Human Genome Sciences Reports Positive Long-Term Data for BENLYSTA(TM) in Patients With Active Systemic Lupus Erythematosus

ROCKVILLE, Md. — Human Genome Sciences, Inc. (Nasdaq: HGSI) today announced the presentation of results from a long-term Phase 2 continuation trial showing that BENLYSTA(TM) (belimumab, formerly LymphoStat-B(R)) was associated with sustained improvement in disease activity across multiple clinical measures, decreased frequency of disease flares, and was generally well tolerated through four years on treatment in combination with standard of care in patients with serologically active systemic lupus erythematosus (SLE).

The results were presented today in Copenhagen at the 2009 Congress of the European League Against Rheumatism (EULAR).

“Based on the results presented at EULAR 2009, the apparent durability of clinical effect and the favorable safety profile observed for belimumab suggest that belimumab has the potential to become an important new treatment for patients with SLE,” said Joan T. Merrill, M.D., a study investigator, Program Chair, Clinical Pharmacology Research Program, Oklahoma Medical Research Foundation, Oklahoma City, and Professor, Department of Medicine, University of Oklahoma Health Sciences Center.

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.

“We are encouraged by the sustained improvement in serologically active SLE patients treated with belimumab through four years,” said William W. Freimuth, M.D., Ph.D., Vice President, Clinical Research – Immunology, Rheumatology and Infectious Diseases. “We are also encouraged by the safety data presented at EULAR. The incidence rates per 100 patient years of all adverse event categories, including serious adverse events, overall adverse events, and serious infections were similar for belimumab and placebo during the 52-week double-blind period, and remained the same or decreased over four years of continuous treatment. Belimumab could represent a significant advance in the treatment of SLE if Phase 2 results are confirmed in the Phase 3 trials that are currently ongoing.”

BENLYSTA(TM) Selected as Belimumab Brand Name; Phase 3 Results Expected in July and November 2009

HGS and GlaxoSmithKline (GSK) have selected BENLYSTA as the brand name for belimumab (formerly known as LymphoStat-B). HGS and GSK expect to report the first Phase 3 data for BENLYSTA in July 2009 from the BLISS-52 trial, with results from BLISS-76 anticipated in November 2009. BLISS-52 and BLISS-76 are the largest clinical trials ever conducted in lupus patients. BENLYSTA is being developed by HGS and GSK under a co-development and commercialization agreement entered into in August 2006.

Key Findings from the Phase 2 Study Continuation through Four Years

The data presented today at EULAR 2009 showed that continued treatment with belimumab (BENLYSTA) is associated with sustained improvement or stabilization of SLE disease activity and with decreased frequency of SLE disease flares in serologically active patients through four years of treatment. The overall incidence of adverse events (in general and by system organ class), serious adverse events, infections, malignancies and laboratory abnormalities decreased or stabilized over time from Week 52 to Week 208.

The evidence of sustained clinical effect from Week 52 to Week 208 in serologically active patients who were treated with belimumab from initiation of the Phase 2 study includes:

* An increase from 46% to 57% in the response rate selected as the primary efficacy endpoint of the Phase 3 trials (defined by an improvement in SELENA SLEDAI score of 4 points or greater, no BILAG worsening, and no worsening in Physician’s Global Assessment; post hoc; intention-to-treat analysis).

* A decrease from 62% to 16% in the overall frequency of SLE disease flares, and from 8% to 1% in the frequency of severe disease flares, as measured by the SELENA SLEDAI Flare Index.

* A decrease from 23% to 5% in the frequency of patients experiencing one new BILAG A organ domain score (which would indicate a severe flare of lupus disease activity) or more than one new BILAG B organ domain score (which would indicate a moderate flare of disease activity).

The data presented at EULAR 2009 suggest that belimumab was generally well tolerated and may be safely administered long-term in patients with SLE. By Week 208, overall belimumab exposure was 1192 patient years. The incidence rates per 100 patients in all adverse event categories, including serious adverse events, overall adverse events, and serious infections, were similar for belimumab and placebo during the 52-week double-blind period, and remained the same or decreased over four years of continuous treatment.

To view the EULAR poster presentation reporting results of the Phase 2 long-term continuation study of BENLYSTA through four years, click here.

About the Phase 2 Study of BENLYSTA in SLE

The primary objectives of the Phase 2 study were to evaluate the efficacy and safety of belimumab (BENLYSTA) 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 belimumab (1, 4 or 10 mg/kg) or placebo administered intravenously over a 52-week treatment period, in addition to standard-of-care therapy. At the end of 52 weeks, 345 patients chose to participate in an optional 24-week extension phase of the study, during which all patients received belimumab. At Week 76, 296 patients chose to remain on belimumab treatment in an open-label long-term continuation phase of the Phase 2 trial, in which all patients are receiving 10 mg/kg belimumab. As of June 1, 2009, 213 patients remained on belimumab treatment in the continuation study.

In June 2006, HGS reported the 52-week results of the Phase 2 trial, which demonstrated that belimumab significantly reduced disease activity versus placebo in patients with serologically active SLE across multiple clinical measures, exhibited clinically relevant biological activity, and appeared generally safe and well tolerated. Frequency and severity of adverse events were similar to placebo. Among the findings at Week 52 was a significantly improved response rate among serologically active patients, 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. This response rate is the primary efficacy endpoint in the ongoing pivotal Phase 3 clinical trials.

About BENLYSTA (belimumab)

BENLYSTA 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 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 BLyS 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 definitive co-development and co-commercialization agreement under which HGS has responsibility for conducting the BENLYSTA 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, the National Institute of Arthritis and Musculoskeletal and Skin Diseases at, or Lupus Europe at

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 and cancer.

The Company’s primary focus is rapid progress toward the commercialization of its two lead drugs, Albuferon(R) (albinterferon alfa-2b) for hepatitis C and BENLYSTA(TM) (belimumab, formerly LymphoStat-B(R)) for lupus. Albuferon has now completed Phase 3 development, and the filing of global marketing applications is expected in fall 2009. Two Phase 3 trials of BENLYSTA are ongoing, with results expected in July and November 2009.

In April 2009, HGS completed delivery of 20,000 doses of ABthrax(TM) (raxibacumab) to the U.S. Strategic National Stockpile for use in the event of an emergency for the treatment of inhalation anthrax. The Company also has several drugs in earlier stages of clinical development for the treatment of cancer, led by the TRAIL receptor antibody HGS-ETR1 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 pipeline including darapladib, currently in Phase 3 development as a potential treatment for coronary heart disease, and Syncria(R) (albiglutide), currently in Phase 3 development as a potential treatment for type 2 diabetes.

For more information about HGS, please visit the Company’s web site at Health professionals and patients interested in clinical trials of HGS products may inquire via e-mail to [email protected] or by calling HGS at (301) 610-5790, extension 3550.

HGS, Human Genome Sciences, ABthrax, Albuferon, BENLYSTA 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 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, while the Company has begun shipment of ABthrax to the U.S. Strategic National Stockpile, the Company will continue to face risks related to FDA’s approval of the Company’s Biologics License Application for ABthrax. If the Company is unable to meet requirements associated with the ABthrax contract, future revenues from the sale of ABthrax to the U.S. Government will not occur. 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.