PDCD1 and neoplasm: The prominent role of local T cell responses in tumor elimination is highlighted by the clinical success of therapies blocking key immune-inhibitory receptors upregulated in antigen-activated T cells such as CTLA-4 and the programmed cell death 1/programmed death ligand 1 (PD-1/PD-L1) pathways (collectively referred to as immune checkpoint blockers [ICBs]).