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