Two Phase 3 trials to provide the pivotal data to support global marketing applications for LymphoStat-B

ROCKVILLE, MD, USA | May 30, 2007 | Human Genome Sciences, Inc. (NASDAQ: HGSI) today announced that dosing has begun in BLISS-52, the second of two pivotal Phase 3 clinical trials of LymphoStat-B® (belimumab) in patients with active systemic lupus erythematosus (SLE). Dosing in BLISS-76, the first Phase 3 trial of LymphoStat-B, began in February 2007. LymphoStat-B is being developed by HGS and GlaxoSmithKline (GSK) under a definitive development and commercialization agreement entered into in August 2006.

“We believe that LymphoStat-B could address the significant medical need of patients suffering from SLE, and we are pleased to announce that both Phase 3 trials of this novel and potentially important compound are now underway,” said H. Thomas Watkins, President and Chief Executive Officer, HGS. “These trials, assuming that they are successful, will provide the pivotal data to support global marketing applications for LymphoStat-B.”

BLISS-52 is being conducted primarily in Asia, South America and Eastern Europe. BLISS-76 is being conducted primarily in North America and Europe.

“There is a great need for safer and more effective treatments for lupus,” said Professor Sandra V. Navarra, M.D., a principal investigator and head of Rheumatology at the University of Santo Tomas, Manila, Philippines. “The results of previous studies suggest that LymphoStat-B significantly reduced SLE disease activity in serologically active patients. We look forward to further evaluation of LymphoStat-B in larger numbers of patients in the Phase 3 trials.”

SLE is a chronic, life-threatening autoimmune disease. It is estimated that approximately 1.5 million people in the United States and approximately 5 million worldwide suffer from various forms of lupus, including SLE.

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 . Each of the Phase 3 trials will enroll approximately 810 patients. 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. HGS designed the LymphoStat-B Phase 3 program in collaboration with GSK and leading international SLE experts.

“The Phase 3 trials of LymphoStat-B will enroll more than 1600 patients worldwide, 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. “We expect these trials to enroll patients throughout 2007, and expect to complete enrollment of both of our Phase 3 trials of LymphoStat-B in 2008.”

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 will be randomized to one of three treatment groups: 1 mg/kg LymphoStat-B, 10 mg/kg LymphoStat-B, or placebo. Patients will be dosed intravenously on Days 0, 14 and 28, then every 28 days for the duration of the study. All will receive standard of care in addition to study medications. Safety and tolerability will be evaluated by an independent Data Monitoring Committee throughout both studies.

About LymphoStat-B

LymphoStat-B 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, rheumatoid arthritis 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.

LymphoStat-B was generated by HGS through a collaboration with Cambridge Antibody Technology. It has received a “fast-track product" designation from the FDA for its potential use in treating SLE and has been selected for participation in the FDA’s Continuous Marketing Application Pilot 2 Program, in which the FDA provides companies with more extensive feedback to improve the efficiency of the drug development and approval process. The FDA and the European Agency for the Evaluation of Medicinal Products have agreed that the Phase 3 trial design is suitable to support regulatory submissions and potential approval for marketing.

About the Collaboration with GSK

In August 2006, HGS and GSK entered into a definitive 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 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, rheumatoid arthritis and HIV/AIDS. The Company’s primary focus is rapid progress toward the commercialization of its two lead compounds, Albuferon for hepatitis C and LymphoStat-B for lupus – both of which are in Phase 3 clinical trials.

In June 2006, HGS announced that the U.S. government exercised its option under an existing contract to purchase 20,000 doses of ABthrax™ for the treatment of anthrax disease. Other HGS drugs in clinical development include two TRAIL receptor antibodies for the treatment of hematologic and solid malignancies, in addition to an antibody to the CCR 5 receptor for the treatment of HIV/AIDS.

For more information about HGS, visit www.hgsi.com. For more information on LymphoStat-B, visit www.hgsi.com/products/LSB.html. Health professionals or patients interested in LymphoStat-B clinical trials or other studies involving HGS products may inquire via the “Contact Us” section of the Company’s Web site, www.hgsi.com/products/request.html, or by calling (301) 610-5790, extension 3550.

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

SOURCE: Human Genome Sciences, Inc.