In these experiments, naive (CD4+CD62L+CD44intCD25−Foxp3−) T cells isolated from OTII/Foxp3-GFP reporter mice were activated in the presence of TGF-β under three different settings: (a) plus IL-2 (TIL-2 Treg), (b) plus RA (TRA Treg), or (c) plus both RA and IL-2 (TILRA Treg). The gene discussed is SELL; the disease is rheumatoid arthritis.