News Release

Human Genome Sciences to initiate human clinical trials of BLYS

Peer-Reviewed Publication

Human Genome Sciences, Inc.

Trials to begin only one year after discovery announced

Rockville, Maryland -- June 23, 2000 -- Human Genome Sciences, Inc. (Nasdaq: HGSI) today announced that it will initiate human clinical trials of B-lymphocyte stimulator, or BLyS, in patients with Common Variable Immunodeficiency, a serious defect of the immune system. These plans follow a review of HGS' Investigational New Drug application with the U.S. Food and Drug Administration.

Common Variable Immunodeficiency, or CVID, is one of a group of primary immunodeficiency disorders that are characterized by increased susceptibility to infection. Affected individuals suffer from multiple bouts of pneumonia, bronchitis and sinusitis as well as other infections. Patients suffering from CVID require life-long treatment with antibodies to protect against recurrent infection.

BLyS is a protein made by the human body that stimulates the production of antibodies. Antibodies recognize foreign substances and help defend the body against infection by viruses, bacteria and other microorganisms. Patients with CVID fail to make normal quantities of antibodies, or immunoglobulins, making them susceptible to infections. The hope is that by providing BLyS to these patients, they will be able to produce their own antibodies and ward off infections themselves.

Jerry Winkelstein, M.D., Eudowood Professor of Pediatrics at Johns Hopkins University and Chair of the Medical Advisory Committee to the Immune Deficiency Foundation, said, "Patients with Common Variable Immunodeficiency are unable to make adequate amounts of their own antibodies. As a result, they have to depend on antibody treatments for the rest of their life. BLyS may restore their ability to produce antibodies again, which would be a very important advance in their treatment."

David C. Stump, M.D., Senior Vice President, Drug Development of Human Genome Sciences, said, "We are very excited about the prospect of studying BLyS in patients with Common Variable Immunodeficiency. Like human growth hormone or insulin, BLyS is a natural substance made by the human body. It is our hope that BLyS will relieve the symptoms of CVID patients suffering from this life-long debilitating disorder."

Craig A. Rosen, Ph.D. Executive Vice President, Research and Development of Human Genome Sciences, said, "We are initiating human clinical trials of BLyS one year after publishing the news of the protein's discovery and description of its activity in the immune system in Science magazine in July of 1999. The rapid progress from bench to clinic of this new drug is a tribute to the concerted efforts of our drug discovery, development and manufacturing teams as well as to the efforts of our clinical development and regulatory staff."

William A. Haseltine, Ph.D., Chairman and Chief Executive Officer of Human Genome Sciences, said, "The development of BLyS as a candidate to treat this disease, Common Variable Immunodeficiency, and possibly the use of this drug to treat other forms of immune deficiency disease, is an example of our systematic approach to converting knowledge of human genes into drugs to treat serious diseases. We did not discover BLyS by accident, rather we designed a functional proteomics approach to search for naturally occurring substances, proteins made by human genes that stimulate immune function and trigger the production of antibodies. BLyS is one of about 10,000 human proteins that we have evaluated for their potential medical use. Once the BLyS protein was shown to stimulate antibody production, our team of scientists and physicians moved quickly to produce enough protein to conduct the extensive laboratory tests of safety and efficacy needed to initiate human clinical trials."

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For more information about Primary Immunodeficiencies, contact the Immune Deficiency Foundation at 800-296-4433, or visit their website at http://www.primaryimmune.org.

Individuals interested in BLyS or in Common Variable Immunodeficiency clinical trials are encouraged to contact Human Genome Sciences at 301-309-8504 extension 3550, or via the Internet at http://www.hgsi.com.

Human Genome Sciences is a company with the mission to treat and cure disease by bringing new gene-based drugs to patients.

HGS and Human Genome Sciences are registered trademarks of Human Genome Sciences, Inc. For additional information on Human Genome Sciences, Inc., visit the company's web site at www.hgsi.com. Copies of HGSI press releases are also available by fax 24 hours a day at no charge by calling 800-758-5804, ext. 121115. For additional information on BLyS and Common Variable Immunodeficiency please see additional background information attached to a copy of the press release on the HGS website. For more information about HGS' effort to discover cell to cell signaling molecules and high throughput functional genomics program, visit the HGS website and click on "Functional Genomics Program."

Any statements released by Human Genome Sciences, Inc. that are forward looking are made pursuant to the safe harbor provisions of the Private Securities Litigation Reform Act of 1995. Readers are cautioned that forward looking statements involve risks and uncertainties which may affect the company's business prospects and performance. These include economic, competitive, governmental, technological and other factors discussed in the company's filings with the Securities and Exchange Commission on forms 10-K, 10-Q and 8-K.

CONTACT:
David C. Stump, M.D.
Senior Vice President, Drug Development
and
Kate de Santis
Director, Corporate Communications and Investor Relations
Human Genome Sciences
301-309-8504


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