PDCD1 and glioblastoma: Critically, PD-1+ T cells infiltrating C-GBM coexpressed the inhibitory receptor TIGIT at a higher frequency in C-GBM (46% vs. 23%), whereas a higher frequency of PD-1–TIGIT– T cells were found in NC-GBM (36% vs. 17%), suggesting that C-GBM T cells may be more phenotypically exhausted compared with their NC-GBM counterparts (Figure 4, E and F).