TKT and central nervous system cancer: The results showed that GFP-C6 glioma cells exhibited the lowest cell viability after being co-cultured with MSCs-tk in 200 μg/mL ganciclovir (GCV), which demonstrated that MFIONs could improve the bystander effect of MSCs-tk on C6 glioma cells and had the potential to improve the sensitivity to suicide genes by upregulating the expression of Cx43 (Li et al., 2021).