Inhibition and stimulation of the growth of Krebs-2 carcinoma by BCG vaccine.

The effect of BCG vaccine on the growth of imtransplants of Krebs-2 carcinoma in mice was studied. The simultaneous injection of BCG and tumor cells either inhibited tumor growth (BCG given in admixture with tumor cells) or stimulated it (BCG injected contralateral to the tumor transplantation site). The BCG dose was directly related to the effect. Tumor growth was also stimulated by the ip injection of starch or liquid paraffin. In these experiments, the BCG effect was attributed to the redistribution of cells involved in nonspecific and specific tumor resistance. Shortly after BCG prevaccination, particularly when BCG doses were high and mice were susceptible to vaccine infection, BCG was either without effect or stimulated tumor growth; later, however, tumor growth was inhibited regardless of the BCG dose and the injection site of the BCG. The effect of BCG prevaccination was suggested to be due to: 1)the distraction of macrophages and T-lymphocytes to defend the host against the multiplying mycobacteria, and 2)the activation of the pool of these cells that become capable to participate in antitumor resistance after mycobacteria elimination.