MONROVIA, CA – October 18, 2005 – Xencor, Inc., a biotherapeutics company developing protein therapeutics and antibody drugs, announced today that Bassil Dahiyat, Ph.D., President and CEO, will participate on a panel entitled “Antibody Therapeutics on the Rise: Future Antibody Technologies“ during the BIO InvestorForum in San Francisco on Wednesday, October 19 at 9:10 a.m. Dr. Dahiyat will discuss novel approaches to improving the design of antibody therapeutics, including the use of Xencor’s proprietary Protein Design Automation® platform. The panel will be moderated by Jason Kantor, Ph.D., Managing Director and Biotechnology Equity Research Analyst, RBC Capital Markets Corporation. Dr. Dahiyat will also provide a company overview and update during the conference, including the recent close of $20 million Series D round of private equity financing, Wednesday at 4:40 p.m.

The financing, led by Zen Investments, LLC., of Chicago, will fund the initiation of a Phase I clinical trial of Xencor’s proprietary protein therapeutic for the treatment of rheumatoid arthritis, XPro™1595, as well as ongoing development of the company’s pipeline of XmAb™ antibody therapeutics.

To date, Xencor has raised more than $85 million to create multiple antibody and protein drug candidates based on its Protein Design Automation technology platform. In addition to advancing its lead protein therapeutic drug candidate to the clinic, Xencor has licensed protein therapeutic candidates to partner Eli Lilly Company. Xencor is also developing numerous therapeutic antibodies with improved effector functions for internal advancement and for major partners including Genentech and Centocor.

“With the Protein Design Automation technology platform, Xencor has successfully engineered antibodies and proteins with improved potency, stability and selectivity for our own development and for our partners,“ said Bassil Dahiyat, president and CEO of Xencor. “This financing round will enable the company to advance into the clinic our novel ligand and target receptor-specific inhibitor of tumor necrosis factor, XPro™1595, and to continue preclinical development of our broad pipeline of antibody therapeutics.“

About Protein Design Automation Technology

PDA technology combines high performance computing with proprietary molecular biology processes and assays to create very broad protein diversity with exquisite control and efficiency. This technology takes advantage of the information embedded in protein structure to optimize key protein properties, such as binding affinity, selectivity, stability and expression level, which are targeted to yield therapeutic proteins with enhanced safety and efficacy in the clinic. The application of PDA technology creates new intellectual property, continually broadening Xencor’s patent portfolio by generating sets of novel protein sequences that are distinct from naturally occurring proteins.

About Xencor

Xencor, Inc., engineers superior biotherapeutics using its proprietary Protein Design Automation® technology platform. The company is internally advancing both XPro™ protein therapeutic candidates and XmAb™ antibody drug candidates optimized for activity against biologically validated targets. Xencor’s product development is lead by a protein therapeutic drug candidate, XPro™1595, for the treatment of arthritis and other rheumatic disorders and antibody candidates for the treatment of cancer. With multiple partners such as industry leaders Genentech and Roche, Xencor is applying its suite of XmAb antibody Fc domains to improve antibody drug candidates for traits such as potency and sustained half-life. Xencor also develops therapeutic protein variants in collaboration with major pharmaceutical partners. For more information, please visit www.xencor.com.