- Human Genome Sciences’ ABthrax TM shows lifesaving potential -

- HGS on track to deliver 20,000 doses to Strategic National Stockpile beginning in 2008 -

ROCKVILLE, Maryland – December 18, 2007 – Human Genome Sciences, Inc. (Nasdaq: HGSI ) today announced that the results of two animal studies demonstrated the life-saving potential of its human monoclonal antibody drug ABthrax™ (raxibacumab). The results show that a single dose of ABthrax, administered without concomitant antibiotics, improved survival rates by up to 64 percent when administered after animals were symptomatic for anthrax disease as a result of inhalation exposure to massively lethal doses of anthrax spores. These dramatic and statistically significant findings demonstrate a survival benefit in two animal species, which is the requirement for establishing the efficacy of new drugs used to counter bioterrorism.

“We believe that ABthrax offers a significant step forward in the treatment of inhalational anthrax, and could play an important role in strengthening America’s arsenal against bioterrorism,” said H. Thomas Watkins, President and Chief Executive Officer, HGS.

ABthrax, which specifically targets anthrax toxins and is being developed under contract with the Biomedical Advanced Research and Development Authority (BARDA), represents a new way to address the anthrax threat. While antibiotics can kill the Bacillis anthracis bacteria, they are not effective against the deadly toxins that the bacteria produce – the real culprits in anthrax-related deaths. ABthrax targets anthrax toxins after they are released into the blood. In an inhalation anthrax attack, people may not know they are infected with anthrax until the toxins already are circulating in their blood, and it may be too late for antibiotics alone to be effective.

“These results show that ABthrax was highly effective as a treatment for anthrax in both rabbits and monkeys, and acted quickly to provide a significant survival benefit to animals showing clinical symptoms caused by exposure to massively lethal aerosolized doses of anthrax spores,” said David C. Stump, M.D., Executive Vice President, Research and Development, HGS. “The new data are consistent with the results of previous studies in multiple animal models, which demonstrated that a single dose of ABthrax given prophylactically provided up to 100% protection against death.”

HGS said that it has met all milestones to date under the Company’s contract with the U.S. Department of Health and Human Services (HHS), and is on track to deliver ABthrax to the Strategic National Stockpile beginning in 2008.

“We have demonstrated the efficacy of ABthrax in multiple therapeutic and prophylactic animal models of inhalational anthrax , ” said James H. Davis, Ph.D., J.D., Executive Vice President and General Counsel, HGS. “ We have demonstrated that it was generally safe and well tolerated in two clinical trials to date in healthy adults. We have manufactured conformance lots of ABthrax and are currently producing ABthrax for delivery to the Stockpile. We have more work to do, but our interactions with HHS, FDA and CDC continue to be positive, and the ABthrax program is progressing well.”

Research Findings

In one of the animal studies, three groups of monkeys were exposed by inhalation to anthrax spores and treated with either ABthrax or placebo after they showed clinical signs of anthrax disease. After 28 days, the study found that:

64.3 percent of monkeys that received a single high dose of ABthrax survived (p=0.0007 vs. placebo).
50 percent of those that received a low dose survived (p=0.0064 vs. placebo).
None of the monkeys in the placebo control group survived.
A separate study that measured 14-day survival in rabbits also demonstrated a statistically significant survival benefit versus placebo. All ABthrax-treated animals that survived in both studies were rapidly cleared of anthrax toxin and bacteria following intravenous administration of a single dose of ABthrax. In contrast, all placebo-treated animals remained bacteremic or toxemic and died.

HGS also reported today that it has completed the second safety study of ABthrax in human volunteers, bringing the total number of people who have participated in human safety trials to more than 180. The clinical results to date suggest that ABthrax was generally safe and well tolerated. In addition, the new study demonstrated that co-administration of ABthrax with the antibiotic Cipro (ciprofloxacin) did not affect the pharmacokinetics of either Cipro or ABthrax, and suggested that ABthrax can be administered in combination with antibiotics. This is a key finding given the important role that antibiotics are expected to continue to play in the treatment of anthrax disease.

The Need for New Means to Fight Anthrax Infections

Two options are currently available for the prevention or treatment of anthrax infections – a vaccine and antibiotics. Both are essential to dealing with anthrax, but both have limitations. The anthrax vaccine takes several weeks following the initial doses before immunity is detectable, and requires multiple injections over a period of eighteen months, in addition to annual booster vaccination, to maintain protective immunity. Antibiotics are effective in killing anthrax bacteria, but are not effective against the anthrax toxins once those toxins have been released into the blood. Antibiotics also may not be effective against antibiotic-resistant strains of anthrax.

ABthrax is a human monoclonal antibody to Bacillus anthracis protective antigen that was discovered and developed by HGS, using technology that HGS has integrated into the Company as part of its collaboration with Cambridge Antibody Technology. ABthrax was the first investigational agent against anthrax infection to be evaluated in a clinical study following the 2001 anthrax attacks in the United States. In 2003, ABthrax received a Fast Track Product designation from the FDA, as well as an Orphan Drug Designation for its use in the treatment of inhalational anthrax disease.

In contrast to the anthrax vaccine, the protection afforded by a single dose of ABthrax would be immediate following the rapid achievement of appropriate blood levels of ABthrax. In contrast to antibiotics, ABthrax acts against the deadly toxins produced by anthrax bacteria. It may also prevent and treat infections by antibiotic-resistant strains of anthrax.

The ABthrax Contract with the U.S. Government

In June 2006, the U.S. Government exercised its option to purchase ABthrax for the Strategic National Stockpile (Contract Number HHS010020050006C). HGS expects to receive $165 million in revenues from this award, with the majority to come in 2008, when the Company begins to deliver ABthrax. The purchase award was made by the U.S. Department of Health and Human Services (HHS) under the Project BioShield Act of 2004, which is designed to accelerate the development, purchase and availability of medical countermeasures for the Strategic National Stockpile.

Under the contract, HGS will manufacture and deliver 20,000 treatment courses of ABthrax to the Strategic National Stockpile. The Company is also working closely with HHS, FDA and CDC to complete the additional laboratory and clinical testing required to support the filing of a Biologics License Application (BLA), and to support the use of ABthrax in patients with inhalational anthrax disease in the event of an emergency prior to FDA licensure.

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. ABthrax 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, anthrax disease, cancer and other immune-mediated diseases. The Company’s primary focus is rapid progress toward the commercialization of its two key lead drugs, Albuferon® (albinterferon alfa-2b) for hepatitis C and LymphoStat-B® (belimumab) for lupus. Phase 3 clinical trials of both drugs are ongoing. ABthrax (raxibacumab) is in late-stage development for the treatment of anthrax disease. Other HGS drugs in clinical development include two TRAIL receptor antibodies for the treatment of cancers.

For more information about HGS, please visit the Company’s web site at For more information about ABthrax, please visit Health professionals or patients interested in clinical trials or other studies involving HGS products may inquire via the “Contact Us” section of the Company’s web site,, or by calling (301) 610-5790, extension 3550.

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

Safe Harbor Statement

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 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. In addition, the Company will continue to face risks related to animal and human testing, to the manufacture of ABthrax and to FDA concurrence that ABthrax meets the requirements of the ABthrax contract. If the Company is unable to meet the product requirements associated with the ABthrax contract, the U.S. government will not be required to reimburse the Company for the costs incurred or to purchase any ABthrax doses. 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.