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                                                                    EXHIBIT 10.1

                                  TOLERRX, INC.

                              AMENDED AND RESTATED
                           2000 EQUITY INCENTIVE PLAN

1.   PURPOSE

     This Plan is intended to encourage ownership of Common Stock by employees,
consultants and directors of the Company and its Affiliates and to provide
additional incentive for them to promote the success of the Company's business.
The Plan is intended to be an incentive stock option plan within the meaning of
Section 422 of the Code but not all Awards granted hereunder are required to be
Incentive Options.

2.   DEFINITIONS

     As used in the Plan the following terms shall have the respective meanings
set out below, unless the context clearly requires otherwise:

     2.1.  ACCELERATE, ACCELERATED, and ACCELERATION, when used with respect to
an Option, means that as of the time of reference such Option will become
exercisable with respect to some or all of the shares of Common Stock for which
it was not then otherwise exercisable by its terms, and, when used with respect
to Restricted Stock, means that the Risk of Forfeiture otherwise applicable to
such Common Stock shall expire with respect to some or all of the shares of
Restricted Stock then still otherwise subject to the Risk of Forfeiture.

     2.2.  ACQUIRING PERSON means, with respect to any Transaction or any
acquisition described in clause (ii) of the definition of Change of Control, the
surviving or acquiring person or entity in connection with such Transaction or
acquisition, as the case may be, PROVIDED THAT if such surviving or acquiring
person or entity is controlled, directly or indirectly, by any other person or
entity (an "ULTIMATE PARENT ENTITY") that is not itself controlled by any entity
or person that is not a natural person, the term "ACQUIRING PERSON" shall mean
such Ultimate Parent Entity.

     2.3.  AFFILIATE means, with respect to any person or entity, any other
person or entity controlling, controlled by or under common control with the
first person or entity.

     2.4.  AWARD means any grant or sale pursuant to the Plan of Options,
Restricted Stock, or Stock Grants.

     2.5.  AWARD AGREEMENT means an agreement between the Company and the
recipient of an Award, setting forth the terms and conditions of the Award.

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     2.6.  BENEFICIAL OWNERSHIP has the meaning ascribed to such term in Rule
13d-3, or any successor rule thereto, promulgated by the Securities and Exchange
Commission pursuant to the Exchange Act.

     2.7.  BOARD means the Company's Board of Directors.

     2.8.  CHANGE OF CONTROL means (i) the closing of any Sale of the Company
Transaction or (ii) the direct or indirect acquisition, in a single transaction
or a series of related transactions, by any person or Group (other than the
Company or a Controlled Affiliate of the Company) of Beneficial Ownership of
previously outstanding shares of capital stock of the Company if (A) immediately
after such acquisition, such person or Group, together with their respective
Affiliates, shall own or hold shares of capital stock of the Company possessing
at least twenty-five percent (25%) of the total voting power of the outstanding
capital stock of the Company, (B) immediately prior to such acquisition, such
person or Group, together with their respective Affiliates, did not own or hold
shares of capital stock of the Company possessing at least twenty-five percent
(25%) of the total voting power of the outstanding capital stock of the Company,
and (C) within thirty (30) days after the Company is notified or first becomes
aware of such acquisition, whichever is earlier, a majority of the members of
the Board of Directors of the Company as constituted immediately prior to such
acquisition do not consent in writing to exclude such acquisition from the scope
of this definition.

     2.9.  CODE means the Internal Revenue Code of 1986, as amended from time to
time, or any successor statute thereto, and any regulations issued from time to
time thereunder.

     2.10. CONTROLLED AFFILIATE means, with respect to any person or entity, any
other person or entity that is controlled by such person or entity.

     2.11. COMMITTEE means any committee of the Board delegated responsibility
by the Board for the administration of the Plan, as provided in Section 5 of the
Plan. For any period during which no such committee is in existence, "Committee"
shall mean the Board and all authority and responsibility assigned the Committee
under the Plan shall be exercised, if at all, by the Board.

     2.12. COMMON STOCK means common stock, par value $0.001 per share, of the
Company.

     2.13. COMPANY means TolerRx, Inc., a corporation organized under the laws
of the State of Delaware.

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

     2.15. GRANT DATE means the date as of which an Option is granted, as
determined under Section 7.1(a).

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     2.16. GROUP has the meaning ascribed to such term in Section 13(d)(3) of
the Exchange Act or any successor section thereto.

     2.17. INCENTIVE OPTION means an Option which by its terms is to be treated
as an "incentive stock option" within the meaning of Section 422 of the Code.

     2.18. MARKET VALUE means the value of a share of Common Stock on any date
as determined by the Committee.

     2.19. NONSTATUTORY OPTION means any Option that is not an Incentive Option.

     2.20. OPTION means an option to purchase shares of Common Stock.

     2.21. OPTIONEE means a Participant to whom an Option shall have been
granted under the Plan.

     2.22. PARTICIPANT means any holder of an outstanding Award under the Plan.

     2.23. PLAN means this Amended and Restated 2000 Equity Incentive Plan of
the Company, as amended and in effect from time to time.

     2.24. RESTRICTED STOCK means a grant or sale of shares of Common Stock to a
Participant subject to a Risk of Forfeiture.

     2.25. RESTRICTION PERIOD means the period of time, established by the
Committee in connection with an Award of Restricted Stock, during which the
shares of Restricted Stock are subject to a Risk of Forfeiture described in the
applicable Award Agreement.

     2.26. RISK OF FORFEITURE means a limitation on the right of a Participant
to retain an Award of Restricted Stock, including a right in the Company to
reacquire such Restricted Stock at less than its then Market Value, arising
because of the occurrence or non-occurrence of specified events or conditions.

     2.27. SALE OF THE COMPANY TRANSACTION means any Transaction in which the
stockholders of the Company immediately prior to such Transaction, together with
any and all of such stockholders' Affiliates, do not own or hold, immediately
after consummation of such Transaction, shares of capital stock of the Acquiring
Person in connection with such Transaction possessing at least a majority of the
total voting power of the outstanding capital stock of such Acquiring Person.

