The prevalence of chronic hepatitis C virus (HCV) infection is estimated at 3 percent worldwide and at more than 2 percent in the United States. This increases to 4 percent for people between the ages of 40 and 60, and to more than 30 percent for people with AIDS. Although a person with HCV infection can remain asymptomatic for decades, approximately 20 percent of infected individuals will eventually develop significant liver disease, including cirrhosis and liver cancer.
HCV is the leading cause of liver failure and liver transplantation, and accounts for approximately 25 percent of all hepatocellular carcinomas (liver cancer). Consequently, there is a tremendous need to develop new antivirals and a vaccine for HCV.
Much of our current knowledge of HCV is derived from studies with chimpanzees, the only animal besides man that is susceptible to HCV infection. HCV was first identified and cloned from chimpanzee serum derived from an animal inoculated with human serum containing NonA, NonB, Hepatitis, the name given to HCV before it was identified. Since acute HCV infection is uncommonly recognized in humans, much of the scientific understanding of the immunity that leads to viral recovery derives from studies in chimpanzees.
Early studies were discouraging with regard to the prospects of developing a vaccine, since it was questioned whether chimpanzees who recovered from HCV infection were protected from reinfection with the same strain. However, in 2001, Texas Biomed’s Dr. Robert Lanford demonstrated robust protective immunity following rechallenge with similar viruses of the same genotype. However, because the different genotypes of HCV display extraordinary genetic and antigenic diversity, much more than is observed with HIV, it was still unclear whether the protective immunity Dr. Lanford’s team demonstrated against a genotype 1 infection would be sufficiently broad to confer protection across the different HCV genotypes. But in 2004, the group demonstrated the first evidence that prior infection with genotype 1 provides protective immunity to other HCV genotypes, even when animals are challenged with a highly complex mixture containing four genotypes. These studies are the first to demonstrate the feasibility of developing a vaccine protective against all HCV strains.
Today, the chimpanzee colony at Texas Biomed is used for basic research on the pathogenesis of HCV infection, as well as more applied research on the development of new vaccine candidates and the testing of new antivirals before they enter human trials.