than one hundred twenty
(120) days from its filing date to the award. The Parties shall submit to the
Arbitration Panel at the initiation of the arbitration whether the disputed
amount shall be placed in escrow and the decision of the Arbitration Panel in
this respect shall be binding on the Parties. For clarity, if a Dispute exists
regarding payment by one Party to another, then the Non-Defaulting Party shall
not have the right to terminate this Agreement under this Section 9.3 if the
Defaulting Party complies with the arbitration tribunal's decision. In the event
that there is an Adverse Judgment against the Defaulting Party, then prejudgment
interest shall be awarded to the Non-Defaulting Party. The Party against which
an Adverse Judgment is entered shall pay all costs of the arbitration including
the attorneys fees of the other Party.

          9.4.   INSOLVENCY OR BANKRUPTCY. Each Party may, in addition to any
other remedies available to it by law or in equity, terminate this Agreement
effective on written notice

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GENENTECH CONFIDENTIAL

to the other Party in the event the other Party shall have become insolvent or
bankrupt, or shall have made an assignment for the benefit of its creditors, or
there shall have been appointed a trustee or receiver of the other Party or for
all or a substantial part of its property, or any case or proceeding shall have
been commenced or other action taken by or against the other Party in bankruptcy
or seeking reorganization, liquidation, dissolution, winding-up, arrangement,
composition or readjustment of its debts or any other relief under any
bankruptcy, insolvency, reorganization or other similar act or law of any
jurisdiction now or hereafter in effect, or there shall have been issued a
warrant of attachment, execution, distraint or similar process against any
substantial part of the property of the other Party, and any such event shall
have continued for ninety (90) days undismissed, unbonded and undischarged. All
rights and licenses granted under this Agreement are, and shall be deemed to be,
for purposes of Section 365(n) of the Bankruptcy Code, licenses of rights to
"intellectual property" as defined under Section 101(56) of the United States
Bankruptcy Code.

          9.5.   EFFECT OF EXPIRATION OR TERMINATION

                 (a) ACCRUED RIGHTS; SURVIVING OBLIGATIONS. Termination or
expiration of this Agreement for any reason shall be without prejudice to any
rights which shall have accrued to the benefit of either Party prior to such
termination or expiration, and shall not relieve either Party from its
obligations which are expressly indicated to survive expiration or termination
of this Agreement, including, without limitation, those under Sections
3.4(b)(ii), 3.4(c)(i) (last three sentences only), 3.5(a), 7.1, 7.2, 8, 9.5(a),
9.5(b), 10, 11, and 12. Termination is not the sole remedy under this Agreement
and, whether or not termination is effected, all other remedies at law and in
equity will remain.

                 (b) SUBLICENSES. No expiration or termination of this Agreement
(except termination by Genentech without cause under Section 9.2 above) shall be
construed as a termination of any sublicenses granted by Genentech under Section
5, and such sublicenses will remain in effect in accordance with their terms.

                 (c) OTHER SURVIVING OBLIGATIONS.

                         (i)    Upon any termination of this Agreement by
Genentech under Section 9.3 or 9.4, Genentech shall thereafter automatically
have in perpetuity an irrevocable, exclusive (even as to TolerRx) sublicensable,
fully transferable license within the Field in the Territory under TolerRx
Patent Rights, TolerRx Know-how and TolerRx's joint ownership rights in Joint
Patents (as defined in Section 7 herein), to make (and have made), use, sell,
offer for sale and import, Licensed Products, subject to payment to TolerRx of
only the applicable royalties under Sections 6.3 and 6.4 and applicable
milestones under Section 6.2. For clarity, if Genentech terminates this
Agreement under Section 9.3 or 9.4, Genentech shall not owe any other payments
to TolerRx, including but not limited to Operating Profits or Losses, and shall
only owe the applicable royalties under Sections 6.3 and 6.4 and applicable
milestones under Section 6.2. Upon termination by Genentech under Section 9.3 or
9.4, (A) all obligations

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GENENTECH CONFIDENTIAL

and restrictions on Genentech shall terminate, except as expressly set forth in
Sections 6.6, and 9.5(c)(i), and except for TolerRx's right as set forth in
Section 6.8, but such right shall be limited only to verifying royalties under
Sections 6.3 and 6.4 herein and (B) the following sections survive: Sections
7.5(d), 7.6(b), 7.7(b)(2), 5.3 (to the extent applicable), 9.5(a), 9.5(b), and
other sections which are expressly indicated to survive termination.

                         (ii)   Upon any termination of this Agreement by
TolerRx under Section 9.3 or 9.4 or by Genentech without cause under Section
9.2, (A) all rights granted to Genentech by TolerRx shall terminate and revert
to TolerRx, and (B) all obligations and restrictions on Genentech and TolerRx
shall terminate, including but not limited to Section 6, except those rights,
obligations and restrictions that survive under Section 9.5(a) Section 9.5(b),
and other sections which are expressly indicated to survive termination and (C)
thereafter except as provided in Section 9.5 (c) (iii), Genentech shall cease
and continue to cease to research, develop, manufacture, market and sell
Licensed Product. Upon any termination by either Party under Section 9.3 or 9.4
or by Genentech without cause under Section 9.2, or upon expiration of the
Agreement, all rights granted to TolerRx by Genentech (if any) shall terminate,
except that in the case of termination by TolerRx under Section 9.3 or 9.4 or by
Genentech without cause under Section 9.2, the rights (and only such rights)
expressly set forth in Section 9.5(c)(iii) below shall continue (and only to the
extent expressly set forth therein).

                         (iii)  This Section 9.5(c)(iii) shall only apply in the
case of termination without cause by Genentech under Section 9.2 or termination
by TolerRx under Section 9.3 or 9.4. For the purposes of this Section
9.5(c)(iii), except as expressly set forth in Section 9.5(c)(iii)(1) below,
Licensed Product(s) shall only refer to existing Licensed Product(s) which
Genentech was manufacturing in clinical or commercial quantities (if any) prior
to such termination.

                                (1) Only upon termination without cause by
Genentech under Section 9.2 or termination by TolerRx under Section 9.3 or 9.4,
subject to compliance with the terms and conditions of the Separate License
Agreement for Genentech Patents (as defined below), TolerRx shall have a
non-exclusive royalty-bearing, nontransferable, revocable (as provided below in
Section 9.5(c)(iii)(6)), sublicensable, limited license under Genentech Patents
solely to make, use, import, offer to sell and sell the Licensed Products that
Genentech was manufacturing or developing prior to such termination. The Parties
agree to negotiate in good faith the terms of a separate written agreement that
will grant TolerRx such license rights (with royalty rates not to exceed [***]
of net sales) ("Separate License Agreement for Genentech Patents"). With respect
other patent rights owned by Genentech necessary for commercializing Licensed
Products that Genentech was manufacturing in clinical or commercial quantities
(if any) or developing prior to termination, if any, the Parties agree to
negotiate in good faith regarding such rights.

                                (2) TolerRx shall use best efforts to find a
third party source of supply of Licensed Products. To the extent (A) Genentech
has already been

                                  * Confidential treatment requested:
                                    material has been omitted and filed
                                    separately with the Commission.

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GENENTECH CONFIDENTIAL

manufacturing clinical or commercial quantities of Licensed Product prior to
such termination, and (B) to the extent that Genentech determines that doing the
following would not adversely affect its manufacturing of its or its
sublicensees' products, Genentech agrees to supply TolerRx (at Genentech's Fully
Burdened Manufacturing Costs, plus a mark-up of [***]) at Genentech's election,
with (A) a quantity of Licensed Products that is equivalent to a reasonable
[***] of Licensed Product or (B) such lesser amount of Licensed Products as is
necessary for TolerRx to achieve the current milestone (and only that milestone)
on which the Parties were working as of the effective date of termination.

