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                                                                    EXHIBIT 10.2

                                  TOLERRX, INC.

                        2003 EMPLOYEE STOCK PURCHASE PLAN

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<Table>
                                                                           
1.   Purpose..................................................................1

2.   Definitions..............................................................1

3.   Eligibility..............................................................3

4.   Offering Periods.........................................................3

5.   Participation............................................................3

6.   Method of Payment of Contributions.......................................4

7.   Grant of Option..........................................................5

8.   Exercise of Option.......................................................6

9.   Delivery.................................................................6

10.  Voluntary Withdrawal; Termination of Employment..........................6

11.  Interest.................................................................7

12.  Stock....................................................................7

13.  Administration...........................................................7

14.  Designation of Beneficiary...............................................7

15.  Transferability of Options and Shares....................................8

16.  Use of Funds.............................................................8

17.  Reports..................................................................8

18.  Adjustments Upon Changes in Capitalization; Corporate Transactions.......8

19.  Amendment or Termination.................................................10

20.  Notices..................................................................10

21.  Conditions to Issuance of Shares.........................................10

22.  Term of Plan; Effective Date.............................................11
</Table>

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                                  TOLERRX, INC.

                        2003 EMPLOYEE STOCK PURCHASE PLAN

     The following constitute the provisions of the 2003 Employee Stock Purchase
Plan of TolerRx, Inc.

1.   PURPOSE

     The purpose of the Plan is to provide employees of the Company and its
Designated Subsidiaries with an opportunity to purchase Common Stock of the
Company. It is the intention of the Company to have the Plan qualify as an
"Employee Stock Purchase Plan" under Section 423 of the Code. The provisions of
the Plan shall, accordingly, be construed so as to extend and limit
participation in a manner consistent with the requirements of that section of
the Code.

2.   DEFINITIONS

     2.1.  BOARD means the Board of Directors of the Company.

     2.2.  CODE means the Internal Revenue Code of 1986, as amended.

     2.3.  COMMON STOCK means the Common Stock, par value $0.001 per share, of
the Company.

     2.4.  COMPANY means TolerRx, Inc., a Delaware corporation.

     2.5.  COMPENSATION means all regular straight time compensation including
commissions but shall not include payments for overtime, shift premium,
incentive compensation, incentive payments, bonuses and other irregular or
infrequent compensation or benefits.

     2.6.  CONTINUOUS STATUS AS AN EMPLOYEE means the absence of any
interruption or termination of service as an Employee. Continuous Status as an
Employee shall not be considered interrupted in the case of (i) sick leave; (ii)
military leave; (iii) any other leave of absence approved by the Administrator,
provided that such leave is for a period of not more than 90 days, unless
reemployment upon the expiration of such leave is guaranteed by contract or
statute, or unless provided otherwise pursuant to Company policy adopted from
time to time; or (iv) in the case of transfers between locations of the Company
or between the Company and its Designated Subsidiaries.

     2.7.  CONTRIBUTIONS means all amounts credited to the account of a
participant pursuant to the Plan.

     2.8.  CORPORATE TRANSACTION means a merger or consolidation of the Company
with and into another person or the sale, transfer, or other disposition of all
or

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substantially all of the Company's assets to one or more persons (other than any
wholly-owned subsidiary of the Company) in a single transaction or series of
related transactions.

     2.9.  DESIGNATED SUBSIDIARIES means the Subsidiaries which have been
designated by the Board from time to time in its sole discretion as eligible to
participate in the Plan.

     2.10. EMPLOYEE means any person, including an Officer, who is customarily
employed for at least twenty (20) hours per week and more than five (5) months
in a calendar year by the Company or one of its Designated Subsidiaries.

     2.11. EXCHANGE ACT means the Securities Exchange Act of 1934, as amended.

     2.12  INITIAL OFFERING PERIOD means the first Offering Period of the Plan.

     2.13. OFFERING COMMENCEMENT DATE means the first business day of each
Offering Period of the Plan.

     2.14. OFFERING PERIOD means any of the periods, generally of six (6) months
duration, as set forth in Section 4.

     2.15. OFFICER means a person who is an officer of the Company within the
meaning of Section 16 of the Exchange Act and the rules and regulations
promulgated thereunder.

