ROCKVILLE, Maryland – November 30, 2004 – Human Genome Sciences, Inc. (Nasdaq: HGSI) announced today that it has begun dosing patients in a Phase 2 clinical trial of Albuferon™ (albumin-interferon alpha) in combination with ribavirin to evaluate the safety, tolerability and efficacy of Albuferon in patients with chronic hepatitis C who failed to respond to previous interferon alpha-based treatment regimens.

The trial is a Phase 2, randomized, open-label, multi-center, dose-escalation study. It will be conducted in the United States, and will enroll up to 100 patients with chronic hepatitis C who have failed to respond to treatment(s) with any interferon-alpha product. The study design states that approximately 50 percent of the subjects enrolled should be patients who have failed combination therapy that included pegylated interferon alpha plus ribavirin. Patients will be randomized into 3-4 dose groups, and will receive Albuferon administered subcutaneously either 14 or 28 days apart. All patients will receive weight-based oral daily ribavirin at 1000 or 1200 mg in two divided doses. Patients in the trial will receive 48 weeks of treatment, with an additional 24 weeks of follow-up. The primary objective of the Phase 2 study is to evaluate the safety and tolerability of Albuferon in combination with ribavirin in patients who have not responded to previous treatment with regimens containing interferon alpha or pegylated interferon alpha. The study also will evaluate the efficacy of Albuferon in combination with ribavirin. The primary efficacy endpoint will be sustained virologic response, defined as undetectable virus at 24 weeks after the end of therapy.

David Nelson, M.D., a lead investigator in the Phase 2 study, and Associate Professor of Medicine, Medical Director of Liver Transplantation, and Chief of the Hepatobiliary Diseases Section, University of Florida, Gainesville, said, “The current standard of care for the treatment of hepatitis C is a combination of pegylated interferon alpha and ribavirin. This combination cures between 54 percent and 56 percent of all patients completing therapy. That leaves approximately 45 percent of treatment candidates as non-responders. In addition, it is estimated that only 35-45 percent of patients with hepatitis C ever begin therapy, due to the side-effect profiles of the treatment regimens now in use. Hepatitis C represents a significant unmet need. The future complications of the chronic disease, including cancer, will be a major and growing cost and healthcare issue over the next decade. Based on preclinical and clinical evidence to date, we look forward to exploring the potential of Albuferon for use as a treatment in patients with hepatitis C who have not responded to previous interferon alpha-based treatments.” ^1-8

David C. Stump, M.D., Executive Vice President, Drug Development, said, “Albuferon is the subject of a broadening program of clinical study. The study announced today is the second Phase 2 clinical trial that we have initiated to evaluate Albuferon’s potential for the treatment of chronic hepatitis C. The objective of the current study in interferon alpha-experienced patients is to evaluate the safety, tolerability and efficacy of Albuferon in combination with ribavirin. In May 2004, we announced the initiation of a Phase 2 study of Albuferon alone in patients who are naïve to treatment with interferon alpha. ⁹ The ongoing Phase 2 study in treatment-naïve patients should help us identify an optimal range of doses to evaluate in a larger 48-week combination study of Albuferon that we plan to conduct in treatment-naïve patients, while also yielding important additional information about Albuferon’s safety, pharmacology and biological activity. Based on the preclinical and clinical results to date, we believe that Albuferon has the potential to become an important therapeutic option for the treatment of chronic hepatitis C.”

