A 66-year-old man lived 271 days with a genetically modified pig kidney. The case marks a breakthrough in transplant medicine and highlights the urgent search for solutions to organ shortages.
For the first time, a person has lived nine months with a genetically modified pig kidney before receiving a successful human organ transplant. The case, published in The Lancet, marks a new chapter in the ongoing effort 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 work in a human body and lower the risk of rejection. The organ functioned for 271 days—longer than any previous animal-to-human kidney transplant. During this time, Andrews was able to stop dialysis for the first time in two years and regained some independence that standard treatments could not provide.
After the pig kidney was removed, Andrews spent 82 days back on dialysis before receiving a human kidney from a deceased donor, which began functioning immediately.
The medical team, led by Leonardo Riella, faced several complications. At first, the kidney worked well, producing urine right away and filtering up to five liters a day. But within weeks, Andrews’ immune system attacked the organ, and doctors had to increase immunosuppressive drugs. Later, a bacterial infection forced them to reduce these drugs, which led to a new round of rejection—this time from innate immune cells rather than antibodies. Eventually, blood clots and inflammation damaged the kidney beyond repair, and it was removed after nearly nine months.
What happened next was just as notable. A little over two months after the pig kidney was removed, Andrews received a human kidney from a deceased donor. The new organ started working immediately, and seven months later, there were no signs that his body had developed immune problems from the earlier animal transplant. This use of an animal organ as a temporary bridge to a human transplant had never lasted this long or ended with such a positive outcome. According to The Lancet, 231 days after the human transplant, there was still no sign of immune sensitization, which could have made the second transplant more difficult.
Both Europe and the United States 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 does not fully replace kidney function and often reduces quality of life. The search for alternatives has driven decades of research into xenotransplantation, but until now, animal organs rarely lasted more than a few weeks or months in humans.
Researchers describe this as the first successful "bridge-to-human-transplant"—using an animal organ as a temporary solution until a human donor becomes available. The case highlights both the potential of xenotransplantation and the ongoing challenges, such as immune rejection and vascular injury, that must be addressed before wider clinical use.
Gene editing tools like CRISPR have changed what is possible. The pig in Andrews’ case was engineered by eGenesis to reduce immune rejection and remove viral risks. Human genes were added to help control inflammation and clotting, and pig retroviruses were deactivated to prevent infection. These changes allowed the kidney to function longer than any previous attempt, but also revealed 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 important step but stressed that it is still experimental. Only one patient was involved, and the details of the immune response—especially the activity of natural killer cells—need more study. Future research will focus on better immunosuppression and further genetic changes to protect transplanted organs over time.
Tim Andrews’ story stands out from the usual transplant headlines, which often focus on tragedy—like the recent case in Valencia. The ability to use 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 remove the risks or answer the ethical questions around xenotransplantation. But it does show that with careful genetic engineering and clinical management, animal organs can keep a person alive long enough to reach a human donor. The field is still experimental, but the boundaries of transplant medicine are shifting, and what was once thought impossible is now within reach.
