Origin and T cell receptor diversity of Foxo3+CD4+CD25+ T cells

Foxp3(+)CD4(+)CD25(+) regulatory T cells can differentiate from Foxp3(-)CD4(+) medullary thymocytes and Foxp3(-)CD4(+) naive T cells. However, the impact of these two processes on size and composition of the peripheral repertoire of regulatory T cells is unclear. Here we followed the fate of individual Foxp3(+)CD4(+)CD25(+) thymocytes and T cells in vivo in T cell receptor (TCR) transgenic mice that express a restricted but polyclonal repertoire of TCRs. By utilizing high-throughput single-cell analysis, we showed that Foxp3(+)CD4(+) peripheral T cells were derived from thymic precursors that expressed a different TCRs than Foxp3(-)CD4(+) medullary thymocytes and Foxp3(-)CD4(+) T cells. Furthermore, the diversity of TCRs on Foxp3(+)CD4(+) regulatory T cells exceeded the diversity of TCRs on Foxp3(-)CD4(+) naive T cells, even in mice that lack expression of tissue-specific antigens. Our results imply that higher TCR diversity on Foxp3(+) regulatory T cells helps these cells to match the specificities of autoreactive and naive T cells.