Xencor regained all development and commercial rights to XmAb®5871, a first-in-class monoclonal antibody containing the company’s immune inhibitor XmAb Fc domain that targets FcγRIIb to inhibit B-cell function.

Three years ago, under the original agreement, Amgen held an option to an exclusive worldwide license of XmAb5871 following the completion of a predefined Phase II study in rheumatoid arthritis. To date, Xencor has been leading all clinical development of XmAb5871. The new agreement requires Xencor to first discuss with Amgen any proposed license prior to seeking other partners.  This right expires upon the initiation of Phase III clinical testing of XmAb5871, a change of control of Xencor, or October 2019.

According to Xencor, XmAb5871 is currently in a Phase Ib/IIa clinical trial in patients with moderate-to-severe rheumatoid arthritis and topline results are expected by the end of this year. Xencor said it is planning clinical development in multiple autoimmune diseases where B-cell inhibition shows promise, including IgG4-related disease.

“We determined that even with positive data following completion of the ongoing Phase Ib/IIa trial in rheumatoid arthritis, refocusing our development plan on other autoimmune diseases would align better with Xencor's strategy to develop therapies for diseases with the highest unmet need,” said Bassil Dahiyat, Ph.D., president and CEO.  “We approached Amgen to end the original collaboration to allow Xencor the freedom to pursue alternative clinical and commercial paths.  Amgen agreed, provided we grant them a right of first negotiation for a license to XmAb5871.  We plan to start clinical testing in IgG4-related disease in 2015.  We do not plan on starting a Phase 2b rheumatoid arthritis trial in 2015.”

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