Monrovia, Calif. – December 2, 2008 – Xencor, Inc., a company developing protein and antibody therapeutics, will present new data from its pre-clinical anti-CD19 and anti-CD40 programs, XmAb®5574 and XmAb®5485 respectively, for lymphoma and leukemias at the 50th Annual Meeting of the American Society of Hematology being held at the Moscone Convention Center in San Francisco December 6-9, 2008.

New data from the XmAb5574 program will be presented in a poster session titled, “XmAb®5574, an Fc-Engineered Humanized Anti-CD19 Monoclonal Antibody, has Potent In Vitro and In Vivo Activities, and has the Potential for Treating B Cell Malignancies,” on Sunday, December 7 between 6:00-8:00 p.m. in Hall A at the Moscone Center (Poster Board Number: II-715).

The Company will present XmAb5485 data in an oral presentation titled, “An Fc-Engineered Humanized Anti-CD40 Monoclonal Antibody, XmAb5485, Exhibits Potent Activity In Vitro and In Vivo Against Non-Hodgkin Lymphoma, Chronic Lymphocytic Leukemia and Multiple Myeloma,” on Tuesday, December 9 at 7:15 a.m. in room 3006-3008 – West at the Moscone Center.

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 XmAb®5485

XmAb®5485 is a humanized monoclonal antibody that targets the antigen CD40 for treatment of B cell malignancies and autoimmune diseases, and contains a proprietary Xencor XmAb® Fc domain that enhances cytotoxic potency.

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 and half-life. 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, in a Phase I clinical trial for the treatment of Hodgkin lymphoma and anaplastic large 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, MedImmune and Human Genome Sciences, Xencor is applying its suite of XmAb antibody Fc domains to improve antibody drug candidates for traits such as potency and sustained half-life. For more information, please visit www.xencor.com.