PDCD1 and glioblastoma: Despite the fact that the FDA-approved nivolumab targeting programmed cell death protein 1 (PD-1) and Ipilimumab targeting CTLA-4 have displayed clinical therapeutic superiority compared to conventional therapies in multiple types of cancers (13–16), the combination of nivolumab and Ipilimumab shows no significant effects on recurrent glioblastoma (17, 18).