RECOGNITION OF THE EPSTEIN-BARR VIRUS-ENCODED NUCLEAR ANTIGENS EBNA-4 AND EBNA-6 BY HLA-A11-RESTRICTED CYTOTOXIC LYMPHOCYTES-T - IMPLICATIONS FOR DOWN-REGULATION OF HLA-A11 IN BURKITT-LYMPHOMA

Evasion from cytotoxic T-lymphocyte (CTL) surveillance may be an important step in the pathogenesis of Epstein-Barr virus (EBV)-carrying Burkitt lymphoma (BL) as suggested by the consistent down-regulation of all transformation-associated viral antigens, except EBV nuclear antigen 1 (EBNA-1), and of certain HLA class I alleles in BL biopsies and cell lines that maintain the tumor cell phenotype in vitro. The most common HLA class I defect recorded in BL lines is a selective down-regulation of HLA-A11. To gain some insight into the role of HLA-A11 down-regulation in pathogenesis of BL, we have investigated the target specificity of HLA-A11-restricted CTLs derived by stimulation of lymphocytes from three EBV-seropositive individuals with autologous EBV-transformed lymphoblastoid cell lines. Recombinant vaccinia viruses carrying the coding sequences for EBNA-1, -2A, -2B, -5, -3, -4, and -6 (also known as EBNA-1, -2A, -2B, -LP, -3a, -3b, and -3c, respectively) and EBV latent membrane protein 1 were used to induce high levels of expression of the relevant EBV antigen in fibroblasts derived from HLA class I-matched individuals. EBNA-4-expressing fibroblasts were the predominant target of HLA-A11-restricted CTLs in all three donors. A less pronounced and less regular EBNA-6-specific cytotoxic component was found in two of the donors.