PD1 and CD73 on naïve CD4+ T cells synergistically limit responses to self

Vaccination with self and foreign peptides induces weak and strong expansion of antigen-specific CD4 T cells, respectively, but the mechanism is not known. We tested how much the naïve CD4 T cell repertoires specific for self antigens are shaped by negative selection in the thymus by computational analysis of the entire mouse MHCII peptidome and found that negative selection only partially explains the difference between responses to self and foreign. In naïve (uninfected, unimmunized) mice, RNA-Seq identified higher PD1 and CD73 expression on self-specific compared to foreign-specific CD4 T cells. Pharmacological or genetic blockade of PD1 and CD73 significantly increased the vaccine-induced expansion of self-specific CD4 T cells and moved their transcriptomes toward those of foreign-specific CD4 T cells. We conclude that PD1 and CD73 synergistically limit CD4 T cell responses to self. This discovery has implications for the development of tolerogenic vaccines and cancer immunotherapy. Experiment 1: m25+ CD4 T cells from naive C57BL/6J mice were tetramer sorted and subjected to 10x genomics single cell sequencing. A pseudobulk analysis was performed. Experiment 2: m25+ and p6+ CD4 T cells were sorted by tetramers from draining lymph nodes (inguinal and para-aortic) of C57BL/6J mice that were immunized with m25 or p6 (i.m. into both thighs, 1x in CFA) and treated with anti-PD1 and CD73 inhibitor or isotype control/vehicle.