CD4 and infection: Naïve CD4+ T cells purified from Ddb1-TaKO-SMARTA (CD45.1+) and WT-SMARTA (CD45.1+ CD45.2+) mice were mixed at ratio of 1:1 (Supplementary Figure S5A), and then were adoptively transferred into congenic WT recipient mice (CD45.2+) followed by LCMV Armstrong infection.