Xenophagocytosis blockade enhances interspecies chimerism.

Organ shortage remains a major challenge in transplantation medicine. Interspecies blastocyst complementation is a promising approach to generate human organs in livestock hosts. However, getting xenogeneic donor cells to engraft and expand at early stages remains challenging. Here we identify an innate immune barrier, wherein host macrophages selectively recognize and eliminate viable xenogeneic donor cells. These events represent a form of phagoptosis and highlight a xenogeneic clearance process that we term xenophagocytosis. We identify the mechanism by which host macrophages selectively phagocytize xenogeneic donor cells: xenogeneic cells display elevated phosphatidylserine, an "eat-me" signal recognized by host macrophages through phagocytic receptor Axl. Xenophagocytosis blockade improves both rat and human donor chimerism in mouse embryos, indicating a conserved mechanism. These findings reveal potential mechanisms by which innate immune cells eliminate xenogeneic cells in early embryogenesis to preserve species integrity and offer improved strategies for generating human organs in livestock.