Immunofluorescence assays of our GBO sections also confirmed the presence of macrophages and vascular cells, as detected by CD68 and CD31 markers, respectively (Supplementary Figure S13A), supporting the use of three-dimensional GBO models for holistic study of the TME of GBM and evaluating the efficacy of PD1 inhibitors. Here, PECAM1 is linked to glioblastoma.