TKT and glioblastoma: In addition, HSV-TK/GCV has a bystander effect, transporting the anti-tumor active HSV-TK triphosphate to adjacent tumor cells, thereby enhancing the therapeutic efficacy of GBM.728 Chen et al. used PEI-based PNPs with Ang modification for targeted delivery and combination therapy of HSV-TK pDNA and GCV to GBM.729 The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) can enhance the anti-tumor activity of HSV-TK/GCV.730 Chen et al. then transfected MSCs with TRAIL and HSV-TK genes via cationic PNPs for the combination therapy of GBM.731