IL-2 is required for the generation of Treg cells, namely the CD4+Foxp3+CD25+CD127low population in the thymus, and is required for Foxp3+ T cells to exert survival and suppressive functions in autoimmune diseases (21), such as chronic graft-versus-host disease (cGVHD), type 1 diabetes (T1D) and systemic lupus erythematosus (SLE). Here, FOXP3 is linked to chronic graft versus host disease.