FIFTH AMENDMENT TO LEASE

Exhibit 10.1

FIFTH AMENDMENT TO LEASE

THIS FIFTH AMENDMENT TO LEASE (this “Fifth Amendment”) is made as of this 1^st day of December, 2005, by and between ALEXANDRIA REAL ESTATE EQUITIES, INC., a Maryland corporation (“Landlord”), and XCYTE THERAPIES, INC., a Delaware corporation (“Tenant”).

RECITALS

A. Landlord and Tenant have entered into that certain Lease Agreement dated as of June 21, 1999, as amended by that certain First Amendment to Lease dated as of October 23, 2001, that certain Second Amendment to Lease dated as of March 26, 2003, that certain Third Amendment to Lease dated as of November 12, 2003 (the “Third Amendment”), and that certain Fourth Amendment to Lease dated as of April 28, 2004 (as amended, the “Lease”). Pursuant to the Lease, Landlord leases to Tenant certain premises in the building located at 1124 Columbia Street, Seattle, Washington, and more particularly described in the Lease. Capitalized terms used herein without definition shall have the meanings defined for such terms in the Lease.

B. Landlord and Tenant desire, subject to the terms and conditions set forth herein, to amend the Lease to, among other things, effect Tenant’s surrender, on or before November 30, 2005 (the date of such surrender being the “Surrender Date”) of that portion of the Premises within the Building located on the 7^th floor, consisting of approximately 12,630 rentable square feet, and more particularly shown on Exhibit B attached hereto (the “Surrendered Premises”).

NOW, THEREFORE, in consideration of the foregoing Recitals, which are incorporated herein by this reference, the mutual promises and conditions contained herein, and for other good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, Landlord and Tenant hereby agree as follows:

Premises: That portion of the Building located on the first floor known as Suites 110 and 130, containing approximately 8,029 rentable square feet, that portion of the Building known as Suite 120, containing approximately 2,874 rentable square feet, and that portion of the Building known as Suite 70, containing approximately 700 rentable square feet, as determined by Landlord, and all as more particularly shown on Exhibit A.

Commencing on the Effective Date, Exhibit A attached to the Lease is also hereby deleted in its entirety and replaced with Exhibit A attached to this Fifth Amendment.

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(a) This Fifth Amendment is the entire agreement between the parties with respect to the subject matter hereof and supersedes all prior and contemporaneous oral and written agreements and discussions. This Fifth Amendment may be amended only by an agreement in writing, signed by the parties hereto.

(b) This Fifth Amendment is binding upon and shall inure to the benefit of the parties hereto, their respective agents, employees, representatives, officers, directors, divisions, subsidiaries, affiliates, assigns, heirs, successors in interest and shareholders.

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(c) This Fifth Amendment may be executed in any number of counterparts, each of which shall be deemed an original, but all of which when taken together shall constitute one and the same instrument. The signature page of any counterpart may be detached therefrom without impairing the legal effect of the signature(s) thereon provided such signature page is attached to any other counterpart identical thereto except having additional signature pages executed by other parties to this Fifth Amendment attached thereto.

(d) Landlord and Tenant each represent and warrant that it has not dealt with any broker, agent other person (collectively, “Broker”) in connection with this transaction, and that no other Broker brought about this transaction. Landlord and Tenant each hereby agrees to indemnify and hold the other harmless from and against any claims by any Broker claiming a commission or other form of compensation by virtue of having dealt with Landlord or Tenant, as applicable, with regard to this leasing transaction.

(e) Except as amended and/or modified by this Fifth Amendment, the Lease is hereby ratified and confirmed and all other terms of the Lease shall remain in full force and effect, unaltered and unchanged by this Fifth Amendment. In the event of any conflict between the provisions of this Fifth Amendment and the provisions of the Lease, the provisions of this Fifth Amendment shall prevail. Whether or not specifically amended by this Fifth Amendment, all of the terms and provisions of the Lease are hereby amended to the extent necessary to give effect to the purpose and intent of this Fifth Amendment.

[Signatures are on the next page.]

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

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