Scientists Replicate Hepatitis C Virus in Laboratory
New In Vitro Model System Will Allow Study of Therapeutics and Virus Life Cycle
For the first time, scientists have replicated hepatitis C virus
(HCV) in the laboratory. The ability to replicate HCV in cell culture
will allow researchers to better study the life cycle and biology
of this virus and to test potential antiviral compounds, which
may lead to new therapies for the liver disease that results from
infection with HCV. Scientists at the National Institute of Diabetes
and Digestive and Kidney Diseases (NIDDK), one of the National
Institutes of Health (NIH), conducted the study, which appears
in the Feb. 15, 2005 issue of Proceedings of the National Academy
of Sciences (PNAS).
“Until recently, research on this infectious disease has
suffered from the lack of a robust in vitro model system,” says
T. Jake Liang, M.D., Chief of the Liver Diseases Branch of the
NIDDK and co-author of the study. “Our model system produced
viral particles that have all the properties of the whole virus.
This evidence together with an analysis of the replicated viral
RNA supports a conclusion of viral replication and production.”
The NIDDK group used a strain of HCV that would have applications
to the greatest number of people genotype 1, the major
type of HCV of human infections worldwide and the type most resistant
to current therapies. They constructed an HCV replica using a DNA
copy of the original HCV single-strand RNA genome. They placed
the DNA copy between two ribozymes, RNA molecules that have enzymatic
function and can cleave RNA sequence at specific locations. These
two ribozymes were designed to generate the correct ends of the
HCV genome and to act as start and stop buttons to gene activity.
The construct was “naked,” meaning that it contained
only nucleic acids, the genetic material of the virus, and did
not have the HCV viral envelope, a protective shell of lipids and
proteins that surrounds the viral RNA in fully-formed HCV. The
naked HCV construct was then placed into human liver cells in a
cell culture medium.
The NIDDK scientists found evidence of HCV proteins and HCV RNA
within the human liver cells in the culture. Electron microscopy
showed evidence of high levels of viral particles resembling fully-formed
HCV outside of the human liver cells in the culture medium. The
researchers believe that the HCV construct contained within the
human liver cells behaved like a true HCV infection by producing
fully formed copies of the virus and releasing them from the host
cell into the culture medium. Further testing is needed before
the researchers can determine if the viral particles produced in
this system are in fact infectious. Also, this system only represents
the tail end of the viral life cycle viral replication,
assembly and release from host cells. Another HCV model system
is needed to show the beginning stages of the viral life cycle viral
entry into host cells and viral activity in the host cell before
replication.
“With this cell-based system, we can screen compounds with
a cell-based assay to look for inhibitors of virus replication,” says
Liang. “We can also apply this technique to develop model
systems for other similar viruses.”
HCV is a small, enveloped, single-stranded RNA virus in the family
Flaviviridae. HCV is a major cause of liver disease in the United
States and the world. One in a series of hepatitis viruses, HCV
accounts for about 15 percent of acute hepatitis cases, 60 to 70
percent of chronic hepatitis cases, and up to 50 percent of cases
of cirrhosis, end-stage liver disease, and liver cancer. Almost
4 million Americans, or 1.8 percent of the U.S. population, have
antibodies to HCV indicating ongoing or previous infection with
the virus. Approximately 10,000 to 12,000 deaths each year in the
United States are due to HCV.
Heller, Theo; Jonathan Auerbach; Tarice Williams; Tzivia Rachel
Moreen; Allison Jazwinski; Brian Cruz; Neha Jeurkar; Ronda Sapp;
Guangxiang Luo; and T. Jake Liang. “An in vitro model
of hepatitis C virion production.” Proceedings of the
National Academy of Sciences, Vol. 102, No. 7, pp. 2579-2583.
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