One of transplant medicine's biggest bottlenecks is organ shortage. A promising fix involves growing human organs inside livestock embryos — but getting human cells to survive in an animal embryo has proven extremely difficult. Stanford researchers have now discovered why: host macrophages in the embryo actively identify and destroy foreign cells through a process they've named 'xenophagocytosis.' The team found that foreign cells display a molecular 'eat-me' signal (phosphatidylserine) recognized by the macrophage receptor Axl. By blocking this process three different ways — including engineering donor cells to display a 'don't-eat-me' signal — they significantly improved the survival of both rat and human cells in mouse embryos. This breakthrough could accelerate the timeline toward growing transplantable human organs in pigs or other livestock.
