Helios expression defines two distinct populations of Foxp3+ Treg cells

The transcription factor Helios is expressed in a large subset of Foxp3+ Tregs of both mouse and man. We previously demonstrated that Treg induced in peripheral sites (pTreg) from Foxp3- T conventional (Tconv) cells were Helios- and proposed that Helios is a marker of thymic derived Treg (tTreg). To compare the two Treg subpopulations, we generated Helios-GFP reporter mice and crossed them to Foxp3-RFP reporter mice. The Helios+ Treg population expressed a more activated phenotype and had a higher suppressive capacity in vitro. Both populations expressed a highly demethylated TSDR and both subsets were equivalent in their ability to suppress inflammatory bowel disease in vivo. However, Helios+ Treg more effectively inhibited the proliferation of activated, autoreactive splenocytes from scurfy mice. When Helios+ and Helios- Treg were transferred to lymphoreplete mice, both populations maintained comparable Foxp3 expression, but Foxp3 expression was less stable in Helios- Treg when transferred to lymphopenic mice. Gene expression profiling of the two populations demonstrated a large number of differentially expressed genes and that Helios- Treg subpopulation expressed certain genes normally expressed in CD4+Foxp3- T cells. TCR repertoire analysis indicated very little overlap between Helios+ and Helios- Treg. Thus, Helios+ and Helios- Treg subpopulations are phenotypically and functionally distinct, consistent with thymic and peripheral sites of origin, respectively. Because of their superior suppressive activity and enhanced stability Foxp3+Helios+ Treg represent the optimal Treg population for cellular immunotherapy. 5 replicates of wildtype vs knockout Helios gene in Treg cells.