CD274 and glioblastoma: In addition to Ti-Treg cells, there are multiple, redundant immunosuppressive mechanisms associated with GBM, such as immunosuppressive cytokines (TGF-β, PGE2, among others), immune checkpoints [PDL-1, programmed cell death 1 (PD-1), and CTLA-4] and others (3, 15–17).