A 62-year-old man just received the world's first pig kidney transplant. Why experts say animal organs could 'turn medicine on its ear.'

For the first time, a genetically modified pig kidney has been transplanted into a 62-year-old man by surgeons at Massachusetts General Hospital, the facility announced Thursday. Transplanting animal organs into humans is becoming more common, but these procedures remain rare and have yet to significantly extend patients’ lives. Amid an ongoing organ shortage, experts say animal organs could be game-changing, but the challenges are steep and many. Here’s what to know.

What happened in the latest animal organ transplant?

The pig kidney was transplanted into Richard Slayman, who has end-stage kidney disease, during a four-hour surgery that took place on Saturday, according to MGH. Without a transplant, most patients with kidney disease like Slayman’s would need daily dialysis treatments to remove waste that failing kidneys no longer can. Even with this burdensome treatment, the average life expectancy is only five to 10 years, though many patients can survive for up to 30 years, according to the National Kidney Foundation.

Although it wasn’t noted whether Slayman could receive dialysis, experts tell Yahoo Life that he likely couldn’t, because the experimental transplant would need to be no more dangerous than regular care in order to be approved by the Food and Drug Administration.

Since he received the kidney, Slayman’s health has been improving, and the kidney is already producing urine, an encouraging sign that the organ is working and has been accepted by the man’s body.

This is the first time a live person has received a genetically edited pig kidney. Gene editing was used to remove bits of pig DNA that might be harmful to humans and make the organ more compatible with a human body, as well as inactivate retroviruses (the equivalent of “killing” a virus) that are part of a pig’s genome. The latter is important for safe transplantation because patients receiving a new organ have to take immune-system-suppressing drugs to prevent their bodies from rejecting the organ, but these lifesaving medications also make them extremely vulnerable to infection.

This isn’t the first time an animal organ has been transplanted into a human

The transplantation of animal organs into humans — known as xenotransplantation — has a long history. Scientists have been trying to transplant animal organs into humans for nearly two centuries. The first known attempt was made in 1838, when a pig cornea was transplanted into a human’s eye (unsuccessfully). It wasn’t attempted again for more than 50 years.

But xenotransplantation has come a long way and become much more common since the 19th century. It’s now quite common for cow or pig heart valves to be used as replacements for faulty human ones. Slayman, however, is only the third living person to receive a xenotransplant of an entire organ. Other xenotransplantations include:

• David Bennett: In January 2022, Bennett received the world’s first transplant of a genetically modified pig heart, at age 57. He did remarkably well for seven weeks after the surgery, which was performed by researchers at the University of Maryland, with his cardiac health improving and no clear signs that his body was rejecting the organ. But after two months, he died of sudden heart failure. Scientists are studying his case in the hopes of understanding what went wrong, what went right and how to improve the procedure.

• Lawrence Faucette: Faucette became the second person to ever receive a genetically modified pig heart — also transplanted by University of Maryland surgeons — in September 2023. He suffered from end-stage heart disease and wasn’t eligible for a human heart transplant due to internal bleeding. He lived for nearly six weeks before he began to show signs of organ rejection and ultimately died at age 58.

• Transplants into brain-dead patients: Before attempting transplants into living recipients, doctors have tested animal organ transplants into the bodies of patients who were brain-dead, with the consent of their families. Researchers at NYU Langone Health transplanted genetically modified pig hearts into two brain-dead patients in 2022. NYU also transplanted a modified pig kidney into a patient experiencing brain death in July 2023; it functioned for two months. Three such pig kidney transplants were done at the University of Alabama at Birmingham. In China earlier this month, scientists transplanted a genetically modified pig liver into a brain-dead patient for the first time. The liver remained in the body for 10 days without evidence of major issues before being removed as planned, according to an article in Nature.

What an expert says

“This is a really important and significant event,” Dr. Bartley Griffith, a cardiothoracic surgeon and vice chair for innovation at the University of Maryland School of Medicine, tells Yahoo Life. Griffith, who performed the world’s first transplantation of a genetically modified pig heart on Bennett, emphasized that the pig kidney transplant’s importance stretches far beyond a single patient. “The potential power of having an organ you can ‘dial up’ for everyone who needs one is just incredible.”

More than 100,000 Americans are on transplantation lists, and 17 die waiting for new organs each day, according to Organdonor.gov. Only people who meet sometimes stringent requirements receive transplants, and they have to be carefully matched with donor organs for things such as body size and blood type. There also aren’t enough organ donors in the U.S. Transplanted animal organs could change that.

“The reason we’re in this game is that there are so many people who might not get a chance at a transplant,” says Griffith, like people who would like to live long enough to see their grandchildren grow up but are currently considered too old to have good odds of a successful transplant.

Pig organs like the kidney transplanted on March 16 are harvested from cloned animals (which are “treated like kings and queens” and euthanized humanely after living comfortable lives, according to Griffith), which are genetically modified to have organs compatible with humans. Their DNA could potentially be further modified to be ideally matched to their intended recipients, Griffith notes. It could also considerably streamline the transplantation process, which currently is often unpredictable and happens at a moment’s notice when a matching organ becomes available.

“Imagine the empowerment for quality of life, let alone longevity, if you could make an appointment with your doctor and have the pig kidney transplant ready at the day of the appointment,” akin to the routine process for a hip replacement, says Griffith. “That would turn medicine on its ear.” He believes patients who receive xenotransplants might have survival rates that rival human organ transplants in as little as 15 years.

However, when it comes to these experimental transplants, “we don’t know if it’s going to work for a long time, but we guarantee we’re going to learn a lot,” says Griffith. He notes that these kinds of transplants are approved only for patients who have no better options, and that patients and their families are aware of the risks, as well as of their contributions to medicine.

“We promise patients that if they don’t survive, we will continue to learn from the experience and make a better one for the next patient who chooses to undergo this experiment,” Griffith says.