Human Genome Sciences, Inc. (Nasdaq: HGSI) today announced that it has initiated dosing in ACHIEVE 1, one of two pivotal Phase 3 clinical trials of Albuferon(R) (albinterferon alpha 2b) in combination with ribavirin in treatment-naive patients with genotype 1 chronic hepatitis C. Albuferon is being developed by HGS and Novartis under an exclusive worldwide development and commercialization agreement entered into in June 2006.

"We are pleased to advance Albuferon to Phase 3 clinical trials," said H. Thomas Watkins, President and Chief Executive Officer, HGS. "Hepatitis C is the most common chronic blood-borne infection in the developed world. We believe that Albuferon could become the interferon of choice in treatment regimens for this potentially devastating disease. Albuferon is the first drug from HGS research to enter Phase 3 development, so today's announcement is an important step in the transformation of HGS into a commercial organization."

The combination of pegylated interferon alpha and ribavirin is the current standard of care, and produces cures in approximately 50 percent of all genotype 1 HCV patients completing therapy. However, a substantial additional percentage of patients never receive therapy for a variety of reasons. Side effects, many of which are associated with injections of interferon alpha, continue to be a significant treatment-limiting issue. Albuferon requires half as many injections, and clinical results to date suggest the potential for less impairment of health-related quality of life, with efficacy and safety at least comparable to pegylated interferon.

"There continues to be a significant need for more effective and better tolerated treatments for chronic hepatitis C," said John McHutchison, M.D., Professor of Medicine and Director, GI/Hepatology Research, Duke Clinical Research Institute and Duke University Medical Center, Durham, NC. "We look forward to continuing the evaluation of Albuferon in larger populations in Phase 3 trials."

About the Design of the Albuferon Phase 3 Development Program

The Albuferon Phase 3 clinical development program includes two randomized, open-label, active-controlled, multi-center, non-inferiority trials to evaluate the efficacy, safety and impact on health-related quality of life of Albuferon in combination with ribavirin, versus PEGASYS (peginterferon alfa-2a) in combination with ribavirin.

"HGS designed ACHIEVE 1 and ACHIEVE 2/3 working closely with our development and commercialization partner, Novartis, and with leading international experts in the field of hepatitis C," said David C. Stump, M.D., Executive Vice President, Drug Development, HGS. "We also reviewed the pivotal trial designs with U.S. and key European regulatory authorities and received their positive feedback. These studies, assuming that they are successful, will provide the pivotal data to support global marketing applications for Albuferon in 2009."

The Company has initiated dosing in the first Phase 3 trial, ACHIEVE 1, which is being conducted in treatment-naive patients with chronic hepatitis C genotype 1. ACHIEVE 1 will randomize a minimum of 1278 patients into 3 treatment groups, including 2 groups that will receive subcutaneously administered Albuferon once every 2 weeks (900 mcg or 1200 mcg), and an active control group that will receive PEGASYS once every week at a dose of 180 mcg. All patients will receive oral ribavirin concomitantly. The total duration of therapy will be 48 weeks, with 24 weeks of follow-up. The primary efficacy endpoint is sustained virologic response (SVR), defined as undetectable HCV RNA (< 10 IU/mL) at Week 72.

It is expected that the second Phase 3 trial, ACHIEVE 2/3, will be initiated in the first half of 2007. ACHIEVE 2/3 will be conducted in treatment-naive patients with chronic hepatitis C genotype 2 or 3, and will randomize a minimum of 918 patients into 3 treatment groups, which will receive the same doses of Albuferon and PEGASYS administered on the same schedules as ACHIEVE 1, with concomitant administration of oral ribavirin. The total duration of therapy will be 24 weeks, with 24 weeks of follow-up. The primary efficacy endpoint is SVR, defined as undetectable HCV RNA at Week 48.

Higher doses of Albuferon administered every 4 weeks, in combination with ribavirin, will be explored in a separate Phase 2b trial to be conducted by Novartis, beginning in 2007.

About Albuferon

Albuferon is a novel, long-acting form of interferon alpha, which was created by HGS using the Company's 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. HGS received an upfront fee of $45 million. Clinical development, commercial milestone and other payments to HGS could total as much as $507.5 million, including a $45 million upfront payment and $47.5 million payable upon dosing of the first patient in a Phase 3 trial.

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 HGS mission is to discover, develop, manufacture and market innovative drugs that serve patients with unmet medical needs, with a primary focus on protein and antibody drugs.

The HGS clinical development pipeline includes 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. LymphoStat-B, like Albuferon, is expected to advance to Phase 3 trials in 2006.

In June 2006, HGS announced that the U.S. Government exercised its option to purchase 20,000 doses of ABthrax(TM) for the treatment of anthrax disease. Other HGS compounds in clinical development include three TRAIL receptor antibodies for the treatment of cancer, 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, 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 planned 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. 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.
hgsi

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