Human Genome Sciences Announces Interim Results of Phase 2b Monthly-Dosing Trial of ZALBIN™ in Patients with Chronic Hepatitis C

Human Genome Sciences, Inc. (Nasdaq: HGSI) today announced interim results through Week 12 following the end of treatment in a Phase 2b clinical trial conducted by Novartis to evaluate the safety and efficacy of ZALBIN™ (albinterferon alfa-2b), an investigational agent, administered monthly in combination with ribavirin in 391 treatment-naive patients with genotypes 2 and 3 chronic hepatitis C virus. The primary efficacy endpoint is sustained virologic response (SVR) at Week 48 (24 weeks following the end of treatment).

"These interim results may suggest that the efficacy of 1500-mcg albinterferon alfa-2b dosed every four weeks is comparable to the current standard of 180-mcg peginterferon alfa-2a dosed once weekly,” said Stephen Pianko, M.D., F.R.A.C.P., Ph.D., Monash University, Melbourne, Australia. "The results of this study in patients infected with genotypes 2 and 3 hepatitis C support continued evaluation of albinterferon alfa-2b dosed every four weeks in a larger Phase 3 program.”

Sustained virologic response rates at Week 12 (SVR12) following the end of treatment were 81% for the treatment group receiving 1500-mcg albinterferon alfa-2b dosed once every four weeks (q4w), vs. 82% for the treatment group receiving peginterferon alfa-2a (Pegasys) at the standard 180-mcg dose once every week. SVR12 rates were 76% and 75%, respectively, for the 900-mcg q4w and 1200-mcg q4w albinterferon alfa-2b treatment groups.

Overall, the adverse event profile was generally comparable for q4w albinterferon alfa-2b compared with q1w peginterferon alfa-2a. Serious adverse events during treatment in the albinterferon alfa-2b treatment groups were 4% for 900-mcg, 3% for 1200-mcg, and 3% for 1500-mcg, compared with 4% for peginterferon alfa-2a. Rates of discontinuations due to adverse events were: 1% for 900-mcg, 3% for 1200-mcg, 4% for 1500-mcg, and 1% for peginterferon alfa-2a. No increase in serious or severe respiratory events was observed in any albinterferon alfa-2b arm compared to peginterferon alfa-2a. Hematologic reductions were significantly lower in all albinterferon alfa-2b treatment groups.

"With a total requirement of six injections over a 24-week course of treatment, the albinterferon alfa-2b monthly dosing regimen has the potential to offer an important option for the combination treatment of patients infected with genotypes 2 and 3 hepatitis C,” said Mani Subramanian, M.D., Ph.D., Executive Director, Clinical Research - Infectious Diseases, HGS. "We look forward to the full presentation of final results from the current study at an appropriate scientific meeting later in 2010.”

ZALBIN (also known as JOULFERON® outside the U.S.) is being developed by HGS and Novartis under an exclusive worldwide co-development and commercialization agreement entered into in 2006. The two companies have successfully completed Phase 3 development of ZALBIN dosed every two weeks. HGS has submitted a Biologics License Application (BLA) to the FDA in the United States for ZALBIN dosed every two weeks and has received confirmation that its submission was accepted for filing with a PDUFA target date of October 4, 2010. Novartis has submitted a Marketing Authorization Application to the European Medicines Agency (EMA) in Europe for the same dosing regimen under the brand name JOULFERON®.

About the Design of the Phase 2b Monthly Dosing Trial

This Phase 2b trial is a randomized, open-label, multi-center, active-controlled, dose-ranging study to evaluate the safety and efficacy of albinterferon alfa-2b administered every four weeks plus daily ribavirin in treatment-naïve patients with genotypes 2 and 3 chronic hepatitis C. 391 patients were randomized in a 4:4:4:3 ratio into four treatment groups, including three that received albinterferon alfa-2b administered once every four weeks (900 mcg, 1200 mcg or 1500 mcg), in addition to the active-control group, which received peginterferon alfa-2a at the standard 180-mcg dose once every week. All patients in the study received 800-mg daily oral ribavirin. The total duration of treatment was 24 weeks. The primary efficacy endpoint is sustained virologic response (SVR) at Week 48 (24 weeks following the end of treatment).

