Increased efficiency of immunotherapy using irradiated tumor cells.

The efficacy of irradiated tumor cells combined with chemotherapy or non-specific immunostimulation with complete Freund's adjuvant was tested in a model of minimal residual tumor-bearing syngeneic mice. Male C57BL/6J mice were innoculated in the right rear leg with live tumor cells from a methylcholanthrene induced fibrosarcoma. The tumor was resected when it reached 0.7 cm in diameter and animals were treated with doses of irradiated tumor cells (XTC) from the primary tumor ranging in number from 1 X 10(3) to 9 X 10(3). Best survival was noted using 5 X 10(3) XTC combined with irradiated tumor cells of liver or pulmonary metastases origin, complete Freund's adjuvant or cytoxan. The combination of irradiated tumor cells of metastatic origin did not enhance the therapeutic effect of XTC alone. Freund's adjuvant was not of benefit in enhancing the efficacy of XTC. However, improved survival was noted when chemotherapy in the form of cytoxan was used to supplement XTC. Our data suggests that XTC is more efficacious as a mode of immunotherapy than are live tumor cells. The dose of XTC used is critical in determining its effect. Chemotherapy appears to enhance the benefit of XTC.