Isolation of cytotoxic T lymphocytes from healthy seropositive individuals specific for peptide epitopes from Epstein-Barr virus nuclear antigen 1: implications for viral persistence and tumor surveillance.

The question of whether Epstein-Barr nuclear antigen 1 (EBNA1) includes cytotoxic T lymphocyte (CTL) epitopes has generated considerable scientific interest, primarily due to its important implications for the overall biology of Epstein-Barr virus (EBV). Earlier studies have suggested that EBV-associated malignancies that express only EBNA1 escape virus-specific immune surveillance since this antigen is not a target for CTL recognition. In the present report we have used a modified protocol to demonstrate that EBNA1 includes sequences which can be recognized by both polyclonal and clonal CTLs. CD4+ CTL clones were isolated from a healthy, seropositive donor that recognized the peptide epitope TSLYNLRRGTALA from EBNA1 in association with HLA DR1. Interestingly, these CTLs are unable to lyse EBV-infected B cells suggesting that EBNA1 may not be endogenously processed and/or presented to the host CTL response. Despite recent suggestions that glycine-alanine repeat sequences within EBNA1 can inhibit endogenous processing, target cells infected with recombinant vaccinia vectors encoding truncated EBNA1 proteins, without these repeat sequences, were not recognized by this CTL clone. Thus it seems that the presence of glycine-alanine repeats is not responsible for inhibiting the processing of the class II-restricted epitope defined in this study. These results substantiate the view that EBV-infected normal and malignant cells, where viral gene expression is limited to EBNA1, can resist CTL-mediated immune surveillance in vivo.