     2.28. SECURITIES ACT means the Securities Act of 1933, as amended.

     2.29. STOCK GRANT means the grant of shares of Common Stock not subject to
restrictions or other forfeiture conditions.

     2.30. TEN PERCENT OWNER means a person who owns, or is deemed within the
meaning of Section 422(b)(6) of the Code to own, stock possessing more than 10%
of the total combined voting power of all classes of stock of the Company (or
any parent or

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subsidiary corporations of the Company, as defined in Section 424(e) and (f),
respectively, of the Code). Whether a person is a Ten Percent Owner shall be
determined with respect to each Option based on the facts existing immediately
prior to the Grant Date of such Option.

     2.31. TRANSACTION means any merger or consolidation of the Company with or
into another person or entity or the sale or transfer of all or substantially
all of the assets of the Company, in each case in a single transaction or in a
series of related transactions.

3.   TERM OF THE PLAN

     Unless the Plan shall have been earlier terminated by the Board, Awards may
be granted under this Plan at any time in the period commencing on the effective
date of approval of the Plan by the Board and ending immediately prior to the
tenth anniversary of the earlier of the adoption of the Plan by the Board or
approval of the Plan by the Company's stockholders. Awards granted pursuant to
the Plan within such period shall not expire solely by reason of the termination
of the Plan. Awards of Incentive Options granted prior to stockholder approval
of the Plan are hereby expressly conditioned upon such approval, but in the
event of the failure of the stockholders to approve the Plan shall thereafter
and for all purposes be deemed to constitute Nonstatutory Options.

4.   STOCK SUBJECT TO THE PLAN

     Subject to adjustment in accordance with the provisions of Section 8 of the
Plan, the aggregate number of shares of Common Stock that may initially be
issued pursuant to or subject to outstanding Awards granted under the Plan
will not exceed 3,000,000. Notwithstanding the foregoing, and subject to
adjustment in accordance with the provisions of Section 8 of the Plan, no
more than an aggregate of 5,000,000 shares of Stock may be issued pursuant to
the exercise of Incentive Stock Options granted under the Plan. For purposes
of applying the foregoing limitations, if any Option expires, terminates, or
is cancelled for any reason without having been exercised in full, or if any
Award of Restricted Stock is forfeited by the recipient, the shares not
purchased by the Optionee or forfeited by the recipient shall again be
available for Awards thereafter to be granted under the Plan. Shares of
Common Stock issued pursuant to the Plan may be either authorized but
unissued shares or shares held by the Company in its treasury.

5.   ADMINISTRATION

     The Plan shall be administered by the Committee; PROVIDED, HOWEVER, that at
any time and on any one or more occasions the Board may itself exercise any of
the powers and responsibilities assigned the Committee under the Plan and when
so acting shall have

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the benefit of all of the provisions of the Plan pertaining to the Committee's
exercise of its authorities hereunder; AND PROVIDED FURTHER that the Committee
may delegate to an executive officer or officers the authority to grant Awards
hereunder to employees who are not officers, and to consultants, in accordance
with such guidelines as the Committee shall set forth at any time or from time
to time. Subject to the provisions of the Plan, the Committee shall have
complete authority, in its discretion, to make or to select the manner of making
all determinations with respect to each Award to be granted by the Company under
the Plan in addition to any other determination allowed the Committee under the
Plan including, without limitation: (a) the employee, consultant or director to
receive the Award; (b) the form of Award; (c) whether an Option (if granted to
an employee) will be an Incentive Option or a Nonstatutory Option; (d) the time
of granting an Award; (e) the number of shares subject to an Award; (f) the
exercise price of an Option or purchase price for shares of Restricted Stock or
for a Stock Grant and the method of payment of such exercise price or such
purchase price; (g) the term of an Option; (h) the vesting period of shares of
Restricted Stock and any acceleration thereof; (i) the exercise date or dates of
an Option and any acceleration thereof; and (j) the effect of termination of any
employment, consulting or Board member relationship with the Company or any of
its Affiliates on the subsequent exercisability of an Option or on the Risk of
Forfeiture of Restricted Stock. In making such determinations, the Committee may
take into account the nature of the services rendered by the respective
employees, consultants and directors, their present and potential contributions
to the success of the Company and its Affiliates, and such other factors as the
Committee in its discretion shall deem relevant. Subject to the provisions of
the Plan, the Committee shall also have complete authority to interpret the
Plan, to prescribe, amend and rescind rules and regulations relating to it, to
determine the terms and provisions of the respective Award Agreements (which
need not be identical), and to make all other determinations necessary or
advisable for the administration of the Plan. The Committee'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 the Plan or
an Award made pursuant to hereto.

6.   AUTHORIZATION AND ELIGIBILITY

     The Committee may grant from time to time and at any time prior to the
termination of the Plan one or more Awards, either alone or in combination with
any other Awards, to any employee of or consultant to one or more of the Company
and its Affiliates or to any non-employee member of the Board or of any board of
directors (or similar governing authority) of any Affiliate. However, only
employees of the Company, and of any parent or subsidiary corporations of the
Company, as defined in Sections 424(e) and (f), respectively, of the Code, shall
be eligible for the grant of an Incentive Option. Further, in no event shall the
number of shares of Common Stock covered by Options or other Awards granted to
any one person in any one calendar year (or portion of a year) ending after such
date exceed thirty (30%) of the aggregate number of shares of Common Stock
subject to the Plan.

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     Each grant of an Award shall be subject to all applicable terms and
conditions of the Plan (including but not limited to any specific terms and
conditions applicable to that type of Award set out in the following Section),
and such other terms and conditions, not inconsistent with the terms of the
Plan, as the Committee may prescribe. No prospective Participant shall have any
rights with respect to an Award, unless and until such Participant has executed
an agreement evidencing the Award, delivered a fully executed copy thereof to
the Company, and otherwise complied with the applicable terms and conditions of
such Award.