     2.16. OFFERING TERMINATION DATE means the last business day of each
Offering Period of the Plan.

     2.17. PLAN means this Employee Stock Purchase Plan.

     2.18. PURCHASE PRICE means with respect to an Offering Period an amount
equal to 85% of the Fair Market Value (as defined in Section 7.2 below) of a
Share on the Offering Commencement Date or on the Offering Termination Date,
whichever is lower; provided, however, that (i) if there is an increase in the
number of Shares available for issuance under the Plan as a result of a
stockholder-approved amendment to the Plan, (ii) all or a portion of such
additional Shares are to be issued with respect to the Offering Period underway
at the time of such increase ("Additional Shares"), and (iii) the Fair Market
Value of a Share of Common Stock on the date of such increase (the "Approval
Date Fair Market Value") is higher than the Fair Market Value on the Offering
Commencement Date for such Offering Period, then in such instance the Purchase
Price with respect to Additional Shares shall be 85% of the Approval Date Fair
Market Value or the Fair Market Value of a Share of Common Stock on the Offering
Termination Date, whichever is lower.

     2.19. SHARE means a share of Common Stock, as adjusted in accordance with
Section 18 of the Plan.

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                                       -3-

     2.20. SUBSIDIARY means a corporation, domestic or foreign, of which not
less than 50% of the voting shares are held by the Company or a Subsidiary,
whether or not such corporation now exists or is hereafter organized or acquired
by the Company or a Subsidiary.

3.   ELIGIBILITY

     3.1.  Any person who is an Employee as of the Offering Commencement Date of
a given Offering Period shall be eligible to participate in such Offering Period
under the Plan, subject to the requirements of Sections 5.1 and 5.3 and the
limitations imposed by Section 423(b) of the Code.

     3.2.  Any provisions of the Plan to the contrary notwithstanding, no
Employee shall be granted an option under the Plan (i) if, immediately after the
grant, such Employee (taking into account stock which would be attributed to
such Employee pursuant to Section 424(d) of the Code) would own capital stock of
the Company and/or hold outstanding options to purchase stock possessing five
percent (5%) or more of the total combined voting power or value of all classes
of stock of the Company or of any Subsidiary of the Company, or (ii) if such
option would permit his or her rights to purchase stock under all employee stock
purchase plans (described in Section 423 of the Code) of the Company and its
Subsidiaries to accrue at a rate which exceeds twenty-five Thousand Dollars
($25,000) of the Fair Market Value (as defined in Section 7.2 below) of such
stock (determined at the time such option is granted) for each calendar year in
which such option is outstanding at any time.

4.   OFFERING PERIODS

     Each Offering Period will begin on January 1 or July 1 and end on the next
following June 30 or December 31, respectively. However, the first Offering
Period shall commence on the beginning of the effective date of the Registration
Statement on Form S-1 for the initial public offering of the Company's Common
Stock (the "IPO Date") and continue until December 31, 2003. At any time and
from time to time, the Board may change the duration and/or the frequency of
Offering Periods with respect to future Offering Periods or suspend operation of
the Plan with respect to Offering Periods not yet commenced.

5.   PARTICIPATION

     5.1.  An eligible Employee may become a participant in the Plan by
completing a subscription agreement on the form provided by the Company and
filing it with the Company's payroll office prior to the applicable Offering
Commencement Date, unless a later time for filing the subscription agreement is
set by the Board for all eligible Employees with respect to a given Offering
Period. The subscription agreement shall set forth the percentage of the
participant's Compensation (subject to Section 6.1 below) to be paid as
Contributions pursuant to the Plan.

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                                       -4-

     5.2.  Payroll deductions shall commence on the first payroll following the
Offering Commencement Date and shall end on the last payroll paid on or prior to
the Offering Termination Date of the Offering Period to which the subscription
agreement is applicable, unless sooner terminated by the participant as provided
in Section 10.

     5.3.  Participation in the Plan for the Initial Offering Period shall be on
the same terms and conditions as are set forth in the Plan in respect of
Offering Periods generally, except as and to the extent otherwise expressly set
forth in this Section 5.3:

           (a)  All eligible Employees as of the Offering Commencement Date of
the Initial Offering Period shall automatically participate in the Plan and be
granted an option pursuant to the Plan as of such Offering Commencement Date.
Eligible Employees shall neither be required to submit a subscription agreement
to participate in the Initial Offering Period nor be permitted to decline to
participate in the Initial Offering Period (but any Contributions of a
participant for the Initial Offering Period may be withdrawn as provided in
Section 10). However, any participation as to subsequent Offering Periods shall
require submission of a subscription agreement and compliance with all other
applicable provisions of the Plan.

