DES and neoplasm: As the majority of pericytes in GBMs are derived from GSCs,23 we constructed GBM xenografts using GSCs (GBM-2) transduced with a Desmin promoter-driven herpes simplex virus thymidine kinase (HsvTK) vector (DesPro-TK) or a control vector (DesPro) (Fig. 2a), and treated the tumor-bearing mice with ganciclovir (GCV) to genetically deplete GSC-derived pericytes in GBM xenografts.