How Genetically Edited Pig Kidney Helped US Man Stay Off Dialysis for 271 Days

A genetically edited pig kidney has functioned successfully inside a 66-year-old American man for 271 days, allowing him to remain free from dialysis while he waited for a human donor organ.

The procedure, carried out by doctors in the United States, represents the longest recorded period a living human has survived without dialysis after receiving a pig kidney.

The patient, Tim Andrews, had end-stage kidney disease when he received the genetically modified pig kidney in January 2025.

How did the pig kidney work?

The procedure is part of an emerging medical field known as xenotransplantation, which involves transplanting organs from animals into humans.

One of the major obstacles is the human immune system. When an organ from another species enters the body, the immune system can recognise it as foreign and launch an attack, potentially destroying the transplanted organ.

To overcome this problem, scientists genetically modify pigs before their organs are used for transplantation.

According to Dr Rommel Ravanan, a consultant nephrologist and chief medical officer for the UK’s NHS Blood and Transplant, advances in genetic technology allow researchers to remove, or “knock out”, certain pig genes so the human body is less likely to recognise the organ as foreign.

The kidney received by Andrews was therefore not simply taken from an ordinary pig and transplanted into him. It had been genetically edited to make it more compatible with the human body.

The modified organ was then transplanted into Andrews as a temporary measure while he waited for a suitable human kidney.

For 271 days, the pig kidney performed enough of the kidney’s essential functions to keep him off dialysis.

Eventually, the transplanted organ was removed and Andrews underwent short-term dialysis before receiving a human donor kidney.

Doctors described the case as the longest dialysis-free survival recorded following pig-to-human kidney transplantation in a living person.

Why was dialysis avoided?

Patients with end-stage kidney disease may require dialysis when their kidneys can no longer adequately remove waste and excess fluid from the blood.

A functioning transplanted kidney can perform those functions, potentially allowing a patient to avoid regular dialysis.

In Andrews’ case, the genetically edited pig kidney provided that function temporarily, effectively acting as a “bridge” until a human kidney became available.

Doctors believe this approach could become particularly important for patients who face long waits for human donor organs.

Why is this important?

The shortage of human organs remains one of the biggest challenges facing transplantation medicine.

Dr Leonardo Riella, lead author of the study and a specialist at the Centre for Transplantation Sciences at Mass General Brigham, said the shortage of organs meant many patients with end-stage kidney disease could not receive human transplants quickly enough.

He said xenotransplantation could initially provide a bridge that enables patients to stay off dialysis while waiting for a human kidney.

Researchers are also investigating whether genetically modified animal organs could eventually become long-term replacements for human organs rather than temporary solutions.

The latest case builds on earlier attempts at pig-to-human kidney transplantation.

In 2024, doctors at Massachusetts General Hospital performed another pig-kidney transplant in a living human. That patient survived for 52 days before dying from heart-related complications that were reported as unrelated to the transplant.

Similar experimental transplants have also been reported in the United States and China since 2022.

The 271-day outcome therefore provides researchers with additional evidence that genetically modified pig kidneys may one day help address the global shortage of human donor organs.

However, doctors and researchers continue to study the long-term safety, durability and effectiveness of xenotransplantation before it can become a routine treatment.