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                                                                   EXHIBIT 10.21

                              CONSULTING AGREEMENT
                               (Peter Barton Hutt)

         This Consulting Agreement (this "Agreement"), dated as of September 18,
2002 (the "Effective Date"), is made by and between Mimeon, Inc., a Delaware
corporation (the "Company"), and Peter Barton Hutt, an individual (the
"Consultant").

         WHEREAS, the Company has engaged and desires to continue to engage the
Consultant to perform consulting services on behalf of the Company and the
Consultant has performed and desires to continue to perform such services on the
terms and conditions hereinafter set forth.

         NOW, THEREFORE, in consideration of the premises and the mutual
covenants set forth herein the parties hereby agree as follows:

         1.       CONSULTING SERVICES.

                  (a)      The Company hereby retains the Consultant and the
Consultant hereby agrees to perform such consulting and advisory services
relating to the Field of Interest (as defined below) as the Company may request
and as set forth in SCHEDULE A (the "Consulting Services"). For purposes of this
Agreement, "Field of Interest" shall mean the field of regulatory strategies for
drug development.

                  (b)      The Consultant agrees to make himself available to
render the Consulting Services, at such times and locations as may be mutually
agreed, from time to time as requested by the Company. Except as provided in
SCHEDULE A, the Consultant may deliver the Consulting Services over the
telephone, in person or by written correspondence. Notwithstanding the
foregoing, the Consultant shall not be required to devote more than an average
of one day per month to the performance of the Consulting Services.

                  (c)      The Consultant agrees to devote his best efforts to
performing the Consulting Services. The Consultant shall comply with all rules,
procedures and standards promulgated from time to time by the Company with
regard to the Consultant's access to and use of the Company's property,
information, equipment and facilities.

         2.       COMPENSATION.  The Company shall pay the Consultant a
consulting fee as provided in SCHEDULE A. The Company will reimburse the
Consultant for such reasonable business expenses as are incurred by the
Consultant in the performance of Consulting Services for the Company and
pre-approved in writing by the Company.

         3.       INDEPENDENT CONTRACTOR. In furnishing the Consulting Services,
the Consultant understands that he will at all times be acting as an independent
contractor of the Company and, as such, will not be an employee of the Company
and will not by reason of this Agreement or by reason of his Consulting Services
to the Company be entitled to participate in or to receive any benefit or right
under any of the Company's employee benefit or welfare plans (including, without
limitation, any social security or unemployment plans or payments). The
Consultant also will be responsible for paying all withholding and other taxes
required by law to be paid as and when the same become due and payable.
Consultant shall not enter into any agreements or incur any obligations on
behalf of the Company.

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         4.       TERM. The parties agree that the term of this Agreement shall
be retroactive to April 1, 2002 and will end on the first anniversary of the
Effective Date or upon earlier termination as provided below (the "Term");
provided, that the Term may be extended for successive one year periods by
mutual agreement of the Company and the Consultant prior to the expiration or
termination of this Agreement. This Agreement may be terminated at any time by
written agreement of both parties.

         5.       EXCEPTIONS TO THIS AGREEMENT.

                  (a)      CERTAIN OTHER CONTRACTS. The Company acknowledges
that the Consultant is now or may become a party to agreements with third
parties relating to the disclosure of information, the ownership of inventions,
restrictions against competition and/or similar matters. The Consultant
represents and agrees that the execution, delivery and performance of this
Agreement does not and will not conflict with any other agreement, policy or
rule applicable to the Consultant. The Consultant will not (i) disclose to the
Company any information that he is required to keep secret pursuant to an
existing confidentiality agreement with a third party, (ii) use the funding,
resources, facilities or inventions of any third party to perform the Consulting
Services, or (iii) perform the Consulting Services in any manner that would give
any third party rights to any intellectual property created in connection with
such services.

                  (b)      PRIOR INVENTIONS. The Consultant has informed the
Company, in writing, of any and all Inventions (as defined in Section 7) which
he claims as his own or otherwise intends to exclude from this Agreement because
it was developed by him prior to the date of this Agreement. The Consultant
acknowledges that after execution of this Agreement he shall have no right to
exclude any Inventions from this Agreement.

