EXHIBIT 10.5


FOURTH AMENDMENT TO PURCHASE AND SALE CONTRACT


THIS FOURTH AMENDMENT TO PURCHASE AND SALE CONTRACT ("Amendment") is
entered into as of July 27, 2006, by and between TECHNOLOGY SQUARE FINANCE, LLC,
a Massachusetts limited liability company ("Seller") and ARE-MA REGION
NO. 31, LLC, a Delaware limited liability company ("Buyer").  


R E C I T A L S


WHEREAS, Seller and Buyer entered into that certain Purchase and Sale
Contract dated as of July 3, 2006, as amended by a First Amendment to Purchase
and Sale Contract (the "First Amendment") dated as of July 10, 2006, a
Second Amendment to Purchase and Sale Contract (the "Second Amendment")
dated as of July 14, 2006, and a Third Amendment to Purchase and Sale Contract
dated as of July 26, 2006  (the "Third Amendment")(as so amended, the
"Agreement") with respect to certain real and personal property (the
"Property") located at Technology Square, Cambridge, Massachusetts, which
Property is more particularly described in the Agreement; and 


WHEREAS, Seller and Buyer have agreed to amend the Agreement as more
particularly set forth below.


NOW, THEREFORE, for mutual consideration, the receipt and sufficiency of
which are hereby acknowledged by the parties, Seller and Buyer hereby amend the
Agreement as follows:


1.  Capitalized Terms.  Capitalized terms not defined herein shall have
the meanings ascribed to them in the Agreement.


2.  Extension of Closing Date.  The first paragraph of Article 6 of the
Agreement is hereby amended by deleting therefrom the date "July 27, 2006" and
replacing it with the date "July 28, 2006."


3.  Post-Closing Reconciliation.  The parties hereby acknowledge and
agree that all prorations with respect to the Closing shall be made as of July
28, 2006.  The parties hereby further acknowledge and agree that for the purpose
of Closing, they shall continue to use the 7th Revised Bilateral Settlement
Statement, which contemplates a closing date of July 27, 2006, and any
additional proations shall be treated as a post closing reconciliation between
the parties.


4.  Counterparts.  This Amendment may be executed in one or more
counterpart copies, all of which counterparts shall have the same force and
effect as if all parties hereto had executed a single copy of this Amendment.



5.  Ratification.  Except as amended hereby, the Agreement shall remain
in full force and effect.


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IN WITNESS WHEREOF, the parties have executed this Amendment as of the day
and year first above written.



SELLER:

TECHNOLOGY SQUARE FINANCE, LLC, a Massachusetts limited
liability company


By:Massachusetts Institute of Technology, 

a Massachusetts charitable corporation, 

its Manager


By:   /s/ Steven C. Marsh   

Name:  Steven C. Marsh 

Its:   Managing Director, Real Estate













BUYER:

ARE-MA REGION NO. 31, LLC, a Delaware limited

liability company


By:Alexandria Real Estate Equities, L.P., 

a Delaware limited partnership, 

its Managing Member



By:ARE-QRS Corp., 

a Maryland corporation,

its General Partner




By:  /s/ Jennifer Pappas

Name:  Jennifer Pappas

Its:  V.P & Assistant Secretary













Acknowledgement by Escrow Agent



Escrow Agent acknowledges the terms of the foregoing Amendment, and agrees to
continue to be bound by those terms of the Agreement applicable to the Escrow
Agent.


ESCROW AGENT:

Chicago Title Insurance Company



By:  /s/ Gus Aguilar

Name:  Gus Aguilar

Its:  AVP/Senior Escrow Officer