Amgen and Xencor, Inc. have announced that they will
collaborate to develop XmAb®5871, an Fc- engineered monoclonal antibody dually
targeting CD19 and CD32b. XmAb5871 is currently in late-stage preclinical
development for the treatment of autoimmune diseases.  

Under the terms of the agreement, 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. Xencor will
receive an up-front and early development milestone payments. If Amgen does
exercise its option, Amgen will assume responsibility for future development,
Xencor will receive an option-exercise fee which, combined with the up-front
and early development milestones, will total $75 million, and Xencor could
receive up to an additional $425 million in clinical, regulatory and
commercialization milestone payments.  Xencor will receive tiered
royalties on future sales of XmAb5871.

Xencor’s CD32b technology is a novel immunomodulatory
platform consisting of engineered Fc domains with selective high affinity
binding to FcyRIIb (CD32b), a receptor with dominant inhibitory activity on B
cells and other immune cells. The CD32b pathway has never been therapeutically
exploited and applied to high affinity antibodies targeting immune cells.

“XmAb5871 provides a novel approach to suppress B-cell
function which will enhance Amgen’s internal efforts in inflammatory
diseases,” said Joseph P. Miletich, M.D., Ph.D., senior vice president,
Research & Development at Amgen.  “We are delighted to have the
opportunity to partner with Xencor in exploring their novel immunomodulatory
approach.”

“Amgen’s long-time leadership in antibody development
for oncology and inflammatory diseases aligns seamlessly with Xencor’s pipeline
development,” said Bassil Dahiyat, Ph.D., chief executive officer of Xencor.
“We expect that XmAb5871 will soon become the fifth XmAb-engineered
antibody in clinical development.  This program is a testament to the
progress we’ve made expanding the XmAb platform into autoimmune disease with
our CD32b technology, which is at the core of the XmAb5871 compound. The option
deal structure allows us to continue to lead the development of XmAb5871 while
also leveraging Amgen’s experience in developing novel biologics for unmet
medical needs.”