DEMONSTRATION OF THE FUNCTIONAL IMPORTANCE OF THE GAL EPITOPE IN AN EX-VIVO MODEL OF XENOTRANSPLANTATION

The galactose alpha 1-3 galactose terminal disaccharide (Gal epitope) has been identified as the major porcine xenoantigen recognised by xen oantibody in human plasma. Elimination or suppression of the epitope o r antibody will be a major factor in overcoming hyperacute rejection. Inhibition of the antibody by depletion or elimination of the epitope by gene knockout may reveal the importance of other xenoantibodies, an d in addition elimination of the epitope may unmask or produce other x enoantibody combinations. This study aims to determine the relative im portance of anti-Gal antibody and Gal epitope elimination in a functio nal model of xenotransplantation, ex vivo perfusion of mouse hearts wi th human plasma on a Langendorff apparatus. Perfusion of mouse hearts with human plasma depleted of anti-Gal antibody demonstrates a protect ive effect compared to hearts perfused with undepleted plasma with pro longation of survival time from 24.1 to 44.5 min. Similarly, eliminati on of the epitope is also protective. Hearts from Gal knockout mice, w hich were generated by gene targeting of the alpha 1,3 galactosyltrans ferase gene, and hearts from appropriate control mice were perfused wi th human plasma. Gal knockout mice hearts demonstrated an increase in survival time from 10.2 to 33.8 min compared to control hearts. This w as accompanied by a decrease in C3c and IgM, but little change in IgG deposition. The protective effect is incomplete, probably due to the e ffect of antibodies against non-Gal xenoantigens. There was no functio nal evidence for generation of neo-antigens in the Gal KO mice that we re recognised by naturally occurring human xenoantibodies.