                                (3) At TolerRx's written request, if and only if
Genentech has already been manufacturing clinical or commercial quantities of
Licensed Product prior to such termination, then subject to compliance with the
terms and conditions of this Agreement, Genentech agrees to provide either to
TolerRx or to a designated Third Party contract manufacturer (and only to
TolerRx or such manufacturer, but not both), who does not sell its own products
and has expertise in recombinant protein manufacture and cell culture biology
(including but not limited to having experience and know-how necessary to
manufacture proteins at commercial scales), and who is reasonably acceptable to
Genentech, Genentech's know-how, if any, specifically related to the
manufacturing process of such existing Licensed Product and that is necessary
for TolerRx or such Third Party to assume manufacture of such existing Licensed
Product ("Licensed Product Manufacturing Know-how"). Licensed Product
Manufacturing Know-how shall only consist of such know-how owned by Genentech
(if any) that is necessary for TolerRx or such designated contract manufacturer
to achieve the current milestone (and only that milestone) on which the Parties
were working as of the effective date of termination. For example, if the
Agreement is terminated during the Phase I Clinical Trial, then such Licensed
Product Manufacturing Know-how to be transferred shall only consist of such
know-how (if any) necessary to complete such Phase I Clinical Trial.
Notwithstanding anything else, Licensed Product Manufacturing Know-how shall be
limited to such know-how for manufacturing the agent targeting, binding to, or
recognizing CD4 and shall exclude know-how related to any Genentech proprietary
product or manufacture thereof. Such Licensed Product Manufacturing Know-how is
deemed to be Confidential Information of Genentech regardless of whether such
information is marked "Confidential." Without limiting TolerRx's obligations,
TolerRx shall (and shall cause its contract manufacturer to) hold all such
Licensed Product Manufacturing Know-how in confidence, not disclose such
information to any person or entity (other than employees of TolerRx and such
designated contract manufacturer bound to similar confidentiality obligations
who have a legitimate "need to know") and to use such information solely for
manufacturing the existing Licensed Product that Genentech was manufacturing in
clinical or commercial quantities (if any) prior to such termination. For
clarity, TolerRx shall (and shall cause such contract manufacturer to) not use
such Licensed Product Manufacturing Know-how for any other purpose, including
but not limited to any other product or process. TolerRx shall not allow any
person or entity, other than itself or such designated contract manufacturer
described above, to manufacture Licensed Product using Licensed Product
Manufacturing Know-how. TolerRx's confidentiality obligations and
indemnification under this Section 9.5(c)(iii)(3) and Section 9.5(c)(iii)(4)
below shall survive in perpetuity, notwithstanding

                                  * Confidential treatment requested:
                                    material has been omitted and filed
                                    separately with the Commission.

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GENENTECH CONFIDENTIAL

Section 8.1 above or anything else. Any action or inaction by such contract
manufacturer shall be deemed an action or inaction of TolerRx and TolerRx shall
be responsible for any breach of any obligations hereunder by such contract
manufacturer. Such contract manufacturer shall be bound by an enforceable
writing for Genentech's benefit to at least the same limitations and
restrictions as the limitations and restrictions on TolerRx. TolerRx indemnifies
Genentech and its Affiliates and sublicensees from any and all claims, damages,
liability, settlement, attorneys' fees and expenses, as incurred, on account of
any breach of this Section 9.5 or any action or inaction of TolerRx or its
contract manufacturer. For clarity, Licensed Product Manufacturing Know-how, if
any, is provided nonexclusively, and remains Genentech's property and
intellectual property at all times.

                                (4) Genentech shall transfer to TolerRx, at
TolerRx's cost, all Regulatory Approvals and applications for Regulatory
Approvals for the Licensed Product(s) that Genentech holds at the time of
termination. Genentech shall also provide to TolerRx all pre-clinical and
clinical data produced by Genentech in developing the Licensed Products
hereunder (if any) that Genentech holds at the time of termination. All of the
foregoing Regulatory Approvals, applications therefor, and pre-clinical and
clinical data shall be deemed Confidential Information of Genentech,
notwithstanding Section 8.1 above or anything else, regardless of whether such
information is marked "Confidential" or not, and shall be used only for the sale
of such Licensed Product manufactured by TolerRx or by such contract
manufacturer. TolerRx shall pay all costs associated with the transfers
(including but not limited to out-of-pocket costs and fully-burdened personnel
costs) in this Section 9.5(c)(iii).

                                (5) The Parties agree that if Genentech provides
such Licensed Product Manufacturing Know-how in accordance with this Section
9.5(c)(iii), then TolerRx has access to, is privy to, and may use such Licensed
Product Manufacturing Know-how as set forth in this Section 9.5(c)(iii), and
that it is impossible to determine the extent to which TolerRx has used such
information. Accordingly, TolerRx agrees to pay the royalty set forth below on
Net Sales of all Licensed Products. If Genentech has transferred Licensed
Product Manufacturing Know-how to TolerRx or such Third Party contract
manufacturer, TolerRx shall pay to Genentech a royalty to be negotiated in good
faith between the Parties and not to exceed [***]. If the Parties agree on a
lower royalty rate or if the foregoing royalty rate to be paid by TolerRx is
[***], then Genentech shall be obligated to provide Licensed Product
Manufacturing Know-how to the extent expressly set forth in this Section
9.5(c)(iii), otherwise Genentech shall not be obligated to provide Licensed
Product Manufacturing Know-how. The terms applicable to Genentech (and payments
by Genentech) under Sections 6.6 and 6.8 (including but not limited to the right
for Genentech to audit TolerRx to verify the appropriate royalties owed to
Genentech herein) shall apply to TolerRx and such royalty payments by TolerRx.
TolerRx shall comply with the last sentence of Section 6.7, to the extent
applicable. All payments hereunder due to Genentech shall be made in U.S.
Dollars by bank wire transfer to the: [***]. The Parties shall agree to a
process transfer plan for such Licensed Product Manufacturing Know-how and all
of Genentech's obligations under this Agreement shall be deemed fulfilled when
the tasks set forth in such plan are complete.

                                  * Confidential treatment requested:
                                    material has been omitted and filed
                                    separately with the Commission.

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GENENTECH CONFIDENTIAL

                                (6) Upon any breach of Section 9.5(c)(iii)
herein by TolerRx, all rights and licenses granted to TolerRx and all
obligations of Genentech under this Section 9.5(c)(iii) shall terminate
immediately upon notice, and TolerRx shall immediately cease (and shall cause
its contract manufacturer to cease) any and all use of Licensed Product
Manufacturing Know-how, Genentech Patents and any other Confidential Information
of Genentech, and shall return all copies, extracts, and derivatives of the
foregoing to Genentech. This Section 9.5(c)(iii)(6) shall survive any
termination of this Agreement.

                                (7) Genentech agrees to negotiate in good faith
with TolerRx regarding a royalty-bearing license to TolerRx for TolerRx's use of
trademarks owned by Genentech with respect to Licensed Product.

