Xenotransplantation: in vitro analysis of synthetic alpha-galactosyl inhibitors of human anti-Gal alpha 1 -> 3Gal IgM and IgG antibodies

Pig-to-human xenotransplantation might be an option to overcome the increas ing shortage of human donor organs. However, naturally occurring antibodies in human blood against the Gal alpha 1-->3Gal antigen on pig endothelial c ells lead to hyperacute or, if prevented, acute or delayed vascular rejecti on of the pig graft. The purpose of this study was therefore to evaluate sy nthetic oligosaccharides with terminal Gal alpha 1-->3Gal to inhibit antige n-binding and cytotoxicity of anti-alpha Gal antibodies against pig cells. Different oligosaccharides were synthesized chemically and by a combined ch emico-enzymatic approach. These included monomeric di-, tri, and pentasacch arides, a polyacrylamide-conjugate (PAA-Bdi), as well as di-, tetra-, and o ctamers of Gal alpha 1-->3Gal. All were tested for inhibitory activity by a nti-alpha Gal ELISA and complement-dependent cytotoxicity tests. PAA-Bdi wa s the best inhibitor of binding as well as cytotoxicity of anti-alpha Gal a ntibodies. Monomeric oligosaccharides efficiently prevented binding of anti -alpha Gal IgG, but less well that of anti-alpha Gal IgM, with tri- and pen tasaccharides showing a better efficacy than the disaccharide. The two tris accharides Gal alpha 1-->3Gal beta 1-->4GlcNAc and Gal alpha 1-->3Gal beta 1-->3GlcNAc were equally effective. Oligomers of Gal alpha 1-->3Gal were mo re effective than monomers in blocking the binding of anti-alpha Gal IgG, H owever, they could not block IgM binding, nor could they match the efficacy of PAA-Bdi, We conclude that oligosaccharides with terminal Gal alpha 1--> 3Gal, most effectively as PAA-conjugates, can prevent binding and cytotoxic ity of human anti-alpha Gal in vitro. The PAA-Bdi conjugate might be most s uited for use as a Sepharose-bound immunoabsorption material.