Helios and Helios Treg subpopulations are phenotypically and functionally distinct and express dissimilar TCR repertoires.

The transcription factor Helios is expressed in a large subset of Foxp3 Tregs. We previously proposed that Helios is a marker of thymic derived Treg (tTreg), while Helios Treg were induced from Foxp3 T conventional (Tconv) cells in the periphery (pTreg). 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, had a slightly higher suppressive capacity in vitro and expressed a more highly demethylated TSDR but 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 demonstrated a large number of differentially expressed genes and showed that Helios Treg 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 and express dissimilar TCR repertoires.