| Malignant brain tumors are generally lethal soon after their diagnosis, and the five-year survival rate for the patient is low in spite of neurosurgery, radiation therapy, and/or chemotherapy. Gene therapy has the potential to improve patient survival and quality of life by delivering specific combinations of therapeutic genes directly to the tumor for localized treatment.; We have based our cancer gene therapy for glioma on a highly attenuated variant of the Lister strain of vaccinia virus (VV) which has been proven to be a safe and effective vaccine vector. Other advantages include a wide host range, a strong promoter system, a high cloning capacity for foreign genes, and a high level of foreign gene expression. The project goal is to develop an effective and safe vaccinia-mediated glioma gene therapy combining immunotherapy with interleukin (IL)-2 and interleukin (IL)-12 and a tumor suppressor (p53). We propose the hypothesis that this specific combination of therapeutic genes has a synergistic inhibitory effect on glioma growth and describe a mechanism to account for this synergy.; We report that recombinant vaccinia vectors carrying cytokine genes efficiently transduced rat C6 glioma cells and expressed IL-2 or IL-12 or both in vitro and in vivo. We achieved delivery and high-level expression of four foreign genes (two cytokines and two reporters) in a single vector. The VV vector alone induced a marked response by natural killer (NK) cells and monocytes/macrophages, which contributed to tumor growth inhibition, but did not induce a generalized virus infection, which suggested vaccinia vector safety. Although a significant growth inhibition of subcutaneously implanted gliomas in athymic mice (associated with NKT lymphocyte activation in the spleen and IFN-γ and TNF-α induction in the tumor) was achieved at a low dose of cytokine carrying vectors (100 PFU, plaque forming units), some mice exhibited adverse cytokine effects. However, combining this immunotherapy with tumor suppressor gene therapy produced a significant synergistic inhibition of glioma growth (associated with activation of local and systemic NK cells) without the adverse cytokine effects. Altogether these findings support our hypothesis and mechanism for therapeutic synergy. |