         6.       CONFIDENTIAL INFORMATION.

                  (a)      While providing the Consulting Services to the
Company and thereafter, the Consultant shall not, directly or indirectly, (i)
use any Confidential Information (as defined below) other than pursuant to his
provision of the Consulting Services by and for the benefit of the Company, or
(ii) disclose to anyone outside of the Company any such Confidential
Information.

                  (b)      The term "Confidential Information" as used
throughout this Agreement shall mean all trade secrets, proprietary information
and other data or information (and any tangible evidence, record or
representation thereof), written or oral, whether prepared, conceived or
developed by a consultant or employee of the Company (including the Consultant)
or received by the Company from an outside source, which is in the possession of
the Company (whether or not the property of the Company). Without limiting the
generality of the foregoing, Confidential Information shall include:

                           (1)      any Invention, idea, know-how, improvement,
invention, innovation, development, concept, technical data, design, formula,
device, pattern, sequence, method, process, composition of matter, technology,
computer program or software, source code, object code, algorithm, model,
diagram, flow chart, product specification or design, plan for a new or revised
product, sample, compilation of information, or work in process, or parts
thereof,

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and any and all revisions and improvements relating to any of the foregoing (in
each case whether or not reduced to tangible form and whether or not patentable
or copyrightable); and

                           (2)      the name of any customer, supplier,
employee, prospective customer, sales agent or consultant, any sales plan,
marketing material, plan or survey, business plan or opportunity, product or
development plan or specification, business proposal, financial record, or
business record or other record or information relating to the present or
proposed business of the Company.

                  (c)      Notwithstanding the foregoing, the term Confidential
Information shall not apply to information which the Company has voluntarily
disclosed to the public without restriction or which has otherwise lawfully
entered the public domain.

                  (d)      The Consultant acknowledges that the Company from
time to time has in its possession information (including product and
development plans and specifications) which represent information which is
claimed by others to be proprietary and which the Company has agreed to keep
confidential. The Consultant agrees that all such information shall be
Confidential Information for purposes of this Agreement.

                  (e)      The Consultant agrees that all originals and all
copies of materials containing, representing, evidencing, recording, or
constituting any Confidential Information, however and whenever produced
(whether by the Consultant or others), shall be the sole property of the
Company.

                  (f)      The Consultant represents that his retention as a
consultant with the Company and his performance under this Agreement does not,
and shall not, breach any agreement that obligates him to keep in confidence any
trade secrets or confidential or proprietary information of his or of any other
party or to refrain from competing, directly or indirectly, with the business of
any other party. The Consultant shall not disclose to the Company any trade
secrets or confidential or proprietary information of any other party.

                  (g)      The Consultant acknowledges that the Company from
time to time may have agreements with other Persons (as defined in Section
12(j)) or with the United States Government, or agencies thereof, that impose
obligations or restrictions on the Company regarding inventions made during the
course of work under such agreements or regarding the confidential nature of
such work. The Consultant agrees to be bound by all such obligations and
restrictions that are known to him and to take all action necessary to discharge
the obligations of the Company under such agreements.

         7.       INVENTIONS.

                  (a)      CERTAIN INVENTIONS MADE BY OTHERS. During the Term of
this Agreement, the Consultant will use his best efforts to promptly disclose to
the President of the Company, fully, in writing and on a confidential basis, (i)
technology and product opportunities which come to the attention of the
Consultant in the Field of Interest, and (ii) any invention, improvement,
discovery, process, formula or method or other intellectual property relating to
or useful in, the Field of Interest, whether or not patentable or copyrightable,
and whether or not discovered or developed by Consultant.

