3.5 μg of the FOXP3 promoter luciferase reporter vector and 0.5 μg phRL-TK were added to 3 × 106 CD4+ T cells resuspended in 100 μL 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.