The results of a Phase 1/2 clinical trial of Albuferon in interferon alpha-experienced adults with chronic hepatitis C were presented at the November 2004 Annual Meeting of the American Association for the Study of Liver Diseases (AASLD). ^10-11 Data presented on 119 patients demonstrate that Albuferon is well tolerated, has a prolonged half-life, is biologically active, and able to reduce viral load with dose-dependent magnitude and durability. On average, patients participating in the Phase 1/2 clinical trial had been treated previously for approximately 63 weeks with interferon alpha-containing regimens. Ninety-two percent of the patients (110 of 119) were infected with hepatitis C virus genotype 1, which accounts for nearly seventy percent of all HCV infections in North America. Patients were treated with one or two doses of Albuferon administered subcutaneously 14 days apart. Doses administered ranged from 7-900 mcg. The Phase 1/2 clinical trial results show that Albuferon is well tolerated, with adverse events that were mostly transient and mild to moderate in severity, and with no discontinuations due to adverse events or reductions in hematologic cell counts. Preliminary immunogenicity data presented at the AASLD meeting show that Albuferon immunogenicity occurs at rates consistent with those reported for other interferon alpha-based therapies, with no apparent correlation between the emergence of Albuferon antibodies and adverse events, antiviral response or pharmacokinetics. The vast majority of Albuferon antibody titers were low (<100 ng/mL). Viral load levels represent the quantity of hepatitis C virus in the blood and are a marker for drug activity. Forty-seven percent of Albuferon-treated patients in the combined single-dose and two-dose cohorts at doses of 120-900 mcg experienced an antiviral response, as demonstrated by reductions in viral load of 1.0 log or greater. The data presented show that both magnitude and duration of early anti-viral response were dose-dependent.

Albuferon is a novel, long-acting form of interferon alpha. Recombinant interferon alpha is approved for the treatment of hepatitis C, hepatitis B and a broad range of cancers. Human Genome Sciences modified interferon alpha to improve its pharmacological properties by using the company’s proprietary albumin fusion technology.

Hepatitis C infection is an inflammation of the liver caused by the hepatitis C virus. It is the most common chronic blood-borne infection in the developed world, and afflicts approximately four million people in the United States. The hepatitis C virus is transmitted primarily through significant or repeated exposures to infected blood. Intravenous drug use and sexual contact with infected persons account for the majority of new hepatitis C infections. 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.

Health professionals interested in more information about trials involving Human Genome Sciences products are encouraged to inquire via the Contact Us section of the company’s web site, www.hgsi.com/products/request.html, or by calling (301) 610-5790, extension 3550.

Human Genome Sciences is a company with the mission to treat and cure disease by bringing new gene-based protein and antibody drugs to patients.

HGS, Human Genome Sciences and Albuferon are trademarks of Human Genome Sciences, Inc.

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. 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.

Footnotes

1. Strader DB, Wright T, Thomas DL, and Seeff, LB. AASLD Practice Guideline: Diagnosis, Management, and Treatment of Hepatitis C. Hepatology 2004 April; 39 (4): 1147-1171.
2. Hadziyannis SJ, Sette H, Morgan TR, et al. Peginterferon- α 2a and ribavirin combination therapy in chronic hepatitis C. Ann Intern Med 2004; 140:346-355.
3. Shiffman ML, Di Bisceglie AM, Lindsay KL, et al. Peginterferon alfa-2a and ribavirin in patients with chronic hepatitis C who have failed prior treatment. Gastroenterology 2004; 126:1015-1023.
4. Zeng N, Cohen CK, Schwartz P, Rai R. Treatment of HCV infected patients, including non-responders to PEG-IFN alfa-2b/RBV, with PEG-IFN alfa-2a/RBV: the Johns Hopkins experience. Digestive Disease Week 2004 Internet Conference Report. Abstract #1233.
5. Zeuzem S. Heterogeneous virologic response rates to interferon-based therapy in patients with chronic hepatitis C: who responds less well? Ann Intern Med 2004; 140:370-381.
6. PEGASYS® Physicians Desk Reference. (Last updated December 2002).
7. PEG-INTRON® Physicians Desk Reference. (Last updated August 2002).
8. Management of Hepatitis C: 2002. National Institutes of Health Consensus Development Conference.
9. (HGSI Press Release) Human Genome Sciences Initiates Phase 2 Clinical Trial of Albuferon™ for the Treatment of Chronic Hepatitis C. May 26, 2004.
10. Balan V, et al. Albuferon™ -- A Novel Therapeutic Agent for Hepatitis C: Results of a Phase 1/2 Study in Treatment Experienced Subjects with Chronic Hepatitis C. 55^th Annual Meeting of the American Association for the Study of Liver Diseases, Boston. November 2, 2004. Oral presentation (Abstract #265).
11. (HGSI Press Release) Human Genome Sciences Reports Positive Results of Phase 1/2 Clinical Trial of Albuferon™ in Chronic Hepatitis C. November 2, 2004.