St. Louis, Dec. 6, 2000 — Scientists studying the virus that causes hepatitis C have found a way to grow it rapidly in the lab so they can perform genetic studies on it. The inability to replicate the virus quickly and reliably in cell cultures has been a serious handicap to progress against the disease, which affects approximately 170 million people worldwide. In the United States, hepatitis C is the major cause of liver transplants.
"This is a strong, workable system that we can use to learn how this poorly understood virus causes disease and to develop drugs against it," said Keril J. Blight, Ph.D.
Blight is first author of a paper in the Dec. 8 issue of Science that reports the results. She is a research associate in the lab of Charles M. Rice, Ph.D., professor of molecular microbiology at Washington University School of Medicine in St. Louis. The work was completed at the School of Medicine before Rice was appointed the Maurice R. and Corinne P. Greenberg Professor and head of the Laboratory of Virology and Infectious Disease at Rockefeller University in New York.
The current combination therapy against hepatitis C — interferon plus ribavirin — fails to cure 80 percent of those infected. About 20 percent of people with chronic infection develop cirrhosis of the liver, which often leads to liver failure and, in some cases, liver cancer. But little is known about how the hepatitis C virus eludes destruction by the immune system and establishes a chronic infection.
Building on previous work with RNA, the genetic material of the virus, Rice's group inserted altered viral sequences into human liver cells. The researchers identified many mutations that enabled the virus to start reproducing more efficiently. The mutations clustered in the gene for a nonstructural protein called NS5A.
Nine of the alterations were spelling mistakes in the gene for NS5A. The 10th was the deletion of a long piece of the gene. Many of the 10 mutant RNAs reproduced thousands of times more effectively in cultured cells than did the unmutated RNA of the virus.
The researchers suggest that human liver cells in culture might contain a protein that interacts with part of NS5A to prevent the virus from multiplying. When the viral protein becomes altered, the interaction no longer can take place, and replication proceeds full tilt. Hepatitis C virus mutated in the NS5A region therefore will permit laboratory studies, including those that might lead to a vaccine.
"For the first time, powerful genetic and genomics approaches can be used to unravel the molecular details of hepatitis C virus replication and its interaction with host cells," Rice said. "We hope that this technology will speed up both fundamental research and drug discovery."
Blight KJ, Kolykhalov AA, Rice CM. Efficient initiation of HCV RNA replication in cell culture. Science, Dec. 8, 2000.
The work was supported by grants from the Public Health Service and Greenberg Medical Foundation.
Journal
Science