Treatment with 5-aza-2′-deoxycytidine allows IL-2 induction of FOXP3 expression in NK cells. (A) Human NKL cells were treated with 2 different doses of 5-aza-2′-deoxycytidine for 3 days and then incubated with or without IL-2 for 18 hours. FOXP3 expression was then assessed by quantitative PCR. (B) Primary CD3^-CD56⁺ NK cells were isolated from the blood of a healthy donor and treated with 5-aza-2′-deoxycytidine for 3 days at 10 μM. Cells were then incubated with or without IL-2 for an additional 18 hours before FOXP3 gene expression was tested by quantitative PCR.