Human Genome Sciences, Inc. (Nasdaq: HGSI) today announced the top-line final results of a Phase 2b clinical trial of Albuferon(R) (albinterferon alfa-2b) in combination with ribavirin in treatment-naive patients with genotype 1 chronic hepatitis C. The Company expects to make a full presentation of the final results at an appropriate scientific meeting later in 2007.

"The final Phase 2b results confirm and extend the findings of several studies, which suggest that Albuferon may offer efficacy at least comparable to peginterferon alfa-2a, with half the injections and possibly less impairment of quality of life," said John McHutchison, M.D., Coordinating Center Principal Investigator for the Phase 2b trial, and Professor of Medicine and Associate Director, Duke Clinical Research Institute and Duke University Medical Center, Durham, North Carolina. "We are extremely pleased with the high quality of the data that have emerged from the Phase 2b study, and we look forward to continuing the evaluation of the 900-mcg and 1200-mcg doses of Albuferon in larger populations in Phase 3 trials."

The primary efficacy endpoint of the Phase 2b trial of Albuferon was sustained virologic response (SVR), defined as undetectable viral load (HCV RNA75 kg) who were treatment-adherent, 71.2% of those in the combined groups receiving Albuferon every two weeks achieved SVR, versus 53.3% for patients receiving Pegasys once a week. The ability to maintain efficacy in heavier patients is of particular importance in certain markets, including the United States, where a large percentage of patients weigh more than 75 kg.

Top-Line Final Results by Treatment Group

The top-line final results of the Phase 2b trial at Week 24 following the completion of therapy include the following SVR rates and other findings:

Albuferon 900-mcg Every Two Weeks (Albuferon 900 Q2w)

-- Based on an intention-to-treat (ITT) analysis, 58.5% of patients in the Albuferon 900 Q2w treatment group achieved SVR, vs. 57.9% for Pegasys administered every week.

-- In heavier patients (>75 kg) who were treatment-adherent, 74.2% of those in the Albuferon 900 Q2w treatment group achieved SVR, versus 53.3% for Pegasys.

-- Among all treatment-adherent patients in the Albuferon 900 Q2w treatment group, 72.3% achieved SVR, versus 66.7% for Pegasys.

-- Based on the SF-36 Health Survey, patients in the Albuferon 900 Q2w treatment group reported less impairment of health-related quality of life, compared with patients in the Pegasys treatment group, as measured by both physical component and mental component SF-36 summary measures at all time-points throughout the 48-week treatment period.

-- Fewer working patients in the Albuferon 900 Q2w treatment group reported missing 7 days or more of work during the month prior to their visits at Weeks 12 and 24, vs. the Pegasys group (Week 12: 3.0% for Albuferon 900 Q2w vs. 19.2% for Pegasys; Week 24: 5.8% for Albuferon 900 Q2w, vs. 22.4% for Pegasys).

-- The rate of discontinuations due to adverse events was 9.3% in the Albuferon 900 Q2w treatment group, vs. 6.1% in the Pegasys group.

"The 900-mcg Albuferon dose has the potential to offer patients an attractive therapeutic option, requiring half as many injections as Pegasys, with more favorable quality of life effects and favorable sustained virologic response data," said David C. Stump, M.D., Executive Vice President, Research and Development, HGS.

Albuferon 1200-mcg Every Two Weeks (Albuferon 1200 Q2w)

-- ITT analysis shows that 55.5% of patients in the Albuferon 1200 Q2w treatment group achieved SVR, vs. 57.9% for Pegasys administered every week.

-- In heavier patients (>75 kg) who were treatment-adherent, 67.9% of those in the Albuferon 1200 Q2w treatment group achieved SVR, versus 53.3% for Pegasys every week.

-- Among all treatment-adherent patients in the Albuferon 1200 Q2w treatment group, 70.6% achieved SVR, versus 66.7% for Pegasys.

-- ITT analysis shows that the Albuferon 1200 Q2w treatment group exhibited a robust early antiviral response (reduction in hepatitis C RNA viral load to below the level of quantitation): 74.5% for Albuferon 1200 Q2w at Week 12, vs. 65.8% for Pegasys. The Albuferon 1200 Q2w treatment group also had the most rapid time to HCV RNA negativity.

-- The rate of discontinuations due to adverse events was 18.2% in the Albuferon 1200 Q2w treatment group, vs. 6.1% in the Pegasys group. Adverse events observed were those typically expected with interferon therapy. Dose reductions were attempted in only 30.0% of Albuferon subjects prior to discontinuation, versus 42.9% for Pegasys.

