What are the immunologically active components of Bacille Calmette-Guerin in therapy of superficial bladder cancer?

The subcomponents of bacille Calmette-Guerin (BCG) involved in the mechanis m of action of intravesical BCG immunotherapy used for prophylaxis of super ficial bladder cancer recurrences have been poorly investigated. We purifie d various BCG subcomponents and analyzed in vitro their ability to enhance a Th1 polarized immune response as well as to increase lymphocyte-mediated cytotoxicity against bladder tumors, Human peripheral blood mononuclear cel ls (PBMCs) from healthy purified protein derivative-positive subjects were incubated for 7 days with whole BCG and various fractions (BCG cell wall, p lasma membrane, cytosol, purified polysaccharides as glucan or arabinomanna n, purified native proteins from BCG culture filtrate, recombinant 22 kDa p rotein, phosphate transporter PstS-2 and -3 proteins). IFN-gamma, IL-12, IL -2, and IL-6 production by stimulated PBMCs was compared to unstimulated co ntrols and the phenotype of expanded cells analyzed by flow cytometry (FACS analysis). A Cr-51-release assay monitored the cytotoxicity of amplified e ffector cells against T24 bladder tumor cells. Live BCC and most of its sub components (with the exception of cytosol, PstS-2 and -3) significantly enh anced IFN-gamma and IL-12 secretion, expanded CD3(-)CD56(+) cells and the n on-MHC-restricted cytotoxicity against bladder tumor cells compared to unst imulated controls (all P < 0.001, t-test), IL-2 receptor blockage resulted in a clear reduction in the cytotoxic activity of stimulated PBMCs, Numerou s BCG subcomponents thus provide positive stimuli for Th I cell differentia tion and enhance in vitro, non-MHC-restricted cytotoxicity against bladder tumor cells. Our findings provide the basis for the therapeutic use of seve ral of these subfractions in experimental animal models bearing bladder tum ors. Int. J, Cancer 87: 844-852, 2000, (C) 2000 Wiley-Liss, Inc.