Document:

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                                                                   Exhibit 10.13

THIS WARRANT AND THE SHARES ISSUABLE HEREUNDER HAVE NOT BEEN REGISTERED UNDER
THE SECURITIES ACT OF 1933, AS AMENDED, OR ANY STATE SECURITIES LAWS, AND MAY
NOT BE SOLD, PLEDGED, OR OTHERWISE TRANSFERRED WITHOUT AN EFFECTIVE
REGISTRATION THEREOF UNDER SUCH ACT AND LAWS OR, SUBJECT TO SECTION 5.3
HEREOF, AN OPINION OF COUNSEL REASONABLY SATISFACTORY TO THE CORPORATION AND
ITS COUNSEL, THAT SUCH REGISTRATION IS NOT REQUIRED.

                           WARRANT TO PURCHASE STOCK

Issuer: Alnylam Pharmaceuticals, Inc., a Delaware corporation
Number of Shares: As set forth below
Class of Stock: Series B Convertible Preferred Stock, $0.0001 par value per
share
Exercise Price: $2.50, subject to adjustment
Issue Date: December 18, 2002
Expiration Date: December 18, 2012

     FOR THE AGREED UPON VALUE of $1.00, and for other good and valuable
consideration, the receipt and sufficiency of which are hereby acknowledged,
this Warrant is issued to SILICON VALLEY BANK (together with its successors and
permitted assigns, "Holder") by Alnylam Pharmaceuticals, Inc., a Delaware
corporation (the "Company").

     Subject to the terms and conditions hereinafter set forth, the Holder is
entitled upon surrender of this Warrant and a duly executed Notice of Exercise
in substantially the form attached hereto as Appendix 1 (the "Notice of
Exercise"), at the principal office of the Company, 790 Memorial Drive, Suite
202, Cambridge, Massachusetts 02139 or such other office as the Company shall
notify the Holder of in writing, to purchase from the Company up to such number
of fully paid and non-assessable shares of the Company's Series B Convertible
Preferred Stock, $0.0001 par value per share (the "Class") as shall equal the
Initial Shares (as defined below) plus the Additional Shares (as defined
below), if any, at a purchase price per Share of Two Dollars Fifty Cents ($2.50)
(the "Exercise Price"). This Warrant may be exercised in whole or in part at
any time and from time to time until 5:00 PM, Eastern time, on the Expiration
Date set forth above, and shall be void thereafter. Until such time as this
Warrant is exercised in full or expires, the Exercise Price and the number of
Shares are subject to adjustment from time to time as hereinafter provided.

     As used herein:

     "Initial Shares" means Twelve Thousand Five Hundred (12,500) shares of the
Class; and

     "Additional Shares" means Twelve Thousand Five Hundred (12,500) shares of
the Class; provided, that this Warrant shall become exercisable for the
Additional Shares, if at all, only from and after such date on or before April
30, 2004, if any, as the total aggregate of Credit Extensions
<PAGE>
(as defined in that certain Loan and Security Agreement of even date herewith
between the Company and Silicon Valley Bank (the "Loan Agreement")) made by
Bank (as defined in the Loan Agreement) first exceed One Million Two Hundred
Fifty Thousand Dollars ($1,250,000.00) regardless of the amount of Obligations
(as defined in the Loan Agreement) outstanding on such date.

     "Shares" means the Initial Shares and the Additional Shares; provided,
that the number of Additional Shares for which this Warrant is or may become
exercisable shall be adjusted from time to time upon the occurrence of one or
more events requiring such adjustment as set forth in this Warrant as if this
Warrant were exercisable for such Additional Shares as of the date of any such
required adjustment.

     Notwithstanding the foregoing definition of Class, upon and after the
automatic or voluntary conversion, redemption or retirement of all (but not less
than all) of the outstanding shares of such Class, including without limitation
the Company's initial registered underwritten public offering and sale of its
securities ("IPO"), then from and after the date upon which all such outstanding
shares have been so converted, redeemed or retired, "Class" shall mean the
Company's Series B-1 Convertible Preferred Stock, $0.0001 par value per share
("Series B-1 Stock") or common stock, $0.0001 par value per share ("Common
Stock"), as applicable, and this Warrant shall be exercisable for such number of
shares of Series B-1 Stock or Common Stock, as the case may be, as shall equal
the number of shares of Series B-1 Stock or Common Stock, as the case may be,
into which the Shares would have been converted pursuant to the Company's
Certificate of Incorporation, as amended, including without limitation the
Certificate of Designation, if any, applicable to the same class or series of
preferred stock as the Shares (the "Certificate") had the Shares been issued and
outstanding immediately prior to such conversion, redemption or retirement, and
the Exercise Price shall be the Series B-1 Stock conversion price or Common
Stock conversion price, as the case may be, as determined pursuant to the
Certificate immediately prior to such conversion, redemption or retirement (all
subject to further adjustment as provided herein).

ARTICLE 1. EXERCISE.

     1.1  Method of Exercise. Holder may exercise this Warrant by delivering
this Warrant together with a duly executed Notice of Exercise to the principal
office of the Company. Unless Holder is exercising the conversion right set
forth in Section 1.2, Holder shall also deliver to the Company a check for the
aggregate Exercise Price for the Shares being purchased.

     1.2  Conversion Right. In lieu of exercising this Warrant as specified in
Section 1.1, Holder may from time to time convert this Warrant, in whole or in
part, into a number of Shares determined as follows:

                         X=Y(A-B)/A
     where:
                         X=the number of Shares to be issued to the Holder.

                                      -2-
<PAGE>

                    Y = the number of Shares with respect to which this Warrant
                    is being exercised.

                    A = the Fair Market Value (as determined pursuant to Section
                    1.3 below) of one Share.

                    B = the Exercise Price.

          1.3  Fair Market Value.

               1.3.1 If shares of the Class (or shares of the Company's stock
into which shares of the Class are convertible or exchangeable) are traded on a
nationally recognized securities exchange or over the counter market, the fair
market value of a Share shall be the closing price of a share of the Class (or
the closing price of a share of the Company's stock for which shares of the
Class are convertible or exchangeable, multiplied by the number of shares of
such stock into which one share of the Class is convertible or exchangeable)
reported for the business day immediately preceding the date of Holder's Notice
of Exercise to the Company, provided that the Company receives such Notice of
Exercise not later than five (5) business days following the date thereof.

               1.3.2 If shares of the Class (or shares of the Company's stock
into which shares of the Class are convertible or exchangeable) are not traded
on a nationally recognized securities exchange or over the counter market, the
Board of Directors of the Company shall determine fair market value in its
reasonable good faith judgment.

          1.4  Delivery of Certificate and New Warrant. Promptly after Holder
exercises or converts this Warrant, the Company at its sole expense shall
promptly deliver to Holder (i) certificates for the Shares acquired upon such
exercise, and (ii) if this Warrant has not been fully exercised or converted and
has not expired, a new warrant of like tenor representing the Shares for which
this Warrant is still exercisable.

          1.5  Replacement of Warrants. On receipt of evidence reasonably
satisfactory to the Company of the loss, theft, destruction or mutilation of
this Warrant and, in the case of loss, theft or destruction, on delivery of an
indemnity agreement reasonably satisfactory in form and amount to the Company
or, in the case of mutilation, on surrender and cancellation of this Warrant,
the Company at its expense shall execute and deliver, in lieu of this Warrant, a
new warrant of like tenor.

          1.6  Assumption on Sale, Merger, or Consolidation of the Company.

               1.6.1 "Acquisition". For the purpose of this Warrant,
"Acquisition" means any sale, assignment, transfer, exclusive license, or other
disposition of all or substantially all of the assets of the Company, or any
acquisition, reorganization, consolidation, or merger of the Company where the
holders of the Company's outstanding voting equity securities immediately prior
to the

                                      -3-

<PAGE>
transaction beneficially own less than a majority of the outstanding voting
equity securities of the surviving or successor entity immediately following
the transaction.

           1.6.2.    Assumption of Warrant.  Upon the closing of any Acquisition
(other than an Acquisition in which the consideration received by the Company's
stockholders consists solely of cash), and as a condition precedent thereto, the
successor or surviving entity shall assume the obligations of this Warrant, and
this Warrant shall be exercisable for the same securities and property as would
be payable for the Shares issuable upon exercise of the unexercised portion of
this Warrant as if such Shares were outstanding on the record date for the
Acquisition and subsequent closing. The Exercise Price shall be adjusted
accordingly, and the Exercise Price and number and class of Shares shall
continue to be subject to adjustment from time to time in accordance with the
provisions hereof.

ARTICLE 2. ADJUSTMENTS TO THE SHARES.

           2.1  Stock Dividends, Splits, Etc.  If the Company declares or pays a
dividend on the outstanding shares of the Class, payable in shares of the Class,
Common Stock or other securities, or subdivides the outstanding shares of the
Class into a greater number of shares of the Class, or subdivides the shares of
the Class in a transaction that increases the amount of Common Stock into which
such shares are convertible, then upon exercise of this Warrant, for each Share
acquired, Holder shall receive, without additional cost to Holder, the total
number and kind of securities to which Holder would have been entitled had
Holder owned the Shares of record as of the date the dividend or subdivision
occurred.

           2.2  Reclassification, Exchange or Substitution.  Upon any
reclassification, exchange, substitution, reorganization or other event that
results in a change of the number and/or class of the securities issuable upon
exercise or conversion of this Warrant, Holder shall be entitled to receive,
upon exercise or conversion of this Warrant, the number and kind of securities
and property that Holder would have received for the Shares if this Warrant had
been exercised immediately before such reclassification, exchange, substitution,
reorganization or other event. The Company or its successor shall promptly issue
to Holder a new warrant of like tenor for such new securities or other property.
The new warrant shall provide for adjustments which shall be as nearly
equivalent as may be practicable to the adjustments provided for in this Article
2 including, without limitation, adjustments to the Exercise Price and to the
number of securities or property issuable upon exercise of the new warrant. The
provisions of this Section 2.2 shall similarly apply to successive
reclassifications, exchanges, substitutions, reorganizations or other events.

           2.3  Adjustments for Combinations, Etc.  If the outstanding shares of
the Class are combined or consolidated, by reclassification or otherwise, into a
lesser number of shares, the Exercise Price shall be proportionately increased
and the number of Shares issuable upon exercise or conversion of this Warrant
shall be proportionately decreased.

                                      -4-

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     2.4  No Impairment. The Company shall not, by amendment of the Certificate
or its by-laws or through a reorganization, transfer of assets, consolidation,
merger, dissolution, issue, or sale of securities or any other voluntary
action, avoid or seek to avoid the observance or performance of any of the
terms to be observed or performed under this Warrant by the Company, but shall
at all times in good faith assist in carrying out of all the provisions of this
Article 2 and in taking all such action as may be necessary or appropriate to
protect Holder's rights under this Article against impairment.

     2.5  Adjustments for Dilutive Issuances. The number of shares of Common
Stock for which the Shares are convertible shall be adjusted from time to time
in accordance with Section 2(e)(iv) of Article Fourth of the Certificate as if
the Shares were issued and outstanding on and as of the date of any such
required adjustment.

     2.6  Fractional Shares. No fractional Shares shall be issuable upon
exercise or conversion of the Warrant and the number of Shares to be issued
shall be rounded down to the nearest whole Share. If a fractional Share
interest arises upon any exercise or conversion of this Warrant, the Company
shall eliminate such fractional Share interest by paying Holder an amount
computed by multiplying such fractional interest by the Fair Market Value
(determined in accordance with Section 1.3 above) of one Share.

     2.7  Certificate as to Adjustments. Upon each adjustment of the Exercise
Price, number or class of Shares or number of shares of Common Stock or other
securities for which the Shares are convertible or exchangeable, the Company at
its expense shall promptly compute such adjustment, and furnish Holder with a
certificate of its chief financial officer setting forth such adjustment and
the facts upon which such adjustment is based. The Company shall at any time
and from time to time, upon written request, furnish Holder with a certificate
setting forth the Exercise Price, number and class of Shares and conversion
ratio in effect upon the date thereof and the series of adjustments leading to
such Exercise Price, number and class of Shares and conversion ratio.

ARTICLE 3. REPRESENTATIONS AND COVENANTS OF THE COMPANY.

     3.1  Representations and Warranties. The Company hereby represents and
warrants to the Holder as follows:

          (a)  All Shares which may be issued upon the due exercise of this
Warrant, and all Common Stock or other securities, if any, issuable upon due
conversion of the Shares, shall, upon issuance, be duly authorized, validly
issued, fully paid and non-assessable, and free of any liens and encumbrances
except for restrictions on transfer provided for herein or under applicable
federal and state securities laws.

          (b)  The Company covenants that it shall at all times cause to be
reserved and kept available out of its authorized and unissued shares such
number of shares of its Series B Convertible Preferred Stock, Series B-1 Stock
and Common Stock and other securities as will be

                                      -5-
<PAGE>
sufficient to permit the exercise in full of this Warrant and the conversion of
the Shares into shares of Series B-1 Stock, Common Stock or such other
securities.

          (c) On and as of the date hereof, (i) $2.50 is the lowest price per
share for which shares of the Class have been sold or issued by the Company, and
the lowest exercise or conversion price per share for which shares of the Class
may be purchased or acquired upon the exercise or conversion of outstanding
securities exercisable or convertible by their terms for shares of the Class,
and (ii) the Common Stock conversion price in effect for shares of the Class as
determined pursuant to the Certificate is $2.50.

          (d) The execution and delivery by the Company of this Warrant and the
performance of all obligations of the Company hereunder, including the issuance
to Holder of the right to acquire the Shares, have been duly authorized by all
necessary corporate action on the part of the Company, and this Warrant is not
inconsistent with the Certificate and/or the Company's by-laws, does not
contravene any law or governmental rule, regulation or order applicable to it,
does not and will not contravene any provision of, or constitute a default
under, any material indenture, mortgage, contract or other instrument to which
it is a party or by which it is bound, and constitutes a legal, valid and
binding agreement of the Company, enforceable in accordance with its terms,
subject to laws of general application relating to bankruptcy, insolvency and
the relief of debtors and the rules or principles of equity governing specific
performance, injunctive relief and other equitable remedies.

     3.2 Notice of Certain Events. If the Company proposes at any time (a)to
declare any dividend or distribution upon outstanding shares of the Class,
whether in cash, property, stock, or other securities and whether or not a
regular cash dividend; (b)to offer for subscription pro rata to the holders of
outstanding shares of the Class any additional shares of stock of any class or
series or other rights; (c)to effect any reclassification or recapitalization of
any of its securities; or (d)to merge or consolidate with or into any other
corporation, or sell, lease, license, or convey all or substantially all of its
assets, or to liquidate, dissolve or wind up; then, in connection with each such
event, the Company shall give Holder(1) at least 10 days prior written notice of
the date on which a record will be taken for such dividend, distribution, or
subscription rights (and specifying the date on which the holders of securities
of the Company shall be entitled to receive such dividend, distribution or
rights) or for determining rights to vote, if any, in respect of the matters
referred to in (c) and (d) above; and (2) in the case of the matters referred to
in (c) and (d) above at lease 10 days prior written notice of the date when the
same will take place (and specifying the date on which the holders of securities
of the Company will be entitled to exchange their securities of the Company for
securities or other property deliverable upon the occurrence of such event).

     3.3 Registration Under Securities Act of 1933, as amended. The Company
grants registration rights to the Holder of this Warrant for any Common Stock
issued and issuable upon exercise hereof or upon conversion of the Shares issued
and issuable hereunder, on the terms and conditions on which registration rights
are granted to the investor parties to that certain Amended and Restated
Registration Rights Agreement dated as of July 25, 2002 among the Company and
the
<PAGE>
other parties listed on Schedule A thereto, as amended and in effect from time
to time (the "Registration Rights Agreement"), provided, however, that the
Holder will have no right to request registration under Section 2 of the
Registration Rights Agreement. Holder hereby agrees to be subject to and bound
by all of the terms and provisions of the Registration Rights Agreement
applicable to the investor parties thereto. The Company represents and warrants
to Holder that the Company's foregoing grant of registration rights (a) has been
duly authorized by all necessary corporate action of the Company's Board of
Directors and shareholders, (b) will not violate the Certificate or the
Company's by-laws, each as amended, (c) will not violate or cause a breach or
default (or an event which with the passage of time or the giving of notice or
both, would constitute a breach or default) under any agreement, instrument,
mortgage, deed of trust or other arrangement to which the Company is a party or
by which it or any of its assets is subject or bound, and (d) does not require
the approval, consent or waiver of or by any shareholder, registration rights
holder or other third party which approval, consent or waiver has not been
obtained as of the date of issuance of this Warrant.

