Document:

<PAGE>
                                                                   EXHIBIT 10.44

                          TRADEMARK SECURITY AGREEMENT

      This TRADEMARK SECURITY AGREEMENT (this "Trademark Security Agreement") is
made this 5th day of April, 2007, among the Grantors listed on the signature
pages hereof (collectively, jointly and severally, "Grantors" and each
individually "Grantor"), and THE BANK OF NEW YORK TRUST COMPANY, N.A., in its
capacity as Collateral Agent for itself, the Holders and the Trustee (together
with its successors and assigns in such capacity, "Collateral Agent").

                              W I T N E S S E T H:

      WHEREAS, pursuant to that certain Indenture dated of November 30, 2004 (as
amended, restated, amended and restated, supplemented or otherwise modified from
time to time, including all exhibits and schedules thereto, the "Indenture")
among Altra Industrial Motion, Inc., a Delaware corporation ("Company"), each of
the Guarantors named therein ("Guarantors"), The Bank of New York Trust Company,
N.A., as Trustee (in such capacity, the "Trustee"), and Collateral Agent,
Company has issued to the Holders its 9% Senior Secured Notes Due 2011, and may
issue from time to time additional notes in connection with the provisions of
the Indenture (as the same may be amended and restated, supplemented or
otherwise modified from time to time, collectively, the "Notes");

      WHEREAS, as a condition precedent to the initial purchase by the Holders
of the Notes, Company and Guarantors (each in their respective capacity as a
Grantor) executed and delivered to Collateral Agent, for the benefit of the
Holders, Trustee and Collateral Agent, that certain Security Agreement dated as
of November 30, 2004 (including all annexes, exhibits or schedules thereto, as
from time to time amended and restated, supplemented or otherwise modified, the
"Security Agreement")

      WHEREAS, as a condition precedent to the purchase by the Holders of
additional Notes in the aggregate principal amount of $105,000,000, the Grantors
shall have executed and delivered to Collateral Agent, for the benefit of the
Holders, Trustee and Collateral Agent, that certain Supplement No. 1 to Security
Agreement dated as of the date hereof (including all annexes, exhibits or
schedules thereto, the "Supplement"); and

      WHEREAS, pursuant to the Security Agreement, as modified by the
Supplement, the Grantors are required to execute and deliver to Collateral
Agent, for the benefit of the Trustee, the Collateral Agent and the Holders,
this Trademark Security Agreement.

      NOW, THEREFORE, in consideration of the premises and mutual covenants
herein contained and for other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, each Grantor hereby agrees as
follows:

      1. DEFINED TERMS. All capitalized terms used but not otherwise defined
herein have the meanings given to them in the Security Agreement and/or the
Indenture.

      2. GRANT OF SECURITY INTEREST IN TRADEMARK COLLATERAL. Each Grantor hereby
grants to Collateral Agent, for the benefit of the Trustee and the Holders, a
continuing first priority security interest (subject to Permitted Liens) in all
of such Grantor's right, title and interest in, to and under the following,
whether presently existing or hereafter created or acquired (collectively, the
"Trademark Collateral"):

            (a) all of its Trademarks and rights in and to Trademark
Intellectual Property Licenses to which it is a party including those referred
to on Schedule I hereto;

            (b) all extensions, modifications and renewals of the foregoing;

<PAGE>

            (c) all goodwill of the business connected with the use of, and
symbolized by, each Trademark; and

            (d) all products and proceeds of the foregoing, including, without
limitation, any claim by such Grantor against third parties for past, present or
future (i) infringement or dilution of any Trademark, or (ii) injury to the
goodwill associated with any Trademark.

      3. SECURITY AGREEMENT. The security interests granted pursuant to this
Trademark Security Agreement are granted in conjunction with the security
interests granted to Collateral Agent, for the benefit of the Trustee, the
Collateral Agent and the Holders, pursuant to the Security Agreement. Each
Grantor hereby acknowledges and affirms that the rights and remedies of
Collateral Agent with respect to the security interest in the Trademark
Collateral made and granted hereby are more fully set forth in the Security
Agreement, the terms and provisions of which are incorporated by reference
herein as if fully set forth herein.

      4. AUTHORIZATION TO SUPPLEMENT. Grantors hereby authorize Collateral Agent
unilaterally to modify this Agreement by amending Schedule I to include any
trademarks, registrations, or applications therefor (including, without
limitation, extensions or renewals) which become part of the Trademark
Collateral under the Security Agreement. Notwithstanding the foregoing, no
failure to so modify this Trademark Security Agreement or amend Schedule I shall
in any way affect, invalidate or detract from Agent's continuing security
interest in all Collateral, whether or not listed on Schedule I.

      5. COUNTERPARTS. This Trademark Security Agreement may be executed in any
number of counterparts, each of which shall be deemed to be an original, but all
such separate counterparts shall together constitute but one and the same
instrument. Any signatures delivered by a party by facsimile transmission or by
e-mail transmission shall be deemed an original signature hereto.

                           [signature pages follow]

                                       2
<PAGE>

      IN WITNESS WHEREOF, each Grantor has caused this Trademark Security
Agreement to be executed and delivered by its duly authorized officer as of the
date first set forth above.

GRANTORS:
                                      TB WOOD'S INCORPORATED,
                                      a Pennsylvania corporation, as a Grantor

                                            By: /s/ William T. Fejes, Jr.
                                                --------------------------------
                                            Name: William T. Fejes, Jr.
                                            Title: President, CEO and Director

                                      PLANT ENGINEERING CONSULTANTS, LLC,
                                      a Tennessee limited liability company, as
                                      a Grantor

                                            By: /s/ William T. Fejes, Jr.
                                                --------------------------------
                                            Name: William T. Fejes, Jr.
                                            Title: President

                                      TB WOOD'S ENTERPRISES, INC.,
                                      a Delaware corporation, as a Grantor

                                            By: /s/ Joseph C. Horvath
                                                --------------------------------
                                            Name: Joseph C. Horvath
                                            Title: President and Treasurer

                                      TB WOOD'S CORPORATION,
                                      a Delaware corporation, as a Grantor

                                            By: /s/ William T. Fejes, Jr.
                                                --------------------------------
                                            Name: William T. Fejes, Jr.
                                            Title: President, CEO and Director

COLLATERAL AGENT:                     THE BANK OF NEW YORK TRUST
                                      COMPANY, N.A.,
                                      as Collateral Agent

                                      By:    /s/ Sandee Parks
                                             -----------------------------------
                                      Name:  Sandee Parks
                                             -----------------------------------
                                      Title: Vice President
                                             -----------------------------------

                SIGNATURE PAGE OF TRADEMARK SECURITY AGREEMENT

<PAGE>

                                   SCHEDULE I
                                       to
                          TRADEMARK SECURITY AGREEMENT

                      TRADEMARK REGISTRATIONS/APPLICATIONS

<TABLE>
<CAPTION>
                                                  APPLICATION/
    GRANTOR                                       REGISTRATION
                     COUNTRY          MARK             NO.        APP/REG DATE
--------------------------------------------------------------------------------
<S>              <C>             <C>             <C>             <C>
TB Wood's        United States   ALL-PRO         75/290,731/     5/12/1997/
Enterprises,                                     2,165,737       6/16/1998
Inc.
--------------------------------------------------------------------------------
TB Wood's        United States   BRAKETRON       73/254,657/     3/19/1980/
Enterprises,                                     1,164,393       8/11/1981
Inc.
--------------------------------------------------------------------------------
TB Wood's        United States   DECK            73/581,633/     2/7/1986/
Enterprises,                                     1,409,209       9/16/1986
Inc.                             (stylized)
--------------------------------------------------------------------------------
TB Wood's        United States   DISC-O-TORQUE   72/285,224/     11/20/1967/
Enterprises,                                     859,264         10/29/1968
Inc.
--------------------------------------------------------------------------------
TB Wood's        United States   DURA-FLEX       73/158,649/     2/13/1978/
Enterprises,                                     1,116,828       4/24/1979
Inc.
--------------------------------------------------------------------------------
TB Wood's        United States   E-FLOW          75/280,015/     4/23/1997/
Enterprises,                                     2,169,361       6/30/1998
Inc.
--------------------------------------------------------------------------------
TB Wood's        United States   E-trAC          73/491,494/     7/24/1984/
Enterprises,                     (Stylized)      1,333,061       4/30/1985
Inc.
--------------------------------------------------------------------------------
TB Wood's        United States   E-TROL+PLUS     75/273,178/     4/11/1997/
Enterprises,                                     2,156,683       5/12/1998
Inc.
--------------------------------------------------------------------------------
</TABLE>

                                       i
<PAGE>

<TABLE>
<CAPTION>
                                                  APPLICATION/
    GRANTOR                                       REGISTRATION
                     COUNTRY          MARK             NO.        APP/REG DATE
--------------------------------------------------------------------------------
<S>              <C>             <C>             <C>             <C>
TB Wood's        United States   FIRST IN        73/526,310/     3/11/1985/
Enterprises,                     COUPLINGS       1,361,466       9/24/1985
Inc.
--------------------------------------------------------------------------------
TB Wood's        United States   FORM-FLEX       75/273,175/     4/11/1997/
Enterprises,                                     2,152,362       4/21/1998
Inc.
--------------------------------------------------------------------------------
TB Wood's        United States   IMD             75/272,935/     4/11/1997/
Enterprises,                                     2,261,432       7/13/1999
Inc.
--------------------------------------------------------------------------------
TB Wood's        United States   NLS             75/273,181/     4/11/1997/
Enterprises,                                     2,152,366       4/21/1998
Inc.
--------------------------------------------------------------------------------
TB Wood's        United States   PDA-TRAC        78/329,999      11/19/2003/
Enterprises,                                     2,986,366       8/16/2005
Inc.
--------------------------------------------------------------------------------
TB Wood's        United States   PETRO-TRAC      78/052,072/     3/8/2001/
Enterprises,                                     2,641,082       10/22/2002
Inc.
--------------------------------------------------------------------------------
TB Wood's        United States   POOLE           75/251,697/     2/28/1997/
Enterprises,                                     2,191,918       9/29/1998
Inc.
--------------------------------------------------------------------------------
TB Wood's        United States   QT POWER CHAIN  76/403,299/     5/2/2002/
Enterprises,                                     2,723,745       6/10/2003
Inc.
--------------------------------------------------------------------------------
TB Wood's        United States   ROTO-CAM        72/285,223/     11/20/1967/
Enterprises,                                     859,263         10/29/1968
Inc.
--------------------------------------------------------------------------------
TB Wood's        United States   ROTO-CONE       72/015,359/     9/10/1956/
Enterprises,                                     676,279         3/31/1959
Inc.
--------------------------------------------------------------------------------
</TABLE>

                                       ii
<PAGE>

<TABLE>
<CAPTION>
                                                  APPLICATION/
    GRANTOR                                       REGISTRATION
                     COUNTRY          MARK             NO.        APP/REG DATE
--------------------------------------------------------------------------------
<S>              <C>             <C>             <C>             <C>
TB Wood's        United States   SPEEDLIGN       78/350,700/     1/12/2004/
Enterprises,                                     2,991,827       9/6/2005
Inc.
--------------------------------------------------------------------------------
TB Wood's        United States   S-TRAC          75/272,936/     4/11/1997/
Enterprises,                                     2,257,668       6/29/1999
Inc.
--------------------------------------------------------------------------------
TB Wood's        United States   SUPERSTART      74/104,389/     10/9/1990/
Enterprises,                                     1,686,040       5/12/1992
Inc.
--------------------------------------------------------------------------------
TB Wood's        United States   SURE GRIP       71/640,418/     1/6/1953/
Enterprises,                     (stylized)      645,415         5/14/1957
Inc.
--------------------------------------------------------------------------------
TB Wood's        United States   SURE-FLEX       72/043,720/     1/9/1958/
Enterprises,                                     668,649         10/21/1958
Inc.                             (stylized)
--------------------------------------------------------------------------------
TB Wood's        United States   SURE-GRIP       71/575,508/     3/15/1949/
Enterprises,                                     646,423         6/4/1957
Inc.
--------------------------------------------------------------------------------
TB Wood's        United States   SURE-GRIP       73/136,699/     8/8/1977/
Enterprises,                                     1,109,150       12/19/1978
Inc.
--------------------------------------------------------------------------------
TB Wood's        United States   TRUETUBE        75/273,177/     4/11/1997/
Enterprises,                                     2,152,364       4/21/1998
Inc.
--------------------------------------------------------------------------------
TB Wood's        United States   ULTRACON        72/300,318/     6/13/1968/
Enterprises,                                     862,655         12/31/1968
Inc.
--------------------------------------------------------------------------------
TB Wood's        United States   ULTRACON II     75/273,179/     4/11/1997/
Enterprises,                                     2,150,835       4/14/1998
Inc.
--------------------------------------------------------------------------------
</TABLE>

                                       iii
<PAGE>

<TABLE>
<CAPTION>
                                                  APPLICATION/
    GRANTOR                                       REGISTRATION
                     COUNTRY          MARK             NO.        APP/REG DATE
--------------------------------------------------------------------------------
<S>              <C>             <C>             <C>             <C>
TB Wood's        United States   ULTRA-HELIX     75/559,570/     9/25/1998/
Enterprises,                                     2,351,349       5/23/2000
Inc.
--------------------------------------------------------------------------------
TB Wood's        United States   ULTRA-V         73/001,734/     10/9/1973/
Enterprises,                                     1,001,969       1/21/1975
Inc.
--------------------------------------------------------------------------------
TB Wood's        United States   ULTRA-V         73/003,203/     10/10/1973/
Enterprises,                                     1,001,970       1/21/1975
Inc.
--------------------------------------------------------------------------------
TB Wood's        United States   U-TROL          73/104,511/     10/26/1976/
Enterprises,                                     1,070,167       7/26/1977
Inc.
--------------------------------------------------------------------------------
TB Wood's        United States   VAR-A-CONE      75/273,180/     4/11/1997/
Enterprises,                                     2,152,365       4/21/1998
Inc.
--------------------------------------------------------------------------------
TB Wood's        United States   W TB WOOD'S     75/107,136/     5/20/1996/
Enterprises,                     (and design)    2,059,245       5/6/1997
Inc.
--------------------------------------------------------------------------------
TB Wood's        United States   WIN-TRAC        78/306,778/     9/29/2003/
Enterprises,                                     2,961,309       6/7/2005
Inc.
--------------------------------------------------------------------------------
TB Wood's        United States   WOOD'S@WORK     76/402,992/     5/2/2002/
Enterprises,                                     2,801,090       12/30/2003
Inc.
--------------------------------------------------------------------------------
</TABLE>

                                       iv<PAGE>
                                                                   Exhibit 10.44

                                167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 1

                                 LEASE AGREEMENT

     THIS LEASE AGREEMENT is made as of this 31ST day of October, 2006, between
ARE-MA REGION NO. 23, LLC, a Delaware limited liability company ("Landlord"),
and IDERA PHARMACEUTICALS, INC., a Delaware corporation ("Tenant").

                             BASIC LEASE PROVISIONS

ADDRESS:     167 Sidney Street, Cambridge, Massachusetts

PREMISES:    That certain approximately 26,589 rentable square foot building
             (the "BUILDING"), along with the real property on which the
             Building is located and all improvements thereon and appurtenances
             thereto, located at 167 Sidney Street, Cambridge, Massachusetts, as
             shown on EXHIBIT A.

PROJECT:     Collectively, the Premises and the adjacent parking lot, owned by
             Landlord and located at 170 Sidney Street, Cambridge, Massachusetts
             (the "PARKING LOT")

BASE RENT:   $96,163.55, per month   RENTABLE AREA OF PREMISES: 26,589 sq. ft.

SECURITY DEPOSIT:  $619,551.30       TARGET COMMENCEMENT DATE:  May 15, 2007

RENT COMMENCEMENT DATE: Commencement Date

RENT ADJUSTMENT PERCENTAGE: 3.5%

BASE TERM: Beginning on the Commencement Date and ending eighty-four (84) months
from the first day of the first full month of the Term (as defined in Section 1)
hereof.

PERMITTED USE: research and development laboratory, related office and other
related uses in compliance with the provisions of Section 7 hereof.

