Two years ago, Tim Andrews was so worn out that all he wanted to do was sleep. Diabetes and high blood pressure had destroyed his kidneys, and the frequent dialysis treatments that kept him alive by filtering his blood were grueling. Though only 66, he had no energy or appetite, was too weak to walk and had experienced two heart attacks.
“I was dying,” Mr. Andrews said. A kidney transplant could have saved his life, but the organs are in short supply. Roughly 90,000 people are on the waiting list for a kidney transplant, and on average, 11 people die every day while waiting for one, according to United Network for Organ Sharing. And his rare blood type meant that Mr. Andrews’ odds of getting a matching human kidney were especially slim.
So when he heard that doctors at Mass General Brigham were transplanting patients with kidneys from genetically modified pigs, he reached out.
“I figured, if I’m going to die, I might as well do something for humanity and be part of this experiment,” he said.
Mr. Andrews received a genetically modified pig kidney on Jan. 25, 2025, and lived with it for nine months. This year, he became the first known patient to receive a human donor kidney after a pig kidney transplant, a milestone described in a paper published Thursday in The Lancet.
His case provides early proof of an intriguing concept in transplant medicine: that pig kidneys, while not yet a permanent solution, could offer “bridges” to transplants with human organs. The kidneys come from pigs that have undergone numerous genetic edits, including some designed to prevent a severe organ rejection response and others to inactivate viruses in the pig genome.
By using the pig kidneys as a stopgap, doctors hope to keep patients alive while they make their way up the waiting list for a human kidney, and to provide a respite from dialysis, which can be debilitating.
“Dialysis causes so much wear and tear on our patients that they become too sick to get a transplant, or die while waiting,” said Dr. Leonardo V. Riella, the paper’s lead author and associate director of the Legorreta Center for Clinical Transplant Tolerance at Mass General Brigham.
The idea that pig kidneys could be used this way wasn’t a given. When researchers first considered the idea, there was a concern that patients who had received a pig kidney might become more prone to rejecting a human kidney later.
But Mr. Andrews’s experience, along with that of one other patient, suggests that “it doesn’t seem to change how you react to human tissue at all,” said Mike Curtis, president and chief executive at eGenesis, the biotechnology company that produces the genetically modified pigs used at Mass General Brigham and helped fund the study.
“Right now, we don’t think there’s any downside of having a pig kidney followed by a human kidney, but when we started this, we had no idea that that would be true,” Dr. Curtis said.
Altogether, five patients at Mass General Brigham have received pig kidneys produced by eGenesis under a Food and Drug Administration program allowing expanded access for patients who have no other treatment options. Three, including Mr. Andrews, lived with the organs for more than eight months, the company said Thursday. (One patient died of an unexpected cardiac event shortly after transplantation, and one patient was transplanted only in June.)
The nine months Mr. Andrews spent with the animal organ were critical to getting his health back on track, his doctors said. The pig’s kidney made urine and cleared waste from his body 24 hours a day, seven days a week, doing what dialysis does by machine only every other day, during hourslong sessions. His diet improved, and he regained muscle mass.
“It gave me life,” Mr. Andrews said.
Doctors who specialize in kidney disease are often struck by how miserable patients say they are on dialysis. “The message from patients — and it was very shocking for us — is that life on dialysis is no life,” Dr. Riella said. “So they’re all looking for that alternative, which is why so many patients have volunteered and stepped forward, even with all the unknowns of research.”
The new research is the latest advance in the field of cross-species transplantation, or xenotransplantation, which has progressed at a remarkable pace in recent years, with advances in genetic engineering and cloning and the development of new anti-rejection drugs. The F.D.A. has allowed the experimental procedures under strict oversight.
Dr. Muhammad Mohiuddin, a professor of surgery at the University of Maryland School of Medicine and a pioneer in xenotransplantation, said even he was impressed by the speed of development and the support among patients and the public generally.
Dr. Mohiuddin spent decades putting pig hearts into baboons before being involved in the first transplant of a genetically modified pig’s heart into a human patient in 2022. “I never imagined in my lifetime that I would see the human translation of this,” he said, adding, “The initial progress with nonhuman primates in the lab was slow.”
The first heart recipients had very advanced disease and died shortly after receiving the pig hearts. But just a few years later, in March 2024, surgeons at Mass General in Boston transplanted the first kidney from a gene-edited pig into a human patient, Rick Slayman. Mr. Slayman, 62, was discharged from the hospital two weeks later, but he had a chronic heart condition and died within two months of an apparently unrelated cardiac event.
More work is ongoing. EGenesis is starting a formal clinical trial next year with 33 patients. Another biotechnology company that produces genetically modified pigs, United Therapeutics Corporation, began a clinical trial of its kidneys in November 2025 and will soon start a second trial, it said in a statement this week. It is also starting a very small clinical trial of pig heart transplants to humans, the statement said.
Dr. Curtis, the eGenesis executive, said that while “bridge” kidneys would prove valuable, the ultimate goal was to develop pig kidneys that could last as long as human transplants.
“Maybe the first more reachable goal is for this treatment to be a bridge, and maybe 10 or 15 years from now, we may be talking about an alternative as good as human kidneys,” Dr. Riella said. “We’re at the beginning of the journey.”
Mr. Andrews had to be hospitalized several times while he had the pig kidney, and ultimately it had to be removed after blood clots formed in the organ’s vessels and damaged it. He resumed dialysis briefly, and in January he received a human kidney from a matching donor.
Although he has had some health problems since, he said he was fitter than he had been in years and was back to living much of the year in a cabin by a pond. He swims and kayaks in the pond and takes short bike rides, and his appetite — dampened during dialysis — is back.
“I went from thinking I had months, maybe a year, because I just felt so bad,” he said of his time on dialysis. But his transplants have changed the way he looks at life, he said. “When you say ‘stop and smell the roses,’ that’s my life now. I look at everything and go ‘wow.’”
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