Human Genome Sciences Modifies Dosing in ACHIEVE Trials of Albuferon

Rockville, Maryland - January 23, 2008 - Human Genome Sciences Inc. (Nasdaq: HGSI) announced today that it will modify the dosing in one arm of each of its ACHIEVE clinical trials of Albuferon (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 [Roche's pegylated interferon alfa-2a] 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, MD, 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-naïve 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.