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

将猪的器官移植给人类是解决供体器官短缺的一种可能方案。尽管宿主巨噬细胞至少部分参与了移植异种细胞的快速清除，但巨噬细胞诱导异种细胞杀伤的机制尚未完全阐明。我们证明了人网状内皮巨噬细胞可以在没有抗体或补体调理作用的情况下吞噬猪细胞，并且去除猪细胞中的α1，3-半乳糖基异种抗原并不能阻止这种吞噬。我们还证明了CD47的种间不相容显著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对人巨噬细胞的吞噬具有保护作用，我们通过将人CD47表达质粒导入猪B淋巴瘤样细胞，建立了表达人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，无论有没有抗体调理。这些结果表明CD47的种间不亲和性在巨噬细胞对异种细胞的排斥反应中起重要作用。猪细胞表达CD47的基因操作可能通过抑制CD47-Sirpα信号通路，为预防巨噬细胞介导的异种移植排斥反应提供新的途径。

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.