Surgeons have successfully transplanted a genetically modified pig heart into a human for the second time. The recipient, a 58-year-old man with terminal heart disease, is breathing on his own, and his new heart is functioning without any mechanical support.

On 20 September, Bartley Griffith at the University of Maryland and his colleagues performed the surgery on Lawrence Faucette, who was ineligible for a transplant with a human heart due to a pre-existing vascular disease and complications with internal bleeding. The pig heart transplant was the only option for Faucette, who would have otherwise died from heart failure, according to the surgery team.

“We are once again offering a dying patient a shot at a longer life,” said Griffith in a statement. “We are hopeful that he will get home soon to enjoy more time with his wife and the rest of his loving family.”

The first pig-to-human heart transplant occurred in January 2022. The recipient, David Bennett, died two months later, potentially due to a pig virus called porcine cytomegalovirus. As a result, researchers have developed more sensitive tests to screen donor organs for the virus. Hospital officials told the New York Times those tests were done on the pig heart used in Faucette’s operation.

One of the main concerns with xenotransplantation – the transfer of animal organs to humans – is transplant rejection. This is when the immune system attacks the organ, eventually causing organ failure. The heart Faucette received came from a pig with 10 genetic modifications that reduce the likelihood of rejection. His doctors are also treating him with a novel medication that blocks a protein involved in activating immune responses.

“This transplant is another remarkable achievement for medicine and humanity,” said Bert O’Malley at the University of Maryland in a statement. “We are immensely proud to have taken another significant leap toward a day when people who need a life-saving organ transplant can get one.”

Xenotransplantation is a promising solution to the shortage of donor organs. Nearly 105,000 people in the US are waiting for an organ transplant, and every day 17 of them die, according to the US Health Resources and Services Administration. Researchers in the field are hopeful that the US Food and Drug Administration will approve clinical trials of xenotransplantation within the next few years.