Priming with CpG-enriched plasmid and boosting with protein formulated with CpG oligodeoxynucleotides and Quil A induces strong cellular and humoral immune responses to hepatitis C virus NS3.

Cell-mediated immune responses to hepatitis C virus (HCV) proteins play a key role in recovery from infection. The NS3 protein of HCV is of special interest, since it is one of the most conserved proteins and NS3-specific immune responses are stronger and more frequently observed in patients resolving the infection than in chronically infected patients. Since these characteristics make NS3 an attractive vaccine candidate, the objective of this study was to optimize NS3-specific immune responses. Results from this group first demonstrated that a plasmid enriched with 24 CpG motifs (pBISIA24-NS3) tends to induce the strongest and most consistent Th1-biased immune response. Subsequently, it was shown that NS3 formulated with CpG oligodeoxynucleotide and Quil A (rNS3+CpG+Quil A) adjuvants induces a balanced immune response in mice, whereas rNS3 combined with either CpG or Quil A elicits a Th2-biased response. To further enhance NS3-specific cell-mediated immune responses, a vaccination regime consisting of priming with pBISIA24-NS3, followed by boosting with rNS3+CpG+Quil A, was explored in mice and pigs. When compared to immunization with rNS3+CpG+Quil A, this regime shifted the immune response to a Th1-type response and, accordingly, enhanced MHC I-restricted killing by cytotoxic T lymphocytes in mice. Although immunization with pBISIA24-NS3 also induced a Th1-biased response, including cytotoxicity in the mice, the humoral response was significantly lower than that induced by the DNA prime-protein boost regime. These results demonstrate the advantage of a DNA prime-protein boost approach in inducing a strong NS3-specific cell-mediated, as well as humoral, immune response, in both inbred laboratory and outbred large animal species.