Preventive effect of Propionibacterium acnes on metastasis in mice rendered tolerant to tumor-associated transplantation antigens.

The present study was carried out to investigate the preventive effect of Propionibacterium acnes (P. acnes) on metastasis formation of C3H/He mice which has been rendered tolerant to tumor-associated transplantation antigen (TATA) of syngeneic X5563 plasmacytoma. C3H/He mice inoculated intravenously (iv) with 10(6) 7000 R X-irradiated X5563 tumor cells 3 times at 4-day intervals. These pretreated mice could not develop immune resistance against X5563 tumor even after the appropriate immunization procedure. In these TATA-tolerant mice, enhanced metastasis associated with the development of visually apparent metastatic nodules in the spleens was observed after intradermal (id) implantation with viable tumor cells, even if the tumor was resected surgically 7 days thereafter. Administration of P. acnes to these TATA-tolerant mice appreciably reduced the metastasis formation. Although the growth of the id primary tumor was not affected by injection with P. acnes, the combined treatment of surgical resection of the primary tumor and P. acnes administration resulted in complete protection against metastasis in TATA-tolerant mice. These results unequivocally demonstrated that the administration of P. acnes is effective for preventing the outbreak of metastasized tumors, which are readily inducible in the TATA-tolerant state.