About the Collaboration with Novartis

Under an exclusive worldwide co-development and commercialization agreement entered into in 2006, HGS and Novartis will co-commercialize albinterferon alfa-2b in the United States as ZALBIN™, and will share clinical development costs, U.S. commercialization costs and U.S. profits equally. Novartis will be responsible for commercialization of albinterferon alfa-2b as JOULFERON® in the rest of the world, and will pay HGS a royalty on those sales. These brand names will be subject to confirmation by health authorities at the time of product approval.

HGS has primary responsibility for the bulk manufacture of albinterferon alfa-2b, and Novartis will have responsibility for commercial manufacturing of the finished drug product. Clinical development, commercial milestone and other payments to HGS could total as much as $507.5 million, including $207.5 million received to date. The remaining payments to HGS under the agreement relate to the achievement of certain regulatory approval and commercial milestones.

About ZALBIN (albinterferon alfa-2b)

ZALBIN (also known as JOULFERON) is a genetic fusion of human albumin and interferon alfa created using proprietary HGS albumin-fusion technology. Human albumin is the most prevalent naturally occurring blood protein in the human circulatory system, persisting in circulation in the body for approximately 19 days. Research has shown that genetic fusion of therapeutic proteins to human albumin decreases clearance and prolongs the half-life of the therapeutic proteins.

ZALBIN dosed once every two weeks has completed Phase 3 development. In April 2009, positive Phase 3 results of ZALBIN in patients with chronic hepatitis C were presented at the 44th annual meeting of the European Association for the Study of the Liver in Copenhagen. Data from two pivotal Phase 3 trials, ACHIEVE 1 and ACHIEVE 2/3, showed that ZALBIN met its primary endpoint of non-inferiority to Pegasys (peginterferon alfa-2a). With half the injections, ZALBIN achieved a rate of sustained virologic response comparable to Pegasys in these studies; rates of serious and/or severe adverse events were also comparable.

About Hepatitis C

Hepatitis C is an inflammation of the liver caused by the hepatitis C virus. It is estimated that as many as 170 million people worldwide are infected with hepatitis C virus. This includes nearly four million people in the United States. When detectable levels of HCV persist in the blood for at least six months, a person is diagnosed with chronic hepatitis C. Hepatitis C virus can cause serious liver disease, leading to cirrhosis, primary liver cancer and even death. Patients infected with the genotype 1 hepatitis C virus account for approximately 75% of the chronic hepatitis C patients in the U.S.

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 lupus, hepatitis C, inhalation anthrax and cancer.

The Company’s primary focus is rapid progress toward the commercialization of its two lead drugs, BENLYSTA™ (belimumab) for systemic lupus and ZALBIN™ (albinterferon alfa-2b) for hepatitis C. Phase 3 development has been completed successfully for both BENLYSTA and ZALBIN. The submission of marketing applications for BENLYSTA is planned in the U.S., Europe and other regions in the second quarter of 2010. A BLA has been submitted for ZALBIN to the FDA in the United States, and an MAA has been submitted under the brand name JOULFERON® to the EMA in Europe.

In April 2009, HGS completed the delivery of 20,000 doses of raxibacumab to the U.S. Strategic National Stockpile for use in the event of an emergency to treat inhalation anthrax. In July 2009, HGS secured a new purchase order for 45,000 doses and delivered the first 5,600 doses to the Stockpile under the new order in November 2009.

HGS also has several drugs in earlier stages of development for treatment of cancer, led by the TRAIL receptor antibody mapatumumab and a small-molecule antagonist of inhibitor-of-apoptosis proteins. In addition, HGS has substantial financial rights to certain products in the GSK clinical pipeline including darapladib, in Phase 3 development in patients with coronary heart disease, and Syncria® (albiglutide), in Phase 3 development in patients with type 2 diabetes.

For more information about HGS, please visit the Company’s web site at www.hgsi.com. Health professionals and patients interested in clinical trials of HGS products may inquire via e-mail to medinfo@hgsi.com or by calling HGS at (877) 822-8472.

HGS, Human Genome Sciences, BENLYSTA, and ZALBIN are trademarks of Human Genome Sciences, Inc. Other trademarks referenced are the property of their respective owners.

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 Human Genome Sciences’ unproven business model, its dependence on new technologies, the uncertainty and timing of clinical trials, Human Genome Sciences’ 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, Human Genome Sciences’ 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 SEC. 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.