SAN ANTONIO -- Researchers have found new hope in
the battle against hepatitis C, the No. 1 cause of liver failure and liver
transplantation in the United States. Studies at the Southwest Foundation for
Biomedical Research offer the first evidence that a vaccine against all
strains of this elusive virus should be possible, since chimpanzees that have
previously cleared infection with one strain of the virus show protective
immunity to multiple strains.
While a vaccine could be years away, the finding is significant.
Scientists previously had thought that prior infection with hepatitis C virus
(HCV) only produced immunity to the specific strain with which one had been
infected, said lead investigator Dr. Robert E. Lanford of the Southwest
Foundation for Biomedical Research in San Antonio (SFBR). Lanford, his
colleagues at SFBR, and collaborators at the Johns Hopkins University School
of Medicine in Baltimore detail their discovery in an article published in the
Journal of Virology for its first edition for the month of February 2004.
Hepatitis C has six different genotypes, or highly divergent groups of
viruses, with numerous strains within each genotype. Researchers and
pharmaceutical companies have tried for years to develop an HCV vaccine,
focusing primarily on genotype 1, the most common genotype in the United
States and Europe. But there has been doubt that an HCV vaccine for one
genotype could be effective against others.
The discovery by Lanford's group that a potential vaccine against one
HCV strain could produce protective immunity to multiple strains was based on
research with chimpanzees at SFBR's Southwest National Primate Research Center
in San Antonio. Chimpanzees, initially developed by scientists at NIH and
SFBR as an animal model for HCV, are the only animals besides humans that can
be infected with the virus. As with humans, some chimpanzees maintain chronic
infections, while others manage to clear their infection; however, unlike
humans, chronically infected chimpanzees do not develop liver disease.
SFBR scientists found that chimpanzees that had cleared previous infection
with genotype 1 later showed protective immunity when rechallenged with
several different HCV strains. That was true even when the animals were
challenged with a highly complex mixture containing strains from genotypes 1,
2, 3 and 4 - the four major genotypes affecting most HCV victims around the
Lanford explained that this finding has significant implications for
eventual development of an HCV vaccine "because it means when we are able to
make an effective vaccine and immunize a population, people should be
protected against all strains of hepatitis C to which they might be exposed."
In addition to being the No. 1 cause for cirrhosis of the liver, HCV
infects an estimated 3 percent of the world population, and accounts for
25 percent of all cases of liver cancer in the United States.
Source: Southwest Foundation for Biomedical Research