Author, James Gallagher
Role, BBC health and science reporter
Published 3 hours ago
Reading time: 3 minutes
American patient Tim Andrews' kidneys are failing. Last year, he received a kidney transplant from a pig. The pig kidney functioned normally in his body for 271 days, setting a current international record for the longest time.
Andrews said the transplant gave him "renewed hope" and spared him months of trips to the hospital and relying on a dialysis machine to filter his blood, commonly known as kidney dialysis.
However, the pig kidney eventually lost function and was removed. Andrews then required a brief period of dialysis until a suitable human donor organ could be found.
Due to the chronic shortage of organs for transplantation, doctors and scientists are studying xenotransplantation, which is the use of organs from other species for human transplants.
A team from Mass General Brigham and Women's Hospital in the United States said Andrews' case shows that pig organs have the potential to serve as a "bridge" before the advent of human organ transplants.
There are currently about 100,000 people in the United States on the waiting list for a kidney transplant, but only about 25,000 kidney transplants are performed each year. In the UK, more than 7,000 people are waiting for a kidney transplant.
Doctors told Andrews that he might have to wait seven years to be on the transplant list, but the average life expectancy of dialysis patients is about five years.
"I'm running out of time... it's very frustrating," he said.
He described the idea of transplanting pig kidneys as bringing "hope" and being "a light at the end of the tunnel".
"Hope is the most important thing - the chance to get off the (dialysis) machine and live your life."
Pigs are considered one of the most suitable animals for xenotransplantation. Their organs are roughly the same size as humans, and humans have accumulated experience raising pigs for many years.
But you can't just go to a farm and take a kidney from a pig and transplant it into a human. The body immediately recognizes this organ as foreign and launches a devastating immune attack that ultimately destroys the kidney. Within minutes, the kidneys turn black as every cell is torn apart and clots begin to form inside.
So researchers bred Yucatan miniature pigs and made 69 genome modifications to "humanize" their organs.
These genetic modifications removed some characteristics of pig cells that would be recognized and attacked by the human immune system; at the same time, some human DNA was added to act like a camouflage net to help pig tissues avoid detection by the immune system.
The researchers also further modified the genes to inactivate the viruses hidden in the pigs' DNA and avoid infection.
Andrews' end-stage renal disease is caused by type 2 diabetes. He received a xenogeneic kidney transplant on January 25, 2025, when he was 66 years old.
According to details just published in the medical journal The Lancet, the transplanted pig kidneys began functioning immediately.
The kidney continued to function for 271 days before being removed in October of the same year. Andrews then underwent dialysis for 82 days before receiving a human donor kidney in January this year. Currently, the donated kidney is functioning well.
Dr. Leonardo Riella of the Center for Transplantation Science at Brigham and Women's Hospital at Massachusetts General Hospital said that "we are in a crisis" due to insufficient organs for transplantation.
"We're trying very hard to bring hope, and we do think that xenotransplantation can be an alternative for patients who don't have a living donor. It could potentially allow them to avoid dialysis and go straight to a transplant," he said.
