3. IL-4 gene transfer alone or in combination with HSV-TK/GCV for the treatment of experimental malignant gliomas

Growth of U-87 or C6 gliomas co-implanted in nude mice with retroviral producer cells (VPC) expressing the Herpes Simplex Virus-thymidine kinase (HSV-tk) gene is only partially impaired by treatment with ganciclovir (GCV). The effect of GCV is even less evident when C6 and VPC are co-implanted into rat brain and that tumors from C6 cells carrying the HSV-tk gene are not eradicated by GCV, even if they are still sensitive to GCV. These limits of the HSV-tk/GCV system in glioma gene therapy may be due to insufficient gene transfer and/or insufficient delivery of GCV. Combination of HSV-tk and one or more cytokines, may improve the therapeutic efficacy. Among cytokines, interleukin-4 (IL-4), because of its partially T-cell independent anti-tumor action, seems a good candidate for the treatment of malignant gliomas, since these malignancies express factors that inhibit significantly T cell function. We found that in nude mice, GCV treatment restrained tumor growth more effectively after co-injection of C6 cells with a mixture of VPC transducing IL-4 and HSV-tk genes than after co-injection with either IL-4 or HSV-tk VPC only. In immunocompetent Sprague-Dawley rats, expression of IL-4 after co-injection of C6 and IL-4 VPC cells was also effective in inhibiting tumor growth of C6 brain tumors, 38% of the animals surviving for at least two months. Increased and prolonged therapeutic efficacy was obtained by transducing both IL-4 and HSV-tk genes and about 2/3 of the animals were long-term survivors. Recent data obtained with VPC expressing higher levels of IL-4 showed increased percentage of long-term survivors with this treatment alone (70%) and suggest that high levels of IL-4 might render less relevant the contribution of HSV-tk/GCV to this form of therapy.