ADDRESS FOR RENT PAYMENT:              LANDLORD'S NOTICE ADDRESS:
385 E. Colorado Boulevard, Suite 299   385 E. Colorado Boulevard, Suite 299
Pasadena, CA 91101                     Pasadena, CA 91101
Attention: Accounts Receivable         Attention: Corporate Secretary

TENANT'S NOTICE ADDRESS:               GUARANTOR OF LEASE: None
PRIOR TO COMMENCEMENT DATE:
                           ----------
345 Vassar Street
Cambridge, MA 02139
Attention: Robert Andersen

Following Commencement Date:
                            ----------
167 Sidney Street
Cambridge, MA  02139
Attention:
           ----------

                  (C) All rights reserved - Alexandria Real Estate Equities 2001
                                        CONFIDENTIAL - DO NOT COPY OR DISTRIBUTE

BOS111 12048473.9

<PAGE>

                                167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 2

The following Exhibits and Addenda are attached hereto and incorporated herein
by this reference:

[X] EXHIBIT A - PREMISES DESCRIPTION    [X] EXHIBIT B - DESCRIPTION OF PROJECT
[X] EXHIBIT C - WORK LETTER             [X] EXHIBIT D - COMMENCEMENT DATE
[X] EXHIBIT E - RULES AND REGULATIONS   [X] EXHIBIT F - TENANT'S PERSONAL
[X] EXHIBIT G - ENVIRONMENTAL REPORTS                   PROPERTY

     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.

     2. DELIVERY; ACCEPTANCE OF PREMISES; COMMENCEMENT DATE. Landlord shall use
reasonable efforts to deliver the Premises to Tenant on or before the Target
Commencement Date, with Landlord's Work, if any, Substantially Completed
("DELIVERY" or "DELIVER"). If, notwithstanding such efforts, Landlord fails to
timely Deliver the Premises, Landlord shall not be liable to Tenant for any loss
or damage resulting therefrom, and this Lease shall not be void or voidable
except as provided herein. If Landlord does not Deliver the Premises within 60
days of the Target Commencement Date for any reason other than Force Majeure
Delays and Tenant Delays, this Lease may be terminated by Tenant by written
notice to Landlord, and if so terminated by Tenant: (a) the Security Deposit, or
any balance thereof (i.e., after deducting therefrom any amounts to which
Landlord is entitled under the provisions of this Lease), shall be returned to
Tenant, and (b) neither Landlord nor Tenant shall have any further rights,
duties or obligations under this Lease, except with respect to provisions which
expressly survive termination of this Lease. As used herein, the terms
"LANDLORD'S WORK," "TENANTS' WORK," "FORCE MAJEURE DELAYS," "TENANT DELAYS" and
"SUBSTANTIALLY COMPLETED" shall have the meanings set forth for such terms in
the Work Letter attached hereto as Exhibit C (the "WORK LETTER"). If Tenant does
not elect to void this Lease within 5 business days of the lapse of such 60 day
period (or, if such 60 day period is extended by mutual written agreement of the
parties, within 5 business days after the expiration of such extended period),
such right to void this Lease shall be waived and this Lease shall remain in
full force and effect.

     The "COMMENCEMENT DATE" shall be the earliest of: (i) the date Landlord
Delivers the Premises to Tenant; (ii) the date Landlord could have Delivered the
Premises but for Tenant Delays; and (iii) the date Tenant conducts any business
in the Premises or any part thereof. Upon request of either party, the other
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 D;
provided, however, either party's failure to execute and deliver such
acknowledgment shall not affect the other's rights hereunder. The "TERM" of this
Lease shall be the Base Term, as defined above in the Basic Lease Provisions and
any Extension Terms which Tenant may elect pursuant to Section 39 hereof.

     Except as set forth in the Work Letter and in this Lease, if applicable:
(i) Tenant shall accept the Premises in their condition as of the Commencement
Date, subject to all applicable Legal Requirements (as defined in Section 7
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 possession was taken. Any occupancy of the Premises by
Tenant before the Commencement Date shall be subject to all of the terms and
conditions of this Lease, including the obligation to pay Rent.

     Except as specifically set forth in Sections 11 and 27 hereof, 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

<PAGE>

                                167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 3

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. Landlord in
executing this Lease does so in reliance upon Tenant's representations,
warranties, acknowledgments and agreements contained herein.

     3. RENT.

          (a) BASE RENT. 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. Tenant shall pay to Landlord in advance, without demand, abatement,
deduction or set-off (except as otherwise expressly provided for herein),
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, or to such other
person or at such other place as Landlord may from time to time designate in
writing. Payments of Base Rent for any fractional calendar month shall be
prorated. The obligation of Tenant to pay Base Rent and other sums to Landlord
and the obligations of Landlord under this Lease are independent obligations,
such that Tenant shall have no right at any time to abate, reduce, or set-off
any Base Rent or Additional Rent (as defined in Section 3(b)) due hereunder
except for any abatement as may be expressly provided in this Lease.

          (b) ADDITIONAL RENT. In addition to Base Rent, Tenant agrees to pay to
Landlord as additional rent ("ADDITIONAL RENT") 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.

     4. BASE RENT ADJUSTMENTS. Base Rent shall be increased on each annual
anniversary of the first day of the first full month during the Term of this
Lease (each an "ADJUSTMENT DATE") by multiplying the Base Rent payable
immediately before such Adjustment Date by the Rent Adjustment Percentage and
adding the resulting amount to the Base Rent payable immediately before such
Adjustment Date. Base Rent, as so adjusted, shall thereafter be due as provided
herein. Base Rent adjustments for any fractional calendar month shall be
prorated.

     5. OPERATING EXPENSES. It is the express understanding and agreement of
Landlord and Tenant that the Rent due and payable hereunder shall be absolutely
net to Landlord, so that this Lease shall yield to Landlord the Rent specified
above during the Term, and that, except as otherwise expressly set forth herein,
all costs, expenses and obligations of every kind and nature whatsoever relating
to the Project shall be paid by Tenant (including, but not limited to, Taxes,
Utilities, insurance premiums, and the replacement of capital items) (any of the
foregoing being referred to herein as an "OPERATING EXPENSE"), without cost or
obligation of any type to Landlord whatsoever. Landlord and Tenant shall
cooperate in order to have all invoices and statements of charges delivered
directly to Tenant for payment by the providers of any Utilities (as hereinafter
defined) or services. If and to the extent Landlord shall receive any invoice or
other statement for charges for which Tenant is responsible hereunder, Landlord
shall deliver such invoice to Tenant promptly so as to permit Tenant to pay such
invoice prior to its due date. If, for any reason, any such amount must be paid
by Landlord directly rather than by Tenant, Landlord shall pay such amount,
subject to reimbursement by Tenant, and Tenant shall reimburse Landlord for such
amount within ten (10) days after Tenant's receipt of written notice of such
charge, which notice shall include copies of the original invoice for Tenant's
information.

     6. SECURITY DEPOSIT. Tenant shall deposit with Landlord, upon delivery of
an executed copy of this Lease to Landlord, a security deposit (the "SECURITY
DEPOSIT") for the performance of all of Tenant's obligations hereunder in the
amount set forth in the Basic Lease Provisions, which Security Deposit shall be
in the form of an unconditional and irrevocable letter of credit (the "LETTER OF
CREDIT"): (i) in form and substance reasonably satisfactory to Landlord, (ii)
naming Landlord as beneficiary, (iii) expressly allowing Landlord to draw upon
it at any time from time to time by delivering to the issuer notice that
Landlord is entitled to draw thereunder, (iv) issued by an FDIC-insured
financial institution reasonably

<PAGE>

                                167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 4

satisfactory to Landlord, and (v) redeemable by presentation of a sight draft in
the Commonwealth of Massachusetts. If Tenant does not provide Landlord with a
substitute Letter of Credit complying with all of the requirements hereof at
least 10 days before the stated expiration date of any then current Letter of
Credit, Landlord shall have the right to draw the full amount of the current
Letter of Credit and hold the funds drawn in cash without obligation for
interest thereon as the Security Deposit. The Security Deposit shall be held by
Landlord as security for the performance of Tenant's obligations under this
Lease. The Security Deposit is not an advance rental deposit or a measure of
Landlord's damages in case of Tenant's default. Upon each occurrence of a
Default (as defined in Section 20), Landlord may use all or any part of the
Security Deposit to pay delinquent payments due under this Lease, and to satisfy
any other obligations or liabilities of Tenant arising hereunder as a
consequence of such Default, without prejudice to any other remedy provided
herein or provided by law. Upon any such use of all or any portion of the
Security Deposit, Tenant shall pay Landlord on demand the amount that will
restore the Security Deposit to the amount set forth in the Basic Lease
Provisions. 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. Upon bankruptcy or other
debtor-creditor proceedings against Tenant, the Security Deposit shall be deemed
to be applied first to the payment of Rent and other charges due Landlord for
periods prior to the filing of such proceedings. Upon any such use of all or any
portion of the Security Deposit, Tenant shall, within 5 days after demand from
Landlord, restore the Security Deposit to its original amount. 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), shall be
returned to Tenant (or, at Landlord's option, to the last assignee of Tenant's
interest hereunder) within 45 days after the expiration or earlier termination
of this Lease and the surrender of the Premises to Landlord in accordance with
Section 28 hereof. Landlord shall provide an itemized list of the amounts, if
any, deducted from the Security Deposit at the time of the return of the same to
Tenant.

     If Landlord transfers its interest in the Project or this Lease, Landlord
shall either (a) transfer any Security Deposit then held by Landlord to a person
or entity assuming Landlord's obligations under this Section 6, or (b) return to
Tenant any Security Deposit then held by Landlord and remaining after the
deductions permitted herein. Upon such transfer to such transferee or the return
of the Security Deposit to Tenant, Landlord shall have no further obligation
with respect to the Security Deposit, and Tenant's right to the return of the
Security Deposit shall apply solely against Landlord's transferee. The Security
Deposit is not an advance rental deposit or a measure of Landlord's damages in
case of Tenant's default. Landlord's obligation respecting the Security Deposit
is that of a debtor, not a trustee, and no interest shall accrue thereon.

     Provided that no Default shall have occurred in each instance, Tenant shall
have the right to reduce the amount of the Security Deposit by delivery to
Landlord of replacement Letters of Credit in the form required herein in
accordance with the following schedule:

          (a) On or after the second anniversary of the Commencement Date, the
Security Deposit may be reduced to an amount equal to the sum of (i) five (5)
months' Base Rent, and (ii) five (5) months' estimated parking fees at the then
current rate;

          (b) On or after the third anniversary of the Commencement Date, the
Security Deposit may be reduced to an amount equal to the sum of (i) four (4)
months' Base Rent, and (ii) four (4) months' parking fees at the then current
rate; and

          (c) On or after the fourth anniversary of the Commencement Date, the
Security Deposit may be reduced to an amount equal to the sum of (i) three (3)
months' Base Rent, and (ii) three (3) months' parking fees, at the then current
rate.

     Notwithstanding the foregoing, if Tenant is in Default under the Lease at
any time following any such reduction, the Security Deposit shall be increased
to an amount equal to 6 times the then applicable monthly Base Rent and parking
fees, as determined by Landlord in Landlord's reasonable discretion, and

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                                167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 5

Tenant shall have no further right to reduce the Security Deposit. Such
increased Security Deposit shall be paid to Landlord in the form of a
replacement Letter of Credit in the amount set forth in Landlord's notice within
10 days of Landlord's written demand. If Tenant is required to increase the
Security Deposit in accordance with this Section, then from and after the date
such monies are deposited with Landlord, the "SECURITY DEPOSIT" shall be deemed
to be the amount then held by Landlord hereunder.

     7. USE. The Premises shall be used solely for the Permitted Use set forth
in the Basic Lease Provisions, and in compliance with all laws, orders,
judgments, ordinances, regulations, codes, directives, permits, licenses,
covenants and restrictions now or hereafter applicable to the Premises, and to
the use and occupancy thereof, including, without limitation, the Americans With
Disabilities Act, 42 U.S.C. Section 12101, et seq. (together with the
regulations promulgated pursuant thereto, "ADA") (collectively, "LEGAL
REQUIREMENTS" and each, a "LEGAL REQUIREMENT"). Tenant shall, upon 5 days'
written notice from Landlord, discontinue any use of the Premises which is
declared by any Governmental Authority (as defined in Section 9) having
jurisdiction to be a violation of a Legal Requirement. Tenant will not use or
permit the Premises to be used for any purpose or in any manner that would void
Tenant's or Landlord's insurance. Tenant shall reimburse Landlord promptly upon
demand for any additional premium charged for any such insurance policy by
reason of Tenant's failure to comply with the provisions of this Section or
otherwise caused by Tenant's use and/or occupancy of the Premises. Tenant will
use the Premises in a careful, safe and proper manner and will not commit or
permit 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, 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. Tenant shall cause any
equipment or machinery to be installed in the Premises so as to reasonably
prevent sounds or vibrations from the Premises from extending outside the
Premises so as to avoid disturbing occupants of adjacent properties. Tenant
shall not place any machinery or equipment in excess of the loading capacity of
the floor in or upon the Premises or transport or move such items in the
Building elevators without the prior written consent of Landlord. Except as may
be provided under the Work Letter, Tenant shall not, without the prior written
consent of Landlord, use the Premises in any manner which will require
ventilation, air exchange, heating, gas, steam, electricity or water beyond the
existing capacity of the Project (as such capacity may from time to time be
supplemented in accordance with the applicable provisions of this Lease).

     Landlord shall, at Landlord's expense, make any alterations or
modifications to Landlord's Work which may be necessary to cause Landlord's Work
to comply with any Legal Requirement which was enacted and applicable to the
Premises at the time of Delivery. In addition, Landlord shall, at Landlord's
expense (to the extent such Legal Requirement was enacted and was applicable to
the Premises prior to the date hereof), or at Tenant's expense (to the extent
such Legal Requirement was enacted or became applicable to the Premises after
the date hereof or is applicable to the Premises solely by reason of Tenant's
particular use of the Premises) make any alterations or modifications to the
Parking Lot or the exterior of the Building that are required by Legal
Requirements, including the ADA. Tenant, at its sole expense, shall make any
alterations or modifications to the interior of the Premises that are required
by Legal Requirements (including, without limitation, compliance of the Premises
with the ADA). Notwithstanding any other provision herein to the contrary,
Tenant shall be responsible for any and all demands, claims, liabilities,
losses, costs, expenses, actions, causes of action, damages or judgments, and
all reasonable expenses incurred in investigating or resisting the same
(including, without limitation, reasonable attorneys' fees, charges and
disbursements and costs of suit) (collectively, "CLAIMS") arising out of or in
connection with Legal Requirements, and Tenant shall indemnify, defend, hold and
save Landlord harmless from and against any and all Claims arising out of or in
connection with any failure of the Premises to comply with any Legal
Requirement.

     Tenant shall have the right to request Landlord to contest the validity or
application of any Legal Requirement which adversely affects Tenant's access to
or use of the Project for the Permitted Use. Landlord shall have the right to
refuse Tenant's request, and Tenant shall have no right thereafter to contest
such Legal Requirement, if Landlord determines, in Landlord's sole but
reasonable discretion, that Tenant's contest of such Legal Requirement, whether
or not successful, would adversely affect Landlord's future operation, ownership
or management of the Project. If Landlord refuses to undertake

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                                167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 6

any such contest for any other reason, Tenant shall have the right to contest by
appropriate legal proceedings diligently conducted in good faith, at Tenant's
sole cost and expense, the validity or application of such Legal Requirement,
subject to the following:

     (a) If by the terms of any such Legal Requirement, compliance therewith
pending the prosecution of any such proceeding may legally be delayed without
the incurrence of any lien, charge or liability of any kind against the Premises
or any part thereof and without subjecting Landlord to any liability, civil or
criminal, for failure so to comply therewith, Tenant may delay compliance
therewith until the final determination of such proceeding; and

     (b) If any lien, charge or civil liability would be incurred by reason of
any such delay, Tenant nevertheless may contest such Legal Requirement as
aforesaid, provided that Tenant furnishes to Landlord security reasonably
satisfactory to Landlord against any loss or injury by reason of such delay.

