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                                                                   EXHIBIT 10.11

                        DATED 28 SEPTEMBER 2001

                       BTG INTERNATIONAL LIMITED

                                - and -

                             TOLERRX, INC

                           LICENCE AGREEMENT

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                                 INDEX

<Table>
<Caption>
Clause                     Heading                                          Page
------                     -------                                          ----
<S>                        <C>                                               <C>
 1                         Definitions                                       1
 2                         Payments                                          7
 3                         Commencement and duration                         7
 4                         Licences and Patents                              8
 5                         Exclusivity                                       10
 6                         Know-how                                          11
 7                         Royalties                                         12
 8                         Accounting for royalties                          16
 9                         Currency and taxes                                17
10                         Verification                                      17
11                         Suspension of royalties and Payments              17
12                         Undertakings by the Licensees                     18
13                         Marking                                           19
14                         Supplementary Protection                          19
                             Certificates
15                         Exclusion of liability: Indemnity
                           and Warranties                                    20
16                         Termination                                       22
17                         Rights on termination                             23
18                         Miscellaneous                                     25
19                         Notices                                           25
20                         Law and Jurisdiction                              26
21                         Force Majeure                                     26
First Schedule             The Patents                                       27
Second Schedule            The Cell Lines                                    30
Third Schedule             The Genetic Material                              31
Fourth Schedule            Sub-Licence Terms                                 32
</Table>

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

THIS DEED is made the 28 day of September 2001 BETWEEN:

(1) BTG INTERNATIONAL LIMITED whose company registration number in England is
2664412 and whose registered office is at 10 Fleet Place, Limeburner Lane,
London, EC4M 7SB, England, United Kingdom ("BTG"); and

(2) TOLERRX, INC a company registered under the laws of Delaware and whose
principal office is at 675 Massachusetts Avenue, 14th Floor, Cambridge, MA
02139, USA ("the Licensee").

WHEREAS:

A.      BTG is the registered proprietor and/or is beneficially entitled to the
patents and patent applications specified in the First Schedule.

B.      BTG owns or controls certain technical information and data, and the
copyright in such items, all relating to the inventions which are the subject of
the said patents and patent applications.

C.      The Licensee has requested the grant of licences under such patents,
patent applications, information and data, and BTG is willing to grant such
licences on the terms set out below.

NOW in consideration of the mutual undertakings contained herein, IT IS HEREBY
AGREED as follows:

1.      DEFINITIONS

1.1     IN this Agreement the following terms shall have the following meanings:

        1.1.1   "Accounting Date"       31 March, 30 June, 30 September and 31
                                        December in each year;

        1.1.2   "Accounting Period"     the period commencing on the Effective
                                        Date and ending on the next Accounting
                                        Date and each subsequent period ending
                                        on the subsequent Accounting Date and in
                                        the case of the final Accounting Period,
                                        the lesser period ending on the date of
                                        expiry or termination;

        1.1.3   "the Biological
        Material"                       (a)  the Genetic Material and any
                                        changes to the Genetic Material made by
                                        Licensee; and

                                        (b)  any biological or chemical material
                                        produced from any of the Cell Lines or
                                        the Genetic Material; and

                                        (c)  the amino-acid sequences of the
                                        antibody as set out in the claims of the
                                        Patents;

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        1.1.4   "the Cell Lines"        the cell lines specified in the Second
                                        Schedule;

        1.1.5   "Chargeable
                Transaction"            the manufacture, use, sale or other
                                        disposal of a Product by the Licensee or
                                        Sub-licensee, provided always where such
                                        sale or other disposal is made by the
                                        Licensee or Sub-licensee to another
                                        company within its Group for further
                                        sale or disposal then the Chargeable
                                        Transaction shall be the first sale or
                                        other disposal outside that Group
                                        provided further that neither use of
                                        Product in research or clinical trials
                                        nor distribution of samples as part of
                                        Product promotion shall be deemed
                                        Chargeable Transactions as long as no
                                        consideration of any nature whatsoever
                                        is received by the Licensee,
                                        Sub-licensee or any Group Company in
                                        relation thereto and provided always
                                        that if on the sale or other disposal of
                                        Product by or on behalf of the Licensee,
                                        Sub-licensee or relevant Group company
                                        (as the case may be) the Product is not
                                        in Final Form then the Chargeable
                                        Transaction shall be the first sale of
                                        Product which is in Final Form;

        1.1.6   "Connected Persons"     means a person or entity that is under
                                        the Control of or that Controls or is
                                        under common Control with the Licensee
                                        or a Sub-licensee (as the context may
                                        require);

        1.1.7   "Control"               the direct or indirect ownership of more
                                        than 50% of the securities having the
                                        power to vote on or direct the affairs
                                        of the relevant entity, or the right to
                                        appoint the majority of the directors of
                                        the board or the ability to direct the
                                        management and policies, of the relevant
                                        entity;

        1.1.8   "Deductions"            normal trade discounts, charge backs,
                                        rebates and refunds and credits actually
                                        given, amounts actually written off as
                                        bad debts as evidenced in the Licensee's
                                        (or if applicable Sub-licensee's)
                                        audited accounts (provided that if such
                                        deducted amounts are subsequently
                                        received the Licensee shall account to
                                        BTG for the relevant royalties) and,
                                        where such items are specifically shown
                                        in the invoice and are actually incurred
                                        and paid by the

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                                        Licensee or Sub-licensee, any
                                        government-mandated charges, surcharges,
                                        levy or assessments, sales, import or
                                        Value Added Taxes and the costs of
                                        delivery and transit insurance, but not
                                        commissions or cash discounts;

        1.1.9   "Development Plan"      a development and marketing plan for
                                        Products verified by the President and
                                        Chief Executive Officer of the Licensee
                                        as a true record of the Licensee's plans
                                        to develop, obtain necessary regulatory
                                        approvals, manufacture and commercially
                                        exploit and market Products in each of
                                        the regions of United States of America,
                                        Europe and Japan including, where
                                        appropriate, relevant milestones;

        1.1.10  "Dollars"               US dollars;

        1.1.11  "the Effective Date"    the date of this Agreement;

        1.1.12  "Europe"                those countries which are from time to
                                        time members of the European Community
                                        or the European Free Trade Association;

        1.1.13  "Final Form"            fully formulated, in final form packaged
                                        for ultimate consumer use and suitable
                                        for purchase by a purchaser or
                                        distributor who is not undertaking
                                        substantial product support and
                                        marketing (e.g., a drug wholesaler, a
                                        pharmacist or group of pharmacists, a
                                        chain of drug retailers or a hospital or
                                        central purchasing department for a
                                        group of hospitals);

        1.1.14  "the Genetic Material"  the plasmids specified in the Third
                                        schedule;

        1.1.15  "Group"                 the Licensee or a Sub-licensee (as
                                        appropriate in the context) and, as from
                                        time to time, any Connected Person of
                                        the Licensee or Sub-licensee (as
                                        applicable);

        1.1.16  "the Inventors"         Professor Herman Waldmann; Mark Frewin;
                                        Sarah Louise Bolt; Michael Ronald Clark;
                                        Scott David Gorman and Edward Graham
                                        Routledge;

        1.1.17  "Know-how"              all confidential and proprietary
                                        technical information, data, knowledge,
                                        inventions, techniques, processes,
                                        systems, formulae, records and other
                                        materials and information supplied to
                                        the Licensee hereunder and which relate

                                        3
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                                        to the Biological Material and the Cell
                                        Lines (including that already provided
                                        by or on behalf of the BTG prior to the
                                        Effective Date or by the Inventors to
                                        the extent that ownership of such
                                        information has been assigned by the
                                        Inventors to BTG);

        1.1.18  "Launch Date"           the first arm's length sale of Product
                                        by the Licensee or any Sub-licensee in
                                        any country following the grant of
                                        Regulatory Approval for such country;

        1.1.19  "the Licences"          the licences granted or to be granted
                                        under this Agreement;

        1.1.20  "Licensee Technology"   all inventions, patents, patent
                                        applications, information, data and
                                        materials (other than Stealth
                                        Technology) owned by Licensee at the
                                        time of termination of this Agreement
                                        and to which the Licensee has the right
                                        to grant a license and that results from
                                        research and/or development of Product
                                        and that may be used for developing,
                                        making, producing or otherwise
                                        commercialising Product;

        1.1.21  "Net Selling Price"     the price of Products the subject of a
                                        Chargeable Transaction calculated as
                                        follows:

                                        1.1.21.1   in the case of an arm's
                                                   length sale or other
                                                   disposal, the gross price as
                                                   charged or invoiced (before
                                                   taxes and discounts), less
                                                   any Deductions; or

                                        1.1.21.2   in the case of use of a
                                                   Product in a country, or of a
                                                   sale of Product in a country
                                                   in combination with a product
                                                   that is not a Product or in
                                                   combination with a service,
                                                   and if in either case there
                                                   is no price set forth for the
                                                   Product for such use or in
                                                   such combination, then the
                                                   price shall be the price of
                                                   Product in such country when
                                                   sold alone and if there is no
                                                   such sale, then the parties
                                                   shall reach agreement on a
                                                   price for the Product used in
                                                   such a process or as part of
                                                   such

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                                                   a combination, and in the
                                                   absence of such agreement,
                                                   the price will be determined
                                                   by an independent auditor
                                                   (acting as an expert and not
                                                   an arbitrator) and appointed
                                                   by agreement by the parties
                                                   (or in the absence of such
                                                   agreement by the President
                                                   for the time being of The Bio
                                                   Industry Association in the
                                                   United Kingdom) with the
                                                   decision of such auditor
                                                   being final and binding on
                                                   the parties;

        1.1.22  "the Patents"           the patents and applications for patents
                                        specified in the First Schedule and any
                                        patent which may be granted pursuant to
                                        any of such applications; and

                                        1.1.22.2   any patents and applications
                                                   corresponding to such patents
                                                   and applications which may be
                                                   granted to or made by BTG in
                                                   other countries; and