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                  (b)      INVENTIONS MADE BY THE CONSULTANT. The Consultant
agrees that all Confidential Information and all other discoveries, inventions,
developments, ideas, concepts, trademarks, service marks, logos, methods,
processes, products, formulas, computer programs or software, source code,
object code, algorithms, machines, apparatuses, items of manufacture or
composition of matter, or any new uses therefor or improvements thereon, or any
designs, specifications or modifications or configurations of any kind, or works
of authorship of any kind, including, without limitation, compilations and
derivative works, whether or not patentable or copyrightable, written,
conceived, developed, reduced to practice or otherwise made by the Consultant,
either alone or with others, and in any way related to the Field of Interest or
to tasks assigned to the Consultant during the course of his relationship with
the Company, whether or not written, conceived, developed, reduced to practice
or made on the Company's premises, during the Term or thereafter if resulting or
directly derived from Confidential Information (collectively "Inventions"), and
any and all services and products which embody, emulate or employ any such
Invention or Confidential Information shall be the sole property of the Company
and all copyrights, patents, patent applications, patent rights, trademarks,
trade secrets rights and reproduction rights to, and other proprietary rights
in, each such Invention or Confidential Information, whether or not patentable
or copyrightable, shall belong exclusively to the Company. The Consultant agrees
that, to the fullest extent possible, all such Inventions shall constitute works
made for hire under the copyright laws of the United States, and, to the extent
any Invention does not constitute a work made for hire, hereby assigns to the
Company upon creation all Inventions and any and all copyrights, patents and
other proprietary rights he may have in any Invention, together with the right
to file and/or own, wholly without restrictions, applications for United States
and foreign patents, trademark registration and copyright registration and any
patent, or trademark or copyright registration issuing thereon and the
Consultant appoints any officer of the Company as his duly authorized attorney
to execute, file, prosecute and protect the same before any government agency,
court or authority. The Consultant hereby waives all claims to moral rights in
any Inventions.

         8.       CONSULTANT'S OBLIGATION TO KEEP RECORDS. Consultant shall make
and maintain adequate and current written records of all Inventions, and shall
disclose all Inventions promptly, fully, in writing and on a confidential basis
to the President of the Company immediately upon development of the same and at
any time upon request. Such records shall be available to and remain the sole
property of the Company at all times.

         9.       CONSULTANT'S OBLIGATION TO COOPERATE. The Consultant will, at
any time during or after the Term of this Agreement, upon request of the
Company, execute all documents and perform all lawful acts which the Company
considers necessary or advisable to secure its rights hereunder and to carry out
the intent of this Agreement. Without limiting the generality of the foregoing,
the Consultant will assist the Company in any reasonable manner to obtain for
its own benefit patents, copyrights or other proprietary rights in any and all
countries with respect to all Inventions assigned pursuant to Section 7, and the
Consultant will execute, when requested, all applications and assignments of all
patents, copyrights and other proprietary rights in the Inventions to the
Company or its designees, and any other lawful documents deemed necessary by the
Company to carry out the purposes of this Agreement, and the Consultant will
further assist the Company in every way to enforce any patents, copyrights and
other proprietary rights obtained, including testifying in any suit or
proceeding involving any of said patents, copyrights or other proprietary rights
or executing any documents deemed necessary by the Company, all

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without further consideration than provided for herein. It is understood that
reasonable out-of-pocket expenses of the Consultant's assistance incurred at the
request of the Company under this Section 9 will be reimbursed by the Company.

         10.      NONSOLICITATION. During the Term, the Consultant shall not (i)
solicit, encourage, or take any other action which is intended to induce any
employee of, or consultant to, the Company (or any other Person who may have
been employed by, or may have been a consultant to, the Company during the Term)
to terminate his or her employment or relationship with the Company in order to
become employed by or otherwise perform services for any other Person or (ii)
solicit, endeavor to entice away from the Company or otherwise interfere with
the relationship of the Company with any Person who is, or was within the
then-most recent 12 month period, a client or customer of the Company.

         11.      RETURN OF PROPERTY. Upon expiration or termination of the
Consultant's engagement with the Company, or at any other time upon request of
the Company, the Consultant shall return promptly any and all Confidential
Information, including customer or prospective customer lists, other customer or
prospective customer information or related materials, computer programs,
software, electronic data, specifications, drawings, blueprints, medical
devices, samples, reproductions, sketches, notes, notebooks, memoranda, reports,
records, proposals, business plans, or copies of them, other documents or
materials, tools, equipment, or other property belonging to the Company or its
customers which the Consultant may then possess or have under his control. The
Consultant further agrees that upon expiration or termination of his engagement
he shall not take with him any documents or data in any form or of any
description containing or pertaining to Confidential Information or any
Inventions.

