Completion of enrollment in second Phase 3 trial expected by end of summer. First Phase 3 data now expected by mid-2009, with all Phase 3 data expected in fall 2009

ROCKVILLE, Maryland, USA | April 22, 2008 | Human Genome Sciences, Inc. (NASDAQ: HGSI) today announced that it has completed enrollment and initial dosing in BLISS-52, one of two pivotal Phase 3 clinical trials of LymphoStat-B(R) (belimumab) in patients with active systemic lupus erythematosus (SLE). LymphoStat-B is being developed by HGS and GlaxoSmithKline (GSK) under a co-development and commercialization agreement entered into in August 2006.

“We continue to be excited by LymphoStat-B’s potential. Assuming it is successful in Phase 3, we believe that LymphoStat-B could represent a breakthrough in the treatment of SLE,” said H. Thomas Watkins, President and Chief Executive Officer, HGS. “With enrollment now completed in the BLISS-52 trial, we are on track to have our first Phase 3 data for LymphoStat-B available by mid-2009, and all Phase 3 data available in fall 2009.”

BLISS-52 was initiated in May 2007, and has enrolled and randomized a total of 867 patients at 90 clinical sites in 13 countries, primarily in Asia, South America and Eastern Europe. Completion of enrollment for the other pivotal Phase 3 trial of belimumab, BLISS-76, is expected by the end of summer 2008. BLISS-76, which was initiated in February 2007, is being conducted primarily in North America and Europe, and will enroll and randomize a minimum of 810 subjects.

“The results of previous studies suggest that belimumab significantly reduced SLE disease activity in serologically active patients,” said Professor Sandra V. Navarra, M.D., a principal investigator and head of Rheumatology at the University of Santo Tomas, Manila, Philippines. “There is a great need for better tolerated and more effective treatments for lupus, and we look forward to seeing the first Phase 3 data for belimumab by mid-2009.”
About the LymphoStat-B Phase 3 Development Program

The LymphoStat-B 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 LymphoStat-B 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 LymphoStat-B Phase 3 program in collaboration with GSK and leading international SLE experts.

“A total of nearly 1700 patients worldwide will be enrolled and randomized in the Phase 3 trials of belimumab, making this the largest double-blinded clinical development program ever undertaken in lupus patients,” said William W. Freimuth, M.D., Ph,D., Vice President, Clinical Research – Immunology, Rheumatology and Infectious Diseases, HGS. “Today’s milestone brings us closer to seeing Phase 3 data that we hope will confirm belimumab’s promise as a potential treatment for patients with SLE. We are grateful for the superb performance of our clinical investigators, whose diligence made it possible to complete the enrollment of BLISS-52 ahead of our fall 2008 projection.”

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 are 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 study medication. Safety and tolerability are evaluated by an independent Data Monitoring Committee throughout both studies.

About LymphoStat-B

LymphoStat-B (belimumab) is a human monoclonal antibody that specifically recognizes and inhibits the biological activity of B-lymphocyte stimulator, or BLyS(R). 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 infections. 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. Pre-clinical and clinical studies demonstrate that B-cell antagonists can reduce autoantibody levels and help control autoimmune disease activity.

About the Collaboration with GSK

In August 2006, HGS and GSK entered into a co-development and commercialization agreement under which HGS has responsibility for conducting the LymphoStat-B Phase 3 trials, with assistance from GSK. The companies will share equally in Phase 3/4 development costs, sales and marketing expenses, and profits of any product commercialized under the agreement.
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 (belimumab) for lupus. Phase 3 clinical trials of both drugs are ongoing.

ABthrax (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. Other HGS drugs in clinical development include two TRAIL receptor antibodies for the treatment of cancer. In addition, HGS1029, a small-molecule antagonist of IAP (inhibitor of apoptosis) proteins, is expected to enter Phase 1 clinical trials for the treatment of cancer in early 2008. HGS also has substantial financial rights to certain products in the GlaxoSmithKline clinical development pipeline.

For information about HGS, please visit the Company’s web site at www.hgsi.com. Health professionals or patients interested in clinical trials of HGS products may inquire via email to clinical_trials@hgsi.comThis e-mail address is being protected from spam bots, you need JavaScript enabled to view it , or by calling (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.