Paradoxical effects of immunopotentiators on tumors and tumor viruses.

Growth of tumors was inhibited or enhanced in mice by a synthetic (pyran) or a biologic (corynebacterium parvum) immunopotentiator. Marked inhibition of leukemogenesis induced by Friend leukemia virus was produced by prophylactic intraperitoneal treatment with pyran, while intravenous treatment with pyran (in the same dose and regimen) significantly enhanced growth of tumor virus. Paradoxical effects were also seen with the biologic immunopotentiator C. parvum in solid tumor systems. Treatment with C. parvum either potentiated disease or had no effect on the life span of most mice bearing the Lewis lung carcinoma. In contrast, the same treatment could produce a high percentage of tumor regressions in mice bearing the MCA 2182 sarcoma, although the effect was somewhat variable. These data, which show that a change in route of drug administration or in the type of tumor treated may reverse the effect of treatment, emphasize that the mechanism of action of immunopotentiators must be elucidated before consistent beneficial treatment of tumor viruses or tumors can be achieved.