Tumor-specific T-lymphocyte cytotoxicity enhanced by low dose of C. parvum.

Three routes of immunotherapy with Corynebacterium parvum (CP) on an ascitic Friend virus-induced leukemia were evaluated. Only the intraperitoneal route, which provided optimal contact between CP and tumor cells, showed prolonged mean survival time. Greatest effectiveness was obtained with multiple injections of CP at weekly intervals and with small initial tumor load. Of particular interest was that lower dosages of CP (5 and 25 micrograms) gave longer protection than dosages of 50 and 250 micrograms. Using in vitro 125I-iododeoxyuridine release assay, these lower dosages were shown to selectively enhance the cytotoxicity associated with T lymphocytes, whereas higher dosages appeared to primarily augment the activity of phagocytes. Moderate natural killer cell activity was observed with both the lower and higher dosages of CP. Data from this study indicate that route of administration, dosage of CP, and size of tumor burden are crucial variables determining optimal response to immunotherapy.