PDCD1 and neoplasm: In addition, the blockade of immune checkpoint molecules (e.g. programmed cell death protein 1, PD-1; cytotoxic T lymphocyte-associated protein 4, CTLA-4) using antibodies has demonstrated great promise for sculpting tumor immunogenicity in certain solid tumors (e.g. melanoma and non-small cell lung cancer) 8; however, response rates to immune checkpoint inhibitors tremendously vary in different tumor types, which is mainly attributed to the complex nature of TME 9.