                                        1.1.22.3   any re-issues or extensions
                                                   of such patents and any
                                                   Supplementary Protection
                                                   Certificates in respect of
                                                   such patents and any division
                                                   and continuations of such
                                                   applications;

        1.1.23  "Phase II Clinical
        Trial"                          an investigation or series of
                                        investigations to assess the efficacy
                                        and safety of a medical product in
                                        patients as approved by the appropriate
                                        Regulatory Authority, excluding
                                        specifically the first study or studies
                                        (whether approved by a Regulatory
                                        Authority or not) whose principal
                                        objective is to evaluate safety across a
                                        range or doses in a small number of
                                        subjects (Phase I);

        1.1.24  "Phase III Clinical
        Trial"                          an investigation or a series of
                                        investigations to assess the efficacy
                                        and safety of a medicinal product on a
                                        significantly large group of patients
                                        with the objective of obtaining
                                        Regulatory Approval and as approved by
                                        the appropriate Regulatory Authority;

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        1.1.25  "Product"               a product: (i) that but for this license
                                        in the country where made, used, or sold
                                        or otherwise disposed of infringes a
                                        claim that is in force, at the time, of
                                        a Patent as to which Licensee has a
                                        license under this Agreement; or (ii) is
                                        produced from or by use of the Cell
                                        Lines, Biological Material or any
                                        fragment thereof as to which Licensee
                                        has a license under this Agreement;

        1.1.26  "Product Licence"       any licence issued by a Regulatory
                                        Authority whereby the manufacture, use,
                                        or sale or other disposal of Products is
                                        authorised;

        1.1.27  "Regulatory Approval"   the approval of the relevant Regulatory
                                        Authority for products to be placed on a
                                        market;

        1.1.28  "Regulatory Authority"  the body having responsibility for the
                                        regulation of medicinal products in a
                                        particular market;

        1.1.29  "Relevant Company"      the Licensee; each Sub-licensee; each
                                        Connected Person of the Licensee and
                                        each Sub-licensee; each member of each
                                        Group and each company acting on behalf
                                        of any of the above;

        1.1.30  "Stealth Patent"        means a patent application(s) and/or
                                        patent(s) that claims an antibody and/or
                                        use thereof that has a reduced
                                        immunological immune response other than
                                        by producing a chimeric or humanized
                                        antibody;

        1.1.31  "Stealth Technology"    Stealth Patent together with all
                                        biological and other materials, cell
                                        lines, confidential information and data
                                        in written or other permanent form in
                                        the Licensee's possession or control
                                        related to the inventions the subject of
                                        such patents or patent applications;

        1.1.32  "Sub-licence"           a written sub-licence or sub-sub-licence
                                        of any of the Licenses or any written
                                        agreement or written commitment for the
                                        grant of a sub-licence or
                                        sub-sub-licence of any of the Licenses;

        1.1.33  "Sub-licensee"          the recipient of a Sub-licence or a
                                        sub-sub-licence;

        1.1.34  "Sub-licence Terms"     the terms contained in the Fourth
                                        Schedule;

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        1.1.35  "Supplementary
        Protection Certificates"        supplementary protection certificates
                                        granted pursuant to Certificates"
                                        Council Regulation (EEC) No. 1768/92
                                        ("the SPC Regulation") and any like
                                        rights granted by any government,
                                        authority or agency; and

        1.1.36  "Territory"             the World.

2.      PAYMENTS

2.1     THE Licensee shall pay to BTG:

        2.1.1   within seven (7) days of the Effective Date the sum of
                [*******]; and

        2.1.2   before 30 March, 2002, the sum of [*******]; and

        2.1.3   upon commencement by a Relevant Company of the first Phase III
                Clinical Trials of a Product in any country, the sum of
                [*******]; and

        2.1.4   upon receipt by a Relevant Company of the first Regulatory
                Approval of a Product in any country, the sum of [*******].

        2.1.5   the royalties specified in Clause 7; and

        2.1.6   the share of the down payments specified in Clause 7.6.

2.2     All sums referred to in this Agreement are not refundable. Subject to
clause 7, the obligation on the Licensee to make the payments set out in clauses
2.1.3 and 2.1.4 shall be in addition to the obligation on the Licensee to pay to
BTG a share of the down payments specified in Clause 7.6.

2.3     WHEN making any payment under this Agreement the Licensee shall also pay
any Value Added Tax payable. Where the Licensee has to pay Value Added Tax, BTG
shall provide the Licensee with a Value Added Tax invoice in respect of the
relevant payment.

3.      COMMENCEMENT AND DURATION

3.1     THIS Agreement shall come into force on the Effective Date.

3.2     SUBJECT to Clauses 16 and 17:

        3.2.1   the Licences under the Patents shall continue in force in each
                country until all of the Patents of that country have expired;

                3.2.2 the Licences in respect of the know-how and/or the
                Biological Material and/or the Cell Lines shall continue in
                force in each country until the date on which the know-how and
                the Biological Material and the Cell Lines have entered the
                public domain in the relevant country otherwise than through

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

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                breach or default by or through the Licensee or any Sub-licensee
                or any person receiving the same from them;

        3.2.3   the Agreement shall continue in force until all of the royalty
                obligations have expired after which the Licensee shall have a
                fully paid up, non-cancellable licence which is equivalent in
                scope to that held by the Licensee immediately before the expiry
                of the said royalty obligations.

3.3     THE Licensee shall be responsible for obtaining any requisite
registration or governmental approval of this Agreement and of acts to be
carried out pursuant to or in connection with this Agreement (including in
particular that of transferring the know-how and/or Biological Material and/or
the Cell Lines (or part thereof) from the UK to the USA) and the Licensee shall
expeditiously take all necessary steps to obtain the same.

4.      LICENCES AND PATENTS

4.1     BTG grants to the Licensee on and from the Effective Date:

        4.1.1   Subject to Clause 5, exclusive licenses under the Patents to
                make, and have made Products and to use, sell, offer for sale,
                import and otherwise dispose of Products so made for therapeutic
                or preventive use in human healthcare; and

        4.1.2   non-exclusive licenses for the purposes set out in Clause 4.1.1
                above to use:

                4.1.2.1   the Biological Material and the Cell Lines; and

                4.1.2.2.  the Know-how; and

                4.1.2.3   the copyright in the know-how;

        such licences are without geographical restriction and, subject to the
        fact that the Patents only relate to some countries, are worldwide, and
        are sub-licensable.

4.2     BTG shall not use and shall not grant rights to or disclose the Know-how
and/or the Biological Material and/or the Cell Lines to any third party during
the period from the Effective Date to the date falling ten years after the date
when a Product is first put on the market within Europe by the Licensee, any
Sub-licensee or any other licensee of BTG as to which BTG has the right, if any,
to grant a license under this Agreement. If the Licensee loses exclusivity for
the Licences under the Patents pursuant to clauses 5.1 or 5.4 then the
restriction on BTG under this clause shall also terminate as regards the
relevant territory.

4.3     The restriction referred to in clause 4.2 and the exclusivity of the
licences under the Patents shall be qualified by and subject to the right of the
Inventors to carry out non-commercial work in relation to the Cell Lines and the
Biological Materials (including but not limited to by way of collaborations with
third party academic institutions); in the event that such research produces a
cell line which produces antibodies with the same specificity as those claimed
in the Patents and such cell line and the intellectual property rights related
thereto are assigned to BTG then BTG shall notify the Licensee of such
assignment and (on written request by the Licensee) such cell line and
intellectual property rights shall be licensed

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to the Licensee hereunder (and form part of the Patents, Know-how, Cell Lines or
the Biological Material as appropriate).

4.4     WITHOUT prejudice to Clause 3.2, the Licences are granted for the
purpose only of making, having made, using, selling, offering for sale,
importing and otherwise disposing of Products during the life of this Agreement.
The Licenses shall not be used for any other purpose unless and until the
Know-how and the Biological Material and the Cell Lines have come into the
public domain otherwise than through breach or default of the Licensee or the
copyright in the Know-how has expired.

4.5     BTG shall, at the request and expense of the Licensee, execute any
further formal document which may be necessary to give effect to this Agreement
in any part of the Territory. Until such licence shall be granted formally, this
Agreement shall take effect as a licence.

4.6     At the cost and expense of BTG, BTG shall use its reasonable endeavours
to file, prosecute and maintain such of the Patents as it considers, in its sole
discretion, appropriate for the purposes of commercialising Products. If BTG
desires to allow any of the Patents to lapse, become abandoned or disclaimed, it
shall first notify the Licensee of that fact in advance. The Licensee shall have
the right, exerciseable by submission of written notice to BTG within 30 days of
receipt by the Licensee of BTG's notice and subject to the following payment
obligation, to require that BTG continues to file, prosecute and maintain all or
any of the Patents for the remaining duration of this Agreement. The Licensee
shall indemnify BTG against all out of pocket costs and expenses incurred in
undertaking such actions. For the avoidance of doubt, the Licensee shall not be
required to pay BTG royalties in respect of Products manufactured or sold in the
country the subject of the Patents set out in the notice from BTG of intention
to lapse, abandon or disclaim.

4.7     In respect of any country in which the Licenses to the Patents hereunder
remain exclusive, if any of the Patents is infringed by a third party, Licensee
shall have the right and option but not the obligation to bring an action for
infringement, at its sole expense, against such third party in the name of BTG
and/or in the name of Licensee, and to join BTG as a party plaintiff if
required, provided that the Licensee shall indemnify BTG in respect of any
liabilities, costs or expenses that BTG may incur as a result of the same other
than those that arise out of any misconduct by BTG. The Licensee shall be
obliged to satisfy such indemnity irrespective of whether any damages or other
sums are received in respect of the suit. Licensee shall promptly notify BTG of
any such infringement and shall consult with, and give good faith reasonable
consideration to BTG's requirements BTG in relation to the prosecution of any
action for such infringement. Any recovery of damages by Licensee for any such
suit shall be applied first in satisfaction of any unreimbursed expenses and
legal fees of Licensee relating to the suit. If requested by BTG, the Licensee
shall provide BTG with evidence of the Licensee having incurred such deducted
costs and expenses. The balance remaining from any such recovery shall be
considered as Net Selling Price of Product subject to royalties under Clause
7.1. In the event that Licensee is unwilling, within a reasonably timely fashion
to pursue an action for infringement, upon written notice to BTG by Licensee
that an unlicensed third party is an infringer of a Patent, BTG shall have the
right and option, but not the obligation, at BTG's cost and expense, to initiate
infringement litigation and to retain any recovered damages.