                           ARTICLE 10 INDEMNIFICATION

          10.1.  INDEMNIFICATION BY GENENTECH. Genentech hereby agrees to
indemnify, defend and hold harmless TolerRx and its subsidiaries, parent
corporations, Affiliates, officers, directors, agents, and employees, from and
against any and all third party suits, claims, actions, demands, liabilities,
settlements, expenses and/or loss (including reasonable legal expense and
attorneys' fees) to the extent payable to such third party (collectively,
"LOSSES") and arising out of or resulting from Genentech's or its third party
sublicensee's performance of work under this Agreement, or the manufacturing,
developing, distribution, testing, labeling, marketing, use or sale of Licensed
Products by Genentech or its third party sublicensees in the Territory, except
to the extent such Losses arise out of or result from the negligence or willful
misconduct of TolerRx, TolerRx's breach of any terms of this Agreement or
violation of any applicable law or regulation. For clarity, the foregoing does
not include an indemnity regarding infringement of third party patent or
trademark rights. In addition, Genentech hereby agrees to indemnify, defend and
hold harmless TolerRx and its subsidiaries, parent corporations, Affiliates,
officers, directors, and employees harmless from and against any and all Losses
resulting from a breach by Genentech of any of its representations or warranties
under Section 11.2 of this Agreement.

          10.2.  INDEMNIFICATION BY TOLERRX. TolerRx hereby agrees to indemnify,
defend and hold harmless Genentech and its subsidiaries, parent corporations,
Affiliates, officers, directors, agents, and employees from and against any and
all Losses arising out of or resulting from TolerRx's performance of work (if
any) or clinical trials under this Agreement or the testing, development or use
of the Licensed Products or any actions of any TolerRx MSLs except to the extent
such Losses arise out of or result from the negligence or willful misconduct of
Genentech, Genentech's breach of any terms of this Agreement or violation of any
applicable law or regulation. For clarity, the foregoing does not include an
indemnity regarding infringement of third party patent or trademark rights. In
addition, TolerRx hereby agrees to indemnify, defend and hold harmless Genentech
and its subsidiaries, parent corporations, Affiliates, officers, directors,
sublicensees and employees from and against any and

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all Losses resulting from a breach by TolerRx of any of its representations or
warranties under Section 11.1 of this Agreement.

          10.3.  NOTICE. A Party's compliance with this Section 10.3 is a
condition of indemnification under this Section 10 by the other Party. A person
or entity that intends to claim indemnification under this Section (the
"Indemnitee") shall promptly notify the other Party (the "Indemnitor") of any
loss, claim, damage, liability or action in respect of which the Indemnitee
intends to claim such indemnification, and the Indemnitor shall assume sole
control of the defense and settlement thereof with counsel selected by
Indemnitor and reasonably satisfactory to the Indemnitee whether or not such
third party claim is rightfully brought; provided, however, that an Indemnitee
shall have the right to retain its own counsel to participate in such defense,
with the fees and expenses to be paid by the Indemnitee. The indemnity agreement
in this Section shall not apply to amounts paid in settlement of any loss,
claim, damage, liability or action if such settlement is effected without the
consent of the Indemnitor, which consent shall not be withheld or delayed
unreasonably. The failure to deliver notice to the Indemnitor within a
reasonable time after the commencement of any such action, only if prejudicial
to its ability to defend such action, shall relieve such Indemnitor of any
liability to the Indemnitee under this Section. All delays of sixty (60) days or
more shall be deemed prejudicial. Except as provided in the Agreement, the
omission to so deliver notice to the Indemnitor will not relieve it of any
liability that it may have to any Indemnitee otherwise than under this Section.
The Indemnitee under this Section, its employees and agents, shall cooperate
fully with the Indemnitor and its legal representatives in the investigations of
any action, claim or liability covered by this indemnification and the defense
thereof. The Indemnitor shall have the right to settle any loss, claim, damage,
liability or action only if the Indemnitee is fully indemnified with respect
thereto by the Indemnitor. A settlement requires the consent of the Indemnitee,
which consent shall not be withheld unreasonably, only if the settlement
requires Indemnitee to bear other affirmative obligations (beyond the payment of
money damages and beyond obligations required by this Agreement).

          10.4.  INSURANCE.

                 (a) During the Term, and thereafter for the period of time
required below, each Party shall maintain an ongoing basis, COMMERCIAL GENERAL
LIABILITY ("CGL") insurance, including contractual liability, in the minimum
amount of $5,000,000 per occurrence and $10,000,000 annual aggregate combined
single limit for bodily injury and property damage liability. Commencing not
later than 30 days prior to the first use in humans of the first potential
Licensed Product and thereafter for the period of time required below each Party
shall obtain and maintain on an ongoing basis PRODUCTS LIABILITY ("PL")
insurance (including contractual liability) in the amount of at least
$10,000,000 per occurrence and annual aggregate combined single limit for bodily
injury and property damage liability. All of the above insurance coverage shall
be maintained with an insurance company or companies having an A.M. Best rating
of X-VII or better.

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                 (b) Within thirty (30) days after the Effective Date with
respect to the commercial general liability coverage, and not later than 30 days
prior to the first use in humans of the first potential Licensed Product with
respect to the products liability coverage, upon request of the other Party,
each Party shall provide to the other Party certificates evidencing all such
required coverage hereunder. Thereafter Genentech shall maintain such insurance
coverage without interruption during the Term and for 10 years after the
expiration or termination of the Term. TolerRx shall maintain such insurance
coverage without interruption during and after the Term until the later of: (A)
10 years after the expiration or termination of the Term or (B) ten (10) years
after the last sale of the last Licensed Product in the Territory by TolerRx as
permitted under Section 9.5(c)(iii), if applicable. Each Party shall provide
certificates evidencing such insurance coverage without interruption on an
annual basis (by no later than the annual renewal date for such coverage) during
the period of time for which such coverage must be maintained. Each Party shall
name the other Party as additional insureds under their respective CGL insurance
and PL insurance policies. The CGL and PL insurance policies shall be an
occurrence form, but if only a claims-made form is available, then it may be in
a claims-made form, subject to compliance with all of the terms of this Section
10.4. Each of the above insurance policies shall be primary insurance with
respect to each Party's own participation under this Agreement. The aggregate
deductibles under such CGL and PL insurance policies shall be satisfactory to
the other Party. At the request of either Party, the Parties agree to review and
discuss the requirements under this Section 10.4. Such insurance coverage shall
be subject to periodic review by the JSC and may be modified by the JSC.

          10.5.  SURVIVAL. This Section 10 shall survive termination or
expiration of this Agreement.

          10.6.  LIMITATION OF LIABILITY. EXCEPT FOR NONPAYMENT BY EITHER PARTY,
BREACH OF CONFIDENTIALITY OBLIGATIONS UNDER THIS AGREEMENT, SECTIONS 8,
9.5(c)(iii), 10 AND/OR 12.3 (AND/OR BREACH OF SUCH SECTIONS), IN NO EVENT SHALL
EITHER PARTY BE LIABLE WITH RESPECT TO ANY SUBJECT MATTER OF THIS AGREEMENT
UNDER ANY CONTRACT, NEGLIGENCE, STRICT LIABILITY OR OTHER LEGAL OR EQUITABLE
THEORY (I) FOR ANY AMOUNTS IN EXCESS, IN THE AGGREGATE, OF THE FEES PAID TO
TOLERRX HEREUNDER DURING THE TWELVE-MONTH PERIOD PRIOR TO THE DATE THE CAUSE OF
ACTION AROSE OR (II) FOR ANY INDIRECT, EXEMPLARY, SPECIAL, INCIDENTAL OR
CONSEQUENTIAL DAMAGES OR LOST DATA OR LOSS PROFITS OR (III) FOR ANY MATTER
BEYOND SUCH PARTY'S REASONABLE CONTROL, EVEN IF SUCH PARTY HAS BEEN ADVISED OF
THE POSSIBILITY OF SUCH LOSS OR DAMAGE. THIS SECTION DOES NOT LIMIT LIABILITY
FOR BODILY INJURY OF A PERSON.

