For example, monoclonal antibodies targeting programmed cell death protein 1 (PD-1) protein and its ligand programmed death-ligand (PDL-1) to enhance the cytotoxic activity of CD8+ T cells has been found to be successful in other cancers such as melanoma and non-small cell lung cancer but failed to show success in GBM as reported by the CheckMate phase III clinical trial (NCT02017717) [43]. Here, PDCD1 is linked to cancer.