PDCD1 and neoplasm: Given that Tfh-pseudotime is correlated with PDCD1 expression (Figure 9C), this suggests that PDCD1 expression and the Tfh-effector process are induced during the earlier phases of effector T cell activity, and that the activation processes in PDCD1high T cells are suppressed, presumably through PD1–PDL1 interactions in the tumor environment (55).