Epigenetic programing of CD4+ T cell proliferation, survival and function during chronic viral infection

Project Summary CD4+ helper T cells provide critical effector functions to combat viral diseases and are a key cell type for vaccine- induced immunological protection against viruses. During response to chronic viral infections, stimulation by persistent antigen and inflammatory cytokines can induce dysfunction that limits helper T cell function that contributes to subsequent viral persistence and chronic viral diseases. While such dysfunction is well-described for exhausted CD8+ T cells generated by chronic antigen stimulation, the mechanistic basis for dysfunctional CD4+ T cells generated during chronic infection are poorly understood. We hypothesize that the dysfunctional state of virus-specific CD4+ T cells during chronic infection is programed in part through the acquisition of epigenetic programing by changes in DNA methylation at key genes that regulate T cell functions such as cell proliferation, survival, and effector functions. This hypothesis is based on our key preliminary data from our studies of virus-specific CD4+ T cells that are deficient in Tet2 and Dnmt3a, enzymes that regulate active demethylation and de novo methylation of CpG dinucleotides of DNA, respectively. Using a highly novel experimental model to study cell-intrinsic programing of virus-specific CD4+ T cells, we have found that the combined deficiency of Tet2 and Dnmt3a results in CD4+ T cells with a remarkably unique capacity to maintain proliferative, survival, and functional capacities during chronic viral infection. The three specific aims of our proposal will define how chronic antigen stimulation contributes to Tet2-mediated active demethylation and Dnmt3a-mediated de novo methylation programing that drives CD4+ T cell dysfunction. We will use highly innovative conditional knockout in vivo virus-specific CD4+ T cell models, combined with whole genome DNA methylation sequencing to identify epigenomic programing and associated transcription factor pathways that contribute to impaired proliferation, survival, and effector functions of chronically-stimulated CD4+ T cells. Finally, we will determine whether disruption of such epigenetic programing results in CD4+ T cells capable of improved help for exhausted CD8+ T cells and improved viral control and clearance of chronic viral infections. Together, these studies will reveal critical mechanistic insights into CD4+ T cell programing that could be targeted for improving strategies to prevent and treat chronic viral infections.