A genetically modified pig kidney functioned inside a 66-year-old US man for 271 days, the longest recorded time for a pig kidney to work in a human. The procedure, called kidney xenotransplantation, uses specially modified pig organs designed to reduce rejection and make them safer for humans. The breakthrough could help address the global shortage of donor kidneys, with more than 90,000 people in the US currently waiting for a transplant, according to transplant data.
Record-Breaking Transplant at Massachusetts General Hospital
Tim Andrews, who had developed end-stage kidney disease linked to type 2 diabetes, received the experimental pig kidney transplant at Massachusetts General Hospital in January 2025. Before the transplant, his condition was becoming difficult to manage. “I had a little bit of a shortage of time, it becomes very depressing,” Andrews said, explaining what life was like before receiving the pig kidney. The experimental procedure gave him something he had been missing. “Hope is the biggest thing, the chance to be free from the [dialysis] machine and live your life,” he said.
The kidney started working immediately after the transplant. For nine months, it helped Andrews avoid dialysis while he waited for a permanent human donor kidney. However, the organ eventually failed. Doctors noticed early signs of rejection, but they were able to control the reaction by adjusting his medication. After about six months, the kidney’s blood vessels started developing problems. The organ became inflamed and later stopped working.
How Pig Kidney Transplants Work
Scientists genetically modify pig organs to reduce the risk of rejection and make them more compatible with the human immune system. The procedure is called kidney xenotransplantation (pronounced zee-no-trans-plan-TAY-shin). It involves transplanting a kidney from a genetically modified pig into a human recipient. The idea behind it is simple: there are far more people who need kidney transplants than there are available human donor kidneys. Because kidneys from pigs are similar in size and perform many of the same functions as human kidneys, scientists believe they could become another source of organs in the future.
A functioning kidney helps the body: remove waste products and extra fluid, control blood pressure, and balance minerals and vitamins. Researchers believe a successful pig kidney could potentially last for decades, similar to a human donor kidney, although this is still being studied.
Why Pig Kidneys Need Genetic Modification
The human immune system sees animal organs as foreign objects and attacks them. That is why scientists genetically modify the pigs before they are born. These special pigs are raised in highly controlled environments, and their organs are changed to make them more compatible with humans. The genetic changes are designed to: remove pig genes that trigger strong human immune reactions, add human genes that help the organ avoid rejection, and reduce the risk of viruses naturally found in pigs affecting humans.
Interestingly, doctors did not find signs that antibodies were attacking the kidney, meaning the exact reason for the failure is still unclear. The pig kidney was removed in October 2025. Andrews spent another 82 days on dialysis before receiving a human donor kidney in January 2026. Doctors say that kidney is currently working well.
Future of Xenotransplantation
Kidney xenotransplantation is still considered an experimental treatment and has only been used in very limited cases. In 2025, the US Food and Drug Administration (FDA) approved the first human clinical trials for the procedure, allowing researchers to properly test whether it is safe and effective. Scientists say the goal is not necessarily to replace human kidney donations completely, but to create another option for people who have no living donor or who may wait years for a transplant.
Dr Leonardo Riella from the Mass General Brigham Centre for Transplantation Sciences said the shortage of human organs remains a major challenge. “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,” he said. For now, Andrews’ case shows both sides of the technology — the excitement of a future where animal organs can save human lives, and the reality that scientists still have important problems to solve. But for kidney patients spending years attached to dialysis machines while waiting for a donor, even a temporary solution could mean one important thing: more time, and more hope.
