FREMONT, California and ROCKVILLE, Maryland – May 12, 2003 – Abgenix, Inc. (Nasdaq: ABGX) and Human Genome Sciences, Inc. (Nasdaq: HGSI) announced today that Human Genome Sciences has acquired an exclusive worldwide license from Abgenix to develop and commercialize a fully human monoclonal antibody to the CCR5 receptor. CCR5 is a human chemokine receptor shown to be required for infection by human immunodeficiency virus (HIV), the cause of Acquired Immunodeficiency Syndrome (AIDS). Human Genome Sciences generated the CCR5 human monoclonal antibody (CCR5 mAb) using the Abgenix XenoMouse® technology.

The CCR5 receptor is a co-receptor on the cell surface that, together with CD4, mediates the binding of HIV and its entry into the cell. Research has shown that the CCR5 receptor is the primary co-receptor for enabling HIV transmission and replication from the early stages of disease through progression to AIDS. Research also has demonstrated that people with a deficiency of the CCR5 receptor are resistant to HIV infection or have slower HIV/AIDS disease progression, and that blocking the biological function of CCR5 with antagonists or chemokines can inhibit HIV replication.^{1, 2, 3, 4}

CCR5 mAb is designed to bind to and block the CCR5 receptor and thereby prevent the entry of HIV into cells of the immune system. Results of preclinical studies to date show that CCR5 mAb specifically binds to the CCR5 receptor and is capable of neutralizing HIV replication in vitro. Additional preclinical studies are currently underway to support an Investigational New Drug application (IND) that would seek clearance from the U.S. Food and Drug Administration (FDA) to begin Phase 1 clinical trials of CCR5 mAb.

Under the terms of a 1999 agreement, which was amended in 2001, Human Genome Sciences will pay clinical development milestone payments and royalties to Abgenix if the CCR5 mAb is successfully developed and commercialized.⁵ CCR5 mAb will be manufactured in the Human Genome Sciences manufacturing facility in Rockville, Maryland.

Raymond M. Withy, Ph.D., President and Chief Executive Officer, Abgenix, said, “Today’s announcement provides further validation for the use of the Abgenix XenoMouse technology with genomics-derived targets. We are delighted to see a product candidate from one of our early technology licensing agreements advancing through development.”

William A. Haseltine, Ph.D., Chairman and Chief Executive Officer of Human Genome Sciences, said, “HIV infection is a serious threat to health worldwide. The number of newly infected HIV/AIDS patients is rising rapidly. In addition, given the increased emergence of HIV resistance to existing treatments, such as small molecule inhibitors of HIV protease and reverse transcriptase, there is a great need for novel treatment options. CCR5 is among the most interesting and important biological targets in a new class of drugs that inhibit viral entry. Human Genome Sciences generated CCR5 mAb using the Abgenix XenoMouse® technology. We are pleased with the success of our collaboration with Abgenix to date, and look forward to continuing to work together to identify promising antibody drug candidates.”

Abgenix is a biopharmaceutical company focused on the discovery, development and manufacturing of human therapeutic antibodies. For more information on Abgenix, visit the company's website at www.abgenix.com.

Human Genome Sciences is a company with the mission to treat and cure disease by bringing new gene-based drugs to patients. For additional information on Human Genome Sciences, please visit our web site at www.hgsi.com.

HGS and Human Genome Sciences are trademarks of Human Genome Sciences, Inc. XenoMouse is a registered trademark of Abgenix, Inc.

This announcement contains forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended. The forward-looking statements are based on Human Genome Sciences' current intent, belief and expectations. These statements are not guarantees of future performance and are subject to certain risks and uncertainties that are difficult to predict. Actual results may differ materially from these forward-looking statements because of the Company's unproven business model, its dependence on new technologies, the uncertainty and timing of clinical trials, the Company's ability to develop and commercialize products, its dependence on collaborators for services and revenue, its substantial indebtedness and lease obligations, its changing requirements and costs associated with planned facilities, intense competition, the uncertainty of patent and intellectual property protection, the Company's dependence on key management and key suppliers, the uncertainty of regulation of products, the impact of future alliances or transactions and other risks described in the Company's filings with the Securities and Exchange Commission. Existing and prospective investors are cautioned not to place undue reliance on these forward-looking statements, which speak only as of today's date. Human Genome Sciences undertakes no obligation to update or revise the information contained in this announcement whether as a result of new information, future events or circumstances or otherwise.

Statements made in this press release about Abgenix's technologies, product development activities, collaborative arrangements and manufacturing activities, other than statements of historical fact, and about its projected financial results, 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, product manufacturing, 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.

# # #

Footnotes:
1. Deng H, Liu R, Ellmeier W, Choe S, Unutmaz D, Burkhart M, Di Marzio P, Marmon S, Sutton RE, Hill CM, Davis CB, Peiper SC, Schall TJ, Littman DR, Landau NR. Identification of a major co-receptor for primary isolates of HIV-1. Nature. 1996 Jun 20; 381(6584): 661-6.
2. Huang Y, Paxton WA, Wolinsky SM, Neumann AU, Zhang L, He T, Kang S, Ceradini D, Jin Z, Yazdanbakhsh K, Kunstman K, Erickson D, Dragon E, Landau NR, Phair J, Ho DD, Koup RA. The role of a mutant CCR5 allele in HIV-1 transmission and disease progression. Nat Med. 1996 Nov; 2(11): 1240-3.
3. Cooley LA and Lewin SR. HIV-1 cell entry and advances in viral entry inhibitor therapy. J Clin Vir 2003; 26: 121-132.
4. Reynes J, Rouzier R, Kanouni T, Baillat V, Baroudy B, Keung A, Hogan C, Markowitz M, and Laughlin M. SCH C: Safety and antiviral effects of a CCR5 receptor antagonist in HIV-1- infected subjects. Conference on Retroviruses and Opportunistic Infections 2002.
5. (HGSI Press Release) Human Genome Sciences And Abgenix Enter A Broad Collaboration To Create Fully Human Antibody Therapeutics. December 1, 1999.

CONTACTS:
Human Genome Sciences:
Jerry Parrott, Vice President, Corporate Communications
301-315-2777
Kate de Santis, Director, Investor Relations
301-251-6003

Abgenix:
Ami Knoefler Director, Corporate Communications
510-284-6350 or 415-608-2514