Second, the immunosuppressive GBM microenvironment is the primary reason for the aforementioned limited efficacy, especially for T cells, including immunosuppressive immune cells (Tregs, MDSCs, and TAMs), tumor cell-derived inhibitory cytokines, and the upregulated expression of immune checkpoint receptors on T cells and of PD-L1 on tumor cells. This evidence concerns the gene CD274 and glioblastoma.