Cells were transduced with retrovirus coding WT or each mutant FoxP3 and sorted for viable Thy1.1hi after 72 hr of transduction. Chromatin IPed with specific Abs was eluted from the Protein-G beads, treated with 1µg DNase-free RNase (Roche) for 30 min at 37°C and with Proteinase K (Roche) for 2 hrs at 37°C followed by reverse cross-linking by leaving the plate at 65°C overnight. DNA from reverse cross-linked material was purified with SPRI beads (Agencourt AMPure XP beads, Beckman Coulter); and sequential steps of end-repair, A-base addition, adaptor-ligation and PCR amplification (15 cycles) were performed to prepare the ChIP-seq library for each sample.