ERVW-1 and bacterial infectious disease: To determine the full extent of effector T cell heterogeneity during acute bacterial infection and resolve contributions of TCR usage-based cell intrinsic versus extrinsic cues in directing naïve T cell fates, we infected B6 mice with Listeria monocytogenes (L.m.)expressing lymphocytic choriomeningitis virus (LCMV) envelope glycoprotein-derived antigenic peptide gp66-80 (L.m.-gp66) and performed scRNA-seq and TCR-seq on FACS purified I-Ab:gp66 tetramer-bound effector CD4+ T cells on day 7 after infection (Fig. 1 a).