PDCD1 and neoplasm: MDSC-mediated suppression also encompasses the involvement of immune checkpoint molecules where PD-L1 being a prominent molecule in this context (Ballbach et al. 2017; Iwata et al. 2016), which interacts with the programmed cell death protein 1 (PD-1) present in T lymphocytes, inhibiting proliferation, survival, and effector functions (cytotoxicity, cytokine release), or mediating apoptosis of tumor-specific T cells.