ROCKVILLE, Maryland – June 12, 2008 – Human Genome Sciences, Inc. (Nasdaq: HGSI) today announced the presentation of results from a long-term Phase 2 continuation trial showing that LymphoStat-B® (belimumab) was associated with sustained improvement in disease activity across multiple clinical measures, decreased frequency of disease flares, potential steroid-sparing activity, and was generally well tolerated through three years on treatment in combination with standard of care in patients with serologically active systemic lupus erythematosus (SLE). The results are the subject of a number of oral and poster presentations today in Paris at the 2008 Congress of the European League Against Rheumatism (EULAR).

“Based on the results presented at EULAR 2008, the clinical benefit observed for belimumab at Week 52 of this Phase 2 study appears to be durable through three years,” said Richard Furie, M.D., Chief, Division of Rheumatology and Allergy-Clinical Immunology, North Shore Long Island Jewish Health System, Lake Success, NY, and Professor of Medicine, Albert Einstein College of Medicine. “We observe that patients who crossed over from placebo to belimumab after Week 52 have also shown improvement across multiple clinical measures. The durability of clinical effect and the favorable safety profile observed for belimumab suggest that it has the potential to play an important role in the treatment of SLE.”

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.

“At Week 52 in belimumab patients with serologically active SLE, we saw significant reductions in SLE disease activity versus placebo based on multiple measures of clinical effect, including the response rate chosen as the primary efficacy endpoint of the Phase 3 trials,” said William W. Freimuth, M.D., Ph.D., Vice President, Clinical Research – Immunology, Rheumatology and Infectious Diseases. “We are encouraged by the continued improvement in these patients through three years. 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.”

LymphoStat-B (belimumab) is being developed by HGS and GlaxoSmithKline (GSK) under a co-development and commercialization agreement entered into in August 2006. The first Phase 3 data for LymphoStat-B are expected by mid-2009, and all Phase 3 data to support regulatory filings are expected in fall 2009.

Key Findings from the Phase 2 Study Continuation Through Three Years

The data presented today at EULAR 2008 demonstrate that continued treatment with belimumab is associated with sustained improvement or stabilization of SLE disease activity in serologically active patients through three years of treatment. Belimumab decreased the frequency of SLE disease flares and reduced the need for high-dose steroids in these patients over time. The overall incidence of adverse events (in general and by system organ class), serious adverse events, infections, malignancies and laboratory abnormalities continued to decrease or stabilize from Week 52 to Week 160.

The evidence of sustained clinical effect in belimumab-treated patients from Week 52 to Week 160 includes:

• An increase from 46% to 52% among serologically active patients based on the combined response rate selected as the primary efficacy endpoint of the Phase 3 trials (intention-to-treat analysis).
• A decrease over time in the overall frequency of SLE disease flares, and in the frequency of severe disease flares, in patients who remained on belimumab through three years, as measured by the SELENA SLEDAI flare index.
• A greater proportion of patients in the belimumab group reduced their prednisone dose from baseline compared with the placebo group in the double-blind phase of the study, and this number continued to increase through three years.
• Reversion of autoantibody levels from positive to negative (anti-dsDNA, anti-RNP, anti-Smith).
• Stable reductions in immunoglobulins, with no increase in infections or infectious events over time.
• An increase in C3 and C4 complement among patients with low complement at baseline.

About the Phase 2 Study of LymphoStat-B in SLE

The primary objectives of the Phase 2 study were to evaluate the efficacy and safety of belimumab (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 belimumab or placebo (1, 4 or 10 mg/kg) 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 May 21, 2008, 235 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 combination of measures is the primary efficacy endpoint in the ongoing pivotal Phase 3 clinical trials.

About LymphoStat-B (belimumab)

LymphoStat-B (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. Pre-clinical and clinical studies demonstrate that B-cell antagonists can reduce autoantibody levels and help control autoimmune disease activity.

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 and a small-molecule antagonist of IAP (inhibitor of apoptosis) proteins for the treatment of cancer. In addition, HGS has substantial financial rights to three products in the GlaxoSmithKline clinical development pipeline.

To view the EULAR oral presentation reporting results of the Phase 2 long-term continuation study of LymphoStat-B through three years, click here. To view the EULAR poster presentation reporting the safety profile of LymphoStat-B through three years, click here. To view the EULAR poster presentation reporting the progressive normalization of autoantibody, immunoglobulin and complement levels over three years of treatment with LymphoStat-B, click here. To view the EULAR poster presentation reporting evidence of LymphoStat-B’s potential steroid-sparing activity, click here. For more information on LymphoStat-B, visit www.hgsi.com/belimumab.html. 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 . For more information about HGS, visit www.hgsi.com. Health professionals or patients interested in clinical trials of HGS products may inquire via email to This 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, BLyS and LymphoStat-B are trademarks of Human Genome Sciences, Inc.

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, the Company will continue to face risks related to animal and human testing, to the manufacture of ABthrax and to FDA concurrence that ABthrax meets the requirements of the ABthrax contract. If the Company is unable to meet the product requirements associated with the ABthrax contract, the U.S. government will not be required to reimburse the Company for the costs incurred or to purchase any ABthrax doses, and we will not receive any of the expected revenues relative to ABthrax. 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.

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