ARTICLE 4. REPRESENTATIONS AND WARRANTIES OF THE HOLDER. Holder represents and
warrants to the Company as follows:

     4.1  Purchase for Own Account. Subject to Silicon Valley Bank's right to
transfer this Warrant and the Shares (and/or the securities, if any, issued and
issuable upon conversion of the Shares) to its parent corporation Silicon
Valley Bancshares and/or any other affiliate, this Warrant and the Shares to be
acquired upon exercise hereof will be acquired for investment for Holders'
account, not as nominee or agent, and not with a view to sale or distribution
in violation of applicable federal and state securities laws.

     4.2  Investment Experience. Holder understands that the purchase of this
Warrant and the Shares covered hereby involves substantial risk. Holder (a) has
experience as an investor in unregistered securities, (b) has sufficient
knowledge and experience in financial and business affairs that it can evaluate
the risks and merits of its investment in this Warrant and the Shares, and (c)
can bear the economic risk of such Holder's investment in this Warrant and the
Shares.

     4.3  Accredited Investor. Holder is an "accredited investor" as such term
is defined in Regulation D under the Securities Act of 1933, as amended (the
"Securities Act").

     4.4  Restricted Securities. Holder understands that this Warrant and the
securities to be issued upon exercise hereof must be held indefinitely unless
subsequently registered under the Securities Act and qualified under any
applicable state securities laws, or unless exemptions from registration and
qualification are otherwise available. Holder is aware of the provision of Rule
144 promulgated under the Securities Act.

ARTICLE 5. MISCELLANEOUS.

     5.1  Intentionally Omitted.

                                      -7-
<PAGE>

          5.2  Legends. This Warrant and the Shares (and the securities
issuable, directly or indirectly, upon conversion of the Shares, if any) shall
be imprinted with a legend in substantially the following form:

     THIS SECURITY HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF
     1933, AS AMENDED, OR ANY STATE SECURITIES LAWS, AND MAY NOT BE SOLD,
     PLEDGED OR OTHERWISE TRANSFERRED WITHOUT AN EFFECTIVE REGISTRATION
     THEREOF UNDER SUCH ACT AND LAWS OR, SUBJECT TO SECTION 5.3 OF THAT
     CERTAIN WARRANT TO PURCHASE STOCK ISSUED BY THE CORPORATION TO SILICON
     VALLEY BANK DATED AS OF DECEMBER 16, 2002, AN OPINION OF COUNSEL
                             -----------------
     REASONABLY SATISFACTORY TO THE CORPORATION AND ITS COUNSEL THAT SUCH
     REGISTRATION IS NOT REQUIRED.

          5.3  Compliance with Securities Laws on Transfer. This Warrant and the
Shares (and the securities, if any, issued and issuable upon conversion of the
Shares) may not be transferred or assigned in whole or in part without
compliance with applicable federal and state securities laws by the transferor
and the transferee (including, without limitation, the delivery of investment
representation letters and legal opinions reasonably satisfactory to the
Company, as reasonably requested by the Company). The Company shall not require
Holder to provide an opinion of counsel if the transfer is to Silicon Valley
Bancshares or other affiliate of Holder.

          5.4  Transfer Procedure. Following its receipt of this executed
Warrant, Silicon Valley Bank will transfer same in whole or in part to its
parent corporation Silicon Valley Bancshares, and thereafter Holder and/or
Silicon Valley Bancshares may, subject to Section 5.3 above, transfer all or
part of this Warrant and/or the Shares (or the securities, if any, issued and
issuable upon conversion of the Shares) at any time and from time to time by
giving the Company notice of the portion of the Warrant and/or Shares (or the
securities, if any, issued and issuable upon conversion of the Shares) being
transferred setting forth the name, address and taxpayer identification number
of the transferee and surrendering this Warrant to the Company for reissuance to
the transferee(s)(and Holder if applicable); provided, that at all times prior
to the Company's IPO, Holder shall not, without the prior written consent of
the Company, transfer this Warrant (or any part hereof), any Shares, or any
securities issued or issuable upon conversion of the Shares, to any person who
directly competes with the Company, unless such transfer is in connection with
an Acquisition of the Company by any such person.

          5.5  Notices. All notices and other communications from the Company to
the Holder, or vice versa, shall be deemed delivered and effective when given
personally, or mailed by first-class registered or certified mail, postage
prepaid, or sent via reputable overnight courier service, fee prepaid, at such
address as may have been furnished to the Company or the Holder, as the case may
be, in writing by the Company or such holder from time to time, but in all
cases, unless instructed in writing otherwise, the Company shall deliver a copy
of all notices to Holder to Silicon Valley Bank, Treasury Department, 3003
Tasman Drive, HA 200, Santa Clara, California 95054.

                                      -8-

<PAGE>

           5.6  Waiver. This Warrant and any term hereof may be changed, waived,
discharged or terminated only by an instrument in writing signed by the party
against which enforcement of such change, waiver, discharge or termination is
sought.

          5.7  Attorneys Fees. In the event of any dispute between the parties
concerning the terms and provisions of this Warrant, the party prevailing in
such dispute shall be entitled to collect from the other party all costs
incurred in such dispute, including reasonable attorneys' fees.

          5.8  Governing Law. This Warrant shall be governed by and construed in
accordance with the laws of The Commonwealth of Massachusetts, without giving
effect to its principles regarding conflicts of law.

          5.9  No Rights as a Shareholder. Except as specifically provided in
this Warrant, Holder shall have no rights as a shareholder of the Company in
respect of the Shares issuable hereunder unless and until Holder exercises this
Warrant as to all or any of such Shares.

                  [REMAINDER OF PAGE LEFT BLANK INTENTIONALLY]

<PAGE>
     IN WITNESS WHEREOF, the Company has caused this Warrant to Purchase Stock
to be executed as an instrument under seal by its duly authorized
representative as of the date first above written.

ATTEST:                                "COMPANY"

                                       ALNYLAM PHARMACEUTICALS, INC.

By: /s/ Jeffrey Wiesen                 By: /s/ John G. Conley
   -----------------------------          ----------------------------------
Name: Jeffrey Wiesen                   Name: John G. Conley
Title: Secretary                       Title: VP, Strategy & Finance

Agreed to and accepted by:

SILICON VALLEY BANK

By: /s/ Douglas Marshall
   -----------------------------
Name: Douglas Marshall
Title: Vice President
<PAGE>
                                   APPENDIX 1

                               NOTICE OF EXERCISE

     1.   The undersigned hereby elects to purchase _______ shares of the
__________ stock of ______________ pursuant to Section 1.1 of the attached
Warrant, and tenders herewith payment of the Exercise Price of such shares in
full.

     1.   The undersigned hereby elects to convert the attached Warrant into
Shares in the manner specified in Section 1.2 of the attached Warrant. This
conversion is exercised with respect to _____________ of shares of the
_______________Stock of _____________________.

     [Strike paragraph that does not apply.]

     2.   Please issue a certificate or certificates representing said shares
in the name of the undersigned or in such other name as is specified below:

                    _________________________________________
                          (Name)

                    _________________________________________

                    _________________________________________
                          (Address)

     3.   The undersigned represents it is acquiring the shares solely for its
own account and not as a nominee for any other party and not with a view toward
the resale or distribution thereof except in compliance with applicable
securities laws.

                                             ___________________________________
                                                   (Signature)

____________________
     (Date)<PAGE>

                                                                   EXHIBIT 10.14

                                LEASE AGREEMENT

     THIS LEASE AGREEMENT is dated as of August 5, 2002, between
ARE-770/784/790 MEMORIAL DRIVE, LLC, a Delaware limited liability company
("LANDLORD"), and ALNYLAM PHARMACEUTICALS, INC., a Delaware corporation
("TENANT").

ADDRESS:        790 Memorial Drive, Cambridge, Massachusetts 02139

PREMISES:       That portion of the Building, designated as Suite 2C, containing
                approximately 3,990 rentable square feet, as determined by
                Landlord, as shown on EXHIBIT A.

PROJECT:        The real property on which the Building is located, together
                with all improvements thereon and appurtenances thereto as
                described on EXHIBIT B.

BASE RENT:      $19,285.00, per month

TENANT'S SHARE: 8.0%

SCIENCE HOTEL(sm) SERVICE FEES:  $4,655.00, per month

SECURITY DEPOSIT: $19,285.00     TARGET COMMENCEMENT DATE:  September 1, 2002

RENT COMMENCEMENT DATE:          The day which is two (2) months after the
                                 Commencement Date (as defined herein)

TERM:           The period commencing on the Commencement Date and expiring
                twelve (12) months after the first day of the first full
                calendar month commencing on or after the Commencement Date

PERMITTED USE:  Research and development laboratory, related office and other
                related uses consistent with the character of the Project and
                otherwise in compliance with the provisions of Section 8
                hereof.

ADDRESS FOR RENT PAYMENT:  LANDLORD'S NOTICE ADDRESS:   TENANT'S NOTICE ADDRESS:
135 N. Los Robles Avenue   135 N. Los Robles Avenue     790 Memorial Drive
Suite 250                  Suite 250                    Cambridge, MA 02139
Pasadena, CA 91101         Pasadena, CA 91101           Attention:
Attention: Accounts        Attention: Corporate         FACSIMILE
           Receivable                 Secretary
                           Facsimile: (626) 578-0770

     1.  LEASE OF PREMISES.  Upon and subject to all of the terms and
conditions hereof, Landlord hereby leases the Premises to Tenant and Tenant
hereby leases the Premises from Landlord. The portions of the Project that are
for the non-exclusive use of tenants of the Project are collectively referred
to herein as the "COMMON AREAS." The portions of the Building, including the
dark room, conference room, glass wash rooms and storage areas, that are for
the non-exclusive use of tenants of the Building are more particularly shown on
EXHIBIT A hereto and are collectively referred to herein as the "SCIENCE
HOTEL(sm) SHARED AREAS". Tenant shall have the non-exclusive right, in common
with other tenants of the Project, to use the Common Areas, and the
non-exclusive right, together with other tenants of the Building, to use the
Science Hotel(sm) Shared Areas. Landlord reserves the right to modify the
Common Areas and Science Hotel(sm) Shared Areas, so long as such changes will
not unreasonably interfere with Tenant's access to or use of the Premises or of
the Science Hotel (sm) Services (as hereinafter defined), or Tenant's parking
rights hereunder.

              (C) All Rights Reserved 2001 Alexandria Real Estate Equities, Inc.
                                                     CONFIDENTIAL -- DO NOT COPY

<PAGE>
Short Form 3N Laboratory Lease                         ADDRESS/TENANT - PAGE 2

     2.   DELIVERY; ACCEPTANCE OF PREMISES; COMMENCEMENT DATE. Landlord shall
use reasonable efforts to deliver the Premises to Tenant for the conduct of
Tenant's business on or before the Target Commencement Date with the Tenant
Improvements Substantially Complete (as those terms are defined in Section 7
hereof) ("DELIVERY" or "DELIVER"). Tenant shall deliver all of Tenant's
requirements for the Tenant Improvements to Landlord, in writing, within three
(3) business days after the date of final execution of this Lease,and shall
coordinate its activities within the Building with Landlord in order to minimize
interference with any work which Landlord may be doing within the Building for
Tenant or any other tenant of the Building. If Landlord fails to so Deliver the
Premises (other than as a result of Tenant's failure to deliver Tenant's
requirements for the Tenant Improvements within such three (3) business day
period as aforesaid), Landlord shall not be liable to Tenant for any loss or
damage resulting therefrom, and this Lease may be terminated by Tenant by
facsimile notice to Landlord within thirty (30) days after the Target
Commencement Date, and if so terminated by Tenant: (a) the Security Deposit, or
any balance thereof (i.e., after deducting therefrom all amounts to which
Landlord is entitled under the provisions of this Lease as a result of Tenant's
default hereunder), shall be returned to Tenant, and (b) neither Landlord nor
Tenant shall have any further rights, duties or obligations under this Lease.
The "COMMENCEMENT DATE" shall be the later of (i) the date on which Tenant has
obtained all necessary permits and approvals authorizing its proposed research
and development activities within the Premises (collectively, the "R&D
PERMITS"), but in no event more than sixty (60) days after the date of final
execution of this Lease, and (ii) the date that Landlord has Substantially
Completed the Tenant Improvements and delivered full possession of the same to
Tenant. Tenant shall deliver all of the applications for the R&D Permits,
completed to the best of Tenant's ability, within seven (7) business days after
the execution and delivery of this Lease. Thereafter, if, despite reasonable
efforts of Tenant and Landlord (and provided Tenant has delivered the completed
applications for the R&D Permits within such seven (7) business day period as
aforesaid), the R&D Permits have not been obtained within sixty (60) days after
the date of final execution of this Lease, either Tenant or Landlord may
terminate this Lease upon five (5) days prior written notice to the other. Prior
to the Commencement Date and beginning upon the execution and delivery of this
Lease by Landlord and Tenant, provided Tenant has provided a certificate of
insurance, indicating that Tenant has obtained insurance of the types and in the
amounts required to be maintained by Tenant pursuance to Section 16 hereof,
Tenant shall have access to the Premises for purposes of readying the Premises
for Tenant's occupancy and shall have the right to occupy the Premises for
office use only. The date on which such occupancy for office use begins shall be
referred to herein as the "EARLY OCCUPANCY DATE". The period between the Early
Occupancy Date and the Commencement Date is referred to herein as the "EARLY
OCCUPANCY PERIOD". If this Lease is terminated by Landlord or Tenant as a result
of Tenant's inability to obtain the R&D Permits, Tenant shall surrender the
Premises to Landlord, subject to the terms and conditions set forth in Section
26 hereof, within five (5) days after the delivery of such notice of
termination. Upon request of Landlord, Tenant shall execute and deliver a
written acknowledgment of the Commencement Date and the expiration date of the
Term when such are established in the form of the "Acknowledgement of
Commencement Date" attached to this Lease as EXHIBIT C; provided, however,
Tenant's failure to execute and deliver such acknowledgement shall not affect
Landlord's rights hereunder.

     Subject to Landlord's completion of the Tenant Improvements and Landlord's
obligations set forth in Section 13 hereof, effective as of the Early Occupancy
Date, (i) Tenant shall accept the Premises in their condition as of such date,
subject to all applicable Legal Requirements (as defined in Section 8 hereof);
(ii) Landlord shall have no obligation for any defects in the Premises; and
(iii) Tenant's taking possession of the Premises shall be conclusive evidence
that Tenant accepts the Premises and that the Premises were in good condition
at the time of Delivery.

     Tenant agrees and acknowledges that neither Landlord nor any agent of
Landlord has made any representation or warranty with respect to the condition
of all or any portion of the Premises or the Project, and/or the suitability of
the Premises or the Project for the conduct of Tenant's business, and Tenant
waives any implied warranty that the Premises or the Project are suitable for
the Permitted Use. This Lease constitutes the complete agreement of Landlord
and Tenant with respect to the subject matter hereof and supersedes any and all
prior representations, inducements, promises, agreements, understandings and
negotiations which are not contained herein.

              (C) All Rights Reserved 2001 Alexandria Real Estate Equities, Inc.
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Short Form 3N Laboratory Lease                           ADDRESS/TENANT - PAGE 3

     3.   BASE RENT.

     (a)  The first month's Base Rent and the Security Deposit shall be due and
payable on delivery of an executed copy of this Lease to Landlord. Commencing on
the first day of the first month after the Rent Commencement Date, Tenant shall
pay to Landlord in advance, monthly installments of Base Rent on or before the
first day of each calendar month during the Term hereof, in lawful money of the
United States of America, at the office of Landlord for payment of Rent set
forth above. Payments of Base Rent for any fractional calendar month shall be
prorated. Tenant shall have no right at any time to abate, reduce, or set-off
any Rent due hereunder.

