ChIP-seq libraries were prepared as previously described46 (link). Briefly, 10 million CD8+ T cells were fixed with 1% formaldehyde at 37 °C for 10 min, sonicated, and fragmented chromatin was immunoprecipitated with anti-STAT5B or anti-H3K27ac antibodies that were coupled to Magna ChIP protein A/G magnetic beads (EMD Millipore, 16-663). ChIP-seq DNA libraries were prepared with the KAPA LTP Library Preparation Kit and barcoded with NEXTflex DNA barcodes, quantified, and sequenced on an Illumina HiSeq 3000 system.