Inhibition of anti-Gal IgG binding to porcine endothelial cells by synthetic oligosaccharides.
Rejection of pig-to-human or pig-to-primate xenografts is mediated by the natural anti-Gal antibody, which interacts with alpha-galactosyl epitopes (i.e., Gal alpha1-3Gal beta1-4GlcNAc-R) abundantly expressed on porcine cells. The objective of this study was to determine the ability of various synthetic oligosaccharides to inhibit the binding of anti-Gal IgG molecules to porcine endothelial cells in vitro. Such inhibition ultimately may help to reduce or to prevent the in vivo antibody-dependent cell cytotoxicity (ADCC) reaction. In the absence of complement-mediated hyperacute rejection, the ADCC induced by anti-Gal IgG molecules is likely to cause the chronic rejection of xenografts. The synthetic free alpha-galactosyl epitope (Gal alpha1-3Gal beta1-4GlcNAc) was found to be 300-fold more effective than melibiose or alpha-methyl galactoside in inhibiting anti-Gal binding to porcine endothelial cells, and to prevent >90% of the antibody binding at a concentration of 1 mM. The disaccharide Gal alpha1-3Gal was ten-fold less effective than the free alpha-galactosyl epitope. Accordingly, the affinity of the disaccharide to anti-Gal, as measured by equilibrium dialysis, was seven-fold lower than that of the trisaccharide. The effective concentration of oligosaccharides inhibiting anti-Gal is independent of the antibody affinity, but is dependent on the concentration of the antibody. Based on the small difference in affinity between Gal alpha1-3Gal beta1-4GlcNAc and Gal alpha1-3Gal beta1-4GIc, and the large difference in the price of N-acetyllactosamine vs. lactose, it is suggested that lactose may be considered as an appropriate starting material for synthesizing large amounts of a trisaccharide that effectively neutralizes anti-Gal.
Galili
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Department of Microbiology and Immunology, Medical College of Pennsylvania, Philadelphia, 19129, USA.
Matta
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KL
D000818:Animals; D000920:Antibody-Dependent Cell Cytotoxicity / Q000187:drug effects; D002240:Carbohydrate Sequence; D002478:Cells, Cultured; D004727:Endothelium / Q000378:metabolism; D000939:Epitopes / Q000378:metabolism; D005690:Galactose / Q000276:immunology*; D007074:Immunoglobulin G / Q000097:blood / Q000378:metabolism*; D007075:Immunoglobulin M / Q000378:metabolism; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000494:pharmacology*; D013552:Swine
D000939:Epitopes; D007074:Immunoglobulin G; D007075:Immunoglobulin M; D009844:Oligosaccharides; D005690:Galactose