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        In any infringement suit, subject to this clause 4.7, if either party
institutes to enforce Patents pursuant to this Agreement, the other party hereto
shall, at the request of the party initiating such suit, cooperate in all
reasonable respects and, to the extent possible, on receipt of reasonable
notice, have its employees testify when requested and, so far as it is free to
do so, make available relevant records, papers, information, samples, specimens,
and the like.

5.      EXCLUSIVITY

5.1     BTG may at any time terminate the exclusivity of the Licences by giving
sixty (60) days written notice to the Licensee if the grant and continuation of
an exclusive Licence in the Territory would be contrary or a violation of
applicable anti-trust or competition law PROVIDED THAT if the ground for
termination referred to herein only relates to a particular country in the
Territory, then BTG's right under this Clause 5.1 shall be restricted to that
country.

5.2     IT is hereby declared that BTG has agreed to grant exclusivity in
respect of the Licences under the Patents on the basis that the parties consider
that this Agreement is concerned with the introduction and protection of a new
technology, and by reason of the scale of research that needs to be undertaken
and of the risk that is involved in manufacturing and marketing a product which
is unfamiliar to users at the Effective Date.

5.3     IF the Commission of the European Communities withdraws the benefit of
its Regulation 240/96, or that Regulation expires and is not replaced by another
Regulation of similar or equivalent effect, the Licences shall forthwith become
non-exclusive in Europe, except for such measure of exclusivity as the parties
may then agree to be appropriate, taking into account the provisions of Article
81(3) of the Treaty of Rome.

5.4     Subject to receipt of notification pursuant to clause 7.13, BTG may at
any time terminate the exclusivity of the Licences in any country by giving the
Licensee five days (5) written notice to that effect. Such Licenses shall
include the right to Sub-licence and shall be non-exclusive but otherwise on the
terms hereof.

5.5     In the event that the Licenses become non-exclusive in whole or in part
pursuant to Clause 5.1 and/or 5.3, then BTG will not grant any licenses with
respect to the Patents and/or Biological Material and/or Cell Lines and/or the
Know-how and/or the copyright in the Know-how except and only to the extent that
is required by any applicable law, rule, or regulation.

5.6     In the event that the exclusivity of the License is terminated under
Section 5.1 or 5.3 then following the date of the first commercial sale in any
country (by a third party licensee of the Patents other than by or on behalf of
the Licensee or any Sub-licensee) of a Product in Final Form following the
granting of a Product Licence in that country, the royalty rate solely in
respect of the manufacture or sale of Products in that country shall be reduced
to [*************] but in no event shall Licensee be paying a royalty greater
than any third party granted a license under Patents.

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

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6.      KNOW-HOW

6.1     THE Licensee shall arrange and pay the costs of and be responsible for,
copying, shipment to the Licensee and storage of the Know-how and/or the
Biological Material and/or the Cell Lines and such shipment and storage shall be
at the Licensee's risk.

6.2     Subject to Clause 6.3, the Licensee shall, by using at least the same
degree of care which it uses with respect to its own information and material of
a similar nature, keep the Know-how, disclosed in writing by BTG and designated
in writing by BTG as confidential, and/or the Biological Material and/or the
Cell Lines confidential to the Licensee, and to such of its officers and
employees and (subject to clause 6.3 and solely in respect of the know-how but
not Biological Materials or Cell Lines) its consultants and advisors, as are, in
each case, bound by obligations of confidence and need to be informed for the
purposes of this Agreement, and shall ensure that the know-how and/or the
Biological Material and/or the Cell Lines are not disclosed to others orally or
in writing or by any act of transfer, save to the extent that the know-how
and/or the Biological Material and the Cell Lines:

        6.2.1   as evidenced by the Licensee's written, records, were lawfully
                known to or lawfully possessed by the Licensee prior to its
                communication or transfer by or through BTG and were not
                communicated to or supplied to the Licensee subject to any
                restrictions on disclosure or use PROVIDED THAT this exemption
                shall not be applicable in respect of any know-how and/or
                Biological Material and/or Cell Lines communicated or disclosed
                (directly or indirectly) by any or all of the Inventors to the
                Licensee; or

        6.2.2   is necessarily disclosed by the sale of Products embodying any
                of the know-how; or

        6.2.3   is or becomes in the public domain, otherwise than by any
                default of the Licensee, or persons acquiring the same from the
                Licensee; or

        6.2.4   as evidenced by the Licensee's written records, becomes known to
                or in the possession of the Licensee by the action of a third
                party not in breach of any obligation of confidence PROVIDED
                THAT this exemption shall not be applicable in respect of any
                know-how and/or Biological Material and/or Cell Lines
                communicated or supplied (directly or indirectly) by any or all
                of the Inventors to the Licensee.

                Without limiting the effect of this clause, a combination of
                parts of the know-how shall not be deemed to be in the public
                domain by reason only that each separate part is in the public
                domain.

        IT is acknowledged by the Parties that, from time to time, the Inventors
        may act as consultants to the Company and to such extent, the Company
        may disclose Biological Materials and/or Cell Lines and/or know-how to
        the relevant Inventors, provided that they are bound by obligations of
        confidence no less onerous than those contained in clause 6.2 above in
        respect of the same.

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6.3     Licensee shall have the right to disclose and permit a third party to
use the Know-how and/or the Biological Material and/or the Cell Lines in
pursuing and/or exercising the rights granted to Licensee under the Agreement
provided that such third party agrees to confidentiality obligations no less
onerous than those of Clause 6.2 and where necessary subject to the terms of a
Sub-licence.

6.4     During the term of this Agreement, it is contemplated that Licensee will
disclose to BTG written confidential information that is owned or controlled by
Licensee or that Licensee is obligated to maintain in confidence ("Confidential
Information"). BTG agrees to retain Licensee's Confidential Information
disclosed to it in writing and marked as confidential in confidence and not to
disclose any such Confidential Information to a third party without the prior
written consent of Licensee and to use the confidential Information only for the
purposes of this Agreement. The obligations of confidentiality of this clause
6.4 will not apply to Confidential Information that:

                     (i)   was known or generally known to the public prior to
                 its disclosure hereunder; or

                     (ii)  subsequently becomes known to the public by some
                 means other than a breach of this Agreement;

                     (iii) is subsequently disclosed to the receiving party by a
                 third party without a breach of an obligation of
                 confidentiality to Licensee; or

                     (iv)  is independently developed by the employees or agents
                 of BTG without any knowledge of the Confidential Information
                 provided Licensee; or

                     (v)   is already lawfully known to or lawfully possessed by
                 BTG prior to its communication by the Licensee and was not
                 supplied to BTG subject to any restrictions on disclosure or
                 use; or

                     (vi)  is required to be disclosed pursuant to any law,
                 order of a court of competent jurisdiction or rules of any
                 competent regulator.

6.5     The obligations of non-use and confidentiality of this Article 6 shall
terminate five (5) years after termination of this Agreement.

7.      ROYALTIES

7.1     SUBJECT to Clauses 4.6, 7.2, 7.3 and 7.13 below, the Licensee shall pay
to BTG in respect of Products that are Products as a result of Clause 1.1.25(i)
and are the subject of Chargeable Transactions and as provided in Clause 17.2 on
such Products held on termination, a royalty at the rate of [*******] on the Net
Selling Price.

7.2     IF, in respect of any Chargeable Transaction all of the following apply:

        7.2.1   the Licensee is also paying patent royalties to a third
                party/third parties; and

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

                                       12
<Page>

        7.2.2   that the third party/parties (as the case may be) is not/are not
                a Connected Person(s) of the Licensee; and

        7.2.3   such patent royalties are paid under an arm's length BONA FIDE
                licence; and

        7.2.4   those patent royalties are for rights to patents which are
                deemed by the Licensee (acting reasonably) to be required for
                the commercialisation, manufacture or sale of the Products in
                question;

        7.2.5   the sum of such patent royalties with all of the characteristics
                set out in 7.2.1 to 7.2.4 above and the royalties payable to BTG
                under Clause 7.1 above would in total ("the Total Royalty")
                amount to more than [*******] on the Net Selling Price for that
                Chargeable Transaction ("the Cut-off Royalty"),

        then the royalty to be paid to BTG on that Chargeable Transaction shall
        be reduced by one half of the amount that the Total Royalty exceeds the
        Cut-off Royalty provided that in no event shall the royalty payable to
        BTG be reduced under this Clause 7.2 below [*******] on the Net Selling
        Price for the relevant Chargeable Transaction. (By way of illustration
        if the Total Royalties equal [*******] then the royalty payable to BTG
        would be [*******].

        If requested by BTG the Licensee shall promptly provide to BTG: (i) a
        copy of the relevant licence agreements supporting its requirement to
        pay royalties to third parties; and (ii) evidence that the conditions
        set out in clauses 7.2.1, 7.2.2, 7.2.3 and 7.2.4 have been fulfilled.

        FOR the avoidance of doubt, the right of set-off of Third Party
        Royalties under this clause 7.2 shall only apply to royalties payable
        under clause 7.1 and not to any other amount payable under this
        Agreement (including but not limited to the payments under clause 2 or
        the minimum payments to BTG pursuant to clause 7.3).

