CD4 and infection: Then, we sorted virus-specific SMARTA TFH cells and TH1 cells from the SMARTA chimera mice on days 2, 5 and 8 after the infection (Supplementary Figure S1a–c) and subsequently performed an ATAC-Seq assay to measure the transposase-accessible chromatin.40 We also sorted naïve SMARTA cells (CD4+CD25−CD62L+CD44−) as a control (Supplementary Figure S1d).