Genetically modified pig kidney sustains patient for 271 days as bridge to human transplant

A bridge xenotransplantation

Tim Andrews, a 66-year-old patient from New Hampshire with end-stage renal disease caused by type 2 diabetes, lived for 271 days with a genetically edited pig kidney before successfully receiving a human organ. Prior to the procedure, Andrews had spent two years on dialysis and faced an estimated seven-year wait for a human organ, with doctors giving him only a 9% probability of receiving a deceased donor kidney within five years against a 40% risk of mortality. On 25 January 2025, a surgical team led by Leonardo Riella at Massachusetts General Hospital in Boston transplanted a kidney from a Yucatan miniature pig named Wilma. The organ began producing urine immediately, freeing Andrews from dialysis for nearly nine months.

Genetic modification and medical response

The donor organ was developed by biotech firm eGenesis using Crispr technology to enact 69 distinct genomic modifications. These edits inactivated porcine endogenous retroviruses, eliminated swine surface proteins that trigger human immune attacks, and inserted human genes to provide immunological camouflage. Two weeks after the operation, clinicians detected and treated a mild T-cell mediated rejection episode. Six months into the trial, progressive vascular damage developed in the graft, exacerbated by a tissue blood clot and a subsequent bacterial infection that compelled doctors to reduce immunosuppressive therapies. The organ sustained renal function until its removal in October 2025.

Doctor Leonardo Riella, director of kidney transplantation at Massachusetts General Hospital, framed the procedure as an intermediate bridge therapy.

We know that the best treatment option for patients with end-stage renal disease who have developed kidney failure is transplantation, but we simply do not have enough human organs to perform transplants in time.

Transition to a human kidney

After surgeons removed the animal kidney, Andrews returned to dialysis for 82 days before receiving a kidney from a deceased human donor in January 2026. Medical findings published in The Lancet confirmed that after six months of post-transplant monitoring, the human kidney functioned with no signs of rejection or porcine viral transmission. The 271-day duration surpassed the previous 52-day duration from the first living human xenotransplant in 2024. During his nine months with the pig kidney, Andrews regained physical independence, performing household tasks and walking his dog, Cupcake.

Andrews described the effect of living without dialysis machines during the trial.

Hope is the biggest thing, the chance to be free from the machine and live your life.

The donor organ deficit

The procedure is the first completed clinical bridge from a pig kidney xenotransplant to a successful human organ transplant. In the United States, roughly 100,000 patients remain on kidney waiting lists, while hospitals perform only about 25,000 transplants annually. Comparable deficits affect other regions: 53,343 people waited for donor organs across the European Union in 2025, more than 7,000 wait in the United Kingdom, and Turkey registered 3,299 kidney transplants out of 5,095 total organ procedures in 2025. Following Andrews' procedure, a fifth eGenesis recipient under US Food and Drug Administration expanded-access protocols reached 285 days with a functioning pig kidney as of September 2026.