7.   SPECIFIC TERMS OF AWARDS

     7.1.  OPTIONS.

           (a)  DATE OF GRANT. The granting of an Option shall take place at the
time specified in the Award Agreement. Only if expressly so provided in the
applicable Award Agreement shall the Grant Date be the date on which the Award
Agreement shall have been duly executed and delivered by the Company and the
Optionee.

           (b)  EXERCISE PRICE. The price at which shares of Common Stock may be
acquired under each Incentive Option shall be not less than 100% of the Market
Value of Common Stock on the Grant Date, or not less than 110% of the Market
Value of Common Stock on the Grant Date if the Optionee is a Ten Percent Owner.
The price at which shares may be acquired under each Nonstatutory Option shall
not be so limited solely by reason of this Section.

           (c)  OPTION PERIOD. No Incentive Option may be exercised on or after
the tenth anniversary of the Grant Date, or on or after the fifth anniversary of
the Grant Date if the Optionee is a Ten Percent Owner. The Option period under
each Nonstatutory Option shall not be so limited solely by reason of this
Section.

           (d)  EXERCISABILITY. An Option may be immediately exercisable or
become exercisable in such installments, cumulative or non-cumulative, as the
Committee may determine. In the case of an Option not otherwise immediately
exercisable in full, the Committee may Accelerate such Option in whole or in
part at any time; PROVIDED, HOWEVER, that in the case of an Incentive Option,
any such Acceleration of such Incentive Option would not cause such Incentive
Option to fail to comply with the provisions of Section 422 of the Code or the
Optionee consents to such Acceleration.

           (e)  EFFECT OF TERMINATION OF EMPLOYMENT, CONSULTING OR BOARD MEMBER
RELATIONSHIP. Unless the Committee shall provide otherwise with respect to any
Option, if the Optionee's employment, consulting or Board member relationship
with the Company and its Affiliates ends for any reason, including because an
entity with which the Optionee has an employment, consulting or Board member
relationship ceases to be an Affiliate of the Company, any outstanding Option
held by the Optionee shall cease to be exercisable in any respect not later than
ninety (90) days following that event and, for the period it remains exercisable
following that event, shall be exercisable only to the extent exercisable at the
date of that event. Military or sick leave or other bona fide leave

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shall not be deemed a termination of employment, PROVIDED that it does not
exceed the longer of ninety (90) days or the period during which the absent
Optionee's reemployment rights, if any, are guaranteed by statute or by
contract.

           (f)  TRANSFERABILITY. Except as otherwise provided in this subsection
(f), Options shall not be transferable, and no Option or interest therein may be
sold, transferred, pledged, assigned, or otherwise alienated or hypothecated,
other than by will or by the laws of descent and distribution. Except as
otherwise provided in this subsection (f), all of a Participant's rights in any
Option may be exercised during the life of the Participant only by the
Participant or the Participant's legal representative. However, the Committee
may, at or after the grant of a Nonstatutory Option, provide that such Option
may be transferred by the recipient to a family member; PROVIDED, HOWEVER, that
any such transfer is without payment of any consideration whatsoever and that no
transfer of an Option shall be valid unless first approved by the Committee,
acting in its sole discretion. For this purpose, "family member" means any
child, stepchild, grandchild, parent, stepparent, spouse, former spouse,
sibling, niece, nephew, mother-in-law, father-in-law, son-in-law,
daughter-in-law, brother-in-law, or sister-in-law, including adoptive
relationships, any person sharing the Participant's household (other than a
tenant or employee), a trust in which the foregoing persons have more than fifty
percent (50%) of the beneficial interests, a foundation in which the foregoing
persons (or the Participant) control the management of assets, and any other
entity in which these persons (or the Participant) own more than fifty percent
(50%) of the voting interests.

           (g)  METHOD OF EXERCISE. An Option may be exercised by the Optionee
giving written notice, in the manner provided in Section 15, specifying the
number of shares of Common Stock with respect to which the Option is then being
exercised. The notice shall be accompanied by payment in the form of cash or
check payable to the order of the Company in an amount equal to the exercise
price of the shares of Common Stock to be purchased or, if the Committee had so
authorized on the grant of an Incentive Option or on or after grant of a
Nonstatutory Option (and subject to such conditions, if any, as the Committee
may deem necessary to avoid adverse accounting effects to the Company) by
delivery to the Company of shares of Common Stock having a Market Value equal to
the exercise price of the shares to be purchased. Payment may also be made
through and under the terms and conditions of any formal cashless exercise
program authorized by the Company entailing the sale of Common Stock subject to
an Option in a brokered transaction (other than to the Company). Receipt by the
Company of such notice and payment in any authorized or combination of
authorized means shall constitute the exercise of the Option. Within thirty (30)
days thereafter but subject to the remaining provisions of the Plan, the Company
shall deliver or cause to be delivered to the Optionee or his agent a
certificate or certificates for the number of shares then being purchased. Such
shares shall be fully paid and nonassessable. Notwithstanding any of the
foregoing provisions in this subsection (g) to the contrary, (A) no Option shall
be considered to have been exercised unless and until all of the provisions
governing such exercise specified in the Plan and in the relevant Award
Agreement shall have been duly complied with; and (B) the obligation of the
Company to issue any shares upon exercise

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of an Option is subject to the provisions of Section 9.1 hereof and to
compliance by the Optionee with all of the provisions of the Plan and the
relevant Award Agreement.

           (h)  LIMIT ON INCENTIVE OPTION CHARACTERIZATION. An Incentive Option
shall be considered to be an Incentive Option only to the extent that the number
of shares of Common Stock for which the Option first becomes exercisable in a
calendar year do not have an aggregate Market Value (as of the date of the grant
of the Option) in excess of the "current limit". The current limit for any
Optionee for any calendar year shall be $100,000 MINUS the aggregate Market
Value at the date of grant of the number of shares of Common Stock available for
purchase for the first time in the same year under each other Incentive Option
previously granted to the Optionee under the Plan, and under each other
incentive stock option previously granted to the Optionee under any other
incentive stock option plan of the Company and its Affiliates. Any shares of
Common Stock which would cause the foregoing limit to be violated shall be
deemed to have been granted under a separate Nonstatutory Option, otherwise
identical in its terms to those of the Incentive Option.

