BACILLUS-CALMETTE-GUERIN PLUS INTERLEUKIN-2 AND OR GRANULOCYTE/MACROPHAGE-COLONY-STIMULATING FACTOR ENHANCES IMMUNOCOMPETENT CELL PRODUCTION OF INTERFERON-GAMMA, WHICH INHIBITS B16F10 MELANOMA CELL-GROWTH IN-VITRO/

Although immunotherapy with bacillus Calmette Guerin (BCG) is an estab lished adjuvant treatment for malignant melanoma, the mechanism of its role in this process is unclear. To investigate the possible contribu tion of tumor-inhibitory cytokines Induced by BCG, B16F10 melanoma cel l growth in culture was assessed in response to purified cytokines and conditioned media of BCG-stimulated splenocytes. Interferon-gamma (IF N gamma) was the most potent single agent (IC50 approximate to 50 pg/m l). Tumor necrosis factor a was substantially weaker (IC50>10 ng/ml) b ut provided synergy with IFN gamma. None of the other cytokines such a s interleukin-2 (IL-2), IL-4, IL-6, IL-10, IL-12, or granulocyte/macro phage-colony-stimulating factor had direct antitumor activity against B16F10 melanoma cells. However, when IL-2 and/or GM-CSF were combined with BCG either by exogenous addition or through endogenous production by novel cytokine-secreting recombinant BCG (rBCG), a substantial inc rease in INF gamma production by splenocytes was observed. Antitumor a ctivity of this conditioned medium directly cell-elated with IFN gamma concentration and was completely blocked by neutralizing antibody to IFN gamma. These results suggest that BCG may exert part of its antitu mor action on melanoma through the induction of IFN gamma, which can b e greatly enhanced through the concomitant addition of IL-2 and/or GM- CSF. Furthermore, by utilizing rBCG that secrete these cytokines, it m ay be possible to potentiate the antitumor effect of BCG directly at t he site of BCG inoculation.