         12.      MISCELLANEOUS.

                  (a)      ENTIRE AGREEMENT. This Agreement and the documents
referred to herein constitute the entire agreement among the parties with
respect to the subject matter hereof and supersede all other prior agreements
and understandings, both written and oral, between the parties with respect to
such subject matter.

                  (b)      ASSIGNMENT. This Agreement shall be binding upon and
inure to the benefit of the parties hereto and their respective successors and
permitted assigns, provided, however, that the obligations of the Consultant are
personal and shall not be assigned by him. Any non-consented-to assignment or
delegation by the Consultant, whether express or implied or by operation of law,
shall be void and shall constitute a breach and a default by the Consultant.

                  (c)      AMENDMENTS AND SUPPLEMENTS.  This Agreement may not
be altered, changed or amended, except by an instrument in writing signed by the
parties hereto.

                  (d)      NO WAIVER. The terms and conditions of this Agreement
may be waived only by a written instrument signed by the party waiving
compliance. The failure of any party hereto to enforce at any time any of the
provisions of this Agreement shall in no way be construed to be a waiver of any
such provision, nor in any way to affect the validity of this Agreement or any
part hereof or the right of such party thereafter to enforce each and every such

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provision. No waiver of any breach of or non-compliance with this Agreement
shall be held to be a waiver of any other or subsequent breach or
non-compliance.

                  (e)      GOVERNING LAW.  This Agreement shall be governed by,
and construed and enforced in accordance with, the substantive laws of the
Commonwealth of Massachusetts, without regard to its principles of conflicts of
laws.

                  (f)      NOTICE. All notices and other communications
hereunder (other than Consulting Services, which shall be delivered in the
manner specified in Section 1 and SCHEDULE A) shall be in writing and shall be
deemed given if delivered by hand, sent by facsimile transmission with
confirmation of receipt, sent via a reputable overnight courier service with
confirmation of receipt requested, or mailed by registered or certified mail
(postage prepaid and return receipt requested) to the parties at the following
addresses (or at such other address for a party as shall be specified by like
notice), and shall be deemed given on the date on which delivered by hand or
otherwise on the date of receipt as confirmed:

         To the Company:

                  Mimeon, Inc.
                  45 Moulton Street
                  Cambridge, MA  02138
                  Attention:  President
                  Fax:  617.876.8012

         To the Consultant:

                  Peter Barton Hutt
                  c/o Covington & Burling
                  1201 Pennsylvania, NW
                  Washington, DC 20004
                  Fax: 202-778-5522

                  (g)      REMEDIES. The Consultant recognizes that money
damages alone would not adequately compensate the Company in the event of breach
by the Consultant of this Agreement, and the Consultant therefore agrees that,
in addition to all other remedies available to the Company at law, in equity or
otherwise, the Company shall be entitled to injunctive relief for the
enforcement hereof. All rights and remedies hereunder are cumulative and are in
addition to and not exclusive of any other rights and remedies available at law,
in equity, by agreement or otherwise.

                  (h)      SURVIVAL; VALIDITY. (i) Notwithstanding the
termination of the Consultant's relationship with the Company (whether pursuant
to Section 4 or otherwise), the Consultant's covenants and obligations set forth
in Sections 6, 7, 9, 10, 11 and 12 shall remain in effect and be fully
enforceable in accordance with the provisions thereof. (ii) In the event that
any provision of this Agreement shall be determined to be unenforceable by
reason of its extension for too great a period of time or over too large a
geographic area or over too great a range of activities, it shall be interpreted
to extend only over the maximum period of time, geographic area or range of
activities as to which it may be enforceable. (iii) If, after application of
Section 12(h)(ii), any

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provision of this Agreement shall be determined to be invalid, illegal or
otherwise unenforceable by a court of competent jurisdiction, the validity,
legality and enforceability of the other provisions of this Agreement shall not
be affected thereby. (iv) Except as otherwise provided in this Section 12(h),
any invalid, illegal or unenforceable provision of this Agreement shall be
severable, and after any such severance, all other provisions hereof shall
remain in full force and effect.

