MONROVIA, Calif.—(BUSINESS WIRE)—Xencor, Inc., a leader in antibody optimization, has selected two humanized monoclonal antibody candidates, XmAb™ 5574 and XmAb™ 5483, for IND-enabling pre-clinical development for the treatment of B-cell malignancies and autoimmune diseases. XmAb 5574 and XmAb 5483 target the antigens CD19 and CD40, respectively. CD19 is a validated target for B-cell cancers and inflammatory diseases. CD40 is a validated target for B-cell cancers and a variety of solid tumor cancers including bladder, renal and ovarian cancer. Xencor has started pre-clinical studies that will allow the Company to file Investigational New Drug (IND) applications with the U.S. Food and Drug Administration for these candidates.

Xencor’s lead antibody candidate, XmAb™ 2513, a humanized monoclonal antibody that targets the antigen CD30 for the treatment of Hodgkin’s disease and T-cell lymphoma, will enter Phase 1 clinical trials in late 2007.

“With the addition of XmAb 5574 and 5483 to our pipeline, we are building on our strategy to advance novel antibody candidates through the clinic based on the antibody engineering capability of our XmAb technology,” said Bassil Dahiyat, Ph.D., president and chief executive officer at Xencor. “Both candidates have demonstrated high cytotoxic potency, conferred by our XmAb Fc technology, and have the potential to be highly effective cancer therapies.”

Each of Xencor’s antibody drug candidates was developed using Xencor’s XmAb™ antibody engineering tools. XmAb™ technologies are a suite of proprietary antibody Fc domains and antibody engineering tools that enable the creation of humanized therapeutic antibody candidates with significantly enhanced potency, affinity and ease of production.

Xencor’s portfolio of unique antibody candidates have demonstrated increased tumor killing power by over 100-fold using its proprietary XmAb™ Fc technology. The Company’s growing library consists of over 2,000 Fc variants that have been engineered for select amino acid changes to provide a wide range of immunological properties and increased antibody half-life.

About Xencor, Inc.

Xencor, Inc. engineers superior biotherapeutics using its proprietary XmAb™ technology and is a leader in the field of antibody Fc engineering to significantly improve antibody potency, safety, and half-life. The company is advancing XmAb™ antibody drug candidates optimized for activity against biologically validated targets into the clinic, led by XmAb™2513, for the treatment of Hodgkin’s disease and T-cell lymphoma. 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 a variety of antibody drug candidates. For more information, please visit www.xencor.com.