MONROVIA, Calif., April 26, 2013 – Xencor announced today that MorphoSys AG has dosed the first patient in a Phase 2 clinical trial of MOR208 in B-cell acute lymphoblastic leukemia (B-ALL). MOR208 is a potent anti-CD19 monoclonal antibody Fc optimized for high cytotoxic function for which MorphoSys licensed exclusive worldwide rights from Xencor in 2010. The dosing of the first patient in the study triggers an undisclosed milestone payment to Xencor.

The US-based study is an open-label, multicenter, single-arm clinical trial designed to assess the efficacy of MOR208 in patients suffering from relapsed or refractory B-ALL. Secondary outcome measures include response duration, safety and pharmacokinetics of MOR208. In total, 30 patients are planned to be enrolled. More information on the trial can be found by searching for MOR208 at www.clinicaltrials.gov.

"Preclinical and early clinical studies of MOR208 have shown promising anti-tumor activity and supported this additional study in ALL as well as another study in Non Hodgkin's Lymphoma which is expected to start shortly," said Bassil Dahiyat, Ph.D., Chief Executive Officer of Xencor. "Xencor monoclonal antibody candidates continue to advance in clinical development and showcase the value of our XmAb® Fc technology."

MOR208 has shown in a Phase 1/2a trial encouraging signs of preliminary anti-tumor activity and an acceptable safety and tolerability profile in patients with high-risk, heavily pretreated chronic lymphocytic leukemia (CLL) or small lymphocytic lymphoma (SLL). In addition to the phase 2 trial in B-ALL MorphoSys is about to start a second Phase 2 trial in Non-Hodgkin's Lymphoma (NHL).

B-cell malignancies, such as B-ALL, NHL and CLL affect more than one hundred and fifty thousand patients in the seven major markets each year. The target molecule CD19 is expressed more broadly and earlier in B-cell development than CD20, the target of the marketed cancer drug Rituxan®. Therefore targeting CD19 could potentially allow for an even broader therapeutic use of MOR208 than marketed anti-CD20 antibodies.

About XmAb® High ADCC Technology
XmAb® High ADCC technology can increase the potency of therapeutic antibodies by specifically engaging the body's immune system against target antigen cells. Xencor's proprietary suite of XmAb® Fc variants allows the selective improvement of antibody cytotoxic properties by enhancing antibody-dependent cell cytotoxicity (ADCC), phagocytosis and/or complement activation. Increased antibody potency has the potential to improve antibody efficacy in a variety of therapeutic areas, including oncology, infectious disease and autoimmune disorders.

About Xencor, Inc.
Xencor, Inc. engineers superior biotherapeutics using its proprietary Protein Design Automation® technology platform, and is a leader in the field of antibody engineering to significantly improve antibody half-life, immune-regulatory function and potency. The company is advancing multiple XmAb® antibody drug candidates in the clinic, including XmAb®5871 targeting CD32b and CD19 for autoimmune diseases, and an anti-CD30 candidate XmAb®2513 for the treatment of Hodgkin's lymphoma. Xencor is also advancing a portfolio of biosuperior versions of blockbuster antibody drugs engineered for superior half-life and dosing schedule. Xencor has entered into multiple partnerships with industry leaders such as Amgen, Pfizer, Janssen, MorphoSys, Boehringer Ingelheim, CSL Ltd. and Human Genome Sciences. In these partnerships Xencor is applying its suite of proprietary antibody Fc domains to improve antibody drug candidates for traits such as sustained half-life and/or potency. For more information, please visit www.xencor.com.

Xencor Media Contact
Heidi Chokeir, Ph.D.
Canale Communications for Xencor
Tel: 619-849-5377
heidi@canalecomm.com