Elucidation of mechanisms for macrophage-mediated xenograft refection and a novel approach to prevent macrophage-mediated xenograft rejection by gene introduction of human CD47 to xenogenic cells

猪的异种器官移植到人类身上是一个可能的解决方案，用于移植的供体器官短缺。尽管已知宿主巨噬细胞至少在一定程度上有助于快速清除移植的异种细胞，但巨噬细胞诱导杀死异种细胞的机制尚未得到充分解决。我们在这里证明了人网状内皮巨噬细胞可以在没有抗体或补体调理的情况下吞噬猪细胞，并且从猪细胞中去除α1,3-半乳糖异种抗原不能阻止其吞噬。我们还证明了CD47的种间不相容性显著地促进了巨噬细胞对异种细胞的吞噬。为了进一步确定人CD47在猪细胞上的表达是否能够保护猪免受人巨噬细胞的吞噬，我们用表达人CD47的质粒转染猪B淋巴瘤样细胞，产生了表达人CD47的猪细胞系。人CD47在猪细胞上的表达从根本上降低了细胞对人网状内皮巨噬细胞吞噬的敏感性，无论是否存在抗体调理。这些结果表明，CD47的种间不相容性显著促进了巨噬细胞对异种细胞的排斥反应。通过基因操作猪细胞来表达人CD47可能为通过抑制CD47- sirp α信号传导来预防巨噬细胞介导的异种移植排斥提供了一种新的途径。

Xenotransplantation of pig organs to humans is a possible solution for the shortage of donor organs for transplantation. Although host macrophages are known to contribute at least in part to rapid clearance of transplanted xenogeneic cells, the mechanisms underlying macrophage-induced killing of xenogeneic cells has not been fully addressed. We here demonstrated that human reticulo-endothelial macrophages can phagocytose porcine cells in the absence of antibody or complement opsonization, and that the removal of α1,3-galactosyl xenoantigens from the porcine cells failed to prevent the phagocytosis. We also demonstrated that the interspecies incompatibility of CD47 significantly contributes to the phagocytosis of xenogeneic cells by macrophages. To further determine whether the expression of human CD47 on porcine cells could confer protection from phagocytosis by human macrophages, we generated human CD47-expressing porcine cell lines by transfecting the porcine B lymphoma-like cells with a human CD47 expressing plasmid. Human CD47 expression on porcine cells radically reduced the susceptibility of the cells to phagocytosis by human reticulo-endothelial macrophages, regardless of the presence or absence of antibody opsonization. These results indicate that the interspecies incompatibility of CD47 significantly contributes to the rejection of xenogeneic cells by macrophages. Genetic manipulation of porcine cells for expression of human CD47 may provide a novel approach in preventing macrophage-mediated xenograft rejection through inhibitory CD47-SIRPα signaling.