A genetically modified pig kidney has kept a 66-year-old man with kidney failure alive for a record nine months and successfully acted as a “bridge” to a human transplant in a world first, according to a case report published in the Lancet medical journal.
Tim Andrews, from New Hampshire, was seriously ill with end-stage kidney disease caused by type 2 diabetes. He had only a 9% chance of receiving a human kidney within five years, against a more than 40% risk of dying or being removed from the waiting list.
Surgeons at Mass General Brigham, a non-profit, integrated academic healthcare system in Massachusetts, transplanted a kidney from Wilma, a Yucatan miniature pig, into Andrews in January 2025. The organ was genetically engineered to be compatible with his immune system.
Record survival and bridge to human transplant
The kidney kept Andrews free of dialysis for nine months, the longest period ever recorded, before it began failing and he received a kidney from a dead human donor. It was also the first time a pig’s kidney had been used as a temporary “bridge” to a human transplant.
Andrews described the pig kidney transplant as a “miracle”, adding: “I was alive, and I hadn’t been in a long time.” He was able to cook, vacuum and take long walks with his dog, Cupcake, he said.
The team behind the transplant said Andrews successfully lived with the genetically edited kidney for 271 days before receiving a human kidney. His case represents the longest dialysis-free survival following pig kidney xenotransplantation in a living human, and the world’s first transition to human kidney transplantation.
Genetically engineered to evade rejection
Before the transplant, Wilma the pig had received 69 edits to her genome. Some of these were designed to dodge viruses that might pose a risk to humans, while others made the organ more compatible with humans, reducing the odds of immune rejection.
Transplanting genetically engineered pig organs has long been proposed as a solution to the organ shortage. But the first pig kidney transplant into a living person, in 2024, ended after 52 days when the patient died from unrelated heart problems, and no previous studies had documented xenograft survival beyond two months, according to the Lancet.
After roughly six months, damage developed in the pig kidney’s blood vessels which progressed to organ failure and the kidney was removed nine months after transplantation. After several months back on dialysis, Andrews received a kidney from a dead human donor, which worked well during six months of follow-up.
Implications for the organ shortage
“The organ shortage is the greatest crisis we have right now in transplantation,” said Dr Leonardo Riella, of the Center for Transplantation Sciences and the Division of Nephrology at Mass General Brigham. “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.”
There were no new antibodies against human tissue detected, indicating the pig kidney had not made it harder for the human kidney transplant to work successfully. No pig viruses or other pig pathogens were detected at any point.
The team cautioned that this was a single patient with no comparison group, and that the outcome reflected careful patient selection and intensive specialist care that may not be available elsewhere. Further clinical trials will be needed, but the success opens the door to pig kidney transplants as a bridge for other people facing long waits for a human kidney.
“The patients are the true pioneers here,” Riella said. “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.”
