Xenotransplantation—transplanting organs from one species into another—has long been considered the fusion energy of medicine: perpetually the future. Pigs are the preferred donors: they are easy to breed, have organs of roughly the right size, and are physiologically similar enough to humans while being distant enough cousins to ease ethical worries that might derail the use of apes or monkeys.
Both eGenesis and United Therapeutics (through its subsidiary Revivicor), as well as ClonOrgan, a Chinese firm, produce donor pigs in much the same way. Scientists take skin cells from adult pigs and disable three or four genes that cause violent immune reactions in humans, then insert six or seven human genes to help prevent rejection, blood clotting and inflammation. Edited cells are used to create cloned pigs by transferring their nuclei into porcine egg cells, which are then implanted into sows. The ten-edit pig has become the basic organ-donor formula, though companies sometimes add further edits to differentiate themselves. Much of this progress is due to CRISPR gene-editing technology, whose pioneers won a Nobel prize in 2020.
Jeffrey Platt, a surgeon at the University of Michigan, published the first experiment on transplanting genetically modified pig organs into monkeys in 1995. In 2024 Richard Slayman received the first pig kidney transplant at Massachusetts General Hospital; he later died for reasons unrelated to his new organ. On January 25th 2025 Tim Andrews, a pensioner from New Hampshire, received a pig kidney at MGH that lasted 271 days—a record—before being removed on October 23rd as its function declined. Towana Looney received a pig kidney from Revivicor in November 2024 but had it removed after rejection set in when doctors lowered her immunosuppressant drugs to fight an unrelated infection.
In September 2025 the FDA gave eGenesis permission to start full-scale clinical trials of pig kidneys; United Therapeutics received similar permission in February 2025. United Therapeutics has also performed two pig-heart transplants and has permission to test its "UThymoKidney", which combines a pig kidney with porcine thymus tissue in the hope of training the recipient's immune system to tolerate the new organ.
The Global Observatory on Donation and Transplantation, run by the WHO and the Spanish Transplant Organisation, reckons less than 10% of those around the world who need a transplant get one. In America around 13 people a day die on waiting lists. Scarcity fuels a black market in which patients pay tens of thousands of dollars for organs of dubious provenance.
eGenesis has approval to trial a pig-liver perfusion system that keeps the organ outside the patient's body but hooked up to the circulatory system, using an organ-preserving device developed by OrganOx, a spin-out from the University of Oxford. The aim is to keep the patient alive until a human organ is ready.
In March and August 2025 Chinese research teams linked to ClonOrgan transplanted a pig liver and lung into two brain-dead people, as well as a kidney into a living patient. Another Chinese group put a porcine liver into a living patient in October 2025.
The decision doesn't have to be logical; it was unanimous.