     (b)  In addition to Base Rent, commencing on the Commencement Date, Tenant
agrees to pay to Landlord as additional rent ("ADDITIONAL RENT"): (i) Tenant's
Share of Operating Expenses (as defined in Section 5), and (ii) any and all
other amounts Tenant assumes or agrees to pay under the provisions of this
Lease, including, without limitation, any and all other sums that may become due
by reason of any default of Tenant or failure to comply with the agreements,
terms, covenants and conditions of this Lease to be performed by Tenant, after
any applicable notice and cure period. Tenant's obligation to pay Base Rent and
Additional Rent hereunder are collectively referred to herein as "RENT". During
the Early Occupancy Period, Tenant shall pay to Landlord Landlord's reasonably
estimated Operating Expenses incurred in connection with Tenant's use and
occupancy of the Premises ("EARLY OCCUPANCY RENT"). Tenant shall pay the Early
Occupancy Rent to Landlord within ten (10) business days after receipt of
Landlord's written statement of such expenses. Payment of the Early Occupancy
Rent shall be subject to the terms and conditions for the payment of Additional
Rent under this Lease. Payments of Early Occupancy Rent for any fractional
calendar month shall be prorated.

     4.   SCIENCE HOTEL (SM) SERVICES FEE. Beginning on the Commencement Date,
Tenant shall pay, in advance, monthly installments of the Science Hotel (sm)
Services Fee on or before the first day of each calendar month during the Term
hereof, in lawful money of the United States of America, to ARE-CLC Laboratory
Specialists, LLC, or its successors or assigns (the "SCIENCE HOTEL (SM) SERVICES
PROVIDER"), as consideration for the provision of "SCIENCE HOTEL (SM) SERVICES"
as more particularly described in that certain agreement, of even date herewith
(the "SCIENCE HOTEL (SM) SERVICES AGREEMENT"), between the Science Hotel (sm)
Services Provider and Tenant. The Science Hotel (sm) Services Provider shall
bill Tenant directly for the Science Hotel (sm) Services Fee pursuant to the
terms of the Science Hotel (sm) Services Agreement. Any default by Tenant under
the Science Hotel (sm) Services Agreement shall constitute a Default hereunder
and any default by Tenant hereunder shall constitute a Default under the Science
Hotel (sm) Services Agreement.

     5.   OPERATING EXPENSE PAYMENTS. During each month of the Term, commencing
on the Commencement Date, on the same date that Base Rent is due, Tenant shall
pay Landlord an amount equal to 1/12 of Tenant's Share of Landlord's written
estimate of Operating Expenses for each calendar year during the Term (the
"ANNUAL ESTIMATE"). Such estimate for the 12-month period beginning on the
anticipated Commencement Date is attached hereto as SCHEDULE 1. Payments for any
fractional calendar month shall be prorated. The term "OPERATING EXPENSES" means
all Building and Project related operating costs in connection with the
operation of the shell and core of the Building and the Premises, site
improvements, maintenance, taxes, utilities and insurance (but expressly
excluding all costs of capital improvements and repairs), reasonably determined
by Landlord, in accordance with Landlord's normal practice, to be properly
allocable to tenants in the Building and/or the Project, including as Additional
Rent administration rent in the amount of three percent (3%) of Base Rent.
Within 90 days after the expiration of the Term or any Extension Term (as
defined in Section 38 hereof) Landlord shall furnish to Tenant a statement (an
"Annual Statement") showing in reasonable detail: (a) the total and Tenant's
Share of actual Operating Expenses for the previous calendar year or any portion
of such calendar year included in the Term or the Extension Term, as applicable,
and (b) the total of Tenant's payments in respect of Operating Expenses for such
year or partial year. If Tenant's Share of actual Operating Expenses for such
year or partial year exceeds Tenant's payments of Operating Expenses for such
year or partial, the excess shall be due and payable by Tenant as Rent within 30
days after delivery of such Annual Statement to Tenant. If Tenant's payments of
Operating Expenses for such year or partial year exceed Tenant's Share of actual
Operating Expenses for such year or partial year, Landlord shall

              (C) All Rights Reserved 2001 Alexandria Real Estate Equities, Inc.
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Short Form 3N Laboratory Lease                          ADDRESS/TENANT -- PAGE 4

pay the excess to Tenant within 30 days after delivery of such Annual Statement,
except that after the expiration or earlier termination of the Term or any
Extension Term, or if Tenant is delinquent in its obligation to pay Rent,
Landlord shall pay the excess to Tenant after deducting all other amounts due
Landlord.

     6.   SECURITY DEPOSIT. Tenant shall deposit with Landlord upon delivery of
an executed copy of this Lease to Landlord and at all times during the Early
Occupancy Period and the Term maintain security (the "SECURITY DEPOSIT") for
the performance of all of its obligations in the amount set forth in the Basic
Lease Provisions, which security shall be in the form of an unconditional and
irrevocable letter of credit (the "LETTER OF CREDIT") in form and substance and
issued by an institution satisfactory to Landlord. Upon each occurrence of a
Default (as defined in Section 18), Landlord may use all or any part of the
Security Deposit to pay delinquent payments due under this Lease, and the cost
of any damage, injury, expense or liability caused by such Default, without
prejudice to any other remedy provided herein or by law. Tenant hereby waives
the provisions of any law, now or hereafter in force, which provide that
Landlord may claim from a security deposit only those sums reasonably necessary
to remedy defaults in the payment of Rent, to repair damage caused by Tenant or
to clean the Premises, it being agreed that Landlord may, in addition, claim
those sums reasonably necessary to compensate Landlord for any other loss or
damage, foreseeable or unforeseeable, caused by the act or omission of Tenant
or any officer, employee, agent or invitee of Tenant.

     7.   TENANT IMPROVEMENT ALLOWANCE.

     (a)  TI ALLOWANCE. Landlord shall make available to Tenant an allowance
(the "TI ALLOWANCE") in the maximum amount of $26,950.00. The TI Allowance shall
be used solely in payment of costs ("TI COSTS") incurred in connection with the
design and construction of minor alterations and additions to the building
standard laboratory improvements in the Premises in accordance with designs and
plans submitted by Tenant and approved by Landlord (the "TENANT IMPROVEMENTS").
The Tenant Improvements shall be designed and constructed by architects (the "TI
ARCHITECT") and contractors selected by Landlord and approved by Tenant. All
disbursements of the TI Allowance shall be in accordance with this Lease.
Notwithstanding anything to the contrary contained herein, the TI Allowance
shall not be used to purchase any furniture, personal property or other
materials or equipment, including, but not be limited to, biological safety
cabinets and other scientific equipment not incorporated into the Improvements.
The Tenant Improvements shall be substantially complete ("Substantially
Complete") when they can be used by Tenant for research and development and
laboratory purposes, except for minor "punchlist" items that will not materially
interfere with Tenant's use of the Tenant Improvements or the Premises. Tenant
shall have the right to inspect the Tenant Improvements upon completion and
Landlord and Tenant shall produce a "punch list" of items to be completed by
Landlord based on such inspection. Landlord shall use reasonable efforts to
complete substantially all of such punch list items within thirty (30) days
after the Commencement Date.

     (b)  EXCESS TI COSTS. It is understood and agreed that Landlord is under no
obligation to bear any portion of the cost of any of the Tenant Improvements
except to the extent of the TI Allowance. If at any time and from time-to-time,
the remaining TI Costs are projected to exceed the remaining unexpended TI
Allowance, then, if Landlord is overseeing the installation of said Tenant
Improvements, Landlord shall cease such work and advise Tenant immediately.
Tenant shall either (1) deposit with Landlord, as a condition precedent to
Landlord's obligation to complete the Tenant Improvements, 100% of the then
current TI Costs in excess of the remaining TI Allowance ("EXCESS TI COSTS"), or
(2) redesign Tenant's improvement design so as to reduce the remaining TI Costs
until there are no longer any Excess TI Costs. If Tenant fails to deposit, or is
late in depositing, any Excess TI Costs with Landlord, Landlord shall have all
of the rights and remedies set forth in the Lease for nonpayment of Rent
(including, but not limited to, the right to interest at the Default Rate and
the right to assess a late charge), and for purposes of any litigation
instituted with regard to such amounts the same will be considered Rent. Any
Excess TI Costs, together with the remaining TI Allowance, is herein referred to
as the "TI FUND." Funds so deposited by Tenant shall be the first thereafter
disbursed to pay TI Costs. Notwithstanding anything to the contrary set forth in
this Section 7(b), Tenant shall be fully and solely liable for TI Costs and the
cost of any minor variations from the approved plans and specifications in

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Short Form 3N Laboratory Lease                          ADDRESS/TENANT - PAGE 5

excess of the TI Allowance. If upon Substantial Completion of the Tenant
Improvements and the payment of all sums due in connection therewith there
remains any undisbursed TI Fund, Tenant shall be entitled to such undisbursed
TI Fund solely to the extent of any Excess TI Costs deposit Tenant has actually
made with Landlord.

8.   USE. The Premises shall be used solely for the Permitted Use set forth in
the Basic Lease Provisions, in compliance with all laws, orders, judgments,
ordinances, regulations, codes, directives, permits, licenses, covenants and
restrictions now or hereafter applicable to the Premises, and the use and
occupancy thereof (collectively, "LEGAL REQUIREMENTS"). Tenant will use the
Premises in a careful, safe and proper manner and will not commit waste,
overload the floor or structure of the Premises, subject the Premises to use
that would damage the Premises or obstruct or interfere with the rights of
Landlord or other tenants or occupants of the Project, including conducting or
giving notice of any auction, liquidation, or going out of business sale on the
Premises, or using or allowing the Premises to be used for any unlawful purpose.
Landlord acknowledges that Tenant intends to use Hazardous Materials in the
Premises and will create hazardous waste in the course of Tenant's use of the
Premises. Tenant agrees that all such use shall be in accordance with all Legal
Requirements and shall be subject to the provisions of Section 28 hereof.

     9.   HOLDING OVER. Subject to the provisions of Section 38 hereof, if
Tenant remains in possession of the Premises after the expiration or earlier
termination of the Term (or after a termination of the Lease pursuant to Section
2 hereof) without the express written consent of Landlord, (A) Tenant shall
become a tenant at sufferance upon the terms of this Lease except that the
monthly rental shall be equal to 150% of the Rent in effect during the last 30
days of the Term, and (B) Tenant shall be responsible for all damages suffered
by Landlord resulting from or occasioned by Tenant's holding over, including
consequential damages. Acceptance by Landlord of Rent after the expiration of
the Term or earlier termination of this Lease shall not result in a renewal or
reinstatement of this Lease.

     10.  PARKING. Subject to all matters of record, Force Majeure, a Taking
(as defined in Section 17 below) and the exercise by Landlord of its rights
hereunder, Tenant shall have the right, throughout the Early Occupancy Period
and the Term, to park in 4 designated spaces in the parking garage located in
the Project, in those areas designated for non-reserved parking, in common with
other tenants of the Project and subject to Landlord's rules and regulations.
If tenant exercises its Expansion Right pursuant to Section 37 hereof, the
number of Tenant's parking spaces shall be increased pro rata based on the
rentable square footage of the Available Space which is added to the Premises
as a result of such exercise. Until such time, if any, as Landlord provides a
shuttle to public transportation for Tenant's employees at the Premises, Tenant
shall have the right, subject to availability, to use additional parking
spaces, in common with other tenants of the Project, in the garage and in the
surface parking lot at the Project. Landlord shall notify Tenant from time to
time of the number and location of such additional spaces and of any changes in
the availability of such spaces. Landlord shall impose and uniformly enforce
parking rules and regulations upon all users of the parking garage and surface
parking lot in the Project. Landlord shall not be responsible for enforcing
Tenant's parking rights against any third parties, including other tenants of
the Project. Tenant shall pay a license fee for such parking in the amount of
$160 per month for each parking space in the parking garage and $110 per month
for each parking space in the surface parking lot, which license fees may be
adjusted to a market rate annually, upon thirty (30) days prior written notice
of such increase from Landlord to Tenant. Tenant shall comply with the
requirements set forth in EXHIBIT D attached hereto, setting forth certain
governmentally imposed requirements related to parking and transportation
demand management which are binding on tenants in the Project.

     11. UTILITIES, SERVICES. Landlord shall provide, as an Operating Expense
or subject to Tenant's reimbursement obligation as provided herein, and subject
to the terms of this Section 11, utilities to the premises ("UTILITIES").
Tenant shall pay directly to the Utility provider, prior to delinquency, any
separately metered Utilities and services which may be furnished to Tenant or
the Premises during the Term. No interruption or failure of Utilities, from any
cause whatsoever other than Landlord's willful misconduct, shall result in
abatement of Rent.

              (C) All Rights Reserved 2001 Alexandria Real Estate Equities, Inc.
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Short Form 3N Laboratory Lease                          ADDRESS/TENANT -- PAGE 6

          12.     ALTERATIONS. Tenant shall not make any alterations, additions,
or improvements to the Premises of any kind whatsoever without Landlord's prior
written consent.

          13.     LANDLORD'S REPAIRS. Landlord, as an Operating Expense, shall
maintain all of the Project and the Premises, including all HVAC, electrical,
plumbing and mechanical systems and all fixtures and equipment owned and
furnished by Landlord therein, in good repair, reasonable wear and tear and
uninsured losses and damages caused by Tenant, or by any of Tenant's agents,
servants, employees, invitees and contractors (collectively, "TENANT PARTIES")
excluded. Landlord shall repair losses and damages caused by Tenant or any of
Tenant Parties at Tenant's sole cost and expense. Landlord reserves the right to
stop building system services when necessary for maintenance, repairs,
alterations and improvements. Landlord shall have no responsibility or liability
for failure to supply building system services during any such period of
interruption; provided, however, that Landlord shall give Tenant 24 hours
advance notice of any planned stoppage of building system services for routine
maintenance, repairs, alterations or improvements. Landlord shall not be liable
in any legal action for any failure to make any repairs for which Landlord is
responsible hereunder unless such failure shall persist for an unreasonable time
after Tenant's written (or, in the event of an emergency, oral followed
immediately by written) notice of the need for such repairs. In no event shall
Landlord be responsible for any consequential damages arising from Landlord's
failure to make any such repairs and Tenant shall not have the right to abate,
reduce or set-off any Rent due hereunder as a result of any such failure.
Nothing in this Section 13 shall be deemed to supercede or otherwise affect the
limitation on Landlord's liability set forth in Section 33 of this Lease.

          14.     LIENS. Tenant shall discharge, by bond or otherwise, any liens
filed against the Premises or against the Project arising out of work performed
or claimed to have been performed, materials furnished or claimed to have been
or obligations incurred or claimed to have been incurred by Tenant within 10
days after the filing thereof, at Tenant's sole cost.

          15.     INDEMNIFICATION. Tenant hereby indemnifies and agrees to
defend, save and hold Landlord harmless from and against any and all claims for
injury or death to persons or damage to property occurring within or about the
Premises, arising directly or indirectly out of use or occupancy of the Premises
or a breach or default by Tenant in the performance of any of its obligations
hereunder, unless caused solely by the willful misconduct or gross negligence of
Landlord. Landlord shall not be liable to Tenant for, and Tenant assumes all
risk of damage to, personal property (including, without limitation, loss of
records kept within the Premises). Tenant further waives any and all claims for
injury to Tenant's business or loss of income relating to any such damage or
destruction of personal property (including, without limitation, any loss of
records). Landlord shall not be liable for any damages arising from any act,
omission or neglect of any tenant in the Project or of any other third party.

          16. INSURANCE. Landlord shall, as an Operating Expense, maintain such
insurance covering the Project as Landlord shall determine. Tenant, at its sole
cost and expense, shall maintain during both the Early Occupancy Period and the
Term: workers' compensation insurance with no less than the minimum limits
required by law; employer's liability insurance with such limits as required by
law; and commercial general liability insurance, with a minimum limit of not
less than $2,000,000 per occurrence for bodily injury and property damage with
respect to the Premises and the Science Hotel (sm) Shared Areas. The commercial
general liability insurance policies maintained by Tenant shall name Landlord,
its officers, directors, employees, managers, agents, invitees and contractors
(collectively, "LANDLORD PARTIES"), as additional insureds; insure on an
occurrence and not a claims-made basis; be issued by insurance companies which
have a rating of not less than policyholder rating of A and financial category
rating of at least Class X in "Best's Insurance Guide"; shall not be cancelable
for nonpayment of premium unless ten (10) business days prior written notice
shall have been given to Landlord from the insurer; contain a hostile fire
endorsement and a contractual liability endorsement; and provide primary
coverage to Landlord (any policy issued to Landlord providing duplicate or
similar coverage shall be deemed excess over Tenant's policies). Copies of such
policies (if requested by Landlord), or certificates of insurance showing the
limits of coverage required hereunder and showing Landlord as an additional
insured, along with reasonable evidence of the payment of premiums for the
applicable period, shall be

              (C) All rights Reserved 2001 Alexandria Real Estate Equities, Inc.
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Short Form 3N Laboratory Lease                           ADDRESS/TENANT - PAGE 7

delivered to Landlord by Tenant upon commencement of the Early Occupancy Period
and with respect to any renewal of insurance policy, no later than 5 days prior
to the expiration of such policy.

