Identification of novel hepatitis C virus-specific cytotoxic T lymphocyte epiotpe in NS3 region.

Hepatitis C virus (HCV)-specific cytotoxic T lymphocytes (CTL) are thought to be effective in limiting viral spread and in clearing virus during infection. Therefore, we attempted to establish HCV-specific CTL and identify novel HCV-specific CTL epitopes in a patient with acute hepatitis C by a novel screening method using recombinant vaccinia viruses (rVV) and synthetic peptides. CD8(+)CD45RA(-) T cells (memory T cells) were isolated from peripheral blood mononuclear cells (PBMC) of a patient with acute hepatitis C. HCV-specific CTL were cloned at limited dilutions and tested for HCV-specific CTL activity using a standard (51)Cr release assay. CTL assay was performed using rVV expressing regions of HCV-J, and overlapping and truncated synthetic peptides from HCV-J. CTL recognizing the NS3 region were isolated by (51)Cr release assay with rVV-HCV. Isolated CTL were restricted by HLA class I molecules B(*)5603. We confirmed that isolated CTL recognized 8-mer amino acids in the NS3 region of HCV-J by (51)Cr release assay with overlapping and truncated synthetic peptides. In conclusion, we isolated HCV-specific CTL restricted by HLA-B(*)5603 and identified a novel HCV-specific CTL epitope (IPFYGKAI, amino acids 1373-1380) in the NS3 region. The identified HCV-specific CTL epitope might be useful for HCV therapy.

Identification of novel hepatitis C virus-specific cytotoxic T lymphocyte epitopes by ELISpot assay using peptides with human leukocyte antigen-A*2402-binding motifs.

The human leukocyte antigen (HLA)-A*2402 is common in Asians. The authors attempted to identify epitopes for HLA-A*2402-restricted, hepatitis C virus (HCV)-specific CD8(+) T cells by an enzyme-linked immunospot (ELISpot) assay using peripheral blood CD8(+) T cells from HLA-A*2402-positive hepatitis C patients and synthetic HCV peptides based on HLA-A*2402-binding motifs and the amino acid sequence of type 1b HCV. Ten novel epitopes were identified in five of seven HLA-A*2402-positive patients with acute or short-term chronic HCV infection (<3 years), but in none of four with longer-term chronic infection (>10 years). Only one of the ten epitopes proved to be definitely HLA-A*2402-restricted. Another epitope was identified in one of two HLA-A*2402-negative acute hepatitis C patients. In two of the six patients with positive CD8(+) T cell responses, the targeted epitopes were multiple. The same epitope was targeted in two patients. When patients with unresolved acute HCV infection were treated with alpha interferon, peripheral blood HCV-specific CD8(+) T cells decreased with resolution of the hepatitis. In conclusion, CD8(+) T cell responses to HCV infection are heterogeneous. One definite HLA-A*2402-restricted and ten probably non-HLA-A*2402-restricted epitopes were identified. Patients with short-term HCV infection are suitable for searching for novel HCV epitopes, but peripheral blood HCV-specific CD8(+) T cells decrease markedly after loss of antigenic stimulation.

Cytokine-dependent anti-viral role of CD4-positive T cells in therapeutic vaccination against chronic hepatitis B viral infection.

There are several lines of evidence suggesting that specific vaccine therapy with a standard hepatitis B virus (HBV) vaccination reduces HBV replication. The aim of this study was to investigate the anti-viral mechanism of vaccine therapy in chronic hepatitis B patients. Nineteen patients were assigned to receive either vaccine therapy (n = 13) or no treatment as a control (n = 6). Vaccinated patients were analyzed for T cell proliferative responses specific for envelope antigen and cytokine production by antigen-specific T cells. ELISPOT and cytotoxicity assays also were carried out for limited blood samples. Serum HBV DNA levels decreased significantly at 3 months after completion of therapy and thereafter as compared to the baseline ones, and were significantly lower in vaccinated patients than in controls at 12 and 18 months after completion of therapy. Vaccination induced antigen-specific CD4+ T cell proliferative responses in four patients (30.8%). The production of high levels of interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) by antigen-specific T cells was found in six patients (46.0%) who showed significantly lower HBV DNA levels in serum at 6 (P = 0.04) and 18 months (P = 0.005) after completion of therapy than those without high levels of cytokine production. Vaccination did not induce antigen-specific CD8+ T cells or cytotoxic T cells. These results suggest that envelope-specific CD4+ T cells may control directly HBV replication by producing anti-viral cytokines rather than providing help for cytotoxic T cells in therapeutic vaccination against chronic HBV infection.