PDCD1 and glioblastoma: Specifically within the HGG population, a sub-analysis of the large CheckMate 143, a phase 1 clinical trial of nivolumab (anti-PD-1) alone or in combination with ipilimumab, revealed that in a recurrent GBM population, no differences in overall survival were seen with monotherapy vs. combination therapy, but higher toxicity when the anti-CTLA-4 antibody was added to the treatment (135).