7.3     IF the aggregate royalty payments due to be paid by the Licensee
hereunder to BTG in respect of any of the following calendar years are less than
the minimum sums set out below for that year, then the Licensee shall pay BTG
the amount by which the actual royalties payable fall short of the relevant
minimum sum as follows:

<Table>
<Caption>
Period                                             Minimum Sum
--------------------------------------------------------------
<S>                                                <C>
The 12 month period starting on                    [*******]
January 1st in the next calendar year
immediately following the Launch Date
("Year 1").
--------------------------------------------------------------
The 12 month period immediately                    [*******]
following the end of Year 1 ("Year 2")
--------------------------------------------------------------
The 12 month period immediately                    [*******]
following the end of Year 2 ("Year 2")
</Table>

7.4     ROYALTY shall only be payable once in respect of the same Product.

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

                                       13
<Page>

7.5     THE Licensee shall at the request of BTG provide half-yearly forecasts
of the amount of royalties likely to be payable under this Agreement.

7.6     Subject to Clause 7.8, in respect of each lump sum payment (as opposed
to royalties paid as a consequence of actual sales of Products) and non-cash
consideration received by the Licensee (or by any Connected Person of the
Licensee) from a third party for rights granted under a Sub-licence, or for
distribution rights in respect of the Products including, without limitation,
any payments for an option to a Sub-licence, or upon the exercise of any such
options, signature fees, milestone payments and any other lump sum payments
under licences; the Licensee shall in accordance with clause 7.7 pay to BTG the
following percentage of such sums:

        7.6.1   [*******] of such payments if at the time of grant of the
        Sub-licence the Licensee has not granted such licensee a license in
        respect of Stealth Patent; and

        7.6.2   [*******] of such payments if, at the time of grant of the
        Sub-licence, the Licensee has granted a license in respect of Stealth
        Patent and such grant is prior to commencement of a Phase II Clinical
        Trial of a Product; and

        7.6.3   [*******] of such payments for a Sub-license entered into after
        commencement of a Phase II Clinical Trial of a Product that the
        manufacture, use or sale thereof at the time of grant, would infringe a
        claim of a patent or patent application that is a Stealth Patent.

        Notwithstanding the preceding sentence with respect to any such payments
        received with respect to a milestone for a Product that the manufacture,
        use or sale of which does not, at the time of payment, infringe a claim
        of a patent application or patent that is a Stealth Patent, Licensee
        shall pay BTG [*******] of any such milestone payment.

For the purposes of this clause 7.6, the following shall be excluded: (a)
royalties; and (b) amounts received in respect of the research and/or
development of the Product, provided that such sums are actually expended by or
on behalf of the Licensee on such research and/or development within twenty-four
(24) months of receipt. In order to exclude any payment in accordance with (a)
or (b) above, if requested by BTG; the Licensee shall provide evidence to BTG's
reasonable satisfaction that the payments fall in either category. For the
purposes of this Clause 7.6 monies paid for securities of Licensee shall be
excluded to the extent that such payment does not exceed the fair market value
of the securities. IN addition if Licensee receives non-cash consideration under
a Sub-license the fair market value of the non-cash consideration shall be
subject to the payment provisions of this Clause 7.6.1.

7.7     THE Licensee shall, within thirty (30) days of receipt by the Licensee
(or by any Connected Person of the Licensee or Sub-licensee) of each of each
lump sum payment and non cash consideration notify BTG of and provide full
details of each such lump sum payment and non-cash consideration. At the same
time as it gives BTG such notification the Licensee shall pay BTG the sum or
sums due.

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

                                       14
<Page>

7.8     WITH regard to payments received for equity or non-cash consideration
the Licensee shall make its own valuation but BTG may challenge such valuation
in writing. On receipt of either type of challenge the Licensee shall promptly
obtain an independent auditor's certificate specifying the valuation made by the
auditor. Both parties shall abide by the auditor's certificate and shall rectify
any overpayment or underpayment (as the case may be).

7.9     Where Sub-licences are granted by the Licensee prior to the initiation
of the first Phase III Clinical Trial of Products and the Licensee receives a
lump sum payment in respect of such initiation of the first phase III Clinical
Trial of Products, then the Licensee may offset against its obligation to make
payment to BTG under clause 7.6 above, up to [*******]. No provision of this
clause 7 shall reduce the amount of the payment required to be made by the
Licensee to BTG under clause 2.1.3.

7.10    Where Sub-licences are granted by the Licensee prior to the receipt of
the first Regulatory Approval of a Product in any country and the Licensee
receives a lump sum payment in respect of such first Regulatory Approval, then
the Licensee may offset against its obligation to make payment to BTG under
clause 7.6 above, up to [*******]. No provision of this clause 7 shall reduce
the amount of the payment required to be made by the Licensee to BTG under
clause 2.1.4.

7.11    If the Licensee licenses Stealth Technology and/or Licensee Technology
to a Sub-licensee with the intention or result that such Sub-licensee develops,
makes, has made, sells, has sold or otherwise disposes of Products which
incorporate the Stealth Technology and/or Licensee Technology and/or Results,
then all lump sum payments received from such Sub-licensee for Stealth
Technology and/or Licensee Technology for use with respect to Product (whether
recorded as relating to the Sub-licence or the licence to Stealth Technology
and/or Licensee Technology) shall be considered payments to which the revenue
sharing obligations of clause 7.6 apply.

7.12    The Licensee hereby represents and warrants that, with respect to a
chemical substance that binds to CD3 antigen, as at the Effective Date and
subject to the terms of this Agreement, it presently only intends to develop
(itself or via a Relevant Company) a chemical substance which is an antibody (or
a derivative or conjugate thereof) against human CD3 antigen that is claimed in
a Patent.

7.13    On initiation of the first clinical trial by a Relevant Company in
respect of each antibody (or a derivative or conjugate thereof) against human
CD3 antigen, the Licensee shall, within seven (7) days of such event, provide
BTG with written confirmation of whether Licensee believes that the antibody in
question at the time:

(a) infringes a claim of any of the Patent; and/or

(b) is produced from the Biological or the Cell Lines.

In the event that such confirmation indicates that any one or more of the
conditions set out in paragraphs (a) or (b) above are not satisfied, the
Licensee shall provide evidence to BTG to verify that fact.

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

                                       15
<Page>

                7.13.1    If the antibody (or a derivative or conjugate thereof)
                in question satisfies condition (b) but not (a) above, then:

                     (i)  BTG shall have the right to terminate the exclusivity
                          of the Licenses which shall continue as non-exclusive
                          Licenses as set out in clause 5.4 with Licensee having
                          the right to grant sublicenses thereunder; and

                     (ii) the royalty rate for such Products (but not other
                          Products) shall, in respect of the relevant countries
                          be reduced to [*******] with such royalty only being
                          payable in each country for ten (10) years from the
                          date of the first commercial sale of the Product in
                          that country following the granting of a license
                          issued by a Regulatory Authority for the manufacture,
                          use, sale or other disposal of such Products in that
                          country.

8.      ACCOUNTING FOR ROYALTIES

8.1     THE Licensee shall:

        8.1.1   keep true and detailed accounts and records of all royalties and
                other sums due under this Agreement;

        8.1.2   within thirty days after each Accounting Date deliver to BTG a
                statement of all royalties and other sums due for the Accounting
                Period ended on that Accounting Date showing separately the
                Chargeable Transactions in each country, and (where relevant),
                the rate of exchange used or, if it be the case, a statement
                that no royalties are due;

        8.1.3   send with the above statement the amount shown to be due;

        8.1.4   immediately and without demand send to BTG the difference
                between an amount already paid and the correct amount shown to
                be due and payable as a result of verification under Clause 10.

8.2     IN each year the Licensee shall within thirty days (30) after approval
of the Licensees annual report and accounts at the Licensee's shareholders
meeting, deliver to BTG a copy of such annual report and accounts for each such
year.

8.3     ON termination or expiry, the final statement shall be delivered within
thirty days of termination or expiry and shall include details of royalties on
all Products being manufactured and all Products manufactured but not yet
disposed of.

8.4     IF the Licensee defaults in payment of the royalties and other sums due
within the period stated above, the amount due shall bear compound interest,
accruing from day to day, at the rate per annum of Four per cent (4%) above the
Base Rate for the time being of the National Westminster Bank p.l.c.

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

                                       16
<Page>

9.      CURRENCY AND TAXES

9.1     ALL payments shall be made in sterling to [*******] or as otherwise
directed by BTG. Any necessary currency conversion shall be at the rate at which
English bank transfers are made on the last business day of the period to which
the relevant sales and royalty statement relates.

9.2     PAYMENTS shall be made without deduction, other than such amount as the
Licensee is required to deduct or withhold by law. In regard to any such
deduction, the Licensee shall use all reasonable endeavours to assist BTG to
claim recovery or exemption under any double taxation or similar agreement.
Evidence as to the payment of such tax or sum withheld shall, on request, be
given by the Licensee to BTG.

10.     VERIFICATION

10.1    THE Licensee shall permit any authorised representative appointed by
BTG, upon reasonable notice, access to the premises of the Licensee and access
to the accounts, records and relevant documentation of the Licensee and shall
provide such information and explanations as the representative shall require to
verify the statements and to satisfy BTG that the provisions of this Agreement
are being complied with. The representative shall also be permitted to take
copies and extracts. If the verification discloses an underpayment to BTG of
more than 5% of the amount due the Licensee shall promptly on demand reimburse
BTG the fees and costs of the representative, and the reasonable costs incurred
by BTG in respect of the verification. The Licensee shall also provide to such
representative, if so requested, reasonable assistance and information to
establish that the relevant transactions are at arm's length.

10.2    BTG and its authorised representatives shall keep confidential any
information which it may acquire in the exercise of its rights under this Clause
10 with the exception of information which was already known to it, or which BTG
is required to disclose by law or the requirements of any regulator, or which is
or becomes in the public domain otherwise than by any default of BTG.

