Fresh porcine cardiac valves are not rejected in primates

Objective: Transplanted porcine hearts are hyperacutely rejected by human i mmunoglobulin M antibodies against a porcine vascular endothelial molecule, galactose alpha-1,3-galactose, with ensuing human complement activation an d membrane attack complex deposition. It is unclear, however, whether porci ne valve endothelium triggers a similar immune response. We sought to inves tigate whether fresh porcine valves implanted into primates are rejected. Methods: Wild-type porcine hearts before (n = 6) and after (n = 3) heteroto pic transplantation into baboons underwent sectioning and were examined by hematoxylin and eosin staining and immunohistochemistry for galactose alpha -1,3-galactose, primate immunoglobulin M, and membrane attack complex. Results: Examination of untransplanted porcine hearts showed that although cardiac microvascular endothelium strongly expressed the galactose alpha-1, 3-galactose antigen, galactose alpha-1,3-galactose was not detected on the endothelium of porcine aortic and pulmonary valves. Porcine hearts transpla nted into baboon recipients were hyperacutely rejected 60 to 80 minutes aft er implantation. Despite dramatic tissue damage associated with extensive i mmunoglobulin M and membrane attack complex binding on the microvascular en dothelium, the aortic and pulmonary valves were entirely spared. Valves rem ained morphologically intact at explant and showed no signs of immunoglobul in M- and membrane attack complex-mediated damage. Conclusions: The absence of galactose alpha-1,3-galactose expression may pr otect unfixed porcine valves from xenograft rejection in primates. Further investigation of viable porcine valves appears warranted.