PDCD1 and neoplasm: Peripheral mobilization of cytotoxic CD4+ T cells by PD-1 blockade is also suggested by the new appearance of GZMB+ cells in post-atezolizumab blood (4.2%, with 0% pre-atezolizumab) in the same branch C that contains most of the intratumoral T cells, suggesting a T cell phenotype transitioning to the tumor.