Human Genome Sciences and GlaxoSmithKline Announce Positive Phase 3 Study Results for BENLYSTA(TM) in Systemic Lupus Erythematosus

BENLYSTA (Belimumab) Met Its Primary Efficacy Endpoint by Achieving a Statistically Significant Improvement in Patient Response Rate Versus Placebo in BLISS-52; First Drug for Lupus to Reach This Advanced Stage of Clinical Development and Achieve Positive Results, in the Largest Randomized Placebo-Controlled Clinical Trial Ever Completed in SLE Patients

ROCKVILLE, MD and LONDON--(Marketwire - July 20, 2009) - Human Genome Sciences, Inc. (NASDAQ: HGSI) and GlaxoSmithKline PLC (GSK) today announced that BENLYSTA™ (belimumab, formerly LymphoStat-B®) met the primary endpoint in BLISS-52, the first of two pivotal Phase 3 trials in patients with serologically active systemic lupus erythematosus (SLE). In the placebo-controlled BLISS-52 study, the results showed that BENLYSTA plus standard of care achieved a clinically and statistically significant improvement in patient response rate at Week 52, compared with standard of care alone. Study results also showed that belimumab was generally well tolerated, with adverse event rates comparable between belimumab and placebo treatment groups.

"The BLISS-52 results demonstrated that BENLYSTA has the potential to become the first new approved drug in decades for people living with systemic lupus," said H. Thomas Watkins, President and Chief Executive Officer, HGS. "Given the limited treatment options currently available, patients would benefit greatly from potential new treatments. BENLYSTA is an outstanding example of the type of treatment HGS is working to develop and bring to patients. Assuming positive results in November from our second Phase 3 trial of BENLYSTA, we and GSK plan to submit marketing applications in the United States, Europe and other regions in the first half of 2010."

Belimumab is an investigational drug and the first in a new class of drugs called BLyS-specific inhibitors. No new drug for lupus has been approved by regulatory authorities in more than 50 years. Belimumab is being developed by HGS and GSK under a co-development and commercialization agreement entered into in August 2006.

"Lupus is a chronic, often debilitating, and sometimes fatal illness that affects an estimated five million people worldwide and can have a devastating effect on both patients living with the disease and their families," said Carlo Russo, M.D., Senior Vice President, Biopharm Development, GSK. "BENLYSTA is the first medicine being developed specifically for lupus that has reached this late stage of clinical development with positive results. We look forward to completing the pivotal studies, with the hope of bringing this potentially important therapeutic advance to patients suffering from SLE."