Human Genome Sciences Inc. (Nasdaq: HGSI) announced that it will modify the dosing in one arm of each of its ACHIEVE clinical trials of Albuferon(R) (albinterferon alfa-2b) for chronic hepatitis C. Patients in the Phase 3 trials who have been receiving the 1200-mcg dose will now receive a 900-mcg dose. The change is based on recommendations made by the studies' independent Data Monitoring Committee (DMC). HGS continues to expect to have all Phase 3 data available by spring 2009 to support the filing of global marketing authorization applications by fall 2009.

"For some time we have viewed the 900-mcg dose administered every two weeks as the most likely marketed dose of Albuferon," said H. Thomas Watkins, President and Chief Executive Officer, HGS. "The 900-mcg dose demonstrated comparable efficacy and safety to Pegasys in Phase 2 - with half the injections, improvements in quality of life and fewer missed days of work during treatment. We continue to believe that Albuferon could become the market-leading interferon for the treatment of hepatitis C if Phase 2 900-mcg results are confirmed in Phase 3."

Consistent with its charter, the DMC routinely reviews all adverse events for each treatment group. Serious pulmonary adverse events, while expected and rare during interferon therapy, were higher in the treatment group receiving 1200-mcg Albuferon administered every two weeks. The DMC did not express any safety concerns about the 900-mcg dose of Albuferon. Based on the DMC's review and conclusions, the patients receiving a 1200-mcg dose of Albuferon will be moved to the 900-mcg dose.

"The independent Data Monitoring Committee for these trials assessed risk/benefit based on review of unblinded safety and efficacy data for all doses, to which HGS remains blinded, and concluded that dosing should be modified for patients receiving the 1200-mcg dose of Albuferon every two weeks," said David C. Stump, M.D., Executive Vice President, Research and Development, HGS. "HGS and Novartis have chosen to accept the Data Monitoring Committee's recommendation to modify dosing in the 1200-mcg arms in these studies. We are pleased that after careful review by the Data Monitoring Committee, the safety and continued dosing of 900-mcg Albuferon was affirmed. Thus, all Albuferon patients will now receive 900-mcg every two weeks."

About Albuferon

Albuferon is a novel, longer-acting form of interferon alpha that was created using the proprietary HGS albumin-fusion technology. Recombinant interferon alpha is approved for the treatment of hepatitis C, hepatitis B and a broad range of cancers. HGS is currently conducting two pivotal Phase 3 clinical trials of Albuferon in combination with ribavirin: ACHIEVE 1 in treatment-naive patients with genotype 1 chronic hepatitis C, and ACHIEVE 2/3 in treatment-naive patients with genotype 2 or 3 chronic hepatitis C.

Albuferon requires half as many injections as Pegasys, and Phase 2 clinical results suggest that Albuferon could offer efficacy and safety comparable to Pegasys, in addition to the potential for improved quality of life and fewer lost days of work on treatment. Based on these data, HGS believes that Albuferon could become the market-leading interferon for the treatment of hepatitis C if Phase 2 results are confirmed in Phase 3 trials.

Albuferon is being developed by HGS and Novartis under a worldwide co- development and commercialization agreement entered into in June 2006. ACHIEVE 1 and ACHIEVE 2/3, assuming that they are successful, will provide the pivotal data to support global marketing authorization applications for Albuferon, which HGS and Novartis expect to file by fall 2009.

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 and other immune-mediated diseases. The Company's primary focus is rapid progress toward the commercialization of its two key lead drugs, Albuferon for hepatitis C and LymphoStat-B(R) (belimumab) for lupus. Phase 3 clinical trials of both drugs are ongoing.

ABthrax(TM) (raxibacumab) is in late-stage development for the treatment of anthrax disease, and the Company is on track to begin the delivery in 2008 of 20,000 doses of ABthrax to the Strategic National Stockpile under a contract entered into with the U.S. Government in June 2006. Other HGS drugs in clinical development include two TRAIL receptor antibodies for the treatment of cancer. AEG40826, a small-molecule antagonist of IAP (inhibitor of apoptosis) proteins, is expected to enter Phase 1 clinical trials for the treatment of cancer in early 2008.

For more information about HGS, please visit the Company's web site at hgsi. 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

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, 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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