     8. HOLDING OVER. If, with Landlord's express written consent, Tenant
retains possession of the Premises after the termination of the Term, (i) unless
otherwise agreed in such written consent, such possession shall be subject to
immediate termination by Landlord at any time, (ii) all of the other terms and
provisions of this Lease (including, without limitation, the adjustment of Base
Rent pursuant to Section 4 hereof) shall remain in full force and effect
(excluding any expansion or renewal option or other similar right or option)
during such holdover period, (iii) the monthly rental shall be equal to 150% of
Rent in effect during the last 30 days of the Term, and (iv) all other payments
shall continue under the terms of this Lease. If Tenant remains in possession of
the Premises after the expiration or earlier termination of the Term 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 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 of which
Landlord has specifically advised Tenant, in writing. No holding over by Tenant,
whether with or without consent of Landlord, shall operate to extend this Lease
except as otherwise expressly provided, and this Section 0 shall not be
construed as consent for Tenant to retain possession of the Premises. 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.

     9. TAXES. Tenant shall pay all taxes, levies, assessments and governmental
charges of any kind (collectively referred to as "TAXES") imposed by any
federal, state, regional, municipal, local or other governmental authority or
agency, including, without limitation, quasi-public agencies (collectively,
"GOVERNMENTAL AUTHORITY") during the Term, including, without limitation, all
Taxes: (i) imposed on or measured by or based, in whole or in part, on rent
payable to Landlord under this Lease and/or from the rental by Landlord of the
Project or any portion thereof, or (ii) based on the square footage, assessed
value or other measure or evaluation of any kind of the Premises or the Project,
or (iii) assessed or imposed by or on the operation or maintenance of any
portion of the Premises or the Project, including parking, or (iv) assessed or
imposed by, or at the direction of, or resulting from statutes or regulations,
or interpretations thereof, promulgated by, any Governmental Authority, or (v)
imposed as a license or other fee on Landlord's business of leasing space in the
Project. Landlord shall furnish to Tenant promptly upon receipt thereof any bill
for Taxes and Tenant shall pay such bill as and when due but in no event sooner
than within ten (10) days following receipt thereof. Such payment shall be
prorated in the event that such bill relates to any period not included in the
Term of this Lease. In no event shall Taxes include any income, estate,
succession, inheritance, gift, franchise, transfer or excess profit taxes. All
betterments and other assessments otherwise includible as Taxes shall be
amortized over the longest period permitted by applicable law. Tenant may
contest in Landlord's name by appropriate legal proceedings the amount,
validity, or application of any Taxes or liens securing Taxes, subject to the
same requirements as are set forth in Section 7 hereto with respect to contests
of Legal Requirements. If any such Tax is levied or assessed directly against
Tenant, then Tenant shall be responsible for and shall pay the same at such
times and in such manner as the taxing authority shall require. Tenant shall
pay, prior to delinquency, any and all Taxes levied or assessed against any
personal property or trade fixtures placed by Tenant in the Premises, whether
levied or assessed against Landlord or Tenant.

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                                167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 7

     In addition to the foregoing, Tenant shall pay any and all taxes and
assessments imposed on Tenant's personal property, improvements, alterations and
trade fixtures directly to the Governmental Authority imposing any such tax or
assessment, so as to prevent the imposition of any lien, charge or other
liability against the Premises with respect to such taxes or assessments.

     10. PARKING. Subject to Force Majeure, the provisions of Section 18 below,
and the exercise by Landlord of its rights hereunder, Tenant shall have the
right, as an appurtenance hereto, to park in all of the parking spaces in the
Parking Lot. Such use shall be subject to Landlord's reasonable rules and
regulations with respect thereto. Tenant shall pay a parking license fee in the
amount of $165 per month for each space, which fee may be reasonably adjusted by
Landlord upon thirty (30) days' prior written notice to Tenant not more
frequently than once every 12 months throughout the Term, including the
Extension Term, if any, to reflect market rates. In no event may such fee be
increased by more than 5% in the aggregate during the course of any 12 month
period. Landlord shall not be responsible for enforcing Tenant's parking rights
against any third parties, but shall maintain on the Parking Lot signage
reasonably acceptable to Tenant indicating the reservation of all parking spaces
in the Parking Lot for Tenant's exclusive use.

     11. UTILITIES, SERVICES.

     Landlord shall provide, subject to the terms of this Section 11, water,
electricity, heat, light, power, telephone, sewer, and other utilities
(including gas and fire sprinklers to the extent the Project is plumbed for such
services) (collectively, "UTILITIES"). Landlord warrants and represents that the
Premises are currently separately metered. Tenant shall pay directly to the
Utility provider, prior to delinquency, all charges for Utilities 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 eviction or constructive eviction of Tenant, termination of this Lease or the
abatement of Rent.

     12. ALTERATIONS AND TENANT'S PROPERTY. Any alterations, additions, or
improvements made to the Premises or the Project by or on behalf of Tenant,
including additional locks or bolts of any kind or nature upon any doors or
windows in the Premises, but excluding installation, removal or realignment of
furniture, trade fixtures and other personal property and work of a decorative
nature such as painting and carpeting costing less than $20,000 and not
involving any modifications to the structure or connections (other then by
ordinary plugs or jacks) to Building Systems (as defined in Section 13)
("ALTERATIONS") shall be subject to Landlord's prior written consent, which may
be given or withheld in Landlord's sole discretion if any such Alteration
affects the structure of the Building, but which shall otherwise not be
unreasonably withheld or delayed. If Landlord approves any Alterations, Landlord
may impose such conditions on Tenant in connection with the commencement,
performance and completion of such Alterations as Landlord may deem appropriate
in Landlord's reasonable discretion. Any request for approval shall be in
writing, delivered not less than 15 business days in advance of any proposed
construction, and accompanied by plans, specifications and such other
information concerning the nature and cost of the alterations as may be
reasonably requested by Landlord, including the identities and mailing addresses
of all persons performing work or supplying materials. Landlord shall have the
right to approve any contractor selected by Tenant to perform work in the
Premises, provided that such approval shall not be unreasonably withheld or
delayed. Landlord's right to review plans and specifications and to monitor
construction shall be solely for its own benefit, and Landlord shall have no
duty to ensure that such plans and specifications or construction comply with
applicable Legal Requirements. Tenant shall cause, at its sole cost and expense,
all Alterations to comply with insurance requirements and with Legal
Requirements and shall implement at its sole cost and expense any alteration or
modification required by Legal Requirements as a result of any Alterations.
Tenant shall reimburse Landlord, as Additional Rent, for the actual out-of
pocket expense incurred by Landlord (in an amount not to exceed $2,000.00 for
any one project) for review and approval of Tenant's plans and specifications
and monitoring of construction (i.e., engineering plan review, on-site
inspections of work and similar work by or on behalf of Landlord). Before Tenant
begins any Alteration, Landlord may post on and about the Premises notices of
non-responsibility pursuant to applicable law. Tenant shall reimburse Landlord
for, and indemnify and hold Landlord harmless from, any expense incurred by
Landlord by reason of faulty work done by Tenant or its contractors, delays
caused by such work, or inadequate cleanup.

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                                167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 8

     Tenant shall assure payment for the completion of all Alterations work free
and clear of liens, and shall provide (and cause each contractor or
subcontractor to provide) certificates of insurance for workers' compensation
and other coverage in amounts and from an insurance company reasonably
satisfactory to Landlord protecting Landlord against liability for personal
injury or property damage during construction. Upon completion of any
Alterations, Tenant shall deliver to Landlord: (i) sworn statements setting
forth the names of all contractors and subcontractors who did the /work and
final lien waivers from all such contractors and subcontractors; and (ii) "as
built" plans for any such Alteration.

     Other than (i) the items, if any, listed on EXHIBIT F attached hereto, (ii)
any items agreed by Landlord in writing to be included on EXHIBIT F in the
future, and (iii) any trade fixtures, machinery, equipment and other personal
property not paid for out of the TI Fund (as defined in the Work Letter) which
may be removed without material damage to the Premises or which damage shall be
repaired (including capping or terminating utility hook-ups) by Tenant during
the Term (collectively, "TENANT'S PROPERTY"), all property of any kind paid for
with the TI Fund, all Alterations, real property fixtures, built-in machinery
and equipment, built-in casework and cabinets and other similar additions and
improvements built into the Premises so as to become an integral part of the
Premises such as fume hoods which penetrate the roof or plenum area, built-in
cold rooms, built-in warm rooms, walk-in cold rooms, walk-in warm rooms,
deionized water systems, glass washing equipment, autoclaves, chillers, built-in
plumbing, electrical and mechanical equipment and systems, and any power
generator and transfer switch (collectively, "INSTALLATIONS") shall be and shall
remain the property of Landlord during the Term and following the expiration or
earlier termination of the Term, shall not be removed by Tenant at any time
during the Term and shall remain upon and be surrendered with the Premises as a
part thereof in accordance with Section 28 following the expiration or earlier
termination of this Lease; provided, however, that Landlord shall, at the time
its approval of such Installation is requested notify Tenant if it has elected
to cause Tenant to remove such Installation upon the expiration or earlier
termination of this Lease. If Landlord so elects, Tenant shall remove such
Installation upon the expiration or earlier termination of this Lease and
restore any damage caused by or occasioned as a result of such removal,
including, when removing any of Tenant's Property which was plumbed, wired or
otherwise connected to any of the Building Systems, capping off all such
connections and repairing any holes. Notwithstanding the foregoing, Tenant shall
have the right to leave standard office improvements in the Premises upon
surrender. During any such restoration period, Tenant shall pay Rent to Landlord
as provided herein as if said space were otherwise occupied by Tenant.

     13. LANDLORD'S REPAIRS. Landlord, at Landlord's expense, shall maintain all
of the structural elements of the Premises (including, without limitation, the
structural elements of the roof located under the membrane thereof, but not
including the membrane or flashing, which shall remain Tenant's responsibility
pursuant to Section 14 hereof) 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. In addition, Landlord shall maintain the exterior and parking areas of
the Project, subject to reimbursement by Tenant as provided herein, in good
repair, reasonable wear and tear and uninsured losses and damages caused by
Tenant or by any Tenant Party excluded. Landlord's costs for the maintenance of
the exterior and parking areas of the Project shall be reimbursed by Tenant, on
demand, as follows: prior to performing such maintenance or repair, Landlord
shall inform Tenant of the estimated cost. Upon completion, Tenant shall
reimburse Landlord for the actual cost of such work within ten (10) days after
Tenant's receipt of notice of completion and the actual final cost of such work.
Notwithstanding the foregoing, if any such work is of the nature of a capital
repair or replacement, as determined in accordance with generally accepted
accounting principles ("GAAP"), the cost of such work shall be amortized over
the useful life of such improvement as determined in accordance with GAAP, and
Tenant shall pay monthly, as Additional Rent, one-twelfth of the annual
amortized cost. Losses and damages caused by Tenant or any Tenant Party shall be
repaired by Landlord, to the extent not covered by insurance, at Tenant's sole
cost and expense. Tenant shall, promptly after becoming aware of the need
therefor, give Landlord written notice of any repair required by Landlord
pursuant to this Section, after which Landlord shall have a reasonable
opportunity to effect such repair. Landlord shall not be liable for any failure
to make any repairs or to perform any maintenance unless such failure shall
persist for an unreasonable time after Tenant's written notice of the need for
such repairs or maintenance. Tenant waives its rights under any state or local
law to terminate this Lease

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                                167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 9

or to make such repairs at Landlord's expense and agrees that the parties'
respective rights with respect to such matters shall be solely as set forth
herein. Repairs required as the result of fire, earthquake, flood, vandalism,
war, or similar cause of damage or destruction shall be controlled by Section
18.

     14. TENANT'S REPAIRS. Subject to Section 13 hereof, Tenant, at its expense,
shall repair, replace and maintain in good condition all portions of the
Premises, including, without limitation, entries, doors, ceilings, interior
windows, interior walls, and HVAC, plumbing, fire sprinklers, elevators and all
other Building systems (collectively, "BUILDING SYSTEMS"). Tenant shall provide
to Landlord, at least once every year during the Term, copies of all maintenance
records, maintenance logs and service agreements with respect to the Building
Systems. Such repair and replacement may include capital expenditures and
repairs whose benefit may extend beyond the Term. Should Tenant fail to make any
such repair or replacement or fail to maintain the Premises, Landlord shall give
Tenant notice of such failure. If Tenant fails to commence cure of such failure
within 10 days of Landlord's notice, and thereafter diligently prosecute such
cure to completion, Landlord may perform such work and shall be reimbursed by
Tenant for the actual, reasonable cost thereof within 10 days after demand
therefor; provided, however, that if such failure by Tenant creates or could
create an emergency, Landlord may immediately commence cure of such failure and
shall thereafter be entitled to recover the actual, reasonable costs of such
cure from Tenant within 10 days after demand therefor. Subject to Sections 17
and 18, Tenant shall bear the full uninsured cost of any repair or replacement
to any part of the Project that results from damage caused by Tenant or any
Tenant Party and any repair that benefits only the Premises.

     Notwithstanding any other provision of this Lease to the contrary, if
Tenant becomes obligated hereunder to make any repair or replacement to the
Project which is capital in nature, as determined in accordance with GAAP, or is
required to make any improvement in order to comply with a Legal Requirement for
which Tenant is otherwise responsible hereunder (other than on account of a
Legal Requirement applicable solely by reason of Tenant's particular use of the
Premises or of any damage caused by Tenant or any Tenant Party), and in either
case such work is estimated to cost more than $20,000, Landlord shall pay the
cost of such work, subject to reimbursement by Tenant as follows: the cost of
such work shall be amortized over the lesser of (i) the useful life of such work
as determined in accordance with GAAP, or (ii) 7 years, in the case of repairs
or replacements or improvements to the HVAC system and equipment serving the
Premises or, in the case of any other work, such cost shall be amortized over
the useful life of such work as determined in accordance with GAAP, and Tenant
shall thereafter pay monthly, as Additional Rent, one-twelfth of such annual
amortized cost, until the earlier of (x) the payment in full of such amortized
amount or (y) the expiration or earlier termination of the Term. Prior to
performing any such work, whether costing more than $20,000 or not, Tenant shall
notify Landlord in writing, explaining in detail the necessity for such work and
including an estimate of the cost of such work and a list of proposed
contractors to perform such work. Within 30 days after receipt of such notice
Landlord shall, by written notice to Tenant (i) elect to perform such work
itself, if Landlord reasonably believes it can perform or cause such work to be
performed for less than Tenant's estimated cost, in which event such cost
incurred by Landlord, amortized as provided herein, shall be passed through to
Tenant as an Operating Expense, or (ii) authorize Tenant to perform or cause
such work to be performed, in which case Tenant shall promptly commence such
work and thereafter diligently pursue it to completion in accordance with the
provisions of Section 12 hereof and this Section 14.

     15. MECHANIC'S LIENS. Tenant shall discharge, by bond or otherwise, any
mechanic's lien filed against the Premises or against the Project for work
claimed to have been done for, or materials claimed to have been furnished to,
Tenant within 10 days after notice of the filing thereof, at Tenant's sole cost
and shall otherwise keep the Premises and the Project free from any liens
arising out of work performed, materials furnished or obligations incurred by
Tenant. Should Tenant fail to discharge any lien described herein, Landlord
shall have the right, but not the obligation, to pay such claim or post a bond
or otherwise provide security to eliminate the lien as a claim against title to
the Project and the cost thereof shall be immediately due from Tenant as
Additional Rent. If Tenant shall lease or finance the acquisition of office
equipment, furnishings, or other personal property of a removable nature
utilized by Tenant in the operation of Tenant's business, Tenant warrants that
any Uniform Commercial Code Financing Statement filed as a matter of public
record by any lessor or creditor of Tenant will upon its face or by exhibit
thereto

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                               167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 10

indicate that such Financing Statement is applicable only to trade fixtures and
other removable personal property of Tenant located within the Premises. In no
event shall the address of the Project be furnished on the statement without
qualifying language as to applicability of the lien only to trade fixtures and
other removable personal property.

     16. 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 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 negligence of Landlord or any
Landlord Parties. Landlord shall not otherwise 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 hereby
irrevocably 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), unless caused by the
willful misconduct or negligence of Landlord or any Landlord Parties. Landlord
shall not be liable for any damages arising from any act, omission or neglect of
any third party other than Landlord Parties.

