Cells were washed with PBS twice to achieve >85% viable cells in pellets. ATAC-seq protocol was modified from Corces et al. The transpose reaction was performed using TDE1 Tn5 transposase (15027865; Illumina) and TD buffer (15027866; Illumina). The reactions were cleaned up using MinElute PCR Purification Kit (28004; Qiagen) and amplified using NEBNext High-Fidelity 2X PCR Master Mix (M0541S; New England Biolabs Inc.) with a total of 7 cycles. The libraries were cleaned up using MinElute PCR Purification Kit and additionally with AMPure XP beads (Beckman Coulter) to remove primer dimers and large fragments.