Xencor Initiates Phase 1b/2a Trial of XmAb®5871 for Autoimmune Disease

MONROVIA, Calif., Feb. 13, 2013 /PRNewswire/ -- Xencor, Inc. today announced that the first patient has been dosed in a Phase 1b/2a clinical trial of XmAb®5871 in patients with moderate to severe rheumatoid arthritis.  XmAb5871 is the first in a new class of therapeutic antibodies targeting the CD32b (FcγRIIb) pathway in B cells, which shows potential to suppress autoimmune disorders without the side effects caused by B cell depletion. The trial initiation triggered a milestone payment of an undisclosed amount to Xencor from Amgen.

XmAb5871 is a humanized and Fc engineered monoclonal antibody that uses a uniquely selective dual-targeting mechanism for B cell inhibition by co-engaging CD19 and CD32b. Amgen and Xencor entered into an option and co-development agreement for XmAb5871 in January 2011. Amgen has the option to an exclusive worldwide license following the completion of a pre-defined Phase 2 study. Xencor will lead all clinical development until that time and is eligible for early development milestone payments.

"The FcγRIIb pathway is generating increased interest as a novel therapeutic strategy for suppressing autoimmune responses, and XmAb5871 offers a unique and selective approach for engaging this pathway," said Bassil Dahiyat, Ph.D., president and CEO of Xencor. "In this trial, we are looking for disease activity outcomes to inform a larger Phase 2 study and to further support the potential of XmAb5871 in autoimmune diseases such as lupus and rheumatoid arthritis."

The Phase 1b trial will evaluate biweekly doses of XmAb5871 in patients with moderate to severe rheumatoid arthritis and will roll into a Phase 2a placebo controlled study.  Endpoints will include improvements in disease activity scales, serum inflammation markers and mechanism biomarkers. 

XmAb5871 was well tolerated in a Phase 1a dose escalation study that enrolled 48 healthy male subjects and potently inhibited multiple biomarkers of immune function.

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 R&D LLC, 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.

SOURCE Xencor, Inc.