For the first time, a person has lived nine months with a genetically modified pig kidney before receiving a successful human organ transplant. Published in The Lancet, the case adds evidence to efforts to address the global shortage of donor organs.
Tim Andrews, 66, underwent the experimental surgery at Massachusetts General Hospital in Boston on January 25, 2025. The kidney came from a Yucatan minipig and was altered with about 69 genetic changes to help it function in a human body and reduce the risk of rejection. It worked for 271 days, longer than any previous animal-to-human kidney transplant. During that time, Andrews was able to stop dialysis for the first time in two years and regain some independence that standard treatments could not provide.
The medical team, led by Leonardo Riella, faced several complications. Initially, the kidney worked well, producing urine immediately and filtering up to five liters a day. But within weeks, Andrews’ immune system attacked the organ, forcing doctors to increase his immunosuppressive drugs. Later, a bacterial infection led them to reduce the drugs, triggering another round of rejection, this time from innate immune cells rather than antibodies. Blood clots and inflammation eventually damaged the kidney beyond repair. Doctors removed it after nearly nine months.
A little over two months after the pig kidney was removed, Andrews received a human kidney from a deceased donor, 82 days after returning to dialysis. The new organ began working immediately. Seven months later, there were no signs that his body had developed immune problems from the earlier animal transplant. Researchers describe the case as the first successful “bridge-to-human-transplant,” in which an animal organ serves as a temporary solution until a human donor becomes available. The Lancet reported that 231 days after the human transplant, there was still no sign of immune sensitization, which could have made the second transplant more difficult. The case also points to ongoing challenges, including immune rejection and vascular injury.
Europe and the United States both face a severe shortage of donor organs. In 2025, more than 53,000 people were on transplant waiting lists in the EU, and over 100,000 in the US. Dialysis can keep people alive, but it does not fully replace kidney function and often reduces quality of life. The search for alternatives has driven decades of research into xenotransplantation. Until now, animal organs rarely lasted more than a few weeks or months in humans.
Gene-editing tools like CRISPR have changed what is possible. eGenesis engineered the pig in Andrews’ case to reduce immune rejection and remove viral risks. Human genes were added to help control inflammation and clotting, while pig retroviruses were deactivated to prevent infection. These changes helped the kidney function longer than in any previous attempt, but also exposed new problems, especially the role of innate immune cells in late-stage rejection.
Spanish transplant specialists, including Beatriz Domínguez-Gil and Pablo Ramírez, called the case an impressive step but stressed that it remains experimental. Only one patient was involved, and the immune response, particularly the activity of natural killer cells, needs further study. Future research will focus on improved immunosuppression and additional genetic changes to protect transplanted organs over time.
Tim Andrews’ story stands out from transplant headlines that often focus on tragedy, such as the recent case in Valencia. Using animal organs as a temporary bridge could change the outlook for thousands waiting for transplants, offering hope where there was none.
This advance does not eliminate the risks or resolve the ethical questions surrounding xenotransplantation. It shows that careful genetic engineering and clinical management can keep a person alive with an animal organ long enough to reach a human donor. The field remains experimental, but transplant medicine’s boundaries are shifting, bringing what was once thought impossible within reach.