     17. CONDEMNATION AND CASUALTY. If at any time during the Early Occupancy
Period or the Term the Premises are in whole or in part (i) materially damaged
or destroyed by a fire or other casualty or (ii) taken for any public or
quasi-public use under governmental law, ordinance, or regulation, or by right
of eminent domain, or by private purchase in lieu thereof (a "TAKING"), this
Lease shall, at the written election of Landlord or Tenant, terminate as of the
date of such damage, destruction or Taking. Any statute or regulation which is
now or may hereafter be in effect shall have no application to this Lease or any
such damage, destruction or Taking, the parties hereto expressly agreeing that
this Section sets forth their entire understanding and agreement with respect
to such matters. Upon any fire or other casualty or Taking, Landlord shall be
entitled to receive the entire proceeds of the insurance maintained by Landlord
and the entire price or award from any such Taking without, in either case, any
payment to Tenant, and Tenant hereby assigns to Landlord Tenant's interest, if
any, in such proceeds or award.

     18. EVENTS OF DEFAULT. Each of the following events shall be a default
("DEFAULT") by Tenant under this Lease:

     (a) PAYMENT DEFAULTS. Tenant shall fail to pay any installment of Rent or
any other payment hereunder within five (5) business days after written notice
is received from Landlord that such installment is overdue; provided, however,
that Landlord shall not be required to give such a notice more than once in any
twelve (12) month period.

     (b) INSURANCE. Any insurance required to be maintained by Tenant
pursuant to this Lease shall be canceled or terminated or shall expire or shall
be reduced or materially changed, or Landlord shall receive a notice of
nonrenewal of any such insurance and Tenant shall fail to obtain replacement
insurance at least five (5) business days before the expiration of the current
coverage.

     (c) OTHER DEFAULTS. Tenant shall fail to comply with any provision of this
Lease other than those specifically referred to in this Section 18, and, except
as otherwise expressly provided herein, such failure shall continue for a
period of fifteen (15) days after written notice thereof from Landlord to
Tenant (of such additional time as may be reasonably required to cure the
failure if the failure cannot be cured within a 15-day period, provided Tenant
commences to cure within such 15-day period and thereafter diligently pursues
such cure to completion).

Any notice given under Section 18(c) hereof shall: (i) specify the alleged
default, (ii) demand that Tenant cure such default, (iii) be in lieu of, and
not in addition to, or shall be deemed to be in lieu of, any notice required
under any provision of applicable law, and (iv) not be deemed a forfeiture or a
termination of this Lease unless Landlord elects otherwise in such notice.

     19. LANDLORD'S REMEDIES.

     (a) PAYMENT BY LANDLORD; INTEREST. Upon a Default by Tenant hereunder,
Landlord may, without waiving or releasing any obligation of Tenant hereunder,
make such payment or perform such act. All sums so paid or incurred by
Landlord, together with interest thereon, from the date such sums were paid or
incurred, at the annual rate equal to 10% per annum or the highest rate
permitted by law (the "DEFAULT RATE"), whichever is less, shall be payable to
Landlord on demand as Additional Rent. Nothing herein shall be construed to
create or impose a duty on Landlord to mitigate any damages resulting from
Tenant's Default hereunder.

     (b) LATE PAYMENT RENT. Late payment by Tenant to Landlord of Rent and
other sums due will cause Landlord to incur costs not contemplated by this
Lease, the exact amount of which will be extremely difficult and impracticable
to ascertain. Such costs include, but are not limited to, processing and
accounting charges and late charges which may be imposed on Landlord under any
Mortgage covering the Premises. Therefore, if any installment of Rent due from
Tenant is not received by Landlord

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Short Form 3N Laboratory Lease                           ADDRESS/TENANT - PAGE 8

within 5 days after the date such payment is due, Tenant shall pay to Landlord
an additional sum equal to 6% of the overdue Rent as a late charge. The parties
agree that this late charge represents a fair and reasonable estimate of the
costs Landlord will incur by reason of late payment by Tenant. In addition to
the late charge, Rent not paid when due shall bear interest at the Default Rate
from the 5th day after the date due until paid.

     (c)  OTHER REMEDIES.  Upon the occurrence of a Default, Landlord, at its
option, without further notice or demand to Tenant, shall have all rights and
remedies provided at law or in equity.

     20.  ASSIGNMENT AND SUBLETTING.  Tenant shall not, directly or indirectly,
voluntarily or by operation of law, assign this Lease or sublease the Premises
or any part thereof or mortgage, pledge, or hypothecate its leasehold interest
or grant any concession or license within the Premises, and any attempt to do
any of the foregoing shall be void and of no effect.

     21.  ESTOPPEL CERTIFICATE.  Tenant shall, within 10 business days of
written notice from Landlord, execute, acknowledge and deliver an estoppel
certificate on any form reasonably requested by a proposed lender or purchaser.

     22.  QUIET ENJOYMENT.  So long as Tenant shall perform all of the
covenants and agreements herein required to be performed by Tenant, Tenant
shall, subject to the terms of this Lease, at all times during the Term, have
peaceful and quiet enjoyment of the Premises against any person claiming by,
through or under Landlord.

     23.  PRORATIONS.  All prorations required or permitted to be made
hereunder shall be made on the basis of a 360 day year and 30 day months.

     24.  RULES AND REGULATIONS.  Tenant shall, at all times during the Early
Occupancy Period and the Term and any extension thereof, comply with all
reasonable rules and regulations at any time or from time to time established
by Landlord covering use of the Premises and the Project. The current rules and
regulations are attached hereto as EXHIBIT E. If there is any conflict between
said rules and regulations and other provisions of this Lease, the terms and
provisions of this Lease shall control. Landlord shall not have any liability
or obligation for the breach of any rules or regulations by other tenants in
the Project and shall not enforce such rules and regulations in a
discriminatory manner.

     25.  SUBORDINATION.  This Lease and Tenant's interest and rights hereunder
are and shall be subject and subordinate at all times to the lien of any
Mortgage now existing or hereafter created on or against the Project or the
Premises, and all amendments, restatements, renewals, modifications,
consolidations, refinancing, assignments and extensions thereof, without the
necessity of any further instrument or act of the part of Tenant. Tenant
agrees, at the election of the Holder of any such Mortgage, to attorn to any
such Holder. Tenant agrees upon demand to execute, acknowledge and deliver such
instruments confirming such subordination and/or attornment as shall be
requested by any such Holder.

     26.  SURRENDER.  Upon the expiration of the Term or earlier termination of
Tenant's right of possession, Tenant shall surrender the Premises to Landlord
in the same condition as received, free of Hazardous Materials brought upon,
kept, used, stored, handled, treated, generated in, or released or disposed of
from, the Premises by any person other than a Landlord Party (collectively,
"TENANT HAZMAT OPERATIONS") and released of all Hazardous Materials Clearances,
broom clean, ordinary wear and tear and casualty loss and condemnation covered
by Section 17 excepted. At least 2 months prior to the surrender of the
Premises, Tenant shall deliver to Landlord a narrative description of the
actions proposed (or required by any Governmental Authority) to be taken by
Tenant in order to surrender the Premises at the expiration or earlier
termination of the Term, free from any residual impact from the Tenant HazMat
Operations and otherwise released for unrestricted use and occupancy (the
"SURRENDER PLAN"). Such Surrender Plan shall be accompanied by a listing of (i)
all Hazardous Materials licenses and permits held by or on behalf of any Tenant
Party with respect to the Premises, and (ii) all Hazardous Materials used,
stored, handled, treated, generated, released or disposed of from the Premises,
and shall

              (C) All Rights Reserved 2001 Alexandria Real Estate Equities, Inc.
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Short Form 3N Laboratory Lease                           ADDRESS/TENANT - PAGE 9

be subject to the review and approval of Landlord's environmental consultant. In
connection with the review and approval of the Surrender Plan, upon the request
of Landlord, Tenant shall deliver to Landlord or its consultant such additional
non-proprietary information concerning Tenant HazMat Operations as Landlord
shall request. On or before such surrender, Tenant shall deliver to Landlord
evidence that the approved Surrender Plan shall have been satisfactorily
completed and Landlord shall have the right, subject to reimbursement at
Tenant's expense as set forth below, to cause Landlord's environmental
consultant to inspect the Premises and perform such additional procedures as may
be deemed reasonably necessary to confirm that the Premises are, as of the
effective date of such surrender or early termination of the Lease, free from
any residual impact from Tenant HazMat Operations. Tenant shall reimburse
Landlord, as Additional Rent, for the actual out-of pocket expense incurred by
Landlord for Landlord's environmental consultant to review and approve the
Surrender Plan and to visit the Premises and verify satisfactory completion of
the same, which cost shall not exceed $1,500. Landlord shall have the
unrestricted right to deliver such Surrender Plan and any report by Landlord's
environmental consultant with respect to the surrender of the Premises to third
parties, subject to any reasonable confidentiality requirements imposed by
Tenant.

     If Tenant shall fail to prepare or submit a Surrender Plan approved by
Landlord, or if Tenant shall fail to complete the approved Surrender Plan, or if
such Surrender Plan, whether or not approved by Landlord, shall fail to
adequately address any residual effect of Tenant HazMat Operations in, on or
about the Premises, Landlord shall have the right to take such actions as
Landlord may deem reasonable or appropriate to assure that the Premises and the
Project are surrendered free from any residual impact from Tenant HazMat
Operations, the cost of which actions shall be reimbursed by Tenant as
Additional Rent, without regard to the limitation set forth in the first
paragraph of this Section 26.

     Tenant shall immediately return to Landlord all keys and/or access cards to
parking, the Project, restrooms or all or any portion of the Premises furnished
to or otherwise procured by Tenant. If any such access card or key is lost,
Tenant shall pay to Landlord, at Landlord's election, either the cost of
replacing such lost access card or key or the cost of reprogramming the access
security system in which such access card was used or changing the lock or locks
opened by such lost key. Any Tenant's property not so removed by Tenant as
permitted or required herein shall be deemed abandoned and may be stored,
removed, and disposed of by Landlord at Tenant's expense, and Tenant waives all
claims against Landlord for any damages resulting from Landlord's retention
and/or disposition of such property. All obligations of Tenant hereunder not
fully performed as of the termination of the Term, including the obligations of
Tenant under Section 28 hereof, shall survive the expiration or earlier
termination of the Term, including, without limitation, indemnity obligations,
payment obligations with respect to Rent and obligations concerning the
condition and repair of the Premises.

     27.  WAIVER OF JURY TRIAL. TENANT AND LANDLORD WAIVE ANY RIGHT TO TRIAL BY
JURY OR TO HAVE A JURY PARTICIPATE IN RESOLVING ANY DISPUTE, WHETHER SOUNDING IN
CONTRACT, TORT, OR OTHERWISE, BETWEEN LANDLORD AND TENANT ARISING OUT OF THIS
LEASE OR ANY OTHER INSTRUMENT, DOCUMENT, OR AGREEMENT EXECUTED OR DELIVERED IN
CONNECTION HEREWITH OR THE TRANSACTIONS RELATED HERETO.

     28.  Environmental Requirements.

     (a)  PROHIBITION/COMPLIANCE/INDEMNITY. Tenant shall not cause or permit
any Hazardous Materials (as hereinafter defined) to be brought upon, kept,
used, stored, handled, treated, generated in or about, or released or disposed
of from, the Premises or the Project in violation of applicable Environmental
Requirements (as hereinafter defined) by Tenant or Tenant Party. If (i) Tenant
breaches the obligation stated in the preceding sentence, or (ii) the presence
of Hazardous Materials in the Premises during the Early Occupancy Period, the
Term or any holding over results in contamination of the Premises, the Project
or any adjacent property or (iii) contamination of the Premises, the Project or
any adjacent property by Hazardous Materials brought into, kept, used, stored,
handled, treated, generated in or about, or released or disposed of from, the
Premises by anyone other than Landlord and Landlord's employees, agents and
contractors, in the case of the Premises, and by Tenant or a Tenant Party, in
the case of the Project or any adjacent Property, otherwise occurs during the
Early Occupancy

              (c) All Rights Reserved 2001 Alexandria Real Estate Equities, Inc.
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Short Form 3N Laboratory Lease                          ADDRESS/TENANT - PAGE 10

Period, the Term or any holding over, Tenant hereby indemnifies and shall defend
and hold Landlord, its officers, directors, employees, agents and contractors
harmless from any and all actions (including, without limitation, remedial or
enforcement actions of any kind, administrative or judicial proceedings, and
orders or judgments arising out of or resulting therefrom), costs, claims,
damages (including, without limitation, punitive damages and damages based upon
diminution in value of the Premises or the Project, or the loss of, or
restriction on, use of the Premises or any portion of the Project), expenses
(including, without limitation, attorneys', consultants' and experts' fees,
court costs and amounts paid in settlement of any claims or actions), fines,
forfeitures or other civil, administrative or criminal penalties, injunctive or
other relief (whether or not based upon personal injury, property damage, or
contamination of, or adverse effects upon, the environment, water tables or
natural resources), liabilities or losses (collectively, "ENVIRONMENTAL CLAIMS")
which arise during or after the expiration of the Early Occupancy Period and/or
the Term, as applicable, as a result of such contamination. This Indemnification
of Landlord by Tenant includes, without limitation, costs incurred in connection
with any investigation of site conditions or any cleanup, treatment, remedial,
removal, or restoration work required by any federal, state or local
Governmental Authority because of Hazardous Materials present in the air, soil
or ground water above, on, or under the Premises. Without limiting the
foregoing, if the presence of any Hazardous Materials on the Premises, the
Project or any adjacent property caused or permitted by Tenant or any Tenant
Party results in any contamination of the Premises, the Project or any adjacent
property, Tenant shall promptly take all actions at its sole expense and in
accordance with applicable Environmental Requirements as are necessary to return
the Premises, the Project or any adjacent property to the condition existing
prior to the time of such contamination, provided that Landlord's approval of
such action shall first be obtained, which approval shall not unreasonably be
withheld so long as such actions would not potentially have any material adverse
long-term or short-term effect on the Premises or the Project.

     (b)  BUSINESS. As a material inducement to Landlord to allow Tenant to use
Hazardous Materials in connection with its business, Tenant agrees to deliver to
Landlord prior to the Early Occupancy Date a list identifying each type of
Hazardous Materials to be brought upon, kept, used, stored, handled, treated,
generated on, or released or disposed of from, the Premises and setting forth
any and all governmental approvals or permits required in connection with the
presence, use, storage, handling, treatment, generation, release or disposal of
such Hazardous Materials on or from the Premises ("HAZARDOUS MATERIALS LIST").
Tenant shall deliver to Landlord true and correct copies of the following
documents (the "HAZ MAT DOCUMENTS") relating to the use, storage, handling,
treatment, generation, release or disposal of Hazardous Materials prior to the
Early Occupancy Date, or if unavailable at that time, concurrent with the
receipt from or submission to a Governmental Authority: permits; approvals;
reports and correspondence; storage and management plans; and notices of
violations of any Legal Requirements.

     (c)  TENANT'S OBLIGATIONS. Tenant's obligations under this Section 28 shall
survive the expiration or earlier termination of the Lease. During any period of
time after the expiration or earlier termination of this Lease required by
Tenant or Landlord to complete the removal from the Premises of any Hazardous
Materials (including, without limitation, the release and termination of any
licenses or permits restricting the use of the Premises and the completion of
the approved Surrender Plan), Tenant shall continue to pay the full Rent in
accordance with this Lease for any portion of the Premies not relet by Landlord
in Landlord's sole discretion, which Rent shall be prorated daily.

