Chiron Discovers Significant Hepatitis C Binding Mechanism; Data Indicates CD81 Protein May Be A Virus Receptor

October 30, 1998

Milestone Reported in Science, Discovery Could Have Far-Reaching Impact on Vaccine and Therapeutic Product Development

Emeryville, CA, October 29, 1998 - Chiron Corporation (Nasdaq: CHIR) today announced its discovery that a protein molecule (CD81) located on the surface of certain human cell types binds to the hepatitis C virus (HCV). This discovery, reported in the October 30, 1998, issue of Science, provides important clues as to how HCV may penetrate and infect human cells. This knowledge may dramatically advance the development of new vaccines and therapeutics designed to prevent and treat this widespread disease. It is estimated that more than 170 million individuals worldwide suffer from chronic HCV infection.

"The discovery of CD81 binding to HCV is an important scientific milestone in our quest to understand this deadly virus. Chiron scientists characterized what was then known as non-A, non-B hepatitis in 1987," said Lewis T. ("Rusty") Williams, M.D., Ph.D., Chiron's chief scientific officer and president of Chiron Technologies. "This latest discovery is a critical step in discovering and developing targeted therapeutics and vaccines against HCV and HCV-induced disease, and greatly increases our knowledge about the biology of this virus."

Chiron's scientific team, led by Sergio Abrignani, M.D., head of the Immunology Department in Siena, Italy, pioneered this important discovery. Though Chiron researchers characterized HCV more than a decade ago, understanding how the virus infects the liver has been elusive because the virus cannot be easily grown in cell culture. Due to the limitations of HCV culture assays, Chiron scientists relied on a number of alternative approaches to establish the link between HCV's major envelope protein (E2) and the proposed receptor. Using a recombinant form of E2, Chiron scientists were able to demonstrate that it binds with high affinity to selected human cell types. In a preclinical vaccine model, administration of these envelope proteins resulted in protection from HCV challenges and correlated with the presence of antibodies that inhibited the binding of E2 to human cells. Confirmation of virus binding to CD81 was established using a variety of sophisticated immunological and molecular techniques.

Chiron, History of Hepatitis Discovery Milestones

Founded in 1981 with an expertise in infectious diseases and vaccines, Chiron has made significant contributions to preventive and therapeutic approaches for hepatitis, as well as other major infectious diseases. Chiron participated in the development of, and subsequently licensed to Merck, the key component in the first genetically engineered vaccine for humans, which was the hepatitis B (HBV) vaccine.

In 1987, the company characterized the hepatitis C genome. Currently, Chiron is embarking on a Phase I clinical study for a potentially therapeutic and prophylactic HCV candidate vaccine. The company is also proceeding with Phase I evaluations of a therapeutic vaccine for patients infected with HBV.

Hepatitis C -- A Stealth Epidemic

According to the Centers for Disease Control, hepatitis C costs the United States an estimated $600 million annually in medical and work loss. (This figure does not include transplantation costs.) In this country alone, the virus has infected nearly four million individuals, and roughly 30,000 more are diagnosed each year. Currently three percent of the world's population is chronically infected with HCV, the leading cause of liver disease.

HCV is known to enter through the patient's bloodstream, and in a relatively short time the virus settles in the liver. There the virus begins replicating, and in some individuals can eventually lead to scarring of the liver. Patients are most commonly infected through sharing needles or syringes during intravenous drug use or through other exposures to contaminated blood, such as in tattooing, body piercing, and possibly through unprotected sexual contact. Once the disease progresses and the individual becomes chronically infected, symptoms include fatigue, loss of appetite, abdominal pain and nausea. Currently the only available treatments are anti-viral drugs (interferon and ribavirin) which are effective in only a minority of patients.

About Chiron

Headquartered in Emeryville, California, Chiron is a leading biotechnology company that participates in three global healthcare markets: therapeutics, vaccines and blood testing. Chiron also conducts research and development in the fields of recombinant technology, gene therapy, vaccines, small molecule discovery, and genomics.

Chiron, Inc.

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