Currently, immune checkpoint blockade utilizing monoclonal antibodies against PD-1 (programmed cell death-1) or its ligand (PD-L1) is being extensively studied in GBM clinical trials (e.g., NCT02336165, NCT02617589, NCT02550249, NCT02017717); however, their efficacy so far has been very limited. Here, PDCD1 is linked to glioblastoma.