It is worth mentioning that in humans, alterations in IL-2/IL-2R signaling measured by the levels of STAT5 phosphorylation (pSTAT5) and/or reduced IL-2 availability, which have been clearly described and linked to type-1 diabetes (T1D) [48,49,50], result in the impairment of Treg function, but usually not in Treg frequency [34,49]. This evidence concerns the gene IL2RA and type 1 diabetes mellitus.