CD8A and infection: TCF-1 is critical for CD8+ memory T cell responses during infection (Jeannet et al., 2010; Zhou et al., 2010; Xing et al., 2016) and more broadly directs the divergence of CD4+ T cell lineages into T helper type 2 cells (Yu et al., 2009) and follicular cytotoxic and T follicular helper subsets (Choi et al., 2015; Wu et al., 2015; Xu et al., 2015; Leong et al., 2016), but suppresses the differentiation of T helper type 17 (Th17) cells and promotes their stem cell–like properties (Ma et al., 2011; Yu et al., 2011; Zhang et al., 2018; Karmaus et al., 2019).