Genetic immunization generates cellular and humoral immune responses against the nonstructural proteins of the hepatitis C virus in a murine model.

Exposure to hepatitis C virus (HCV) is associated with a high prevalence of persistent viral infection and the development of chronic liver disease and hepatocellular carcinoma. Recovery from acute infection may depend upon the generation of broad-based cellular immune responses to viral structural and nonstructural proteins. We used the DNA-based immunization approach in BALB/c mice to determine whether the HCV nonstructural proteins NS3, NS4, and NS5 will induce Ab responses, CD4+ Th cell proliferation, and cytokine release in response to stimulation by recombinant proteins as well as generate CD8+ CTL activity both in vitro and in vivo. We found that the nonstructural proteins were particularly good immunogens and produced cellular immune responses when administered as a DNA construct. Indeed, a tumor model was established following inoculation of syngenic SP2/0 cells stably transfected with NS5. We observed protection against tumor formation and growth only in mice immunized with the NS5-encoding DNA construct, establishing the generation of significant CTL activity in vivo by this technique. The results indicate that genetic immunization may define the cellular immune response of the host to HCV nonstructural proteins and is a promising approach for vaccine development.