LymphoStat-B® significantly reduced signs and symptoms of SLE disease at 52 Weeks and demonstrated durable clinical and biological activity at 76 weeks

ROCKVILLE, MD, USA | June 14, 2007 | Human Genome Sciences, Inc. (NASDAQ: HGSI) today announced the presentation of Phase 2 trial data demonstrating that LymphoStat-B® (belimumab) significantly reduced disease activity across multiple clinical measures, was well tolerated and improved quality of life in patients with active systemic lupus erythematosus (SLE). The 52-week and 76-week results of the Phase 2 study were the subject of an oral presentation today in Barcelona at the annual congress of the European League Against Rheumatism (EULAR).

“A number of clinical measures used in the Phase 2 study demonstrate that LymphoStat-B produced significant improvements in disease activity in patients with serologically active SLE,” said Ellen Ginzler, M.D., Professor of Medicine and Chief of Rheumatology at the Downstate Medical Center, State University of New York (SUNY) in Brooklyn. “At Week 52, we saw significant reductions in SLE disease activity as measured by the SELENA SLEDAI and BILAG indices and the Physician’s Global Assessment, as well as the patient response rate chosen as the primary efficacy endpoint of the Phase 3 trials. Continued improvements were observed from Week 52 through Week 76 in the 24-week extension phase of the trial.”

Dr. Ginzler noted that reductions observed in activated B cells and anti-dsDNA autoantibodies, as well as the improvements observed in health-related quality of life, were associated with therapeutic response. No increase in infections or infectious events was observed over time. “ We look forward to continuing the evaluation of LymphoStat-B as a potential treatment for SLE in the Phase 3 trials that are now underway,” she said.

Of the patients who completed 52 weeks of treatment in this randomized, double-blind, placebo-controlled Phase 2 trial, 96% (351/364) elected to enter the 24-week open-label extension phase of the trial, and 92% (321/351) of those who entered completed it. Of those completing the extension phase, 78% (250/321) continue to receive LymphoStat-B in a long-term continuation study. The trial began in October 2003.

“We are encouraged that nearly all of the patients who completed the 52-week Phase 2 study chose to continue treatment in the 24-week extension phase,” said William W. Freimuth, M.D., Ph.D., Vice President, Clinical Research – Immunology, Rheumatology and Infectious Diseases, Human Genome Sciences. “Many of these patients began treatment more than three years ago and continue on treatment today. This provides us with a substantial body of data on the long-term effects of LymphoStat-B.”

About the Phase 2 Trial Results
The primary objectives of the Phase 2 study were to evaluate the safety, tolerability and efficacy of LymphoStat-B plus standard of care, versus placebo plus standard of care. A total of 449 patients with active SLE were randomized to receive one of three different doses of LymphoStat-B or placebo (1, 4 or 10 mg/kg) administered intravenously over a 52-week treatment period, in addition to standard-of-care therapy. In the extension phase, all placebo patients received LymphoStat-B at a dose of 10 mg/kg, while patients in the LymphoStat-B 10 mg/kg treatment arm continued on the 10 mg/kg dose, and patients in the 1 mg/kg and 4 mg/kg LymphoStat-B treatment arms were offered the choice of continuing on the same dose or receiving LymphoStat-B at a dose of 10 mg/kg.

In June 2006, HGS reported the 52-week data from the Phase 2 trial of LymphoStat-B in patients with SLE. The 52-week results demonstrated that LymphoStat-B significantly reduced disease activity versus placebo in patients with serologically active SLE, exhibited clinically relevant biological activity, and appeared safe and well tolerated. Frequency and severity of adverse events were similar to placebo, with no increase at higher doses. Among the Phase 2 study findings was a significantly improved response rate among serologically active patients at Week 52, as defined by an improvement in SELENA SLEDAI score of 4 points or greater, no new BILAG A flare and no more than one new BILAG B flare, and no worsening in Physician’s Global Assessment (46% for LymphoStat-B versus 29% for placebo, p<0.01). This combination of measures is the primary efficacy endpoint in the Phase 3 clinical trials.

The data presented at EULAR 2007 demonstrated that LymphoStat-B continued to reduce the signs and symptoms of SLE disease activity throughout the 24-week extension phase of the study, demonstrated durable clinical and biological activity at Week 76, and appeared safe and well tolerated, with no increase in frequency and or severity of adverse events. The evidence of continuing improvement from Week 52 to Week 76 includes:

— An increase from 46% to 56% among serologically active patients in the patient response rate selected as the primary efficacy endpoint of the Phase 3 trials.

— An increase from 29% to 38% in the reduction in SLE disease activity among serologically active patients, as measured by SELENA SLEDAI.

— An increase from 33% to 41% in the reduction in SLE disease activity among serologically active patients, as measured by the Physician’s Global Assessment.

— An increase in the mean improvement in health-related quality of life from 3.0 points to 3.4 points among serologically active patients, as measured by the SF-36 Physical Component Summary score.

— A durable reduction in anti-dsDNA autoantibodies (at least 50% or negative) among patients who were positive for anti-dsDNA at baseline (30% at Week 52; 34% at Week 76).

— Durable or increased reductions from Week 52 to Week 76 in B-cell subsets including total CD20+, naïve (CD20+/CD27-), activated (CD20+/CD69+), and plasmacytoid (CD20+/CD138+).

— An increase in C4 complement among patients with low C4 complement at baseline (33% at Week 52; 46% at Week 76).

— Stable reductions in immunoglobulins, with no increase in infections or infectious events over time.

In addition, the 52-Week data showed that, in serologically active SLE patients, LymphoStat-B:

— Significantly delayed the time to SLE flare after six months (p<0.04);

— Significantly reduced the frequency of patients transitioning from low-dose prednisone (<7.5 mg/day) to high-dose prednisone (>7.5 mg/day) (p<0.05 over multiple time-points);

— Significantly reduced the number of patients experiencing BILAG Neurological and Musculoskeletal organ domain flares at Week 52 (Neurological p=0.04; Musculoskeletal p<0.01); Cardiovascular-Respiratory (p=0.06); and

— Produced significant and clinically meaningful improvements in health-related quality of life.

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.

In August 2006, HGS and GSK entered into a definitive co-development and co-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 disease. The Lupus Foundation of America estimates that approximately 1.5 million Americans suffer from various forms of lupus, including SLE. More than 300,000 people are afflicted with SLE in the United States alone. Lupus can occur at any age, but appears mostly in young people between the ages of fifteen and forty-five. About 90 percent of the individuals 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, the European Lupus Erythematosus Federation at www.elef.rheumanet.org, or the National Institute of Arthritis and Musculoskeletal and Skin Diseases at www.niams.nih.gov.

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.

HGS 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 planned 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. 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.

SOURCE: Human Genome Sciences, Inc.