A genetically modified pig kidney functioned inside a US patient for 271 days, the longest period recorded in a living person, while allowing him to remain free from dialysis as he waited for a human transplant.
Tim Andrews, 66, had end-stage kidney disease caused by type 2 diabetes when surgeons at Mass General Brigham transplanted the organ in January 2025.
The case, published in the Lancet medical journal, also marked the first reported transition from a pig kidney transplant to a successful human kidney transplant.
The kidney came from Wilma, a Yucatan miniature pig whose genome had undergone 69 modifications intended to make the organ more compatible with humans and reduce infection risks.
The transplanted kidney began working immediately and allowed Andrews to avoid regular hospital visits for dialysis.
Doctors treated early signs of immune rejection by adjusting his medication, enabling the kidney to continue functioning.
After roughly six months, however, damage developed in the organ’s blood vessels, accompanied by inflammation and eventual failure.
The precise cause remains unclear because doctors found no evidence of antibodies attacking the pig kidney.
The organ was removed in October 2025 after 271 days.
Andrews then underwent dialysis for 82 days before receiving a kidney from a deceased human donor in January 2026, which has functioned well.
The medical team said Andrews’ experience demonstrates how xenotransplantation, the transplantation of organs between species, could potentially serve as a temporary bridge for patients awaiting scarce human organs.
Around 100,000 people in the United States are waiting for kidneys, while approximately 25,000 kidney transplants take place annually.
Researchers nevertheless cautioned that Andrews represents a single case without a comparison group and received intensive specialist care.
No pig viruses or other pig pathogens were detected, and doctors found no new antibodies against human tissue that could have complicated his subsequent transplant.
The team said further clinical trials would be necessary to establish the safety and durability of the approach.