Current status of viral gene therapy for brain tumours

Malignant glial tumours represent the majority of primary brain tumours. Despite the use of many adjunctive treatment strategies in addition to surgery, the prospect of cure or even long-term survival is poor. In the last decade, there has been an explosion of interest in the development of delivery systems that will allow the expression of exogenous genes in the CNS. For the most part, these systems are based upon modified viruses. To date, the greatest experience has been with retroviruses, herpes simplex virus 1 (HSV), adenovirus and adeno-associated virus (AAV). This review will outline the biology of these viral vectors, modifications permitting in vivo administration and their respective advantages and disadvantages for the treatment of malignant brain tumours. The present obstacles to gene therapy strategies will also be described. To date, no convincing clinical trial has emerged that provides objective proof of the superiority of gene therapy strategies as compared to conventional treatment.