TWIST1 and glioblastoma: Moreover, analysis of mouse GBM tumors showed that Spp1 is robustly up-regulated in the cell cluster of ECs-2 (Fig. 6E), which was characterized as a mesenchymal-like population of ECs with up-regulated Twist1 expression and potential ability to induce Mφ immunosuppression (Fig. 1), suggesting ECs as another major source of OPN production, in addition to macrophages and glioma cells (24, 25).