Enhanced macrophage tumoricidal activity and tumor suppression or regression caused by heat-killed Candida albicans

The growth of line-10 hepatoma in male Sewall Wright strain 2 guinea pigs was totally suppressed when tumor cells were mixed with heat-killed Candida albicans. In a significant number of animals, injection of C. albicans into established tumors 10-12 mm in diameter caused complete, rapid tumor regression. Guinea pigs whose tumors regressed or were suppressed as a result of injection of C. albicans rejected subsequent challenges at distant sites with the line-10 hepatoma, which indicated the development of systemic immunity to the tumor. Untreated control guinea pigs had positive delayed hypersensitivity reactions to intradermally injected C. albicans, which suggested prior natural exposure of the animals to C. albicans antigens. Peritoneal macrophages from mice that had received ip injections of phosphate-buffered saline (PBS) or C. albicans were not cytocidal for mouse 3T12 tumor cells in vitro. However, macrophages from the mice given injections of C. albicans, unlike those from mice given PBS, were markedly tumoricidal in the presence of 1 ng or more endotoxin/ml in vitro. These results demonstrated that heat-killed C. albicans, when inoculated into the peritoneal cavity, increased the tumoricidal potential of peritoneal macrophages.