           (b)  For purposes of determining the exercise price of options
granted on the Offering Commencement Date of the Initial Offering Period, the
Fair Market Value of a Share as of such Offering Commencement Date shall be the
"Price to Public" as set forth in the final prospectus filed with the Securities
and Exchange Commission pursuant to Rule 424 under the Securities Act of 1933,
as amended.

           (c)  At any time after the effectiveness of the Company's
Registration Statement on Form S-8 with respect to the Plan and prior to the
Offering Termination Date, a participant in the Plan for the Initial Offering
Period may deliver by payment in cash or personal check amounts for credit as
Contributions under the Plan with respect to the Initial Offering Period.

           (d)  The total Contributions credited to a participant's account
under the Plan for the Initial Offering Period pursuant to subsection (c) above,
shall not exceed ten percent (10%) of the participant's Compensation for the
Initial Offering Period. Any excess shall be promptly refunded to the
participant following the Offering Termination Date of the Initial Offering
Period.

6.   METHOD OF PAYMENT OF CONTRIBUTIONS

     6.1.  A participant shall elect to have payroll deductions made on each
payday during the Offering Period in an amount not less than one percent (1%)
and not more than ten percent (10%) (or such other percentage as the Board may
establish from time to time before an Offering Commencement Date) of such
participant's Compensation on each payday during the Offering Period. All
payroll deductions made by a participant shall be

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                                       -5-

credited to his or her account under the Plan. A participant may not make any
additional payments into such account.

     6.2.  A participant may discontinue his or her participation in the Plan as
provided in Section 10. In addition, if the Board has so announced to Employees
at least five (5) days prior to the scheduled beginning of the next Offering
Period to be affected by the Board's determination, a participant may, on one
occasion only during each Offering Period, change the rate of his or her
Contributions with respect to the Offering Period by completing and filing with
the Company a new subscription agreement authorizing a change in the payroll
deduction rate. Any such change in rate shall be effective as of the first
payroll period following the date of filing of the new subscription agreement,
if the agreement is filed at least ten (10) business days prior to such period
and, if not, as of the second following payroll period.

     6.3.  Notwithstanding the foregoing, to the extent necessary to comply with
Section 423(b)(8) of the Code and Section 3.2 herein, a participant's payroll
deductions may be decreased during any Offering Period scheduled to end during
the current calendar year to 0%. Payroll deductions reduced to 0% in compliance
with this Section 6.3 shall re-commence automatically at the rate provided in
such participant's subscription agreement at the beginning of the first Offering
Period which is scheduled to end in the following calendar year, unless
terminated by the participant as provided in Section 10.

7.   GRANT OF OPTION

     7.1.  On the Offering Commencement Date of each Offering Period, each
eligible Employee participating in such Offering Period shall be granted an
option to purchase on the Offering Termination Date of that Offering Period a
number of Shares determined by dividing such Employee's Contributions
accumulated prior to such Offering Termination Date and retained in the
participant's account as of the Offering Termination Date by the applicable
Purchase Price. However, the maximum number of Shares an Employee may purchase
during each Offering Period shall be 2,500 shares, and provided further that
such purchase shall be subject to the limitations set forth in Sections 3.2 and
12.

     7.2.  The fair market value of the Company's Common Stock on a given date
(the "Fair Market Value") shall be determined by the Board in its discretion
based on the closing sales price of the Common Stock for such date (or, in the
event that the Common Stock is not traded on such date, on the immediately
preceding trading date), as reported by the National Association of Securities
Dealers Automated Quotation ("Nasdaq") National Market or, if such price is not
reported, the mean of the bid and asked prices per share of the Common Stock as
reported by Nasdaq or, in the event the Common Stock is listed on a stock
exchange, the closing sales price on such exchange on such date (or, in the
event that the Common Stock is not traded on such date, on the immediately
preceding trading date), as reported in The Wall Street Journal.

