In a world first, a man has lived without dialysis for nine months after receiving a genetically modified pig kidney.
Tim Andrews, 66, from New Hampshire, suffered end-stage kidney failure brought on by type 2 diabetes before undergoing the pioneer procedure in the US in January 2025.
Doctors explained that the animal organ, taken from a Yucatan miniature pig and genetically engineered for compatibility with the human immune system, served as a temporary "bridge" while Mr Andrews awaited a transplant from a human donor.
He lived successfully with the genetically edited organ for 271 days before transitioning to a short period of dialysis and subsequently receiving a donor human kidney.
Medical teams said the milestone marks the longest recorded dialysis-free survival following a pig kidney transplant in a living patient, and the first successful transition from pig-to-human kidney transplantation.
It was transplanted in January last year and began working immediately.
After roughly six months, damage developed in the kidney’s blood vessels which progressed to organ failure and the pig kidney was removed.
Mr Andrews later received a kidney from a dead human donor.
In a CNN documentary, he said the pig kidney transplant was a “miracle”, adding: “I was alive, and I hadn’t been in a long time.”
He said he was able to cook, vacuum and take long walks with his dog Cupcake.
Researchers said no pig viruses or other pig pathogens were detected at any point.
They added that the findings support pig kidney transplantation as potentially a bridge for people facing long waits for a human kidney, while highlighting the need for further research.
The team, from Mass General Brigham academic centres and hospitals in the US, published their findings in the Lancet medical journal.
Lead author Dr Leonardo Riella, from the centre for transplantation sciences at Mass General Brigham, said: “The organ shortage is the greatest crisis we have right now in transplantation.
“We know that the best treatment option for patients with end-stage kidney disease who have developed renal failure is transplantation, but we simply don’t have enough human organs to transplant in a timely manner.
“Our vision is that xenotransplantation could help address this gap – initially as a bridge to get patients off dialysis while they wait for a human donor kidney, and potentially, as we establish long-term safety and durability, as a destination therapy in its own right.”
He added: “The patients are the true pioneers here. By stepping forward and being willing to participate in these early-stage studies, they are advancing the science.
“Without their trust and courage, we would not be able to do what we do.”
Another pig kidney transplant to a living human was undertaken in 2024 at Massachusetts General Hospital, where the patient survived 52 days before dying from heart issues unrelated to the transplant.
Dr Rommel Ravanan, chief medical officer for NHS Blood and Transplant in the UK, who is a consultant nephrologist, said the US and China have reported several similar transplants since 2022.
There are currently no clinical trials in the UK for a similar procedure although regulators have looked into how they would work.
He told the Press Association: “Advances in genetics technology enable teams to ‘knock out’ some of the pig genes, so the human body is less able to recognise the organ was different.
“Recent improvements in genetic mapping and the development of techniques such as CRISPR ‘genetic scissors’ have made this more possible.
“Pigs are chosen for several reasons, including that their organ size and anatomy is similar to that of human.
“Public surveys have shown most, but not all, people in the UK are supportive of the idea of lifesaving animal to human transplants.
“People are even more supportive when told animal to human transplants should only be introduced if shown to be safe and effective.
“It’s important to recognise that, even if shown to be effective, there is still a very long way to go before these kinds of transplants could become an everyday reality.
“With the transplant waiting list at an all-time high, and people dying on the transplant waiting list every day, there is an urgent need for more people to support organ donation by joining the NHS Organ Donor Register and talking to their family about their wish to be an organ donor.”
Dr Ravanan said a Department of Health and Social Care-sponsored advisory group of experts has made recommendations to ministers on the UK’s response to pig organ transplants, which were accepted.
“These recommendations cover policy in this field, including regulation, oversight, ethics including animal welfare, and research.”
