Gene Therapy for Murine Renal Cell Carcinoma Using Genetically Engineered Tumor Cells to Secrete lnterleukin-12

To determine the possibility of gene therapy for renal cell carcinoma (RCC) using interleukin- 12 (IL-12), we prepared genetically engineered murine RCC cells (Renca) which secrete IL-12 and evaluated the usefulness of these cells as a tumor vaccine. The IL-12 gene was transduced using MFG retroviral vector. The in vitro characteristics of transfectants―i.e., cell proliferation and expression of surface antigens―were then examined. In vivo tumorigenicity was assessed by subcutaneously injecting each type of cell in syngenic BALB/c mice. For the challenge experiments, the mice rejecting previously injected Renca IL-12 cells were rechallenged with parental cells. To determine the antitumor effect at remote sites, mice were injected with parental cells into the left flank, and then either Renca IL-12 or parental cells were inoculated into the opposite site on day 0 or 1. The transfected cells can secrete 146.7ng/ml/10⁶cells/48 hr of IL-12, as confirmed here by bioassay. The in vitro characteristics of the transfectants were not altered, but in vivo tumorigenicity was significantly reduced. Of the 21 mice that rejected Renca IL-12 cells, 9 failed to develop tumors after the challenge with parental cells. In the mice treated with Renca IL-12 as a vaccine, both number and tumor volume of the mice that developed tumors at remote sites were reduced. IL-12 secreting Renca cells conferred both protective immunity to parental cells and delay of tumor growth at remote sites, indicating that IL-12 secreting Renca cells are a feasible candidate for use in gene therapy of RCC.