PDCD1 and neoplasm: Many reports have revealed that tumor-suppressing miRNAs are responsible for the antitumor immune response by directly regulating the transcription of immune checkpoint molecules, such as PD-1, PD-L1, and CTLA-4; targeting either the PD-1 or PD-L1 checkpoint protein; or regulating both transcription and related proteins simultaneously within the TME [69].