     (d)  DEFINITIONS. As used herein, the term "ENVIRONMENTAL REQUIREMENTS"
means all applicable present and future statutes, regulations, ordinances,
rules, codes, judgments, orders or other similar enactments of any Governmental
Authority regulating or relating to health, safety, or environmental conditions
on, under, or about the Premises or the Project, or the environment, including
without limitation, the following: the Comprehensive Environmental Response,
Compensation and Liability Act; the Resource Conservation and Recovery Act; and
all state and local counterparts thereto, and any regulations or policies
promulgated or issued thereunder. As used herein, the term "HAZARDOUS MATERIALS"
means and includes any substance, material, waste, pollutant, or contaminant
listed or defined as hazardous or toxic, or regulated by reason of its impact or
potential impact on humans, animals and/or the environment under any
Environmental Requirements, asbestos and petroleum, including crude oil or any
fraction thereof, natural gas liquids, liquefied natural gas, or synthetic gas
issuable for fuel (or mixtures

              (C) All Rights Reserved 2001 Alexandria Real Estate Equities, Inc.
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Short Form 3N Laboratory Lease                          ADDRESS/TENANT - PAGE 11

of natural gas and such synthetic gas). As defined in Environmental
Requirements, Tenant is and shall be deemed to be the "OPERATOR" of Tenant's
"FACILITY" and the "OWNER" of all Hazardous Materials brought on the Premises
by Tenant or any Tenant Party, and the wastes, by-products, or residues
generated, resulting, or produced therefrom.

     29.  TENANT'S REMEDIES/LIMITATION OF LIABILITY.  Landlord shall not be in
default hereunder unless Landlord fails to perform any of its obligations
hereunder within 30 days after written notice from Tenant specifying such
failure. TENANT'S SOLE REMEDY FOR ANY BREACH OR DEFAULT BY LANDLORD HEREUNDER
SHALL BE TO TERMINATE THE LEASE AND TENANT HEREBY, TO THE MAXIMUM EXTENT
POSSIBLE, KNOWINGLY WAIVES (i) THE PROVISIONS OF ANY LAW, NOW OR HEREAFTER IN
FORCE WHICH PROVIDE ADDITIONAL OR OTHER REMEDIES TO TENANT AS A RESULT OF ANY
BREACH BY LANDLORD HEREUNDER OR UNDER ANY SUCH LAW OR REGULATION.

     30.  INSPECTION AND ACCESS.  Landlord and its agents, representatives, and
contractors may enter the Premises at any reasonable time, upon reasonable
prior notice, to inspect the Premises and to make such repairs as may be
required or permitted pursuant to this Lease, to perform such environmental
tests as may be reasonably required to confirm Tenant's compliance with the
terms hereof and for any other business purpose. Landlord and Landlord's
representatives may enter the Premises during business hours on not less than
48 hours advance written notice (except in the case of emergencies in which
case no such notice shall be required and such entry may be at any time) for
the purpose of effecting any such repairs, inspecting the Premises, showing the
Premises to prospective purchasers and, during the last year of the Term, to
prospective tenants or for any other business purpose.

     31.  SECURITY.  Tenant acknowledges and agrees that security devices and
services, if any, while intended to deter crime may not in given instances
prevent theft or other criminal acts and that Landlord is not providing any
security services with respect to the Premises. Tenant agrees that Landlord
shall not be liable to Tenant for, and Tenant waives any claim against Landlord
with respect to, any loss by theft or any other damage suffered or incurred by
Tenant in connection with any unauthorized entry into the Premises or any other
breach of security with respect to the Premises. Tenant shall be solely
responsible for the personal safety of Tenant's officers, employees, agents,
contractors, guests and invitees while any such person is in, on or about the
Premises and/or the Project. Tenant shall at Tenant's cost obtain insurance
coverage to the extent Tenant desires protection against such criminal acts.

     32.  BROKERS.  Landlord and Tenant each represents and warrants that it
has not dealt with any broker, agent or other person (collectively, "BROKER")
in connection with this transaction and that no Broker brought about this
transaction other than T3 Realty Advisors, LLC, to whom Landlord shall pay a
commission. Landlord and Tenant each hereby agree to indemnify and hold the
other harmless from and against any claims by any Broker, other than the
broker, if any named in this Section 32, claiming a commission or other form of
compensation by virtue of having dealt with Tenant or Landlord, as applicable,
with regard to this leasing transaction.

     33.  LIMITATION ON LANDLORD'S LIABILITY.  NOTWITHSTANDING ANYTHING SET
FORTH HEREIN OR IN ANY OTHER AGREEMENT BETWEEN LANDLORD AND TENANT TO THE
CONTRARY: (A) LANDLORD SHALL NOT BE LIABLE TO TENANT OR ANY OTHER PERSON FOR
(AND TENANT AND EACH SUCH OTHER PERSON ASSUME ALL RISK OF) LOSS, DAMAGE OR
INJURY, WHETHER ACTUAL OR CONSEQUENTIAL TO: TENANT'S PERSONAL PROPERTY OF EVERY
KIND AND DESCRIPTION, INCLUDING, WITHOUT LIMITATION TRADE FIXTURES, EQUIPMENT,
INVENTORY, SCIENTIFIC RESEARCH, SCIENTIFIC EXPERIMENTS, LABORATORY ANIMALS,
PRODUCT, SPECIMENS, SAMPLES, AND/OR SCIENTIFIC, BUSINESS, ACCOUNTING AND OTHER
RECORDS OF EVERY KIND AND DESCRIPTION KEPT AT THE PREMISES AND ANY AND ALL
INCOME DERIVED OR DERIVABLE THEREFROM; (B) THERE SHALL BE NO PERSONAL RECOURSE
TO LANDLORD FOR ANY ACT OR OCCURRENCE IN, ON OR ABOUT THE PREMISES OR ARISING
IN ANY WAY UNDER THIS LEASE OR ANY OTHER AGREEMENT BETWEEN

              (C) All Rights Reserved 2001 Alexandria Real Estate Equities, Inc.
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Short Form 3N Laboratory Lease                         ADDRESS/TENANT - PAGE 12

LANDLORD AND TENANT WITH RESPECT TO THE SUBJECT MATTER HEREOF AND ANY LIABILITY
OF LANDLORD HEREUNDER SHALL BE STRICTLY LIMITED SOLELY TO LANDLORD'S INTEREST
IN THE PROJECT OR ANY PROCEEDS FROM SALE OR CONDEMNATION THEREOF AND ANY
INSURANCE PROCEEDS PAYABLE IN RESPECT OF LANDLORD'S INTEREST IN THE PROJECT OR
IN CONNECTION WITH ANY SUCH LOSS; AND (C) IN NO EVENT SHALL ANY PERSONAL
LIABILITY BE ASSERTED AGAINST LANDLORD IN CONNECTION WITH THIS LEASE NOR SHALL
ANY RECOURSE BE HAD TO ANY OTHER PROPERTY OR ASSETS OF LANDLORD OR ANY OF
LANDLORD'S OFFICERS, DIRECTORS, EMPLOYEES, AGENTS OR CONTRACTORS. UNDER NO
CIRCUMSTANCES SHALL LANDLORD OR ANY OF LANDLORD'S OFFICERS, DIRECTORS,
EMPLOYEES, AGENTS OR CONTRACTORS BE LIABLE FOR INJURY TO TENANT'S BUSINESS OR
FOR ANY LOSS OF INCOME OR PROFIT THEREFROM.

     34.  SEVERABILITY. If any clause or provision of this Lease is illegal,
invalid or unenforceable under present or future laws, then and in that event,
it is the intention of the parties hereto that the remainder of this Lease
shall not be affected thereby.

     35.  SIGNS; EXTERIOR APPEARANCE. Tenant shall not: (i) attach anything at
any time to any outside wall of the Project, (ii) use any window coverings or
sunscreen other than Landlord's standard window coverings, (iii) place any
articles on the window sills, (iv) place any items on any exterior balcony, or
(v) paint, affix or exhibit any signs or any kind in the Premises which can be
viewed from the exterior of the Premises. Identifying signage at the entryway
to the Premises and as part of the street level directory shall be provided by
Landlord at Landlord's sole cost and expense.

     36.  LANDLORD'S RIGHT TO RELOCATE TENANT. [Intentionally Deleted]

     37.  RIGHT TO EXPAND.

     (a)  EXPANSION IN THE BUILDING. Tenant shall have the one-time right (the
"Expansion Right") to expand the Premises, as follows: At any time following
the Commencement Date, Tenant shall have the right to notify Landlord, in
writing, of Tenant's desire to expand into any Available Space in the Building.
For purposes of this Section 36(a), "Available Space" shall mean any one suite
in the Building which is not occupied by a tenant or which is occupied by an
existing tenant whose lease is expiring within one (1) month or less and such
tenant does not wish to renew (whether or not such tenant has a right to renew)
its occupancy of such suite. Within five (5) business days after Landlord's
receipt of written notice of Tenant's desire to expand into Available Space, if
there is any Available Space in the Building, Landlord shall deliver to
Tenant written notice (the "Expansion Notice") of such Available Space. Tenant
shall have 10 business days following delivery of the Expansion Notice to
deliver to Landlord written notification of Tenant's exercise of the Expansion
Right. Provided that no right to expand is exercised by any tenant with
superior rights, Tenant shall be entitled to lease such Available Space for the
remaining term of the Lease upon the same terms and conditions set forth in
this Lease, including, without limitation the rental rates. The commencement
date for Tenant's lease of such Available Space shall be not more than thirty
(30) days after the date on which Tenant notified Landlord of Tenant's exercise
of the Expansion Right as provided herein.

     (b)  AMENDED LEASE. If: (i) Tenant fails to timely deliver notice
accepting the terms of an Expansion Notice, or (ii) after the expiration of a
period of 30 days from the date Tenant gives notice accepting Landlord's offer
to lease such Available Space, no lease amendment or lease agreement for the
Available Space has been executed, and Landlord tenders to Tenant an amendment
to this Lease setting forth the terms for the rental of the Available Space
consistent with those set forth in the Expansion Notice and otherwise
consistent with the terms of this Lease and Tenant fails to execute such Lease
amendment within 10 business days following such tender, Tenant shall be deemed
to have waived its right to lease such Available Space.

     (c)  EXCEPTIONS. Notwithstanding the above, the Expansion Right shall not
be in effect and may not be exercised by Tenant: (i) during any period of time
that Tenant is in Default under any provision of the Lease; or (ii) if Tenant
has been in Default under any provision of the Lease 1 or more

              (C) All Rights Reserved 2001 Alexandria Real Estate Equities, Inc.
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<PAGE>
Short Form 3N Laboratory Lease                         ADDRESS/TENANT - PAGE 13

times, whether or not the Defaults are cured, during the 12 month period prior
to the date on which Tenant seeks to exercise the Expansion Right.

     (d)  TERMINATION. The Expansion Right shall terminate and be of no further
force or effect even after Tenant's due and timely exercise of the Expansion
Right, if, after such exercise, but prior to the commencement date of the lease
of such Available Space, (i) Tenant fails to timely cure any default by Tenant
under the Lease; or (ii) Tenant has Defaulted 1 or more times during the period
from the date of the exercise of the Expansion Right to the date of the
commencement of the lease of the Available Space, whether or not such Defaults
are cured. The Expansion Right is a one-time right and Tenant shall have no
further rights under this Section 37 following Tenant's exercise of the
Expansion Right as set forth herein.

     (e)  RIGHTS PERSONAL. The Expansion Right is personal to Tenant and is not
assignable.

     (f)  NO EXTENSION. The period of time within which the Expansion Right may
be exercised shall not be extended or enlarged by reason of Tenant's inability
to exercise the Expansion Right.

     38. RIGHT TO EXTEND TERM. Tenant shall have the right to extend the Term
of the Lease upon the following terms and conditions:

     (a)  EXTENSION RIGHTS. Tenant shall have two (2) consecutive rights (each,
an "EXTENSION RIGHT", and collectively, the "EXTENSION RIGHTS") to extend the
term of this Lease for a period, in each case, of a minimum of three (3) months
and a maximum of six (6) months (each, an "EXTENSION TERM") on the same terms
and conditions as this Lease by giving Landlord written notice of its election
to exercise each Extension Right at least two (2) months prior to the expiration
of the Base Term of the Lease or the expiration of any prior Extension Term.
Such notice shall include a statement as to the proposed length of the Extension
Term in question.

     (b)  RIGHTS PERSONAL. The Extension Rights are personal to Tenant and are
not assignable.

     (c)  EXCEPTIONS. Notwithstanding anything set forth above to the contrary,
the Extension Rights shall not be in effect and Tenant may not exercise either
Extension Right: (i) during any period of time that Tenant is in Default under
any provision of this Lease; or (ii) if Tenant has been in Default under any
provision of this Lease 1 or more times, whether or not the Defaults are cured,
during the 12 month period immediately prior to the date that Tenant intends to
exercise either Extension Right, whether or not the Defaults are cured.

     (d)  NO EXTENSIONS. The period of time within which the Extension Rights
may be exercised shall not be extended or enlarged by reason of Tenant's
inability to exercise the Extension Rights.

     (e)  TERMINATION. The Extension Rights shall terminate and be of no
further force or effect even after Tenant's due and timely exercise of the
Extension Rights, if, after such exercise, but prior to the commencement date
of an Extension Term, (i) Tenant fails to timely cure any default by Tenant
under this Lease; or (ii) Tenant has Defaulted 1 or more times during the
period from the date of the exercise of one of the Extension Rights to the date
of the commencement of the applicable Extension Term, whether or not such
Defaults are cured.

     39.  MISCELLANEOUS

     (a)  NOTICES. Except as otherwise provided herein, all notices or other
communications between the parties shall be in writing and shall be deemed duly
given upon delivery or refusal to accept delivery by the addressee thereof if
delivered in person, confirmed receipt by facsimile or upon actual receipt if
delivered by reputable overnight guaranty courier, addressed and sent to the
parties at their addresses set forth above. Landlord and Tenant may from time
to time by written notice to the other designate another address for receipt of
future notices.

              (C) All Rights Reserved 2001 Alexandria Real Estate Equities, Inc.
                                                     CONFIDENTIAL - DO NOT COPY
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Short Form 3N Laboratory Lease                          ADDRESS/TENANT - PAGE 14

     (b)  FINANCIAL STATEMENTS. Tenant has furnished Landlord with true and
correct copies of its most recent unaudited quarterly financial statements prior
to the execution of this Lease and shall furnish Landlord with true and correct
copies of its most recent unaudited quarterly financial statements within
forty-five (45) days after the end of each calendar quarter during the Term and
of its audited annual financial statements when such statements become available
during the Term. Upon Landlord's request, Tenant shall furnish Landlord with
Tenant's most recent business plan; provided, however, that Landlord shall treat
such business plan and financial statements as confidential. Tenant shall also
provide to Landlord, upon Landlord's request with any other financial
information or summaries that Tenant typically provides to its shareholders or
lenders.

     (c)  RECORDATION. Neither this Lease nor a memorandum of lease shall be
filed by or on behalf of Tenant in any public record. Landlord may prepare and
file, and upon request by Landlord Tenant will execute, a memorandum of lease.

     (d)  INTERPRETATION. The normal rule of construction to the effect that any
ambiguities are to be resolved against the drafting party shall not be employed
in the interpretation of this Lease or any exhibits or amendments hereto.

     (e)  NOT BINDING UNTIL EXECUTED. The submission by Landlord to Tenant of
this Lease shall have no binding force or effect, shall not constitute an option
for the leasing of the Premises, nor confer any right or impose any obligations
upon either party until execution of this Lease by both parties.

     (f)  LIMITATIONS ON INTEREST. It is expressly the intent of Landlord and
Tenant at all times to comply with applicable law governing the maximum rate or
amount of any interest payable on or in connection with this Lease. If
applicable law is ever judicially interpreted so as to render usurious any
interest called for under this Lease, or contracted for, charged, taken,
reserved, or received with respect to this Lease, then it is Landlord's and
Tenant's express intent that all excess amounts theretofore collected by
Landlord be credited on the applicable obligation (or, if the obligation has
been or would thereby be paid in full, refunded to Tenant), and the provisions
of this Lease immediately shall be deemed reformed and the amounts thereafter
collectible hereunder reduced, without the necessity of the execution of any new
document, so as to comply with the applicable law, but so as to permit the
recovery of the fullest amount otherwise called for hereunder.

