overexpressed immune checkpoints (ICs) or their ligands, such as PD-1/PD-L1 and CTLA-4, T- cell immunoglobulin mucin domain-3 protein (TIM-3), and lymphocyte- activation gene 3; (4) severe exhaustion of T cells; and (5) increased activation and recruitment of immunosuppressive cells, such as tumor-associated macrophages, regulatory T cells (Tregs), and myeloid-derived suppressor cells (MDSCs) (7). The gene discussed is PDCD1; the disease is neoplasm.