Transfections and reporter gene assays.
T cells were rested in serum-free AIM-V medium (Life Technologies) overnight. 3.5 mug of the FOXP3 promoter luciferase reporter vector and 0.5 mug phRL-TK were added to 3 x 106 CD4+ T cells resuspended in 100 muL of Nucleofector solution (Amaxa Biosystems) and electroporated using the U-15 program of the Nucleofector. After a 24-h culture in serum-free conditions and stimuli as indicated in the figures, luciferase activity was measured by the dual luciferase assay system (Promega Biotech) according to the manufacturer's instructions. Data were normalized by the activity of renilla luciferase. 