                    ARTICLE 11 REPRESENTATIONS AND WARRANTIES

          11.1.  REPRESENTATIONS AND WARRANTIES OF TOLERRX. TolerRx hereby
represents and warrants that:

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                 (a) the execution and delivery of this Agreement and the
performance of the transactions contemplated hereby have been duly authorized by
all appropriate TolerRx corporate action;

                 (b) this Agreement is a legal and valid obligation binding upon
TolerRx and enforceable in accordance with its terms. The execution, delivery
and performance of the Agreement by TolerRx does not conflict with any
agreement, instrument or understanding, oral or written, to which it is a party
or by which it is bound;

                 (c) TolerRx has the rights to transfer to Genentech all
materials contemplated by this Agreement to be so transferred;

                 (d) TolerRx has the right to grant the licenses granted herein;

                 (e) TolerRx has not intentionally concealed any knowledge of
any rights of any third parties that would interfere with the use of the TolerRx
Know-how or practice of the TolerRx Patent Rights by Genentech.

                 (f) TolerRx is not aware of any breach of any of the Third
Party Agreements, and TolerRx shall not intentionally commit any acts or
omissions that would result in a breach of any of the Third Party Agreements
such that the other party thereto would be entitled to terminate such agreement
or amend it in a way that would adversely affect Genentech's rights under this
Agreement (including but not limited to Genentech's ability to manufacture, use,
sell, offer to sell, and import the Licensed Products);

                 (g) to the best of TolerRx's knowledge, as of the Effective
Date, except for the licenses granted herein, no additional licenses,
permissions or releases of rights related to Third Party Agreements are
necessary for Genentech's and its third party sublicensee's manufacture, sale,
use, offer for sale or import of the Licensed Product or other currently
anticipated exercise of its license hereunder;

                 (h) TolerRx shall not exercise any rights it may have with
respect to any of the Third Party Agreements or amend, or waive any of its
rights thereunder in any way that would adversely affect Genentech's rights
under this Agreement (including but not limited to Genentech's ability to
manufacture, use, sell, offer to sell, and import the Licensed Products); and

                 (i) As of the Effective Date, the Third Party Agreements are
the only agreements to which TolerRx is a party that directly relate to making,
using, importing, selling, or offering to sell a Product.

          11.2.  Representations and Warranties of Genentech. Genentech
represents and warrants that:

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                 (a) the execution and delivery of this Agreement and the
performance of the transactions contemplated hereby have been duly authorized by
all appropriate Genentech corporate action; and

                 (b) this Agreement is a legal and valid obligation binding upon
Genentech and enforceable in accordance with its terms. The execution, delivery
and performance of the Agreement by Genentech does not conflict with any
agreement, instrument or understanding, oral or written, to which it is a party
or by which it is bound.

          11.3.  SURVIVAL. The representation, warranties, covenants and
agreements made herein shall survive any investigation made by a Party and the
Parties may fully rely on such representations, warranties, covenants and
agreements.

          11.4.  EACH PARTY MAKES NO OTHER REPRESENTATION OR WARRANTY HEREUNDER
AND EXCEPT AS PROVIDED ABOVE, DISCLAIMS ALL OTHER REPRESENTATIONS AND
WARRANTIES, INCLUDING, BUT NOT LIMITED TO, WARRANTIES OF MERCHANTABILITY OR
FITNESS FOR USE OR WITH RESPECT TO THE VALIDITY, ENFORCEABILITY, OR
PATENTABILITY OF ITS PATENTS OR THAT LICENSED PRODUCT WILL NOT INFRINGE PATENT
RIGHTS OF A THIRD PARTY.

                       ARTICLE 12 MISCELLANEOUS PROVISIONS

          12.1.  NO PARTNERSHIP. The Parties are independent contractors and
nothing in this Agreement is intended or shall be deemed to constitute a
partnership, agency, distributorship, fiduciary, employer-employee or joint
venture relationship between the Parties. No Party shall incur any debts or make
any commitments for or bind the other, except to the extent, if at all,
specifically and expressly provided herein.

          12.2.  NO OTHER RIGHTS. This Agreement does not convey to TolerRx any
rights in any Genentech Patents or Licensed Product Manufacturing Know-how
(except as expressly and unambiguously set forth in Section 9.5(c)(iii)) or any
other intellectual property of Genentech by implication, estoppel or otherwise,
and title and all rights to the Genentech Patent Rights, Licensed Product
Manufacturing Know-how, and any other intellectual property of Genentech shall
at all times remain vested in Genentech. No right or license is granted by
TolerRx to Genentech hereunder except as expressly granted under this Agreement.
Nothing herein shall restrict Genentech (whether in conjunction with third
party(ies) or independently) from researching, developing or commercializing a
product that contains an agent targeting, binding to or recognizing CD4, that is
not covered by this Agreement.

          12.3.  ASSIGNMENTS. Neither Party shall be entitled to assign this
Agreement or its rights or obligations hereunder without the express written
consent of the other Party hereto, except that both Genentech and TolerRx may
otherwise assign this Agreement and their respective rights and transfer their
respective duties hereunder to an Affiliate or to any assignee

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GENENTECH CONFIDENTIAL

of all or substantially all of their respective businesses (or that portion
thereof to which this Agreement relates) or in the event of their respective
merger or consolidation or similar transaction. Such assignment shall not
relieve the assignor of its obligations hereunder. No assignment and transfer
shall be valid or effective unless and until the assignee/transferee shall agree
in writing to be bound by the provisions of this Agreement in which case the
Agreement will inure to the benefit of such successors and assigns. Any
assignment not in accordance with this Section 12.3 shall be void.

          12.4.  FURTHER ACTIONS. Each Party agrees to execute, acknowledge and
deliver such further instruments, and to do all such other acts, as may be
necessary or appropriate in order to carry out the purposes and intent of this
Agreement.

          12.5.  USE OF NAMES. No right, express or implied, is granted by this
Agreement to use in any manner the names "TolerRx" or "Genentech" or any other
trade name or trademark of TolerRx or Genentech without the prior written
consent of the other Party.

          12.6.  PUBLIC ANNOUNCEMENTS. Neither Party shall make any public
announcement, press release, or other public disclosure concerning this
Agreement or the subject matter hereof without the prior written consent of the
other Party. The Parties consent to the press release of Exhibit D.

          12.7.  ENTIRE AGREEMENT; AMENDMENTS. This Agreement constitutes and
contains the entire understanding and agreement of the Parties and cancels and
supersedes any and all prior negotiations, correspondence, understandings and
agreements, whether verbal or written, between the Parties respecting the
subject matter hereof, and all past dealing or industry custom. Except to the
extent expressly set forth in Section 5.3 herein, Genentech does not acknowledge
any agreements between TolerRx and third parties. No waiver, modification or
amendment of any provision of this Agreement shall be valid or effective unless
made in writing and signed by a duly authorized representative of each of the
Parties and clearly understood by both Parties to be a waiver, modification or
amendment of the Agreement.

          12.8.  SEVERABILITY. If any provision of this Agreement shall be held
by a court of competent jurisdiction to be illegal, invalid or unenforceable,
that provision shall be limited or eliminated to the minimum extent necessary so
that this Agreement shall otherwise remain in full force and effect and
enforceable.

