Reduction of the major porcine xenoantigen Ga1 alpha(1,3)Gal by expression of alpha(1,2)fucosyltransferase

Although removal of the Gal alpha(1,3)Gal antigen from pigs would prevent hyperacute graft rejection, the technique of homologous recombination to knock out the alpha 1,3galactosyltransferase gene is not available for pigs, and an alternative strategy is presented. As both alpha 1,3galactosyltransferase and alpha 1,2fucosyltransferase use the same substrate (N-acetyl lactosamine), competition between the transferases in vitro and in vivo was examined. The data show that there is indeed a hierarchy of these glycosyltransferases competing for the same substrate, and that alpha 1,2fucosyltransferase takes precedence over alpha 1,3galactosyltransferase: a) COS cells simultaneously transfected with cDNA clones encoding alpha 1,2fucosyltransferase and alpha 1,3galactosyltransferase show preferential expression of the H substance (synthesised by alpha 1,2fucosyltransferase) rather than Gal alpha(1,3)Gal (synthesised by alpha 1,3galactosyltransferase), even though alpha 1,3galactosyltransferase mRNA and functional enzyme was present. b) In a pig kidney cell line that expressed both the Gal alpha(1,3)Gal and H, the increased expression of H induced by the transfection and stable expression of alpha 1,2fucosyltransferase resulted in decreased expression of Gal alpha(1,3)Gal. c) Coexpression of alpha 1,2fucosyltransferase and alpha 1,3galactosyltransferase in either COS cells or the pig cell line resulted in decreased human antibody binding and complement-mediated cell lysis. d) Transgenic mice, ubiquitously expressing alpha 1,2fucosyltransferase show a major decrease in Gal alpha-(1,3)Gal expression and a decrease in natural human antibody binding. These findings have important implications for xenotransplantation in that alpha 1,2fucosyltransferase transgenic pigs could be a source of donors for xenotransplantation to humans.