[ATAC-seq] Lamina propria cells were isolated and Tregs were sorted by flow cytometry. [ATAC-seq] Large intestinal CD4+TCRβ+YFP+ Tregs were sorted and subjected to ATAC-Seq according to a published protocol (Buenrostro et al., 2013) with a modification in the library purification step. Briefly, 5x10^4 sorted Tregs were washed once with 50 ul PBS, and then lysed in lysis buffer (10 mM Tris-HCl pH 7.4, 10 mM NaCl, 3 mM MgCl2, 0.1% IGEPAL CA-630) on ice. Pelleted nuclei were resuspended in transposition reaction mix with Tn5 transposase (Illumina) and incubated at 37℃ for 30 min with gentle shaking. The DNA was purified with MinElute PCR Purification Kit (Qiagen) and was used as a template of PCR with 10 cycles of amplification. The library was cleaned up with 1.2x SPRIselect beads (Beckman Coulter), to exclude the small fragments, before sequencing with Illumia HiSeq 2500.