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                                                                  EXHIBIT 10.1



                           LOAN MODIFICATION AGREEMENT

         This Loan Modification Agreement (this "Loan Modification Agreement")
is entered into as of June 11, 2003, by and between SILICON VALLEY BANK, a
California-chartered bank, with its principal place of business at 3003 Tasman
Drive, Santa Clara, California 95054 and with a loan production office located
at One Newton Executive Park, Suite 200, 2221 Washington Street, Newton,
Massachusetts 02462, doing business under the name "Silicon Valley East"
("Bank") and GTC BIOTHERAPEUTICS, INC., formerly known as Genzyme Transgenics
Corporation, a Massachusetts corporation with its chief executive office located
at 175 Crossing Boulevard, Suite 410, Framingham, Massachusetts 01702
("Borrower").

1. DESCRIPTION OF EXISTING INDEBTEDNESS AND OBLIGATIONS. Among other
indebtedness and obligations which may be owing by Borrower to Bank, Borrower is
indebted to Bank pursuant to a loan arrangement dated as of March 27, 2002,
evidenced by, among other documents, a certain Loan and Security Agreement dated
as of March 27, 2002 between Borrower and Bank (as may be amended from time to
time, the "Loan Agreement"). The Loan Agreement established: (i) a working
capital line of credit in favor of Borrower in the maximum principal amount of
One Million Dollars ($1,000,000.00) (the "Committed Revolving Line"), (ii) an
equipment line of credit in favor of Borrower in the maximum principal amount of
Four Million Dollars ($4,000,000.00) (the "Committed Equipment Line"), and (iii)
a term loan to the Borrower in the principal amount of up to Six Million Six
Hundred Thousand Dollars ($6,600,000.00) (the "Term Loan"). Capitalized terms
used but not otherwise defined herein shall have the same meaning as in the Loan
Agreement.

Hereinafter, all indebtedness and obligations owing by Borrower to Bank shall be
referred to as the "Obligations".

2. DESCRIPTION OP COLLATERAL. Repayment of the Obligations is secured by the
Collateral as described in the Loan Agreement and by the Collateral as described
in a certain Pledge Agreement dated March 27, 2002 by Borrower in favor of Bank
(together with any other collateral security granted to Bank, the "Security
Documents").

Hereinafter, the Security Documents, together with all other documents
evidencing or securing the Obligations shall be referred to as the "Existing
Loan Documents".

3. DESCRIPTION OF CHANGE IN TERMS.

         A.       MODIFICATIONS TO LOAN AGREEMENT.

                  1.       The outstanding balance of the Term Loan and the
                           Equipment Advances under the Committed Equipment Line
                           shall continue to amortize and be repaid in
                           accordance with the terms of the Loan Agreement.

                  2.       Section 2.1.4 of the Loan Agreement entitled
                           "Equipment Advances" shall be retitled "2002
                           Equipment Advances". All references in the Loan
                           Agreement to the "Committed Equipment Line" shall
                           mean and refer to the "2002 Committed Equipment
                           Line".


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                  3.       Section 2.1.6 of the Loan Agreement entitled
                           "Undisbursed Credit Extensions" shall be renumbered
                           as Section 2.1.7 to appear immediately following
                           Section 2.1.6 (as described below).

                  4.       The Loan Agreement is hereby amended by incorporating
                           into Article 2 the following new Section 2.1.6
                           entitled "2003 Equipment Advances" to appear
                           immediately following Section 2.1.5 thereof:

                                    "2.1.6. 2003 EQUIPMENT ADVANCES.

                                             (a) AVAILABILITY. Through December
                                    31, 2003 (the "2003 Equipment Availability
                                    End Date"), Bank shall make Equipment
                                    Advances under the 2003 Committed Equipment
                                    Line not exceeding the 2003 Committed
                                    Equipment Line. The Equipment Advances under
                                    the 2003 Committed Equipment Line may only
                                    be used to finance Eligible Equipment
                                    purchased after January 1, 2003 and no
                                    Equipment Advances under the 2003 Committed
                                    Equipment Line may exceed 100% of the
                                    equipment invoice excluding taxes, shipping,
                                    warranty charges, freight discounts and
                                    installation expense relating to such
                                    Equipment, unless such costs constitute
                                    Other Equipment. Equipment Advances when
                                    repaid may not be reborrowed.