11.     SUSPENSION OF ROYALTIES AND PAYMENTS

If any of the following events shall occur in respect of the Patents:

11.1    any patent application is finally refused so that the grant of a patent
thereon is unobtainable; or

11.2    any patent application is abandoned or withdrawn; or

11.3    any patent lapses; or

11.4    any patent is declared invalid or unenforceable by a court or tribunal
of competent jurisdiction;

then the royalties payable solely in respect of such patent application or
patent shall cease after the date of the relevant event, but BTG shall be
entitled to all sums which shall have then already fallen due, and whether paid
or unpaid at such date. If such patent application is reinstated or such patent
is restored or is subsequently established as being valid and enforceable,
royalties shall again become payable, together with all

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

                                       17
<Page>

royalties which would have been payable if the relevant event had not occurred.

11.5    In the event that BTG is in material breach of any of the warranties
under clause 15.6 or is in material breach of any of BTG's obligations under
this Agreement, upon written notice from Licensee to BTG specifying the breach,
unless such breach is cured within sixty (60) days after such notice, Licensee
may discontinue all payments under this Agreement without being in breach of
this Agreement until BTG cures the breach set forth in such notice, save that
once BTG has cured the applicable breach such amounts shall again become payable
as if the relevant breach had not occurred.

12.     UNDERTAKINGS BY THE LICENSEE

THE Licensee:

12.1    shall not at any time make any use of the Know-how and/or the Biological
Material and/or the Cell Lines other than for the purposes of the Licences;

12.2    shall have full control, authority and responsibility for development,
registration and commercialisation of Products.

12.3    shall deliver the Development Plan to BTG within three (3) months of the
Effective Date and on each anniversary of the Effective Date deliver to BTG an
updated Development Plan (which shall provide for no less timely development and
commercialisation of Products in the Territory than as set out in the initial
Development Plan). BTG and the Licensee shall seek to agree the initial
Development Plan by good faith discussions within the period of 30 days from the
date of receipt of the Development Plan by BTG. In addition, the Licensee shall
further deliver to BTG at intervals of six (6) months short written reports of
the evaluation, development, regulatory and commercialisation work, manufacture,
use and sales carried out by and for the Licensee in relation to Products during
the preceding six month period. Such reports shall also contain details of all
studies and estimated time scales for the initiation and completion of the
various regulatory stages and the development of and commercial prospects for
Products. The Licensee shall arrange for its staff to answer any reasonable
questions that BTG may raise with such question and answer sessions to be either
on the telephone or at a meeting (as reasonably requested by BTG).

12.4    undertakes to BTG that when selling Product as part of a package with
other products the Licensee shall ensure that it does not favour the other
products, or discriminate against the Product, in terms of pricing, discounts,
or in any other way which would adversely affect the royalties due to BTG under
this Agreement;

12.5    shall use reasonable commercial efforts to develop Products in
accordance with the Development Plan (with the efforts of Sub-licensees, members
of the Licensee's Group and collaborators being considered as efforts of the
Licensee in this regard);

12.6    shall use all reasonable commercial endeavours to market and sell and to
continue to market and sell Products in the Territory following receipt of a
Product Licence;

                                       18
<Page>

12.7    on obtaining each Regulatory Approval and/or Product Licence, or the
like in relation to Products, promptly deliver to BTG a copy of the same; and

12.8    shall give BTG written notice with seven (7) days of the Launch Date for
each country.

13.     MARKING

THE Licensee shall legibly mark the Products or, if not practicable, then any
associated packaging or literature, with the relevant patent or application
number.

14.     SUPPLEMENTARY PROTECTION CERTIFICATES

14.1    IN the event that BTG wishes to make any application for a Supplementary
Protection Certificate or Certificates in respect of Products the Licensee shall
promptly take all necessary steps to facilitate such application.

14.2    IN particular, but without limitation, the Licensee shall:

                14.2.1 promptly notify BTG of the number and date of the first
                and any subsequent authorisation to place Products on the market
                in any country in which BTG may be able to apply for any
                extension of the Patents or Supplementary Protection
                Certificate;

                14.2.2 promptly and free of charge provide to BTG:

                         14.2.2.1 a copy of every authorisation fulfilling the
                         requirements of Article 8.1(b) of the SPC Regulation
                         (and of any additional applicable requirements imposed
                         by relevant national law) in respect of all Products;

                         14.2.2.2 additional information fulfilling the
                         requirements of Article 8.1(c) of SPC Regulation and a
                         copy of the notice publishing the authorisation in the
                         appropriate official publication (and information and
                         documents fulfilling any additional requirements
                         imposed by relevant national law);

                14.2.3 permit use of documents and information provided pursuant
                to this clause for the purpose of such application for a

                                       19
<Page>

                Supplementary Protection Certificate or Certificates.

14.3    BTG shall be entitled to disclose any Regulatory Approval or Product
Licence or any part thereof to any relevant authorities for the purposes of
obtaining a Supplementary Protection Certificate in respect of the Products or
any extension of the Patents.

14.4    BTG shall notify the Licensee of the grant of every Supplementary
Protection Certificate in respect of Products.

14.5    BTG shall not be obliged to apply for grant of any Supplementary
Protection Certificates.

14.6    FOR the avoidance of doubt the Licensee shall not be entitled to make an
application for or participate in negotiations for grant of any Supplementary
Protection Certificate.

15.     EXCLUSION OF LIABILITY; INDEMNITY AND WARRANTIES

15.1    SAVE as expressly stated herein, no representation condition or warranty
whatsoever is made or given by or on behalf of BTG. All conditions and
warranties, arising by operation of law or otherwise:

        15.1.1  to the effect that any of the Patents or the Know-how or the
                copyright therein are valid or enforceable, or

        15.1.2  to the effect that any of the acts hereby licensed or agreed to
                be licensed by BTG will not infringe the rights of third
                parties; or

        15.1.3  in relation to the provision or use of the Know-how or its
                fitness for purpose, accuracy or completeness; or

        15.1.4  in relation to the provision, storage or use of the Biological
                Material and/or the Cell Lines or its fitness for purpose or
                completeness;

        are hereby expressly excluded. For the avoidance of doubt in relation to
        15.1.1, 15.1.2 and 15.1.4 above, the Licensee hereby acknowledges that
        it may require licences from third parties to utilise the Biological
        Material and/or the Cell Lines.

15.2    BTG shall be under no liability whatsoever to the Licensee (whether in
negligence or otherwise, in contract or in tort) for any expense, loss, death,
damage or injury of any kind (including any loss of profit or consequential
damage) sustained by the Licensee or any third party which arises directly or
indirectly from any cause or circumstance referred to in sub-clause 15.3 below.

15.3    THE Licensee acknowledges that it bears all risks and liabilities
associated with its own activities under this Agreement. Subject to Clause 15.5
the Licensee shall indemnify BTG against all claims and actions by and all
damages awarded to any third party against BTG (and any related costs and
expenses) which arise directly or indirectly from:

                                       20
<Page>

        15.3.1  the evaluation, development, manufacture, use, storage,
                transportation, sale or disposal of Products by the Licensee or
                any Sub-licensee or any persons on their behalf; or

        15.3.2  the use of the Patents or copyright in the Know-how by the
                Licensee or any Sub-licensee or any persons on their behalf; or

        15.3.3  the provision to, evaluation by or use of the Know-how by the
                Licensee or any Sub-licensee or any persons on their behalf; or

        15.3.4  the provision, storage, transportation, evaluation or use of the
                Biological Material and/or the Cell Lines by the Licensee or any
                Sub-licensee or any persons on their behalf; or

        15.3.5  the use by the Licensee or any Sub-licensee or any persons on
                their behalf any technical or other advice given by BTG or any
                of its officers, employees or agents to the Licensee or from any
                reliance by the Licensee or any third party thereon.

15.4    UPON the initiation of clinical trials to be conducted by the Licensee
hereunder and for six (6) years after termination of this Agreement the Licensee
shall, at its own cost effect and maintain in force with reputable insurers,
adequate insurance in respect of the development, storage, manufacture, use and
supply of Products and/or the Biological Material and/or the Cell Lines and
shall provide evidence of such insurance to BTG on request. Any consequent
policy shall name BTG as additional insured; waive any right of subrogation of
the insurers against BTG; be primary and without right of contribution from
other insurance which may be available to BTG. In the event that a court
determines that the Licensee has failed to meet its obligations to obtain or
maintain adequate insurance, BTG may terminate this Agreement provided however
that this Agreement may not be terminated on this ground unless the Licensee has
been given at least ninety (90) days to cure such failure and has failed to do
so.

15.5    Licensee shall have the right to control the defense compromise or
settlement of any action or claim to be indemnified under Clause 15.3 and BTG
shall use all reasonable endeavours to cooperate with Licensee and Licensee's
counsel in the defense of any such claim or action. Licensee shall have the
right to select counsel. BTG shall not settle or compromise any claim, action or
damages without the written consent of Licensee and the indemnification shall
not apply to any claim, action or damages that is settled or compromised without
such consent. BTG shall promptly notify Licensee of any claim or action that is
to be indemnified and the failure to do so shall relieve Licensee of its
indemnification and defense obligations. The indemnification shall not apply to
any claim or action that arises from the intentional conduct or wrong doing (or
intentional failure to act when required to do so) of BTG.

15.6    BTG warrants and represents that, as at the date hereof: (i) it owns all
right, title and interest in and to the Patents, Biological Material (other than
in respect of any changes to the Genetic Material made by the Licensee) and Cell
Lines licensed under the Agreement to the extent

                                       21
<Page>

necessary to grant the rights granted to the Licensee hereunder; (ii) except as
set forth in Clause 4.3 no other person or entity has any rights or license or
interest in or to the Patent, Biological Material (subject to the above
exclusion) or Cell Lines; (iii) it has the right to grant the rights and
licenses granted hereunder and that this Agreement validly grants to Licensee
the rights and licenses granted hereunder; (iv) that, except as specifically
permitted herein, BTG will not grant any rights or licenses to any third party
in or to the Patents, Biological Material (as described above) or Cell Lines;
and (iv) except for the patents, as far as it is aware, BTG does not own or
control any patent or patent application that would necessarily be infringed by
manufacture, use or sale of all and any Products.