           (i)  NOTIFICATION OF DISPOSITION. Each person exercising any
Incentive Option granted under the Plan shall be deemed to have covenanted with
the Company to report to the Company any disposition of such shares prior to the
expiration of the holding periods specified by Section 422(a)(1) of the Code
and, if and to the extent that the realization of income in such a disposition
imposes upon the Company federal, state, local or other withholding tax
requirements, or any such withholding is required to secure for the Company an
otherwise available tax deduction, to remit to the Company an amount in cash
sufficient to satisfy those requirements.

           (j)  RIGHTS PENDING EXERCISE. No person holding an Option shall be
deemed for any purpose to be a stockholder of the Company with respect to any of
the shares of Common Stock issuable pursuant to his Option, except to the extent
that the Option shall have been exercised with respect thereto and, in addition,
a certificate shall have been issued therefor and delivered to such holder or
his agent.

     7.2.  RESTRICTED STOCK.

           (a)  PURCHASE PRICE. Shares of Restricted Stock shall be issued under
the Plan for such consideration, in cash, other property or services, or any
combination thereof, as is determined by the Committee.

           (b)  ISSUANCE OF CERTIFICATES. Subject to subsection (c) below, each
Participant receiving an Award of Restricted Stock shall be issued a stock
certificate in respect of such shares of Restricted Stock. Such certificate
shall be registered in the name of such Participant, and, if applicable, shall
bear an appropriate legend referring to the terms, conditions, and restrictions
applicable to such Award substantially in the following form:

     The transferability of this certificate and the shares represented by this
     certificate are subject to the terms and conditions of the TolerRx, Inc.

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     Amended and Restated 2000 Equity Incentive Plan and an Award Agreement
     entered into by the registered owner and TolerRx, Inc. Copies of such Plan
     and Agreement are on file in the offices of TolerRx, Inc.

           (c)  ESCROW OF SHARES. The Committee may require that the stock
certificates evidencing shares of Restricted Stock be held in custody by a
designated escrow agent (which may but need not be the Company) until the
restrictions thereon shall have lapsed, and that the Participant deliver a stock
power, endorsed in blank, relating to the Common Stock covered by such Award.

           (d)  RESTRICTIONS AND RESTRICTION PERIOD. During the Restriction
Period applicable to shares of Restricted Stock, such shares shall be subject to
limitations on transferability and a Risk of Forfeiture arising on the basis of
such conditions related to the performance of services, Company or Affiliate
performance or otherwise as the Committee may determine and provide for in the
applicable Award Agreement. Any such Risk of Forfeiture may be waived or
terminated, or the Restriction Period shortened, at any time by the Committee on
such basis as it deems appropriate.

           (e)  RIGHTS PENDING LAPSE OF RISK OF FORFEITURE OR FORFEITURE OF
AWARD. Except as otherwise provided in the Plan or the applicable Award
Agreement, at all times prior to lapse of any Risk of Forfeiture applicable to,
or forfeiture of, an Award of Restricted Stock, the Participant shall have all
of the rights of a stockholder of the Company, including the right to vote the
shares of Restricted Stock.

           (f)  EFFECT OF TERMINATION OF EMPLOYMENT, CONSULTING OR BOARD MEMBER
RELATIONSHIP. Unless otherwise determined by the Committee at or after grant and
subject to the applicable provisions of the Award Agreement, if a Participant's
employment, consulting or Board member relationship with the Company and its
Affiliates ends for any reason during the Restriction Period, including because
an entity with which the Participant has an employment, consulting or Board
member relationship ceases to be an Affiliate of the Company, all shares of
Restricted Stock still subject to Risk of Forfeiture shall be forfeited or
otherwise subject to return to or repurchase by the Company on the terms
specified in the Award Agreement; PROVIDED, HOWEVER, that military or sick leave
or other bona fide leave shall not be deemed a termination of employment, if it
does not exceed the longer of ninety (90) days or the period during which the
absent Participant's reemployment rights, if any, are guaranteed by statute or
by contract.

           (g)  LAPSE OF RESTRICTIONS. If and when the Restriction Period
expires without a prior forfeiture of the Restricted Stock, the certificates for
such shares shall be delivered to the Participant promptly if not theretofore so
delivered.

     7.3.  STOCK GRANTS.

           (a)  IN GENERAL. Stock Grants shall be issued for such consideration,
in cash, other property or services, or any combination thereof, as is
determined by the Committee. Without limiting the generality of the foregoing,
Stock Grants may be

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awarded in such circumstances as the Committee deems appropriate, including
without limitation in recognition of significant contributions to the success of
the Company or its Affiliates or in lieu of compensation otherwise already due.
Stock Grants shall be made without forfeiture conditions of any kind.

           (b)  ISSUANCE OF CERTIFICATES. Each Participant receiving a Stock
Grant shall be issued a stock certificate in respect of such Stock Grant. Such
certificate shall be registered in the name of such Participant, and, if
applicable, shall bear an appropriate legend referring to the terms, conditions,
and restrictions applicable to such Award substantially in the following form:

     The transferability of this certificate and the shares represented by this
     certificate are subject to the terms and conditions of the TolerRx, Inc.
     Amended and Restated 2000 Equity Incentive Plan. A copy of such Plan is on
     file in the offices of TolerRx, Inc.

     7.4.  AWARDS TO PARTICIPANTS OUTSIDE THE UNITED STATES. The Committee may
modify the terms of any Award under the Plan granted to a Participant who is, at
the time of grant or during the term of the Award, resident or primarily
employed outside of the United States in any manner deemed by the Committee to
be necessary or appropriate in order that such Award shall conform to laws,
regulations, and customs of the country in which the Participant is then
resident or primarily employed, or so that the value and other benefits of the
Award to the Participant, as affected by foreign tax laws and other restrictions
applicable as a result of the Participant's residence or employment abroad,
shall be comparable to the value of such an Award to a Participant who is
resident or primarily employed in the United States. An Award may be modified
under this Section 7.4 in a manner that is inconsistent with the express terms
of the Plan, so long as such modifications will not contravene any applicable
law or regulation.

