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Hepatitis C virus specific (HCV-specific) CD8+ cytotoxic T cells play a critical role in viral clearance. Low HCV-specific cytotoxic T lymphocyte (CTL) responses in chronic HCV infection may favor the persistence of virus, whereas stimulation and expansion of HCV-specific CTL activity may assist elimination of HCV infection. Helper T cells control the intensity of CD8+ T-cell responses and helper T-cell responses are known to be compromised in chronic carriers of HCV. In this study, we wanted to ascertain if strengthening the Th response could increase the intensity of CTL activity against HCV target antigens. We selected a synthetic CTL peptide NS31073-1081), two Th1 epitopes, peptide NS3358-375 and NS5B155-172, and one Th2 epitope, peptide NS3505-521. By using the four peptides alone or in combinations, we stimulated peripheral blood cells isolated from a chronic hepatitis C patient in vitro and then analyzed CD8 T cells specific for the NS31073-1081 CTL epitope in A2 tetramer staining and cytotoxicity assays. The results demonstrated that CTL responses could be augmented by helper T-cell epitopes NS3358-375 and NS5B155-172. Th2 epitope NS3505-521 inhibited augmentation of CTL activity by Th1 epitopes. This inhibitory effect could be overcome by combining the two Th1 epitopes NS3358-375 and NS5B155-172 together with NS3505-521. Under such conditions, CTL frequency was restored, but cytotoxic activity remained low suggesting that the help provided under these cultures was sufficient to drive proliferation of CTL, but not sufficient to drive differentiation into mature killer cells. These results may provide some insights into compromised CTL activity in HCV viral persistence. [Copyright &y& Elsevier]

A disturbing feature of hepatitis C virus (HCV) is its long-term persistence in roughly 85% of those infected. Escape mutants may play a major role in HCV persistence. Our previous studies have identified a human leukocyte antigen DRB1*15 (HLA-DRB1*15) restricted Th1 epitope in the HCV NS3 protein, NS3358-375, and escape variants of this epitope that may emerge under immune selection. Such variants attenuate or fail to stimulate T-cell proliferation. Here we provide data from peripheral blood mononuclear cells derived from four HLA-DRB1*15 patients chronically infected with HCV, and report that naturally occurring single amino acid substitutions in the Th1 epitope NS3358-375 fail to stimulate proliferation, which is accompanied by a shift in cytokine secretion patterns from one characteristic of a Th1 antiviral responses to a Th2 form. Further, in one patient, we demonstrate that HCV variant peptides can effectively inhibit host polyclonal peripheral T-cell proliferation. We speculate that this phenomenon may be a factor in chronic HCV infection. [Copyright &y& Elsevier]