CD274 and glioblastoma: In addition, activation of the PI3K pathway in GBM cells results in the expression of the immune checkpoint ligand PD-L1 (Figure 6c); additionally, activation of the Ras–MAPK pathway induces the expression of IL6 and TGF-β, which enhances the recruitment of TAMs and inhibits both dendritic cells (DC) and lymphocytes infiltration into the tumor.