Freshly sorted, live mouse T cells were washed with PBS containing 0.04% BSA, and the cell count was determined. Nuclei were isolated using the 10x Genomics Low Cell Input Nuclei Isolation protocol. Briefly, cells were centrifuged at 300×g for 5 min at 4°C and resuspended in 50µL PBS + 0.04% BSA. After centrifugation, 45µL of the supernatant was removed, and 45µL of chilled Lysis Buffer was added. The suspension was gently mixed and incubated on ice for 3-5 min. Chilled Wash Buffer was added without mixing, followed by centrifugation at 500×g for 5 min. Supernatant was removed, and 45 µL of chilled Diluted Nuclei Buffer was added. After a second centrifugation, the pellet was resuspended in 7µL of chilled Diluted Nuclei Buffer. Nuclei concentration was counted and used immediately for transposition Single-cell ATAC-seq libraries were prepared using the Chromium Next GEM Single Cell ATAC Reagent Kits v2 (10x Genomics, Pleasanton, CA) per manufacturer's instructions. Transposed nuclei were loaded with gel beads and reagents onto a Chromium Next GEM Chip H and processed on the Chromium X instrument to generate barcoded Gel Beads-in-emulsion (GEMs). GEMs underwent thermal cycling for barcoding, followed by recovery, Dynabead and SPRIselect cleanup, sample indexing PCR, and dual-sided SPRI size selection. Final libraries were quantified with the Qubit dsDNA HS assay (Thermo Fisher Scientific) and assessed using the TapeStation (Agilent Technologies, Santa Clara, CA). Libraries were sequenced on a NovaSeq (Illumina, San Diego, CA), producing approximately 200 million paired-end 150 bp reads per sample.