QuickLinks -- Click here to rapidly navigate through this document

Exhibit 10.5

This instrument is subject to the terms of a Subordination Agreement dated the
date hereof by and between Genzyme Corporation and Silicon Valley Bank.

SUBORDINATED SECURED PROMISSORY NOTE

$4,772,850.00
 
April 4, 2002
Boston, Massachusetts

        For value received, the undersigned Genzyme Transgenics Corporation
("GTC") promises to pay to Genzyme Corporation ("Genzyme"), or order, at its
office at One Kendall Square, Cambridge, MA 02139, the principal sum of Four
Million Seven Hundred Seventy-Two Thousand Eight Hundred Fifty Dollars
($4,772,850.00), in two equal installments of Two Million Three Hundred
Eighty-Six Thousand Four Hundred Twenty-Five Dollars ($2,386,425.00), the first
such installment to be due and payable on April 4, 2005, and the second such
installment to be due and payable on April 4, 2006.

        1.    Interest.    The principal amount from time to time outstanding
shall bear interest computed at a rate equal to the LIBOR Rate plus one percent
(1.00%) per annum, which interest rate shall change on the date of each change
in the LIBOR Rate. "LIBOR Rate" means the rate for a ninety (90) day period
(each such 90-day period a "LIBOR Period") appearing in The Wall Street Journal
two Banking Days prior to the commencement of such LIBOR Period and effective as
of the first day of such LIBOR Period. The initial LIBOR Period shall commence
on the date of this Note. If any LIBOR Period would otherwise end on a date that
is not a Banking Day, such LIBOR Period shall instead end on the next succeeding
Banking Day. "Banking Day" means a day on which commercial banks are open for
business in Boston, Massachusetts and, with respect to determinations of the
LIBOR Rate, on which the London interbank market is open. Interest shall be
payable in arrears on each of June 30th, September 30th, December 31st, and
March 31st of each year following the date hereof, with the final interest
payment due and payable on the date the final principal payment on this Note is
made. Interest on this Note shall be computed on the basis of a year of 365 days
for the actual number of days elapsed.

        2.    Prepayment.    GTC, at its option, shall have the right from time
to time, without premium or penalty, to prepay this Note at any time in part or
in whole. GTC shall also pay all accrued but unpaid interest at the time of any
such prepayment. No principal amounts of this Note voluntarily prepaid by GTC
may be reborrowed pursuant to the provisions of this Note. Any partial payment
of the indebtedness evidenced by this Note shall be applied first to interest
hereon accrued to the date of payment, then to the payment of other amounts
(except principal) at the time unpaid hereunder, and finally to the unpaid
principal hereof. Partial prepayments shall be in an aggregate principal amount
of $100,000 or a whole multiple thereof.

        3.    Payments.    All payments of principal, interest and other amounts
payable on or in respect of this Note or the indebtedness evidenced hereby shall
be made to Genzyme at the address specified above and in lawful money of the
United States of America, in funds immediately available to Genzyme as it may
direct. Whenever any payment to be made in respect of this Note becomes due on a
day which is a Saturday, Sunday or legal holiday, the maturity of such payment
shall be extended to the next succeeding Banking Day and interest hereon shall
accrue during such extensions.

        4.    Default and Acceleration.    Each of the following events shall
constitute a default (a "Default") hereunder: (a) the failure to make any
payment of principal or interest within five (5) days of the date when due;
(b) GTC defaults on any other indebtedness owed to the holders of Senior
Indebtedness (as defined in Section 15), beyond any applicable period of grace;
or (c) GTC makes an assignment for the

1

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

benefit of creditors, or bankruptcy or similar proceedings are commenced by or
against GTC, or all or a substantial part of GTC's property is attached or a
receiver, trustee or other custodian is appointed therefor. At the option of
Genzyme, all principal, interest, and any other amounts payable on or in respect
of this Note shall become immediately due and payable without notice or demand
upon the occurrence at any time of any Default, provided, however, that upon any
Default specified in subsection (c) above this Note shall become immediately due
and payable without any demand, notice or other action by Genzyme.

