TKT and glioblastoma: According to the FACS data obtained, a significant reduction of surviving tumor cells was observed after coculture of HSV-TK expressing MSCs with CMFDA stained U87, G55T2 or GL261 glioblastoma cells and addition of GCV (21.2+/-1.0%, 16.8+/-0.8% or 11.0+/-0.1% surviving tumor cells, respectively) compared to control samples without GCV treatment (Figure 2C).