     7.5.  AUTOMATIC GRANTS TO NON-MANAGEMENT DIRECTORS.

           (a)  Each non-management director shall be granted upon his
initial election to the board an Award covering 30,000 shares of Common
Stock, which Award shall be, at the election of each non-management director,
in the form of either (i) an Option which shall become exercisable,
cumulatively, in a series of three (3) successive, equal annual installments,
with the first installment to become exercisable on, or at any time after,
the first year anniversary of the Grant Date or (ii) Restricted Stock for
which the Risk of Forfeiture shall expire in a series of three (3)
successive, equal annual installments, with the first installment to expire
on, or at any time after, the first year anniversary of the grant date of the
Award.

           (b)  Each non-management director shall be granted automatically
each year on the anniversary of the first date of his or her term of service on
the Board an Award

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covering 20,000 shares of Common Stock, which Award shall be, at the election
of each non-management director, in the form of either (i) an Option which
shall become fully exercisable on the first year anniversary of the Grant
Date or (ii) Restricted Stock for which the Risk of Forfeiture shall expire
on the first year anniversary of the grant date of the Award.

8.   ADJUSTMENT PROVISIONS

     8.1.  ADJUSTMENT FOR CORPORATE ACTIONS. All of the share numbers set forth
in the Plan reflect the capital structure of the Company as of November 3,
2003. Subject to the provisions of Section 8.2, if subsequent to such date
the outstanding shares of Common Stock (or any other securities covered by
the Plan by reason of the prior application of this Section) are increased,
decreased, or exchanged for a different number or kind of shares or other
securities, or if additional shares or new or different shares or other
securities are distributed with respect to such shares of Common Stock or
other securities, through merger, consolidation, sale of all or substantially
all the property of the Company, reorganization, recapitalization,
reclassification, stock dividend, stock split, reverse stock split, or other
distribution with respect to such shares of Common Stock, or other
securities, an appropriate and proportionate adjustment will be made in (i)
the maximum numbers and kinds of shares provided in Section 4, (ii) the
numbers and kinds of shares or other securities subject to the then
outstanding Awards, (iii) the exercise price for each share or other unit of
any other securities subject to then outstanding Options (without change in
the aggregate purchase price as to which such Options remain exercisable),
and (iv) the repurchase price of each share of Restricted Stock then subject
to a Risk of Forfeiture in the form of a Company repurchase right.

        8.2.  CHANGE OF CONTROL. Subject to the applicable provisions of the
Award Agreement, in the event of a Change of Control, the Board of Directors
shall have the discretion, exercisable in advance of, at the time of, or
(except to the extent otherwise provided below) at any time after, such
Change of Control, to provide for any or all of the following (subject to and
upon such terms as the Board of Directors may deem appropriate): (A) the
Acceleration of any or all outstanding Options (including Options that are
assumed or replaced pursuant to clause (C) below) that are not exercisable in
full at the time the Change of Control, such Acceleration to become effective
at the time of the Change of Control, or at such time following the Change of
Control that the employment, consulting or Board member relationship of the
applicable Optionee or Optionees with the Company and its Affiliates
terminates, or at such other time or times as the Board of Directors shall
determine; (B) the termination of any or all of the Company's repurchase
rights with respect to Restricted Stock Awards, such termination to become
effective at the time of the Change of Control, or at such time following the
Change of Control that the employment, consulting or Board member
relationship with the Company and its Affiliates of the Participant or
Participants that hold such Restricted

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                                     - 12 -

Stock Awards terminates, or at such other time or times as the Board of
Directors shall determine; (C) the assumption of outstanding Options, or the
substitution of outstanding Options with equivalent options, by the acquiring
or succeeding corporation or entity (or an affiliate thereof); or (D) the
termination of all Options (other than Options that are assumed or
substituted pursuant to clause (C) above) that remain outstanding at the time
of the consummation of the Change of Control, PROVIDED THAT, the Board of
Directors shall have made the determination to effect such termination prior
to the consummation of the Change of Control and the Board of Directors shall
have given, or caused to be given, to all Optionees written notice of such
potential termination at least five (5) business days prior to the
consummation of the Change of Control. Notwithstanding the foregoing, subject
to the applicable provisions of the Award Agreement, in the event of the
closing of a Sale of the Company Transaction in which the acquiring or
succeeding corporation or entity does not have an equity incentive plan under
which all outstanding Options may be assumed or pursuant to which options may
be issued in substitution of all outstanding Options, the vesting of all
outstanding Options shall Accelerate by one year, such Acceleration to become
effective upon the closing of the Sale of the Company Transaction. The
provisions of this Section 8.2 shall not be construed as to limit or restrict
in any way the Committee's general authority under Sections 7.1(d) or 7.2(d)
hereof to Accelerate Options in whole or in part at any time or to waive or
terminate at any time any Risk of Forfeiture applicable to shares of
Restricted Stock. Each outstanding Option that is assumed in connection with
a Change of Control, or is otherwise to continue in effect subsequent to a
Change of Control, will be appropriately adjusted, immediately after the
Change of Control, as to the number and class of securities and the price at
which it may be exercised in accordance with Section 8.1.

     8.3.  DISSOLUTION OR LIQUIDATION.   Upon dissolution or liquidation of the
Company, each outstanding Option shall terminate, but the Optionee (if at the
time he or she has an employment, consulting or Board member relationship with
the Company or any of its Affiliates) shall have the right, immediately prior to
such dissolution or liquidation, to exercise the Option to the extent
exercisable on the date of such dissolution or liquidation.

