Richard "Rick" Slayman, 62, underwent the four-hour transplant at a hospital in Boston in March.

It marked the first time a genetically modified pig kidney was transplanted into a living patient. Surgeons said they believed the organ would last for at least two years.

Slayman's family announced his death yesterday, thanking the doctors who carried out the world-first surgery for their "enormous efforts".

They said the animal-to-human transplant - known as a xenotransplant - gave them "seven more weeks with Rick, and our memories made during that time will remain in our minds and hearts".

The transplant team at Massachusetts General Hospital (MGH) said they did not have any indication he died as a result of the transplant.

Slayman, from Weymouth, Massachusetts, previously had a kidney transplant at MGH in 2018, but had to go back on dialysis last year after it showed signs of failure.

As he needed frequent procedures as a result of dialysis complications, his doctors suggested a pig kidney transplant.

His family said Slayman wanted to undergo the procedure to give hope to those on waiting lists for transplants, adding: "Rick accomplished that goal and his hope and optimism will endure forever."

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Pig kidneys had previously been transplanted into brain-dead donors, but only temporarily. Two men have also received hearts from pigs, with both dying within months of their prodecures.

A month after Slayman's transplant, New Jersey's Lisa Pisano became the second person in the world to undergo a pig kidney transplant, and the first to have surgery while also having a mechanical heart pump surgically implanted.

The 54-year-old said she "took a chance" after suffering heart and kidney failure, which left her too ill to qualify for a traditional transplant.

More than 100,000 people are on the transplant waiting list in the US - most need a kidney, but thousands die waiting.

In the UK, the NHS said that in the year to March last year, there were 6,959 patients waiting for an organ transplant.

It said 439 patients died while on the active list waiting for it and a further 732 were removed from the transplant list, "mostly as a result of deteriorating health and ineligibility for transplant".