          12.9.  CAPTIONS. The headings and captions to this Agreement are for
convenience only, and are to be of no force or effect in construing or
interpreting any of the provisions of this Agreement.

          12.10. APPLICABLE LAW. This Agreement shall be governed in all
respects by the internal laws of the State of Delaware (as if made and entered
into between Delaware residents and fully executed within Delaware) without
regard to its conflict of laws provisions and without regard to the United
Nations Convention on Contracts for the International Sale of Goods.

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          12.11. NOTICES AND DELIVERIES. Any notice, requests, delivery,
approval or consent required or permitted to be given under this Agreement shall
be in writing and shall be deemed to have been sufficiently given if delivered
in person, transmitted by facsimile with a confirming copy sent by overnight
courier or registered mail to the Party to whom it is directed at its address
shown below or such other address as such party shall have last given by notice
to the other Party. Any such notice, requests, delivery, approval or consent
shall be deemed received on the date of facsimile or hand delivery, one business
day after deposit with an overnight courier, or 3 business days after deposit of
the registered mail with the U. S. postal service.

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GENENTECH CONFIDENTIAL

                 If to TolerRx,

                 addressed to:

                 TolerRx, Inc.
                 300 Technology Square
                 Cambridge, MA 02139

                 Tel.: 617-354-8100
                 Fax:  617-354-8300

                 with a copy to:

                 Carella, Byrne, Bain, Gilfillan,
                 Cecchi, Stewart & Olstein
                 6 Becker Farm Road
                 Roseland, New Jersey 07068
                 Tel.: (973) 994-1700
                 Fax:  ((73) 994-1744

                 If to Genentech,

                 addressed to:

                 GENENTECH, INC.
                 1 DNA Way
                 South San Francisco, CA 94080
                 Attention: Corporate Secretary
                 Telephone: (650) 225-1000
                 Fax: (650) 952-9881

                 with a copy to:

                 Vice President of Business Development
                 Telephone: (650) 225-3705
                 Fax: (650) 225-3009

          12.12. FORCE MAJEURE. Neither Party shall lose any rights hereunder or
be liable to the other Party for damages or losses on account of failure of
performance by the defaulting

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Party if the failure is occasioned by government action, war, terrorism, supply
shortage, labor disputes or shortages, viral contamination, earthquake, fire,
explosion, flood, strike, lockout, embargo, act of God, or any other cause
beyond the reasonable control of the defaulting Party, provided that the Party
claiming force majeure has exerted reasonable commercial efforts to avoid or
remedy such force majeure; PROVIDED, HOWEVER, that in no event shall a Party be
required to settle any labor dispute or disturbance.

          12.13. DISPUTE RESOLUTION.

                 (a) INTERNAL RESOLUTION. For clarity, any and all issues
relating to the development and commercialization of the Licensed Products
(including but not limited to the Development Plan and content thereof, and
development and commercialization budgets) shall not be subject to this Section
12.13 but shall be resolved by the JSC in accordance with Section 2.2. For
clarity, a Dispute on the conclusions of the audit by the public accountant set
forth in Section 6.8 or disputes solely on Genentech's failure to apply the
methodology set forth in Section A.5 of Exhibit A attached hereto shall be
resolved in accordance with this Section 12.13. The Parties shall attempt to
settle all other disputes, controversies or claim arising out of or relating to
the validity, enforceability or performance of this Agreement, including
disputes relating to alleged breach or termination of this Agreement but
excluding any determination as to the validity or enforceability of the Parties'
intellectual property or infringement or claim interpretation relating to a
Party's patents (hereinafter, the "DISPUTE"), in accordance with the provisions
of this Section 12.13. The Parties have entered into the Agreement in good faith
and in the belief that it is mutually advantageous to them. It is with that same
spirit of cooperation that they pledge to attempt to resolve any Dispute
amicably. Accordingly, the Parties agree that if any Dispute should arise, it
shall then be referred to a member of senior management from each of the
Parties. If those individuals are unable to resolve the disagreement, the
Parties shall mediate their Dispute with a mediator mutually agreeable between
the Parties.

                 (b) ARBITRATION. Should the mediator be unable to resolve the
Dispute, (other than those issues excluded from this Section 12.13 in Section
12.13(a) above) all Disputes arising out of or relating to the validity,
enforceability or performance of this Agreement, or the breach or termination
thereof, shall be settled by final and binding arbitration pursuant to the
Commercial Arbitration Rules of the American Arbitration Association as
hereinafter provided:

                         (i)    The arbitration shall be conducted by a panel of
three arbitrators ("the Panel"). Each party shall nominate in the request for
arbitration and the answer thereto one arbitrator and the two arbitrators so
named will then jointly appoint the third arbitrator as chairman of the Panel.
If one Party fails to nominate its arbitrator or, if the Parties' arbitrators
cannot agree on the person to be named as chairman within thirty (30) days, the
President of the American Arbitration Association shall make the necessary
appointments for arbitrator or chairman.

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                         (ii)   The place of arbitration shall be in San
Francisco, California and the arbitration proceedings shall be held in English.
The procedural law of California shall apply where the said Arbitration Rules
are silent.

                         (iii)  The Panel is empowered to award any remedy
allowed by law, including money damages, prejudgment interest and attorneys'
fees, and to grant final, complete, interim or interlocutory relief, including
injunctive relief, but excluding punitive damages and multiple damages. For
purposes of all arbitration proceedings, the Parties shall be deemed to have
waived any right to such punitive damages or multiple damages. The decision of
the arbitration tribunal must be in writing and must specify the basis on which
the decision was made, and the award of the arbitration tribunal shall be final
and judgement upon such an award may be entered in any competent court or
application may be made to any competent court for judicial acceptance of such
an award and order of enforcement.

          12.14. SOLE JURISDICTION FOR INTELLECTUAL PROPERTY DISPUTES. With
regard to any disputes, controversy, or claim arising out of this Agreement
involving any determination as to the validity or enforceability of the Parties'
intellectual property, or infringement or claim interpretation relating to a
Party's patents, the jurisdiction and venue for actions related to the subject
matter hereof shall be the U.S. federal court in Delaware. The parties agree
that any such action related to this subject matter shall be brought solely in
the United States District Court ("USDC") for Delaware ("DE"). The parties
hereby submit to personal jurisdiction in the USDC for DE and waive all claims
of improper forum, forum non conveniens, or other objection to the laying of
venue in such court. Both parties consent to the jurisdiction of such courts and
agree that process may be served in the manner provided herein for giving of
notices or otherwise as allowed by Delaware or federal law.

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

                            [Signature page follows.]

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          IN WITNESS WHEREOF, the Parties have caused this Agreement to be
executed by their respective duly authorized representatives as of Effective
Date.

TOLERRX, INC.                              GENENTECH, INC.

By:     /s/ D.J. Ringler                   By:     /s/ Lou Lavigne
        ------------------------------             -----------------------------

Name:   D.J. Ringler                       Name:   Lou Lavigne
        ------------------------------             -----------------------------

Title:  CEO
        ------------------------------

                                           By:     /s/ Stephen Juelsgaard
                                                   -----------------------------

                                           Name:   Stephen Juelsgaard
                                                   -----------------------------

                                                   23 Dec 02

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

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                                    EXHIBIT A

              FINANCIAL PLANNING, ACCOUNTING AND REPORTING FOR THE
                    TOLERRX/GENENTECH COLLABORATION AGREEMENT

This Exhibit A is applicable only if TolerRx properly exercises the US
Profit/Loss Sharing Option and makes the US Cost Sharing Payments in accordance
with Section 6.5 and continues to make all balancing payments on time as
required by this Exhibit A so that each Party bears its appropriate percentage
of shared US Costs. For clarity, the definitions of "Net Sales" and "Fully
Burdened Manufacturing Cost" are applicable to Section 6 of the Agreement. For
clarity, Licensed Products(s) as referred to in this Exhibit A, shall only refer
to the Licensed Products(s) for which TolerRx has exercised and continues to
participate in the US Profit/Loss Sharing Option in accordance with Section 6.5
and Exhibit A.

