New culture method for hepatitis C virus
Researchers open the way for improved study of hepatitis C virus by devising a novel virus culture system that allows replication of patient-isolated virus in nontransformed hepatocytes, instead of culture-adapted virus strains in transformed cell lines. The related report by Lazaro et al, "Hepatitis C virus replication in transfected and serum-infected cultured human fetal hepatocytes," appears in the February issue of The American Journal of Pathology.
Hepatitis C virus (HCV) infection affects approximately 170,000,000 people worldwide. HCV liver disease, which may induce liver inflammation, cirrhosis, and/or hepatocellular carcinoma, represents the foremost reason for liver transplantation in much of the U.S.
Study of HCV replication within liver cells, or hepatocytes, has been hampered by a lack of adequate virus culture systems. Some systems allow the virus to infect cells but do not permit prolonged replication and production of virus, while other systems rely on derivatives of permissive virus isolates for efficient replication in transformed (mutated) cell lines. Still lacking has been a system to sustain replication of novel virus isolates from patients using nontransformed hepatocytes.
Nelson Fausto of the University of Washington School of Medicine has crossed this hurdle using a human fetal hepatocyte culture system that was previously developed in his lab. Using this system, his group has demonstrated sustained replication and production of virus particles for at least 2 months, with these virus particles able to infect new cells.
In their first experiments, Fausto and colleagues transfected hepatocyte cultures with HCV genomic RNA and found replication of HCV RNA genomes and production of core protein (for virus particle formation). Release of infectious virus particles was confirmed, as media from these cells were able to infect naive hepatocytes. Finally, virus particles were examined by electron microscopy and shown to possess the expected size and shape of HCV virus particles.
Once the system was established, the group examined whether sera from patients carrying HCV could infect the human fetal hepatocytes. When sera from patients infected with different HCV strains were added to the hepatocyte culture system, viral replication occurred and new virus particles were produced.
In both transfection and infection models, virus particles were released in a cyclical manner, with bursts of virus produced every 10-14 days. This is similar to what has been reported during clinical HCV infection, possibly due to the host's natural defenses. Interestingly, cultured hepatocytes responded to viral replication by displaying signs of distress and cell death and by expressing interferon-beta, a cellular antiviral, in an effort to control the infection.
This culture system provides a breakthrough in studying HCV replication in nontransformed hepatocytes, the natural target of the virus. By allowing infection by patient serum containing a wide array of virus strains, this system may allow better understanding of the differences between different strains, further improving treatment strategies.