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                                       -6-

8.   EXERCISE OF OPTION

     Unless a participant withdraws from the Plan as provided in Section 10, his
or her option for the purchase of Shares will be exercised automatically on the
Offering Termination Date of an Offering Period, and the maximum number of full
Shares subject to the option will be purchased at the applicable Purchase Price
with the accumulated Contributions in his or her account. No fractional Shares
shall be issued. The Shares purchased upon exercise of an option hereunder shall
be deemed to be transferred to the participant on the Offering Termination Date.
During his or her lifetime, a participant's option to purchase Shares hereunder
is exercisable only by him or her.

9.   DELIVERY

     As promptly as practicable after each Offering Termination Date of each
Offering Period, the Company shall arrange the delivery to each participant, as
appropriate, of a certificate representing the Shares purchased upon exercise of
his or her option. Any payroll deductions accumulated in a participant's account
which are not sufficient to purchase a full Share shall be retained in the
participant's account for the subsequent Offering Period, subject to earlier
withdrawal by the participant as provided in Section 10 below.  Any other
amounts left over in a participant's account after an Offering Termination Date
shall be returned to the participant.

10.  VOLUNTARY WITHDRAWAL; TERMINATION OF EMPLOYMENT

     10.1. A participant may withdraw all but not less than all of the
Contributions credited to his or her account under the Plan at any time prior to
each Offering Termination Date by giving written notice to the Company. All of
the participant's Contributions credited to his or her account will be paid to
him or her promptly after receipt of his or her notice of withdrawal and his or
her option for the current Offering Period will be automatically terminated, and
no further Contributions for the purchase of Shares will be made during the
Offering Period.

     10.2. Upon termination of the participant's Continuous Status as an
Employee prior to the Offering Termination Date of an Offering Period for any
reason, including retirement or death, the Contributions credited to his or her
account will be returned to him or her or, in the case of his or her death, to
the person or persons entitled thereto under Section 14, and his or her option
will be automatically terminated.

     10.3. In the event an Employee fails to remain in Continuous Status as an
Employee of the Company for at least twenty (20) hours per week during the
Offering Period in which the employee is a participant, he or she will be deemed
to have elected to withdraw from the Plan and the Contributions credited to his
or her account will be returned to him or her and his or her option terminated.

     10.4. A participant's withdrawal during an Offering Period will not have
any effect upon his or her eligibility to participate in a succeeding Offering
Period or in any similar plan which may hereafter be adopted by the Company.

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                                       -7-

11.  INTEREST

     No interest shall accrue on the Contributions of a participant in the Plan.

12.  STOCK

     12.1. Subject to adjustment as provided in Section 18, the maximum number
of Shares which shall be made available for sale under the Plan shall be 150,000
Shares. Notwithstanding the foregoing, and subject to adjustment in accordance
with Section 18 no more than an aggregate of 150,000 Shares may be issued
pursuant to this Plan. If the Board determines that, on a given Offering
Termination Date, the number of shares with respect to which options are to be
exercised may exceed (i) the number of shares of Common Stock that were
available for sale under the Plan on the Offering Commencement Date, or (ii) the
number of shares available for sale under the Plan on such Offering Termination
Date, the Board may in its sole discretion provide that the Company shall make a
pro rata allocation of the Shares available for purchase on such Offering
Commencement Date or Offering Termination Date, as applicable, in as uniform a
manner as shall be practicable and as it shall determine in its sole discretion
to be equitable among all participants exercising options to purchase Common
Stock on such Offering Termination Date. The Company may make pro rata
allocation of the Shares available on the Offering Commencement Date of the
applicable Offering Period pursuant to the preceding sentence, notwithstanding
any authorization of additional Shares for issuance under the Plan by the
Company's stockholders subsequent to such Offering Commencement Date.

     12.2. The participant shall have no interest or voting right in Shares
covered by his or her option until such option has been exercised.

     12.3. Shares to be delivered to a participant under the Plan will be
registered in the name of the participant or in the name of the participant and
his or her spouse, as directed by the participant.

13.  ADMINISTRATION

     The Board, or a committee named by the Board, shall supervise and
administer the Plan and shall have full power to adopt, amend and rescind any
rules deemed desirable and appropriate for the administration of the Plan and
not inconsistent with the Plan, to construe and interpret the Plan, and to make
all other determinations necessary or advisable for the administration of the
Plan. The Board's determinations made in good faith on matters referred to in
this Plan shall be final, binding and conclusive on all persons having or
claiming any interest under this Plan.

