PDCD1 and neoplasm: siRNA can target different molecules, such as programmed cell death-1 (PD-1) and its ligand (PD-L1), as well as interleukin 10 receptor, STAT3, and transforming growth factor-β receptor, on the surface of immune cells and/or tumor cells, which participate actively in the process of immune activation, to lessen tumor evasion from the host’s immune system and boost the immune response against tumors [69,70,71,72].