     17. INSURANCE. Landlord shall maintain all risk property and, if
applicable, sprinkler damage insurance covering the full replacement cost of the
Project. Landlord shall further procure and maintain commercial general
liability insurance with a single loss limit of not less than $2,000,000 for
bodily injury and property damage with respect to the Project. Landlord may, but
is not obligated to, maintain such other insurance and additional coverages as
it may reasonably deem necessary, including, but not limited to, flood,
environmental hazard and earthquake, loss or failure of building equipment,
errors and omissions, rental loss during the period of repair or rebuilding,
workers' compensation insurance and fidelity bonds for employees employed to
perform services and insurance for any improvements installed by Tenant or which
are in addition to the standard improvements customarily furnished by Landlord
without regard to whether or not such are made a part of the Project. Landlord
shall provide a certificate from Landlord's insurer evidencing such insurance to
Tenant from time to time at Tenant's written request. The Project may be
included in a blanket policy (in which case the cost of such insurance allocable
to the Project will be determined by Landlord based upon the insurer's cost
calculations). Landlord shall calculate the monthly amount owed by Tenant to
reimburse Landlord for the costs of Landlord's insurance (subject to proration
in the event that any portion of the applicable policy period is not included in
the Term of this Lease) and Tenant shall reimburse Landlord for such costs
within thirty (30) days after Tenant's receipt of such invoice.

     Tenant, at its sole cost and expense, shall maintain at all times during
the Term: all risk property insurance with business interruption and extra
expense coverage, covering the full replacement cost of all trade fixtures and
other removable personal property installed or placed in the Premises by Tenant
at Tenant's expense; 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. The commercial general liability insurance
policy shall name Landlord and Alexandria Real Estate Equities, Inc. and their
respective officers, directors, employees, managers, agents, invitees and
contractors (collectively, "LANDLORD PARTIES"), as additional insureds; shall
insure on an occurrence and not a claims-made basis; shall 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 30 days prior written
notice shall have been given to Landlord from the insurer; contain a hostile
fire endorsement and a contractual liability endorsement; and shall 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 and Alexandria
Real Estate Equities, Inc. as additional insureds, along with reasonable
evidence of the payment of premiums for the applicable period, shall be
delivered to Landlord by Tenant upon commencement of the Term and upon each
renewal of said insurance. Required coverage may be maintained by means of any
combination of "umbrella" or "blanket" policies with an aggregate per location
endorsement which specifically provides that the amount

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                               167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 11

of insurance shall not be prejudiced by other losses covered by any such blanket
policy. Tenant shall, at least 5 days prior to the expiration of such policies,
furnish Landlord with renewal certificates.

     In each instance where insurance is to name Landlord as an additional
insured, Tenant shall upon written request of Landlord also designate and
furnish certificates so evidencing Landlord as additional insured to: (i) any
lender of Landlord holding a security interest in the Project or any portion
thereof, (ii) the landlord under any lease wherein Landlord is tenant of the
real property on which the Project is located, if the interest of Landlord is or
shall become that of a tenant under a ground or other underlying lease rather
than that of a fee owner, and/or (iii) any management company retained by
Landlord to manage the Project.

     The property insurance obtained by Landlord and Tenant shall include a
waiver of subrogation by the insurers and all rights based upon an assignment
from its insured, against Landlord or Tenant, and their respective officers,
directors, employees, managers, agents, invitees and contractors ("RELATED
PARTIES"), in connection with any loss or damage thereby insured against.
Neither party nor its respective Related Parties shall be liable to the other
for loss or damage caused by any risk insured against under property insurance
required to be maintained hereunder, and each party waives any claims against
the other party, and its respective Related Parties, for such loss or damage.
The failure of a party to insure its property shall not void this waiver.
Landlord and its respective Related Parties shall not be liable for, and Tenant
hereby waives all claims against such parties for, business interruption and
losses occasioned thereby sustained by Tenant or any person claiming through
Tenant resulting from any accident or occurrence in or upon the Premises or the
Project from any cause whatsoever. If the foregoing waivers shall contravene any
law with respect to exculpatory agreements, or shall not be commercially
available, the liability of Landlord or Tenant shall be deemed not released but
shall be secondary to the other's insurer.

     Landlord may require insurance policy limits to be raised to bring coverage
limits to levels then being generally required of new tenants of comparable
properties in the City of Cambridge, Massachusetts.

     18. RESTORATION. If, at any time during the Term, the Project or the
Premises are damaged or destroyed by a fire or other insured casualty, Landlord
shall notify Tenant within 60 days after discovery of such damage as to the
amount of time Landlord reasonably estimates it will take to restore the Project
or the Premises, as applicable (the "RESTORATION PERIOD"). If the Restoration
Period is estimated to exceed 12 months (the "MAXIMUM RESTORATION PERIOD"),
either Landlord or Tenant may, by written notice to the other within 30 days
following Tenant's receipt of such estimate, elect to terminate this Lease as of
the date that is 75 days after the date of such election. Unless either party so
elects to terminate this Lease, Landlord shall, subject to receipt of sufficient
insurance proceeds (with any deductible to be treated as a current Operating
Expense), promptly restore the Project and the Premises (including without
limitation any improvements installed by Tenant or by Landlord and paid for by
Tenant), subject to delays arising from the collection of insurance proceeds,
from Force Majeure events or as needed to permit Tenant to obtain any license,
clearance or other authorization of any kind required to enter into and restore
the Premises issued by any Governmental Authority having jurisdiction over the
use, storage, handling, treatment, generation, release, disposal, removal or
remediation of Hazardous Materials (as defined in Section 30) in, on or about
the Premises (collectively referred to herein as "HAZARDOUS MATERIALS
CLEARANCES"); provided, however, that if repair or restoration of the Premises
is not substantially complete as of the end of the Maximum Restoration Period
or, if longer, the Restoration Period, Tenant may, in Tenant's sole and absolute
discretion, elect to terminate this Lease within 60 days thereafter (but prior
to such substantial completion) and this Lease shall terminate as of the date
that is 75 days after the later of: (i) the date on which such termination
notice was received by Landlord, or (ii) the date all required Hazardous
Materials Clearances are obtained. In addition, if despite Landlord's diligent
efforts, repair or restoration of the Premises is not substantially complete as
of the end of the Maximum Restoration Period or, if longer, the Restoration
Period, as a result of any Force Majeure, Landlord may, in Landlord's sole and
absolute discretion, elect to terminate this Lease within 60 days thereafter and
this Lease shall terminate as of the date that is 75 days after the later of:
(i) the date on which such termination notice was received by Landlord, or (ii)
the date all required Hazardous Materials

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                               167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 12

Clearances are obtained. Notwithstanding any termination of this Lease as
described in this section, Landlord shall retain any Rent paid and the right to
any Rent payable by Tenant prior to such election by Landlord or Tenant.

     Tenant, at its expense, shall promptly perform, subject to delays arising
from the collection of insurance proceeds, from Force Majeure (as defined in
Section 34) events or to obtain Hazardous Material Clearances, all repairs or
restoration not required to be done by Landlord and shall promptly re-enter the
Premises and commence doing business in accordance with this Lease.
Notwithstanding the foregoing, Landlord may terminate this Lease if the Premises
are damaged during the last 1 year of the Term and Landlord reasonably estimates
that it will take more than 2 months to repair such damage, or if the Project or
the Premises are substantially damaged by a casualty against which Landlord is
not required to insure hereunder. Rent shall be equitably abated from the date
all Hazardous Material Clearances which are required to permit Landlord to enter
the Premises are obtained until the Premises are repaired and restored. Such
abatement shall be the sole remedy of Tenant, and except as provided in this
Section 18, Tenant waives any right to terminate the Lease by reason of damage
or casualty loss.

     The provisions of this Lease, including this Section 18, constitute an
express agreement between Landlord and Tenant with respect to any and all damage
to, or destruction of, all or any part of the Premises, or any other portion of
the Project, and any statute or regulation which is now or may hereafter be in
effect shall have no application to this Lease or any damage or destruction to
all or any part of the Premises or any other portion of the Project, the parties
hereto expressly agreeing that this Section 18 sets forth their entire
understanding and agreement with respect to such matters.

     19. CONDEMNATION. If the whole or any substantial part of the Premises or
the Project is 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" or "TAKEN"), and the Taking would in Landlord's
reasonable judgment either prevent or materially interfere with Tenant's use of
the Premises or materially interfere with or impair Landlord's ownership or
operation of the Project, then upon written notice by Landlord this Lease shall
terminate and Rent shall be apportioned as of said date. Landlord shall provide
written notice to Tenant of Landlord's finding as to whether such Taking will
prevent or materially interfere with Tenant's use of the Premises, or materially
interfere with or impair Landlord's ownership or operation of the Premises, as
applicable, within 30 days after the date of such Taking. If Tenant disputes any
such finding, Tenant shall notify Landlord of such dispute within 10 days after
receipt of Landlord's notice and such dispute shall thereafter be resolved by
arbitration in accordance with the provisions of Section 39(b) hereof. If the
Arbitrator or Arbitrators (as defined in Section 39(b)) determine that any such
Taking will prevent or materially interfere with Tenant's use of the Premises,
then Tenant shall have the right to terminate this Lease upon 30 days prior
written notice to Landlord. If the Arbitrator or Arbitrators determine that any
such Taking will materially interfere with or impair Landlord's ownership or
operation of the Project, then Landlord shall have the right to terminate this
Lease upon 30 days' prior written notice to Tenant. If part of the Premises or
the Project shall be Taken, and this Lease is not terminated as provided above,
Landlord shall (subject to the same provisions applicable to any restoration by
Landlord pursuant to Section 18) promptly restore the Premises and the Project
as nearly as is commercially reasonable under the circumstances to their
condition prior to such partial Taking and the rentable square footage of the
Building, the rentable square footage of the Premises and the Rent payable
hereunder during the unexpired Term shall be reduced to such extent as may be
fair and reasonable under the circumstances. Upon any such Taking, Landlord
shall be entitled to receive the entire price or award from any such Taking
without any payment to Tenant, and Tenant hereby assigns to Landlord Tenant's
interest, if any, in such award. Tenant shall have the right, to the extent that
same shall not diminish Landlord's award, to make a separate claim against the
condemning authority (but not Landlord) for such compensation as may be
separately awarded or recoverable by Tenant for moving expenses and damage to
Tenant's trade fixtures, if a separate award for such items is made to Tenant.
Tenant hereby waives any and all rights it might otherwise have pursuant to any
provision of state law to terminate this Lease upon a partial Taking of the
Premises or the Project.

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

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                               167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 13

          (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
twice 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, and Tenant shall fail to obtain replacement
insurance within ten (10) business days after receipt of notice thereof from
Landlord or Tenant's insurer, as applicable, or Landlord shall receive a notice
of nonrenewal of any such insurance and Tenant shall fail to obtain replacement
insurance at least 20 days before the expiration of the current coverage.

          (c) ABANDONMENT. Tenant shall abandon the Premises.

          (d) IMPROPER TRANSFER. Tenant's interest in this Lease shall be
attached, executed upon, or otherwise judicially seized and such action is not
released within 90 days of the action.

          (e) LIENS. Tenant shall fail to discharge or otherwise obtain the
release of any lien placed upon the Premises in violation of this Lease within
10 days after Tenant receives notice that any such lien is filed against the
Premises.

          (f) INSOLVENCY EVENTS. Tenant or any guarantor or surety of Tenant's
obligations hereunder shall: (A) make a general assignment for the benefit of
creditors; (B) commence any case, proceeding or other action seeking to have an
order for relief entered on its behalf as a debtor or to adjudicate it a
bankrupt or insolvent, or seeking reorganization, arrangement, adjustment,
liquidation, dissolution or composition of it or its debts or seeking
appointment of a receiver, trustee, custodian or other similar official for it
or for all or of any substantial part of its property (collectively a
"PROCEEDING FOR RELIEF"); (C) become the subject of any Proceeding for Relief
which is not stayed or dismissed within 90 days of its filing or entry; or (D)
die or suffer a legal disability (if Tenant, guarantor, or surety is an
individual) or be dissolved or otherwise fail to maintain its legal existence
(if Tenant, guarantor or surety is a corporation, partnership or other entity)
and fail to reinstate such legal existence within 5 business days after receipt
of written notice thereof.

          (g) ESTOPPEL CERTIFICATE OR SUBORDINATION AGREEMENT. Tenant fails to
execute any document required from Tenant under Sections 22(g) or 27 within 5
days after a second notice requesting such document.

          (h) OTHER DEFAULTS. Tenant shall fail to comply with any provision of
this Lease other than those specifically referred to in this Section 20, and,
except as otherwise expressly provided herein, such failure shall continue for a
period of 20 days after written notice thereof from Landlord to Tenant.

Any notice given under Section 20(h) 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, any notice required under any
provision of applicable law, and (iv) not be deemed a forfeiture or a
termination of this Lease; provided that if the nature of Tenant's default
pursuant to Section 20(h) is such that it cannot be cured by the payment of
money and reasonably requires more than 20 days to cure, then Tenant shall not
be deemed to be in default if Tenant commences such cure within said 20 day
period and thereafter diligently prosecutes the same to completion within a
reasonable time thereafter. Notwithstanding the foregoing, if Landlord
determines, in Landlord's reasonable judgment, that delay of such cure shall or
may result in the imposition of fines, liens, claims, judgments or other
penalties against Landlord or the Project, or will otherwise have a material
detrimental effect on Landlord's ownership or operation of the Property, or on
the value of the Property, Landlord shall so notify Tenant in writing and
thereafter such cure shall be completed by Tenant no later than 60 days from the
date of Landlord's original notice given under Section 20(h) hereof.

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                               167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 14

     21. LANDLORD'S REMEDIES.

          (a) PAYMENT BY LANDLORD; INTEREST. Upon the occurrence of a Default,
Landlord, at its option, without further notice or demand to Tenant, shall have
in addition to all other rights and remedies provided in this Lease, at law or
in equity, the option to pursue any one or more of the following remedies, each
and all of which shall be cumulative and nonexclusive, without any notice or
demand whatsoever.

               (i) Terminate this Lease, or at Landlord's option, Tenant's right
to possession only, in which event Tenant shall immediately surrender the
Premises to Landlord, and if Tenant fails to do so, Landlord may, to the extent
permitted by law, without further notice and without prejudice to any other
remedy which it may have for possession or arrearages in rent, enter upon and
take possession of the Premises and expel or remove Tenant and any other person
who may be occupying the Premises or any part thereof, without being liable for
prosecution or any claim or damages therefor;

               (ii) Upon any termination of this Lease, whether pursuant to the
foregoing Section 21(c)(i) or otherwise, Landlord may recover from Tenant the
following:

                    (1) The worth at the time of award of any unpaid rent which
has been earned at the time of such termination; plus

                    (2) The worth at the time of award of the amount by which
the unpaid rent which would have been earned after termination until the time of
award exceeds the amount of such rental loss that Tenant proves could have been
reasonably avoided; plus

                    (3) The worth at the time of award of the amount by which
the unpaid rent for the balance of the Term after the time of award exceeds the
amount of such rental loss that Tenant proves could have been reasonably
avoided; plus

                    (4) Any other amount necessary to compensate Landlord for
all the detriment proximately caused by Tenant's failure to perform its
obligations under this Lease or which in the ordinary course of things would be
likely to result therefrom, specifically including, but not limited to,
brokerage commissions and advertising expenses incurred, expenses of remodeling
the Premises or any portion thereof for a new tenant, whether for the same or a
different use, and any special concessions made to obtain a new tenant; and

                    (5) At Landlord's election, such other amounts in addition
to or in lieu of the foregoing as may be permitted from time to time by
applicable law.

     The term "RENT" as used in this Section 21 shall be deemed to be and to
     mean all sums of every nature required to be paid by Tenant pursuant to the
     terms of this Lease, whether to Landlord or to others. As used in Sections
     21(c)(ii) (A) and (B), above, the "WORTH AT THE TIME OF AWARD" shall be
     computed by allowing interest at the Default Rate. As used in Section
     21(c)(ii)(C) above, the "WORTH AT THE TIME OF AWARD" shall be computed by
     discounting such amount at the discount rate of the Federal Reserve Bank of
     San Francisco at the time of award plus 1%.