14.  DESIGNATION OF BENEFICIARY

     14.1. A participant may file a written designation of a beneficiary who is
to receive any Shares and cash, if any, from the participant's account under the
Plan in the event of such participant's death subsequent to the end of an
Offering Period but prior to

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delivery to him or her of such Shares and cash. Any such beneficiary shall also
be entitled to receive any cash from the participant's account under the Plan in
the event of such participant's death prior to the Offering Termination Date of
an Offering Period.

     14.2. Such designation of beneficiary may be changed by the participant at
any time by written notice. In the event of the death of a participant and in
the absence of a beneficiary validly designated under the Plan who is living at
the time of such participant's death, the Company shall deliver such Shares
and/or cash to the executor or administrator of the estate of the participant,
or if no such executor or administrator has been appointed (to the knowledge of
the Company), the Company, in its discretion, may deliver such Shares and/or
cash to the spouse or to any one or more dependents or relatives of the
participant, or if no spouse, dependent or relative is known to the Company,
then to such other person as the Company may designate.

15.  TRANSFERABILITY OF OPTIONS AND SHARES

     Neither Contributions credited to a participant's account nor any rights
with regard to the exercise of an option or to receive Shares under the Plan may
be assigned, transferred, pledged or otherwise disposed of in any way (other
than by will, the laws of descent and distribution, or as provided in Section
14) by the participant. Any such attempt at assignment, transfer, pledge or
other disposition shall be without effect, except that the Company may treat
such act as an election to withdraw funds in accordance with Section 10. In
addition, if the Board has so announced to Employees at least five (5) days
prior to the scheduled beginning of the next Offering Period to be affected by
the Board's determination, any Shares acquired on the Offering Termination Date
of such Offering Period may be subject to restrictions specified by the Board on
the transfer of such Shares.

16.  USE OF FUNDS

     All Contributions received or held by the Company under the Plan may be
used by the Company for any corporate purpose, and the Company shall not be
obligated to segregate such Contributions from its other assets.

17.  REPORTS

     Individual accounts will be maintained for each participant in the Plan.
Statements of account will be given to participating Employees at least
annually, which statements will set forth the amounts of Contributions, the per
Share Purchase Price, the number of Shares purchased and the remaining cash
balance, if any.

18.  ADJUSTMENTS UPON CHANGES IN CAPITALIZATION; CORPORATE TRANSACTIONS

     18.1. ADJUSTMENT. Subject to any required action by the stockholders of the
Company, the number of shares covered by each option under the Plan which has
not yet been exercised and the number of Shares which have been authorized for
issuance under the Plan but have not yet been placed under option (collectively,
the "Reserves"), as well

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                                       -9-

as the maximum number of shares of Common Stock which may be purchased by a
participant in an Offering Period, the number of shares of Common Stock set
forth in Section 12.1 above, and the price per Share of Common Stock covered by
each option under the Plan which has not yet been exercised, shall be
proportionately adjusted for any increase or decrease in the number of the
Company's issued Shares resulting from a stock split, reverse stock split, stock
dividend, combination or reclassification of the Common Stock (including any
such change in the number of Shares of Common Stock effected in connection with
a change in domicile of the Company), or any other increase or decrease in the
number of Shares effected without receipt of consideration by the Company;
provided however that conversion of any convertible securities of the Company
shall not be deemed to have been "effected without receipt of consideration."
Such adjustment shall be made by the Board, whose determination in that respect
shall be final, binding and conclusive.

