The patient was able to live with the transplanted pig kidney, which functioned for 271 days. This period is the longest recorded for such a successful transplant.
Tim Andrews reported that this transplant gave him 'hope' and allowed him to avoid months of hospitalization for dialysis—a procedure of renal replacement therapy where a machine removes waste and excess fluid from the blood.
The operation was performed by doctors from Mass General Brigham hospital in Boston, Massachusetts, USA. They claim that their work demonstrates the possibility of using pig organs as a 'bridge' until a human transplant becomes available.
The patient was told that waiting on the list could take about seven years, whereas people can only live about five years on dialysis. Tim told the BBC that the situation was 'very depressing,' but the idea of a pig transplant became a 'light at the end of the tunnel' for him.
Nevertheless, this pig organ eventually failed and was removed. The exact reason remained unclear, as doctors stated there were no signs of an antibody attack on the pig kidney.
After a short period of dialysis, Tim was able to find a human donor. He suffered from end-stage renal failure caused by type 2 diabetes, and his kidneys began to fail. He was 66 years old when he underwent xenotransplantation on January 25, 2025. The results were positive and were published in the specialized journal Lancet.
However, after 271 days, in October, the organ was removed. Tim had been undergoing dialysis for 82 days before receiving a human kidney in January of this year, which is still functioning well.
Doctors and scientists are studying xenotransplantation (the use of organs from other species) due to the shortage of donor organs. Pigs are considered ideal animals for such transplants because their organs are approximately the right size, and experience in raising them has existed for many years.
Leonardo Riella, one of the doctors responsible for Tim's transplant, explained: 'We work hard to bring hope, and we truly believe that xenotransplantation can be an alternative for patients who do not have a living donor, to avoid dialysis and move them toward transplantation.'
However, it is mistaken to assume that one can simply take a pig kidney from a farm and implant it into a human. The human body would immediately recognize the organ as foreign and begin a destructive immune attack.
To make these organs part of the solution, researchers created miniature Yucatan pigs that underwent 69 genetic modifications to 'humanize' their organs. These changes include removing certain characteristics of pig cells that the immune system might recognize and attack, as well as adding human DNA that acts as a camouflage network to help 'hide' the pig tissue, along with additional adjustments deactivating viruses hidden in pig DNA to prevent infections.
In the United States, about 100,000 people are waiting for kidneys, but only 25,000 transplants are performed annually. In Portugal, the waiting list is about 2,000 people, with 525 operations performed in 2025.