Genetically modified pig kidney helps 66-year-old US man stay off dialysis for record nine months

A genetically modified pig kidney has kept a 66-year-old man with end-stage kidney disease off dialysis for a record nine months before he successfully received a human donor kidney. The case is being seen as a significant step for xenotransplantation, particularly for patients who face long waits for a suitable human organ.

Tim Andrews, from New Hampshire in the US, had kidney failure linked to type 2 diabetes and had only a 9% chance of receiving a human kidney within five years. Doctors at Mass General Brigham, a major healthcare system in Massachusetts, transplanted the kidney from a genetically modified Yucatan miniature pig named Wilma into him in January 2025. The organ worked for 271 days before beginning to fail, after which Andrews received a kidney from a deceased human donor.

The kidney kept Andrews free from dialysis for nine months, marking the longest dialysis-free survival recorded after a pig kidney was transplanted into a living person. It was also the first reported case in which a pig kidney served as a temporary “bridge” before a patient went on to receive a human kidney.
Details of the case were published in The Lancet.

Andrews described the transplant as a “miracle”, adding, “I was alive, and I hadn’t been in a long time.” He said being off dialysis allowed him to cook, vacuum and take long walks with his dog, Cupcake. Before the transplant, Wilma’s genome had undergone 69 genetic edits. These were intended to make the kidney more compatible with a human immune system and reduce the risk of rejection, while some edits were designed to guard against viruses that could pose a risk to humans.

The shortage of human organs remains a major problem in transplantation, and the need far exceeds supply. This has fuelled interest in genetically modified animal organs as a potential way to help patients who may otherwise spend years waiting for a donor. Dr Leonardo Riella of the Center for Transplantation Sciences and the Division of Nephrology at Mass General Brigham in Massachusetts said, “The organ shortage is the greatest crisis we have right now in transplantation.”

He added, “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, and potentially, as we establish long-term safety and durability, as a destination therapy in its own right.”

The pig kidney eventually developed blood-vessel damage after around six months, which progressed to organ failure. After the organ was removed, Andrews spent several months back on dialysis before receiving a human kidney, which was working well during six months of follow-up.
Importantly, doctors found no new antibodies against human tissue, suggesting the pig kidney had not made the later human transplant more difficult. No pig viruses or other pig pathogens were detected at any point.

The researchers have stressed that this was a single-patient case without a comparison group. The outcome also involved careful patient selection and intensive specialist care, which may not be available in every setting. Further clinical trials will be needed before pig kidney transplantation can be considered more widely. Still, the case suggests that a genetically modified pig kidney could one day serve as a bridge for other patients facing long waits for a human donor.

“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.”