Induction of cytotoxic T lymphocytes with peptides in vitro: Identification of candidate T-cell epitopes in hepatitis B virus X antigen

Cytotoxic T lymphocytes (CTL) have been suggested to contribute to viral cl earance during hepatitis B virus (HBV) infection. To induce effective CTL a gainst viral infection by peptide vaccination, it is essential to identify the epitope peptides recognized by CTL. Here, 15 peptide sequences that con tain HLA-A2.1-restricted CTL binding consensus motif were identified on hep atitis B virus X (HBx) protein and synthesized for further characterization . In the binding assay, 8 of 15 synthetic peptides enhanced the expression of HLA-A2.1 molecules on the surface of T2 cells, a human transport-associa ted antigen processing-deficient cell line. This result implies that these eight peptides are able to bind to the HLA-A2.1 molecules. These peptides w ere further tested for their ability to activate CTL. from peripheral blood mononuclear cells (PBMCs) isolated from HBV chronic carriers. Five of eigh t tested peptides activated PBMC-derived T cells, resulting in the lysis of the target T2 cells pulsed with the same peptide. Furthermore, the CTL res ponses to HBx antigen in HBV chronic carriers were shown to be polyclonal, multispecific, and mediated mainly by CD8(+) T cells. In contrast, these re sponses were not detected in uninfected healthy blood donors. Although the five CTL epitope peptides identified in this study have not been proven to be the naturally processed epitopes in HBV-infected hepatocytes, they could be: candidates for peptide-based immunotherapy against HBV infection.