Bystander killing effect of tymidine kinase gene-transduced adult bone marrow stromal cells with ganciclovir on malignant glioma cells.

Transduction of the suicide gene of Herpes simplex virus thymidine kinase (Hsv-tk) into glioma cells or neural stem cells combined with pro-drug ganciclovir (GCV) treatment has been effective to treat experimental glioma in the rat through the bystander effect. Bone marrow stromal cells (MSCs) in the adult bone marrow have tropism for brain tumors and act as tumor stromal cells. Whether adult MSCs expressing Hsv-tk can also act as effector cells of the bystander killing effect on murine glioma cells was investigated. In vitro study of co-culture between 9L/LacZ (9L) glioma cells and Hsv-tk-transduced MSCs (MSCs/tk(+)) followed by GCV administration in the culture medium resulted in apparent nuclear morphological changes in the 9L glioma cells surrounding the MSCs/tk(+). 9L glioma cell survival in the presence of MSCs/tk(+) and GCV treatment was quantitatively measured and showed significant decrease of 9L glioma cell proliferation with higher MSCs/tk(+) ratio and GCV concentration. Intracerebral co-inoculation experiments in Fisher rats used 9L glioma cells and either MSCs/tk(+) or Hsv-tk-non-transduced MSCs (MSCs/tk(−)) followed by intraperitoneal injection of GCV (100 mg/kg, daily for 7 days). The animals co-inoculated with 9L glioma cells and MSCs/tk(+) showed significant retardation of tumor growth and prolongation of survival time compared with the animals with 9L glioma cells and MSCs/tk(−). Quantitative findings were established of the novel effects of adult MSCs/tk(+) as effector cells of the bystander killing effect on glioma cells.