A genetically modified pig kidney functioned inside a New Hampshire patient for a record 271 days without dialysis, according to findings published in The Lancet medical journal and statements from Massachusetts General Hospital. The milestone in xenotransplantation offers a potential bridge for thousands of people facing end-stage organ failure while waiting for human donors.
Tim Andrews Breaks Survival Record with Yucatan Miniature Pig Kidney
Tim Andrews, a 68-year-old retired grocery store manager from Barrington, New Hampshire, received the experimental organ on Jan. 25, 2025, when he was 66, according to Mass General. Diagnosed with end-stage kidney disease linked to type 2 diabetes, Andrews faced long odds for a human organ. According to reporting by The Guardian, he had roughly a 9 percent chance of receiving a human kidney within five years, while facing a greater than 40 percent risk of dying or dropping off the waiting list. The BBC reported that patients can wait up to seven years for a match, while average survival on dialysis sits near five years.
Faced with this timeline, Andrews agreed to the xenotransplant. The organ came from Wilma, a Yucatan miniature pig whose genome underwent 69 modifications, according to Mass General and BBC reports. These edits removed cell features that trigger immediate human immune attacks, added human DNA to camouflage the tissue, and deactivated embedded retroviruses to prevent infection.
“As soon as I woke up after the surgery, the cloud of dialysis disappeared,” Andrews said, according to an Instagram post by Mass General. “I felt re-energised and revitalized. It was a miracle.”
Medical Milestones and Comparison with Prior Xenotransplantation Cases
The 271-day duration marks the longest recorded period that a genetically modified pig kidney has functioned inside a living human, according to Mass General. It also represents the first reported case where a pig kidney successfully acted as a temporary bridge before a patient transitioned to a human donor kidney.
Did you know? Mass General performed the world’s first pig-to-human kidney transplant in 2024 on Richard “Rick” Slayman, who lived for 52 days before passing away from cardiac causes unrelated to the procedure, according to hospital statements. Another prominent recipient, Towana Looney, lived with a pig kidney for 130 days before its removal in April 2025 due to rejection, according to a representative for NYU Langone Health.
During his nine months without dialysis, Andrews managed early signs of immune system rejection through medication adjustments, according to BBC coverage. However, after roughly half a year, blood vessels within the organ began sustaining damage and inflammation set in, leading to the kidney’s eventual failure. Doctors removed the organ, and Andrews underwent 82 days of dialysis before receiving a human donor kidney in January of this year, which hospital reports indicate is currently functioning well.
Addressing the National Organ Shortage Crisis
More than 100,000 people currently sit on the national transplant waiting list in the United States, with the vast majority waiting for a kidney, while only about 25,000 kidney transplants are performed each year, according to Dr. Leonardo Riella, lead author of the study from the Center for Transplantation Sciences at Mass General Brigham. In the UK, more than 7,000 people remain on the waiting list, according to BBC figures.
“The organ shortage is the greatest crisis we have right now in transplantation,” Riella wrote in findings published by Mass General. Researchers envision xenotransplantation closing this gap by initially serving as a bridge off dialysis, and potentially functioning as a destination therapy once long-term safety and durability are established.
While doctors initially estimated a decade before pig kidneys become widely viable, Andrews noted that researchers now point to a five-year horizon. “I may live to see it,” he told NBC News.
Frequently Asked Questions
Why are pig kidneys used in xenotransplantation?
Pigs are considered ideal donors because their organ sizes roughly match human anatomy, and agricultural practices for raising them under controlled conditions are well-established, according to medical reports from Mass General and BBC coverage.
How does the human body react to a pig organ?
Without genetic modification, the human immune system immediately identifies animal tissue as foreign, launching an aggressive attack that causes the organ to clot and fail within minutes. Yucatan miniature pigs undergo 69 genomic edits to hide the tissue from human immune responses and disable viral DNA, according to BBC reporting.
What happens when a pig kidney fails in a patient?
As demonstrated in Tim Andrews’ case, surgeons can remove the failing pig organ, place the patient temporarily back on dialysis, and successfully perform a subsequent transplant using a human donor kidney, according to The Lancet study findings.
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