COLLABORATION AGREEMENT

EXHIBIT 10.1

Execution Version

CONFIDENTIAL PROVISIONS REDACTED

COLLABORATION AGREEMENT

THIS COLLABORATION AGREEMENT (the “Agreement”) is entered into as of September 12, 2005 (the “Effective Date”) by and between Protein Design Labs, Inc., a Delaware corporation having its offices at 34801 Campus Drive, Fremont, California 94555 (“PDL”), and Biogen Idec MA Inc., a Massachusetts corporation having offices at 14 Cambridge Center, Cambridge, Massachusetts 02142 (“Biogen Idec”). PDL and Biogen Idec may each be referred to in this Agreement individually as a “Party” and collectively as the “Parties.”

RECITALS

WHEREAS, PDL possesses worldwide rights to develop, manufacture, market, and sell certain proprietary antibodies directed at certain antigens (such antigens defined below as “Collaboration Targets”) and;

WHEREAS, PDL has research and development programs for such antibodies as well and for certain compounds relating to the Collaboration Targets; and

WHEREAS, Biogen Idec and PDL wish to collaborate in the research, development, manufacturing and commercialization of products for the Collaboration Targets, including such antibodies and compounds, under the terms and conditions set forth below.

NOW THEREFORE, in consideration of the foregoing premises and the mutual covenants contained herein, the Parties, intending to be legally bound, agree as follows:

ARTICLE 1

DEFINITIONS

The following capitalized terms, whether used in the singular or the plural, shall have the following meanings as used in this Agreement unless otherwise specifically indicated:

*Certain information on this page has been omitted and filed separately with the commission. Confidential treatment has been requested with respect to the omitted portions.