Xenophagocytosis blockade enhances interspecies chimerism.

Organ shortage remains a major challenge in transplantation medicine. Interspecies blastocyst complementation offers a promising strategy to generate human organs in livestock. However, efficient xenogeneic donor cell engraftment remains challenging. Here, we identify an innate immune barrier wherein host macrophages selectively eliminate viable xenogeneic donor cells, a process we term xenophagocytosis. Mechanistically, xenogeneic cells display elevated phosphatidylserine, an "eat-me" signal recognized by host macrophages through phagocytic receptor Axl. We demonstrate three orthogonal strategies for xenophagocytosis blockade: genetic ablation of macrophages or the Axl receptor in the host embryo or overexpression of the "don't-eat-me" signal CD47 or the phosphatidylserine-regulating flippase ATP11C in donor cells. Xenophagocytosis blockade enhances rat and human donor chimerism in mouse embryos and improves interspecies pancreas complementation efficiency. These findings reveal a previously unrecognized innate immune barrier that safeguards species integrity during early embryogenesis and provide mechanistic insights to enhance xenogeneic chimerism for generating human organs in livestock.