CD274 and glioblastoma: From the initial stages of GBM development, GBM-conditioned PCs acquire an immunosuppressive phenotype characterized by the secretion of high levels of anti-inflammatory cytokines (IL10, IL6, TGF-β), the expression of immunosuppressive molecules such as programmed death-ligand 1 (PDL-1), and the reduced expression of co-stimulatory molecules (IL2).