Genetically modified pig kidney keeps man alive for record nine months

A genetically modified pig kidney has kept a 66-year-old man with end-stage kidney disease alive without dialysis for a record nine months, marking the first time a pig kidney has successfully served as a temporary “bridge” to a human kidney transplant.

Tim Andrews, from New Hampshire, was suffering from severe kidney failure caused by type 2 diabetes. Doctors said he had only a 9% chance of receiving a human kidney within five years, while facing a more than 40% risk of dying or being removed from the transplant waiting list.

Tim Andrews preparing for surgery in January 2025

Surgeons at Mass General Brigham in Massachusetts transplanted a kidney from a genetically modified Yucatan miniature pig named Wilma into Andrews in January 2025. The kidney functioned for 271 days, allowing him to remain free of dialysis before it began to fail.

After the pig kidney was removed, Andrews spent several months back on dialysis before receiving a kidney from a deceased human donor. The human kidney was functioning well after six months of follow-up, according to findings published in the medical journal The Lancet.

The transplant represents the longest dialysis-free survival recorded following a pig kidney xenotransplant in a living person. It is also the first documented case in which a patient successfully moved from a pig kidney transplant to a human kidney transplant.

Before the procedure, Wilma’s genome underwent 69 genetic modifications. Some changes were intended to reduce the risk of viruses being transmitted to humans, while others were designed to make the pig kidney more compatible with the human immune system and reduce the risk of rejection.

Andrews described the procedure as a “miracle”, saying it allowed him to return to everyday activities. He said he was able to cook, vacuum and take long walks with his dog.

The development could offer a potential solution to the severe shortage of human organs available for transplantation. Kidney transplantation provides the best survival prospects and quality of life for patients with end-stage kidney disease, but the global demand for donor kidneys far exceeds the supply.

Dr Leonardo Riella of Mass General Brigham said the shortage of organs remains “the greatest crisis” in transplantation. He said genetically modified animal organs could initially be used to help patients avoid dialysis while they wait for a human donor kidney and could eventually become a long-term treatment option if their safety and durability are established.

The pig kidney began showing damage to its blood vessels after about six months, eventually leading to organ failure and its removal nine months after transplantation.

Doctors found no new antibodies against human tissue following the procedure, suggesting the pig kidney did not make Andrews’ subsequent human transplant more difficult. No pig viruses or other pig pathogens were detected at any point.

The researchers cautioned that the result is based on a single patient with no comparison group. They said the outcome also depended on careful patient selection and intensive specialist care that may not be available in all settings.

Further clinical trials will be needed to determine whether genetically modified pig kidneys can safely and reliably be used as a bridge for other patients facing long waits for human organs.

The researchers said the case nevertheless provides new evidence that pig kidney transplantation could help address the global organ shortage and potentially offer patients a way to remain off dialysis while waiting for a human kidney.