Efficient IL-2R signaling differentially affects stability, function, and composition of the regulatory T cell pool

Signaling via the interleukin 2 receptor (IL-2R) is a requisite for Treg cell identity and function. However, it is not completely understood to what degree IL-2R signaling is required for Treg cell homeostasis, lineage stability and function during both resting and inflammatory conditions. Here, we characterized a spontaneous mouse mutant endowed with a hypomorphic Tyr129His variant of CD25, the a chain of the IL 2R, which resulted in diminished receptor expression and reduced IL-2R signaling. Under non-inflammatory conditions Cd25-Y129H mice harbored substantially lower numbers of peripheral Treg cells with stable Foxp3 expression that prevented the development of spontaneous autoimmune diseases. In contrast, Cd25-Y129H Treg cells failed to efficiently induce immune suppression and lost linage commitment in a T cell transfer colitis model, indicating that unimpaired IL-2R signaling is critical for Treg cell function in inflammatory environments. Moreover, single-cell RNA sequencing of Treg cells revealed that impaired IL-2R signaling profoundly affected the balance of central and effector Treg cell subsets. Thus, partial loss of IL-2R signaling differentially interferes with maintenance, heterogeneity and suppressive function of the regulatory T cell pool. CD4+Foxp3+ Treg cells were sorted from spleens of WT or CD25-Y129H Foxp3-GFP mice by flow cytometry and subjected to single-cell RNA sequencing (10x genomics).