Full-length EBNA1 mRNA-transduced dendritic cells stimulate cytotoxic T lymphocytes recognizing a novel HLA-Cw*0303- and -Cw*0304-restricted epitope on EBNA1-expressing cells

Epstein-Barr virus (EBV)-encoded nuclear antigen 1 (EBNA1) is an attractive target for immunotherapy against EBV-associated malignancies because it is expressed in all EBV-positive cells. Although CD8⁺ cytotoxic T-lymphocyte (CTL) epitope presentation is largely prevented by its glycine-alanine-repeat domain (GAr), the use of mRNA-transduced dendritic cells (DCs) would offer the advantage of priming EBNA1-specific CTLs. After stimulation with GAr-containing EBNA1 -transduced monocyte-derived DCs, two EBNA1-specific CTL clones, B5 and C6, were isolated successfully from a healthy donor. These CTLs recognize peptides in the context of HLA-B*3501 and HLA-Cw*0303, respectively. A novel epitope, FVYGGSKTSL, was then identified, presented by both HLA-Cw*0303 and -CW*0304, which are expressed by > 35% of Japanese, > 20% of Northern Han Chinese and > 25% of Caucasians. The mixed lymphocyte-peptide culture method revealed that FVYGGSKTSL-specific CTL-precursor frequencies in HLA-Cw*0303- or -Cw*0304-positive donors were between 1 × 10^-5 and 1 × 10^-4 CD8⁺ T cells. Moreover, both CTL clones inhibited growth of HLA-matched EBV-transformed B lymphocytes in vitro, and B5 CTLs produced a gamma interferon response to EBNA1 -expressing gastric carcinoma cells in the context of HLA-Cw*0303. These data demonstrate that EBNA1 mRNA-transduced DCs may be useful tools for inducing EBNA1 -specific CTLs that might be of clinical interest for CTL therapy of EBV-associated malignancies.