     (g)  CHOICE OF LAW. Construction and interpretation of this Lease shall be
governed by the internal laws of the state in which the Premises are located,
excluding any principles of conflicts of laws.

     (h)  TIME. Time is of the essence as to the performance of Tenant's
obligations under this Lease.

     IN WITNESS WHEREOF, Landlord and Tenant have executed this Lease as of the
day and year first above written.

                                        TENANT:

                                        ALNYLAM PHARMACEUTICALS, INC., a
                                        Delaware corporation

                                        By: /s/ John Conley
                                           -----------------------------------
                                            John Conley, Treasurer

                                        LANDLORD:

                                        ARE-770/784/790 MEMORIAL DRIVE, LLC,
                                        a Delaware limited liability company

              (C) All Rights Reserved 2001 Alexandria Real Estate Equities, Inc.
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<PAGE>
Short Form 3N Laboratory Lease                         ADDRESS/TENANT -- PAGE 15

                         By: ALEXANDRIA REAL ESTATE EQUITIES, L.P., managing me

                         By: ARE-QRS CORP, general partner

                         By: Joel S. Marcus
                             --------------------------------------------------

                         Its: CEO
                              -------------------------------------------------

              (C) All Rights Reserved 2001 Alexandria Real Estate Equities, Inc.
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<PAGE>
Short Form 3N Laboratory Lease                          Address/Tenant - Page 16

                               EXHIBIT A TO LEASE

                            DESCRIPTION OF PREMISES
<PAGE>
Short Form 3N Laboratory Lease                          Address/Tenant - Page 17

                               EXHIBIT B TO LEASE

                             DESCRIPTION OF PROJECT

<PAGE>
Short Form 3N Laboratory Lease                          Address/Tenant - Page 18

                               EXHIBIT C TO LEASE

                      ACKNOWLEDGMENT OF COMMENCEMENT DATE

     This ACKNOWLEDGMENT OF COMMENCEMENT DATE is made this ____ day of
__________,__________, between ARE-770/784/790 Memorial Drive, LLC, a Delaware
limited liability company ("LANDLORD"), and Alnylam Pharmaceuticals, Inc., a
Delaware corporation ("TENANT"), and is attached to and made a part of the
Lease dated __________,__________, (the "LEASE"), by and between Landlord and
Tenant. Any initially capitalized terms used but not defined herein shall have
the meanings given them in the Lease.

     Landlord and Tenant hereby acknowledge and agree, for all purposes of the
Lease, that the Commencement Date of the Base Term of the Lease is __________,
__________, and the termination date of the Base Term of the Lease shall be
midnight on __________,__________.

     IN WITNESS WHEREOF, Landlord and Tenant have executed this ACKNOWLEDGMENT
OF COMMENCEMENT DATE to be effective on the date first above written.

TENANT:

ALNYLAM PHARMACEUTICALS, INC., a Delaware
corporation

By:
    -----------------------------------
    John Conley, Treasurer

LANDLORD:

ARE-770/784/790 MEMORIAL DRIVE, LLC, a Delaware
limited liability company

By: ALEXANDRIA REAL ESTATE EQUITIES, L.P., managing me

By: ARE-QRS CORP., general partner

By:
    -----------------------------------

Its:
     ----------------------------------

<PAGE>
Short Form 3N Laboratory Lease                          Address/Tenant - Page 19

                               EXHIBIT D TO LEASE

               GOVERNMENT PARKING AND TRANSPORTATION REQUIREMENTS

CITY OF CAMBRIDGE - PARKING AND TRANSPORTATION DEMAND MANAGEMENT PLAN

1. Tenant shall identify an employee representative or liaison to work with the
Employee Transportation Coordinator.

2. Tenant shall participate in employee incentive programs, developed by the
Employee Transportation Coordinator, to encourage the use of alternative modes
of transportation.

3. Tenant shall charge employees for the full cost of their parking, either
directly or through a commuter choice program.

4. Tenant's Human Resources representative shall coordinate with the Employee
Transportation Coordinator to incorporate the distribution of the Commuter
Services Program, New Employee Orientation Packet as part of Tenant's internal
orientation system.

5. Tenant shall participate in all programs, studies, surveys, monitoring and
reports as required by the Parking and Transportation Demand Management Plan.

CITY OF CAMBRIDGE - IPOP SPECIAL PERMIT

1. Tenant shall provide a 100% subsidy of transit passes including commuter rail
passes to all employees at the site.

NEIGHBORHOOD GROUPS SETTLEMENT AGREEMENT

1. Tenant's employees and invitees are prohibited from making left turns onto
Pleasant Street from the commercial curb cut during the hours of 7-9 a.m. and
4-7 p.m. weekdays.

<PAGE>
Short Form 3N Laboratory Lease                         ADDRESS/TENANT -- PAGE 20

                               EXHIBIT E TO LEASE

                             RULES AND REGULATIONS
                             ---------------------

     1.   The sidewalk, entries, and driveways of the Project shall not be
obstructed by Tenant, or any Tenant Party, or used by them for any purpose
other than ingress and egress to and from the Premises.

     2.   Tenant shall not place any objects, including antennas, outdoor
furniture, etc., in the parking areas, landscaped areas or other areas outside
of its Premises, or on the roof of the Project.

     3.   Except for animals assisting the disabled, no animals shall be
allowed in the offices, halls, or corridors in the Project.

     4.   Tenant shall not disturb the occupants of the Project or adjoining
buildings by the use of any radio or musical instrument or by the making of
loud or improper noises.

     5.   If Tenant desires telegraphic, telephonic or other electric
connections in the Premises, Landlord or its agent will direct the electrician
as to where and how the wires may be introduced; and, without such direction,
no boring or cutting of wires will be permitted. Any such installation or
connection shall be made at Tenant's expense.

     6.   Tenant shall not install or operate any steam or gas engine or
boiler, or other mechanical apparatus in the Premises, except as specifically
approved in the Lease. The use of oil, gas or inflammable liquids for heating,
lighting or any other purpose is expressly prohibited. Explosives or other
articles deemed extra hazardous shall not be brought into the Project.

     7.   Parking any type of recreational vehicles is specifically prohibited
on or about the Project. Except for the overnight parking of operative
vehicles, no vehicle of any type shall be stored in the parking areas at any
time. In the event that a vehicle is disabled, it shall be removed within 48
hours. There shall be no "For Sale" or other advertising signs on or about any
parked vehicle. All vehicles shall be parked in the designated parking areas in
conformity with all signs and other markings. All parking will be open parking,
and no reserved parking, numbering or lettering of individual spaces will be
permitted except as specified by Landlord.

     8.   Tenant shall maintain the Premises free from rodents, insects and
other pests.

     9.   Landlord reserves the right to exclude or expel from the Project any
person who, in the judgment of Landlord, is intoxicated or under the influence
of liquor or drugs or who shall in any manner do any act in violation of the
Rules and Regulations of the Project.

     10.  Tenant shall not cause any unnecessary labor by reason of Tenant's
carelessness or indifference in the preservation of good order and cleanliness.
Landlord shall not be responsible to Tenant for any loss of property on the
Premises, however occurring, or for any damage done to the effects of Tenant by
the janitors or any other employee or person.

     11.  Tenant shall give Landlord prompt notice of any defects in the water,
lawn sprinkler, sewage, gas pipes, electrical lights and fixtures, heating
apparatus, or any other service equipment affecting the Premises.

     12.  Tenant shall not permit storage outside the Premises, including
without limitation, outside storage of trucks and other vehicles, or dumping of
waste or refuse or permit any harmful materials to be placed in any drainage
system or sanitary system in or about the Premises.

ladb01 28464923.2 072301 1134P 98459290               c All Rights Reserved 2001
                                    Alexandria Real Estate Estate Equities, Inc.
                                                     CONFIDENTIAL -- DO NOT COPY

<PAGE>
SHORT FORM 3N LABORATORY LEASE                           ADDRESS/TENANT-PAGE 21

     13.  All moveable trash receptacles provided by the trash disposal firm
for the Premises must be kept in the trash enclosure areas, if any, provided
for that purpose.

     14.  No auction, public or private, will be permitted on the Premises or
the Project.

     15.  No awnings shall be placed over the windows in the Premises except
with the prior written consent of Landlord.

     16.  The Premises shall not be used for lodging, sleeping or cooking or
for any immoral or illegal purposes or for any purpose other than that
specified in the Lease. No gaming devices shall be operated in the Premises.

     17.  Tenant shall ascertain from Landlord the maximum amount of electrical
current which can safely be used in the Premises, taking into account the
capacity of the electrical wiring in the Project and the Premises and the needs
of other tenants, and shall not use more than such safe capacity. Landlord's
consent to the installation of electric equipment shall not relieve Tenant from
the obligation not to use more electricity than such safe capacity.

     18.  Tenant assumes full responsibility for protecting the Premises from
theft, robbery and pilferage.

     19.  Tenant shall not install or operate on the Premises any machinery or
mechanical devices of a nature not directly related to Tenant's ordinary use of
the Premises and shall keep all such machinery free of vibration, noise and air
waves which may be transmitted beyond the Premises.
<PAGE>

                               AMENDMENT TO LEASE

         This Amendment to Lease is dated as of this 9th day of September, 2002
("Amendment"), by and between ARE-770/784/790 Memorial Drive, LLC, a Delaware
limited liability company ("Landlord") and Alnylam Pharmaceuticals, Inc., a
Delaware corporation ('Tenant").

                                   Background

         Landlord is the owner of that certain parcel of land, with the
improvements thereon, known as 790 Memorial Drive, Cambridge, Massachusetts.
Pursuant to that certain Lease Agreement, dated as of August 5,2002 ("Lease"),
Landlord agreed to lease to Tenant, and Tenant leased from Landlord, a portion
of such property more particularly described in the Lease. Landlord and Tenant
have discovered an error in the Lease and have entered into this Amendment for
the purpose of correcting such error.

         NOW, THEREFORE, for good and valuable consideration, the receipt and
sufficiency of which is hereby acknowledged, and intending to be legally bound
hereby, the parties hereto agree as follows:

         1.       The first sentence of Section 7(a) of the Lease is hereby
deleted in its entirety and the following inserted in its place: "Landlord shall
make available to Tenant an allowance (the "TI ALLOWANCE") in the maximum amount
of $39,990.00."

         2.       All other terms and conditions of the Lease, as so amended,
shall remain in full force and effect, as so amended.

         IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
executed, under seal, as of the day and year first above written.

                            TENANT;

                            ALNYLAM PHARMACEUTICALS, INC., a Delaware
                            corporation

                            BY: /s/ John Conley
                               ---------------------------------------------
                               John Conley, Treasurer

                            LANDLORD:

                            ARE-770/784/790 MEMORIAL DRIVE, LLC, a Delaware
                            limited liability company

                            BY: ALEXANDRIA REAL ESTATE EQUITIES, L.P., managing
                            member

                            BY: ARE-QRS CORP., general partner

                            BY: /s/ Joel S. Marcus
                               ---------------------------------------------

                            ITS: CEO

<PAGE>

                            SECOND AMENDMENT TO LEASE

         THIS SECOND AMENDMENT TO LEASE (this "Amendment") is dated as of the
25th day of March, 2003, by and between ARE-770/784/790 MEMORIAL DRIVE LLC, a
Delaware limited liability company ("Landlord") and ALNYLAM PHARMACEUTICALS,
INC., a Delaware corporation ("Tenant").

         A.       Pursuant to that certain Lease between Landlord and Tenant,
dated as of August 5, 2002, as amended by that certain Amendment to Lease dated
as of September 9, 2002 (as so amended, the "Original Lease") (together, the
Original lease and this Amendment are referred to herein as the "Lease"),
Landlord agreed to lease to Tenant, and Tenant leased from Landlord, certain
premises located in the building known as 790 Memorial Drive, Cambridge,
Massachusetts (the "Building"), as further identified in the Original Lease (the
"Premises"), subject to the terms and conditions more particularly set forth in
the Original Lease.

         B.       Landlord and Tenant now desire to expand the rentable area of
the Premises and adjust the amount of the Base Rent due under the Lease as more
particularly described herein, and to cause other changes to the Lease in
accordance with the terms and conditions set forth in this Amendment.

         NOW, THEREFORE, for good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, and intending to be legally bound
hereby, the parties hereto agree as follows:

         1.       From and after the date hereof, the Original Lease is hereby
amended to add the following new definitions to the Basic Lease Provisions:

3D Expansion Premises:                   One thousand sixty-two (1,062) rentable
                                         square feet on the third (3rd) floor of
                                         the 790 Premises, being a portion of
                                         that area of the Building designated as
                                         Suite 3D, as shown on Exhibit A-l
                                         attached hereto and incorporated herein
                                         by this reference.

3D Expansion Premises Effective Date:    January 24, 2003

3C Expansion Premises:                   Two thousand five hundred (2,500)
                                         rentable square feet on the third (3rd)
                                         floor of the 790 Premises, being a
                                         portion of that area of the Building
                                         designated as Suite 3C, as shown on
                                         Exhibit A-2 attached hereto and
                                         incorporated herein by this reference.

3C Expansion Premises Effective Date:    April 15, 2003.

2D Expansion Premises                    Two thousand six hundred ninety-five
                                         (2,695) rentable square feet on the
                                         second (2nd) floor of the

<PAGE>

                                         Building, designated as Suite 2D, as
                                         shown on Exhibit A-3 attached hereto
                                         and incorporated herein by this
                                         reference.

2D Expansion Premises Effective Date:    March 1,2003.

Additional Science Hotel (sm) Services Fee: $1,347.50 per month.

         2.       Commencing on the 3D Expansion Premises Effective Date and
ending on the 2D Expansion Premises Effective Date, the definitions of
"Premises", "Base Rent", and "Tenant's Share" set forth in the Basic Lease
Provisions of the Original Lease are hereby deleted and the following new
definitions are added to the Lease:

Premises:                                Those portions of the Building,
                                         designated as Suite 2C and Suite 3D,
                                         containing, in the aggregate,
                                         approximately Five Thousand Fifty-Two
                                         (5,052) rentable square feet, as shown
                                         on the attached Exhibits A and A- 1.

Base Rent:                               $24,329.50 per month

Tenant's Share:                          10.6%

         3.       Commencing on the 2D Expansion Premises Effective Date and
ending on the 3C Expansion Premises Effective Date, the definitions of
"Premises", "Base Rent", and "Tenant's Share" set forth in the Basic Lease
Provisions of the Original Lease are hereby deleted and the following new
definitions are added to the Lease:

Premises:                                Those portions of the Building,
                                         designated as Suite 2C, Suite 2D and
                                         Suite 3D, containing, in the aggregate,
                                         approximately seven thousand seven
                                         hundred forty-seven (7,747) rentable
                                         square feet, as shown on the attached
                                         Exhibits A, A-l and A-3.

Base Rent:                               $37,355.33 per month.

Tenant's Share:                          16.3%

         4.       Commencing on the 3C Expansion Premises Effective Date and
continuing thereafter during the Term of the Lease, unless sooner terminated as
provided herein, the definitions of "Premises", "Base Rent", and "Tenant's
Share" set forth in the Basic Lease Provisions of the Original Lease are hereby
deleted and the following new definitions are added to the Lease:

Premises:                                Those portions of the Building,
                                         designated as Suite 2C, Suite 2D and
                                         Suite 3C, containing, in the

                                       2
<PAGE>

                                         aggregate, approximately nine thousand
                                         one hundred eight-five (9,185) rentable
                                         square feet, as shown on the attached
                                         Exhibits A, A-2 and A-3.

Base Rent:                               $44,394.16 per month

Tenant's Share:                          19.3%

         5.       Commencing on the 3C Expansion Premises Return Date, as
hereinafter defined, and continuing thereafter during the Term of the Lease,
including any Extension Term, the definitions of "Premises", "Base Rent", and
"Tenant's Share" set forth in the Basic Lease Provisions of the Original Lease
are hereby deleted and the following new definitions are added to the Lease:

Premises:                                Those portions of the Building,
                                         designated as Suite 2C and Suite 2D,
                                         containing, in the aggregate,
                                         approximately six thousand six hundred
                                         eighty-five (6,685) rentable square
                                         feet, as shown on the attached Exhibits
                                         A and A-3.

