CCL21 and glioblastoma: To generate a syngeneic mouse model of CCL21-deficient GBM, we first knocked down CCL21 in GL261 and CT-2A GBM cells by lentiviral transfection of GFP-coupled CCL21a-targeting shRNA and FACS-sorted for GFP+ cells, which resulted in a 50% reduction of Ccl21 transcript expression (Supplementary Fig. 6a, b).