Immunological protection induced by bacillus Calmette-Guérin treatment in a murine bladder tumor model

Background: It has been previously reported that MBT-2 tumor growth is completely inhibited when mice are inoculated with bacillus Calmette–Guerin (BCG). In this study it was examined whether or not vaccination with a mixture of BCG and MBT-2 cells also induces immunological protection against murine bladder tumors. Methods: Seven hundred thousand MBT-2 cells and 1 mg of BCG (Tokyo172 strain) per mouse were injected subcutaneously into female C3H/HeN mice. Four and eight weeks after vaccination with this mixture, animals were reinoculated with MBT-2 cells alone or MBT-2 cells cocultured with BCG. Results: Animals vaccinated with a mixture of BCG and MBT-2 cells showed MBT-2 tumor growth but completely rejected the MBT-2 cells cocultured with BCG. MBT-2 cells cocultured with BCG developed into tumors when they were inoculated into the control animals. Splenocytes prepared from vaccinated animals showed specific cytocidal activity against MBT-2 cells precultured with BCG. Conclusions: The results suggest that a mixture of BCG and MBT-2 cells induces antitumor immunological protection against BCG- or MBT-2-associated antigens presented on MBT-2 cells precultured with BCG.