Unanticipated effect of BCG in mice treated by radiotherapy.

Female C57 Bl/6 mice (6-8 weeks old) bearing the Lewis or the MBL-2 tumor received a localized irradiation (1,600 Rads; Cobalt 60) three days after the tumor implantation. We compared the association of irradiation and Immuno-BCG-F (1 mg/mice i.v.) with three control groups (no treatment, irradiation alone, Immuno-BCG-F alone). The timing and number of BCG injections varied in the different sub-groups. Results were improved in the Lewis tumor system when BCG was injected just after the end of the irradiation. Efficiency improved with the number of injections (P less than 0.05). In the MBL-2 system, depending on the timing of BCG injections we observed significant survival prolongation (irradiation + BCG) as compared to control groups. It has to be noted that the use of BCG alone enhanced tumor growth in two models.