        5.    Costs of Collection.    Should the indebtedness evidenced by this
Note or any part thereof be collected by action at law, or in bankruptcy,
receivership or other court proceedings, or should counsel be retained for
collection of this Note after Default, GTC agrees to pay, upon demand by
Genzyme, in addition to principal and interest and other sums, if any, due and
payable hereon, court costs and reasonable attorneys' fees and other collection
charges, together with interest thereon at the rate applicable under this note,
unless prohibited by law, all without relief from valuation or appraisement
laws.

        6.    Security Interest.    As security for the Secured Obligations
described in Section 7 hereof, GTC hereby grants to Genzyme a security interest
in and lien on all of the tangible and intangible personal property and fixtures
of GTC described below, whether now owned or existing or hereafter acquired or
arising, together with any and all additions thereto and replacements therefor
and proceeds and products thereof (hereinafter referred to collectively as the
"Collateral"):

                (a)  All goods, equipment, inventory, contract rights or rights
to payment of money, license agreements, franchise agreements, general
intangibles (including payment intangibles), accounts (including health-care
receivables), documents, instruments (including any promissory notes), chattel
paper (whether tangible or electronic), cash, deposit accounts, fixtures,
letters of credit rights (whether or not the letter of credit is evidenced by a
writing), commercial tort claims, securities, and all other investment property
supporting obligations, and financial assets, whether now owned or hereafter
acquired, wherever located; and

                (b)  All GTC's books and records (including ledgers, records
regarding GTC's assets or liabilities, the Collateral, business operations or
financial condition and all computer programs or discs or any equipment
containing the information) relating to the foregoing and any and all claims,
rights and interests in any of the above and all substitutions for, additions,
attachments, accessories, accessions and improvements to and replacements,
products, proceeds and insurance proceeds of any or all of the foregoing.

The Collateral does not include any Intellectual Property. For purposes of this
Section, "Intellectual Property" shall mean copyright rights, copyright
applications, copyright registrations and like protections in each work of
authorship and derivative work, whether published or unpublished, now owned or
later acquired; any patents, trademarks, service marks and applications
therefor; any trade secret rights, including any rights to unpatented
inventions, now owned or hereafter acquired. Notwithstanding the foregoing, the
Collateral shall include all accounts, license and royalty fees and other
revenues, proceeds, or income arising out of or relating to any of the foregoing
intellectual property.

        To the extent a court of competent jurisdiction holds that a security
interest in any Intellectual Property is necessary to have a security interest
in any accounts, license and royalty fees and other revenues, proceeds, or
income arising out of or relating to any of the foregoing Intellectual Property,
then the Collateral shall, effective as of the date hereof, include the
Intellectual Property, to the extent necessary to permit perfection of the
Genzyme's security interest in such accounts, license and royalty fees and other
revenues, proceeds, or income arising out of or relating to any of the
Intellectual Property.

2

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

        Any of the foregoing terms which are defined in the Uniform Commercial
Code shall have the meaning provided in the Uniform Commercial Code of the
Commonwealth of Massachusetts, as amended and in effect from time to time, as
supplemented and expanded by the foregoing.

        7.    Secured Obligations.    The security interest hereby granted shall
secure the due and punctual payment and performance of the following liabilities
and obligations of GTC (herein called the "Secured Obligations"):

                (a)  Principal and interest on the Loan; and

                (b)  Any and all other obligations of GTC to Genzyme, whether
now existing or hereafter arising (including all costs, fees, premiums,
penalties or other obligations), under this Note, and under the Letter Agreement
between Genzyme and GTC dated as of even date (the "Letter Agreement"), as any
of them may be amended and restated from time to time.

        8.    Representations, Warranties and Covenants of GTC.    GTC hereby
represents, warrants and covenants to Genzyme that:

                (a)  The execution, delivery and performance of this Note have
been duly authorized.

                (b)  GTC will not sell or otherwise dispose of any Collateral or
any interest therein other than in the ordinary course of GTC's business.

