| Abstract: |
Our previous investigations revealed that a tumor vaccine established by interleukin-2 (IL-2) gene modification of murine bladder cancer cells (MBT-2) with retrovirus vector can cure the tumors previously established in the mouse bladder. Establishment of tumor vaccine needs several steps of in vitro preparations of tumor cells, however, these procedures are not successful in every clinical cases. To avoid in vitro genetical manipulations of tumor tissue, in vivo gene transfection may be an ideal way for establishing a tumor vaccine. One means of in vivo modification of tumor cells with IL-2 gene is to inoculate the retroviral producer cell line into the tumor as it will provide a constant local level of retroviral packaged cytokine. Helper-free amphotropic packaging cells (GP+envAM12) producing retrovirus encoding IL-2 gene were injected into tumors which were preestablished by intradermal injection of mice with MBT-2 cells. The packaging cells (5×105) were injected three times weekly. The tumors of these mice were resected perfectly and the mice were subsequently rechallenged with MBT-2 cells. All the mice rejected subsequent challenge of MBT-2 cells. CTL assay using spleen cells of these mice demonstrated high specific lysis against parental cells. These results indicated that tumor cells transfection in vivo by the use of helper cell line with IL-2 gene could work to stimulate an immune response and to establish specific immunity against parental tumor cells. A vaccination with genetically modified tumor cells with higher IL-2 titer are expected to establish stronger immunity. Herpes simplex virus (HSV) is expected to be a useful vector for gene delivery because of its ability to infect non-proliferating cells and high expression of the transfected gene in the cells. High transfection rate, such as 66%, was observed by /i -galactosidase gene delivery of MBT-2 cells with HSV vector. IL-2 gene transfection with HSV vector demonstrated one thousand fold greater expression of IL-2 by MBT-2 cells. In an in vivo gene delivery with instilling HSV containing IL-2 gene into the rat bladder, IL-2 secretion of the bladder epithelial cells with high titer was detected. These results demonstrated that instillation of HSV carrying cytokine genes into the animalis bladder may able to establish in situ tumor vaccine and cure the established bladder cancer. |
