Human Genome Sciences (HGSI) and GlaxoSmithKline Announce Positive Results in Second of Two Phase 3 Trials of BENLYSTA(TM)

ROCKVILLE, MD and LONDON — (Marketwire) — 11/02/09 — Human Genome Sciences, Inc. (NASDAQ: HGSI) and GlaxoSmithKline PLC (GSK) today announced that BENLYSTA(TM) (belimumab) met the primary endpoint in BLISS-76, the second of two pivotal Phase 3 trials in seropositive patients with systemic lupus erythematosus (SLE). BLISS-76 study results through 52 weeks showed that belimumab 10 mg/kg plus standard of care achieved a statistically significant improvement in patient response rate as measured by the SLE Responder Index at Week 52, compared with placebo plus standard of care. Study results also showed that belimumab was generally well tolerated, as demonstrated by a similar rate of discontinuations due to adverse events across treatment groups, with overall adverse event rates comparable between belimumab and placebo treatment groups.

“The BLISS-76 results confirm our view 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. “We take great pride in the innovation and scientific rigor that has made it possible to bring BENLYSTA to this point. We plan to submit marketing applications in the first half of 2010, following discussions with regulatory authorities in the United States, Europe and other regions. We will continue to work with GSK to advance this drug to the market where it may benefit patients with significant need.”

Carlo Russo, M.D., Senior Vice President, Biopharm Development, GSK, said, “The results from this second pivotal Phase 3 trial reinforce our belief that belimumab could deliver a significant therapeutic option for patients with lupus who have had no new treatment in fifty years. We look forward to continuing our collaboration with HGS in order to bring this important medicine to patients.”

The data from the BLISS-76 study were analyzed after 52 weeks, in accord with the study protocol, in support of a potential Biologics License Application in the United States and Marketing Authorization Applications in Europe and other regions. However, the BLISS-76 study is ongoing and will continue for 24 more weeks. Additional data will be available following completion of the full 76-week study period. Belimumab is an investigational drug and the first in a new class of drugs called BLyS-specific inhibitors. Belimumab is being developed by HGS and GSK under a co-development and commercialization agreement entered into in August 2006.