How pig organs may soon save lives

For years Tim Andrews, a pensioner from New Hampshire, suffered with failing kidneys. Dialysis could not stop a steady decline in his health. “Most likely I was going to pass away before I got to the point where I would be able to get a human transplant,” Mr Andrews says. Then he read about Richard Slayman, who in 2024 had received a “xenotransplant”: an organ taken from another species.

Mr Andrews contacted the medical team at Mass General Hospital (MGH), the hospital in Massachusetts that had carried out the operation. On January 25th surgeons at MGH gave him a kidney from a genetically modified pig. His new organ lasted 271 days—a record.

Xenotransplantation is the fusion energy of medicine. As the well-worn joke goes, it is the future—and always will be. But that punchline is starting to sound out of touch. Both Mr Andrews and Mr Slayman, being very sick, received their organs on exceptional compassionate grounds (Mr Slayman later died, for reasons unrelated to his new organ). But in September the Food and Drug Administration, an American medical regulator, gave eGenesis, the company that provided Mr Andrews’s kidney, permission to start full-scale clinical trials of pig kidneys—an early step on the road to wider medical use. United Therapeutics, which produces pig organs through its subsidiary Revivicor, was given permission to do the same in February. Both eGenesis and United Therapeutics expect to begin transplanting organs imminently.

The technology offers great promise. The Global Observatory on Donation and Transplantation, run by the World Health Organisation and the Spanish Transplant Organisation, reckons that less than 10% of those around the world who need a transplant get one. Even in rich countries demand exceeds supply: in America around 13 people a day die while on waiting lists. Scarcity fuels a black market, in which patients pay tens of thousands of dollars for organs of dubious provenance.

Pigs could ease that shortage. They are easy to breed and have organs of roughly the right size. Being mammals, they are physiologically somewhat similar to humans—while being distant enough cousins to ease the ethical worries that might derail attempts to use apes or monkeys. But things have moved slowly. Jeffrey Platt, a surgeon at the University of Michigan, published the first experiment on transplanting pig organs into monkeys in 1995.

Much of the recent progress due to to a new gene-editing technology called CRISPR , whose pioneers won a Nobel prize in 2020. CRISPR allows scientists to more easily edit the pig genome in order to make porcine organs more tolerable to humans. One of the biggest problems with transplants of any kind is rejection, in which the recipient’s immune system recognises the new organ as foreign and attacks it. Keeping a lid on rejection with human-to-human transplants often requires the lifelong use of immunosuppressant drugs, which have side-effects and leave recipients vulnerable to infections. That problem is greatly magnified when the organ comes from an entirely different species.

Revivicor and eGenesis—as well as ClonOrgan, a Chinese firm that has produced organs for transplant into a couple of human patients—make their gene edited 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. They then insert six or seven human genes, which also help to prevent rejection, as well as problems related to blood clotting and inflammation.

Next, edited cells are used to create cloned pigs by removing the cells’ nuclei, which contain their DNA, and putting them into porcine egg cells. Once these eggs are fertilised, and implanted into surrogate sows, the result is gene-edited piglets. Although the companies sometimes add further edits to set themselves apart, the ten-edit pig has become the basic organ-donor formula.

The resulting organs work well in monkeys. Results in people, however, have been less clear-cut. Mr Andrews, whose kidney was provided by eGenesis, was managing rejection issues reasonably well with drugs. But the function of his new kidney was falling, and on October 23rd it had to be removed. Mr Andrews is now back on dialysis, and on the waiting list for a human transplant. He is the second recipient whose new kidney has failed. Towana Looney, who received her kidney from Revivicor in November 2024, had hers removed after her body rejected it—a consequence of doctors lowering her dose of immunosuppressant drugs to allow her body to fight off an unrelated infection.

Mike Curtis, eGenesis’s boss, thinks the upcoming trials will teach the field a lot. Improvements may be possible in both gene editing and post-transplant care. He has high hopes for eGenesis’s collaboration with Eledon, a firm trialling a new anti-rejection drug called tegoprubart, which it hopes will have fewer side-effects than existing drugs. Revivicor, for its part, is testing a drug called ravulizumab that is already prescribed for autoimmune disorders.

Meanwhile, eGenesis has approval for a trial of a pig-liver perfusion system. Unlike a full transplant, this keeps the organ outside the patient’s body, although hooked up to his circulatory system. With help from an organ-preserving device developed by OrganOx, a spin-out from the University of Oxford, the hope is that the pig liver can keep the patient alive until a human organ is ready. In March and August Chinese research teams linked to ClonOrgan said that they had 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 earlier this month.

Now that Mr Andrews’s kidney has been removed, the only person living with a pig kidney in America is Bill Stewart, an athletics coach who received his in June. But Mr Stewart will not be alone for long: MGH is scheduled to perform a third transplant later this year.

Correction (29 October 2025): The piece has been updated to reflect that FDA clearance was granted to United Therapeutics rather than Revivicor, its subsidiary company.