A genetically modified pig kidney functioned in a US man for 271 days, setting a new record for pig-to-human kidney transplantation and offering fresh hope to patients facing long waits for human donor organs.

The landmark case involved Tim Andrews, a 66-year-old man from New Hampshire with end-stage kidney disease. Surgeons at Massachusetts General Hospital transplanted a kidney from a genetically engineered Yucatan miniature pig into Andrews in January 2025.

The experimental organ enabled Andrews to remain free from dialysis for about nine months, marking the longest documented period a genetically modified pig kidney has functioned in a living human.

The kidney, from a pig named Wilma, underwent 69 genetic modifications designed to make it more compatible with the human body. The alterations were intended to reduce the risk of immune rejection and prevent potentially harmful pig viruses from being transmitted to the recipient.

After functioning for 271 days, the pig kidney began to deteriorate because of damage to its blood vessels. Doctors subsequently removed the organ and Andrews returned to dialysis temporarily.

He later received a human donor kidney, which functioned successfully during follow-up. Researchers found no evidence that his previous exposure to the pig kidney had made the human transplant more difficult.

The case is particularly significant because it represents the first reported use of a genetically modified pig kidney as a temporary “bridge” to a human kidney transplant.

Dr Leonardo Riella of Massachusetts General Hospital said xenotransplantation could initially provide patients with an alternative to prolonged dialysis while they wait for a suitable human organ.

The breakthrough comes as demand for kidney transplants continues to far exceed the supply of donated human organs. Researchers have therefore been investigating genetically modified animal organs as a potential additional source for transplantation.

Pigs are considered promising because their organs are similar in size and function to human organs. Advances in gene editing have allowed scientists to remove genes associated with immune rejection, introduce human genes to improve compatibility and deactivate viruses that could pose risks to recipients.

However, specialists caution that the development remains experimental. Andrews’ experience involved a single patient and intensive specialist care, meaning the results cannot yet establish that pig kidneys are safe and effective for widespread use.

Further clinical trials will be necessary to determine how long the organs can function, how patients respond over the long term and whether the procedure can eventually become a routine treatment.

The progress nevertheless marks an important step in xenotransplantation the use of animal organs in human and could eventually help address the shortage of donor kidneys that leaves many patients dependent on dialysis while waiting for a transplant.