SUMMARY: The authors evaluted the efficacy of vaccination with murine renal cell carcinoma (Renca) secreting the granulocyte-macrophage colony-stimulating factor (GM-CSF) gene and interleukin-6 (IL-6) gene for the treatment of Renca tumor. Murine GM-CSF and murine IL-6 genes were introduced and expressed in Renca cells (Renca-GM-CSF and Renca-IL-6). For a prevaccination study, wild-type Renca cells were injected subcutaneously into Balb/c mice that had been vaccinated three times with inactivated wild-type Renca, Renca-GM-CSF, Renca-IL-6, or a mixture of Renca-GM-CSF and Renca-IL-6 cells 7, 14, and 21 days before this tumor inoculation. For vaccination experiments, Renca tumor-bearing (8 to 10 mm) mice were injected subcutaneously weekly for 3 weeks with inactivated wild-type Renca cells, or either one or a combination of Renca-GM-CSF and Renca-IL-6. A nonvaccinated control was included in all experiments. The animals were monitored for survival and tumor development for 8 weeks. Mice inoculated with wild-type Renca alone died from the tumor within 35 days. Renca-IL-6 grew slower than wild-type Renca (p < 0.05). No tumor was produced by Renca-GM-CSF. Prevaccination with the combination of Renca-GM-CSF and Renca-IL-6 prevented subsequently inoculated wild-type Renca from forming tumors, and prevaccination with either one of them, compared with prevaccination with wild-type Renca, retarded tumor growth and prolonged survival time. Tumor-bearing mice vaccinated with wild-type Renca died within 42 days. Vaccination with Renca-GM-CSF or Renca-IL-6 alone prolonged the survival time, but only Renca-GM-CSF drastically reduced the tumor size. Vaccination with the combination of them achieved complete remission. Neither of the cytokine-secreting cells enhanced the expression of MHC class I or II molecules. Autologous tumor cell vaccine secreting GM-CSF is effective in preventing and treating established tumors. Its efficacy is enhanced by the cosecretion of IL-6.