PDCD1 and central nervous system cancer: Human monoclonal antibodies (mAbs) against the immune system response modulators CTLA-4 (ipilimumab) and programmed cell death-1 (PD-1) (pembrolizumab and nivolumab) have been reported to achieve a significant clinical benefit for multiple cancers, but also have low efficacy in the treatment of gliomas (17, 18).