     18.2. CORPORATE TRANSACTIONS. In the event of a dissolution or liquidation
of the Company, the Offering Period then in progress will terminate immediately
prior to the consummation of such action, unless otherwise provided by the
Board. In the event of a Corporate Transaction, each option outstanding under
the Plan shall be assumed or an equivalent option shall be substituted by the
successor corporation or a parent or Subsidiary of such successor corporation.
In the event that the successor corporation refuses to assume or substitute for
outstanding options, the Offering Period then in progress shall be shortened and
a new Offering Termination Date shall be set (the "New Offering Termination
Date"), as of which date the Offering Period then in progress will terminate.
The New Offering Termination Date shall be on or before the date of consummation
of the transaction and the Board shall notify each participant in writing, at
least ten (10) days prior to the New Offering Termination Date, that the
Offering Termination Date for his or her option has been changed to the New
Offering Termination Date and that his or her option will be exercised
automatically on the New Offering Termination Date, unless prior to such date he
or she has withdrawn from the Offering Period as provided in Section 10. For
purposes of this Section 18, an option granted under the Plan shall be deemed to
be assumed, without limitation, if, at the time of issuance of the stock or
other consideration upon a Corporate Transaction, each holder of an option under
the Plan would be entitled to receive upon exercise of the option the same
number and kind of shares of stock or the same amount of property, cash or
securities as such holder would have been entitled to receive upon the
occurrence of the transaction if the holder had been, immediately prior to the
transaction, the holder of the number of Shares of Common Stock covered by the
option at such time (after giving effect to any adjustments in the number of
Shares covered by the option as provided for in this Section 18); provided
however that if the consideration received in the transaction is not solely
common stock of the successor corporation or its parent (as defined in Section
424(e) of the Code), the Board may, with the consent of the successor
corporation, provide for the consideration to be received upon exercise of the
option to be solely common stock of the successor corporation or its parent
equal in Fair Market Value to the per Share consideration received by holders of
Common Stock in the transaction.

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                                      -10-

     The Board may, if it so determines in the exercise of its sole discretion,
also make provision for adjusting the Reserves, as well as the price per Share
of Common Stock covered by each outstanding option, in the event that the
Company effects one or more reorganizations, recapitalizations, rights offerings
or other increases or reductions of Shares of its outstanding Common Stock, and
in the event of the Company's being consolidated with or merged into any other
corporation.

19.  AMENDMENT OR TERMINATION

     19.1. The Board may at any time and for any reason terminate or amend the
Plan. Except as provided in Section 18, no such termination of the Plan may
affect options previously granted, provided that the Plan or an Offering Period
may be terminated by the Board on an Offering Termination Date or by the Board's
setting a new Offering Termination Date with respect to an Offering Period then
in progress if the Board determines that termination of the Plan and/or the
Offering Period is in the best interests of the Company and its stockholders or
if continuation of the Plan and/or the Offering Period would cause the Company
to incur adverse accounting charges as a result of the Plan. Except as provided
in Section 18 and in this Section 19, no amendment to the Plan shall make any
change in any option previously granted which adversely affects the rights of
any participant.

     19.2. Without stockholder consent and without regard to whether any
participant rights may be considered to have been adversely affected, the Board
(or its committee) shall be entitled to change the Offering Periods, limit the
frequency and/or number of changes in the amount withheld during an Offering
Period, establish the exchange ratio applicable to amounts withheld in a
currency other than U.S. dollars, permit payroll withholding in excess of the
amount designated by a participant in order to adjust for delays or mistakes in
the Company's processing of properly completed withholding elections, establish
reasonable waiting and adjustment periods and/or accounting and crediting
procedures to ensure that amounts applied toward the purchase of Common Stock
for each participant properly correspond with amounts withheld from the
participant's Compensation, and establish such other limitations or procedures
as the Board (or its committee) determines in its sole discretion advisable
which are consistent with the Plan.

20.  NOTICES

     All notices or other communications by a participant to the Company under
or in connection with the Plan shall be deemed to have been duly given when
received in the form specified by the Company at the location, or by the person,
designated by the Company for the receipt thereof.

21.  CONDITIONS TO ISSUANCE OF SHARES

     Shares shall not be issued with respect to an option unless the exercise of
such option and the issuance and delivery of such Shares pursuant thereto shall
comply with all applicable provisions of law, domestic or foreign, including,
without limitation, the

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                                      -11-

Securities Act of 1933, as amended, the Exchange Act, the rules and regulations
promulgated thereunder, applicable state securities laws and the requirements of
any stock exchange upon which the Shares may then be listed, and shall be
further subject to the approval of counsel for the Company with respect to such
compliance.

     As a condition to the exercise of an option, the Company may require the
person exercising such option to represent and warrant at the time of any such
exercise that the Shares are being purchased only for investment and without any
present intention to sell or distribute such Shares if, in the opinion of
counsel for the Company, such a representation is required by any of the
aforementioned applicable provisions of law.

