CBMS-3 Potent bystander effect in suicide gene therapy using genetically engineered stem cells from human exfoliated deciduous teeth

HSV thymidine kinase (TK)/ganciclovir (GCV) has a long history of application in malignant glioma and we have previously demonstrated its bystander effect on gliomas using several stem cell types as a vehicle. The main reason for applying stem cells is that they have a unique tumor-trophic activity that allows them to deliver TK genes efficiently to nearby the tumor. Stem cells from human exfoliated deciduous teeth (SHED) are mesenchymal stem cells easily harvested from dental pulp and no studies have reported suicide gene therapy using SHED as a carrier for malignant gliomas. For transduction of SHED with the HSVTK gene (SHEDTK), we used HSVTK retrovirus-producing cells.In vitro experiments showed a significant migration ability of SHEDTK toward tumor-conditioned medium and representative tumor growth factors. We also detected a significant bystander effect of SHEDTK on gliomas in the presence of GCV. In vitro time-lapse imaging showed that both SHEDTK and glioma cells underwent gradual morphological apoptosis and activation of caspase 3/7 was observed in both cell types. In intracranial tumor models using nude mice, SHEDTK migrated around the U87 cell mass implanted in the contralateral hemisphere. Additionally, coculture suspensions of SHEDTK and U87-luciferase cells were xeno-transplanted followed by intraperitoneal administration of GCV for 10 days. All mice of treatment group survived for more than 100 days, whereas those treated without GCV died of tumor growth with median survival of 42 days after tumor implantation. Furthermore, pre-existing intracranial U87 model mice were injected intratumorally with SHEDTK followed by GCV administration as described above. The tumor volume was significantly reduced during the treatment period, and over-all surivial in treatment group is prolonged significantly to that of control groups. These results indicate that SHEDTK-based suicide gene therapy might offer a new promising therapeutic modality for human malignant gliomas.