Cells  were trypsinized, counted, and 50,000 cells were placed per tube. Briefly, cells were washed with cold PBS at 4°C and lysed for 10 min at 4°C, before proceeding with the ATAC protocol. Cell pellets were resuspended in the transposase reaction mix [5 µl 2× TD buffer, 0.5 µl transposase (Illumina) and 4.5 µl nuclease-free water] and incubated at 37°C for 30 min. DNA from the transposase reaction was purified with a DNA Clean & Concentrator-5 Kit (Zymo Research). PCR amplification was performed using Nextera PCR primers. The optimal number of cycles was determined via quantitative real-time PCR (qPCR) to stop the amplification before saturation. Libraries were purified with AMPure beads. Dual-side purification of the libraries was performed, and the libraries were resuspended in 20 μl of H2O. All libraries were QCed using Bioanalyzer and Qubit. Libraries were sequenced on a Novaseq sequencer at the New York Genome Center.