Surgeons at Massachusetts General Hospital have removed a genetically engineered pig kidney from a 67-year-old New Hampshire man after a period of decreasing kidney function, the hospital confirmed to WIRED in a statement. The organ functioned for nearly nine months, longer than previous pig organ transplants, before it was removed on October 23.

Tim Andrews received the pig kidney on January 25 after being on dialysis for more than two years due to end-stage kidney disease. His rare blood type meant that he faced a much longer wait time for a human donor kidney than most patients, who already wait on average three to five years for a kidney.

The shortage of human donors has pushed scientists to look to animals as a potential source of organs. Kidneys are the most in demand, with nearly 90,000 people waiting to receive one in the US alone. Due to the shortage of organs, the US performed just 28,000 kidney transplants in 2024.

Pig organs are being explored as an option, though genetic differences between pigs and humans mean they would be swiftly rejected if they were transplanted into a person. Scientists have therefore turned to gene editing to make pig organs more compatible with the human body, and have so far carried out a handful of experimental transplants.

Andrews was the fourth person in the world to receive a kidney from a genetically engineered donor pig. The first, Richard Slayman, whose surgery was also performed at Massachusetts General, died in May 2024 almost two months after his transplant. A second person, Lisa Pisano, had a combined pig kidney transplant and heart pump surgery at NYU Langone Health, but had the kidney removed in May 2024 after less than two months due to failure. Pisano later passed away. Towana Looney became the third pig kidney recipient, again at NYU Langone, and lived with the organ for more than four months before surgeons removed it in April this year due to organ rejection.

Since Andrews’ surgery, a patient in China has received an edited pig kidney, and surgeons at Massachusetts General have transplanted one into another patient, 54-year-old Bill Stewart, bringing the total number of people known to have received pig kidneys to six.

Before the pig kidney transplants, two patients received genetically engineered pig hearts at the University of Maryland in 2022 and 2023 but never became healthy enough to leave the hospital. They both died within two months of their procedures.