On day 8 post-infection (p.i.), CD45.2+CD8+KLRG1+ IL-7Ra– cells were sort-purified as terminally differentiated effector CD8+ T cells. On ≥ day 60 p.i., CD45.2+CD8+CD62L+ cells were purified as central memory CD8+ T cells. From the lymph nodes of uninfected P14 TCR-Tg mice, CD62L+CD44lo-med CD8+ cells were isolated as naïve CD8+ T cells. The cell sorting was performed on on FACSAria (BD Biosciences). Sorted CD8+ T cells were cross-linked with 1% formaldehyde in medium for 10 minutes, processed using truChIP Chromatin Shearing Reagent Kit (Covaris), and sonicated for 5 minutes on Covaris S2 ultrasonicator. The sheared chromatin was immunoprecipitated with anti-H3K4me1 (Abcam, ab8895), H3K4me3 (Millipore, 17-614), H3K27me3 (Millipore, 17-622), or H3K27Ac (Abcam, ab4729) and washed as previously described73. The immunoprecipitated DNA and input DNA segments were used for PCR quantification or library construction.