PDCD1 and neoplasm: In addition, the tumor develops many strategies to evade an immune response, including immune suppressors such as regulatory T cells (Treg) and myeloid-derived suppressor cells (MDSC) [6], immune checkpoint cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), programmed death protein 1 (PD-1)/PD-L1 [7] and T cell dysfunction [8].