Two years ago, Tim Andrews was so exhausted that all he wanted to do was sleep. Diabetes and high blood pressure destroyed his kidneys, and the frequent dialysis treatments that kept him alive by filtering his blood were exhausting. Although only 66 years old, he had no energy or appetite, was too weak to walk, and had suffered two heart attacks.
"I was dying," Andrews said. A kidney transplant could have saved his life, but organs were in short supply. According to the United Network for Organ Sharing, approximately 90,000 people are waiting for a kidney transplant, and an average of 11 people die every day while waiting. And because Andrews' blood type is rare, his chances of receiving a matching human kidney are particularly slim.
So when he heard doctors at the Brigham at Massachusetts General Hospital were transplanting kidneys from genetically modified pigs to patients, he reached out to them.
"I thought, if I'm going to die, I might as well do something for humanity and be a part of this experiment," he said.
On January 25, 2025, Andrews received a genetically modified pig kidney transplant and lived with it for nine months. This year, he became the first known patient to receive a kidney from a human donor following a pig kidney transplant, a landmark achievement described in a paper published in The Lancet on Thursday.
His case provides preliminary evidence for an intriguing concept in transplant medicine: that pig kidneys, while not yet a permanent solution, could serve as a "bridge" to human organ transplants. The pig kidneys come from pigs that have undergone extensive gene editing, some of which are designed to prevent severe organ rejection and some of which are used to inactivate viruses in the pig's genome.
Doctors hope the pig kidneys will serve as a bridge option to keep patients alive while they wait for a human kidney transplant, and to spare them the ordeal of potentially debilitating dialysis.
"Dialysis takes such a toll on our patients that they become too sick to receive a transplant or die while waiting," said lead author Dr. Leonardo Liera, associate director of the Brigham Legoretta Clinical Transplant Tolerance Center at Massachusetts General Hospital.
The idea that pig kidneys could be used in this way is not a given. When researchers first considered the idea, there were concerns that patients who had received pig kidneys might be more likely to reject human kidneys later on.
But Mr. Andrews' experience and that of another patient suggest that "it doesn't seem to change how you respond to human tissue at all," said Mike Curtis, eGenesis president and chief executive. eGenesis is the biotech company that produced the genetically modified pigs used by the Brigham at Massachusetts General Hospital and partially funded the research.
"Currently, we don't see any downside to transplanting a pig kidney and then a human kidney, but we didn't know that would be true when we started this work," Curtis said.
At the Massachusetts General Hospital Brigham, a total of five patients received eGenesis-produced pig kidneys under a U.S. Food and Drug Administration program that allows expanded use for patients with no other treatment options. Three patients, including Andrews, survived with the organs for more than eight months, the company said Thursday. (One patient died from an unexpected cardiac event shortly after transplantation, and the other patient did not receive a transplant until June.)
Andrews' doctors say the nine months he spent with the animal parts were crucial to getting his health back on track. The pig kidney produces urine and removes waste from the body 24 hours a day, seven days a week, while dialysis can only be done through a machine for several hours every other day. His diet improved and his muscle mass returned.
"It gave me life," Andrews said.
Doctors who specialize in kidney disease are often shocked by how painful life on dialysis is in the mouths of their patients. “The message from patients was very shocking to us, saying that life on dialysis is not life at all,” Liela said. "So they're all looking for alternatives, and that's why so many patients are coming forward voluntarily, even though the research is full of unknowns."
The new research is the latest advance in the field of cross-species transplantation, known as xenotransplantation. In recent years, with the advancement of genetic engineering and cloning technology, and the development of new anti-rejection drugs, the field has developed at an alarming rate. The U.S. Food and Drug Administration has allowed these experimental surgeries to be performed under strict supervision.
Dr. Mohammad Mohiuddin, a professor of surgery at the University of Maryland School of Medicine and a pioneer in xenotransplantation, said even he has been impressed by how quickly the field has grown and by the broad support from patients and the public.
Mohiuddin spent decades transplanting pig hearts into baboons before participating in the first operation to transplant a genetically modified pig heart into a human patient in 2022. “I never imagined that I would see this technology used in humans in my lifetime,” he said, adding that “initial progress in nonhuman primates in the laboratory was slow.”
The first recipients of the hearts were so terminally ill that they died shortly after receiving the pig hearts. But just a few years later, in March 2024, surgeons at Massachusetts General Hospital in Boston transplanted the first gene-edited pig kidney into a human patient, Rick Sleiman. Slimane, 62, was discharged from hospital two weeks later, but he suffered from chronic heart disease and died within two months of an apparently unrelated cardiac event.
More work is underway. eGenesis will launch a formal clinical trial involving 33 patients next year. United Therapeutics, another biotech company that produces genetically modified pigs, said in a statement this week that it had launched a clinical trial of pig kidneys in November 2025 and would launch a second trial soon. The company is launching a very small clinical trial of transplanting pig hearts into humans, the statement also said.
Curtis, the eGenesis executive, said that while "transitional" kidneys will prove valuable, the ultimate goal is to develop pig kidneys that can last as long as human transplants.
"Perhaps the first more achievable goal is to make this treatment a transitional treatment, and maybe 10 or 15 years from now we might be talking about an alternative that's as good as a human kidney," Liela said. “We are at the beginning of this journey.”
