A team of researchers led by scientists at The Rockefeller University has produced for the first time an infectious form of the hepatitis C virus (HCV) in laboratory cultures of human cells. The finding, reported in the June 9 issue of Science Express, will allow scientists to study every stage of the HCV life cycle and develop drugs to treat this life-threatening disease that affects more than 170 million people around the world.
"The inability to reproduce aspects of the hepatitis C virus life cycle in cell culture has slowed research progress on this important human pathogen," says senior author Charles M. Rice, Ph.D., Maurice R. and Corinne P. Greenberg Professor and head of the Laboratory of Virology and Infectious Disease at Rockefeller.
"This system lays the foundation for future test tube studies of the virus life cycle and may help in the development of new drugs for combating HCV," adds Rice, who is the scientific director of the Center for the Study of Hepatitis C, a collaborative research and clinical effort of Rockefeller, Weill Medical College of Cornell University, and New York Presbyterian Hospital.
Like all viruses, HCV cannot replicate by itself; instead it takes over the machinery of a host cell to make copies of itself. Much about the life cycle of HCV remains poorly understood because scientists have been unable to reproduce an infectious form of HCV that they can observe in cell cultures. The method developed by Rice and his colleagues, including scientists at the Massachusetts Institute of Technology and the Scripps Research Institute, changes that.
"The hallmark of viruses is their ability to exist in a form outside the host cell capable of infecting new cells," says first author Brett Lindenbach, Ph.D., a postdoctoral fellow in Rice's lab. "Our method replicates and produces virus particles that can infect new cells, initiating replication in them and leading to the production of more virus particles."
Although little is know about the HCV life cycle, researchers think that in humans the virus enters a liver cell and delivers its RNA and proteins into the cell cytoplasm. HCV carries its genetic information in its RNA, which is separated from the protein, copied, and then joined with new protein components before being released from the liver cell to infect other cells.
Lindenbach, Rice and their colleagues named their infectious cell culture virus HCVcc. Already HCVcc is yielding new knowledge about HCV. In a separate set of experiments, the researchers used HCVcc to confirm that a molecule called CD81, which sits on the surface of the human cell membrane, plays a crucial role in the entry of HCV.
Scientists have known that a protein produced by HCV, called E2, binds to CD81, and they believed that this interaction is necessary for the virus to bind to target cells.
The Rockefeller researchers showed that CD81 molecules that are not attached to the surface of host cells compete with membrane-bound CD81 and inhibit entry of HCV into the cell. They also showed that HepG2 cells, which do not express CD81 but can support HCV RNA replication, could not be infected by HCVcc unless they were engineered to express CD81.
Liver failure due to hepatitis C is the leading cause of liver transplants in the United States, and about 25 percent of liver cancer cases in the country are associated with HCV. Although about 85 percent of those who are infected develop chronic infection, the virus usually remains undetected for years, or even decades, until it causes advanced liver disease.
Lindenbach's and Rice's co-authors are Matthew J. Evans, Andrew J. Syder, Benno Wölk, Timothy L. Tellinghuisen and Jane A. McKeating at Rockefeller; Christopher C. Liu and Richard O. Hynes at the Howard Hughes Medical Institute, Center for Cancer Research, MIT; and Toshiaki Maruyama and Dennis R. Burton at The Scripps Research Institute.
This research was supported by the National Cancer Institute and the National Institute of Allergy and Infectious Diseases, both part of the federal government's National Institutes of Health. Additional support was provided by the Charles H. Revson Foundation (to Evans) and the German Science Foundation (to Wölk). Lindenbach is a recipient of the Howard Temin Award of the National Cancer Institute.