This EXHIBIT A covers financial planning, accounting policies and procedures to
be followed in determining US Cost Sharing Payments and Operating Profits or
Losses and related sharing of revenue and expenses. This Exhibit A only covers
sharing of Operating Profits or Losses (including revenues and expenses)
relating to developing and commercializing Licensed Products within the United
States. Genentech shall be obligated to share Operating Profits or Losses as set
forth in Section 6.5 and this Exhibit A only during the time period set forth in
and subject to Section 6.5(b).

For purposes of this EXHIBIT A only, the accounting of Genentech's operations
related to the development and commercialization of Licensed Products in the
United States shall be referred to as the "COLLABORATION". The Collaboration is
not and shall not be characterized by either Party as a legal entity, pass
through or otherwise, for financial accounting or income tax reporting purposes,
and has been defined for identification purposes only. For the purposes of this
Agreement, any references to charging costs to the Collaboration means that such
costs shall be included in the calculation of "US Costs." For the purposes of
this Exhibit A, any references to costs incurred "by or for Genentech" "by
Genentech or for its account" or "by or on behalf of Genentech" or the like,
shall only refer to such costs incurred by Genentech or on behalf of Genentech
by Genentech's third party sublicensees and shall not refer to any costs
incurred by or on behalf of TolerRx.

For avoidance of doubt, pre-approved costs incurred by TolerRx in performing
TolerRx Development Plan Work shall be chargeable to the Collaboration (such
costs shall hereinafter be referred to as "TolerRx Development Plan Work
Costs").

All capitalized terms used herein without definition shall have the meanings
ascribed thereto in the Agreement, unless otherwise expressly provided herein.
The contents of this EXHIBIT A are hereby incorporated into the Agreement and
are governed by the terms and conditions of the Agreement, including, without
limitation, the confidentiality provisions set forth therein. All reports or
information related to this Exhibit A required to be disclosed hereunder are
deemed Confidential Information of Genentech, regardless of whether such reports
or information are marked confidential or not.

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GENENTECH CONFIDENTIAL

A.1.    PRINCIPLES OF REPORTING

(a)     SHARING US COSTS. US Costs shall be shared by TolerRx and Genentech as
provided in Sections 3.3 and 6.5 of the Agreement. The Parties shall establish a
Joint Finance Committee to be composed of one (1) employee representative
appointed by each Party, to coordinate the activities set forth in this Exhibit
A. Such representatives shall include individuals with expertise and
responsibilities in the areas of accounting, cost allocation, budgeting and
financial reporting. The JFC shall operate by consensus and in accordance with
the JSC's instructions, subject to the following sentence. If the JFC is unable
to resolve a dispute regarding any issue presented to it, such dispute shall be
referred to the JSC for resolution in accordance with Section 2.2. Any disputes
solely on Genentech's failure to apply the methodology set forth in Section A.5
herein or a Dispute on the conclusions of the audit by the public accountant set
forth in Section 6.8 shall be resolved in accordance with Section 12.13 of the
Agreement. All other disputes (including but not limited to budget disputes)
shall be resolved by the JSC in accordance with Section 2.2.

Results of the Collaboration will be reported by Genentech as follows:

<Table>
<Caption>
                                                   Genentech    TolerRx    Total
                                                   ---------    -------    -----
          <S>                                      <C>          <C>        <C>
          Gross Sales

          less Sales Returns and Allowances

              =  Net Sales

          less Cost of Sales

              = Gross Profits

          less Marketing Costs

          less Sales Costs

          less Development Costs

          less Other Operating Income/Expense

          less General and Administrative Costs

          less Distribution Costs

              = Operating Profits or Losses
</Table>

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GENENTECH CONFIDENTIAL

It is the intention of the Parties that the interpretation of these definitions
will be consistent with generally accepted accounting principles ("GAAP") in the
U.S.

Without limiting the foregoing, prior to the time that Gross Sales are obtained,
the Parties may eliminate the above line items related to sales and the support
of sales, and the costs thereof, and use only those terms relevant to the
sharing of Development Costs.

A.2.    REPORTING.The fiscal year of the Collaboration will be a calendar year.

Reporting by each Party for Collaboration revenues and expenses will be
performed as follows:

<Table>
<Caption>
Reporting Event                     Frequency            Timing of Submission
---------------                     ---------            --------------------
<S>                                 <C>                 <C>
Actuals (including draft            Quarterly           Q1-Q3:         + 45 days
   settlement statements)                                Q4:           + 45 days

Forecasts                           Quarterly            Q1-Q3         + 45 days
(rest of year - by month)

Settlement payments between
The Parties                         Quarterly            Quarter end   +60 days

Preliminary Budgets                 Annually             September 15
(one year)

Final Commercial
And Development Budget              Annually             October 15
(one year - by quarter)

Long Range Plan                     Annually             April 15
(current year plus 5 years)
</Table>

TolerRx shall provide to Genentech within thirty (30) days after the end of each
quarter a calculation of TolerRx Development Plan Work Costs. Genentech will be
responsible for the preparation of consolidated reports on the Collaboration
(including US Costs and any Operating Profit or Loss), and calculation of the
sharing and determination of the cash settlement. Genentech will provide to
TolerRx within forty-five (45) days of Genentech's quarter end a statement
showing the calculations of the Operating Profit or Loss sharing (or calculation
of expenses to be shared) and cash settlement required in a format substantially
listed above.

The financial representatives from the Parties (i.e. the Joint Finance Committee
members) will meet as appropriate but at least quarterly to review the
following:

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                           -        Development Costs

                           -        actual results

                           -        forecasts

                           -        budgets

                           -        Sales Returns and Allowances

                           -        other financial matters determined by JSC,
                                    including Genentech's methodologies for
                                    charging costs to the Collaboration, for
                                    determination of actuals, forecasts, budgets
                                    and long range plans and the results of
                                    applying such methodologies.

A.3.    BUDGET.

Budgets will be prepared annually with detailed development and business plans
for clinical trials, drug approval applications, strategy for product
introduction, sales and promotion efforts, as determined by Genentech.
Responsibility for the budget and a five (5) year long range plan will rest with
Genentech, who will develop budgets for development and commercialization to be
presented to the JSC and JPT annually.

After Genentech develops the budget and provides a copy of such budget to the
JSC, any material changes to such budget shall be reviewed by the JSC. Genentech
may make nonmaterial changes to the budget from time to time. For clarity,
Genentech shall retain the final authority to determine the budget (including
but not limited to Marketing Costs, Distribution Costs, Sales Costs, US Costs,
and Development Costs).

A.4.    PAYMENTS BETWEEN THE PARTIES.

Subject to Section 6.5(b), Genentech and TolerRx agree to share the Operating
Profit or Loss in the United States resulting from the Agreement in the
following manner:

            (a)     Genentech shall be allocated [***] of the Operating Profits
                    or Losses and

            (b)     TolerRx shall be allocated [***] of the Operating Profits or
                    Losses.

