REDUCTION IN GAL-ALPHA-1,3-GAL EPITOPE EXPRESSION IN TRANSGENIC MICE EXPRESSING HUMAN H-TRANSFERASE

There is now considerable evidence implicating anti-Gal xenoantibodies as a key instigator in the hyperacute rejection of discordant xenogra fts. As a consequence it is generally held that elimination or reducti on of the Gal/anti-Gal component is critical to overcoming hyperacute rejection. We have recently shown that in mice inactivation of the Gal T gene by homologous recombination completely eliminates the expressio n of the Gal-epitope and that hearts from these mice demonstrate prolo nged survival when perfused ex vivo with human plasma. Unfortunately t his strategy is currently not feasible in pigs because the technology to isolate porcine embryonic stem cells, which are critical for homolo gous recombination, is not yet available. This study investigates an a lternative competition-based transgenic strategy to suppress the level of the Gal epitope by expression of H-transferase (alpha 1,2-fucosylt ransferase) an enzyme which has the same substrate specificity (lactob iose) as alpha 1,3-galactosyltransferase. In vitro transfection of mur ine cells with H-transferase reduced Gal-epitope expression by 80-90%. A similar reduction in Gal expression was observed on PBL and thymocy tes from H-transferase transgenic mice. This reduction in Gal epitope expression resulted in a marked reduction in the reactivity of these c ells with human serum. In tissues from these mice the reduction in Gal expression was inversely proportional to the endogenous level of Gal. The results of this study support pursuing this strategy as a means t o reduce the xenoantigenicity of porcine tissues.