library_construction_protocol: Naïve CD8+ T cell subsets (TN and VM) were FACS sorted by staining for CD8, CD4, CD44, CD122 and Viability Dye. Cells were sorted into PBS + 2% BSA  + 2mM EDTA. FACS sorted cells were permeabilized in lysis buffer (10 mM Tris-Cl pH 8.0, 300 mM sucrose, 10 mM NaCl, 2 mM MgAc2, 6 mM CaCl2, 0.2% NP-40 (Igepal), 0.5 mM DTT, 1x Pierce protease inhibitor (Thermo Scientific), and 40 units of RiboLock RNase inhibitor (Thermo Scientific) per 10 mL buffer) by brief aggressive pipetting, washed with buffer W (10 mM Tris-Cl pH 8.0, 300 mM sucrose, 10 mM NaCl, 2 mM MgAc2, 0.008% Tween20, 0.5 mM DTT, 1x protease inhibitor, and 40 units of RiboLock RNase inhibitor per 10 mL buffer), and resuspended in storage buffer (50 mM Tris-Cl pH 8.3, 40% glycerol, 5 mM MgCl2, 0.1 mM EDTA, 0.5 mM DTT, 1x protease inhibitor, and 40 units of RiboLock RNase inhibitor per 10 mL buffer). The cells were pelleted at 1000 g for 8 minutes for each step of buffer change. The permeabilized cells were counted, snap-frozen in liquid nitrogen, and stored at -80°C. Libraries were prepared by the TREx core at Cornell University from 25,000 permeabilized cells as described in Buenrostro et al. (2015) and Corces et al. (2017). Briefly, frozen permeabilized cells were thawed, washed twice in ATAC-RSBbuffer containing 0.1% Tween20, resuspended in Transposition Mix (Nextera DNA Sample Preparation Kit, Illumina) containing 0.1% Tween20 and PBS, and incubated for 30 minutes at 37°C with shaking (1000 rpm). After column cleanup, libraries were amplified using Nextera PCR oligos (Nextera Index Kit, Illumina) and Ultra II Q5 Master Mix (NEB) for a total of 11 PCR cycles. The libraries were cleaned up twice (in series) with a 2:1 ratio of SPRIselect beads (Beckman Coulter).