22.  TERM OF PLAN; EFFECTIVE DATE

     The Plan shall become effective upon the IPO Date. It shall continue in
effect for a term of five (5) years unless sooner terminated under Section 19.

<Page>

                                                                          SAMPLE

                                  TOLERRX, INC.

                        2003 EMPLOYEE STOCK PURCHASE PLAN

                             SUBSCRIPTION AGREEMENT

                                                               New Election ____

                                                         Change of Election ____

     1.    I, __________________, hereby elect to participate in the TolerRx,
Inc. 2003 Employee Stock Purchase Plan (the "Plan") for the Offering Period
__________, _____ to ______________, _____, and subscribe to purchase shares of
the Company's Common Stock in accordance with this Subscription Agreement and
the Plan.

     2.    I elect to have Contributions in the amount of _____% of my
Compensation, as those terms are defined in the Plan, applied to this purchase.
I understand that this amount must not be less than 1% and not more than 10% of
my Compensation during the Offering Period. (Please note that no fractional
percentages are permitted).

     3.    I hereby authorize payroll deductions from each paycheck during the
Offering Period at the rate stated in Item 2 of this Subscription Agreement. I
understand that all payroll deductions made by me shall be credited to my
account under the Plan and that I may not make any additional payments into such
account. I understand that all payments made by me shall be accumulated, without
interest or earnings, for the purchase of shares of Common Stock at the
applicable purchase price determined in accordance with the Plan. I further
understand that, except as otherwise set forth in the Plan, shares will be
purchased for me automatically on the Offering Termination Date of each Offering
Period unless I otherwise withdraw from the Plan by giving written notice to the
Company for such purpose.

     4.    I understand that I may discontinue at any time prior to the Offering
Termination Date my participation in the Plan as provided in Section 10 of the
Plan. I acknowledge that, unless I discontinue my participation in the Plan as
provided in Section 10 of the Plan, my election will continue to be effective
for each successive Offering Period.

     5.    I have received a copy of the complete TolerRx, Inc. 2003 Employee
Stock Purchase Plan. I understand that my participation in the Plan is in all
respects subject to the terms of the Plan.

     6.    Shares purchased for me under the Plan should be issued in the
name(s) of (name of employee or employee and spouse only):

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                                       -2-

                                               _________________________________

                                               _________________________________

     7.    In the event of my death, I hereby designate the following as my
beneficiary(ies) to receive all payments and shares due to me under the Plan:

NAME: (Please print)
                                               _________________________________
                                               (First)      (Middle)     (Last)

__________________________                     _________________________________
(Relationship)                                 (Address)

                                               _________________________________

     8.    I understand that if I dispose of any shares received by me pursuant
to the Plan within 2 years after the Offering Commencement Date (the first day
of the Offering Period during which I purchased such shares) or within 1 year
after the Offering Termination Date, I will be treated for federal income tax
purposes as having received ordinary compensation income at the time of such
disposition in an amount equal to the excess of the fair market value of the
shares on the Offering Termination Date over the price which I paid for the
shares, regardless of whether I disposed of the shares at a price less than
their fair market value at the Offering Termination Date. The remainder of the
gain or loss, if any, recognized on such disposition will be treated as capital
gain or loss.

     I hereby agree to notify the Company in writing within 30 days after the
date of any such disposition, and I will make adequate provision for federal,
state or other tax withholding obligations, if any, which arise upon the
disposition of the Common Stock. The Company may, but will not be obligated to,
withhold from my compensation the amount necessary to meet any applicable
withholding obligation including any withholding necessary to make available to
the Company any tax deductions or benefits attributable to the sale or early
disposition of Common Stock by me.

     9.    If I dispose of such shares at any time after expiration of the
2-year and 1-year holding periods, I understand that I will be treated for
federal income tax purposes as having received compensation income only to the
extent of an amount equal to the lesser of (1) the excess of the fair market
value of the shares at the time of such disposition over the purchase price
which I paid for the shares under the option, or (2) 15% of the fair market
value of the shares on the Offering Commencement Date. The remainder of the gain
or loss, if any, recognized on such disposition will be treated as capital gain
or loss.

     I understand that this tax summary is only a summary and is subject to
change. I further understand that I should consult a tax advisor concerning
certain tax implications of the purchase and sale of stock under the Plan.

