Abgenix Introduces Enhanced Version of XenoMouse Technology.

Business Editors/Health & Medical Writers

FREMONT, Calif.--(BW HealthWire)--Dec. 4, 2001

Abgenix, Inc. (Nasdaq:ABGX) announced today at the IBC Antibody Engineering Conference in San Diego, Calif., the launch of new versions of XenoMouse(R) mice that produce fully human monoclonal antibodies that contain both lambda and kappa light chains. Other transgenic mouse technologies in the commercial sector make human antibodies that contain only kappa light chains. Abgenix expects these strains of mice, making both human IgG kappa and human IgG lambda monoclonal antibodies, to expand significantly the number and diversity of XenoMouse-derived antibody product candidates for its collaborators and for itself.

The purpose of adding the human Ig lambda(lambda light chain genes) to XenoMouse strains of mice is to capture and to mimic more completely the full repertoire of the human antibody response. Approximately 40% of human antibodies have lambda light chains (Ig lambda) and the other 60% have kappa light chains (Ig kappa). Building on the foundation of the previous versions of XenoMouse mice, these new transgenic mice possess the complete immunoglobulin gene locus for making human lambda light chain antibodies in addition to genes encoding human heavy chain antibodies and human kappa light chain antibodies.

"The generation of these new strains of XenoMouse mice demonstrates our commitment to maintaining technological leadership in the antibody field," said R. Scott Greer, chairman and CEO of Abgenix. "Our comprehensive program of antibody technologies, which includes the XenoMouse and XenoMax platforms, intrabodies and catalytic antibodies, provides Abgenix and its collaborators with state-of-the-art tools for creating antibody-based therapeutic products."

Introduction of the complete lambda light chain locus, containing 30 functional V genes, by Abgenix scientists extends the earlier achievement of Dr. Marianne Bruggemann of the Babraham Institute in the United Kingdom. Bruggemann previously generated a transgenic mouse bearing approximately half of the human lambda light chain locus and demonstrated that these genes were functional. Abgenix licensed the lambda light chain genes and obtained certain related materials from the Medical Research Council of the United Kingdom to make this new strain of XenoMouse animals.

Abgenix's XenoMouse technology involves transgenic mouse strains that possess an immune system in which the mouse antibody-producing genes have been inactivated and functionally replaced by most of the human antibody-producing genes. The XenoMouse animal's immune system still recognizes human antigens as foreign, but instead of producing mouse antibodies it produces fully human antibodies. Abgenix has developed multiple strains of XenoMouse mice that produce different classes of IgG antibodies (IgG1, IgG2, IgG4) for optimally choosing the antibody product candidate to a given disease indication.

Abgenix's XenoMax(TM) technology allows researchers to rapidly scan the majority of the immune repertoire of an immunized XenoMouse animal, and to identify B-cells that produce antibodies with the desired functional properties and the optimum affinities. Using rapid microplate-based assays to measure and rank antibodies according to design goals (e.g., potency, affinity, specificity), individual B-cells producing extremely high-quality antibodies can be identified and the antibody encoding genes recovered. XenoMax technology bypasses the generation of hybridomas and speeds product development timelines by allowing researchers to move directly into pre-clinical assessment of panels of suitable recombinant candidate antibody products, each ready for manufacturing scale-up.

Abgenix is a biopharmaceutical company focused on the development and commercialization of human monoclonal antibody therapies for a variety of diseases. The company's antibody technology program, which includes XenoMouse(R) and XenoMax(TM) technologies, enables the rapid generation and selection of high affinity, fully human antibody product candidates to disease targets appropriate for antibody therapy. Abgenix leverages its leadership position in human antibody technology by building a large and diversified product portfolio through the establishment of licensing arrangements with multiple pharmaceutical, biotechnology and genomics companies and through the development of its own internal proprietary products. For more information on Abgenix, visit the company's website at www.abgenix.com.

Statements made in this press release about Abgenix's technologies, 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.

Note: In the symbols "IgG1," "IgG2" and "IgG4," the numerals are subscript.