ROCKVILLE, Maryland – November 2, 2004 – Human Genome Sciences, Inc. (Nasdaq: HGSI) announced today that results from a Phase 1/2 clinical trial of Albuferon™ in treatment-experienced adults with chronic hepatitis C 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. The results were presented at the 55 th Annual Meeting of the American Association for the Study of Liver Diseases (AASLD), which concludes today in Boston, MA. Albuferon is Human Genome Sciences' long-acting form of recombinant interferon alpha.

In an oral presentation, entitled “Albuferon – A Novel Therapeutic Agent for Hepatitis C: Results of a Phase 1/2 Study in Treatment-Experienced Subjects with Chronic Hepatitis C” (Abstract #265), data were presented on 119 patients treated in a multi-center, open-label, dose-escalation study. ¹ The Phase 1/2 clinical trial was designed to evaluate the safety, tolerability, immunogenicity, and pharmacokinetics of Albuferon in adults with chronic hepatitis C who have failed previous interferon alpha treatments. A ntiviral activity also was evaluated. One hundred and nineteen subjects were enrolled into twenty-two treatment cohorts. Ninety-two percent of the patients (110 of 119) were infected with hepatitis C virus (HCV) genotype 1, which accounts for nearly seventy percent of all HCV infections in the United States and is generally regarded as the most difficult HCV genotype to treat. Patients participating in the study had been treated for an average of 63 weeks with interferon alpha or pegylated interferon alpha, either alone or in combination with ribavirin, prior to entering the Albuferon study. Patients in the Phase 1/2 clinical trial received one or two doses of Albuferon administered subcutaneously fourteen 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. A newly developed, highly sensitive assay, meeting current requirements for detecting the presence of antibodies to interferon alpha, was used to evaluate immunogenicity. Preliminary immunogenicity data presented at the AASLD meeting show that the vast majority of Albuferon antibody titers were low (<100 ng/mL) and that there is no apparent correlation between the emergence of antibodies and adverse events, antiviral response or pharmacokinetics. It was determined that 11.8 percent of the patients participating in the Phase 1/2 study had pre-existing antibodies to interferon. The observed rate of emerging Albuferon antibody-positive subjects was 10.9 percent. The immunogenicity rates reported for pegylated interferons in treatment-naïve subjects range from 6.0-15.0 percent. The observed rate of neutralizing antibodies was 2.5 percent. [Please note that the preceding sentence corrects the observed rate of neutralizing antibodies from 1.7 percent to 2.5 percent, consistent with the actual presentation slides, which were distributed via live-link along with this press release.] The reported rates for neutralizing antibodies for pegylated interferons range from 1.0-5.0 percent in treatment-naïve subjects. It was observed that 3.4 percent of those participating in the trial had pre-existing antibodies to albumin, while the observed rate of emerging albumin antibody-positive subjects was 1.7 percent.

The data presented show that Albuferon remains in the blood substantially longer than is reported for recombinant interferon alpha and pegylated interferon alpha. Albuferon is detectable for up to four weeks following a single subcutaneous injection. The C max (peak drug level) increases in a linear manner over the dose range evaluated. Albuferon exhibits a median half-life of 140 hours, supporting dosing at intervals of 2-4 weeks. This compares to a reported mean elimination half-life of 80 hours (50-140 hours) for Pegasys and 40 hours (22-60 hours) for PEG-Intron. ^{2, 3}

Viral load levels represent the quantity of hepatitis C virus in the blood and are a marker for drug activity. Forty-seven percent (37/78) 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. Mathematical modeling of viral dynamics and kinetic analysis of the viral decline in the single-dose cohorts demonstrate that the antiviral response was biphasic, with a dose-dependent first phase decline in viral load during the first one-two days, followed by a slower second phase decline until day 14. The data presented show that both magnitude and duration of early anti-viral response were dose-dependent.

Vijayan Balan, M.D., a lead investigator and Director, Hepatobiliary Clinic, Division of Transplant Medicine and Division of Gastroenterology and Hepatology, Mayo Clinic Hospital, Phoenix, AZ, said, "Currently, most patients with chronic hepatitis C are treated with pegylated interferon once weekly, along with daily doses of ribavirin. The available therapies frequently are associated with side effects that often require dose adjustments and can require discontinuation of treatment. There is a significant need to provide these patients with treatment options that are more convenient and hopefully have fewer side effects. The clinical results presented today demonstrate that Albuferon has a favorable safety and tolerability profile, is biologically active and able to reduce viral load with dose-dependent magnitude and durability. The pharmacokinetic behavior of Albuferon supports dosing at intervals of two to four weeks. Further evaluation of Albuferon as a potential treatment for chronic hepatitis C is warranted in Phase 2 clinical trials.”

David C. Stump, M.D., Executive Vice President, Drug Development, said, “We are encouraged by the results presented today from our Phase 1/2 study of Albuferon in patients with chronic hepatitis C, particularly considering that the study was conducted in a heavily pretreated population. The data show that Albuferon is well tolerated, with mostly transient adverse events that were mild to moderate in severity, and with no discontinuations due to adverse events. We used a new, more sensitive assay to evaluate immunogenicity, which meets the current requirements for detecting the presence of antibodies to interferon. The preliminary immunogenicity data presented today show rates consistent with those reported for other interferon alpha-based therapies, with no apparent correlation between the emergence of these antibodies and adverse events, antiviral response or pharmacokinetics. Importantly, significant evidence of antiviral activity was observed. Nearly half of the patients treated with Albuferon at doses greater than 120 mcg experienced reductions in their viral load of 1.0 log or greater. Both magnitude and duration of viral response were dose-dependent. Based on the clinical and preclinical results to date, we are continuing to evaluate Albuferon in Phase 2 studies.”

Craig A. Rosen, Ph.D., President and Chief Operating Officer, said, “The results reported today reinforce our belief that Albuferon has the potential to provide these patients with a new long-acting treatment option, with a considerably more convenient treatment schedule, and perhaps with improved efficacy or safety.”

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. Albumin fusion technology allows scientists to create novel, next-generation protein drugs by fusing the gene that expresses human albumin to the gene that expresses a therapeutically active protein. Albuferon results from the genetic fusion of human albumin and interferon alpha. Human Genome Sciences is developing Albuferon for use in the treatment of chronic hepatitis C.

Hepatitis C infection is an inflammation of the liver caused by the hepatitis C virus. Hepatitis C infection is currently the most common chronic blood-borne infection in the United States, afflicting four times as many people as are infected with HIV, the virus that causes AIDS. The hepatitis C virus is transmitted primarily through significant or repeated exposures to infected blood. In the United States, 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. Approximately four million people in the United States are infected with the hepatitis C virus, and between sixty and eighty-five percent of hepatitis C-infected people develop chronic hepatitis C. A four-fold increase in the number of adults diagnosed with chronic hepatitis C is projected from 1990 to 2015. ⁴

For additional information on Human Genome Sciences, please visit our web site at www.hgsi.com . For more information on Albuferon, see www.hgsi.com/products/albuferon.html .

Health professionals interested in the Albuferon trial or any other study involving HGSI products are encouraged to inquire via the Contact Us section of the Human Genome Sciences web site, www.hgsi.com/products/request.html , or by calling us at (301) 610-5790, extension 3550.

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

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