     8.4.  RELATED MATTERS.   Any adjustment in Awards made pursuant to this
Section 8 shall be determined and made, if at all, by the Committee and shall
include any correlative modification of terms, including of Option exercise
prices, rates of vesting or exercisability, Risks of Forfeiture and applicable
repurchase prices for Restricted Stock, which the Committee may deem necessary
or appropriate so as to ensure that the rights of the Participants in their
respective Awards are not substantially diminished nor enlarged as a result of
the adjustment and corporate action other than as expressly contemplated in this
Section 8. No fraction of a share shall be purchasable or deliverable upon
exercise, but in the event any adjustment hereunder of the number of shares
covered by an Award shall cause such number to include a fraction of a share,
such number of shares shall be adjusted to the nearest smaller whole number of
shares. No adjustment of an Option exercise price per share pursuant to this
Section 8 shall result in an exercise price which is less than the par value of
the Common Stock.

<Page>

                                     - 13 -

9.   SETTLEMENT OF AWARDS

     9.1.  VIOLATION OF LAW. Notwithstanding any other provision of the Plan or
the relevant Award Agreement, if, at any time, in the reasonable opinion of the
Company, the issuance of shares of Common Stock covered by an Award may
constitute a violation of law, then the Company may delay such issuance and the
delivery of a certificate for such shares until (i) approval shall have been
obtained from such governmental agencies, other than the Securities and Exchange
Commission, as may be required under any applicable law, rule, or regulation and
(ii) in the case where such issuance would constitute a violation of a law
administered by or a regulation of the Securities and Exchange Commission, one
of the following conditions shall have been satisfied:

           (a)  the shares are at the time of the issue of such shares
effectively registered under the Securities Act; or

           (b)  the Company shall have determined, on such basis as it deems
appropriate (including an opinion of counsel in form and substance satisfactory
to the Company) that the sale, transfer, assignment, pledge, encumbrance or
other disposition of such shares or such beneficial interest, as the case may
be, does not require registration under the Securities Act or any applicable
state securities laws.

     9.2.  RESTRICTIONS ON RIGHTS IN STOCK. Any Common Stock to be issued
pursuant to Awards granted under the Plan shall be subject to such stop-transfer
orders and other restrictions as the Committee may deem advisable under the
rules, regulations, and other requirements of any stock exchange upon which the
Common Stock is then listed, and any applicable federal or state securities law,
and the Committee may cause a legend or legends to be put on any such
certificates to make appropriate reference to such restrictions.

     9.3.  INVESTMENT REPRESENTATIONS. The Company shall be under no obligation
to issue any shares covered by an Award unless the shares to be issued pursuant
to Awards granted under the Plan have been effectively registered under the
Securities Act or the Participant shall have made such written representations
to the Company (upon which the Company believes it may reasonably rely) as the
Company may deem necessary or appropriate for purposes of confirming that the
issuance of such shares will be exempt from the registration requirements of
that Act and any applicable state securities laws and otherwise in compliance
with all applicable laws, rules and regulations, including but not limited to
that the Participant is acquiring shares for his or her own account for the
purpose of investment and not with a view to, or for sale in connection with,
the distribution of any such shares.

     9.4.  REGISTRATION. If the Company shall deem it necessary or desirable to
register under the Securities Act or other applicable statutes any shares of
Common Stock issued or to be issued pursuant to Awards granted under the Plan,
or to qualify any such shares of Common Stock for exemption from the Securities
Act or other applicable statutes, then the Company shall take such action at its
own expense. The Company may

<Page>

                                     - 14 -

require from each recipient of an Award, or each holder of shares of Common
Stock acquired pursuant to the Plan, such information in writing for use in any
registration statement, prospectus, preliminary prospectus or offering circular
as is reasonably necessary for such purpose and may require reasonable indemnity
to the Company and its officers and directors from such holder against all
losses, claims, damage and liabilities arising from such use of the information
so furnished and caused by any untrue statement of any material fact therein or
caused by the omission to state a material fact required to be stated therein or
necessary to make the statements therein not misleading in the light of the
circumstances under which they were made.

     9.5.  LOCK-UP. Without the prior written consent of the Company or the
managing underwriter in any public offering of shares of Common Stock, no
Participant shall sell, make any short sale of, loan, grant any option for the
purchase of, pledge or otherwise encumber, or otherwise dispose of, any shares
of Common Stock during the one hundred-eighty (180) day period commencing on the
effective date of the registration statement relating to any underwritten public
offering of securities of the Company. The foregoing restrictions are intended
and shall be construed so as to preclude any Participant from engaging in any
hedging or other transaction that is designed to or reasonably could be expected
to lead to or result in, a sale or disposition of any shares of Common Stock
during such period even if such shares of Common Stock are or would be disposed
of by someone other than such Participant. Such prohibited hedging or other
transactions would include, without limitation, any short sale (whether or not
against the box) or any purchase, sale or grant of any right (including without
limitation any put or call option) with respect to any shares of Common Stock or
with respect to any security that includes, relates to, or derives any
significant part of its value from any shares of Common Stock. Without limiting
the generality of the foregoing provisions of this Section 9.5, if, in
connection with any underwritten public offering of securities of the Company,
the managing underwriter of such offering requires that the Company's directors
and officers enter into a lock-up agreement containing provisions that are more
restrictive than the provisions set forth in the preceding sentence, then (a)
each Participant (regardless of whether or not such Participant has complied or
complies with the provisions of clause (b) below) shall be bound by, and shall
be deemed to have agreed to, the same lock-up terms as those to which the
Company's directors and officers are required to adhere; and (b) at the request
of the Company or such managing underwriter, each Participant shall execute and
deliver a lock-up agreement in form and substance equivalent to that which is
required to be executed by the Company's directors and officers.

     9.6.  PLACEMENT OF LEGENDS; STOP ORDERS; ETC. Each share of Common Stock to
be issued pursuant to Awards granted under the Plan may bear a reference to the
investment representations made in accordance with Section 9.3 in addition to
any other applicable restrictions under the Plan, the terms of the Award and to
the fact that no registration statement has been filed with the Securities and
Exchange Commission in respect to such shares of Common Stock. All certificates
for shares of Common Stock or other securities delivered under the Plan shall be
subject to such stock transfer orders and other restrictions as the Committee
may deem advisable under the rules, regulations, and

<Page>

                                     - 15 -

other requirements of any stock exchange upon which the Common Stock is then
listed, and any applicable federal or state securities law, and the Committee
may cause a legend or legends to be placed on any such certificates to make
appropriate reference to such restrictions.

