Vigorous hepatitis C virus-specific CD4+ and CD8+ T cell responses induced by protein immunization in the presence of montanide ISA720 plus synthetic oligodeoxynucleotides containing immunostimulatory cytosine-guanine dinucleotide motifs

Abstract

Background. A prophylactic vaccine for hepatitis C virus (HCV) requires generation of strong humoral as well as CD4+ and CD8+ T cell responses. Methods. The immunomodulatory effects of the combination of 2 adjuvants, synthetic oligodeoxynucleotides containing immunostimulatory cytosine-guanine dinucleotide motifs emulsified with Montanide ISA720 (M-ISA720/CpG), were investigated using the murine model. Results. Administration of recombinant HCV (rHCV) nonstructural (NS) 3 and NS5B proteins plus M-ISA720/ CpG (hereafter, "M-ISA720/CpG/rHCV protein") induced high anti-NS3 and anti-NS5B immunoglobulin (Ig) G titers, with the IgG2a isotype being predominant. NS3- and NS5B-specific Interferon (IFN)-γ- and interleukin-2-producing CD4+ T cell responses, as assessed by enzyme-linked immunospot assay, were significantly more vigorous in mice immunized with M-ISA720/CpG/rHCV protein than in control mice immunized without adjuvant. NS3- and NS5B-specific IFN-γ-producing CD8+ T cell percentages, as measured by direct ex vivo intracellular cytokine staining assay, were, respectively, a mean ± SD of 0.14% ± 0.04% and 0.15% ± 0.05% in mice immunized with M-ISA720/CpG/rHCV protein. Furthermore, boosting with recombinant NS3 expression plasmid DNA after priming with M-ISA720/CpG-adjuvanted rNS3 strikingly enhanced both CD4+ and CD8+ T cell responses. Conclusion. Immunization with M-ISA720/CpG/rHCV protein is capable of inducing potent humoral as well as HCV-specific T helper type 1-biased CD4+ and CD8+ T cell responses. A DNA boost after a protein prime-a reversal of the conventional approach-may provide an alternative path to the development of an effective HCV vaccine.