*2.3. Exosome Isolation*

GAMs were cultured in serum-free medium for 48 h (with and without pacritinib treatment, 0.5 μM) before exosome isolation. Culture medium was collected and a standard procedure was performed accordingly [12]. In short, we carried out a serial centrifugation procedure (500× *g* for 10 min, 1200× *g* for 20 min, and 10,000× *g* for 30 min), followed by filtration with a 0.22 μm pore syringe and a spin at 100,000× *g* for 60 min. The collected pellet was washed in PBS three times before another ultracentrifugation at 100,000× *g* for 60 min. The exosomes were used for further analyses. A small portion of the pellet was processed for transmission electron microscopic examination. In brief, purified exosomes were fixed with 1% glutaraldehyde (1 h, room temperature) and washed, followed by 1% reduced osmium tetroxide fixation (1 h). The sample was washed, stained with 0.3% thiocarbohydrazide, and fixed again in OsO4. Finally, the sample was embedded into Epon. Ultrathin sections were placed on formvar-coated grids. Electron microscopy (EM) analysis was performed as

previously described [13]. The flowchart of GBM cell lines either treated with exosomes or mimics or inhibitors is listed in the Supplementary Materials.