                (c)  GTC hereby irrevocably authorizes Genzyme, at any time and
from time to time, to file in any jurisdiction financing statements and
amendments thereto that contain all information required by Article 9 of the
Uniform Commercial Code (including Part 5 thereof) for the sufficiency or filing
office acceptance of any financing statement or amendment. GTC agrees to furnish
to Genzyme promptly upon request any information reasonably required by Genzyme
in order to properly prepare and file such financing statements.

        9.    Rights and Remedies of Genzyme.    Upon the occurrence and during
the continuance of any Default, Genzyme shall have the following rights and
remedies:

                (a)  All rights and remedies provided by law, including, without
limitation, those provided by the Uniform Commercial Code; and

                (b)  All rights and remedies provided in this Note.

        10.    Right of Genzyme to Dispose of Collateral, etc.    Upon the
occurrence and during the continuance of a Default, but subject to the
provisions of the Uniform Commercial Code or other applicable law, Genzyme shall
have the right to take possession of the Collateral and, in addition thereto,
the right to enter upon any premises on which the Collateral or any part thereof
may be situated and remove the same therefrom. Genzyme may require GTC to make
the Collateral (to the extent the same is moveable) available to Genzyme at a
place to be designated by Genzyme which is reasonably convenient to both parties
or transfer any information related to the Collateral to Genzyme by electronic
medium. Unless the Collateral is perishable or threatens to decline speedily in
value or is of a type customarily sold on a recognized market, Genzyme will give
GTC at least ten (10) days' prior written notice in writing of the time and
place of any public sale thereof or of the time after which any private sale or
any other intended disposition thereof is to be made. Any such notice shall be
deemed to meet any requirement hereunder or under any applicable law (including
the Uniform Commercial Code) that reasonable notification be given of the time
and place of such sale or other disposition. Genzyme may comply with any
applicable state or federal law requirements in connection with a disposition of
the Collateral and compliance will not be considered adversely to affect the
commercial reasonableness of any sale of the Collateral.

        11.    Proceeds of Collateral.    After deducting all reasonable costs
and expenses of collection, storage, custody, sale or other disposition and
delivery (including legal costs and reasonable attorneys'

3

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

fees) and all reasonable other charges against the Collateral, the residue of
the proceeds of any such sale or disposition shall be applied to the payment of
the Secured Obligations and any surplus shall be returned to GTC or to any
person or party lawfully entitled thereto (including, if applicable, any other
creditors of GTC). In the event the proceeds of any sale, lease or other
disposition of the Collateral hereunder are insufficient to pay all of the
Secured Obligations in full, GTC will be liable for the deficiency, together
with interest thereon at the rate provided for herein, and the reasonable cost
and expenses of collection of such deficiency, including (to the extent
permitted by law), without limitation, reasonable attorneys' fees, expenses and
disbursements.

        12.    Waivers, etc.    No delay or omission on the part of Genzyme or
any holder hereof in exercising any right hereunder shall operate as a waiver of
such right or of any other right of Genzyme or such holder, nor shall any delay,
omission or waiver on any one occasion be deemed a bar to or waiver of the same
or any other right on any future occasion. GTC waives presentment, demand,
notice, protest and, except as is otherwise provided herein, all other demands
and notices in connection with this Note or the enforcement of Genzyme's rights
hereunder or in connection with any Secured Obligations or any Collateral. No
delay or omission on the part of Genzyme in exercising any right hereunder shall
operate as a waiver of such right or of any other right hereunder. Any waiver of
any such right on any one occasion shall not be construed as a bar to or waiver
of any such right on any future occasion.

        13.    Termination; Assignment, etc.    When all the Secured Obligations
have been paid in full, the security interest in the Collateral created hereby
shall terminate. In such event, Genzyme agrees to execute appropriate releases
of liens on the Collateral upon the request of GTC and at GTC's expense. No
waiver by Genzyme or by any subsequent holder of Secured Obligations of any
default shall be effective unless in writing, nor shall it operate as a waiver
of any other default or of the same default on a future occasion. In the event
of a sale or assignment of part or all of the Secured Obligations by Genzyme or
any subsequent holder, such party may assign or transfer its respective rights
and interest under this Note in whole or in part to the purchaser or purchasers
of such Secured Obligations, whereupon such purchaser or purchasers shall become
vested with all of the powers and rights of Genzyme hereunder.