               (iii) Landlord may continue this Lease in effect after Tenant's
Default and recover rent as it becomes due (Landlord and Tenant hereby agreeing
that Tenant has the right to sublet or assign hereunder, subject only to
reasonable limitations). Accordingly, if Landlord does not elect to terminate
this Lease following a Default by Tenant, Landlord may, from time to time,
without terminating this Lease, enforce all of its rights and remedies
hereunder, including the right to recover all Rent as it becomes due.

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                               167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 15

               (iv) Whether or not Landlord elects to terminate this Lease
following a Default by Tenant, Landlord shall have the right to terminate any
and all subleases, licenses, concessions or other consensual arrangements for
possession entered into by Tenant and affecting the Premises or may, in
Landlord's sole discretion, succeed to Tenant's interest in such subleases,
licenses, concessions or arrangements. Upon Landlord's election to succeed to
Tenant's interest in any such subleases, licenses, concessions or arrangements,
Tenant shall, as of the date of notice by Landlord of such election, have no
further right to or interest in the rent or other consideration receivable
thereunder.

               (v) Independent of the exercise of any other remedy of Landlord
hereunder or under applicable law, Landlord may conduct an environmental test of
the Premises as generally described in Section 30[(d) hereof, at Tenant's
expense.

          (b) EFFECT OF EXERCISE. Exercise by Landlord of any remedies hereunder
or otherwise available shall not be deemed to be an acceptance of surrender of
the Premises and/or a termination of this Lease by Landlord, it being understood
that such surrender and/or termination can be effected only by the express
written agreement of Landlord and Tenant. Any law, usage, or custom to the
contrary notwithstanding, Landlord shall have the right at all times to enforce
the provisions of this Lease in strict accordance with the terms hereof; and the
failure of Landlord at any time to enforce its rights under this Lease strictly
in accordance with same shall not be construed as having created a custom in any
way or manner contrary to the specific terms, provisions, and covenants of this
Lease or as having modified the same and shall not be deemed a waiver of
Landlord's right to enforce one or more of its rights in connection with any
subsequent default. A receipt by Landlord of Rent or other payment with
knowledge of the breach of any covenant hereof shall not be deemed a waiver of
such breach. To the greatest extent permitted by law, Tenant waives the service
of any statutory notice to quit, and also waives all right of redemption in case
Tenant shall be dispossessed by a judgment or by warrant of any court or judge,
and Tenant agrees that, upon Landlord's termination of this Lease as provided
herein, Landlord shall be entitled to re-entry and possession in accordance with
the terms hereof. Any reletting of the Premises or any portion thereof shall be
on such terms and conditions as Landlord in its sole discretion may determine.
Landlord shall not be liable for, nor shall Tenant's obligations hereunder be
diminished because of, Landlord's failure to relet the Premises or collect rent
due in respect of such reletting or otherwise to mitigate any damages arising by
reason of Tenant's Default.

     22. ASSIGNMENT AND SUBLETTING.

          (a) GENERAL PROHIBITION. Without Landlord's prior written consent
subject to and on the conditions described in this Section 22, 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. If
Tenant is a corporation, partnership or limited liability company, the shares or
other ownership interests thereof which are not actively traded upon a stock
exchange or in the over-the-counter market, a transfer or series of transfers
whereby 25% or more of the issued and outstanding shares or other ownership
interests of such corporation are, or voting control is, transferred (but
excepting transfers upon deaths of individual owners) from a person or persons
or entity or entities which were owners thereof at time of execution of this
Lease to persons or entities who were not owners of shares or other ownership
interests of the corporation, partnership or limited liability company at time
of execution of this Lease, shall be deemed an assignment of this Lease
requiring the consent of Landlord as provided in this Section 22.

          (b) PERMITTED TRANSFERS. If Tenant desires to assign, sublease,
hypothecate or otherwise transfer this Lease or sublet the Premises (other than
pursuant to a Permitted Assignment, as defined below), then at least 15 business
days, but not more than 45 business days, before the date Tenant desires the
assignment or sublease to be effective (the "ASSIGNMENT DATE"), Tenant shall
give Landlord a notice (the "ASSIGNMENT NOTICE") containing such information
about the proposed assignee or sublessee, including the proposed use of the
Premises and any Hazardous Materials proposed to be used, stored handled,
treated, generated in or released or disposed of from the Premises, the

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                               167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 16

Assignment Date, any relationship between Tenant and the proposed assignee or
sublessee, and all material terms and conditions of the proposed assignment or
sublease, including a copy of any proposed assignment or sublease in its final
form, and such other information as Landlord may deem reasonably necessary or
appropriate to its consideration whether to grant its consent. Landlord may, by
giving written notice to Tenant within 15 business days after receipt of the
Assignment Notice: (i) grant such consent, (ii) refuse such consent, in its sole
and absolute discretion, if the proposed assignment, hypothecation or other
transfer or subletting concerns more than (together with all other then
effective subleases) 60% of the Premises, (iii) refuse such consent, in its
reasonable discretion, if the proposed subletting concerns (together with all
other then effective subleases) 60% or less of the Premises (provided that
Landlord shall further have the right to review and approve or reasonably
disapprove the proposed form of sublease prior to the effective date of any such
subletting), or (iv) except in the case of a Permitted Assignment (as defined in
Section 22(c) below) terminate this Lease with respect to the space described in
the Assignment Notice as of the Assignment Date if any such sublease is for a
period equaling substantially the remainder of the Term (an "ASSIGNMENT
TERMINATION"). If Landlord delivers notice of its election to exercise an
Assignment Termination, Tenant shall have the right to withdraw such Assignment
Notice by written notice to Landlord of such election within 5 business days
after Landlord's notice electing to exercise the Assignment Termination. If
Tenant withdraws such Assignment Notice, this Lease shall continue in full force
and effect. If Tenant does not withdraw such Assignment Notice, this Lease, and
the term and estate herein granted, shall terminate as of the Assignment Date
with respect to the space described in such Assignment Notice. No failure of
Landlord to exercise any such option to terminate this Lease, or to deliver a
timely notice in response to the Assignment Notice, shall be deemed to be
Landlord's consent to the proposed assignment, sublease or other transfer.
Tenant shall reimburse Landlord for all of Landlord's reasonable out-of-pocket
expenses in connection with its consideration of any Assignment Notice in an
amount not to exceed $2,000.00 for any one transfer.

          (c) PERMITTED ASSIGNMENTS. Notwithstanding the foregoing, Landlord's
consent to an assignment of this Lease or a subletting of any portion of the
Premises to any entity controlling, controlled by or under common control with
Tenant shall not be required, provided that Landlord shall have the right to
review the form of any such sublease or assignment solely for the purpose of
confirming that such form properly subordinates any sublease or assignment to
the terms and conditions of this Lease, does not purport to release Tenant from
any of Tenant's obligations hereunder or increase any of Landlord's obligations
hereunder, and is not otherwise in violation of any of the terms hereof. In
addition, Tenant shall have the right to assign this Lease, upon 30 days prior
written notice to Landlord but without obtaining Landlord's prior written
consent, to a corporation or other entity which is a successor-in-interest to
Tenant, by way of merger, consolidation or corporate reorganization, or by the
purchase of all or substantially all of the assets or the ownership interests of
Tenant provided that (i) such merger or consolidation, or such acquisition or
assumption, as the case may be, is for a good business purpose and not
principally for the purpose of transferring the Lease, and (ii) the net worth
(as determined in accordance with GAAP) of the assignee is not less than the net
worth (as determined in accordance with GAAP) of Tenant as of the date of
Tenant's most current quarterly or annual financial statements, and (iii) such
assignee shall agree in writing to assume all of the terms, covenants and
conditions of this Lease arising after the effective date of the assignment (any
of the transfers described in this Section 22(c) are hereinafter referred to as
a "PERMITTED ASSIGNMENT" and any of the transferees as hereinafter referred to
as a "PERMITTED ASSIGNEE").

          (d) ADDITIONAL CONDITIONS. As a condition to any such assignment or
subletting, whether or not Landlord's consent is required, Landlord may require:

               (i) that any subtenant agree, in writing at the time of such
subletting, that if Landlord gives such party notice that Tenant is in default
under this Lease, such party shall thereafter make all payments otherwise due
Tenant directly to Landlord, which payments will be received by Landlord without
any liability except to credit such payment against those due under the Lease,
and any such third party shall agree to attorn to Landlord or its successors and
assigns should this Lease be terminated for any reason; provided, however, in no
event shall Landlord or its successors or assigns be obligated to accept such
attornment; and

<PAGE>

                               167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 17

               (ii) A list of Hazardous Materials, certified by the proposed
assignee or sublessee to be true and correct, which the proposed assignee or
sublessee intends to use, store, handle, treat, generate in or release or
dispose of from the Premises, together with copies of all documents relating to
such use, storage, handling, treatment, generation, release or disposal of
Hazardous Materials by the proposed assignee or subtenant in the Premises or on
the Project, prior to the proposed assignment or subletting, including, without
limitation: permits; approvals; reports and correspondence; storage and
management plans; plans relating to the installation of any storage tanks to be
installed in or under the Project (provided, said installation of tanks shall
only be permitted after Landlord has given its written consent to do so, which
consent may be withheld in Landlord's sole and absolute discretion); and all
closure plans or any other documents required by any and all federal, state and
local Governmental Authorities for any storage tanks installed in, on or under
the Project for the closure of any such tanks. Neither Tenant nor any such
proposed assignee or subtenant is required, however, to provide Landlord with
any portion(s) of the such documents containing information of a proprietary
nature which, in and of themselves, do not contain a reference to any Hazardous
Materials or hazardous activities.

          (e) NO RELEASE OF TENANT, SHARING OF EXCESS RENTS. Notwithstanding any
assignment or subletting, Tenant and any guarantor or surety of Tenant's
obligations under this Lease shall at all times remain fully and primarily
responsible and liable for the payment of Rent and for compliance with all of
Tenant's other obligations under this Lease. If the Rent due and payable by a
sublessee or assignee other than pursuant to a Permitted Assignment (or a
combination of the rental payable under such sublease or assignment plus any
bonus or other consideration therefor or incident thereto in any form) exceeds
the sum of (i) the rental payable under this Lease (excluding however, any Rent
payable under this Section) and (ii) any of the following directly related to
any such sublease: actual and reasonable brokerage fees, legal costs and, to the
extent required pursuant to the terms of any such sublease, any design fees or
construction costs ("EXCESS RENT"), then Tenant shall be bound and obligated to
pay Landlord as Additional Rent hereunder 50% of such Excess Rent within 10 days
following receipt thereof by Tenant. If Tenant shall sublet the Premises or any
part thereof, Tenant hereby immediately and irrevocably assigns to Landlord, as
security for Tenant's obligations under this Lease, all rent from any such
subletting, and Landlord as assignee and as attorney-in-fact for Tenant, or a
receiver for Tenant appointed on Landlord's application, may collect such rent
and apply it toward Tenant's obligations under this Lease; except that, until
the occurrence of a Default, Tenant shall have the right to collect such rent.

          (f) NO WAIVER. The consent by Landlord to an assignment or subletting
shall not relieve Tenant or any assignees of this Lease or any sublessees of the
Premises from obtaining the consent of Landlord to any further assignment or
subletting nor shall it release Tenant or any assignee or sublessee of Tenant
from full and primary liability under the Lease. The acceptance of Rent
hereunder, or the acceptance of performance of any other term, covenant, or
condition thereof, from any other person or entity shall not be deemed to be a
waiver of any of the provisions of this Lease or a consent to any subletting,
assignment or other transfer of the Premises.

          (g) PRIOR CONDUCT OF PROPOSED TRANSFEREE. Notwithstanding any other
provision of this Section 22, if (i) the proposed assignee or sublessee of
Tenant has been required by any prior landlord, lender or Governmental Authority
to take remedial action in connection with Hazardous Materials contaminating a
property, where the contamination resulted from such party's action or use of
the property in question, (ii) the proposed assignee or sublessee is subject to
an enforcement order issued by any Governmental Authority in connection with the
use, storage, handling, treatment, generation, release or disposal of Hazardous
Materials (including, without limitation, any order related to the failure to
make a required reporting to any Governmental Authority), or (iii) because of
the existence of a pre-existing environmental condition in the vicinity of or
underlying the Project, the risk that Landlord would be targeted as a
responsible party in connection with the remediation of such pre-existing
environmental condition would be materially increased or exacerbated by the
proposed use of Hazardous Materials by such proposed assignee or sublessee,
Landlord shall have the absolute right to refuse to consent to any assignment or
subletting to any such party.

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                               167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 18

     23. ESTOPPEL CERTIFICATE. Tenant shall, within 10 business days of written
notice from Landlord, execute, acknowledge and deliver a statement in writing in
any form reasonably requested by a proposed lender or purchaser, (i) certifying
that this Lease is unmodified and in full force and effect (or, if modified,
stating the nature of such modification and certifying that this Lease as so
modified is in full force and effect) and the dates to which the rental and
other charges are paid in advance, if any, (ii) acknowledging that there are not
any uncured defaults on the part of Landlord hereunder, or specifying such
defaults if any are claimed, and (iii) setting forth such further information
with respect to the status of this Lease or the Premises as may be reasonably
requested thereon. Any such statement may be relied upon by any prospective
purchaser or encumbrancer of all or any portion of the real property of which
the Premises are a part. Tenant's failure to deliver such statement within 5
business days following a second request therefor shall, at the option of
Landlord, be conclusive upon Tenant that the Lease is in full force and effect
and without modification except as may be represented by Landlord in any
certificate prepared by Landlord and delivered to Tenant for execution. Landlord
shall provide an estoppel certificate of like tenor to Tenant or any third party
designated by Tenant within 10 business days after written request therefor.

     24. 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.

     25. PRORATIONS. All prorations required or permitted to be made hereunder
shall be made on the basis of the number of actual days in the applicable
accounting period.

     26. RULES AND REGULATIONS. Tenant shall, at all times during 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.

     27. SUBORDINATION. Landlord hereby represents that there is currently no
Mortgage affecting the Premises. This Lease and Tenant's interest and rights
hereunder are hereby made and shall be subject and subordinate at all times to
the lien of any Mortgage 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 on the part of Tenant; provided,
however that so long as there is no Default hereunder, Tenant's right to
possession of the Premises shall not be disturbed by the Holder of any such
Mortgage. 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 such instruments of
attornment as shall be reasonably requested by any such Holder, provided any
such instruments contain appropriate non-disturbance provisions assuring
Tenant's quiet enjoyment of the Premises as set forth in Section 24 hereof.
Notwithstanding the foregoing, any such Holder may at any time subordinate its
Mortgage to this Lease, without Tenant's consent, by notice in writing to
Tenant, and thereupon this Lease shall be deemed prior to such Mortgage without
regard to their respective dates of execution, delivery or recording and in that
event such Holder shall have the same rights with respect to this Lease as
though this Lease had been executed prior to the execution, delivery and
recording of such Mortgage and had been assigned to such Holder. The term
"MORTGAGE" whenever used in this Lease shall be deemed to include deeds of
trust, security assignments and any other encumbrances, and any reference to the
"HOLDER" of a Mortgage shall be deemed to include the beneficiary under a deed
of trust.

     28. 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, subject to any Alterations or Installations
permitted by Landlord to remain in the Premises, 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

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                               167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 19

OPERATIONS") and released of all Hazardous Materials Clearances, broom clean,
ordinary wear and tear and casualty loss and condemnation covered by Sections 18
and 19 excepted. At least 3 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 (including any Installations permitted by Landlord to
remain in 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 current 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 be
subject to the review and approval of Landlord's environmental consultant, in
the exercise of such consultant's reasonable professional judgment. 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 reasonably 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
reasonably 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 $5,000.
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.

     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 are
reasonable or appropriate to assure that the Premises and the Project are
surrendered free from any residual impact from Tenant HazMat Operations, the
reasonable 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 28.

     Tenant shall, at the expiration or earlier termination of the Term of this
Lease, 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, Alterations and 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 30 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. Any termination of this Lease in advance
of the scheduled expiration of the Term hereof shall be without prejudice to
claims of either party accruing prior to such termination, except to the extent
agreed in writing by the parties at the time of such termination.

     29. 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.

