First-in-class treatment for inhalation anthrax

ROCKVILLE, MD, USA | May 21, 2009 | Human Genome Sciences, Inc. (Nasdaq: HGSI) today announced that it has submitted a Biologics License Application (BLA) to the U.S. Food and Drug Administration (FDA) for its human monoclonal antibody drug ABthrax(TM) (raxibacumab) for the treatment of inhalation anthrax.

The BLA submission includes the results of two randomized placebo-controlled studies conducted in rabbits and monkeys to evaluate the efficacy of raxibacumab. These studies showed a survival benefit in two relevant animal species, which is the requirement for establishing the efficacy of new drugs used to counter bioterrorism. The submission also includes the results of safety studies of raxibacumab conducted in healthy human volunteers.

"Based on the results of our efficacy and safety studies, we believe raxibacumab has the potential to be an important new treatment for inhalation anthrax," said Sally D. Bolmer, Ph.D., R.A.C, Senior Vice President, Development and Regulatory Affairs, HGS. "In addition, the raxibacumab BLA is the first HGS has submitted, so it represents a significant milestone for our Company."

Raxibacumab is a first-in-class treatment for anthrax, and is being developed under a contract entered into in 2006 with the Biomedical Advanced Research and Development Authority (BARDA) of the Office of the Assistant Secretary for Preparedness and Response (ASPR), U.S. Department of Health and Human Services (HHS).

In the first quarter of 2009, under the BARDA contract, HGS achieved its first product sales by initiating the delivery of 20,000 doses of raxibacumab to the U.S. Strategic National Stockpile for emergency use in the treatment of inhalation anthrax. HGS recognized $153.8 million in raxibacumab revenue in the first quarter, including $127.8 million in product sales. The Company has now completed delivery and expects to recognize at least $8.0 million in additional raxibacumab revenue in the second quarter of 2009. The BLA is also being filed under the BARDA contract, and HGS will receive $10 million from the U.S. Government upon FDA licensure of raxibacumab.

About Anthrax

Anthrax infection is caused by a spore-forming bacterium, Bacillus anthracis, which multiplies in the body and produces lethal toxins. Most anthrax fatalities are caused by the irreversible effects of the anthrax toxins. Research has shown that the bacteria produce protective antigen, the key facilitator in the progression of anthrax infection at the cellular level. After protective antigen and the anthrax toxins are produced by the bacteria, protective antigen binds to the anthrax toxin receptor on cell surfaces and forms a protein-receptor complex that makes it possible for the anthrax toxins to enter the cells. Raxibacumab blocks the binding of protective antigen to cell surfaces and prevents the anthrax toxins from entering and killing the cells.

ABOUT HUMAN GENOME SCIENCES

The mission of HGS is to apply great science and great medicine to bring innovative drugs to patients with unmet medical needs. The HGS clinical development pipeline includes novel drugs to treat hepatitis C, lupus, inhalation anthrax and cancer.

The Company’s primary focus is rapid progress toward the commercialization of its two lead drugs, Albuferon(R) (albinterferon alfa-2b) for hepatitis C and LymphoStat-B(R) (belimumab) for lupus. Albuferon has now completed Phase 3 development, and the filing of global marketing applications is expected in fall 2009. Two Phase 3 clinical trials of LymphoStat-B are ongoing, with results expected in July and November 2009.

In January 2009, HGS began delivery of 20,000 doses of ABthrax(TM) (raxibacumab) to the U.S. Strategic National Stockpile for use in the event of an emergency for the treatment of inhalation anthrax. The Company also has several drugs in earlier stages of clinical development for the treatment of cancer, led by the TRAIL receptor antibody HGS-ETR1 and a small-molecule antagonist of IAP (inhibitor of apoptosis) proteins. In addition, HGS has substantial financial rights to certain products in the GSK clinical pipeline including darapladib, currently in Phase 3 development as a potential treatment for coronary heart disease, and Syncria(R) (albiglutide), currently in Phase 3 development as a potential treatment for type 2 diabetes.

For more information about HGS, please visit the Company’s web site at www.hgsi.com. Health professionals and patients interested in clinical trials of HGS products may inquire via e-mail to clinical_trials@hgsi.com or by calling HGS at (301) 610-5790, extension 3550.

HGS, Human Genome Sciences, ABthrax, Albuferon and LymphoStat-B are trademarks of Human Genome Sciences, Inc.

SOURCE Human Genome Sciences, Inc.