PDCD1 and glioblastoma: Interestingly, expression of genes for CD155 (PVR), PD-L1, and ICOS-L, the ligands for TIGIT, PD1, and ICOS, respectively, was also significantly associated with decreased OS and DFS, whereas upregulated expression of other IC gene ligands did not affect these parameters in GBM patients (Figures 2A, B).