<Page>

                                       -3-

     10.   I hereby agree to be bound by the terms of the Plan. The
effectiveness of this Subscription Agreement is dependent upon my eligibility to
participate in the Plan.

SIGNATURE:
           --------------------------------

SOCIAL SECURITY #:
                   ------------------------

DATE:
      -------------------------------------

<Page>

                                                                          SAMPLE

                                  TOLERRX, INC.

                        2003 EMPLOYEE STOCK PURCHASE PLAN

               EXERCISE AGREEMENT FOR THE INITIAL OFFERING PERIOD

     1.    I have received a copy of the complete TolerRx, Inc. 2003 Employee
Stock Purchase Plan. I understand that my participation in the Plan is in all
respects subject to the terms of the Plan.

     2.    Shares purchased for me under the Plan should be issued in the
name(s) of (name of employee or employee and spouse only):

                                               _________________________________

                                               _________________________________

     3.    In the event of my death, I hereby designate the following as my
beneficiary(ies) to receive all shares due to me under the Plan:

NAME: (Please print)
                                        ________________________________________
                                               (First)      (Middle)     (Last)

__________________________                     _________________________________
(Relationship)                                 (Address)

                                               _________________________________

     4.    I understand that if I dispose of any shares received by me pursuant
to the Plan within 2 years after the Offering Commencement Date (the first day
of the Offering Period during which I purchased such shares) or within 1 year
after the Offering Termination Date, I will be treated for federal income tax
purposes as having received ordinary compensation income at the time of such
disposition in an amount equal to the excess of the fair market value of the
shares on the Offering Termination Date over the price which I paid for the
shares, regardless of whether I disposed of the shares at a price less than
their fair market value at the Offering Termination Date. The remainder of the
gain or loss, if any, recognized on such disposition will be treated as capital
gain or loss.

     I hereby agree to notify the Company in writing within 30 days after the
date of any such disposition, and I will make adequate provision for federal,
state or other tax withholding obligations, if any, which arise upon the
disposition of the Common Stock. The Company may, but will not be obligated to,
withhold from my compensation the amount necessary to meet any applicable
withholding obligation including any

<Page>

                                       -2-

withholding necessary to make available to the Company any tax deductions or
benefits attributable to the sale or early disposition of Common Stock by me.

     5.    If I dispose of such shares at any time after expiration of the
2-year and 1-year holding periods, I understand that I will be treated for
federal income tax purposes as having received compensation income only to the
extent of an amount equal to the lesser of (1) the excess of the fair market
value of the shares at the time of such disposition over the purchase price
which I paid for the shares under the option, or (2) 15% of the fair market
value of the shares on the Offering Commencement Date. The remainder of the gain
or loss, if any, recognized on such disposition will be treated as capital gain
or loss.

     I understand that this tax summary is only a summary and is subject to
change. I further understand that I should consult a tax advisor concerning
certain tax implications of the purchase and sale of stock under the Plan.

     6.    I hereby agree to be bound by the terms of the Plan. The
effectiveness of this Subscription Agreement is dependent upon my eligibility to
participate in the Plan.

SIGNATURE:
           --------------------------------

SOCIAL SECURITY #:
                  -------------------------

DATE:
       ------------------------------------

<Page>

                                                                          SAMPLE

                                  TOLERRX, INC.

                        2003 EMPLOYEE STOCK PURCHASE PLAN

                              NOTICE OF WITHDRAWAL

     I, _____________, hereby elect to withdraw my participation in the TolerRx,
Inc. 2003 Employee Stock Purchase Plan (the "Plan") for the Offering Period that
began on _________________, ________. This withdrawal covers all Contributions
credited to my account and is effective on the date designated below.

     I understand that all Contributions credited to my account will be paid to
me within ten (10) business days of receipt by the Company of this Notice of
Withdrawal and that my option for the current period will automatically
terminate, and that no further Contributions for the purchase of shares can be
made by me during the Offering Period.

     The undersigned further understands and agrees that he or she shall be
eligible to participate in succeeding Offering Periods only by delivering to the
Company a new Subscription Agreement.

Dated:
       -------------------                    ----------------------------------
                                                     Signature of Employee

                                              ----------------------------------
                                                    Social Security Number