IL‐2 administration was associated with preferential, sustained expansion of functional Tregs (while maintaining the immune response to infections) resulting in reduced chronic GVHD. IL‐2 restores homeostasis of CD4+ T cell subsets through selective increase of Stat5 phosphorylation in Tregs and a decrease of phosphorylated Stat5 in conventional CD4+ T cells. Here, IL2 is linked to chronic graft versus host disease.