Inhibition of murine sarcoma cell adherence to polystyrene substrata by bacillus Calmette-Guérin: evidence for fibronectin-mediated direct antitumor activity of BCG.

Bacillus Calmette-Guérin (BCG) inhibited adherence of S180 mouse sarcoma cells and WI38 human diploid fibroblasts to the polystyrene substratum of 24-well cluster dishes in a dose-dependent manner. This property was retained by washed or heat-killed bacilli, but not by the vaccine filtrate or by the spent bacterial culture medium. Adhesion of bacilli to nonadherent S180 cells was demonstrated by light and scanning electron microscopy, but was not seen after trypsinization of adherent cells, indicating that bacilli bind to cell-surface adhesins. Preincubation of bacilli with human fibronectin abolished their ability to inhibit S180 adherence, suggesting that the phenomenon may be mediated by interaction of bacilli with cell-surface fibronectin. Fibronectin pretreatment of the bacteria also decreased their inhibition of S180 tumor growth in vivo, indicating that this mechanism may be at least partly responsible for BCG vaccine's observed antineoplastic activity.

Relative tumor inhibitory and stimulatory activities of BCG vaccine preparations, lots and substrains in a quantitative mouse sarcoma bioassay.

A quantitative in vivo assay for BCG anticancer efficacy was developed to maximize detection of tumor-antagonistic mechanisms. Cultured S180 sarcoma cells admixed with various quantities of Mycobacterium bovis-BCG organisms were injected subcutaneously into CFW Swiss-Webster mice and response was measured as tumor incidence 14 days after injection. Assay of various BCG substrains, lots and killed preparations revealed characteristic patterns of BCG dose-dependent tumor inhibition and enhancement that suggest the existence in the vaccine of multiple active components, the relative concentrations of which vary among cultures. Inhibition of tumor growth by high doses of BCG (greater than 10 micrograms dry weight) was found to be a function of total cell mass and not of the bacterial viability, suggesting that this activity is dependent upon one or more heat-stable components.