CD274 and glioma: Early studies demonstrated that PD-L1 expressed by glioma cells inhibits T-lymphocyte functions and induces apoptosis of tumor-specific T-lymphocytes mainly via decreasing cytokines production (e.g., IFN-γ, IL-2 and IL-10) (Wintterle et al., 2003; Ahn et al., 2013).