Experience-Driven Development: Effector/Memory-Like αE+Foxp3+ Regulatory T Cells Originate from Both Naive T Cells and Naturally Occurring Naive-Like Regulatory T Cells

Naturally occurring Foxp3+CD25+CD4+ regulatory T cells (Treg) have initially been described as anergic cells; however, more recent in vivo studies suggest that Tregs vigorously proliferate under both homeostatic as well as inflammatory conditions. We have previously identified a subset of murine CD4+ Tregs, which is characterized by expression of the integrin αEβ7 and which displays an effector/memory-like phenotype indicative of Ag-specific expansion and differentiation. In the present study, the αE+ Treg subset was found to contain a large fraction of cycling cells under homeostatic conditions in healthy mice. Using an adoptive transfer system of Ag-specific T cells, we could demonstrate that the vast majority of transferred natural, naive-like CD25+CD4+ Tregs acquired expression of the integrin αEβ7 upon tolerogenic application of Ag via the oral route. In addition, using the same system, Foxp3+ Tregs could be de novo induced from conventional naive CD25−CD4+ T cells, and this conversion was associated with concomitant expression of αE. These findings suggest that Tregs expressing the integrin αE are effector/memory Tregs with a high turnover rate that can develop in the periphery upon Ag contact under tolerogenic conditions, both from thymic-derived CD25+CD4+ Tregs with a naive-like phenotype as well as from conventional naive T cells.