Oncolytic viral therapy and immunotherapy of malignant brain tumors: Two potential new approaches of translational research

Brain tumors arise at a rate of nearly 5/100,000 in the general population, with over 17,000 U.S. residents being diagnosed each year. Approximately 60% of all brain tumors are gliomas, which are derived from interstitial tissue of the brain, such as astrocytic or ependymal tissue, or oligodendrocytes. The traditional protocols for treatment of malignant gliomas include diagnostic surgery, followed by regimens of radio- and chemotherapies. In the case of chemotherapy, the treatment protocols have remained nearly unchanged for over 30 years despite high mortality rates, and with little to no improvement in outcome. New advances in the fields of molecular biology and immunology have resulted in new possibilities for treating malignant gliomas by targeting cellular and molecular mechanisms of tumor cells, and stand in contrast to traditional forms of treatment. In the field of gene therapy, the possibility of using oncolytic viruses, such as HSV-1, for glioma therapy -specifically, of high grade astrocytomas - is being explored, and trials have begun using a replication-selective mutant strain known as G207. An increased understanding of the role of the cytokine TGF-β2 has led to developments of anti-sense immunotherapy targeting this factor. The two examples mentioned here are discussed in this review and cited as possible improvements in the treatment of high grade astrocytomas.