The second person ever has received a transplant with a genetically modified pig kidney.
Tim Andrews, a 66-year-old who lives in Concord, N.H., has end-stage kidney disease and had been on dialysis for more than two years to compensate for his failing kidney function. He received the pig kidney at Massachusetts General Hospital on Jan. 25. as part of a new study authorized by the U.S. Food and Drug Administration (FDA), which will include a total of three patients.
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Andrews was discharged on Feb. 1 and is staying in the Boston area for follow-up before returning home. Doctors say the transplanted pig kidney is functioning normally and producing urine.
The hope is that pig kidneys could help ease the organ-shortage problem in the U.S. According to the transplant team, Andrews had just a 9% chance of receiving a human kidney in the next five years, and a nearly 50% chance of being removed from the transplant wait list because of his deteriorating health. His dialysis left him unable to continue with many of his usually activities, and he had a heart attack in 2023. As of last September, nearly 90,000 people were waiting for a kidney, and in 2023, just over 27,000 transplants were performed—revealing the gap between demand and supply that xenotransplants, or animal-to-human transplants, could address.
How pig kidneys can work in humans
The challenge with this type of transplant is that the human body often rejects foreign tissue. Andrews’ pig kidney is possible because of several new genetic advances including cloning and the gene-editing platform CRISPR, which allowed scientists to modify the organ to make it more compatible with the human immune system. The company that created the the kidney, eGenesis, removed three major pig proteins on the organ, introduced seven human genes to reduce the chances it would be rejected, and disabled certain viruses in the pig genome that would have been harmful to the patient.
This process has been done once before. Richard Slayman, who was 62 at the time of his transplant in March 2024, recovered well, but died two months later due to causes unrelated to the kidney, according to his doctors.
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With Andrews, “it’s the exact same kidney and the same genetic [modifications] that Mr. Slayman received,” says Michael Curtis, CEO of eGenesis. “We learned enough from Mr. Slayman to say it looks good enough, and the data are compelling enough that we should absolutely try again.”
There is one major change, however, from Slayman’s case. The surgical team, in consultation with the FDA, decided to operate on a patient with less-severe end-stage kidney disease. While Slayman had been on dialysis for eight years and had had a kidney transplant and heart disease, Andrews had only been on dialysis for two years and has a stronger cardiovascular system. That may lead to better outcomes for Andrews and give doctors more insights about who is a good transplant candidate: someone with severe enough kidney disease, but who isn’t too ill that they can’t benefit from the transplant.
“Xenotransplant represents a turning point by eliminating organ shortage as a barrier to transplant,” said Dr. Leonardo Riella, medical director for kidney transplantation at Massachusetts General Hospital, at a press briefing. “It offers a solution far superior to dialysis.”
Just as Slayman did, Andrews also received an experimental drug called tegoprubart to suppress his immune system and increase the chances that the pig kidney would not be rejected. Developed by Eledon Pharmaceuticals, the drug is being studied in several trials involving human kidney transplants.
Next step: clinical trials
eGenesis isn’t the only company developing pig organs for human transplant. In February, the FDA approved the first large trial of pig kidneys in people, conducted by United Therapeutics, which also modifies pig organs to make them more compatible for humans. The trial will ultimately involve 50 patients, if the first few do well after 12 weeks.
Curtis says that the encouraging results from the first two pig-kidney patients, Slayman and Andrews, are leading to discussions about other animal organs that could be transplanted, including pig hearts. Results from baboons that have received genetically modified pig hearts are so far “impressive,” he says. While the company and transplant surgeons initially planned on using pig hearts as a bridge for patients waiting for human hearts—for anywhere from 100-200 days—the baboons have survived for more than 500 days. “The results suggest that maybe we can do destination transplants and don’t have to go through bridge,” says Curtis. But more studies will be needed before that’s clear.
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For now, Andrews’ transplant team will monitor his health closely; his progress will determine when and whether the next two patients in the trial receive pig kidneys.
“The first time I saw Tim in the clinic, he was frail and struggling with complications from diabetes,” Riello said at the press conference. “Dialysis was taking a severe toll on his body, and his path to transplant [with a human kidney] was not certain.” But when Andrews was discharged, he walked out of the hospital on his own, holding his wife’s hand.
“Tim’s journey is more than one patient’s success,” Riello said. “It represents hope for the millions suffering from kidney failure, and brings us one step closer to making xenotransplant a viable, widespread solution for the organ shortage crisis.”