     9.7.  TAX WITHHOLDING. Whenever shares of Common Stock are issued or to be
issued pursuant to Awards granted under the Plan, the Company shall have the
right to require the recipient to remit to the Company an amount sufficient to
satisfy federal, state, local or other withholding tax requirements if, when,
and to the extent required by law (whether so required to secure for the Company
an otherwise available tax deduction or otherwise) prior to the delivery of any
certificate or certificates for such shares. The obligations of the Company
under the Plan shall be conditional on satisfaction of all such withholding
obligations and the Company shall, to the extent permitted by law, have the
right to deduct any such taxes from any payment of any kind otherwise due to the
recipient of an Award.

10.  RESERVATION OF STOCK

     The Company shall at all times during the term of the Plan and any
outstanding Options granted hereunder reserve or otherwise keep available such
number of shares of Common Stock as will be sufficient to satisfy the
requirements of the Plan (if then in effect) and such Options and shall pay all
fees and expenses necessarily incurred by the Company in connection therewith.

11.  NO SPECIAL SERVICE RIGHTS

     Nothing contained in the Plan or in any Award Agreement shall confer upon
any recipient of an Award any right with respect to the continuation of his or
her employment, consulting or Board member relationship with the Company (or any
Affiliate), or interfere in any way with the right of the Company (or any
Affiliate), subject to the terms of any separate employment, consulting or Board
member agreement or provision of law or corporate articles or by-laws to the
contrary, at any time to terminate such employment, consulting or Board member
agreement or to increase or decrease, or otherwise adjust, the other terms and
conditions of the recipient's employment, consulting or Board member
relationship with the Company and its Affiliates.

12.  NONEXCLUSIVITY OF THE PLAN

     Neither the adoption of the Plan by the Board nor the submission of the
Plan to the stockholders of the Company shall be construed as creating any
limitations on the power of the Board to adopt such other incentive arrangements
as it may deem desirable, including without limitation, the granting of stock
options and restricted stock other than under the Plan, and such arrangements
may be either applicable generally or only in specific cases.

<Page>

                                     - 16 -

13.  TERMINATION AND AMENDMENT OF THE PLAN

     The Board may at any time terminate the Plan or make such amendments or
modifications of the Plan as it shall deem advisable. In the event of the
termination of the Plan, the terms of the Plan shall survive any such
termination with respect to any Award that is outstanding on the date of such
termination, unless the holder of such Award agrees in writing to terminate such
Award or to terminate all or any of the provisions of the Plan that apply to
such Award. Unless the Board otherwise expressly provides, any amendment or
modification of the Plan shall affect the terms of any Award outstanding on the
date of such amendment or modification as well as the terms of any Award made
from and after the date of such amendment or modification; PROVIDED, HOWEVER,
that, except to the extent otherwise provided in the last sentence of this
paragraph, (i) no amendment or modification of the Plan shall apply to any Award
that is outstanding on the date of such amendment or modification if such
amendment or modification would reduce the number of shares subject to such
Award, increase the purchase price applicable to shares subject to such Award or
materially adversely affect the provisions applicable to such Award that relate
to the vesting or exercisability of such Award or of the shares subject to such
Award, (ii) no amendment or modification of the Plan shall apply to any
Incentive Option that is outstanding on the date of such amendment or
modification if such amendment or modification would result in such Incentive
Option no longer being treated as an "incentive stock option" within the meaning
of Section 422 of the Code and (iii) no amendment or modification of the Plan
shall apply to any Award that is outstanding on the date of such amendment or
modification unless such amendment or modification of the Plan shall also apply
to all other Awards outstanding on the date of such amendment or modification.
In the event of any amendment or modification of the Plan that is described in
clause (i), (ii) or (iii) of the foregoing proviso, such amendment or
modification of the Plan shall apply to any Award outstanding on the date of
such amendment or modification only if the recipient of such Award consents in
writing thereto.

     The Committee may amend or modify, prospectively or retroactively, the
terms of any Award theretofore granted without amending or modifying the terms
of the Plan itself, PROVIDED that as amended or modified such Award is
consistent with the terms of the Plan as in effect at the time of the amendment
or modification of such Award, but no such amendment or modification of such
Award shall, without the written consent of the recipient of such Award, reduce
the number of shares subject to such Award, increase the purchase price
applicable to shares subject to such Award, adversely affect the provisions
applicable to such Award that relate to the vesting or exercisability of such
Award or of the shares subject to such Award, otherwise materially adversely
affect the terms of such Award (except for amendments or modifications to the
terms of such Award or of the stock subject to such Award that are expressly
permitted by the terms of the Plan or that result from any amendment or
modification of the Plan in accordance with the provisions of the first
paragraph of this Section 13), or, if such Award is an Incentive Option, result
in such Incentive Option no longer being treated as an "incentive stock option"
within the meaning of Section 422 of the Code.

<Page>

                                     - 17 -

14.  INTERPRETATION OF THE PLAN

     In the event of any conflict between the provisions of this Plan and the
provisions of any applicable Award Agreement, the provisions of such Award
Agreement shall control, but insofar as possible the provisions of the Plan and
such Award Agreement shall be construed so as to give full force and effect to
all such provisions.

