First Phase 3 data, from BLISS-52 trial, expected by mid-2009. – Data from second Phase 3 trial, BLISS-76, expected by fall 2009

ROCKVILLE, MD, USA | August 27, 2008 | Human Genome Sciences, Inc. (Nasdaq: HGSI – News) today announced it has completed enrollment and initial dosing in BLISS-76, the second of two pivotal Phase 3 randomized clinical trials of LymphoStat-B(R) (belimumab) in patients with active systemic lupus erythematosus (SLE). Belimumab is being developed by HGS and GlaxoSmithKline (GSK) under a co-development and commercialization agreement entered into in August 2006.

"If LymphoStat-B is successful in Phase 3, we believe that it could represent a breakthrough in the treatment of patients suffering from SLE," said H. Thomas Watkins, President and Chief Executive Officer, HGS. "We have now completed enrollment in both of our LymphoStat-B Phase 3 trials. We are on track to have data from our first Phase 3 trial by mid-2009, and data from our second Phase 3 trial by fall 2009. Assuming positive results, we anticipate a BLA filing in the United States in the first half of 2010."

BLISS-76 was initiated in February 2007, and has enrolled and randomized 826 patients at 133 clinical sites in 19 countries, primarily in North America and Europe. In April 2008, BLISS-52, the first of the two belimumab Phase 3 trials, completed the enrollment of 867 patients at 90 clinical sites in 13 countries, primarily in Asia, South America and Eastern Europe.

"The BLISS studies are the largest double-blinded clinical trials ever conducted in lupus," said Joan T. Merrill, M.D., F.A.C.R., study investigator, and Program Chair, Clinical Pharmacology Research Program, Oklahoma Medical Research Foundation. "There is a significant need for new and more effective treatments for these patients, and we look forward to having the belimumab Phase 3 results available in 2009."

About the LymphoStat-B (belimumab) Phase 3 Development Program

The belimumab Phase 3 development program includes two double-blind, placebo-controlled, multi-center Phase 3 superiority trials — BLISS-52 and BLISS-76 — to evaluate the efficacy and safety of belimumab plus standard of care, versus placebo plus standard of care, in patients with serologically active SLE. The design of the two trials is similar, but the duration of therapy in the two studies is different — 52 weeks for BLISS-52 and 76 weeks for BLISS-76. The data from BLISS-76 will be analyzed after 52 weeks in support of a potential Biologics License Application (BLA). HGS designed the belimumab Phase 3 program in collaboration with GSK and leading international SLE experts.

"The belimumab clinical investigators have done a tremendous job in completing the randomization and initial dosing of BLISS-52 and BLISS-76 on our original timeline, despite the size and complexity of these studies," said Ann L. Wang, Vice President, Clinical Operations, HGS. "They have enrolled nearly 1700 patients worldwide into these Phase 3 trials. We are one step closer to results that we hope will confirm belimumab’s potential to offer a significant new treatment option for patients with SLE."

The primary efficacy endpoint of BLISS-52 and BLISS-76 is the patient response rate at Week 52, as defined by: a reduction from baseline of at least 4 points on the SELENA SLEDAI disease activity scale; no worsening of disease as measured by the Physician’s Global Assessment (worsening defined as an increase of more than 0.30 points from baseline); no new BILAG A organ domain score (which would indicate a severe flare of lupus disease activity) and no more than one new BILAG B organ domain score (which would indicate a moderate flare of disease activity).

In each of the two Phase 3 trials, patients have been randomized to one of three treatment groups: 1 mg/kg belimumab, 10 mg/kg belimumab, or placebo. Patients are dosed intravenously on Days 0, 14 and 28, then every 28 days for the duration of the study. All receive standard of care therapy in addition to the study medication. Safety and tolerability are evaluated by an independent Data Monitoring Committee throughout both studies.

About LymphoStat-B (belimumab)

Belimumab is a human monoclonal antibody that specifically recognizes and inhibits the biological activity of B-lymphocyte stimulator, or BLyS®. BLyS is a naturally occurring protein discovered by HGS that is required for the development of B-lymphocyte cells into mature plasma B cells. Plasma B cells produce antibodies, the body’s first line of defense against infection. In lupus and certain other autoimmune diseases, elevated levels of BLyS are believed to contribute to the production of autoantibodies – antibodies that attack and destroy the body’s own healthy tissues. The presence of autoantibodies appears to correlate with disease severity. Preclinical and clinical studies demonstrate that B-cell antagonists can reduce autoantibody levels and help control autoimmune disease activity.

About Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is a chronic, life-threatening autoimmune disease. Approximately 1.5 million people in the United States and approximately 5 million worldwide suffer from various forms of lupus, including SLE. Lupus can occur at any age, but appears mostly in young people ages 15 to 45. About 90 percent of those diagnosed with lupus are women. African-American women are about three times more likely to develop lupus, and it is also more common in Hispanic, Asian and American Indian women. Symptoms may include extreme fatigue, painful and swollen joints, unexplained fever, skin rash and kidney problems. Lupus can lead to arthritis, kidney failure, heart and lung inflammation, central nervous system abnormalities, inflammation of the blood vessels and blood disorders. For more information on lupus, visit the Lupus Foundation of America at www.lupus.org or the European Lupus Erythematosus Federation at www.elef.rheumanet.org.

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, 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(R) (belimumab) for lupus. Phase 3 clinical trials of both drugs are ongoing.

ABthrax(TM) (raxibacumab) is in late-stage development for the treatment of inhalation anthrax, and the Company is on track to begin the delivery in fall 2008 of 20,000 doses of ABthrax to the Strategic National Stockpile under a contract entered into with the U.S. Government in June 2006. HGS also has three drugs in clinical development for the treatment of cancer, including two TRAIL receptor antibodies 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 development pipeline.

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.