Antitumor effects of bacillus Calmette-Guerin in a syngeneic rat bladder tumor model system, RBT323.

We have studied the antitumor effects of Bacillus Calmette-Guerin (RIVM strain) in the syngeneic rat bladder tumor model RBT323. In an immunohistochemical infiltrate study we compared the antitumor effects of BCG with the immunopathological findings in order to get more insight into the possible effector mechanisms of BCG. The antitumor effects of BCG appeared not to be dose-dependent, in the dose range tested. In rechallenge experiments no difference in growth of control tumors was seen between rats pretreated- or not pretreated with BCG. There was, however, a significant increase in antitumor effect of BCG after pretreatment with BCG. Immunohistological examination of BCG treated tumors revealed infiltrates consisting of macrophages, B-cells and T-cells. These results imply that whereas no specific response against the RBT323 cells is generated by BCG treatment, possibly BCG induced antigens do serve as immunogens in this nonimmunogenic syngeneic rat bladder tumor model system.