Focus on Arts and Ecology

The first six months after an organ transplant are the riskiest for recipients. 

By Rachel Fieldhouse, 08 September 2025

A 67-year-old US man is still alive more than six months after receiving a kidney from a genetically modified pig. This is the longest a pig organ has survived in a living person. Researchers say the outcome is a landmark case of successful xenotransplantation — the process of transplanting organs from animals to humans.

The recipient, Tim Andrews, had end-stage kidney disease and had been receiving dialysis for more than two years before he underwent the surgery in January. He has been dialysis-free since receiving the kidney. Andrews was one of three patients to receive genetically modified pig kidneys supplied by the biotechnology company eGenesis in Cambridge, Massachusetts, on compassionate grounds.

Reaching six months’ survival is an amazing feat, says Wayne Hawthorne, a transplant surgeon at the University of Sydney in Australia. The first six months is the period of “highest risk for the patient and also the transplant”, he adds. Possible complications include anaemia and graft rejection, when the immune system attacks the new organ. “The six-month time point marks that things have gone extremely well,” Hawthorne says. Reaching 12 months would be another milestone and a “fantastic long-term outcome”, he adds.

Previously, the recipient with longest-surviving genetically modified pig organ was a 53-year-old US woman, Towana Looney, who had a functioning pig kidney for four months and nine days. However, the organ was removed earlier this year because her immune system began to reject it.

Genetically modified

Andrews received a kidney from a pig with three types of genetic modification. One involved the elimination of three antigens to prevent organ rejection; another the addition of seven human genes that reduce inflammation and the risk of bleeding complications. Retroviruses that are found in the pig genome were also deactivated.

Another patient, a 54-year-old man named Bill Stewart, will have survived for three months with a modified pig kidney on 14 September.

Hawthorne says that the fact both patients have survived for so long shows how much progress has been made to improve xenotransplantation. Between the 1960s and 1990s, the survival of people who received transplanted animal organs — including from pigs and chimpanzees — ranged from four minutes up to 70 days1. In recent years, recipients of genetically modified pig organs have typically survived for a couple of months at most.

Although most pig-organ transplants have been performed on compassionate grounds, clinical trials have been approved to test how safe and effective such transplants are. Earlier this year, the US Food and Drug Administration (FDA) approved the first clinical trial for genetically modified pig kidneys, led by United Therapeutics, a biotechnology firm based in Maryland and North Carolina. This week, eGenesis announced that it has received FDA approval to trial its modified pig kidney in up to 33 people aged 50 or older with end-stage kidney disease. The company and OrganOx, a biotechnology company based in Oxford, UK, were also approved to test the safety of transplanting genetically modified pig livers in April.

References

(Sources: Nature)