In ectopic and enforced expression experiments, in vitro differentiated CD8+ T cells transduced with TOX+GFP or control GFP only (>2 biological replicates each) were sorted on GFP expression 6 days following initial activation to a purity of >98%. ATAC libraries were generated as described previously with minor changes. Briefly, nuclei from 50,000 cells were isolated using a lysis solution composed of 10mM Tris-HCl, 10mM NaCl, 3mM MgCl2, and 0.1% IGEPAL CA-630. Immediately following cell lysis, nuclei were pelleted in low-bind 1.5ml tubes (Eppendorf) and resuspended in TD Buffer with Tn5 transposase (Illumina). Transposition reaction was performed at 37 degrees Celsius for 45 minutes. DNA fragments were purified from enzyme solution using MinElute Enzyme Reaction Cleanup Kit (Qiagen). Libraries were barcoded (Nextera Index Kit, Illumina) and amplified with NEBNext High Fidelity PCR Mix (New England Biolabs). Library quality was assessed using a TapeStation instrument.