WASHINGTON — An individual who identifies as a science enthusiast has recently become the latest American to receive an experimental pig kidney transplant. This marks a pivotal moment in the ongoing exploration to determine if animal organs could be a viable option to save human lives.

The 54-year-old New Hampshire man is faring well after his June 14 operation, doctors at Massachusetts General Hospital announced Monday.

“I really wanted to contribute to the science of it,” Bill Stewart, an athletic trainer from Dover, New Hampshire, told The Associated Press.

Additionally, the team at Mass General celebrates another significant milestone: a pig kidney has sustained another individual from New Hampshire, Tim Andrews, without the need for dialysis for an impressive seven months and counting. This sets a new record as the previous longest duration for a gene-edited pig organ transplant was 130 days.

Drawing from the experiences of the New Hampshire patients and other isolated experimental attempts, the Food and Drug Administration has given its approval for pig producer eGenesis to commence a detailed study of kidney xenotransplants.

“Currently, we’re facing a scarcity,” noted Dr. Leonardo Riella, a kidney expert at Mass General who will contribute to leading the upcoming clinical trial.

There are over 100,000 individuals on the U.S. transplant waiting list, the majority of whom require a kidney, and thousands perish while waiting. To address this issue, scientists are genetically modifying pigs to make their organs more compatible with humans and less prone to immediate rejection by the human immune system.

The initial trials, involving two hearts and two kidneys, yielded short-term results and were conducted on severely ill patients. Meanwhile, Chinese scientists have also revealed a kidney xenotransplant, though limited details were shared. An unfortunate case in Alabama, where a pig kidney lasted 130 days before rejection led to its removal, forcing the recipient back to dialysis, prompted researchers to focus on patients who are not critically ill.

In New Hampshire, high blood pressure caused Stewart’s kidneys to fail but he had no other health problems. It can take up to seven years for people with his blood type to find a matching kidney from a deceased donor, and some would-be living donors didn’t qualify. After two years in dialysis, he heard about Mass General’s most recent xenotransplant recipient – Andrews – and applied to be the next candidate.

“I’ve always been a little bit of a science nerd,” Stewart said. Conscious of how new these experiments are, he sought out Andrews for advice and ultimately decided, “worst case scenario, they can always take it out.”

Thrilled to no longer have his time and energy sapped by dialysis, Stewart said he’s easing back into desk duties at work and visited his old dialysis clinic to “let everyone know I’m doing all right and maybe kind of give some people some hope.”

Riella, the kidney specialist, said Stewart had his anti-rejection drugs adjusted to counter an early concern and that Andrews has needed similar adjustments. He said it’s far too early to predict how long pig kidneys might be able to last – but it would be useful even if initially they can buy people time off dialysis until they get a matching human organ.

“A year, hopefully longer than that – that’s already a huge advantage,” he said.

The new eGenesis trial will provide gene-edited pig kidney transplants to 30 people age 50 or older who are on dialysis and the transplant list. Another developer of gene-edited pig organs, United Therapeutics, is about to start enrolling people in a similar FDA-approved study.

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The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Department of Science Education and the Robert Wood Johnson Foundation. The AP is solely responsible for all content.