Additionally, PD-L1 on glioblastoma cells directly promotes effector T-cell exhaustion and anergy [55], resulting in a sparse distribution of CD8+ cytotoxic T cells being detected in the glioblastoma parenchyma, with those present often being refractory to direct T-cell-receptor stimulation [56] (Figure 1). This evidence concerns the gene CD8A and glioblastoma.