A genetically modified pig kidney functioned inside a human patient for a record-breaking 271 days, according to doctors at Mass General Brigham. The milestone offers new insight into xenotransplantation as a potential bridge for patients facing severe organ shortages.
The Historic Transplant Timeline
Tim Andrews, a 66-year-old patient experiencing end-stage kidney disease caused by type 2 diabetes, received the experimental organ on January 25, 2025, according to the Lancet medical journal. The procedure took place at Massachusetts General Hospital, where surgical teams attached the animal organ to the patient’s internal blood vessels to filter waste from his bloodstream.
The kidney functioned immediately after surgery, sparing Andrews months of regular hospital visits for dialysis. According to Mass General Brigham, the organ continued operating for 271 days before failing in October 2025. Following the removal of the pig kidney, Andrews underwent 82 days of dialysis before receiving a human donor kidney in January of this year.
Genetic Modifications and Immune Challenges
Medical researchers utilize Yucatan miniature pigs for xenotransplantation because their organs match human sizing and the animals are widely farmed. However, transplanting unmodified animal tissue into a human triggers an immediate, aggressive immune response that destroys the organ within minutes. To prevent this, the donor kidney used in this case underwent 69 genomic modifications, according to details published in the Lancet.
These laboratory alterations removed specific pig cell features that normally attract human immune attacks, inserted human DNA segments to disguise the tissue, and disabled viruses hidden within the pig genome. Despite these adjustments, doctors observed early signs of rejection that required medication adjustments. After approximately six months, the kidney’s blood vessels sustained damage, leading to inflammation and eventual organ failure, though clinicians noted no specific signs of antibodies attacking the tissue.
Addressing the National Organ Shortage
The demand for viable organs far exceeds the available supply, creating what Dr. Leonardo Riella of the Center for Transplantation Sciences at Mass General Brigham described as a “crisis”. Approximately 100,000 individuals remain on waiting lists for kidney transplants in the United States, while annual transplants total roughly 25,000. In the United Kingdom, more than 7,000 patients wait for a donor match.
For patients like Andrews, who was informed he faced a seven-year wait for a human organ while average survival on dialysis is five years, xenotransplantation represents a viable alternative. Dr. Riella stated that the approach aims to provide an option for patients lacking living donors, potentially bypassing long-term dialysis and bridging the gap until a human transplant becomes available.