News Release

Abgenix initiates phase III clinical trial of graft versus host disease therapy

Peer-Reviewed Publication

Porter Novelli

Abgenix to Seek a Corporate Partner to Commercialize ABX-CBL

FREMONT, Calif., December 7, 1999 - Abgenix, Inc. (Nasdaq: ABGX) is initiating a Phase III clinical trial comparing its antibody, ABX-CBL, with standard therapy for patients with steroid-resistant graft-versus-host disease (srGVHD), a serious, life-threatening disorder. Abgenix also indicated that it would seek a corporate partner to assist with the development and commercialization of ABX-CBL.

Abgenix is pursuing the Phase III trial of ABX-CBL based on promising results of a 59 patient Phase II trial of the drug. In that trial, srGVHD patients receiving higher doses of ABX-CBL had more than twice the 180-day survival rate observed in the lowest dose cohort, according to results presented at the annual meeting of the American Society of Hematology (ASH). Survival at 180 days for patients in the higher dose cohorts was 50% versus 22% in the lowest (presumed no effect) dose cohort.

"ABX-CBL demonstrated important clinical benefits as measured by response rate and survival in the Phase II clinical trial," said H. Joachim Deeg, M.D., Department of Transplantation Biology at Fred Hutchinson Cancer Research Center and Principal Investigator for the trial. "Given the limited options available for treating srGVHD patients, ABX-CBL has the potential to be an important new treatment for this disease."

"While we are enthusiastic about ABX-CBL's potential as a much needed treatment for srGVHD, our business strategy is to find corporate partners to commercialize the products we generate," stated R. Scott Greer, president and CEO of Abgenix. "Therefore, we would like to identify a pharmaceutical or biotech company with the development and marketing infrastructure to maximize the commercial potential of ABX-CBL. We plan to begin the Phase III trial on our own, but would like to have a partner on board before it is completed."

GVHD occurs in about 50 percent of patients receiving transplants of stem cells, from which all blood cells derive, when the transplanted cells attack the patient's tissues. Such transplants, or grafts, are used to treat patients with leukemia, certain other serious cancers and immune system disorders. Roughly half of GVHD patients fail to respond to current treatments, which consist of steroid and other drug treatments to suppress the grafted immune cells. Anti-thymocyte globulin (ATG), a horse polyclonal antibody mixture, is a commonly used treatment for GVHD patients who do not respond to first line steroid therapy.

GVHD frequently occurs following the transplantation of genetically different (allogeneic) stem cells, which involves transferring stem cells from the bone marrow or peripheral blood of a healthy donor into an immunosuppressed patient, the host. The transplant is intended to restore normal circulating blood cells and immune cells in patients whose own bone marrow cells and immune system are suppressed by radiation and or chemotherapy and therefore can not mount a sufficient immune response. Often a portion of the graft recognizes the host's own cells as foreign, becomes activated and attacks the cells, resulting in GVHD. The disease typically involves damage to multiple organ systems, including the skin, liver and intestines. GVHD causes extreme suffering and is a frequent cause of death in allogeneic stem cell transplant patients.

ABX-CBL is a monoclonal antibody that binds to CD147, a protein that is upregulated on certain activated immune cells. After ABX-CBL attaches to the CD147 antigen, the resulting complex signals to other immune cells to destroy the tagged cell. By selectively eliminating these cells while leaving other competent immune cells untouched, ABX-CBL may be useful in treating immune system disorders like srGVHD.

In the Phase III trial, Abgenix will compare ABX-CBL to ATG among 92 patients expected to enroll in the multi-center, controlled trial. Survival will be the trial's primary endpoint. The study is expected to take approximately 18-24 months to complete.

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Abgenix is a biopharmaceutical company that develops and intends to commercialize antibody therapeutic products for the treatment of a variety of disease conditions, including transplant-related diseases, inflammatory and autoimmune disorders, cardiovascular disease, infectious disease, and cancer.

Abgenix developed XenoMouse™ technology to enable quick generation of high affinity, fully human antibody product candidates to essentially any disease target appropriate for antibody therapy. Abgenix has collaborative arrangements with multiple pharmaceutical and biotechnology companies involving its XenoMouse technology. In addition, Abgenix has multiple, proprietary antibody product candidates under development internally, three of which are in human clinical trials for graft-versus-host disease, psoriasis and rheumatoid arthritis. For more information, visit Abgenix' Web site at www.abgenix.com.

The Fred Hutchinson Cancer Research Center is an independent, nonprofit research institution dedicated to the development and advancement of biomedical technology to eliminate cancer and other potentially fatal diseases. Recognized internationally for its pioneering work in bone-marrow transplantation, the Center's four scientific divisions collaborate to form a unique environment for conducting basic and applied science. One of 35 National Cancer Institute-designated comprehensive cancer centers in the nation, it is the only one in the Northwest. For more information, visit the Center's Web site at www.fhcrc.org.

Contact:
Kurt Leutzinger
Abgenix, Inc
Vice President and Chief Financial Officer
510-608-6575

Marion E. Glick
Porter Novelli
212-601-8273

Fred Hutchinson Cancer Research Center
Kristen Woodward
Media Relations
206-667-5095

Statements made in this press release about the potential of ABX-CBL and other antibody-based therapies as treatments for various diseases, Abgenix's XenoMouse technology, product development activities and collaborative arrangements other than statements of historical fact, are forward looking statements and are subject to a number of uncertainties that could cause actual results to differ materially from the statements made, including risks associated with the success of clinical trials, the progress of research and product development programs, the regulatory approval process, competitive products, future capital requirements and the extent and breadth of Abgenix's patent portfolio. Please see Abgenix's public filings with the Securities and Exchange Commission for information about risks that may affect Abgenix.


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