Exhibit 99.1

JOINT FILING AGREEMENT

The undersigned hereby agree that statements on Schedules 13G and/or 13D and Forms 3, 4 and 5 with respect to the shares of common stock of Arrowhead Research Corporation and any amendments thereto signed by each of the undersigned shall be filed on behalf of each of the undersigned pursuant to and in accordance with the provisions of Rule 13d-1(k) promulgated under the Securities Exchange Act of 1934, as amended.  The undersigned hereby further agree that this Joint Filing Agreement may be included as an exhibit to such statements or amendments.  This Joint Filing Agreement may be executed in any number of counterparts, all of which taken together shall constitute one and the same instrument.

Dated: October 16, 2013

	Ridgeback Capital Investments L.P.
By:	Ridgeback Capital Investments Ltd., Its General Partner
By:	/s/ Bud Holman
	Name: Bud Holman
	Title: Director

	Ridgeback Capital Investments Ltd.
By:	/s/ Bud Holman
	Name: Bud Holman
	Title: Director

	Ridgeback Capital Management LP
By:	/s/ Bud Holman
	Name: Bud Holman
	Title: Authorized Signatory