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 xenografts. As a consequence it is generally held that elimination or reduction of the Gal/anti-Gal component is critical to overcoming hyperacute rejection. We have recently shown that in mice inactivation of the GalT gene by homologous recombination completely eliminates the expression of the Gal-epitope and that hearts from these mice demonstrate prolonged survival when perfused ex vivo with human plasma. Unfortunately this strategy is currently not feasible in pigs because the technology to isolate porcine embryonic stem cells, which are critical for homologous recombination, is not yet available. This study investigates an alternative competition-based transgenic strategy to suppress the level of the Gal epitope by expression of H-transferase (alpha 1,2-fucosyltransferase) an enzyme which has the same substrate specificity (lactobiose) as alpha 1,3-galactosyltransferase. In vitro transfection of murine cells with H-transferase reduced Gal-epitope expression by 80-90%. A similar reduction in Gal expression was observed on PBL and thymocytes from H-transferase transgenic mice. This reduction in Gal epitope expression resulted in a marked reduction in the reactivity of these cells 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 to reduce the xenoantigenicity of porcine tissues.