"In the Albuferon Phase 3 trials, we will strongly encourage titration of dose where necessary to ensure tolerability, reduce the rate of discontinuations, and maximize the therapeutic benefit of the robust early antiviral response offered by the 1200-microgram dose on a two-week administration schedule," said Dr. Stump.

Albuferon 1200-mcg Monthly (Albuferon 1200 Q4w)

-- ITT analysis shows that 50.9% of patients in the Albuferon 1200 Q4w treatment group achieved SVR, vs. 57.9% for Pegasys administered every week.

-- In heavier patients (>75 kg) who were treatment-adherent, 61.0% of those in the Albuferon 1200 Q4w treatment group achieved SVR, versus 53.3% for Pegasys administered once every week.

-- Among all treatment-adherent patients in the Albuferon 1200 Q4w treatment group, 62.0% achieved SVR, versus 66.7% for Pegasys.

-- The rate of discontinuations due to adverse events was 12.1% in the Albuferon 1200 Q4w treatment group, vs. 6.1% in the Pegasys group.

-- The number of patients experiencing severe hematologic adverse events was significantly lower in the Albuferon 1200 Q4w treatment group (10.3%, vs. 23.7% for Pegasys, p=0.006).

"We are encouraged that more than half of the patients achieved sustained virologic response in the treatment group receiving Albuferon 1200-mcg once every month," said Dr. Stump. "These data, along with emerging Phase 2 data for a monthly 1500-mcg dose, provide an excellent rationale for the study that we and our collaborator, Novartis, are currently planning to evaluate higher doses of Albuferon administered monthly."

The top-line final Phase 2b results include data through Week 24 following completion of 48 weeks of therapy. The open-label, multi-center, active- controlled, dose-ranging trial enrolled and randomized 458 patients with genotype 1 chronic hepatitis C. Patients were randomized into four treatment groups, three of which received subcutaneously administered Albuferon (900 mcg every two weeks, 1200 mcg every two weeks, and 1200 mcg every four weeks). The fourth treatment group served as the active control group and received 180 mcg of subcutaneously administered peginterferon alfa-2a (Pegasys) once a week. All patients received weight-based oral ribavirin daily. The study was conducted in Australia, Canada, Czech Republic, France, Germany, Israel, Poland and Romania.

About Albuferon

Albuferon is a novel long-acting form of interferon alpha created by HGS using its proprietary albumin fusion technology. Albuferon results from the genetic fusion of human albumin and interferon alpha. Human albumin is the most prevalent naturally occurring blood protein in the human circulatory system, persisting in circulation in the body for over twenty days. Research has shown that genetic fusion of therapeutic proteins to human albumin decreases clearance and prolongs the half-life of the proteins. Recombinant interferon alpha is approved for the treatment of hepatitis C, hepatitis B and a broad range of cancers.

Albuferon is being developed by HGS and Novartis under an exclusive worldwide development and commercialization agreement entered into in June 2006. Under the agreement, HGS and Novartis will co-commercialize Albuferon in the United States, and will share clinical development costs, U.S. commercialization costs and U.S. profits equally. Novartis will be responsible for commercialization in the rest of the world and will pay HGS a royalty on those sales. Clinical development, commercial milestone and other payments to HGS could total as much as $507.5 million, including $92.5 million received to date.

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 the hepatitis C virus in the blood persist for at least six months, a person is diagnosed as having chronic hepatitis C. The hepatitis C virus can cause serious liver disease in a significant proportion of infected individuals, leading to cirrhosis, primary liver cancer, and even death.

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, anthrax disease, cancer, rheumatoid arthritis and HIV/AIDS. The Company's primary focus is rapid progress toward the commercialization of its two lead compounds, Albuferon(R) for hepatitis C, and LymphoStat-B(R) for lupus. Phase 3 clinical trials of both compounds are now underway.

In June 2006, HGS announced that the U.S. Government exercised its option under an existing contract to purchase 20,000 doses of ABthrax(TM) for the treatment of anthrax disease. Other HGS drugs in clinical development include two TRAIL receptor antibodies for the treatment of hematopoietic and solid malignancies, in addition to an antibody to the CCR5 receptor for the treatment of HIV/AIDS.

For more information about HGS, please visit the Company's web site at hgsi. For more information about Albuferon, please visit hgsi/products/albuferon.html. Health professionals or patients interested in Albuferon clinical trials or other studies involving HGS products may inquire via the Contact Us section of the Company's web site, hgsi/products/request.html, or by calling us at (301) 610-5790, extension 3550.

HGS, Human Genome Sciences, ABthrax, Albuferon 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 and clinical trials, 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. 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.

Human Genome Sciences, Inc.
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