                                             (b) INTEREST RATE. Interest accrues
                                    from the date of each Equipment Advance
                                    under the 2003 Committed Equipment Line at
                                    the rate in Section 2.2(a) and is payable on
                                    the Payment Date of each month.

                                             (c) REPAYMENT. Each Equipment
                                    Advances under the 2003 Committed Equipment
                                    Line shall be payable in: (a) 60 consecutive
                                    equal monthly installments of principal
                                    (based upon an amortization schedule of 60
                                    months), plus (b) monthly payments of
                                    accrued interest, on the Payment Date of
                                    each month commencing with the first Payment
                                    Date following the date of such Equipment
                                    Advance and ending on the 2003 Equipment
                                    Maturity Date applicable to such Equipment
                                    Advance.

                                             (d) EQUIPMENT ADVANCE REQUEST. To
                                    obtain an Equipment Advance under the 2003
                                    Committed Equipment Line, Borrower must
                                    notify Bank (the notice is irrevocable) by
                                    facsimile no later than 3:00 p.m. Eastern
                                    time one (1) Business Day before the day on
                                    which the Equipment Advance is to be made.
                                    The notice in the form of EXHIBIT B
                                    (Payment/Advance Form) must be signed by a
                                    Responsible Officer or designee and include
                                    a copy of the invoice for the Equipment
                                    being financed."


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                  5.       The Loan Agreement is hereby amended by deleting the
                           following text appearing as the first sentence of
                           Section 2.2(a) entitled "Interest Rate":

                                    "The principal amounts outstanding under the
                                    Committed Revolving Line, Committed
                                    Equipment Line and the Term Loan shall
                                    accrue interest at a per annum rate equal to
                                    the Bank's Prime Rate."

                           and inserting in lieu thereof the following:

                                    "The principal amounts outstanding under the
                                    Committed Revolving Line, the 2002 Committed
                                    Equipment Line, the Term Loan and the 2003
                                    Committed Equipment Line shall accrue
                                    interest at a per annum rate equal to the
                                    Bank's Prime Rate."

                  6.       The Loan Agreement is hereby amended by deleting the
                           following text appearing in Section 6.2(a) thereof:

                                    "and (v) other financial information
                                    reasonably requested by Bank."

                           and inserting in lieu thereof the following:

                                    "(v) updated projections approved by
                                    Borrower's Board of Directors, no less
                                    frequently than annually within thirty (30)
                                    days of the commencement of such fiscal
                                    year; and (vi) other financial information
                                    reasonably requested by Bank."

                  7.       The Loan Agreement is hereby amended by deleting the
                           following text appearing as the second sentence of
                           Section 6.6 entitled "Primary Accounts":

                                    "In addition to the foregoing, on the
                                    Closing Date, and at all times thereafter,
                                    Borrower and its wholly owned Subsidiaries
                                    shall maintain not less than Ten Million
                                    Dollars ($10,000,000.00) in unrestricted
                                    cash or securities, in accounts with the
                                    Bank or a Bank subsidiary, directed by
                                    Bank."

                           and inserting in lieu thereof the following:

                                    "In addition to the foregoing, Borrower and
                                    its wholly owned Subsidiaries shall
                                    maintain: (i) not less than Ten Million
                                    Dollars ($10,000,000.00) in unrestricted
                                    cash or securities, in accounts with the
                                    Bank or a Bank subsidiary, directed by Bank,
                                    at all times through June 29, 2003, and (ii)
                                    not less than Fifteen Million Dollars
                                    ($15,000,000.00) in unrestricted cash or
                                    securities, in accounts with the Bank or a
                                    Bank subsidiary, directed by Bank,
                                    commencing June 30, 2003 and at all times
                                    thereafter."