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                               167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 20

     30. 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 any Tenant Party. If Tenant
breaches the obligation stated in the preceding sentence, or if the presence of
Hazardous Materials in the Premises during the Term or any holding over results
in contamination of the Premises, the Project or any adjacent property or if
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 otherwise occurs
during 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 Term as a result of such contamination.
Notwithstanding the foregoing, Tenant shall in no event be liable to Landlord or
any Landlord Party hereunder as a result of, and this indemnification of
Landlord and the Landlord Parties by Tenant shall not include Environmental
Claims arising from (i) known conditions existing in, on, under or about the
Premises on or before the date hereof as disclosed by those certain
environmental reports more particularly described on EXHIBIT G hereto, or (ii)
conditions on the Project to the extent Tenant can prove, to Landlord's
reasonable satisfaction, that such condition pre-existed Tenant's occupancy of
the Premises ("PRE-EXISTING ENVIRONMENTAL CONDITIONS"). 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 or delayed 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. Landlord acknowledges that it is not the intent of this
Section 30 to prohibit Tenant from using the Premises for the Permitted Use.
Tenant may operate its business according to prudent industry practices so long
as the use or presence of Hazardous Materials is strictly and properly monitored
according to all then applicable Environmental Requirements. 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
Commencement 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 an updated Hazardous Materials List at least once a year and shall also
deliver an updated list before any new Hazardous Material is brought onto, kept,
used, stored, handled, treated,

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                               167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 21

generated on, or released or disposed of from, the Premises. 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 Commencement 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, notice of violations of any Legal Requirements; plans
relating to the installation of any storage tanks to be installed in or under
the Project (provided, said installation of tanks shall only be permitted after
Landlord has given Tenant its written consent to do so, which consent may be
withheld in Landlord's sole and absolute discretion); all closure plans or any
other documents required by any and all federal, state and local Governmental
Authorities for any storage tanks installed in, on or under the Project for the
closure of any such tanks; and a Surrender Plan (to the extent surrender in
accordance with Section 28 cannot be accomplished in 3 months). Tenant is not
required, however, to provide Landlord with any portion(s) of the Haz Mat
Documents containing information of a proprietary nature which, in and of
themselves, do not contain a reference to any Hazardous Materials or hazardous
activities. It is not the intent of this Section to provide Landlord with
information which could be detrimental to Tenant's business should such
information become possessed by Tenant's competitors.

          (c) TENANT REPRESENTATION AND WARRANTY. Tenant hereby represents and
warrants to Landlord that (i) neither Tenant nor any of its legal predecessors
has been required by any prior landlord, lender or Governmental Authority at any
time to take remedial action in connection with Hazardous Materials
contaminating a property which contamination was permitted by Tenant of such
predecessor or resulted from Tenant's or such predecessor's action or use of the
property in question, and (ii) Tenant is not subject to any enforcement order
issued by any Governmental Authority in connection with the use, storage,
handling, treatment, generation, release or disposal of Hazardous Materials
(including, without limitation, any order related to the failure to make a
required reporting to any Governmental Authority). If this representation and
warranty was not true in all material respects as of the date of this Lease,
Landlord shall have the right to terminate this Lease in Landlord's sole and
absolute discretion.

          (d) LANDLORD OBLIGATIONS. Landlord hereby agrees that Landlord shall
comply with all Legal Requirements and Environmental Requirements with respect
to the Pre-existing Environmental Conditions.

          (e) TESTING. Landlord shall have the right to conduct annual tests of
the Premises to determine whether any contamination of the Premises or the
Project has occurred as a result of Tenant's use. Tenant shall be required to
pay the cost of such annual test of the Premises; provided, however, that if
Tenant conducts its own tests of the Premises using third party contractors and
test procedures reasonably acceptable to Landlord which tests are certified to
Landlord, Landlord shall accept such tests in lieu of the annual tests to be
paid for by Tenant. In addition, at any time, and from time to time, prior to
the expiration or earlier termination of the Term, Landlord shall have the right
to conduct appropriate tests of the Premises and the Project to determine if
contamination has occurred as a result of Tenant's use of the Premises. In
connection with such testing, upon the request of Landlord, Tenant shall deliver
to Landlord or its consultant such non-proprietary information concerning the
use of Hazardous Materials in or about the Premises by Tenant or any Tenant
Party. If contamination has occurred for which Tenant is liable under this
Section 30, Tenant shall pay all costs to conduct such tests. If no such
contamination is found, Landlord shall pay the costs of such tests. Landlord
shall provide Tenant with a copy of all third party, non-confidential reports
and tests of the Premises made by or on behalf of Landlord during the Term
without representation or warranty and subject to a confidentiality agreement.
Tenant shall, at its sole cost and expense, promptly and satisfactorily
remediate any environmental conditions identified by such testing in accordance
with all Environmental Requirements. Landlord's receipt of or satisfaction with
any environmental assessment in no way waives any rights which Landlord may have
against Tenant.

          (f) UNDERGROUND TANKS. If underground or other storage tanks storing
Hazardous Materials located on the Premises or the Project are used by Tenant or
are hereafter placed on the Premises or the Project by Tenant, Tenant shall
install, use, monitor, operate, maintain, upgrade and manage such storage tanks,
maintain appropriate records, obtain and maintain appropriate insurance,

<PAGE>

                               167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 22

implement reporting procedures, properly close any underground storage tanks,
and take or cause to be taken all other actions necessary or required under
applicable state and federal Legal Requirements, as such now exists or may
hereafter be adopted or amended in connection with the installation, use,
maintenance, management, operation, upgrading and closure of such storage tanks.

          (g) TENANT'S OBLIGATIONS. Tenant's obligations under this Section 30
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 Premises not
relet by Landlord in Landlord's sole discretion, which Rent shall be prorated
daily.

          (h) 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
usable for fuel (or mixtures 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.

     31. 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 (unless such performance will, due to the nature of the obligation,
require a period of time in excess of 30 days, then after such period of time as
is reasonably necessary). Upon any default by Landlord, Tenant shall give notice
by registered or certified mail to any Holder of a Mortgage covering the
Premises and to any landlord of any lease of property in or on which the
Premises are located and Tenant shall offer such Holder and/or landlord a
reasonable opportunity to cure the default, including time in the exercise of
all due diligence to obtain possession of the Project by power of sale or a
judicial action if such should prove necessary to effect a cure; provided
Landlord shall have furnished to Tenant in writing the names and addresses of
all such persons who are to receive such notices. Upon the occurrence of a
default by Landlord as provided in this Section 31, Tenant, at its option,
without further notice or demand to Landlord, shall have all rights and remedies
provided at law or in equity. All obligations of Landlord hereunder shall be
construed as covenants, not conditions; and, notwithstanding anything in this
Section 31 to the contrary, Tenant may not terminate this Lease for breach of
Landlord's obligations hereunder.

Notwithstanding the foregoing, if any claimed Landlord default hereunder will
immediately, materially and adversely affect Tenant's ability to conduct its
business in the Premises (a "MATERIAL LANDLORD DEFAULT"), Tenant shall, as soon
as reasonably possible, but in any event within 2 business days of obtaining
knowledge of such claimed Material Landlord Default, give Landlord written
notice of such claim and telephonic notice to Tenant's principal contact with
Landlord. Landlord shall then have 2 business days to commence cure of such
claimed Material Landlord Default and shall diligently prosecute such cure to
completion. If such claimed Material Landlord Default is not a default by
Landlord hereunder, or if Tenant failed to give Landlord the notice required
hereunder within 2 business days of learning of the conditions giving rise to
the claimed Material Landlord Default, Landlord shall be entitled to recover
from Tenant, as Additional Rent, any costs incurred by Landlord in connection
with such cure in excess of the costs, if any, that Landlord would otherwise
have been liable to pay hereunder. If Landlord fails to commence and

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                               167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 23

diligently prosecute to completion the cure of any claimed Material Landlord
Default as provided above, Tenant may commence and prosecute such cure to
completion, and shall be entitled to recover the costs of such cure (but not any
consequential or other damages) from Landlord, to the extent of Landlord's
obligation to cure such claimed Material Landlord Default hereunder, subject to
the limitations set forth in the immediately preceding sentence of this
paragraph and the other provisions of this Lease.

     All obligations of Landlord under this Lease will be binding upon Landlord
only during the period of its ownership of the Premises and not thereafter. The
term "LANDLORD" in this Lease shall mean only the owner for the time being of
the Premises. Upon the transfer by such owner of its interest in the Premises,
such owner shall thereupon be released and discharged from all obligations of
Landlord thereafter accruing, but such obligations shall be binding during the
Term upon each new owner for the duration of such owner's ownership.

     32. INSPECTION AND ACCESS. Landlord and its agents, representatives, and
contractors may enter the Premises during business hours on not less than 48
hours advance 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 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. Landlord shall use reasonable efforts
to minimize interference with Tenant's operations in the Premises in exercising
the rights reserved by Landlord hereunder. Landlord may erect a suitable sign on
the Premises stating the Premises are available to let or that the Project is
available for sale. Landlord may grant easements and create restrictions on or
about the Premises which are not inconsistent with the provisions of this Lease,
provided that no such easement or restriction materially, adversely affects
Tenant's access to or use or occupancy of the Premises for the Permitted Use. At
Landlord's request, Tenant shall execute such instruments as may be necessary
for such easements, dedications or restrictions. Tenant shall at all times,
except in the case of emergencies, have the right to escort Landlord or its
agents, representatives, contractors or guests while the same are in the
Premises, provided such escort does not materially and adversely affect
Landlord's access rights hereunder.

     33. 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 or the Project. 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. 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.

     34. FORCE MAJEURE. Neither party shall be responsible or liable for delays
in the performance of its obligations hereunder (other than the obligation to
pay money) when caused by, related to, or arising out of acts of God, strikes,
lockouts, or other labor disputes, embargoes, quarantines, weather, national,
regional, or local disasters, calamities, or catastrophes, inability to obtain
labor or materials (or reasonable substitutes therefor) at reasonable costs or
failure of, or inability to obtain, utilities necessary for performance,
governmental restrictions, orders, limitations, regulations, or controls,
national emergencies, delay in issuance or revocation of permits, enemy or
hostile governmental action, terrorism, insurrection, riots, civil disturbance
or commotion, fire or other casualty, and other causes or events beyond the
reasonable control of such party ("FORCE MAJEURE").

     35. BROKERS, ENTIRE AGREEMENT, AMENDMENT. 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 Cushman & Wakefield of
Massachusetts, Inc. and Meredith & Grew, Inc. (whose commission shall in each
case be payable by

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                               167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 24

Landlord under a separate agreement). Landlord and Tenant each hereby agree to
indemnify and hold the other harmless from and against any claims by any Broker,
other than the brokers named in this Section 35, 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.

     36. 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 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 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.

     37. 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. It is also the intention of the parties to this Lease
that in lieu of each clause or provision of this Lease that is illegal, invalid
or unenforceable, there be added, as a part of this Lease, a clause or provision
as similar in effect to such illegal, invalid or unenforceable clause or
provision as shall be legal, valid and enforceable.

     38. SIGNS; EXTERIOR APPEARANCE. Tenant shall not, without the prior written
consent of Landlord, which may be granted or withheld in Landlord's reasonable
discretion: (i) attach any awnings, exterior lights, decorations, balloons,
flags, pennants, banners, painting, telecommunications equipment or other
projection to the roof or any outside wall of the Project, (ii) coat or
otherwise sunscreen the interior or exterior of any windows, or (iii) paint,
affix or exhibit on any part of the Premises or the Project any signs, notices,
window or door lettering, placards, decorations, or advertising media of any
type which can be viewed from the exterior of the Premises. Tenant shall have
the right to install Tenant's sign placard (subject to Landlord's reasonable
review and approval and to compliance with all applicable Legal Requirements) on
the existing monument sign at the entrance to the Building and to install any
such interior signage within the Building as Tenant may require, all at Tenant's
sole cost and expense.

     39. 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 one consecutive right (the
"EXTENSION RIGHTS") to extend the term of this Lease for five years each (the
"EXTENSION TERM") on the same terms and conditions as this Lease (other than
Base Rent) by giving Landlord written notice of its election to exercise the
Extension Rights at least twelve months prior, and no earlier than fifteenth
months prior, to the expiration of the Base Term of the Lease or the expiration
of any prior Extension Term.

<PAGE>

                               167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 25

Upon the commencement of the Extension Term, Base Rent shall be payable in an
amount equal to the greater of (i) 95% of the then-current Market Rate (as
defined below), and (ii) the Base Rent payable during the final year of the
original Term. Thereafter, Base Rent shall be adjusted on each annual
anniversary of the commencement of such Extension Term by multiplying the Base
Rent payable immediately before such adjustment by the Rent Adjustment
Percentage and adding the resulting amount to the Base Rent payable immediately
before such adjustment. As used herein, "MARKET RATE" shall mean the then fair
market rental rate (taking into account, among other relevant factors, Tenant's
obligations hereunder and the condition of the Building) as determined by
Landlord and agreed to by Tenant or determined by arbitration as hereinafter set
forth, which shall in no event be less than the Base Rent payable as of the date
immediately preceding the commencement of such Extension Term increased by the
Rent Adjustment Percentage multiplied by such Base Rent.

     If, on or before the date which is 120 days prior to the expiration of the
Base Term of this Lease, or the expiration of any prior Extension Term, Tenant
has not agreed with Landlord's determination of the Market Rate and the rent
escalations during such subsequent Extension Term after negotiating in good
faith, Tenant may by written notice to Landlord not later than 120 days prior to
the expiration of the Base Term of this Lease, or the expiration of any then
effective Extension Term, elect arbitration as described in Section 39(b) below.
If Tenant does not elect such arbitration, Tenant shall be deemed to have waived
any right to extend, or further extend, the Term of the Lease and all of the
remaining Extension Rights shall terminate.]

          (b) ARBITRATION.

               (i) Within 10 days of Tenant's notice to Landlord of its election
to arbitrate Market Rate and escalations, each party shall deliver to the other
a proposal containing the Market Rate and escalations that the submitting party
believes to be correct ("EXTENSION PROPOSAL"). If either party fails to timely
submit an Extension Proposal, the other party's submitted proposal shall
determine the Base Rent and escalations for the Extension Term. If both parties
submit Extension Proposals, then Landlord and Tenant shall meet within 7 days
after delivery of the last Extension Proposal and make a good faith attempt to
mutually appoint a single Arbitrator (and defined below) to determine the Market
Rate and escalations. If Landlord and Tenant are unable to agree upon a single
Arbitrator, then each shall, by written notice delivered to the other within 10
days after the meeting, select an Arbitrator. If either party fails to timely
give notice of its selection for an Arbitrator, the other party's submitted
proposal shall determine the Base Rent for the Extension Term. The 2 Arbitrators
so appointed shall, within 5 business days after their appointment, appoint a
third Arbitrator. If the 2 Arbitrators so selected cannot agree on the selection
of the third Arbitrator within the time above specified, then either party, on
behalf of both parties, may request such appointment of such third Arbitrator by
application to any state court of general jurisdiction in the jurisdiction in
which the Premises are located, upon 10 days prior written notice to the other
party of such intent.

               (ii) The decision of the Arbitrator(s) shall be made within 30
days after the appointment of a single Arbitrator or the third Arbitrator, as
applicable. The decision of the single Arbitrator shall be final and binding
upon the parties. The average of the two closest Arbitrators in a three
Arbitrator panel shall be final and binding upon the parties. Each party shall
pay the fees and expenses of the Arbitrator appointed by or on behalf of such
party and the fees and expenses of the single Arbitrator or the third Arbitrator
shall be borne equally by both parties. If the Market Rate and escalations are
not determined by the first day of the Extension Term, then Tenant shall pay
Landlord Base Rent in an amount equal to the Base Rent in effect immediately
prior to the Extension Term and increased by the Rent Adjustment Percentage
until such determination is made. Within 30 days after the determination of the
Market Rate and escalations, the parties shall make any necessary adjustments to
such payments made by Tenant. Landlord and Tenant shall then execute an
amendment recognizing the Market Rate and escalations for the Extension Term.

