A kidney transplanted from a pig functioned inside a US patient for a record 271 days, marking a significant development in efforts to use animal organs to address the global shortage of human donor organs.
The transplant was performed on 66-year-old Tim Andrews at Massachusetts General Hospital on January 25, 2025, after he developed end-stage kidney disease linked to type 2 diabetes.
According to doctors, the transplanted kidney began working immediately and allowed Andrews to avoid dialysis for several months.
The kidney was eventually removed in October 2025 after showing signs of deterioration. Andrews subsequently underwent dialysis for 82 days before receiving a human donor kidney in January 2026, which doctors say has been functioning well.
For Andrews, the experimental procedure offered hope at a time when he faced a lengthy wait for a conventional transplant.
He had been told he could wait as long as seven years for a human kidney, while the average life expectancy for people undergoing dialysis is about five years.
“I had a little bit of a shortage of time… it becomes very depressing,” Andrews said.
Describing the pig kidney transplant as a source of hope, he added: “Hope is the biggest thing, the chance to be free from the [dialysis] machine and live your life.”
Genetically modified pig kidney
The kidney used in the procedure came from a genetically modified Yucatan miniature pig. Scientists have made extensive genetic changes to such animals to reduce the likelihood of their organs being rejected by the human immune system.
The modifications remove certain features of pig cells that trigger an immune response, introduce selected human genes to make the tissue more compatible with the human body and deactivate viruses embedded in the pig’s DNA.
Doctors say these modifications are necessary because an unmodified pig organ would be recognised as foreign by the human immune system and could be rapidly destroyed.
In Andrews’ case, there were early indications that his immune system was beginning to reject the kidney. Doctors were able to control the reaction by adjusting his medication.
However, after about six months, blood vessels within the transplanted kidney began to deteriorate. The organ became inflamed and eventually started to fail.
Doctors said there were no clear signs of antibodies attacking the pig kidney, leaving the exact cause of the failure uncertain.
Potential solution to organ shortage
The case is part of growing research into xenotransplantation, the use of organs from animals in human patients.
Researchers have focused heavily on pigs because their organs are relatively similar in size to human organs, while pigs can also be bred under controlled conditions.
Dr Leonardo Riella of Mass General Brigham’s Centre for Transplantation Sciences said the shortage of organs has created a serious challenge for patients awaiting transplants.
“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.
In the United States, about 100,000 people are waiting for kidney transplants, while only around 25,000 kidney transplants are performed each year. In the UK, more than 7,000 people are also on the kidney transplant waiting list.
Doctors believe pig kidneys could eventually serve as a temporary “bridge” for patients while they wait for a suitable human organ, potentially allowing them to avoid lengthy periods on dialysis.
However, researchers stress that significant challenges remain before xenotransplantation can become a routine treatment.
In their report published in the Lancet, the doctors described Andrews’ case as demonstrating both “the promise and the remaining challenges of clinical kidney xenotransplantation.”
The record 271-day survival of the pig kidney provides further evidence that genetically modified animal organs could one day play a role in addressing the shortage of human donor organs, although more research is needed to establish their long-term safety and effectiveness.
Source: BBC
