Low efficacy of gene therapy for rat BT4C malignant glioma using intra-tumoural transduction with thymidine kinase retrovirus packaging cell injections and ganciclovir treatment

Background. The purpose of this study was to test the use of Herpes Simplex virus thymidine kinase (HSVtk) retrovirus packaging cell injections in the treatment of malignant brain tumours. Methods. Therapeutic effect and tissue responses were examined in vivo in a syngeneic BT4C rat glioma model after HSVtk-producing PA317 packaging cell injections and intraperitoneal ganciclovir (GCV) medication. MRI was used to visualise the tumours before and after the treatment. Immunohistochemica l stainings were performed to study astroglia and microglia responses and a poptosis-mediated cell death. Results. The results suggest that only a limited treatment effect can be ac hieved with HSVtk packaging cell injections with no prolonged survival rate s. Histological examination showed a strong astroglia response but only a m odest microglia response after the treatment. HSVtk and GCV-induced cell de ath was at least partially mediated by apoptosis. It is concluded that HSVt k packaging cell injections and GCV treatment do not lead to eradication of malignant cells in a syngeneic BT4C rat glioma model. The lack of efficacy is most likely due to low gene transfer efficiency and limited life span o f the injected packaging cells inside the tumours. Conclusions Improvements in gene transfer efficiency, and stimulation of im munoresponse against tumour cells might lead to a more effective therapeuti c response in vivo.