Abstract Regulatory T cells (Tregs) are suppressive immune cells used for a variety of clinical and therapeutic applications. Canonical Tregs express CD4, FOXP3, and CD25, which are considered definitive markers of Treg status when used together. However, a subset of noncanonical Tregs expressing only CD4 and FOXP3 have recently been described in some infection contexts. The transcriptional regulation of these cells is still unclear. We found that loss of TCF-1 in all T cells in mice leads to expansion of these cells in multiple tissues in a cell-intrinsic fashion. This effect was not due to aberrant expression of FOXP3, as other functional Treg markers were also expressed. In addition, presence of TCF-1-deficient cells in a chimeric mouse induced increased production of noncanonical Tregs from WT donor cells. Therefore, targeting of TCF-1 may remove suppression on this Treg lineage, increasing the yield of these cells for use in the clinic. Summary sentence Loss of TCF-1 causes expansion of CD25- FOXP3+ noncanonical Tregs, and TCF-1-deficient T cells induce increased production of CD25- Tregs from WT cells.

Loss of TCF-1 regulates production of noncanonical Tregs in a prion-like manner