               (iii) An "ARBITRATOR" shall be any person appointed by or on
behalf of either party or appointed pursuant to the provisions hereof and: (i)
shall be (A) a member of the American

<PAGE>

                               167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 26

Institute of Real Estate Appraisers with not less than 10 years of experience in
the appraisal of improved office and high tech industrial real estate in the
Cambridge, Massachusetts area, or (B) a licensed commercial real estate broker
with not less than 15 years experience representing landlords and/or tenants in
the leasing of high tech or life sciences space in the Cambridge, Massachusetts
area, (ii) devoting substantially all of their time to professional appraisal or
brokerage work, as applicable, at the time of appointment and (iii) be in all
respects impartial and disinterested.

          (c) RIGHTS PERSONAL. Extension Rights are personal to Tenant
(including any Permitted Assignee pursuant to Section 22(c) hereof) and are not
assignable without Landlord's consent, which may be granted or withheld in
Landlord's sole discretion separate and apart from any consent by Landlord to an
assignment of Tenant's interest in the Lease.

          (d) EXCEPTIONS. Notwithstanding anything set forth above to the
contrary, Extension Rights shall not be in effect and Tenant may not exercise
any of the Extension Rights:

               (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 3 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 an
Extension Rights, whether or not the Defaults are cured.

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

          (f) TERMINATION. The Extension Rights shall terminate and be of no
further force or effect even after Tenant's due and timely exercise of an
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 3 or more times during the period from
the date of the exercise of an Extension Rights to the date of the commencement
of the Extension Term, whether or not such Defaults are cured.

     40. MISCELLANEOUS.

          (a) NOTICES. All notices or other communications between the parties
shall be in writing and, if delivered in person, shall be deemed duly given upon
delivery or refusal to accept delivery by the addressee thereof, or if delivered
by reputable overnight guaranty courier, addressed and sent to the parties at
their addresses set forth above, shall be deemed duly given upon actual receipt
or refusal to accept delivery by the addressee thereof. In either case, notices
shall be deemed duly given when delivery is first attempted but cannot be
completed because of a changed address, notice of which was not given hereunder.
Landlord and Tenant may from time to time by written notice to the other
designate another address for receipt of future notices.

          (b) JOINT AND SEVERAL LIABILITY. If and when included within the term
"TENANT," as used in this instrument, there is more than one person or entity,
each shall be jointly and severally liable for the obligations of Tenant.

          (c) FINANCIAL INFORMATION. Tenant shall furnish Landlord with true and
complete copies of (i) Tenant's most recent audited annual financial statements
within 45 days of the end of each of Tenant's fiscal years during the Term, (ii)
Tenant's most recent unaudited quarterly financial statements within 45 days of
the end of each of Tenant's first three fiscal quarters of each of Tenant's
fiscal years during the Term, (iii) at Landlord's request from time to time,
updated business plans, including cash flow projections and/or pro forma balance
sheets and income statements, all of which shall be treated by Landlord as
confidential information belonging to Tenant, (iv) corporate brochures and/or
profiles

<PAGE>

                               167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 27

prepared by Tenant for prospective investors, and (v) any other financial
information or summaries that Tenant typically provides to its lenders or
shareholders. Notwithstanding the foregoing, for so long as Tenant remains a
publicly traded company, Tenant's periodic filings with the Securities and
Exchange Commission shall satisfy the requirements of this section.

          (d) RECORDATION. This Lease shall not be filed by or on behalf of
Landlord or Tenant in any public record. Either party shall, upon written
request of the other, join in the execution of a recordable notice of this Lease
in statutory form.

          (e) 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. Words of any gender used in this Lease shall be held and construed to
include any other gender, and words in the singular number shall be held to
include the plural, unless the context otherwise requires. The captions inserted
in this Lease are for convenience only and in no way define, limit or otherwise
describe the scope or intent of this Lease, or any provision hereof, or in any
way affect the interpretation of this Lease.

          (f) 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.

          (g) 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.

          (h) 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.

          (i) NO WAIVER. No waiver by either party of any provision of this
Lease shall be deemed to have been made unless expressed in writing and signed
by such party.

          (j) TIME. Time is of the essence as to the performance of each party's
obligations under this Lease.

          (k) INCORPORATION BY REFERENCE. All exhibits and addenda attached
hereto are hereby incorporated into this Lease and made a part hereof. If there
is any conflict between such exhibits or addenda and the terms of this Lease,
such exhibits or addenda shall control.

          (l) Notwithstanding any other provision of this Lease, Landlord, for
itself and its employees, agents and contractors, reserves the right to refuse
to perform any repairs or services in any portion of the Premises which,
pursuant to Tenant's routine safety guidelines, practices or custom or prudent
industry practices, require any form of protective clothing or equipment other
than safety glasses. In any such case, Tenant shall contract with parties who
are acceptable to Landlord, in Landlord's reasonable discretion, for all such
repairs and services.

<PAGE>

                               167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 28

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

                                        TENANT:

                                        IDERA PHARMACEUTICALS, INC.,
                                        a Delaware corporation

                                        By: /S/ SUDHIR AGRAWAL
                                            ------------------------------------
                                        Its: Chief Executive Officer

                                        LANDLORD:

                                        ARE-MA REGION NO. 23, LLC, a Delaware
                                        limited liability company

                                        By: Alexandria Real Estate Equities,
                                            L.P., a Delaware limited
                                            partnership, managing member

                                        By: ARE-QRS Corp., a Maryland
                                            corporation, general partner

                                        By: /S/ JENNIFER PAPPAS
                                            ------------------------------------
                                        Its: Vice President, Assistant
                                             Secretary

<PAGE>

                                167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 1

                               EXHIBIT A TO LEASE

                             DESCRIPTION OF PREMISES

                                  (FLOOR PLAN)

                                   First Floor

                                  (FLOOR PLAN)

                                  Second Floor
<PAGE>

                                167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 1

                               EXHIBIT B TO LEASE

                             DESCRIPTION OF PROJECT

PARCEL A

PARCEL ONE

<TABLE>
<S>             <C>
SOUTHEASTERLY   by Sidney Street, 206.40 feet;

SOUTHWESTERLY   by Erie Street, 139.75 feet;

NORTHWESTERLY   by the middle line of a common passageway
                between the granted parcel and Lot A1 as shown
                on the plan hereinafter mentioned, 208.17 feet;
                and

NORTHEASTERLY   by lot marked "B2" as shown on the plan
                hereinafter mentioned by two courses, 68.88
                feet and 84.00 feet, respectively.
</TABLE>

Being shown as Lot A2 on "Plan of Land in Cambridge, Mass. surveyed for Stimpson
Investment Corp." by W.A. Mason & Sons Co. Surveyors dated December 30, 1947 and
recorded with the Middlesex Southern District Registry of Deeds at the end of
Book 7237.

PARCEL TWO

<TABLE>
<S>             <C>
NORTHWESTERLY   by Sidney Street, 100.20 feet;

SOUTHWESTERLY   by Erie Street, 60.00 feet;

SOUTHEASTERLY   by a line parallel to the first mentioned
                bound, 100.20 feet; and

NORTHEASTERLY   by land now or formerly of Carcano and Wells &
                Dana, Trustees, 60 feet.
</TABLE>

PARCEL B

Appurtenant to Parcels 1 and 2 above are the benefits of passageway rights set
forth in the Declaration of Reciprocal Easements and Covenants by and between
HFS Investment, L.L.C., 99 Erie Street L.L.C. and John W. Stimpson & J. Louis
Newell, Jr., as Trustees under the Will of Harry F, Stimpson being Norfolk
County Probate Case No. 99898 dated October 21, 2005 and recorded with the
Middlesex South District Registry of Deeds in Book 46323, Page 233.

<PAGE>

                                167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 1

                               EXHIBIT C TO LEASE

                                   WORK LETTER

     THIS WORK LETTER dated ________________, 2006 (this "WORK LETTER") is made
and entered into by and between ARE-MA Region No. 23, LLC, a Delaware limited
liability company ("LANDLORD"), and Idera Pharmaceuticals, Inc., a Delaware
corporation ("TENANT"), and is attached to and made a part of the Lease dated
_______________, 2006 (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.

     1. GENERAL REQUIREMENTS.

          (a) TENANT'S AUTHORIZED REPRESENTATIVE. Tenant designates Robert
Andersen ("TENANT'S REPRESENTATIVE") as the only person authorized to act for
Tenant pursuant to this Work Letter. Landlord shall not be obligated to respond
to or act upon any request, approval, inquiry or other communication
("COMMUNICATION") from or on behalf of Tenant in connection with this Work
Letter unless such Communication is in writing from Tenant's Representative.
Tenant may change Tenant's Representative at any time upon not less than 5
business days advance written notice to Landlord. Neither Tenant nor Tenant's
Representative shall be authorized to direct Landlord's contractors in the
performance of Landlord's Work (as hereinafter defined).

          (b) LANDLORD'S AUTHORIZED REPRESENTATIVE. Landlord designates Tom
Andrews and Stu Berry (either such individual acting alone, "LANDLORD'S
REPRESENTATIVE") as the only persons authorized to act for Landlord pursuant to
this Work Letter. Tenant shall not be obligated to respond to or act upon any
request, approval, inquiry or other Communication from or on behalf of Landlord
in connection with this Work Letter unless such Communication is in writing from
Landlord's Representative. Landlord may change either Landlord's Representative
at any time upon not less than 5 business days advance written notice to Tenant.
Landlord's Representative shall be the sole persons authorized to direct
Landlord's contractors in the performance of Landlord's Work.

          (c) ARCHITECTS, CONSULTANTS AND CONTRACTORS. Landlord and Tenant
hereby acknowledge and agree that: (i) Margolis + Fishman Inc. shall be the
architect (the "TI ARCHITECT") for the Tenant Improvements, and (ii) The
Richmond Group, Inc., shall be the construction manager (the "TI CONSTRUCTION
MANAGER"), and (iii) any subcontractors for the Tenant Improvements shall be
selected by Landlord.

     2. TENANT IMPROVEMENTS.

          (a) DEFINITIONS. As used herein, "TENANT IMPROVEMENTS" shall mean all
improvements to the Project as shown on the TI Permit Drawings, as defined in
Section 2(b) below, and approved by Landlord and Tenant in accordance with this
Work Letter, exclusive of the improvements described on Schedule A attached
hereto ("LANDLORD'S BASE BUILDING WORK"). "LANDLORD'S WORK" shall mean the work
of constructing the Landlord's Base Building Work and the Tenant Improvements.
The Tenant Improvements are described on the attached Schedule B (the
"PRELIMINARY TI PLANS"). Landlord and Tenant have each approved the Preliminary
TI Plans. Based on the Preliminary TI Plans, the TI Construction Manager has
prepared a budget showing an estimated cost of the Tenant Improvements of
$3,523,641 (the "TI BUDGET"). Other than the Tenant Improvements, any approved
Changes (as defined in Section 4(a) below), and Landlord's Base Building Work,
Landlord shall not have any obligation whatsoever with respect to the finishing
of the Premises for Tenant's use and occupancy.

          (b) PERMIT DRAWINGS. Not later than thirty (30) days following the
execution and delivery of the Lease, Landlord shall cause the TI Architect to
prepare and deliver to Tenant for review and comment construction plans,
specifications and drawings for the Tenant Improvements ("TI PERMIT

<PAGE>

                                167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 2

DRAWINGS"), which TI Permit Drawings shall be prepared substantially in
accordance with the Preliminary TI Plans. In all other respects, Tenant shall be
solely responsible for ensuring that the TI Permit Drawings reflect Tenant's
requirements for the Tenant Improvements. Tenant shall deliver its written
comments on the TI Permit Drawings to Landlord not later than 10 business days
after Tenant's receipt of the same; provided, however, that Tenant may not
disapprove any matter that is consistent with the Preliminary TI Plans without
submitting a Change Request. Landlord, the TI Architect and the TI Construction
Manager shall consider all such comments in good faith and shall, within 10
business days after receipt, notify Tenant how Landlord proposes to respond to
such comments, but, so long as the design reflected in the TI Permit Drawings is
consistent with the Preliminary TI Plans, Tenant's review rights pursuant to the
foregoing sentence shall not (a) delay the design or construction schedule, or
(b) except pursuant to a Change Request, increase the cost of the Tenant
Improvements to an amount greater than the TI Budget. Any disputes in connection
with such comments shall be resolved in accordance with Section 2(c) hereof.
Provided that the design reflected in the TI Permit Drawings is consistent with
the Preliminary TI Plans, Tenant shall approve the TI Permit Drawings submitted
by Landlord, unless Tenant submits a Change Request. Once approved by Tenant,
the TI Permit Drawings shall not be materially modified except as may be
reasonably required in connection with the issuance of the TI Permit (as defined
in Section 3(a) below), or by processing of a Change Request (as defined in
Section 4(a) below).

          (c) APPROVAL AND COMPLETION. It is hereby acknowledged by Landlord and
Tenant that the TI Permit Drawings must be completed and approved not later than
November 30, 2006, in order for the Landlord's Work to be Substantially Complete
(as defined in Section 3(b) below) by the Target Commencement Date (as defined
in the Lease). Upon any dispute regarding the design of the Tenant Improvements,
which is not settled within 10 business days after notice of such dispute is
delivered by one party to the other, Tenant may make the final decision
regarding the design of the Tenant Improvements, provided (i) Tenant acts
reasonably and such final decision is either consistent with or a compromise
between Landlord's and Tenant's positions with respect to such dispute, (ii)
Tenant's decision will not increase the cost of the Tenant Improvements to an
amount greater than the TI Budget, except pursuant to a Change Request, so long
as the design reflected in the TI Permit Drawings is consistent with the
Preliminary TI Plans, and (iii) Tenant's decision will not adversely affect the
base Building, structural components of the Building or any Building Systems (as
defined in Section 14 of the Lease); or Landlord's Base Building Work. Any
changes to the TI Permit Drawings requested by Tenant following Landlord's and
Tenant's approval of same shall be processed as provided in Section 4 hereof.

     3. PERFORMANCE OF LANDLORD'S WORK.

          (a) COMMENCEMENT AND PERMITTING. Landlord shall commence construction
of the Tenant Improvements upon obtaining a building permit (the "TI PERMIT")
authorizing the construction of the Tenant Improvements consistent with the TI
Permit Drawings approved by Tenant. The cost of obtaining the TI Permit shall be
paid by Landlord as part of the cost of the Tenant Improvements. Tenant shall,
as and when requested and without having to incur any additional expense,
reasonably assist Landlord in obtaining the TI Permit. If any Governmental
Authority having jurisdiction over the construction of Landlord's Work or any
portion thereof shall impose terms or conditions upon the construction thereof
that: (i) are inconsistent with Landlord's obligations hereunder, (ii) increase
the cost of constructing Landlord's Work (if such term or condition is imposed
as a result of a Change in the Preliminary TI Plans requested by Tenant), or
(iii) will materially delay the construction of Landlord's Work, Landlord and
Tenant shall reasonably and in good faith seek means by which to mitigate or
eliminate any such adverse terms and conditions.

          (b) COMPLETION OF LANDLORD'S WORK. On or before the Target
Commencement Date (subject to Tenant Delays and Force Majeure Delays), Landlord
shall substantially complete or cause to be substantially completed Landlord's
Work in a good and workmanlike manner, in accordance with the TI Permit and
applicable Legal Requirements (including, without limitation, the obtaining of
any required certificate of use and occupancy with respect to the Landlord's
Work), subject, in each case, to Minor Variations and normal "punch list" items
of a non-material nature that do not interfere with the use of the Premises
("SUBSTANTIAL COMPLETION" or "SUBSTANTIALLY COMPLETE"). Upon Substantial
Completion

<PAGE>

                                167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 3

of Landlord's Work, Landlord shall require the TI Architect and the TI
Construction Manager to execute and deliver, for the benefit of Tenant and
Landlord, a Certificate of Substantial Completion in the form of the American
Institute of Architects ("AIA") document G704. For purposes of this Work Letter,
"MINOR VARIATIONS" shall mean any modifications reasonably required: (i) to
comply with all applicable Legal Requirements and/or to obtain or to comply with
any required permit (including the TI Permit); (ii) to comply with any request
by Tenant for modifications to Landlord's Work; (iii) to comport with good
design, engineering, and construction practices that are not material; or (iv)
to make reasonable adjustments for field deviations or conditions encountered
during the construction of Landlord's Work.

