CD8A and cancer: In chronic infections and cancer, a population of exhausted cells, known as precursors of exhausted CD8+ T (TPEX) cells, are marked by TCF-1 expression and are thought to be analogous to the TSCM cell population identified following vaccination and acute infection (Im et al., 2016; Utzschneider et al., 2016; Wu et al., 2016; Zhou et al., 2010).