Cell pellets from human GBM cells and/or murine pericytes that were co-cultured for 72 hours (5×106 cells), were grafted into C57Black/6 wild type mice brains. Xenografts (10 mice received GBM, 10 mice received GBM+PC, 10 mice received PC and 10 mice received GBM/PC without being co-cultured previously) were performed as described previously  in an immunocompetent mouse model . Cell pellets, prepared as hanging drops, were grafted into mice. Xenografts (1 pellet/mouse) were introduced into the right hemisphere through a small craniotomy (2 to 3 mm from the midline, approximately 1 mm behind the bregma) at 2.5 mm depth, using a stereotactic apparatus and a Pasteur pipette hand-pulled to an internal diameter of 0.38 mm. This produced grafts that integrated into the cortex or the hippocampus. After 4 and 11 weeks post-grafting, mice were perfused using 4% paraformaldehyde (5 mice of each experimental grafts at each fixation time). Brains were embedded in 30% sucrose and cut at 40 μm using a cryostat. For Immunohistochemistry methods and the antibody information, please see Supplementary Text.