Base Rent:                               $32,310.83 per month.

Tenant's Share:                          14.1%

         6.       Lease of 3D Expansion Premises. Landlord hereby demises and
leases to Tenant, and Tenant hereby leases from Landlord, commencing on the 3D
Expansion Premises Effective Date and continuing thereafter until the 3C
Expansion Premises Effective Date (such period being referred to herein as the
"3D Expansion Premises Period") and upon the terms and conditions set forth in
the Lease, the 3D Expansion Premises, as shown on Exhibit A-l attached hereto.
Tenant's right to use and occupancy of the 3D Expansion Premises shall expire on
the 3C Expansion Premises Effective Date or, if the Lease should be terminated
for any reason prior to the 3C Expansion Premises Effective Date, upon the date
of such earlier termination.

         7.       Lease of 3C Expansion Premises. Landlord hereby demises and
leases to Tenant, and Tenant hereby leases from Landlord, commencing on the 3C
Expansion Premises Effective Date and continuing thereafter until the expiration
or earlier termination of the Term of the Lease (as defined in the Original
Lease), unless earlier terminated with respect to the 3C Expansion Premises as
provided in Paragraph 9 herein (such period being referred to herein as the "3C
Expansion Premises Period") and upon the terms and conditions set forth in the
Lease, the 3C Expansion Premises, as shown on Exhibit A-2 attached hereto.
Tenant's right to use and occupancy of the 3C Expansion Premises shall expire on
October 31,2003, the expiration date of the initial twelve (12) month Term of
the Lease or, if the Lease should be terminated for any reason prior to such
anticipated expiration date, upon the date of such earlier termination. The
Tenant shall not have any right to use or occupy the 3C Expansion Premises
beyond the date of such expiration or earlier termination of the initial Term of
the Lease or the earlier termination of the Lease with respect to the 3C
Premises as described in Paragraph 9 (the date of such

                                       3
<PAGE>

expiration or earlier termination being referred to herein as the "3C Expansion
Premises Return Date"), notwithstanding any exercise by Tenant of its Extension
Rights under Paragraph 38 of the Original Lease. The parties agree that, within
three (3) days after the 3C Expansion Premises Return Date, Tenant shall execute
and deliver to Landlord a certificate, in the form attached hereto as Exhibit C,
acknowledging the definitions of Premises, Base Rent and Tenant's Share as set
forth in Paragraph 5 of this Amendment.

         8.       Lease of 2D Expansion Premises. Landlord hereby demises and
leases to Tenant, and Tenant hereby leases from Landlord, commencing on the 2D
Expansion Premises Effective Date and continuing thereafter until the expiration
or earlier termination of the Term of the Lease (as defined in the Original
Lease), including any Extension Term (such period being referred to herein as
the "2D Expansion Premises Period"), and upon the terms and conditions set forth
in the Lease, the 2D Expansion Premises, as shown on Exhibit A-3 attached
hereto. The 2D Expansion Premises shall be considered part of the Premises for
all purposes of the Lease, including, without limitation, the Extension Rights
in Section 38 of the Original Lease. The parties agree that, within three (3)
days after the 3C Expansion Premises Effective Date, Tenant shall execute and
deliver to Landlord a certificate, in the form attached hereto as Exhibit B,
acknowledging the definitions of Premises, Base Rent and Tenant's Share as set
forth in Paragraph 4 of this Amendment.

         9.       Landlord's Right to Terminate. Tenant acknowledges that the
use of the 3C Expansion Premises is subject to the prior right of Infinity
Pharmaceuticals, Inc. ("Infinity") with respect to the 3C Expansion Premises.
Tenant acknowledges and agrees that Infinity has reserved the right to recapture
the 3C Expansion Premises upon thirty (30) days' prior written notice to
Landlord. Tenant further acknowledges and agrees that, if Landlord shall receive
such a recapture notice from Infinity, Landlord shall have the right to
terminate the Lease with respect to the 3C Expansion Premises upon twenty-one
(21) days prior written notice to Tenant, and Tenant shall vacate the 3C
Expansion Premises, leaving it in the same condition as in Paragraph 12 hereof,
prior to the expiration of such twenty-one (21) day period. Tenant shall be
responsible for any and all damages suffered by Landlord as a result of Tenant's
failure to vacate the 3C Expansion Premises as aforesaid, including
consequential damages. The date, if any, on which Tenant vacates the 3C
Expansion Premises in accordance with this Paragraph 9 shall be deemed to be the
3C Expansion Premises Return Date for purposes of this Amendment.

         10.      Premises: Rentable Square Feet; Tenant's Share.

                  a.       Commencing on the 3D Expansion Premises Effective
Date and until the 2D Expansion Premises Effective Date, for all purposes of the
Lease, including, without limitation, the calculation of Base Rent and Tenant's
Share of Operating Expenses (as defined in the Original Lease), all references
in the Lease to the "Premises" shall be deemed to mean the definition of
Premises set forth in Paragraph 2 hereof, all references in the Lease to the
"Rentable Area of the Premises" shall be deemed to mean the Rentable Area of the
Premises set forth in Paragraph 2 hereof, and all references in the Lease to
"Tenant's Share" shall mean the Tenant's Share as set forth in Paragraph 2
hereof. Upon the commencement of the 2D Expansion Premises Period, as described
in Paragraph 8 hereof, this Paragraph lOa shall automatically be of no further
force and effect.

                                       4
<PAGE>

                  b.       Commencing on the 2D Expansion Premises Effective
Date and until the 3C Expansion Premises Effective Date, for all purposes of the
Lease, including, without limitation, the calculation of Base Rent and Tenant's
Share of Operating Expenses (as defined in the Original Lease), all references
in the Lease to the "Premises" shall be deemed to mean the definition of
Premises set forth in Paragraph 3 hereof, all references in the Lease to the
"Rentable Area of the Premises" shall be deemed to mean the Rentable Area of the
Premises set forth in Paragraph 3 hereof, and all references in the Lease to
"Tenant's Share" shall mean the Tenant's Share as set forth in Paragraph 3
hereof. Upon the commencement of the 3C Expansion Premises Period as described
in Paragraph 7 hereof, this Paragraph lOb shall automatically be of no further
force and effect.

                  c.       Commencing on the 3C Expansion Premises Effective
Date and ending on the 3C Expansion Premises Return Date, for all purposes of
the Lease, including, without limitation, the calculation of Base Rent and
Tenant's Share of Operating Expenses (as defined in the Original Lease), all
references in the Lease to the "Premises" shall be deemed to mean the definition
of Premises set forth in Paragraph 4 hereof, all references in the Lease to the
"Rentable Area of the Premises" shall be deemed to mean the Rentable Area of the
Premises set forth in Paragraph 4 hereof, and all references in the Lease to
"Tenant's Share" shall mean the Tenant's Share as set forth in Paragraph 4
hereof. From and after the 3C Expansion Premises Return Date, this Paragraph 10c
shall automatically be of no further force and effect.

                  d.       Commencing on the 3C Expansion Premises Return Date,
for all purposes of the Lease, including without limitation, the calculation of
Base Rent and Tenant's Share of Operating Expenses (as defined in the Original
Lease), all references in the Lease to the "Premises" shall be deemed to mean
the definition of Premises set forth in Paragraph 5 hereof, all references in
the Lease to the "Rentable Area of the Premises" shall be deemed to mean the
Rentable Area of the Premises set forth in Paragraph 5 hereof, and all
references in the Lease to "Tenant's Share" shall mean the Tenant's Share as set
forth in Paragraph 5 hereof.

         11.      Base Rent.

                  a.       Commencing on the 3D Expansion Premises Effective
Date and ending on the 2D Expansion Premises Effective Date, all references in
the Lease to "Base Rent" shall be deemed to mean the Base Rent set forth in
Paragraph 2 of this Amendment. All Base Rent shall be paid by Tenant at the
times and in the manner set forth in the Original Lease.

                  b.       Commencing on the 2D Expansion Premises Effective
Date and ending on the 3C Expansion Premises Effective Date, all references in
the Lease to "Base Rent" shall be deemed to mean the Base Rent set forth in
Paragraph 3 of this Amendment. All Base Rent shall be paid by Tenant at the
times and in the manner set forth in the Original Lease.

                  c.       Commencing on the 3C Expansion Premises Effective
Date and ending on the 3C Expansion Premises Return Date, all references in the
Lease to "Base Rent" shall be deemed to mean the Base Rent set forth in
Paragraph 4 of this Amendment. All Base Rent shall be paid by Tenant at the
times and in the manner set forth in the Original Lease.

                                       5
<PAGE>

                  d.       Commencing on the 3C Expansion Premises Return Date
and continuing thereafter during the Term of the Lease, including any Extension
Term, all references in the Lease to "Base Rent" shall be deemed to mean the
Base Rent set forth in Paragraph 5 of this Amendment. All Base Rent shall be
paid by Tenant at the times and in the manner set forth in the Original Lease.

         12.      Science Hotel (sm) Service Fees. The parties agree that the
amount of the Science Hotel (sm) Service Fees set forth in the Science Hotel
(sm) Services Agreement (as those terms are defined in the Original Lease) shall
not be affected by the addition of the 3D Expansion Premises or the 3C Expansion
Premises. Notwithstanding the foregoing, commencing on the 2D Expansion Premises
Effective Date and expiring on the expiration or earlier termination of the
initial one-year Term of the Lease, Tenant shall pay, in advance, in addition to
the Science Hotel (sm) Services Fee paid by Tenant pursuant to the Science Hotel
(sm) Services Agreement, monthly installments of the Additional Science Hotel
(sm) Services Fee on or before the first day of each calendar month during the
Term hereof to Landlord, or its successors or assigns. If Tenant extends the
Lease Term pursuant to Section 38 of the Lease, Tenant shall not be required to
continue to pay the Additional Science Hotel (sm) Services Fee as set forth in
this Amendment; provided, however, that Tenant shall continue to pay the Science
Hotel (sm) Services Fee payable pursuant to the Science Hotel (sm) Services
Agreement during any Extension Term (as defined in the Original Lease), as
provided in the Original Lease.

         13.      Improvements and Repairs to the Expansion Premises.

                  a.       The parties agree that Landlord shall be under no
obligation to perform any repairs or construct any improvements to the 3D
Expansion Premises or the 3C Expansion Premises, and Tenant shall take the 3D
Expansion Premises and the 3C Expansion Premises "as is", "where is". Tenant
shall have the right, at its sole cost and expense, to install telephone and
data wiring in the 3D Expansion Premises, subject to Landlord's prior review and
approval of all plans and specifications related to such work. No portion of the
TI Allowance (as defined in the Original Lease) shall be applied to the cost of
installing such telephone and data wiring. Tenant shall surrender the 3D
Expansion Premises and the 3C Expansion Premises in the same condition as
received and in accordance with the provisions of Section 26 of the Original
Lease.

                  b.       Landlord shall make available to Tenant an allowance
(the "2D Expansion Premises TI Allowance"), which 2D Expansion Premises TI
Allowance shall be equal to one-half (1/2) of the cost of the 2D Expansion
Premises TI Costs (as hereinafter defined), in the maximum amount of $21,000.
The 2D Expansion Premises TI Allowance shall be used solely in payment of costs
("2D Expansion Premises TI Costs") incurred in connection with the installation
of two additional fume hoods and related plumbing, electrical and mechanical
modifications in the 2D Expansion Premises in accordance with designs and plans
submitted by Tenant and approved by Landlord (the "2D Expansion Premises Tenant
Improvements"). The 2D Expansion Premises Tenant Improvements shall be designed
and constructed by architects and contractors selected by Landlord and approved
by Tenant. All disbursements of the 2D Expansion Premises TI Allowance shall be
in accordance with the Original Lease. Notwithstanding anything to the contrary
contained herein, the 2D Expansion Premises TI

                                       6
<PAGE>

Allowance shall not be used to purchase any furniture, personal property or
other materials or equipment, including, but not limited to, biological safety
cabinets and other scientific equipment not incorporated into the improvements.
Tenant shall surrender the 2D Expansion Premises at the end of the Lease Term in
the same condition as received and in accordance with the provisions of Section
26 of the Original Lease.

         14.      Broker. Each party represents and warrants to the other that
it has not dealt with any broker or person in connection with this Amendment.
Each party hereby indemnifies and agrees to defend and hold the other party
harmless from and against any and all claims for commission, fee or other
compensation by any person who shall claim to have dealt with such party in
connection with this Amendment and for any and all costs incurred in connection
with such claims, including, without limitation, reasonable attorneys' fees and
disbursements.

         15.      Exhibits. All references in the Lease to Exhibit A shall be
deemed to refer to Exhibit A-1 attached hereto during the 3D Expansion Premises
Period. All references in the Lease to Exhibit A shall be deemed to refer to
Exhibits A-l and A-3 during the 2D Expansion Premises Period. All references in
the Lease to Exhibit A shall be deemed to refer to Exhibits A-2 and A-3 during
the 3C Expansion Premises Period. All references in the Lease to Exhibit A shall
be deemed to refer to Exhibit A-3 from and after the 3C Expansion Premises
Return Date.

         16.      Miscellaneous. All other terms and conditions of the Original
Lease, as amended hereby, remain in full force and effect, as so amended. All
capitalized terms used herein and not otherwise defined shall have the meanings
ascribed to them in the Lease. The recitals set forth above are specifically
incorporated into the body of this Amendment and shall be binding upon the
parties hereto. Except as expressly amended hereby, all of the terms and
conditions of the Lease remain unchanged and in full force and effect. This
Amendment is deemed incorporated into the Lease by reference as of the date
hereof; provided, however, in the event of any conflict or inconsistency between
the terms and provisions of the Lease and the terms of provisions of this
Amendment, the terms and provisions of this Amendment shall govern and control.
This Amendment may be executed in any number of counterparts with the same
effect as if all of the signatures on such counterparts appeared on one
document, and each such counterpart shall be deemed to be an original.

                                       7
<PAGE>

         IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
executed as of the day and year first written.

LANDLORD:

ARE-770/784/790 MEMORIAL DRIVE, LLC,
     a Delaware limited liability company

By: ALEXANDRIA REAL ESTATE EQUITIES, L.P.,
     managing member

By: ARE-QRS CORP., general partner

By: /s/ Joel S. Marcus
  ---------------------------------------
Name: Joel S. Marcus
Title: CEO

TENANT:

ALNYLAM PHARMACEUTICALS, INC. a Delaware
corporation

By: /s/ John G. Conley
   --------------------------------------
Name: John G. Conley
Title: VP-Strategy & Finance

                                       8
<PAGE>
                            THIRD AMENDMENT TO LEASE

     THIS THIRD AMENDMENT TO LEASE (this "Amendment") is dated as of the 30th
day of April, 2003, by and between ARE-770/784/790 MEMORIAL DRIVE LLC, a
Delaware limited liability company ("Landlord") and ALNYLAM PHARMACEUTICALS,
INC., a Delaware corporation ("Tenant").

     A.   Pursuant to that certain Lease between Landlord and Tenant, dated as
of August 5, 2002, as amended by that certain Amendment to Lease dated as of
September 9, 2002, and as further amended by that certain Second Amendment to
Lease (the "Second Amendment") dated as of March 25, 2003 (as so amended, the
"Original Lease") (together, the Original Lease and this Amendment are referred
to herein as the "Lease"), Landlord agreed to lease to Tenant, and Tenant leased
from Landlord, certain premises located in the building known as 790 Memorial
Drive, Cambridge, Massachusetts (the "Building"), as further identified in the
Original Lease (the "Premises"), subject to the terms and conditions more
particularly set forth in the Original Lease.

     B.   Pursuant to the Second Amendment, Landlord and Tenant previously
agreed to expand the rentable area of the Premises by the addition of, inter
alia, a portion of that area of the Building known as Suite 3D, as defined and
more particularly described in the Second Amendment as the 3D Expansion
Premises.

     C.   Landlord and Tenant now desire to expand the rentable area of the
Premises by the addition of the remainder of Suite 3D to the Premises and to
adjust the amount of the Base Rent due under the Lease as more particularly
described herein, and to cause other changes to the Lease in accordance with the
terms and conditions set forth in this Amendment.

