Epstein-Barr nuclear antigen 1-specific CD4+ Th1 cells kill Burkitt's lymphoma cells

The γ-herpesvirus, EBV, is reliably found in a latent state in endemic Burkitt's lymphoma. A single EBV gene product, Epstein-Barr nuclear Ag 1 (EBNA1), is expressed at the protein level. Several mechanisms prevent immune recognition of these tumor cells, including a block in EBNA1 presentation to CD8+ killer T cells. Therefore, no EBV-specific immune response has yet been found to target Burkitt's lymphoma. We now find that EBNA1-specific, Th1 CD4+ cytotoxic T cells recognize Burkitt's lymphoma lines. CD4+ T cell epitopes of EBNA1 are predominantly found in the C-terminal, episome-binding domain of EBNA1, and ∼0.5% of peripheral blood CD4+ T cells are specific for EBNA1. Therefore, adaptive immunity can be directed against Burkitt's lymphoma, and perhaps this role for CD4+ Th1 cells extends to other tumors that escape MHC class I presentation.