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                  8.       The Loan Agreement is hereby amended by deleting the
                           definition of "Equipment Advance" appearing in
                           Section 13.1 and inserting in lieu thereof the
                           following:

                                    "EQUIPMENT ADVANCE" is defined in Section
                                    2.1.4 and shall apply to all Equipment
                                    Advances under this Agreement, as amended
                                    from time to time.

                  9.       The Loan Agreement is hereby amended by incorporating
                           into Section 13.1 the following definitions to appear
                           alphabetically therein:

                                    "REVOLVING MATURITY DATE" is March 25, 2004.

                                    "2003 COMMITTED EQUIPMENT LINE" is an
                                    Equipment Advance or Equipment Advances of
                                    up to Two Million Two Hundred Fifty Thousand
                                    Dollars ($2,250,000.00).

                                    "2003 EQUIPMENT AVAILABILITY END DATE" is
                                    defined in Section 2.1.6(a).

                                    "2003 EQUIPMENT MATURITY DATE" is, for each
                                    Equipment Advance under the 2003 Committed
                                    Equipment Line, the sixtieth (60th) Payment
                                    Date following the date of such Equipment
                                    Advance.

4. FEES. The Borrower shall pay to Bank a modification fee equal to $2,500.00,
which modification fee shall be due and payable on the date hereof and shall be
deemed fully earned as of the date hereof. The Borrower shall also reimburse
Bank for all legal fees and expenses incurred in connection with this amendment
to the Existing Loan Documents.

5. RATIFICATION OF PLEDGE AGREEMENT. Borrower hereby ratifies, confirms and
reaffirms, all and singular, the terms and conditions of a certain Pledge
Agreement dated as of March 27, 2002 between Borrower and Bank, and
acknowledges, confirms and agrees that said Pledge Agreement shall remain in
full force and effect and the Collateral defined therein shall continue to
secure the Obligations under the Loan Agreement, as amended hereby.

6. RATIFICATION OF NEGATIVE PLEDGE AGREEMENT. Borrower hereby ratifies, confirms
and reaffirms, all and singular, the terms and conditions of a certain Negative
Pledge Agreement dated as of March 27, 2002 between Borrower and Bank, and
acknowledges, confirms and agrees that said Negative Pledge Agreement shall
remain in full force and effect.

7. ADDITIONAL COVENANTS; RATIFICATION OF PERFECTION CERTIFICATE. Borrower shall
not, without at least thirty (30) days prior written notice to Bank: (i)
relocate its chief executive office, or add any new offices or business
locations (unless such new offices or business locations contain less than Five
Thousand Dollars ($5,000.00) in Borrower's assets or property), or (ii) change
its jurisdiction of organization, or (iii) change its organizational structure
or type, or (iv) change its legal name, or (v) change any organizational number
(if any) assigned by its jurisdiction of organization. Borrower hereby ratifies,
confirms and reaffirms, all


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and singular, the terms and disclosures contained in a certain Perfection
Certificate dated as of March 27, 2002 between Borrower and Bank, and
acknowledges, confirms and agrees the disclosures and information provided by
Borrower to Bank in the Perfection Certificate has not changed, as of the date
hereof.

8. AUTHORIZATION TO FILE. Borrower hereby authorizes Bank to file financing
statements without notice to Borrower, with all appropriate jurisdictions, as
Bank deems appropriate, in order to further perfect or protect Bank's interest
in the Collateral.

9. CONSISTENT CHANGES. The Existing Loan Documents are hereby amended wherever
necessary to reflect the changes described above.

10. RATIFICATION OF LOAN DOCUMENTS. Borrower hereby ratifies, confirms, and
reaffirms all terms and conditions of all security or other collateral granted
to the Bank, and confirms that the indebtedness secured thereby includes,
without limitation, the Obligations.

11. NO DEFENSES OF BORROWER. Borrower agrees that, as of this date, it has no
defenses against the obligations to pay any amounts under the Obligations.

