CD274 and glioblastoma: Interestingly, Franz L Ricklefs et al. noticed that a subgroup of GBM cells secreted PD-L1-containing extracellular vesicle (EV) [16], and GSCs-derived exosomes upregulated PD-L1 expression levels in human monocytes [17], which rendered the possibility that GSCs sustained tumor microenvironment and promoted TMZ-resistance by secreting PD-L1 containing exosomes (PD-L1-ex).