          (c) SELECTION OF MATERIALS. Where more than one type of material or
structure is indicated on the TI Permit Drawings approved by Landlord and
Tenant, the option will be selected at Landlord's sole and absolute subjective
discretion. As to all building materials and equipment that Landlord is
obligated to supply under this Work Letter, Landlord shall select the
manufacturer thereof in its sole and absolute subjective discretion.

          (d) DELIVERY OF THE PREMISES. When Landlord's Work is Substantially
Complete, subject to the remaining terms and provisions of this Section 3(d),
Tenant shall accept the Premises. Tenant's taking possession and acceptance of
the Premises shall not constitute a waiver of: (i) any warranty with respect to
workmanship (including installation of equipment) or material (exclusive of
equipment provided directly by manufacturers), (ii) any non-compliance of
Landlord's Work with applicable Legal Requirements, or (iii) any claim that
Landlord's Work was not completed substantially in accordance with the TI Permit
Drawings (subject to Minor Variations and such other changes as are permitted
hereunder) (collectively, a "CONSTRUCTION DEFECT"). Tenant shall have one year
after Substantial Completion within which to notify Landlord of any such
Construction Defect discovered by Tenant, and Landlord shall remedy or cause the
responsible contractor to remedy any such Construction Defect within 30 days
thereafter (or such additional time as may be reasonably necessary to permit
Landlord to remedy or cause the responsible contractor to remedy such
Construction Defect); provided, however, that Landlord's obligation to remedy or
cause the responsible contractor to remedy such Construction Defect shall be
Landlord's sole obligation hereunder and Tenant hereby waives any claim against
Landlord for any injuries to persons or damage to the Premises or any personal
property of Tenant or any employee of Tenant located in the Premises arising
from any such Construction Defect.

Tenant shall be entitled to receive the benefit of all construction warranties
and manufacturer's equipment warranties relating to equipment installed in the
Premises. If requested by Tenant, Landlord shall attempt to obtain extended
warranties from manufacturers and suppliers of such equipment, provided,
however, that, if the cost of such extended warranties shall cause the cost of
the Tenant Improvements to exceed the TI Budget, Landlord shall promptly so
notify Tenant and Landlord shall not be required to obtain such extended
warranties unless Tenant pays such excess cost. Landlord shall promptly
undertake and complete, or cause to be completed, all punch list items.

          (e) COMMENCEMENT DATE DELAY. Except as otherwise provided in the
Lease, Delivery of the Premises shall occur when Landlord's Work has been
Substantially Completed, except to the extent that completion of Landlord's Work
shall have been actually delayed by any one or more of the following causes
("TENANT DELAY"):

               (i) Tenant's Representative was not available to give or receive
any Communication or to take any other action required to be taken by Tenant
hereunder;

               (ii) Tenant's request for Change Requests (as defined in Section
4(a) below) whether or not any such Change Requests are actually performed;

               (iii) Construction of any Change Requests;

<PAGE>

                                167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 4

               (iv) Tenant's request for materials, finishes or installations
requiring unusually long lead times, but only if Landlord notifies Tenant of
such requirement promptly after receiving such request and Tenant fails to
withdraw such request within 3 business days after receiving such notice;

               (v) Tenant's delay in reviewing, revising or approving plans and
specifications beyond the periods set forth herein;

               (vi) Tenant's delay in providing information critical to the
normal progression of the project. Tenant shall provide such information as soon
as reasonably possible, but in no event longer than one week after receipt of
any request for such information from Landlord;

               (vii) Tenant's delay in making payments to Landlord for Excess TI
Costs (as defined in Section 5(b) below); or

               (viii) Any other act or omission by Tenant or any Tenant Party
(as defined in the Lease), or persons employed by any of such persons which does
not arise from Landlord's failure to comply with Landlord's obligations
hereunder.

If Delivery is delayed for any of the foregoing reasons, then Landlord shall
cause the TI Architect to certify in good faith the date on which the Tenant
Improvements would have been completed but for such Tenant Delay and such
certified date shall be the date of Delivery.

     4. CHANGES. Any Changes (as defined in Section 4(a) below) requested by
Tenant to the Tenant Improvements shall be requested and instituted in
accordance with the provisions of this Section 4 and shall be subject to the
written approval of Landlord and the TI Architect, such approval not to be
unreasonably withheld, conditioned or delayed.

          (a) TENANT'S REQUEST FOR CHANGES. If Tenant shall request changes to
the Tenant Improvements (each, a "CHANGE"), Tenant shall request such Changes by
notifying Landlord in writing in substantially the same form as the AIA standard
change order form (a "CHANGE REQUEST"), which Change Request shall detail the
nature and extent of any such Change. Such Change Request must be signed by
Tenant's Representative. Landlord shall, before proceeding with any Change, use
commercially reasonable efforts to respond to Tenant as soon as is reasonably
possible with an estimate of: (i) the time it will take, and (ii) the
architectural and engineering fees and costs that will be incurred, to analyze
such Change Request (which costs shall be paid from the Excess TI Fund [as
defined in Section 5(b) hereof] to the extent actually incurred, whether or not
such change is implemented). Landlord shall thereafter submit to Tenant in
writing, within 5 business days of receipt of the Change Request (or such longer
period of time as is reasonably required depending on the extent of the Change
Request), an analysis of the additional cost or savings involved, including,
without limitation, architectural and engineering costs and the period of time,
if any, that the Change will extend the date on which Landlord's Work will be
Substantially Complete. Any such delay in the completion of Landlord's Work
caused by a Change, including any suspension of Landlord's Work while any such
Change is being evaluated and/or designed, shall be a Tenant Delay.

          (b) IMPLEMENTATION OF CHANGES. If Tenant: (i) approves in writing the
cost or savings and the estimated extension in the time for completion of
Landlord's Work, if any, and (ii) deposits with Landlord any Excess TI Costs (as
defined in Section 5(b) hereof) required in connection with such Change,
Landlord shall cause the approved Change to be instituted. Notwithstanding any
approval or disapproval by Tenant of any estimate of the delay caused by such
proposed Change, the TI Architect's good faith determination of the amount of
Tenant Delay in connection with such Change shall be final and binding on
Landlord and Tenant.

<PAGE>

                                167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 5

     5. COSTS.

          (a) TI COSTS. "TI COSTS" shall include all costs incurred in
connection with the design and construction of the Tenant Improvements,
including, without limitation, (i) the cost of preparing the Preliminary TI
Plans, the TI Permit Drawings and any additional required plans or drawings, and
(ii) all construction costs and equipment and installation costs. Landlord shall
pay for the TI Costs, subject to the provisions of Section 5(b) hereof.

          (b) EXCESS TI COSTS. "EXCESS TI COSTS" shall include (a) all costs
incurred in connection with the design and construction of Changes, net of any
savings achieved on account of the applicable Change, and (b) Landlord's
out-of-pocket expenses resulting from Tenant Delays. Promptly upon Tenant's
approval thereof, in the case of Changes, or upon Landlord's notice specifying
Landlord's estimated out-of-pocket expenses resulting from Tenant Delays, Tenant
shall pay to Landlord an amount adequate to cover 100% of the Excess TI Costs
(such amount, the "EXCESS TI FUND"). If Tenant fails to deposit, or is late in
depositing, the Excess TI Fund 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.

          (c) DISBURSEMENTS. Landlord shall pay the TI Costs incurred during the
design and construction of the Tenant Improvements and, to the extent Tenant has
funded the Excess TI Costs as provided in Section 5(b) hereof, Landlord shall
pay the cost of Changes. Notwithstanding anything to the contrary set forth in
this Section 5(c), Tenant shall be fully and solely liable for the Excess TI
Costs. Landlord shall provide for at least 5% retainage to be held from the TI
Construction Manager and the construction subcontractors until the time of final
completion (i.e., the completion of punchlist items), and shall obtain final
lien waivers from the TI Construction Manager and the construction
subcontractors upon issuance of final payments thereto. If upon completion of
the Tenant Improvements and any Changes and the payment of all sums due in
connection therewith there remain any undisbursed funds in the Excess TI Fund,
Landlord shall return to Tenant such undisbursed Excess TI Fund solely to the
extent of any Excess TI Costs deposit Tenant has actually made with Landlord.
Tenant shall be entitled to review, at Landlord's office, all records maintained
by or under the control of Landlord regarding the determination of TI Costs and
Excess TI Costs.

     6. TENANT ACCESS.

          (a) TENANT'S ACCESS RIGHTS. Landlord hereby agrees to permit Tenant
access, at Tenant's sole risk and expense, to the Building (i) prior to the
Commencement Date to perform any work ("TENANT'S WORK") required by Tenant other
than Landlord's Work, provided that such entry and Tenant's Work are coordinated
with the TI Architect and the TI Construction Manager, and comply with the Lease
and all other reasonable restrictions and conditions Landlord may impose, and
(ii) prior to the completion of Landlord's Work, to inspect and observe work in
process; all such access shall be during normal business hours or at such other
times as are reasonably designated by Landlord. Notwithstanding the foregoing,
Tenant shall have no right to enter onto the Premises or the Project unless and
until Tenant shall deliver to Landlord evidence reasonably satisfactory to
Landlord demonstrating that any insurance reasonably required by Landlord in
connection with such pre-commencement access (including, but not limited to, any
insurance that Landlord may require pursuant to the Lease) is in full force and
effect. Any entry by Tenant shall comply with all established safety practices
of the TI Construction Manager and Landlord until completion of Landlord's Work
and acceptance thereof by Tenant. Tenant shall have no obligation to pay Rent
during any early entry into the Premises under this Section 6(a).

          (b) NO INTERFERENCE. Neither Tenant nor any Tenant Party (as defined
in the Lease) shall interfere with the performance of Landlord's Work, nor with
any inspections or issuance of final approvals by applicable Governmental
Authorities, and upon any such interference, Landlord shall have the right to
exclude Tenant and any Tenant Party from the Premises and the Project to the
extent

<PAGE>

                                167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 6

necessary, in Landlord and TI Construction Manager's sole judgment, to
prevent delays in the performance and completion of Landlord's Work.

          (c) NO ACCEPTANCE OF PREMISES. The fact that Tenant may, with
Landlord's consent, enter into the Project prior to the date Landlord's Work is
Substantially Complete for the purpose of performing Tenant's Work shall not be
deemed an acceptance by Tenant of possession of the Premises, but in such event
Tenant shall defend with counsel reasonably acceptable by Landlord, indemnify
and hold Landlord harmless from and against any loss of or damage to Tenant's
property, completed work, fixtures, equipment, materials or merchandise, and
from liability for death of, or injury to, any person, caused by the act or
omission of Tenant or any Tenant Party.

     7. MISCELLANEOUS.

          (a) CONSENTS. Whenever consent or approval of either party is required
under this Work Letter, that party shall not unreasonably withhold, condition or
delay such consent or approval, unless expressly set forth herein to the
contrary.

          (b) MODIFICATION. No modification, waiver or amendment of this Work
Letter or of any of its conditions or provisions shall be binding upon Landlord
or Tenant unless in writing signed by Landlord and Tenant.

          (c) COUNTERPARTS. This Work Letter may be executed in any number of
counterparts but all counterparts taken together shall constitute a single
document.

          (d) GOVERNING LAW. This Work Letter shall be governed by, construed
and enforced in accordance with the internal laws of the state in which the
Premises are located, without regard to choice of law principles of such State.

          (e) TIME OF THE ESSENCE. Time is of the essence of this Work Letter
and of each and all provisions thereof.

          (f) DEFAULT. Notwithstanding anything set forth herein or in the Lease
to the contrary, Landlord shall not have any obligation to perform any work
hereunder or to fund any portion of the TI Costs during any period Tenant is in
Default under the Lease.

          (g) SEVERABILITY. If any term or provision of this Work Letter is
declared invalid or unenforceable, the remainder of this Work Letter shall not
be affected by such determination and shall continue to be valid and
enforceable.

          (h) MERGER. All understandings and agreements, oral or written,
heretofore made between the parties hereto and relating to the Tenant
Improvements and Tenant's Work are merged in this Work Letter, which alone (but
inclusive of provisions of the Lease incorporated herein and the final approved
constructions drawings and specifications prepared pursuant hereto) fully and
completely expresses the agreement between Landlord and Tenant with regard to
the matters set forth in this Work Letter.

          (i) ENTIRE AGREEMENT. This Work Letter is made as a part of and
pursuant to the Lease and, together with the Lease, constitutes the entire
agreement of the parties with respect to the subject matter hereof. This Work
Letter is subject to all of the terms and limitation set forth in the Lease, and
neither party shall have any rights or remedies under this Work Letter separate
and apart from their respective remedies pursuant to the Lease.

<PAGE>

                                167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 1

                               EXHIBIT D TO LEASE

                       ACKNOWLEDGMENT OF COMMENCEMENT DATE

     This ACKNOWLEDGMENT OF COMMENCEMENT DATE is made as of this _____ day of
_____________, 2006, between ARE-MA Region No. 23, LLC, a Delaware limited
liability company ("LANDLORD"), and Idera Pharmaceuticals, Inc., a Delaware
corporation ("TENANT"), and is attached to and made a part of the Lease dated as
of ____________, 2006 (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:

                                        IDERA PHARMACEUTICALS, INC.,
                                        a Delaware corporation

                                        By:
                                            ------------------------------------
                                        Its:
                                             -----------------------------------

                                        LANDLORD:

                                        ARE-MA REGION NO. 23, LLC, a Delaware
                                        limited liability company

                                        By: Alexandria Real Estate Equities,
                                            L.P., a Delaware limited
                                            partnership, managing member

                                        By: ARE-QRS Corp., a Maryland
                                            corporation, general partner

                                        By:
                                            ------------------------------------
                                        Its:
                                             -----------------------------------

<PAGE>

                                167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 1

                               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. Except as may be otherwise permitted in the Lease, 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. Tenant shall not disturb the occupants of adjoining buildings by the use
of any radio or musical instrument or by the making of loud or improper noises.

     4. 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 without Landlord's consent, which shall not
be unreasonably withheld or delayed. Any such installation or connection shall
be made at Tenant's expense.

     5. 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.

     6. 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.

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

     8. 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.

     9. 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 if, in Tenant's
reasonable judgment, any such defect may result in damage to the structure of
the Premises or to the sidewalks or parking lot surrounding the Premises.

     10. 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.

     11. 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.

     12. No auction, public or private, will be permitted on the Premises or the
Project without Landlord's prior written consent.

     13. No awnings shall be placed over the windows in the Premises except with
the prior written consent of Landlord pursuant to the applicable provisions of
the Lease.

<PAGE>

                                167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 2

     14. The Premises shall not be used for lodging or cooking (except for
microwave ovens and other appliances not requiring exterior venting, which
Tenant shall be permitted to install in the Premises, and otherwise as an
appurtenance to the Permitted Use as approved by Landlord in advance, which
approval shall not be unreasonably withheld or delayed) or for any illegal
purposes or for any purpose other than that specified in the Lease. No gaming
devices shall be operated in the Premises.

     15. 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.

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

     17. 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>

                                167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 1

                               EXHIBIT F TO LEASE

                           TENANT'S PERSONAL PROPERTY

None

<PAGE>

                                167 SIDNEY STREET/IDERA PHARMACEUTICALS - PAGE 1

                               EXHIBIT G TO LEASE

                              ENVIRONMENTAL REPORTS

     1. Phase I Environmental Site Assessment Report, prepared by Rizzo
Associates ("Rizzo"), dated January 4, 2003;

     2. Limited Subsurface Investigation Report, prepared by Rizzo, dated April
29, 2005;

     3. Human Health and Environmental Risk Characterization Report, prepared by
Rizzo, dated September 16, 2005;

     4. Human Health and Environmental Risk Characterization Report, prepared by
Rizzo, dated August 15, 2005;

     5. Response Action Outcome Statement Report, prepared by Rizzo, dated
October 7, 2005;

     6. Response Action Outcome Statement Report, prepared by Rizzo, dated
August 17, 2005;

     7. Underground Storage Tank Investigation Letter Report, prepared by Rizzo,
dated October 14, 2005;

     8. Immediate Response Action Plan Report, prepared by ENVIRON International
Corporation, dated October, 2005; and

     9. Asbestos Inspection Report, prepared by Covino Environmental Associates
Inc., dated November 17, 2005.

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