Gene therapy for Lewis lung carcinoma with tumor necrosis factor and interleukin 2 cDNAs co-transfected subline

Gene therapy with cytokine cDNA will provide a new tool for cancer treatment. We have already reported that immunization with interleukin-2 (IL2) cDNA transfected Lewis lung carcinoma (LLC) cells induced anti-tumor immunity, which, however, was not strong enough to eradicate an established tumor. In an attempt to develop more effective gene therapy methods, we have used tumor cells co-transfected with IL-2 and tumor necrosis factor (TNF) cDNAs. These cDNAs were introduced into pBMG-Neo and pcDV-X819 vectors, respectively, and then co-transfected into LLC cells. The co-transfectants were selected by incubating them in a medium containing G418 followed by the limiting dilution method twice to obtain IL2 and TNF cDNA co-transfected LLC (LLC-TNF-IL2) cells. When 5 × 10⁵/ml LLC-TNF-IL2 cells were incubated for 48 h, they secreted 7.56 U/ml TNF and 527.0 U/ml IL2 into the culture supernatant. When C57BL/6 mice were transplanted with 1 × 10⁶ LLC-TNF-IL2 cells, all the tumors were rejected. The growth of transplanted LLC, but not B16F10 melanoma cells, was retarded in mice inoculated with LLC-TNF-IL2 on their contralateral sides, which suggests specific immunity was induced. The immunization effect by the co-transfectant was superior to that of the IL2- and TNF-transfectants alone.