PDCD1 and glioblastoma: Unsurprisingly, PD-L1 has to be expressed on GBM cells to evoke a stimulatory effect by blocking the PD-1/PD-L1 interaction since in mice harboring PD-L1 negative LN-229 tumors, no additional stimulatory effect with regard to the amount of TILs was observed by XVir-N-31-anti-PD-L1 (Supplementary Figure S11).