Interplay between IL-10, IFN-γ, IL-17A and PD-1 Expressing EBNA1-Specific CD4 and CD8 T Cell Responses in the Etiologic Pathway to Endemic Burkitt Lymphoma.

Children diagnosed with endemic Burkitt lymphoma (eBL) are deficient in interferon-γ (IFN-γ) responses to Epstein-Barr Nuclear Antigen1 (EBNA1), the viral protein that defines the latency I pattern in this B cell tumor. However, the contributions of immune-regulatory cytokines and phenotypes of the EBNA1-specific T cells have not been characterized for eBL. Using a bespoke flow cytometry assay we measured intracellular IFN-γ, IL-10, IL-17A expression and phenotyped CD4 and CD8 T cell effector memory subsets specific to EBNA1 for eBL patients compared to two groups of healthy children with divergent malaria exposures. In response to EBNA1 and a malaria antigen (SEA-1A), the three study groups exhibited strikingly different cytokine expression and T cell memory profiles. EBNA1-specific IFN-γ-producing CD4 T cell response rates were lowest in eBL (40%) compared to children with high malaria (84%) and low malaria (66%) exposures ( < 0.0001 and = 0.0004, respectively). However, eBL patients did not differ in CD8 T cell response rates or the magnitude of IFN-γ expression. In contrast, eBL children were more likely to have EBNA1-specific CD4 T cells expressing IL-10, and less likely to have polyfunctional IFN-γIL-10 CD4 T cells ( = 0.02). They were also more likely to have IFN-γIL-17A, IFN-γ and IL-17A CD8 T cell subsets compared to healthy children. Cytokine-producing T cell subsets were predominantly CD45RACCR7 T cells, yet PD-1, a marker of persistent activation/exhaustion, was more highly expressed by the central memory (T) and effector memory (T) T cell subsets. In summary, our study suggests that IL-10 mediated immune regulation and depletion of IFN-γ EBNA1-specific CD4 T cells are complementary mechanisms that contribute to impaired T cell cytotoxicity in eBL pathogenesis.