16.     TERMINATION

16.1    THE Licensee may, at any time, terminate this Agreement or any of the
Licences, with or without breach of this Agreement by BTG, by giving not less
than three (3) months notice to that effect. In such notice the Licensee must
specify whether it is terminating on account of breach by BTG, and, if it is,
must give details of that breach.

16.2    Subject to Clause 16.4, BTG may terminate this Agreement, or any of the
Licences or any exclusive rights, upon the happening of any of the following
events:

        16.2.1  if any royalties or other sums payable remain unpaid after the
                due date; or

        16.2.2  if the Licensee is in material breach of any of the terms or
                obligations of this Agreement, other than a payment obligation;
                and other than an obligation under Section 12.5, with the
                provisions of Section 16.3.1. governing any such termination.

        16.2.3  if in the United Kingdom the Licensee has a Receiver or an
                Administrative Receiver or Administrator appointed of the whole,
                or any part, of its undertaking or assets, or in any other
                country has an officer appointed to perform a function analogous
                to that of a Receiver, Administrative Receiver or Administrator;
                or if an order is made, or a resolution passed, for winding-up
                or administering the Licensee, (unless such order or resolution
                is part of a scheme of solvent reconstruction of the Licensee
                which has previously been approved by BTG which approval shall
                not be unreasonably withheld);

        16.2.4  if the Licensee directly or indirectly opposes or assists any
                third party to oppose the grant of any of the Patents or
                disputes or directly or indirectly assists any third party to
                dispute the validity of any of the Patents or the
                confidentiality of the Know-how, except in an action or suit
                brought by BTG against Licensee.

16.3

16.3.1  BTG shall have the right to terminate this Agreement if the Licensee:

                                       22
<Page>

        (i) at any time the Licensee ceases active development and/or
        commercialisation of Products by reference to the latest 6 month report
        produced by the Licensee under clause 12.3 (with the efforts of
        Sub-licensees, members of the Licensee's Group and collaborators being
        considered as efforts of the Licensee in this regard);

        (ii) subject to clause 16.3.3, fails to initiate the clinical trials
        of Products (which for the purposes of this clause 16.3 shall include
        clinical trials undertaken or sponsored by the Licensee or any
        Sub-licensee) by January 1, 2004; or

        (iii) subject to clause 16.3.2, is twelve months or more behind
        schedule on achievement of any milestone as per the Development Plan
        then BTG may, as its sole and exclusive remedy for such delay, serve on
        the Licensee a notice of termination of this Agreement and that notice
        shall have effect six months after the date of service unless within
        that period, the Licensee shall have achieved the relevant Development
        plan milestone.

16.3.2    BTG shall not have the right of termination under clause 16.3.1 (iii),
if the Licensee is using all reasonable endeavors in the circumstances to
develop and to progress towards the marketing of Products in a timely manner and
is prevented from meeting a milestone in the Development Plan due to technical,
safety or efficacy problems outside its reasonable control (including any
significant problems arising under any clinical trials relating to Product). In
event of such delays, the Licensee shall promptly give notice in writing to BTG
of the relevant delay and give evidence to BTG relating thereto. The Licensee
shall deliver to BTG within 2 months of the date of such notice, a revised
Development Plan to take into account such matters and BTG's right of
termination under clause 16.3.1(iii) shall apply equally to such revised
Development Plan.

16.3.3    BTG shall only have the right to terminate this Agreement under clause
16.3.1(ii), if (a) BTG has provided written notice that it will terminate this
Agreement under that clause and (b) within thirty (30) days after receipt of
such written notice Licensee has not paid BTG [*******]. If [*******] is paid to
BTG under this section 16.3.3 such amount shall be fully creditable against any
future payments to be made by Licensee under clauses 2 or 7 of this Agreement.

16.4      With respect to clause 16.2, BTG shall serve on the Licensee a written
notice of termination of the Agreement or any of the Licences or any exclusive
rights that specifies the breach and that notice shall have automatic effect
sixty (60) days after the date of service, unless within that period the
Licensee shall have remedied the breach.

16.5    This Agreement and the rights and licenses granted hereunder may be
terminated or modified only as expressly set forth in a provision of this
Agreement.

17.     RIGHTS ON TERMINATION

17.1    TERMINATION (or expiry) of this Agreement, or of any of the Licenses,
shall be without prejudice to any rights of either party against the other which
may have accrued up to the date of termination.

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

                                       23
<Page>

17.2    ON termination of this Agreement for whatever cause the Licensee shall
pay to BTG royalty in respect of all Products being manufactured at the date of
termination and all Products manufactured and not yet sold. The Licensee shall
then be free to sell or dispose of Products on which royalty has been paid.

17.3    TERMINATION of this Agreement for any reason shall not bring to an end:

        17.3.1  the provisions of clause 4.4;

        17.3.2  the confidentiality obligations of Clause 6.2 until the Know-how
                and the Biological Material and the Cell Lines shall have come
                into the public domain otherwise than through the breach or
                default of the Licensee;

        17.3.3  the obligations of the Licensee in respect of the accounting
                for, payment of and verification of payments and royalties under
                Clauses 2, 7, 8, 9, 10, 17.2, 17.4 and 17.5;

        17.3.4  the obligations contained in Clause 13 in relation to any
                Products falling within Clause 17.2;

        17.3.5  the obligations contained in Clause 15;

17.4    ON early termination the Licensee shall/shall procure transfer to BTG or
destruction (at BTG's option, and in the former case at BTG's expense) of the
Know-how and all copies and/or the Biological Material and/or the Cell Lines
(other than those that include stealth Technology).

17.5    On early termination of this Agreement or the Licenses (except where the
termination is for breach by BTG) the Licensee shall within sixty (60) days of
BTG's request grant to BTG a non-exclusive license with respect to Licensee
Technology to make, use, sell have made, offer for sale, and import Product on
commercially reasonable terms, including the right to grant sublicenses. If the
parties fail to reach agreement with respect to the terms, either party shall
have the right to submit the terms upon which agreement has not been reached to
binding arbitration to a single arbitrator to be agreed between the parties (or
in default nominated by the President for the time being of The Bio Industry
Association in the United Kingdom). Such reference shall be in London, and shall
be deemed to be an arbitration agreement within the meaning of the Arbitration
Acts 1996 or any re-enactment or modification thereof for the time being in
force.

17.6    With respect to Stealth Technology, upon written request of BTG within
sixty (60) days after termination of this Agreement (except where termination is
for breach by BTG), Licensee shall negotiate with BTG with respect to granting a
license to BTG with respect to Stealth Technology in connection with Product to
the extent that Licensee has the ability to do so. Licensee is under no
obligation to enter into such a license and has no liability to BTG for failure
to grant such a license. The granting of the license and/or the terms on which
such a license will be granted is within the sole discretion of Licensee.

17.7    Subject to the following sentence, on termination of this Agreement, BTG
shall, if requested to do so by the Licensee or a Sub-licensee, enter into a
licence agreement on the terms of this Agreement with the relevant

                                       24
<Page>

Sub-licensees. It is acknowledged that BTG shall not be obliged to enter into a
licence with any Sub-licensee who is in breach of its Sub-licence.

At the request of Licensee, BTG shall acknowledge to a sub-licensee in writing
BTG's obligations under this clause 17.7.

18.     MISCELLANEOUS

18.1    THE Licensee shall not assign, charge or otherwise dispose of any of its
rights or obligations under this Agreement, or any of the Licences except that
the Licensee may by submission of written notice to BTG, require this Agreement
to be transferred by way of novation, to a wholly owned Subsidiary or an
acquiror in the case of a merger,- or consolidation or in the case of an
acquisition or transfer of all or substantially all of the Licensee's assets to
which this Agreement relates as long as, at the date of the novation the
Licensee's rights under this Agreement do not represent all, or substantially
all of the Licensee's assets. The Licensee shall reimburse BTG its reasonable
legal costs in respect of any such novation. For the avoidance of doubt, it is
declared that in any such assignment the assignor must transfer all of the
Know-how and Biological Materials to the beneficiary of the novation. Clause 6.2
shall continue to bind the Licensee in the event of such novation.

18.2    The Licensee may grant Sub-Licences (including the right to
sub-sub-license) by written agreement but only on the Sub-Licence Terms.

18.3    THE failure by either party to exercise or enforce any rights under this
Agreement shall not be deemed to be a waiver of any such rights, nor shall any
single or partial exercise of any right, power, or privilege, or further
exercise thereof, operate so as to bar the exercise or enforcement thereof at
any later time.

18.4    THE waiver by either party of any breach of any of the terms of this
Agreement by the other shall not be deemed to be a waiver of any other breach of
the Agreement.

18.5    IF any part or provision of this Agreement is prohibited, or rendered
void or unenforceable, by any legislation, the validity or enforceability of the
Agreement as a whole or of any other part of this Agreement shall not be
affected.

18.6    THE rights and remedies provided in this Agreement are cumulative and
not exclusive of any rights or remedies provided by law or in equity.

18.7    THE Licensee shall not originate any publicity, news release, or other
public announcement, written or oral, whether to the public press, to
shareholders or otherwise, relating to this agreement, to any amendment hereto
or to performance hereunder or to the existence of an arrangement between the
parties without the prior written approval of BTG (such approval not to be
unreasonably withheld or delayed). However this restriction shall not apply to
disclosures required by law or necessary to comply with the rules of any
securities market or applicable regulatory authority.

19.     NOTICES

19.1    ANY notice authorised or required to be given by either party under this
Agreement to the other party, shall be in writing, and shall be deemed

                                       25
<Page>

The COMMON SEAL of BTG
INTERNATIONAL LIMITED was
affixed to this Deed in the
presence of:

[SEAL]                                  /s/ [ILLEGIBLE]
                                        Director/Authorised Signatory

                                        /s/ [ILLEGIBLE]
                                        Authorised Signatory

The COMMON SEAL of TOLERRX, INC
was affixed to this Deed in the
presence of:

                                        /s/ Douglas J. Ringler
                                        Director

                                        /s/ Julio Vega
                                        Secretary<Page>

                                                                   EXHIBIT 10.12

                          REGISTRATION RIGHTS AGREEMENT

     THIS REGISTRATION RIGHTS AGREEMENT is entered into as of February 23, 2001,
by and between Silicon Valley Bank ("Purchaser") and TolerRx, Inc., a Delaware
corporation (the "Company").

