PDCD1 and neoplasm: Tumor-associated acquisition of T-cell dysfunction has been related to increased co-expression of several inhibitory receptors (IRs) including PD1, cytotoxic T lymphocyte antigen 4 (CTLA-4), T-cell immunoglobulin domain and mucin domain-3 (TIM-3), lymphocyte activation gene 3 (LAG-3), and T-cell immunoreceptor with Ig and ITIM domains (TIGIT).