     NOW, THEREFORE, for good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, and intending to be legally bound
hereby, the parties hereto agree as follows:

     1.   From and after the date hereof, the Original Lease is hereby amended
to add the following new definitions to the Basic Lease Provisions:

Additional 3D Expansion Premises:       One Thousand Six Hundred Thirty Three
                                        (1,633) rentable square feet on the
                                        third (3rd) floor of the 790 Premises,
                                        being the remainder of that area of the
                                        Building designated as Suite 3D, as
                                        shown on Exhibit A-4 attached hereto and
                                        incorporated herein by this reference.

Additional 3D Expansion Premises
Effective Date:                         May 1, 2003

     2.   Commencing on the 3C Expansion Premises Effective Date (as defined in
the Second Amendment), subject to the terms of Paragraphs 5 and 6 hereof, the
definitions of "Premises", "Base Rent" and "Tenant's Share" set forth in the
Basic Lease Provisions of the

<PAGE>
Original Lease are hereby deleted and the following new definitions are added
to the Lease:

Premises:         Those portions of the Building, designated as Suite 2C,
                  Suite 2D, a portion of Suite 3C and a portion of that area
                  of the Building designated as Suite 3D, containing, in the
                  aggregate, approximately Ten Thousand Two Hundred Forty Seven
                  (10,247) rentable square feet, as shown on the attached
                  Exhibits A, A-1, A-2 and A-3.

Base Rent:        $49,527.17 per month

Tenant's Share:   21.6%

     3.  Commencing on the Additional 3D Expansion Premises Effective Date and
ending on the expiration or earlier termination of the Term of the Lease (as
defined in the Original Lease) (the "Expiration Date"), the definitions of
"Premises", "Base Rent", and "Tenant's Share" set forth in the Basic Lease
Provisions of the Original Lease are hereby deleted and the following new
definitions are added to the Lease:

Premises:         Those portions of the Building, designated as Suite 2C,
                  Suite 2D, a portion of Suite 3C and Suite 3D, containing, in
                  the aggregate, approximately Eleven Thousand Eight Hundred
                  Eighty (11,880) rentable square feet, as shown on the
                  attached Exhibits A, A-1, A-2, A-3 and A-4.

Base Rent:        $57,420.00 per month

Tenant's Share:   25.0%

     4.  Lease of Expansion Premises.

         (a)  Notwithstanding the provisions of the Second Amendment to the
contrary, Landlord and Tenant hereby agree that Tenant will occupy the 3D
Expansion Premises (as defined in the Second Amendment), in accordance with the
terms and conditions of the Second Amendment, until the expiration or earlier
termination of the Term of the Lease (as defined in the Original Lease).

         (b)  Landlord hereby demises and leases to Tenant, and Tenant hereby
leases from Landlord, commencing on the Additional 3D Expansion Premises
Effective Date and continuing thereafter until the Expiration Date and upon the
terms and conditions set forth in the Lease, the Additional 3D Expansion
Premises, as shown on Exhibit A-4 attached hereto.

                                       2

<PAGE>
     5.   Premises; Rentable Square Feet; Tenant's Share.

          (a)  Commencing on the 3C Expansion Premises Effective Date and
expiring on the Additional 3D Expansion Premises Effective Date, for all
purposes of the Lease, including, without limitation, the calculation of Base
Rent and Tenant's Share of Operating Expenses (as defined in the Original
Lease), all references in the Lease to the "Premises" shall be deemed to mean
the definition of Premises set forth in Paragraph 2 hereof, all references in
the Lease to the "Rentable Area of the Premises" shall be deemed to mean the
Rentable Area of the Premises set forth in Paragraph 2 hereof, and all
references in the Lease to "Tenant's Share" shall mean the Tenant's Share as
set forth in Paragraph 2 hereof.

          (b)  Commencing on the Additional 3D Expansion Premises Effective Date
and until the Expiration Date, for all purposes of the Lease, including, without
limitation, the calculation of Base Rent and Tenant's Share of Operating
Expenses (as defined in the Original Lease), all references in the Lease to the
"Premises" shall be deemed to mean the definition of Premises set forth in
Paragraph 3 hereof, all references in the Lease to the "Rentable Area of the
Premises" shall be deemed to mean the Rentable Area of the Premises set forth in
Paragraph 3 hereof, and all references in the Lease to "Tenant's Share" shall
mean the Tenant's Share as set forth in Paragraph 3 hereof.

     6.   Base Rent.

          (a)  Commencing on the 3C Expansion Premises Effective Date and
expiring on the Additional 3D Expansion Premises Effective Date, all references
in the Lease to "Base Rent" shall be deemed to mean the Base Rent set forth in
Paragraph 2 of this Amendment. All Base Rent shall be paid by Tenant at the
times and in the manner set forth in the Original Lease.

          (b)  Commencing on the Additional 3D Expansion Premises Effective
Date and ending on the Expiration Date, all references in the Lease to "Base
Rent" shall be deemed to mean the Base Rent set forth in Paragraph 3 of this
Amendment. All Base Rent shall be paid by Tenant at the times and in the manner
set forth in the Original Lease.

     7.   Science Hotel(sm) Service Fees. The parties agree that the amount of
the Science Hotel(sm) Service Fees set forth in the Science Hotel(sm) Services
Agreement (as those terms are defined in the Original Lease) shall not be
affected by the addition of the Additional 3D Expansion Premises.

     8.   Improvements and Repairs to the Expansion Premises. The parties agree
that Landlord shall be under no obligation to perform any repairs or construct
any improvements to the Additional 3D Expansion Premises, and Tenant shall take
the Additional 3D Expansion Premises "as is", "where is". Tenant shall surrender
the Additional 3D Expansion Premises in the same condition as received and in
accordance with the provisions of Section 26 of the Original Lease.

     9.   Broker. Each party represents and warrants to the other that it has
not dealt with any broker or person in connection with this Amendment. Each
party hereby indemnifies and agrees to defend and hold the other party harmless
from and against any and all claims for commission, fee or other compensation
by any person who shall claim to have dealt with such

                                       3

<PAGE>
party in connection with this Amendment and for any and all costs incurred in
connection with such claims, including, without limitation, reasonable
attorneys' fees and disbursements.

     10.  Exhibits. All references in the Lease to Exhibit A shall be deemed to
refer to Exhibit A-4 attached hereto during the Additional 3D Expansion
Premises Period.

     11.  Miscellaneous. All other terms and conditions of the Original Lease,
as amended hereby, remain in full force and effect, as so amended. All
capitalized terms used herein and not otherwise defined shall have the meanings
ascribed to them in the Lease. The recitals set forth above are specifically
incorporated into the body of this Amendment and shall be binding upon the
parties hereto. Except as expressly amended hereby, all of the terms and
conditions of the Lease remain unchanged and in full force and effect. This
Amendment is deemed incorporated into the Lease by reference as of the date
hereof; provided, however, in the event of any conflict or inconsistency
between the terms and provisions of the Lease and terms of provisions of this
Amendment, the terms and provisions of this Amendment shall govern and control.
This Amendment may be executed in any number of counterparts with the same
effect as if all of the signatures on such counterparts appeared on one
document, and each such counterpart shall be deemed to be an original.

     IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
executed as of the day and year first written.

LANDLORD:

ARE-770/784/790 MEMORIAL DRIVE, LLC,
     a Delaware limited liability company

By: ALEXANDRIA REAL ESTATE EQUITIES, L.P.,
      managing member

By: ARE-QRS CORP., general partner

By: /s/ Peter J. Nelson
   -----------------------------------------
Name: PETER J. NELSON
     ---------------------------------------
Title: SENIOR VICE PRESIDENT &
       CHIEF FINANCIAL OFFICER
      --------------------------------------

TENANT:

ALNYLAM PHARMACEUTICALS, INC. a Delaware
corporation

By: /s/ John G. Conley
   -----------------------------------------
Name: John G. Conley
     ---------------------------------------
Title: CFO
      --------------------------------------

                                       4
<PAGE>
                           FOURTH AMENDMENT TO LEASE

     THIS FOURTH AMENDMENT TO LEASE (this "Amendment") is dated as of the 30th
day of October, 2003, by and between ARE-770/784/790 MEMORIAL DRIVE LLC, a
Delaware limited liability company ("Landlord") and ALNYLAM PHARMACEUTICALS,
INC., a Delaware corporation ("Tenant").

     A.  Pursuant to that certain Lease between Landlord and Tenant, dated as
of August 5, 2002, as amended by that certain Amendment to Lease dated as of
September 9, 2002, as further amended by that certain Second Amendment to Lease
dated as of March 25, 2003 and as further amended by that certain Third
Amendment to Lease (the "Third Amendment") dated as of April 30, 2003 (as so
amended, the "Original Lease") (together, the Original Lease and this Amendment
are referred to herein as the "Lease"), Landlord agreed to lease to Tenant, and
Tenant leased from Landlord, certain premises located in the building known as
790 Memorial Drive, Cambridge, Massachusetts (the "Building"), as further
identified in the Original Lease (the "Premises"), subject to the terms and
conditions more particularly set forth in the Original Lease.

     B.  Pursuant to the Second Amendment, Landlord and Tenant previously
agreed to expand the rentable area of the Premises by the addition of, inter
alia, a portion of that area of the Building known as Suite 3C, as defined and
more particularly described in the Second Amendment as the 3C Expansion
Premises.

     C.  Landlord and Tenant now desire to expand the rentable area of the
Premises by the addition of 1,490 square feet of space to Suite 3C to the
Premises and to adjust the amount of the Base Rent due under the Lease as more
particularly described herein, and to cause other changes to the Lease in
accordance with the terms and conditions set forth in this Amendment.

     NOW, THEREFORE, for good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, and intending to be legally bound
hereby, the parties hereto agree as follows:

     1.  From and after the date hereof, the Original Lease is hereby amended
to add the following new definitions to the Basic Lease Provisions:

Additional 3C Expansion Premises:   One Thousand Four Hundred Ninety (1,490)
                                    rentable square feet on the third (3rd)
                                    floor of the 790 Premises, as shown on
                                    Exhibit A-5 attached hereto and incorporated
                                    herein by this reference.

Additional 3C Expansion Premises
Effective Date:                     October 1, 2003

Additional 3C Expansion Premises
Termination Date:                   April 30, 2004

<PAGE>
     2.   Commencing on the Additional 3C Expansion Premises Effective Date and
ending on the Additional 3C Expansion Premises Termination Date (the "Expiration
Date"), the definitions of "Premises", "Base Rent", and "Tenant's Share" set
forth in the Basic Lease Provisions of the Original Lease are hereby deleted and
the following new definitions are added to the Lease:

Premises:                               Those portions of the Building,
                                        designated as Suite 2C, Suite 2D, Suite
                                        3C and Suite 3D, containing, in the
                                        aggregate, approximately Thirteen
                                        Thousand Three Hundred Seventy (13,370)
                                        rentable square feet, as shown on the
                                        attached Exhibits A, A-1, A-2, A-3, A-4
                                        and A-5.

Base Rent:                              $64,621.67 per month

Tenant's Share:                         28.1%

     3.   Lease of Expansion Premises. Landlord hereby demises and leases to
Tenant, and Tenant hereby leases from Landlord, commencing on the Additional 3C
Expansion Premises Effective Date and continuing thereafter until the Expiration
Date and upon the terms and conditions set forth in the Lease, the Additional 3C
Expansion Premises, as shown on Exhibit A-5 attached hereto.

     4.   Premises; Rentable Square Feet; Tenant's Share. Commencing on the
Additional 3C Expansion Premises Effective Date and until the Expiration Date,
for all purposes of the Lease, including, without limitation, the calculation of
Base Rent and Tenant's Share of Operating Expenses (as defined in the Original
Lease), all references in the Lease to the "Premises" shall be deemed to mean
the definition of Premises set forth in Paragraph 2 hereof, all references in
the Lease to the "Rentable Area of the Premises" shall be deemed to mean the
Rentable Area of the Premises set forth in Paragraph 2 hereof, and all
references in the Lease to "Tenant's Share" shall mean the Tenant's Share as set
forth in Paragraph 2 hereof.

     5.   Base Rent. Commencing on the Additional 3C Expansion Premises
Effective Date and ending on the Expiration Date, all references in the Lease to
"Base Rent" shall be deemed to mean the Base Rent set forth in Paragraph 2 of
this Amendment. All Base Rent shall be paid by Tenant at the times and in the
manner set forth in the Original Lease.

     6.   Science Hotel (sm) Service Fees. The parties agree that the amount of
the Science Hotel (sm) Service Fees set forth in the Science Hotel (sm) Services
Agreement (as those terms are defined in the Original Lease) shall not be
affected by the addition of the Additional 3C Expansion Premises.

     7.   Improvements and Repairs to the Expansion Premises. The parties agree
that Landlord shall be under no obligation to perform any repairs or construct
any improvements to the Additional 3C Expansion Premises, and Tenant shall take
the Additional 3C Expansion Premises "as is", "where is". Tenant shall surrender
the Additional 3C Expansion Premises in

                                       2

<PAGE>
the same condition as received and in accordance with the provisions of Section
26 of the Original Lease.

     8.   Termination Date. Notwithstanding the provisions of the Second
Amendment to the contrary, Landlord and Tenant hereby agree that Tenant will
occupy the 3C Expansion Premises (as defined in the Second Amendment), in
accordance with the terms and conditions of the Second Amendment, until the
Expiration Date. Landlord and Tenant hereby further agree that Landlord's right
to terminate as set forth in Section 9 of the Second Amendment is deleted, and
Tenant shall have the right to occupy the 3C Expansion Premises and the
Additional 3C Expansion Premises until the Expiration Date.

     Notwithstanding anything to the contrary contained herein or in the
Original Lease, the Term of this Lease with respect to the 3C Expansion
Premises, Additional 3C Expansion Premises, 3D Expansion Premises and
Additional 3D Expansion Premises, as those terms are defined in the Second
Amendment, the Third Amendment and this Amendment, shall expire on April 30,
2004. The Term of this Lease with respect to the remaining portions of the
Premises shall expire upon the expiration or earlier termination of the Term of
the Lease (as defined in the Original Lease).

     9.   Broker. Each party represents and warrants to the other that it has
not dealt with any broker or person in connection with this Amendment. Each
party hereby indemnifies and agrees to defend and hold the other party harmless
from and against any and all claims for commission, fee or other compensation by
any person who shall claim to have dealt with such party in connection with this
Amendment and for any and all costs incurred in connection with such claims,
including, without limitation, reasonable attorneys' fees and disbursements.

     10.  Exhibits. All references in the Lease to Exhibit A shall be deemed to
refer to Exhibits A-1, A-2, A-3, A-4 and A-5 attached hereto and to the Lease,
as applicable, during the Additional 3C Expansion Premises Period.

     11.  Miscellaneous. All other terms and conditions of the Original Lease,
as amended hereby, remain in full force and effect, as so amended. All
capitalized terms used herein and not otherwise defined shall have the meanings
ascribed to them in the Lease. The recitals set forth above are specifically
incorporated into the body of this Amendment and shall be binding upon the
parties hereto. Except as expressly amended hereby, all of the terms and
conditions of the Lease remain unchanged and in full force and effect. This
Amendment is deemed incorporated into the Lease by reference as of the date
hereof; provided, however, in the event of any conflict or inconsistency
between the terms and provisions of the Lease and the terms of provisions of
this Amendment, the terms and provisions of this Amendment shall govern and
control. This Amendment may be executed in any number of counterparts with the
same effect as if all of the signatures on such counterparts appeared on one
document, and each such counterpart shall be deemed to be an original.

                                       3

<PAGE>
     IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
executed as of the day and year first written.

LANDLORD:

ARE-770/784/790 MEMORIAL DRIVE, LLC,
     a Delaware limited liability company

By: ALEXANDRIA REAL ESTATE EQUITIES, L.P.,
     managing member

By: ARE-QRS CORP., general partner

By:     /s/ Joel S. Marcus
      ------------------------
Name:     Joel S. Marcus
      ------------------------
Title:         CEO
      ------------------------

TENANT:

ALNYLAM PHARMACEUTICALS, INC. a Delaware corporation

By:     /s/ John G. Conley
      ------------------------
Name:     John G. Conley
      ------------------------
Title:         CFO
      ------------------------

                                       4

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