12. CONTINUING VALIDITY. Borrower understands and agrees that in modifying the
existing Obligations, Bank is relying upon Borrower's representations,
warranties, and agreements, as set forth in the Existing Loan Documents. Except
as expressly modified pursuant to this Loan Modification Agreement, the terms of
the Existing Loan Documents remain unchanged and in full force and effect.
Bank's agreement to modifications to the existing Obligations pursuant to this
Loan Modification Agreement in no way shall obligate Bank to make any future
modifications to the Obligations. Nothing in this Loan Modification Agreement
shall constitute a satisfaction of the Obligations. It is the intention of Bank
and Borrower to retain as liable parties all makers of Existing Loan Documents,
unless the party is expressly released by Bank in writing. No maker will be
released by virtue of this Loan Modification Agreement.

13. RIGHT OF SET-OFF. In consideration of Bank's agreement to enter into this
Loan Modification Agreement, Borrower and any guarantor hereby reaffirm and
hereby grant to Bank, a lien, security interest and right of setoff as security
for all Obligations to Bank, whether now existing or hereafter arising upon and
against all deposits, credits, collateral and property, now or hereafter in the
possession, custody, safekeeping or control of Bank or any entity under the
control of Silicon Valley Bank (including a Bank subsidiary) or in transit to
any of them. At any time after the occurrence and during the continuance of an
Event of Default, without demand or notice, Bank may set off the same or any
part thereof and apply the same to any liability or obligation of Borrower and
any guarantor even though unmatured and regardless of the adequacy of any other
collateral securing the loan. ANY AND ALL RIGHTS TO REQUIRE BANK TO EXERCISE ITS
RIGHTS OR REMEDIES WITH RESPECT TO ANY OTHER COLLATERAL WHICH SECURES TEE
OBLIGATIONS, PRIOR TO EXERCISING ITS RIGHT OF SETOFF WITH RESPECT TO SUCH
DEPOSITS, CREDITS OR OTHER PROPERTY OF THE BORROWER OR ANY GUARANTOR, ARE HEREBY
KNOWINGLY, VOLUNTARILY AND IRREVOCABLY WAIVED.


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14. JURISDICTION/VENUE. Borrower accepts for itself and in connection with its
properties, unconditionally, the exclusive jurisdiction of any state or federal
court of competent jurisdiction in the Commonwealth of Massachusetts in any
action, suit, or proceeding of any kind against it which arises out of or by
reason of this Loan Modification Agreement; provided, however, that if for any
reason Bank cannot avail itself of the courts of the Commonwealth of
Massachusetts, then venue shall lie in Santa Clara County, California.
NOTWITHSTANDING THE FOREGOING, THE BANK SHALL HAVE THE RIGHT TO BRING ANY ACTION
OR PROCEEDING AGAINST THE BORROWER OR ITS PROPERTY IN THE COURTS OF ANY OTHER
JURISDICTION WHICH THE BANK DEEMS NECESSARY OR APPROPRIATE IN ORDER TO REALIZE
ON THE COLLATERAL OR TO OTHERWISE ENFORCE THE BANK'S RIGHTS AGAINST THE BORROWER
OR ITS PROPERTY.

15. COUNTERSIGNATURE. This Loan Modification Agreement shall become effective
only when it shall have been executed by Borrower and Bank (provided, however,
in no event shall this Loan Modification Agreement become effective until signed
by an officer of Bank in California).

         This Loan Modification Agreement is executed as a sealed instrument
under the laws of the Commonwealth of Massachusetts as of the date first written
above.

BORROWER:                                       BANK:

GTC BIOTHERAPEUTICS, INC.,                      SILICON VALLEY BANK, doing
formerly known as Genzyme Transgenics           business as SILICON VALLEY EAST
Corporation


By: /s/ JOHN B. GREEN                           By: /s/ DOUGLAS MARSHALL
    --------------------------------                ---------------------------

Name:  John B. Green                            Name:  Douglas Marshall

Title: Sr. Vice President and CFO               Title: Vice President


                                                SILICON VALLEY BANK


                                                By: /s/ MAGGIE GARCIA
                                                    ---------------------------

                                                Name:  Maggie Garcia

                                                Title: AVP
                                                (signed in Santa Clara County,
                                                California)


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