Glycans derived from porcine stomach mucin are effective inhibitors of natural anti-alpha-galactosyl antibodies in vitro and after intravenous infusion in baboons.

Abstract

The current shortage of donor organs has stimulated investigation of pig-to-human xenotransplantation as a practical alternative to allotransplantation. However, a major obstacle to this xenotransplantation is hyperacute rejection, which is believed to be initiated by the interaction of natural anti-alpha-galactosyl (alphaGal) antibodies with alphaGal epitopes on pig vascular endothelium. Previously, we reported that neutral oligosaccharides derived from porcine stomach mucin (PSM) are effective inhibitors of human anti-alphaGal IgG in vitro. We now report that O-glycans derived from PSM by beta-elimination (PSMO) reduce the cytotoxicity of both baboon and human sera to pig kidney (PK15) cells in vitro. Crude PSM had some inhibitory effect in vitro, but PSMO were more than 100 times more potent. Moreover, 1 microg/ml of beta-eliminated PSMO that bound to an immunoaffinity column of anti-alphaGal antibodies were four times more efficient than total PSMO in protecting PK15 cells from the cytotoxic effect of baboon or human sera. Blood recovered from baboons after intravenous infusion of PMSO also showed significant protection of PK15 cells. We conclude that PSMO eluted from an anti-alphaGal immunoaffinity column demonstrate potent inhibitory effects against baboon and human serum cytotoxicity to PK15 cells in vitro and when administered intravenously. PSM may provide a cheap and readily available source of glycans that will be of therapeutic value in the prevention of hyperacute rejection.