A genetically modified pig kidney functioned inside a human patient for 271 days, marking the longest recorded period a transplanted animal kidney has worked in a person. The case is being seen as an important development in xenotransplantation and could offer new hope to patients waiting for a human kidney donor.
The transplant was performed on January 25, 2025, on 66-year-old Tim Andrews, who had developed severe kidney disease linked to type 2 diabetes and was suffering from renal failure. Doctors at Mass General Brigham said the procedure highlights the possibility of using pig kidneys as a temporary “bridge” for patients who need an organ while waiting for a human transplant.
According to details published in the medical journal The Lancet, the genetically modified kidney began functioning immediately after the operation and continued working for 271 days.
The kidney eventually stopped functioning and was removed in October 2025. Andrews subsequently spent 82 days on dialysis before receiving a human kidney from a donor in January 2026. His transplanted human kidney is now functioning well.
A Seven-Year Wait for a Human Kidney
Before receiving the pig kidney, Andrews had been told that he might have to wait as long as seven years for a human donor organ. For people dependent on dialysis, the average survival is around five years, making a prolonged wait for transplantation particularly difficult.
“I had a little less time. It gets very frustrating,” Andrews said.
He described the experimental transplant as a source of hope, saying it represented “a light at the end of a dark tunnel.”
“Hope was the biggest thing that gave me the opportunity to get off the machine and live my life,” he said.
The shortage of donor organs has prompted researchers to investigate xenotransplantation, in which organs from animals are transplanted into humans. Around 100,000 people in the United States are waiting for a transplant, while approximately 25,000 transplant procedures are performed each year. In the United Kingdom, more than 7,000 people are waiting for a kidney transplant.
Why Genetically Modified Pig Organs Are Being Studied
Pigs are considered suitable candidates for xenotransplantation because their organs are similar in size to human organs, while humans also have extensive experience raising pigs.
However, an ordinary pig kidney cannot simply be transplanted into a human. The immune system recognises the animal organ as foreign and can launch a severe response against it. Within minutes, damage can begin developing in the kidney, while blood clotting can occur inside the organ and cause it to darken.
To overcome these challenges, researchers have developed genetically modified Yucatan miniature pigs. Their genes have been altered in 69 ways to make their organs more compatible with the human body.
Some modifications remove characteristics on pig cells that can trigger an immune response. Researchers have also introduced certain human DNA to provide a form of biological camouflage, helping the transplanted tissue avoid detection by immune cells.
Additional genetic modifications are designed to deactivate viruses contained within pig DNA, reducing the potential risk of infection following transplantation.
Pig Kidney Worked for 271 Days
Andrews’ transplant represents the longest documented period of functioning for a pig kidney transplanted into a human patient.
Doctors initially observed signs suggesting that his immune system was attacking the transplanted organ. The problem was successfully managed by adjusting his medication.
About six months after the procedure, however, the kidney’s blood vessels began showing signs of damage. The organ became swollen and eventually stopped functioning.
Doctors were unable to establish the precise reason for the failure because they found no evidence of an antibody attack against the kidney.
The researchers said the shortage of available transplant organs means “we are in a crisis.”
Dr Leonardo Riella of Mass General Brigham’s Center for Transplantation Sciences said researchers were working to provide patients with hope and believe xenotransplantation could eventually become an option for people without a suitable donor.
“It could potentially allow us to bypass dialysis and get them to transplantation,” Riella said.
In their report published in The Lancet, the doctors concluded that the case demonstrates both the potential and the challenges involved in clinical kidney xenotransplantation.