Monrovia, Calif. – April 9, 2008 – Xencor, Inc., a company developing protein and antibody therapeutics, will present new data from its pre-clinical CD19 program for lymphoma and leukemias at the Annual Meeting of the American Association for Cancer Research (AACR) being held at the San Diego Convention Center April 12-16, 2008.

The Company will present Tuesday, April 15, 2008 at 1:00 p.m. in a poster session titled, “XmAb™5574: an Fc-Engineered Anti-CD19 Monoclonal Antibody with In Vitro and In Vivo Efficacy against Lymphoma and Leukemia”. (Abstract Number: 4903)

Xencor will present additional data from this program during the American Society of Clinical Oncology (ASCO) 44th Annual Meeting being held at McCormick Place in Chicago, Sunday, June 1, 2008.

About XmAb™5574

XmAb™5574 is a humanized monoclonal antibody that targets the antigen CD19 for treatment of B cell malignancies and autoimmune diseases. XmAb™5574 contains a proprietary Xencor XmAb Fc domain that enhances cytotoxic potency and also downregulates B cell activation.

About Xencor

Xencor, Inc. engineers superior biotherapeutics using its proprietary Protein Design Automation® technology platform and is a leader in the field of antibody Fc engineering to significantly improve antibody potency. The company is advancing XmAb™ antibody drug candidates optimized for activity against biologically validated targets and its XPro™ protein therapeutic candidate into the clinic. Xencor’s product development is led by an antibody candidate, XmAb™2513, for the treatment of Hodgkin’s disease and T-cell lymphoma, and a protein therapeutic drug candidate, XPro™ 1595 DN-TNF, for the treatment of inflammatory disease. With multiple partners, such as industry leaders Genentech, Boehringer Ingelheim, Centocor and MedImmune, Xencor is applying its suite of XmAb antibody Fc domains to improve antibody drug candidates for traits such as increased potency and half-life. For more information, please visit www.xencor.com.