Differential cellular and humoral immune responses to HCV core and HBV envelope proteins after genetic immunizations using chimeric constructs.

Development of a broad based cellular and humoral immune response to hepatitis C virus (HCV) structural proteins may be important for eradication of viral infection. In previous studies in mice we demonstrated that facilitated DNA-based immunization with an HCV core DNA-expression construct stimulated the generation of weak cytotoxic T lymphocyte (CTL), helper T cell (Th), and humoral immune responses against HCV core related epitopes. To enhance the immunogenicity of this non-secreted viral structural protein at both the B- and T-cell level, several chimeric HBV-HCV constructs were prepared which were designed to express and secrete HCV core protein along with various regions of the hepatitis B envelope protein. No secretion of the chimeric proteins into the culture supernatant was detected using sensitive radioimmunoassays. However, such chimeric proteins were capable of generating CD4+ inflammatory T cell and CD8+ CTL activity against both HBV and HCV components of the fusion proteins. It was determined that the proliferative activity of T cells as well as the humoral immune responses to HCV core protein were substantially enhanced by some chimeric fusion proteins as compared to the HCV core protein alone. The strength of the immune responses appeared directly related to the level of Th1 cytokines produced by CD4+ T cells obtained from immunized animals. Further characterization of the immune responses stimulated by these DNA constructs studied helped to define some of the most immunogenic regions of the chimeric proteins that they encode.