PDCD1 and neoplasm: Consistent to this view, two recent scRNA-seq studies have observed the expansion of anti-tumor TCR reperitore in the peripheral blood and clonal replacement of intratumoral tumor-specific T cells following PD-1/PD-L1 blockade (Yost et al., 2019; Wu et al., 2020), suggesting the enhanced T cell priming of tumor neoantigens as a major mechanism underlying effective immunotherapy.