15.  NOTICES AND OTHER COMMUNICATIONS

     Any notice, demand, request or other communication hereunder to any party
shall be deemed to be sufficient if contained in a written instrument delivered
in person or duly sent by first class registered, certified or overnight mail,
postage prepaid, or telecopied with a confirmation copy by regular, certified or
overnight mail, addressed or telecopied, as the case may be, (i) if to the
recipient of an Award, at his or her residence address last filed with the
Company and (ii) if to the Company, at its principal place of business,
addressed to the attention of its Chief Executive Officer, or to such other
address or telecopier number, as the case may be, as the addressee may have
designated by notice to the addressor. All such notices, requests, demands and
other communications shall be deemed to have been received: (i) in the case of
personal delivery, on the date of such delivery; (ii) in the case of mailing,
when received by the addressee; and (iii) in the case of facsimile transmission,
when confirmed by facsimile machine report.

16.  GOVERNING LAW

     The Plan and all Award Agreements and actions taken thereunder shall be
governed, interpreted and enforced in accordance with the laws of the
Commonwealth of Massachusetts, without regard to the conflict of laws principles
thereof.

<Page>
                                  TOLERRX, INC.

                       NONSTATUTORY STOCK OPTION AGREEMENT


         NONSTATUTORY STOCK OPTION AGREEMENT, dated as of _______________ (this
"Agreement"), between TolerRx, Inc., a Delaware corporation (the "Company"), and
___________________ (the "Optionee").

         1. GRANT OF OPTION.

         Pursuant to the Company's Amended and Restated 2000 Equity Incentive
Plan, as amended from time to time (the "Plan"), a copy of which is attached
hereto as Exhibit A, the Company grants to the Optionee an option (the "Option")
to purchase from the Company all or any part of a total of _____________ shares
(the "Optioned Shares") of the Company's common stock, $.001 par value, at a
price of $____________ per share. The Option is granted as of _________________
(the "Grant Date").

         2. CHARACTER OF OPTION.

         The Option is not intended to be treated as an "incentive stock option"
within the meaning of Section 422 of the Internal Revenue Code of 1986, as
amended (the "Code"), but as a nonstatutory stock option within the meaning of
the Code.

         3. DURATION OF OPTION.

         Unless subject to earlier expiration pursuant to the terms of the Plan,
the Option shall expire on ___________.

         4. EXERCISE OF OPTION.

         Until its  expiration  pursuant to Section 3 hereof,  the Option may be
exercised  in the manner  specified  in Section  7.1(f) of the Plan as  follows:
[INSERT VESTING SCHEDULE].

         5. TRANSFER OF OPTIONS.

         The Option may not be transferred except by prior written consent of
the Company.

         6. INCORPORATION OF PLAN TERMS.

         The Option is granted subject to all of the applicable terms and
provisions of the Plan, including but not limited to the limitations on the
Company's obligation to deliver the Optioned Shares upon exercise thereof as set
forth in Section 9 of the Plan.
<Page>
         7. MISCELLANEOUS.

         This Agreement shall be construed and enforced in accordance with the
laws of the Commonwealth of Massachusetts and shall be binding upon and inure to
the benefit of any successor or assign of the Company and any assign, executor,
administrator, trustee, guardian, or other legal representative of the Optionee.

         IN WITNESS WHEREOF, the parties have executed this Agreement as a
sealed instrument as of the date first above written.


TOLERRX, INC.                                 OPTIONEE


By:
     --------------------------------         --------------------------------
        Douglas J. Ringler                       [Insert Name of Optionee]
        President

                                              Address:

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

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

                                              --------------------------------
<Page>
                                  TOLERRX, INC.

                        INCENTIVE STOCK OPTION AGREEMENT


         INCENTIVE STOCK OPTION AGREEMENT, dated as of ___________ (this
"Agreement"), between TolerRx, Inc., a Delaware corporation (the "Company"), and
_________________ (the "Optionee").

         1. GRANT OF OPTION.

         Pursuant to the Company's Amended and Restated 2000 Equity Incentive
Plan, as amended from time to time (the "Plan"), a copy of which is attached
hereto as Exhibit A, the Company grants to the Optionee an option (the "Option")
to purchase from the Company all or any part of a total of _________________
shares (the "Optioned Shares") of the Company's common stock, $.001 par value,
at a price of $_____________ per share. The Option is granted as of
_______________ (the "Grant Date").

         2. CHARACTER OF OPTION.

         The Option is intended to be treated as an "incentive stock option"
within the meaning of Section 422 of the Internal Revenue Code of 1986, as
amended.

         3. DURATION OF OPTION.

         Unless subject to earlier expiration pursuant to the terms of the Plan,
the Option shall expire on the earlier of (i) the tenth anniversary of the Grant
Date or (ii) the 90th day following the termination of the Optionee's employment
with the Company for any reason.

         4. EXERCISE OF OPTION.

         Until its expiration pursuant to Section 3 hereof, the Option may be
exercised in the manner specified in Section 7.1(f) of the Plan as follows:
[INSERT VESTING SCHEDULE (e.g., (i) ____________ percent (___%) of the Optioned
Shares shall vest on and after _________ __, 200_, and (ii) the remaining
_______________ percent (___%) of the Optioned Shares shall vest in a series of
____________ (___) equal installments, in portions of whole shares as nearly
equal as practicable, with each installment vesting on _____________, until all
of the Optioned Shares are fully vested.]

         5. Transfer of Options.

         The Option may not be transferred except by will or the laws of descent
and distribution, and, during the lifetime of the Optionee, may be exercised
only by the Optionee.
<Page>
         6. INCORPORATION OF PLAN TERMS.

         The Option is granted subject to all of the applicable terms and
provisions of the Plan, including but not limited to the limitations on the
Company's obligation to deliver Optioned Shares upon exercise thereof as set
forth in Section 9 of the Plan.

         7. MISCELLANEOUS.

         This Agreement shall be construed and enforced in accordance with the
laws of the Commonwealth of Massachusetts and shall be binding upon and inure to
the benefit of any successor or assign of the Company and any executor,
administrator, trustee, guardian, or other legal representative of the Optionee.

         IN WITNESS WHEREOF, the parties have executed this Agreement as a
sealed instrument as of the date first above written.


TOLERRX, INC.                                 OPTIONEE


By:  --------------------------------         --------------------------------
        Douglas J. Ringler                       [Insert Name of Optionee]
        President

                                              Address:

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

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

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