Mechanisms of anti-tumor action of Corynebacterium parvum. II. Potentiated cytolytic T cell response and its tumor-induced suppression.

Abstract

S.c. implantation of P815 [mouse mastocytoma] tumor cells admixed with C. parvum [Propionibacterium acnes] resulted in the emergence of a tumor that grew for 9-10 days and then regressed. The onset of tumor regression was preceded by the substantial generation in the draining lymph node and spleen of T cells capable of specifically lysing P815 target cells in vitro. The finding that the magnitude of this cytolytic response was much greater than the cytolytic response to a control tumor that grew progressively is consistent with the hypothesis that the anti-tumor action of C. parvum is based on its capacity to augment the production of T cells sensitized to tumor-specific transplantation antigens. This adjuvant action of C. parvum was revealed by additonal experiments in which irradiated, nonreplicating tumor cells were substituted for living tumor cells in the admixture. The potentiated cytolytic response to s.c. injection of an admixture of irradiated tumor cells and C. parvum is evidently responsible for the ability of this admixture to cause the regression of a test tumor growing at a distant site. The failure of the therapeutic admixture to cause the regression of distant test tumors above a certain size was apparently associated with a failure of the admixture to cause a potentiated, anti-tumor cytolytic response. The possibility that this failure was caused by the presence of a tumor-induced state of immunosuppression was discussed.