These findings have catalysed trials pairing PD - 1 inhibitors with RT, vascular-endothelial-growth-factor blockade or chemokine-axis disruption; for example, CXCL12/CXCR4 antagonism enhances lymphocyte trafficking across the blood–brain barrier and augments anti-PD-1 efficacy in murine GBM without additional neuro-toxicity (62). This evidence concerns the gene PDCD1 and glioblastoma.