A 66-year-old man in the United States has lived for nine months with a genetically modified pig kidney, marking a significant milestone in xenotransplantation. The procedure, performed in January 2025, allowed Tim Andrews, who suffered from end-stage kidney disease caused by type 2 diabetes, to remain off dialysis for 271 days before transitioning to short-term dialysis and ultimately receiving a human donor kidney.
The kidney, sourced from a genetically engineered Yucatan miniature pig, was designed to be compatible with the human immune system. It began functioning immediately after transplantation, serving as a temporary “bridge” while Andrews waited for a human organ. This case represents the longest survival period without dialysis following a pig kidney transplant in a living human as well as the first documented transition from a pig kidney to a human donor kidney.
The research team behind the transplant, based at Mass General Brigham academic centers and hospitals, detailed their findings in the medical journal The Lancet. Lead author and nephrologist Dr. Leonardo Riella emphasized the critical shortage of human organs for transplantation as a motivating factor for exploring xenotransplantation. He noted that while human kidney transplants remain the best treatment for patients with renal failure, available organs are insufficient to meet demand. The team envisions that genetically modified animal organs could initially serve as temporary solutions to reduce dialysis dependency and, with further advancements, potentially become long-term alternatives.
Experts from other countries have acknowledged similar developments. Dr. Rommel Ravanan, chief medical officer at Britain’s National Health Service Blood and Transplant, highlighted progress reported in the US and China since 2022, attributing breakthroughs to advances in genetic technology. Tools such as CRISPR have enabled scientists to deactivate specific pig genes that would otherwise trigger rejection by the human immune system. Pigs are preferred donors because their organ size and anatomy closely resemble those of humans. However, Dr. Ravanan cautioned that, despite promising results, xenotransplantation remains far from routine clinical use.
Although the pig kidney initially functioned well, it began to show signs of vascular damage after approximately six months, eventually leading to organ failure and removal. Importantly, tests did not detect any pig viruses or other pathogens throughout the process.
Andrews described his experience as a “miracle” in a documentary, expressing gratitude for the extended period without the severe limitations imposed by kidney failure. Dr. Riella acknowledged the pioneering role of patients like Andrews, whose willingness to participate in early-stage studies is crucial for advancing the field of transplantation science.