Payments to each Party of the percentages of Operating Profit or Loss as
provided above will be made quarterly, within sixty (60) days after the end of
each calendar quarter. Without limiting the foregoing, within sixty (60) days of
the end of each calendar quarter, there shall be reconciliation of the US Costs
which are to be shared and which are incurred during that quarter by Genentech
(including TolerRx Development Plan Work Costs incurred by TolerRx), with a
payment by TolerRx to Genentech or by Genentech to TolerRx to the extent
necessary so that

                                  * Confidential treatment requested:
                                    material has been omitted and filed
                                    separately with the Commission.

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GENENTECH CONFIDENTIAL

each Party bears its appropriate percentage of such shared US Costs. In the
event any payment is late, without limiting Genentech's other remedies
(including but not limited to Sections 6.5(b) and 6.5(c)), TolerRx or Genentech
shall increase the amount otherwise due and payable by adding interest thereon,
computed at the Prime Rate plus one percent (1%). "Prime Rate" means the rate of
interest as published in the weekly Federal Reserve H.15 Bulletin, or any
successor bulletin thereto.

A.5.    COST METHODOLOGY.

Genentech shall provide to TolerRx its costing and accounting methodology in
determining Operating Profits or Losses. TolerRx shall have the right to confirm
that such methodology is consistent with GAAP.

A.6.    START OF OPERATIONS AND EFFECTIVE ACCOUNTING DATE TERMINATION.

Operation of the Collaboration (and costs to be charged to the Collaboration)
will be deemed to have commenced as of the date of the filing of the first IND
by Genentech, only if TolerRx properly exercises the US Profit/Loss Sharing
Option and makes the US Cost Sharing Payments in accordance with Section 6.5 and
Exhibit A. Costs and expenses incurred prior to such date are not chargeable to
the Collaboration, except that costs to be charged to the Collaboration shall
include, but are not limited to, FTE Cost(s) and filing fees for filing of
IND(s) by Genentech.

For reporting and accounting purposes with respect to the Collaboration, the
effective termination date of Operating Profit or Loss sharing arrangement under
this Exhibit A (with regard to the last detailing year in the United States)
will be the earlier of: (A) on a Licensed Product-by-Licensed Product basis, the
nearest month end closest to the end of the period set forth in Section 6.5(b)
or (B) the nearest calendar quarter end prior to the date that TolerRx first
fails to make the applicable balancing payments relating to sharing Operating
Profit or Loss on a timely basis in accordance with this Exhibit A and Section
6.5.

A.7.    DEFINITIONS.

A.7.1.  "ALLOCABLE OVERHEAD" means costs incurred by a Party or for its account
which are attributable to a Party's supervisory, services, occupancy costs,
corporate bonus (to the extent not charged directly to department), and its
payroll, information systems, human relations or purchasing functions and which
are allocated to company departments based on space occupied or headcount or
other activity-based method consistently applied by a Party. Allocable Overhead
shall not include any costs attributable to general corporate activities
including, by way of example, executive management, investor relations, business
development, legal affairs and finance, and shall not duplicate G&A hereunder.

A.7.2.  "COST OF SALES" shall mean the sum of (i) Fully Burdened Manufacturing
Cost (as defined below), (ii) freight, insurance and other costs of shipping
Licensed Product to customers, (iii) any third party royalties payable with
respect to the manufacture, use or sale of Licensed

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GENENTECH CONFIDENTIAL

Product, excluding any royalties already accounted for in Fully Burdened
Manufacturing Cost and (iv) the cost of free Licensed Product for indigent
persons.

A.7.3.  "DEVELOPMENT COSTS" means the development costs INCURRED (including
accruals) by or for Genentech from the date of filing of the first IND by
Genentech, through the later of (a) the date of Regulatory Approval (including
thereafter costs to maintain or expand such Regulatory Approval) in the United
States, or (b) the date of termination of development efforts of the final
Indication of Licensed Product for which Regulatory Approval is sought in the
United States (the "Development Period"). Such costs shall comprise those costs
required to obtain, maintain and/or expand the authorization and/or ability to
manufacture, formulate, fill, ship and/or sell a Licensed Product in commercial
quantities to Third Parties in the United States. Such costs shall include FTE
Cost(s) and filing fees for filing such IND(s).

"Development Costs" shall include, but are not limited to, costs of research or
development, costs of studies on the toxicological, pharmacokinetical,
metabolical or clinical aspects of a Licensed Product conducted internally or by
individual investigators, or consultants necessary for the purpose of obtaining,
maintaining and/or expanding marketing approval of a Licensed Product, process
development, process improvement, and recovery costs, qualification lots, costs
for preparing, submitting, reviewing or developing data or information for the
purpose of submission to a governmental authority to obtain, maintain and/or
expand marketing approval of a Licensed Product, costs of all Phase I Clinical
Trials, Phase II Clinical Trials and Phase III Clinical Trials (including but
not limited to clinical materials) in the United States performed by or for
Genentech, and applicable Allocable Overhead.

"Development Costs" shall include expenses for data management, CROs,
statistical designs and studies, document preparation, and other administration
expenses associated with the clinical testing program or post-marketing studies
required to maintain product approvals. In determining "Development Costs"
chargeable under this Agreement, Genentech will use its project accounting
systems.

"Development Costs" shall include TolerRx Development Plan Work Costs and
TolerRx MSL Costs (to the extent expressly set forth in Section 3.4(f) of the
Agreement) in accordance with the same methodology applied by Genentech.

If a Licensed Product is developed or commercialized in conjunction with another
product, "Development Costs" shall mean only the portion of costs related to
developing and/or commercializing the Licensed Product.

If Genentech performs a study on Licensed Products and uses the results of such
study to commercialize Licensed Products outside the United States, then
Genentech shall remove [***] of the costs of such study from the Collaboration,
which results in a reimbursement of [***] of the costs of such study to TolerRx
via the next applicable balancing payment.

                                  * Confidential treatment requested:
                                    material has been omitted and filed
                                    separately with the Commission.

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GENENTECH CONFIDENTIAL

A.7.4.  "DISTRIBUTION COSTS" means the costs, including applicable Allocable
Overhead, specifically identifiable to the distribution of a Licensed Product by
or for Genentech including customer services, collection of data about sales to
hospitals and other end users, order entry, billing, shipping, credit and
collection and other such activities. For the purpose of this Agreement,
Genentech will charge the Collaboration for Distribution Costs an amount equal
to [***] of Net Sales in any year.

A.7.5.  "FULLY BURDENED MANUFACTURING COST" means one hundred percent (100%) of
Genentech's manufacturing cost (as defined in Genentech's accounting policies
consistently applied), which shall comprise the sum of:

(a)     the cost of goods produced as determined by Genentech in accordance with
GAAP consistently applied by Genentech, including product quality
assurance/control costs, direct labor and materials and product testing cost
incurred in connection with the manufacture and quality control testing of such
product, shipping containers, applicable Allocable Overhead, and other costs
borne by or for Genentech for packaging, transport, customs clearance and
storage of product prior to the time of sale (e.g. freight, customs, duty and
insurance); and

(b)     all of Genentech's allocable intellectual property acquisition and
licensing costs (including royalties) paid to third parties as it relates to the
manufacture of Licensed Product.

If Genentech holds inventory for commercial sales, it shall be permitted to
charge the Collaboration a reasonable and customary carrying charge to
compensate it for its financing and logistical product support.

A.7.6.  "GENERAL AND ADMINISTRATIVE COSTS" means costs chargeable to the
Collaboration equal to [***] of the sum of the Marketing Costs, Sales Costs, and
Development Costs of Genentech.