        14.    Reinstatement.    Notwithstanding the provisions of Section 13,
this Note shall continue to be effective or be reinstated, as the case may be,
if at any time any amount received by Genzyme in respect of the Secured
Obligations is rescinded or must otherwise be restored or returned by Genzyme
upon the insolvency, bankruptcy, dissolution, liquidation or reorganization of
GTC or upon the appointment of any intervener or conservator of, or trustee or
similar official for GTC or any substantial part of any of its properties, or
otherwise, all as though such payments had not been made.

        15.    Subordination.    GTC agrees, and Genzyme by accepting this Note
agrees, that the indebtedness evidenced by this Note is subordinated in right of
payment, to the prior payment in full of all Senior Indebtedness, including
without limitation indebtedness held by Silicon Valley Bank to the extent and in
the manner set forth in the Subordination Agreement dated as of the date hereof
between Genzyme and Silicon Valley Bank (the "Subordination Agreement"), and
that the subordination is for the benefit of the holders of Senior Indebtedness.
"Senior Indebtedness" means the principal of (and premium, if any) and unpaid
interest (including interest which accrues after the commencement of any
proceeding in respect of any reorganization) and any other amounts relating to
indebtedness for borrowed money whether existing now or in the future, including
without limitation, amounts owed by GTC to Silicon Valley Bank, including
without limitation any such amounts owed pursuant to the Loan and Security
Agreement dated as of March 27, 2002 by and between GTC and Silicon Valley Bank.
Genzyme agrees to enter into such other subordination agreements as are
reasonably requested by any other holders of Senior Indebtedness to the same
extent provided in the Subordination Agreement.

4

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

        23.    Miscellaneous.    

                (a)    Notices.    Any notice or communication to GTC or Genzyme
by the other shall be duly given if in writing and delivered in person or by
overnight courier or mailed by first class mail or transmitted by telephone
facsimile transmission (and receipt confirmed) addressed as follows:

    If to GTC:   Genzyme Transgenics Corporation 175 Crossing Boulevard, Suite
410 Framingham, MA 01702 Attention: Jack Green Facsimile: (508) 720-2303     If
to Genzyme:   Genzyme Corporation One Kendall Square Cambridge, Massachusetts
02139 Attention: Chief Financial Officer Facsimile: (617) 252-7852

        Either party by notice to the other may designate additional or
different addresses for subsequent notices or communications. If a notice or
communication is delivered, mailed or transmitted in the manner provided above
within the time prescribed, it is duly given, whether or not the addressee
receives it.

                (b)    Assignment.    No party's rights and obligations under
this Note may be transferred or assigned directly or indirectly without the
prior written consent of the other party, except that (i) a party may transfer
or assign its rights and obligations under this Note to a person or entity into
which it is merged or which has otherwise succeeded to all or substantially all
of its business and assets by merger, reorganization or otherwise, and which has
assumed in writing or by operation of law its obligations under this Note; and
(ii) Genzyme may assign any of its rights under this Note to any other party.
Subject to the foregoing sentence, this Note shall be binding upon and inure to
the benefit of the parties hereto and their successors and assigns.

                (c)    Reference to Letter Agreement.    This Note is entitled
to the benefits of, and evidences obligations incurred under, the Letter
Agreement.

                (d)    Severability.    In case any provision in this Note shall
be invalid, illegal or unenforceable, the validity, legality and enforceability
of the remaining provisions shall not in any way be affected or impaired
thereby.

                (e)    Governing Law.    This Note shall be governed by and
construed in accordance with the laws of the Commonwealth of Massachusetts
(without regard to principles of conflicts of law).

        IN WITNESS WHEREOF, the undersigned has executed this Subordinated
Secured Promissory Note as a sealed instrument on the day and year first above
written.

GENZYME TRANSGENICS CORPORATION
By:
 
/s/  JOHN B. GREEN      

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

Name: John B. Green
Title: Senior Vice President

5

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

QuickLinks

SUBORDINATED SECURED PROMISSORY NOTE