                                    RECITALS

     A.   Concurrently with the execution of this Agreement, Purchaser is
acquiring from the Company a Warrant to Purchase Stock (the "Warrants") pursuant
to which Purchaser has rights to acquire from the Company the Shares (as defined
in the Warrant), which Shares when issued shall be shares of the Company's
common stock, $.001 par value per share ("Common Stock").

     B.   By this Agreement, Purchaser and the Company desire to set forth the
registration rights of the Conversion Shares or the Shares all as provided
herein.

          NOW, THEREFORE, in consideration of the premises and the mutual
promises, covenants and conditions hereinafter set forth, the parties hereto
mutually agree as follows:

     1.   REGISTRATION RIGHTS. The Company covenants and agrees as follows:

          1.1   DEFINITIONS. For purposes of this Section 1:

                (a)   The term "register," "registered," and "registration"
refer to a registration effected by preparing and filing a registration
statement or similar document in compliance with the Securities Act of 1933, as
amended, and the rules and regulations thereunder (the "Securities Act"), and
the declaration or ordering of effectiveness of such registration statement or
document;

                (b)   The term "Registrable Securities" means Common Stock
issuable upon the conversion or exercise of the Warrants.

                (c)   The terms "Holder" or "Holders" means Purchaser and its
qualifying transferees under subsection 1.9 hereof who hold Registrable
Securities.

                (d)   The term "SEC" means the Securities and Exchange
Commission.

                (e)   The terms "Form S-1," "Form S-3" etc. shall mean those
forms with such designations as are required by the SEC and any successor or
replacement forms adopted by the SEC.

          1.2   COMPANY REGISTRATION.

                (a)   REGISTRATION. If at any time or from time to time, the
Company shall determine to register any of its securities, for its own account
or the account of any of its shareholders, other than a registration on
Form S-1, Form S-8 relating solely to employee stock option or purchase plans or
on Form S-4 relating solely to an SEC Rule 145 transaction, the Company will:

                      (i)    promptly give to each Holder written notice thereof
(which shall ?? a list of the jurisdictions in which the Company intends to
attempt to qualify such securities under applicable blue sky or other state
securities laws); and

                      (ii)   include in such registration (and qualifications),
and in any ?? writing involved therein, all the Registrable Securities specified
in a written request or requests, made

<Page>

within 30 days after receipt of such written notice from the Company, by any
Holder or Holders, except as set forth in subsection 1.2(c) below.

                (b)   UNDERWRITING. If the registration of which the Company
gives notice is for a registered public offering involving a firm-commitment
underwriting, the Company shall so advise the Holders as a part of the written
notice given pursuant to subsection 1.2(a)(i). In such event the right of any
Holder to registration pursuant to this subsection 1.2 shall be conditioned upon
such Holder's participation in such underwriting and the inclusion of such
Holder's Registrable Securities in the underwriting to the extent provided
herein. All Holders proposing to distribute their securities through such
underwriting shall (together with the Company and the other shareholders
distributing their securities through such underwriting) enter into an
underwriting agreement in customary form (and not inconsistent with the terms
hereof) with the underwriter or underwriters selected for such underwriting by
the Company.

                (c)   In the case of any registration of Common Stock by the
Company in a firm-commitment underwriting, if the managing underwriters give
written advice to the Company that marketing factors require a limitation on the
number of shares of Common Stock (or other securities convertible into or
exercisable or exchangeable for Common Stock) to be offered and sold by
stockholders of Company in such offering, there shall be included in the
offering: (i) first, all securities proposed by Company to be sold for its
account; and (ii) second, that number of shares of Common Stock, if any,
requested to be included in such registration statement by Holders and by other
stockholders of the Company having contractual rights to include shares in such
registration, on a pro rata basis based upon the number of shares of Common
Stock each Holder and each such other stockholder beneficially owns.

          1.3   Intentionally Omitted.

          1.4   EXPENSES OF REGISTRATION. All expenses incurred in connection
with any registration, qualification or compliance pursuant to this Section 1
including without limitation, all registration, filing and qualification fees,
printing expenses, underwriting fees, discounts and commissions, fees and
disbursements of counsel for the Company and expenses of any special audits
incidental to or required by such registration, shall be borne by the Company.
All expenses of any registered offering not otherwise borne by the Company will
be borne pro rata among the Holders, any other shareholders of the Company
participating in such offering and the Company.

          1.5   REGISTRATION PROCEDURES. In the case of each registration,
qualification or compliance effected by the Company pursuant to this
Registration Rights Agreement, the Company will keep each Holder participating
therein advised in writing as to the initiation of each registration,
qualification and compliance and as to the completion thereof. At its expense
the Company will:

                (a)   Prepare and file with the SEC a registration statement
with respect to such Registrable Securities and use reasonable efforts to cause
such registration statement to become effective, and, upon the request of the
Holders of a majority of the Registrable Securities registered thereunder, keep
such registration statement effective for up to 120 days (the "Effective
Period").

                (b)   Prepare and file with the SEC such amendments and
supplements to such registration statement and the prospectus used in connection
with such registration statement as may be necessary to comply with the
provisions of the Securities Act with respect to the disposition of all
securities covered by such registration statement.

                (c)   Furnish to the Holders such numbers of copies of a
prospectus, including a preliminary prospectus, in conformity with the
requirements of the Securities Act, and such other documents as they may
reasonably request in order to facilitate the disposition of Registrable
Securities owned by them.

                                       -2-
<Page>

                (d)   Use reasonable efforts to register and qualify the
securities covered by such registration statement under such other securities or
Blue Sky laws of such jurisdictions as shall be reasonably requested by the
Holders, provided that the Company shall not be required in connection therewith
or as a condition thereto to qualify to do business or to file a general consent
to service of process in any such states or jurisdictions.

                (e)   In the event of any underwritten public offering, enter
into and perform its obligations under an underwriting agreement, in usual and
customary form, with the managing underwriter of such offering. Each Holder
participating in such underwriting shall also enter into and perform its
obligations under such an agreement provided that all other shareholders of the
Company participating in such offering do the same.

                (f)   Notify each Holder of Registrable Securities covered by
such registration statement at any time when a prospectus relating thereto is
required to be delivered under the Securities Act or the happening of any event
as a result of which the prospectus included in such registration statement, as
then in effect, includes an untrue statement of a material fact or omits 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 then
existing.

          1.6   INDEMNIFICATION.

                (a)   The Company will indemnify each Holder of Registrable
Securities and each of its officers, directors and partners, and each person
controlling such Holder within the meaning of Section 15 of the Securities Act
("controlling person"), and each underwriter, if any, and each controlling
person of such underwriter, with respect to which registration, qualification or
compliance of Registrable Securities has been effected pursuant to this
Registration Rights Agreement, against all claims, losses, expenses, damages and
liabilities (or actions in respect thereto) arising out of or based on any
untrue statement (or alleged untrue statement) of a material fact contained in
any prospectus, offering circular or other document (including any related
registration statement, notification or the like) incident to any such
registration, qualification or compliance, or based on any omission (or alleged
omission) to state therein a material fact required to be stated therein or
necessary to make the statement therein not misleading, or any violation or
alleged violation by the Company of the Securities Act, the Securities Exchange
Act of 1934, as amended, and the rules and regulations thereunder ("Exchange
Act") or any state securities law applicable to the Company or any rule or
regulation promulgated any such state law and relating to action or inaction
required of the Company in connection with any such registration, qualification
or compliance, and will reimburse each such Holder, each of its officers,
directors and partners, and each person controlling such Holder, each such
underwriter and each person who controls any such underwriter, within a
reasonable amount of time after incurred for any reasonable legal and any other
expenses incurred in connection with investigating, defending or settling any
such claim, loss, damage, liability or action; PROVIDED, HOWEVER, that the
indemnity agreement contained in this subsection 1.6(a) shall not apply to
amounts paid in settlement of any such claim, loss, damage, liability, or action
if such settlement is effected without the consent of the Company (which consent
shall not be unreasonably withheld or delayed); AND PROVIDED FURTHER, that the
Company will not be liable in any such case to the extent that any such claim,
loss, damage or liability arises out of or is based on any untrue statement or
omission made in reliance upon and conformity with written information furnished
to the Company by an instrument duly executed by such Holder specifically for
use therein.

                (b)   Each Holder will, if Registrable Securities held by or
issuable to such Holder are included in the securities as to which such
registration, qualification or compliance is being effected, indemnify the
Company, each of its directors, officers and controlling persons, each
underwriter, if any, of the Company's securities covered by such a registration
statement, and each controlling person of such underwriter, and each other
Holder, each of its officers, directors, partners and controlling persons,
against all claims, losses, expenses, damages and liabilities (or actions in
respect thereof) arising out of or based on

                                       -3-
<Page>

any untrue statement (or alleged untrue statement) of a material fact contained
in any such registration statement, prospectus, offering circular or other
document, or any omission (or alleged omission) to state therein a material fact
required to be stated therein or necessary to make the statements therein not
misleading, and will reimburse the Company, such Holders, such directors,
officers, partners, persons or underwriters for any reasonable legal or any
other expenses incurred in connection with investigating, defending or settling
any such claim, loss, damage, liability or action, in each case to the extent,
but only to the extent, that such untrue statement (or alleged untrue statement)
or omission (or alleged omission) is made in such registration statement,
prospectus, offering circular or other document in reliance upon and in
conformity with written information furnished to the Company by an instrument
duly executed by such Holder specifically for use therein; PROVIDED, HOWEVER,
that the indemnity agreement contained in this subsection 1.6(b) shall not apply
to amounts paid in settlement of any such claim, loss, damage, liability or
action if such settlement is effected without the consent of the Holder, (which
consent shall not be unreasonably withheld or delayed); AND PROVIDED FURTHER,
that the total amount for which any Holder shall be liable under this subsection
1.6(b) shall not in any event exceed the aggregate net proceeds received by such
Holder from the sale of Registrable Securities held by such Holder in such
registration.

