Firm will wait for Phase II data before deciding whether to license the CD19/CD32 candidate.

Amgen negotiated an option to acquire an exclusive worldwide license to Xencor’s late preclinical-stage dual-targeting monoclonal antibody (mAb), XmAb®5871, for the treatment of autoimmune diseases. Under terms of the deal Xencor will carry out clinical development of the candidate until the completion of a predefined Phase II study, at which point Amgen’s option will kick in.

Amgen will pay Xencor an up-front fee, early development milestone payments, and, if the firm decides to license XmAb5871, an option exercise fee. The total of these combined payments will be about $75 million. Subsequent clinical, regulatory, and commercialization milestone payments made to Xencor could reach $425 million. Amgen will be responsible for all development and commericalization of XmAb5871 if and when it decides to take up its option to take over the antibody.

XmAb5871 is an Fc-engineered mAb targeting CD19 and CD32b. Xencor has developed an immunomodulatory platform by engineering Fc domains for selective high affinity binding to FcγRIIb (CD32b), a receptor on B cells and other immune cells that the firm claims has not yet been explored therapeutically and applied to high-affinity antibodies targeting immune cells.

“We expect that XmAb5871 will soon become the fifth XmAb-engineered antibody in clinical development,” notes Bassil Dahiyat, Ph.D., Xencor CEO. “This program is a testament to the progress we’ve made expanding the XmAb platform into autoimmune disease with our CD32b technology, which is at the core of the XmAb5871 compound”.

Xencor is developing an in-house and partnered pipeline of protein drug candidates against a range of diseases, based on its XmAb antibody therapeutics and XPro™ protein therapeutics platforms. The firm’s in-house pipeline is headed by the Phase II-stage anti-CD30 antibody XmAb2513, which is in development for the treatment of Hodgkin lymphoma. Partnered products include XmAb 5574 (MOR208), an anti-CD19 monoclonal antibody being developed in collaboration with MorphoSys for the potential treatment of B-cell malignancies. The firms initiated a Phase I trial with XmAb5574 in December 2010.

Oncology mAb candidates partnered separately with Pfizer and Boehringer Ingelheim are also progressing into clinical development. A Phase I trial with a Pfizer-partnered antibody was also initiated in December 2010, and a regulatory submission requesting approval to start a Phase I study with a Boehringer Ingelheim-partnered XmAb product was submitted in October 2010.

The Pfizer collaboration is focused on exploiting Xencor’s Xtend™ half-life prolongation technology and XmAb® ADCC enhancing technology to optimize performance of the company’s therapeutic monoclonal antibodies. The Boehringer Ingelheim partnership is focused on the XmAb engineered Fc platform to improve antibodies against selected targets.

Xencor has additional collaborations ongoing with CSL, Centocor, and Human Genome Sciences, through which its antibody technologies are being applied to improve the features and function of antibody drug candidates.

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