Pig kidney keeps 66-year-old man off dialysis for 9 months before human transplant in world's first

A genetically modified pig kidney kept a 66-year-old US man with end-stage kidney disease off dialysis for nine months before he received a human donor kidney, in what researchers describe as a world first.

Tim Andrews, from New Hampshire, had kidney failure caused by type 2 diabetes. His chances of receiving a human kidney within five years were just 9%, while his risk of dying or being removed from the waiting list was more than 40%.

In January 2025, surgeons transplanted a kidney from a genetically modified Yucatan miniature pig named Wilma into Andrews. The organ worked for 271 days, allowing him to remain free from dialysis for the longest recorded period following a pig kidney transplant in a living human.

The case, published in The Lancet, is also the first reported instance of a pig kidney being used as a temporary “bridge” before a patient received a human transplant.

Andrews called the experience a “miracle”.

“I was alive, and I hadn’t been in a long time.”

He said the transplant allowed him to return to everyday activities, including cooking, vacuuming and taking long walks with his dog, Cupcake.

69 genetic edits to the pig kidney

Before Wilma’s kidney was transplanted, scientists made 69 genetic edits to her genome. Some were intended to reduce the risk of viruses that could potentially affect humans, while others were designed to make the organ more compatible with the human immune system and lower the chances of rejection.

The kidney eventually began to fail. After about six months, damage developed in its blood vessels and progressed to organ failure. It was removed nine months after the transplant.

Andrews then spent several months on dialysis before receiving a kidney from a deceased human donor. The human kidney was functioning well after six months of follow-up.

Researchers also found no new antibodies against human tissue, suggesting the earlier pig kidney had not made the subsequent human transplant more difficult. No pig viruses or other pig pathogens were detected.

Could pig kidneys help tackle the organ shortage?

The shortage of human donor organs is one of the biggest challenges facing transplant medicine. While kidney transplantation offers the best survival and quality of life for people with end-stage kidney disease, demand continues to outstrip supply.

Dr Leonardo Riella of the Center for Transplantation Sciences and the Division of Nephrology at Mass General Brigham said:

“The organ shortage is the greatest crisis we have right now in transplantation,” Riella said. “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.”

Researchers cautioned that this was a single-patient case with no comparison group. Further clinical trials will be needed.

“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.”