Identification of novel HLA-A*0201-restricted CD8+ T-cell epitopes on hepatitis delta virus

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Abstract
Hepatitis delta virus (HDV) superinfection causes a poor prognosis in hepatitis B virus-infected patients and effective therapy is lacking. Cytotoxic T-lymphocyte (CTL) responses play an important role in the pathogenesis of chronic viral hepatitis; however, the CD8+ T-cell epitopes of HDV have never been defined. Potential HLA-A*0201-restricted HDV peptides were selected from the SYFPEITHI database and screened by T2 cell-stabilization assay. HLA-A*0201 transgenic mice on a C57BL/6 background were injected intramuscularly with an HDV DNA vaccine. Splenocytes were stained directly ex vivo with HLA-A*0201–peptide tetramers after immunization. Epitope-specific CTL responses were confirmed by cytotoxic assays. HLA-A2, chronically infected HDV patients were also enrolled, to assess the existence of HDV-specific CD8+ T cells, based on findings in animals. Following HDV DNA vaccination, nearly 0·9 % of the total splenic CD8+ T cells were specific for peptides HDV 26–34 and HDV 43–51 in HLA-A*0201 transgenic mice, which was significantly higher than the number found in non-transgenic mice or in transgenic mice that had been immunized with control plasmid. HDV 26–34- and 43–51-specific CTL lines were able to produce CTL responses to each peptide. Interestingly, HDV 26–34- and HDV 43–51-specific CD8+ T cells were also detectable in two chronically infected HDV patients in the absence of active HDV replication. In conclusion, HDV 26–34 and 43–51 are novel HLA-A*0201-restricted CTL epitopes on genotype I HDV. HDV 26–34- and 43–51-specific CTLs have been detected in chronic hepatitis delta patients without active disease. Evoking CTL responses to HDV may be an alternative approach to controlling HDV viraemia in patients with chronic hepatitis delta.