Tim Andrews, a 66-year-old patient suffering from end-stage kidney disease due to diabetes and high blood pressure, received a genetically modified pig kidney in January 2025, marking a significant advancement in the field of xenotransplantation. The procedure, conducted at Mass General Brigham in Boston, kept him alive for nine months until he was able to receive a human kidney transplant this January, making him the first person known to have undergone such a two-step transplant process.
Andrews faced severe health challenges prior to the pig kidney transplant, including weakness, loss of appetite, and two heart attacks. His rare blood type further complicated the search for a suitable human donor organ, a problem shared by thousands on the kidney transplant waiting list. According to the United Network for Organ Sharing, roughly 90,000 people in the United States await kidney transplants, with an average of 11 deaths daily among those on the list.
The pig kidney Andrews received was sourced from genetically engineered pigs, which underwent multiple genetic alterations to reduce the risk of rejection and eliminate potentially harmful viruses in the pig genome. These modifications aim to improve compatibility and safety for human recipients.
“We were concerned initially that receiving a pig kidney could influence the patient’s immune response to future human transplants,” said Mike Curtis, president and CEO of eGenesis, the biotechnology company that supplied the pig kidneys used in the trial. However, Andrews’s case, along with that of another patient, indicates that the xenotransplant did not adversely affect the acceptance of a subsequent human organ.
Five patients at Mass General Brigham have received pig kidneys under a Food and Drug Administration expanded access program designed for those with no other treatment options. Among these, three— including Andrews— maintained the animal kidneys for more than eight months. One patient died unexpectedly shortly after transplantation, and another received a transplant only recently in June.
According to Dr. Leonardo V. Riella, associate director of the Legorreta Center for Clinical Transplant Tolerance at Mass General Brigham and lead author of a recent study published in The Lancet, the pig kidney acted as a “bridge” while Andrews awaited a human organ. Unlike dialysis, which is intermittent, the transplanted pig kidney enabled continuous filtration of waste and urine production, improving his overall health, dietary intake, and muscle strength.
Andrews did experience complications, including blood clots that damaged the pig kidney, necessitating its removal and a temporary return to dialysis before the human kidney transplant. Despite some subsequent health issues, he has regained strength and enjoys outdoor activities such as swimming, kayaking, and biking.
The success of these initial cases has prompted eGenesis to plan a formal clinical trial of 33 patients next year. Separately, United Therapeutics Corporation, another company working on genetically modified pig organs, initiated a clinical trial of pig kidney transplants in November 2025, with a second trial forthcoming, as well as a small pilot trial involving pig heart transplants.
While the current focus is on using pig kidneys as temporary “bridges” to human transplantation, researchers hope that in the coming decade or so, genetically modified pig organs could serve as long-term alternatives to human donor organs, potentially alleviating the shortage of kidneys available for transplant. Dr. Riella described the progress as “the beginning of the journey” toward that goal.