DNA immunization with hepatitis C virus (HCV) polycistronic genes or immunization by HCV DNA priming-recombinant canarypox virus boosting induces immune responses and protection from recombinant HCV-vaccinia virus infection in HLA-A2.1-transgenic mice.

We studied immune responses to hepatitis C virus (HCV) genes delivered as DNA encoding the entire HCV protein coding genome in two polycistronic plasmids encoding HCV capsid-E1-E2-NS2-NS3 and HCV NS3-NS4-NS5 in HLA-A2.1-transgenic mice. Immune responses to HCV DNA prime and recombinant canarypox virus boost were also studied with the above constructs. At 8 weeks after a canarypox virus boost, the DNA prime/canarypox virus boosting regimen induced potent cellular immune responses to HCV structural and nonstructural proteins on target cells expressing the HLA-A2.1 allele. High frequencies of gamma interferon-secreting cells, as detected by enzyme-linked immunospot assay, were obtained in response to several endogenously expressed HCV proteins. We also observed cytotoxic-T-lymphocyte reactivity in response to endogenously expressed HCV proteins in fresh spleen cells without in vitro expansion. Upon challenge with a recombinant vaccinia virus expressing HCV proteins at 2 months postimmunization, the HCV DNA prime/canarypox virus-immunized mice showed a complete reduction in vaccinia virus titers compared to HCV DNA prime/boost- and mock-immunized controls. Immune responses were still detectable 4 months after canarypox virus boost in immunized mice. Interestingly, at 10 months postimmunization (8 months after canarypox virus boost), the protection in HCV DNA prime/boost-immunized mice against recombinant HCV-vaccinia virus challenge was higher than that observed in HCV DNA prime/canarypox virus boost-immunized mice.