For each independent ATAC-seq experiment, 50,000 CD4+ T cells were washed once with PBS at 4 °C and resuspended in 500 mL lysis buffer (RSB buffer with 0.1% Tween-20) and incubated on ice for 10 min to generate nuclei. After centrifugation at 500g for 10 min, nuclei were resuspended in 54 mL reaction buffer (10 mM Tris-HCl, pH 7.4, 10 mM NaCl, 3 mM MgCl2 and 0.5% IGEPAL CA-630) and mixed with 6 mL 10X transposase mixture (0.5 M Tris-acetate pH 7.5, 1.5 M potassium acetate, 100 mM magnesium acetate, 40 mM spermidine, 2 mL active Tn5 complex. The reaction mixtures were incubated at 37 °C for 30 min, quenched with 500 mL PB Buffer and then purified directly with MinElute PCR purification kit (Qiagen). Transposase reaction products were amplified with Nextera primers (Illumina), size selected with AMPure XP beads (Beckman Coulter) for fragement between 70bp and 1,000 bp and paired-end sequenced with HiSeq2500 sequencer.