A genetically modified pig kidney has functioned inside a human patient for 271 days, marking the longest recorded period for a pig organ to successfully operate in a person, according to US doctors.
The transplant gave patient Tim Andrews renewed hope and spared him months of regular dialysis, which filters waste from the blood when the kidneys can no longer function properly.
Doctors at Mass General Brigham said the case demonstrated the potential of pig organs to act as a “bridge” for patients while they wait for a human donor kidney to become available.
However, the pig kidney eventually stopped functioning and was removed. Andrews underwent dialysis for 82 days before receiving a human donor kidney in January this year, which doctors said is working well.
Andrews, who was 66 when he underwent the transplant on January 25, 2025, had end-stage kidney disease caused by type 2 diabetes. He had been told he could wait as long as seven years for a place at the top of the human transplant list, while the average life expectancy for people undergoing dialysis is around five years.
“I had a little bit of a shortage of time… it becomes very depressing,” he said.
For Andrews, the experimental transplant represented “hope” and the “light at the end of the tunnel”.
“Hope is the biggest thing, the chance to be free from the [dialysis] machine and live your life,” he said.
The field, known as xenotransplantation, involves using organs from animals for human transplantation and is being explored as a potential solution to the global shortage of donor organs.
In the US, around 100,000 people are currently waiting for a kidney, while only about 25,000 kidney transplants are performed each year. In the UK, more than 7,000 people are on the kidney transplant waiting list.
Pigs are considered particularly promising for xenotransplantation because their organs are broadly similar in size to human organs and pigs can be bred under controlled conditions.
However, an ordinary pig kidney cannot simply be transplanted into a human because the immune system would recognise the organ as foreign and rapidly attack it.
Researchers have therefore developed genetically modified Yucatan miniature pigs, with 69 genomic modifications designed to make their organs more compatible with the human body. These changes remove features of pig cells that trigger immune attacks, introduce some human DNA to help the tissue evade the immune system and disable viruses embedded within pig DNA to reduce the risk of infection.
According to the doctors, Andrews’ transplanted kidney began functioning immediately after surgery and continued to work for 271 days before being removed in October 2025.
There were early signs that his immune system was rejecting the organ, but doctors managed to control the reaction by adjusting his medication.
After around six months, however, the kidney’s blood vessels began to suffer damage. The organ became inflamed before eventually starting to fail, although doctors found no evidence of antibodies attacking the pig kidney.
The case was detailed in the Lancet medical journal, with the researchers describing it as evidence of both the “promise” and remaining challenges of clinical kidney xenotransplantation.
Dr Leonardo Riella of Mass General Brigham’s Centre for Transplantation Sciences said the shortage of donor organs meant the medical community was facing “a crisis”.
“We are working really hard to bring hope and we truly feel that xenotransplantation can be an alternative for patients who don’t have a living donor where we could potentially bypass dialysis and get them to a transplant,” he said.
