On Oct. 9, 2025, Beicheng Sun at Anhui Medical University in China and his colleagues have reported the transplantation of a pig’s liver into a 71-year-old man. The recipient’s liver function was considered too poor for a conventional transplant to have a good chance of success, due to a large tumour and heavy scarring from a hepatitis B infection.

Transplanting organs from non-human animals into people could revolutionise medicine, potentially saving thousands of lives that are lost while people wait for organs. Scientists have previously experimented with giving people pig hearts and kidneys, and have now reported transplanting the animal’s liver into a living person for the first time.

To prevent the liver being rejected by his immune system, three genes were deactivated in the pig and seven genes were introduced, so the organ functioned more like a human one. The man also took immune-suppressing drugs, and the team carefully checked that the liver wasn’t infected with any porcine viruses.

But about a month after the procedure, he developed life-threatening clots in his blood vessels, forcing the team to remove the transplant. That was probably partly caused by it excessively activating part of the recipient’s immune system and producing abnormal levels of some blood-clotting proteins, which healthy livers also make. This is probably more likely to occur with pig transplants, due to how different the animal is to a human, says Sun.

Despite the man’s death, the procedure can still be considered a partial success, because he probably otherwise would have died soon after his tumour was removed, says Heiner Wedemeyer at Hannover Medical School in Germany. What’s more, the recipient’s own liver partly regenerated while the transplant was functioning well, which is probably why he lived for months after it was removed, he says.