                  (i)      CONSTRUCTION. A reference to a Section or a Schedule
shall mean a Section in or Schedule to this Agreement unless otherwise expressly
stated. The titles and headings herein are for reference purposes only and shall
not in any manner limit the construction of this Agreement which shall be
considered as a whole. The words "include," "includes" and "including" when used
herein shall be deemed in each case to be followed by the words "without
limitation." Whenever the context may require, any pronouns used herein shall
include the corresponding masculine, feminine or neuter forms, and the singular
form of names and pronouns shall include the plural and vice-versa.

                  (j)      CERTAIN DEFINITIONS.  "Person" shall mean an
individual, a corporation, an association, a partnership, an estate, a trust and
any other entity or organization.

                  (k)      COUNTERPARTS.  This Agreement may be executed in one
or more counterparts, all of which together shall constitute one and the same
Agreement.

                                      *****

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         IN WITNESS WHEREOF, the parties have caused this Consulting Agreement
to be executed as an agreement under seal as of the date first written above.

                                    MIMEON, INC.


                                    By: /s/ Susan K. Whoriskey, Ph.D.
                                       -----------------------------------------
                                    Susan K. Whoriskey, Ph.D
                                    Vice President Licensing and Business
                                    Development


                                    CONSULTANT


                                    /s/ Peter Barton Hutt
                                    --------------------------------------------
                                    Peter Barton Hutt

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                                   SCHEDULE A

         1.       Description of Consulting Services.

                  The Consultant shall provide such consulting services as the
Company reasonably requests in connection with the operation of the Company's
business.

         2.       Compensation.

                  The Company shall grant to Consultant a Non-Statutory Stock
Option to purchase 5,000 shares of Mimeon, Inc. common stock at a purchase price
of $0.278 per share pursuant to and in accordance with the Non-Statutory Stock
Option agreement attached hereto as Exhibit A.

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                              [Letterhead of MOMENTA]


September 29, 2003

Peter Barton Hutt, Esq.
402 Prince Street
Alexandria, Virginia  22314

Dear Peter:

Reference is made to the Consulting Agreement dated September 18, 2002 between
Momenta Pharmaceuticals, Inc. and you (the "Agreement"). Capitalized terms used
herein and not otherwise defined shall have the meanings given such terms in the
Agreement.

Pursuant to Section 4 of the Agreement, Company and Consultant hereby agree to
extend the Term of the Agreement for one additional year, from September 18,
2003 through September 17, 2004 (the "Renewal Period"). Except as otherwise
agreed to in this Letter Agreement, the same terms and conditions as are set
forth in the Agreement shall apply to the rendering of Consulting Services
during the Renewal Period.

As compensation for the Consulting Services during the Renewal Period,
Consultant will be granted an additional non-statutory stock option to purchase
5,000 shares of the Common Stock of the Company, at an exercise price equal to
the fair market value of a share of Common Stock on the date of grant by the
Company, with such option to vest in 12 equal monthly installments over the
one-year Renewal Period.

With respect to Section 4 of the Agreement, Company and Consultant agree that
Company will have the right to terminate the Agreement on written notice to
Consultant in the case of: (a) a breach by Consultant of a material provision of
the Agreement, where such breach cannot be cured or is not cured within fifteen
(15) days after Consultant's receiving written notice of such breach from
Company; (b) a physical or mental inability of Consultant to perform the
Consulting Services, which physical or mental inability exists for a period of
at least one hundred eighty (180) consecutive days; (c) a material and
intentional misappropriation or destruction of Company's funds, properties or
assets; or (d) a conviction of a crime involving moral turpitude or constituting
a felony or an entering of a plea of nolo contendere to the same.

If the foregoing is in conformity with your understanding, please sign both
copies of this Letter Agreement and return one fully-executed copy to me.

Very truly yours,

/s/ Susan K. Whoriskey
Susan K. Whoriskey
Vice President, Licensing and Business Development



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Peter Barton Hutt, Esq.
September 29, 2003
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Agreed and accepted:



/s/ Peter Barton Hutt
-----------------------------
Peter Barton Hutt




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