Therapy of the murine plasmacytoma MOPC 104E: role of the immune response.

The murine plasmacytoma MOPC 104E was susceptible to cytotoxic therapy in female inbred BALB/c mice. Palpable subcutaneous tumors (0.6--1.2 X 10(8) cells) could be cured with a single administration of cyclophosphamide (5--250 mg/kg) or localized irradiation (800--2,400 R). Clonogenic assay showed that, following minimal curative doses of cyclophosphamide or radiation, 0.5--1.5 X 10(6) tumor cells should remain viable. Control animals succumbed to progressive, invariably lethal tumor growth after they were given sc injections of 2--3 X 10(3) tumor cells. Minimal doses of cyclophosphamide, which were curative in control tumor-bearing animals, were ineffective in treating tumor-bearing animals immunosuppressed by 450 R whole-body irradiation. Subsequent experiments measured the ability of animals cured of the murine plasmacytoma to reject secondary challenge with the same tumor. These experiments demonstrated and partially quantitated the substantial role of the immune response in effecting tumor cure following radiotherapy or chemotherapy.