A.7.7.  "GROSS PROFIT" means Net Sales less Cost of Sales of a Licensed Product
by or for Genentech to Third Parties.

A.7.8.  "GROSS SALES" means, on a Licensed Product-by-Licensed Product basis,
the gross invoiced sales prices for all sales of Licensed Product sold by or for
Genentech or its third party sublicensees (including Affiliates to the extent
Genentech has granted a sublicense to such Affiliates) to independent Third
Parties. If a Licensed Product is sold by Genentech or its third party
sublicensees to independent Third Parties for use in combination with or as a
component of other products, notwithstanding the foregoing, "Gross Sales" shall
mean Adjusted Gross Sales. "Adjusted Gross Sales" shall mean the gross invoiced
sales price from such sales multiplied by the fraction B/(A+B), where A is the
gross invoiced sales price for the amount of the other product or components
used in the combination when distributed separately and B is the gross invoiced
sales price for the amount of the Licensed Product used in the combination when
distributed separately.

                                  * Confidential treatment requested:
                                    material has been omitted and filed
                                    separately with the Commission.

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GENENTECH CONFIDENTIAL

A.7.9.  "MARKETING COSTS" means the direct costs incurred by or for Genentech of
marketing, promotion, advertising, Licensed Product promotional materials,
professional education, product related public relations, relationships with
opinion leaders and professional societies, market research (before and after
product approval), healthcare economics studies, post-marketing studies not
required to maintain product approvals, and other similar activities related to
the Licensed Products. Such costs will include both internal costs (e.g.,
salaries, benefits, travel, supplies and materials, etc.), applicable Allocable
Overhead, and outside services and expenses (e.g., consultants, agency fees,
meeting costs, etc.). "Marketing Costs" shall also include activities related to
obtaining reimbursement from payers and costs of sales and marketing data.
"Marketing Costs" will specifically exclude the costs of activities which
promote Genentech's business as a whole without being product specific (such as
corporate image advertising).

A.7.10. "NET SALES" means Gross Sales of a Licensed Product in the Territory
less applicable Sales Returns and Allowances. If TolerRx properly exercises and
participates in the US Profit/Loss Sharing Option under Section 6.5, then (A)
when used in Section 6 of the Agreement, the term "Net Sales" excludes Net Sales
in the United States; and (B) when used in this Exhibit A, the term "Net Sales"
shall only refer to Net Sales in the United States. Bona fide sample units, free
units for indigent persons, and pre-clinical, clinical, or market-focused trial
units of Licensed Product will not be included in any calculations of Net Sales.
Genentech may deduct Sales Returns and Allowances made by or for it and/or its
sublicensees from Gross Sales regardless of the calendar quarter in which such
sales were made. In the event that Genentech or its sublicensees make any
adjustments to such deductions after the associated Net Sales have been reported
pursuant to this Agreement, the adjustments shall be reported by Genentech and
reconciled with the next report and payment of any royalties due.

A.7.11. "OPERATING PROFITS OR LOSSES" means, on a Licensed Product-by-Licensed
Product basis, Net Sales of Licensed Products in the United States less the
following items with respect to each Licensed Product, all for a given period:
Cost of Sales, Marketing Costs, Sales Costs, Development Costs, General and
Administrative Costs, Distribution Costs, and Other Operating Income/Expense.

A.7.12. "Operating Profits" means the amount of Operating Profits or Losses as
calculated in accordance with Exhibit A, when such amount is profit.

A.7.13. "Operating Losses" means the amount of Operating Profits or Losses as
calculated in accordance with Exhibit A, when such amount is loss.

A.7.14. "OTHER OPERATING INCOME/EXPENSE" means other operating income or expense
from or to third parties which is not part of the primary business activity of
the Collaboration, but is income or expense for purposes of the Collaboration
and is limited to the following:

            -       actual inventory write-offs of any Licensed Product,
                    including failed lots

            -       Patent and Trademark Costs

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GENENTECH CONFIDENTIAL

            -       product liability insurance to the extent the Parties obtain
                    a joint policy

            -       indemnification costs of Genentech (as defined in Section 10
                    of the Agreement)

            -       third party payments for royalties and other similar
                    payments applicable to the use and development (but not
                    manufacturing or sales) of Licensed Product

            -       Third Party Royalty Expense (as defined below)

            -       other (to be approved by JSC)

A.7.15. "PATENT AND TRADEMARK COSTS" means the fees and expenses paid to outside
legal counsel and experts, and filing and maintenance expenses, incurred after
the Effective Date in connection with the establishment and maintenance of
rights for intellectual property as described in Section 7 of the Agreement
covering any Licensed Product, and similar costs with respect to trademarks
described in Section 7.7 of the Agreement, including costs of patent
interference, reexamination, reissue, opposition and revocation proceedings and
similar costs with respect to registration of such trademarks and costs of
lawsuits to enforce any intellectual property rights.

A.7.16. "SALES COSTS" means costs, including Allocable Overhead incurred by
Genentech or for its account and specifically identifiable to the sales efforts
of Licensed Products to all markets in the United States including the managed
care market. "Sales Costs" shall include costs associated with sales
representatives for Licensed Product, including compensation, benefits and
travel, supervision and training of the sales representatives, sales meetings,
and other sales expenses. "Sales Costs" will not include the start-up costs
associated with Genentech's sales force, including recruiting, relocation and
other similar costs.

A.7.17. "SALES RETURNS AND ALLOWANCES" means the sum of (a) and (b), where: (a)
is a provision, determined by Genentech under GAAP for sales of Licensed
Products for (i) trade, cash and quantity discounts or price adjustments or
rebates on Licensed Products (including but not limited to discounts or rebates
to governmental or managed care organizations), other than price discounts
granted at the time of invoicing and which are included in the determination of
Gross Sales, (ii) credits or allowances given or made for rejection or return
of, and for uncollectable amounts on, previously sold Licensed Products or for
retroactive price reductions (including Medicare and similar types of rebates
and chargebacks), (iii) taxes, duties or other governmental charges (including
any tax such as a value added or similar tax or government charge other than an
income tax) levied on or measured by the billing amount for Licensed Products,
as adjusted for rebates and refunds, (iv) charges for freight and insurance
directly related to the distribution of Licensed Products, to the extent
included in Gross Sales, (v) credits for allowances given or made for wastage
replacement, and (vi) other special sales programs agreed to by the Parties for
Licensed Products; and (b) is a periodic adjustment of the provision

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GENENTECH CONFIDENTIAL

determined in (a) to reflect amounts actually incurred by Genentech and/or
sublicensees for items (i), (ii), (iii), (iv), (v), and (vi) in clause (a).

A.7.18. "Third Party Royalty Expense" means all payments made by Genentech
(and/or its sublicensee(s) on its behalf) to any third party with respect to the
development, manufacture, import or export, use, offer for sale or sale of any
Licensed Product.

A.7.19. "TolerRx Development Plan Work" means TolerRx's performance of
activities under the Development Plan at the request of the JSC. TolerRx
Development Plan Work shall exclude any work or studies performed by TolerRx
under Section 3.4(b).

A.7.20. "US COSTS" means Sales Returns and Allowances, Cost of Sales, Marketing
Costs, Sales Costs, Development Costs, Other Operating Income/Expense,
Distribution Costs, and General and Administrative Costs. For clarity, US Costs
only refers to such costs incurred by Genentech or on behalf of Genentech by
Genentech's third party sublicensees and shall not refer to any costs incurred
by or on behalf of TolerRx other than TolerRx Development Plan Work Costs.

Execution Copy                       - 10 -

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