                (c)   Each party entitled to indemnification under this
subsection 1.6 (the "Indemnified Party") shall give notice to the party required
to provide indemnification (the "Indemnifying Party") promptly after such
Indemnified Party has actual knowledge of any claim as to which indemnity may be
sought, and shall permit the Indemnifying Party to assume the defense of any
such claim or any litigation resulting therefrom; provided that counsel for the
Indemnifying Party, who shall conduct the defense of such claim or litigation,
shall be approved by the Indemnified Party (whose approval shall not be
unreasonably withheld), and the Indemnified Party may participate in such
defense at such party's expense; and provided further, that the failure of any
Indemnified Party to give notice as provided herein shall not relieve the
Indemnifying Party of its obligations hereunder, unless such failure resulted in
prejudice to the Indemnifying Party; and provided further, that an Indemnified
Party (together with all other Indemnified Parties which may be represented
without conflict by one counsel) shall have the right to retain one separate
counsel, with the fees and expenses to be paid by the Indemnifying Party, if
representation of such Indemnified Party by the counsel retained by the
Indemnifying Party would be inappropriate due to actual or potential differing
interests between such Indemnified Party and any other party represented by such
counsel in such proceeding. No Indemnifying Party, in the defense of any such
claim or litigation, shall, except with the consent of each Indemnified Party,
consent to entry of any judgment or enter into any settlement which does not
include as an unconditional term thereof the giving by the claimant or plaintiff
to such Indemnified Party of a release from all liability in respect to such
claim or litigation.

                (d)   In order to provide for just and equitable contribution in
circumstances in which the indemnification provided for in this Section 1.6 is
due in accordance with its terms but for any reason is judicially determined to
be unenforceable against the Indemnifying Party or otherwise unavailable to the
Indemnified Party in respect to any losses, claims, damages and liabilities
referred to herein, then the Indemnifying Party shall, in lieu of indemnifying
such Indemnified Party, contribute to the amount paid or payable by such
Indemnified party as a result of such losses, claims, damages or liabilities
to which such party may be subject in such proportion as is appropriate to
reflect the relative fault of the Company, on the one hand, and the selling
Holders, on the other hand, in connection with the statements or omissions which
resulted in such losses, claims, damages or liabilities, as well as any other
relevant equitable considerations. The relative fault of the Company and such
selling Holders shall be determined by reference to, among other things, whether
the untrue or alleged untrue statement, or omission or alleged omission, of
material fact related to the information supplied by the Company or such selling
Holders and the parties' relative intent, knowledge, access to information and
opportunity to correct or prevent such statement or omission. The Company and
Holders agree that it would not be just and equitable if contribution pursuant
to this Section 1.6(d) were determined by pro rata allocation or any other
method of allocation which does not take account of the equitable considerations
referred to above. Notwithstanding the provisions of this Section 1.6(d), (i) in
no case shall any Holder be liable or responsible for any amount in excess of
the net proceeds received

                                       -4-
<Page>

by such Holder from the sale of Registrable Securities pursuant to such
registration; and (ii) no person adjudged guilty of fraudulent misrepresentation
(within the meaning of Section 11(f) of the Securities Act) shall be entitled to
contribution from any person who was not adjudged guilty of such fraudulent
misrepresentation. Any party entitled to contribution shall, promptly after
receipt of notice of commencement of any action, suit or proceeding against such
party in respect of which a claim for contribution may be made against another
party or parties under this Section 1.6(d), notify such party or parties from
whom contribution may be sought, but the omission so to notify such party or
parties from whom contribution may be sought shall not, in the absence of actual
prejudice to such party or parties, relieve it or them from such contribution
obligation. No party shall be liable for contribution with respect to any
action, suit, proceeding or claim settled without its written consent.

                1.7   INFORMATION BY HOLDER. Any Holder or Holders of
Registrable Securities included in any registration shall promptly furnish to
the Company such information regarding such Holder or Holders and the
distribution proposed by such Holder or Holders as the Company may request in
writing and as shall be required in connection with any registration,
qualification or compliance referred to herein.

                1.8   RULE 144 REPORTING AND FORM S-3. With a view to making
available to Holders the benefits of certain rules and regulations of the SEC
which may permit the sale of the Registrable Securities to the public without
registration or pursuant to a registration on Form S-3, the Company agrees at
all times to:

                      (a)    make and keep public information available, as
those terms are understood and defined in SEC Rule 144, after 90 days after the
effective date of the first registration filed by the Company for an offering of
its securities to the general public;

                      (b)    take such action, including the voluntary
registration of its Common Stock under Section 12 of the Exchange Act, as is
necessary to enable the Holders to utilize Form S-3 for the sale of their
Registrable Securities, such action to be taken as soon as practicable after
the end of the fiscal year in which the first registration statement filed by
the Company for the offering of its securities to the general public is declared
effective;

                      (c)    file with the SEC in a timely manner all reports
and other documents required of the Company under the Securities Act and the
Exchange Act (at any time after it has become subject to such reporting
requirements); and

                      (d)    so long as a Holder owns any Registrable
Securities, to furnish to such Holder forthwith upon request a written statement
by the Company as to its compliance with the reporting requirements of said Rule
144 (at any time after 90 days after the effective date of the first
registration statement filed by the Company for an offering of its securities to
the general public), and of the Securities Act and the Exchange Act (at any time
after it has become subject to such reporting requirements), or that it qualify
as a registrant whose securities may be resold pursuant to S-3 (at any time
after it so qualifies), a copy of the most recent annual or quarterly report of
the Company, and such other reports and documents so filed by the Company as the
Holder may reasonably request in complying with any rule or regulation of the
SEC allowing the Holder to sell any such securities without registration or
pursuant to such form.

                1.9   TRANSFER OF REGISTRATION RIGHTS. Holders' rights to cause
the Company to register their securities and keep information available, granted
to them by the Company under subsections 1.2, 1.3 and 1.8 may be assigned to a
transferee or assignee of a Holder's Registrable Securities not sold to the
public, provided, that the Company is given written notice by such Holder at the
time of or within a reasonable time after said transfer, stating the name and
address of said transferee or assignee and identifying the securities with
respect to which such registration rights are being assigned.

                                       -5-
<Page>

     2.   GENERAL.

          2.1   WAIVERS AND AMENDMENTS. With the written consent of the record
or beneficial holders of at least a majority of the Registrable Securities, the
obligations of the Company and the rights of the Holders of the Registrable
Securities under this agreement may be waived (either generally or in a
particular instance, either retroactively or prospectively, and either for a
specified period of time or indefinitely), and with the same consent the
Company, when authorized by resolution of its Board of Directors, may enter into
a supplementary agreement for the purpose of adding any provisions to or
changing in any manner or eliminating any of the provisions of this Agreement;
provided, however, that no such modification, amendment or waiver shall reduce
the aforesaid percentage of Registrable Securities without the consent of all of
the Holders of the Registrable Securities. Upon the effectuation of each such
waiver, consent, agreement of amendment or modification, the Company shall
promptly give written notice thereof to the record holders of the Registrable
Securities who have not previously consented thereto in writing. This Agreement
or any provision hereof may be changed, waived, discharged or terminated only by
a statement in writing signed by the party against which enforcement of the
change, waiver, discharge or termination is sought, except to the extent
provided in this subsection 2.1.

          2.2   GOVERNING LAW. This Agreement shall be governed in all respects
by the laws of the Commonwealth of Massachusetts as such laws are applied to
agreements between Massachusetts residents entered into and to be performed
entirely within Massachusetts.

          2.3   SUCCESSORS AND ASSIGNS. Except as otherwise expressly provided
herein, the provisions hereof shall inure to the benefit of, and be binding
upon, the successors, assigns, heirs, executors and administrators of the
parties hereto.

          2.4   ENTIRE AGREEMENT. Except as set forth below, this Agreement and
the other documents delivered pursuant hereto constitute the full and entire
understanding and agreement between the parties with regard to the subjects
hereof and thereof.

          2.5   NOTICES, ETC. All notices and other communications required or
permitted hereunder shall be in writing and shall be mailed by first class mail,
postage prepaid, certified or registered mail, return receipt requested,
addressed (a) if to Holder, at such Holder's address(es) as set forth below, or
at such other address(es) as such Holder shall have furnished to the Company in
writing, or (b) if to the Company, at the Company's address set forth below, or
at such other address as the Company shall have furnished to the Holder in
writing.

          2.6   SEVERABILITY. In case any provision of this Agreement shall be
invalid, illegal, or unenforceable, the validity, legality and enforceability of
the remaining provisions of this Agreement or any provision of the other
Agreements shall not in any way be affected or impaired thereby.

          2.7   TITLES AND SUBTITLES. The titles of the sections and subsections
of this Agreement are for convenience of reference only and are not to be
considered in construing this Agreement.

          2.8   COUNTERPARTS. This Agreement may be executed in any number of
counterparts, each of which shall be an original, but all of which together
shall constitute one instrument.

     IN WITNESS WHEREOF, the parties have caused this Registration Rights
Agreement to be executed by their duly authorized representatives as of the date
first above written.

                                       -6-
<Page>

PURCHASER                                    COMPANY

SILICON VALLEY BANK                          TOLERRX, INC.

By: /s/ Melissa Stepanis                     By: /s/ D. J. Ringler
    -----------------------------------          ------------------------------
Name: Melissa Stepanis                       Name: D. J. Ringler
      ---------------------------------            ----------------------------
Title: Vice President                        Title:  CEO
       --------------------------------             ---------------------------
Address: 2221 Washington, St.                Address: 675 Mass Ave.
         ------------------------------               -------------------------
         Newton, MA 02462                             Cambridge, MA 02139

copy to: Silicon Valley Bank
         Treasury Department
         3003 Tasman Drive, HA-200
         Santa Clara, CA 95054

6215162

                                       -7-

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