Doctors say they’re ‘measurably closer’ to making pig kidneys work for humans
By Jen Christensen, CNN
(CNN) — Doctors at New York University say two new studies show that they are a significant step closer to making kidney transplants from other species a real option in the near future.
Scientists have been searching for years for an alternative to human transplants because the donor supply cannot keep up with demand, particularly where kidneys are concerned.
More than 90,000 people in the US are waiting for a kidney transplant, and about 11 of them die every day, according to UNOS, the nonprofit that manages the nation’s organ donation system. But with an aging population and the rise in conditions like diabetes, high blood pressure and obesity, the need will only grow.
Dialysis can keep a person with end-stage kidney disease alive, but the process can be hard on the body and can typically sustain someone for only about five years, on average.
In the search for an alternative, scientists have been turning to cross-species organ transplants, called xenotransplantation.
One of the biggest hurdles they have to overcome is the body’s tendency to reject an organ transplant. New studies published Thursday in the journal Nature offer more information on how to prevent the body from rejecting the pig kidney, and the researchers say they think they’ve had a breakthrough in understanding how the immune system handles these kinds of transplants.
The rejection issue
The human immune system protects the body from threats like fungus or bacteria, but it can sometimes be a little overprotective.
The immune system cannot distinguish between a bad foreign object that enters the body, like a virus, and a good one, like a donor organ. When either is introduced, the immune system goes into full protection mode, sending antibodies to attack whatever it identifies as the problem. Those antibodies can damage the donor organ and ultimately make a transplant fail.
Even with human-to-human transplants, rejection is a big concern. For the rest of their lives, recipients must take powerful anti-rejection drugs that suppress the immune system. When the donor is a pig, scientists also genetically alter the organ to make it more compatible with the human body.
The new studies aimed to take the closest look possible at how the human body rejects a pig organ.
Doctors at NYU transplanted an organ from a genetically modified pig into a person who was brain-dead: Maurice Miller, 57, who died from a mass in his brain in July 2023.
The doctors said Miller had always wanted to donate his organs but could not do so because he had cancer. Instead, they asked Miller’s family if they would donate his entire body to research.
The researchers thought an organ transplant into a brain-dead person would allow them to test tissue samples and blood in ways that would be too intrusive with a living recipient or even with a non-human primate, said study co-author Dr. Robert Montgomery, chief of the New York University Langone Transplant Institute.
“This decedent might be the most highly studied human in history,” Montgomery said of Miller.
The doctors removed Miller’s own kidneys and transplanted a genetically modified kidney from a specially bred pig from the biotech company Revivicor. Miller’s body was kept alive on a ventilator in the ICU for two months. During that time, doctors biopsied the kidney regularly, monitored his blood and tested other tissue samples.
There were two episodes in which Miller’s body tried to reject the pig kidney, but for the first time in history of xenotransplantation, Montgomery said, they had success with available rejection medication, and the organ continued to function. They stopped the experiment at day 61.
This part of the work, Montgomery explained, would help doctors better understand what immunosuppressive medications would work best in other people who receive pig organs.
“It also will give us a sense of relief moving forward in the clinical trials that we’re in the middle of right now, to know that when you put a pig kidney in a human, from a physiological standpoint, it just does its thing,” Montgomery said. “The kidney is capable of doing most of the things that a human kidney can do, and the things that it doesn’t, we either have redundancy and we don’t necessarily need it, or there’s a few drugs that we need to supplement. But other than that, we’re good to go.”
The new research, he said, “brings us measurably closer to safe pig-to-human organ transplants.”
Creating a detailed map
During the episodes in which Miller’s body started to reject the organ, the doctors were able to create a detailed map of exactly how his immune system reacted to the pig organ and identify the pathways the body was using to reject it. They also were able to map out the genomics associated with those pathways, mapping 5,100 expressed pig and human genes and pinpointing every immune cell in the body to track immune behavior at this uniquely granular level.
“We really were able to tease apart what happened on a nearly daily basis,” said study co-author Dr Brendan Keating, a member of the faculty in the Department of Surgery at the NYU Grossman School of Medicine and the NYU Langone Transplant Institute.
They could also see the differences in immune reaction to a pig organ versus what happens with a transplanted human organ.
The researchers said they identified biomarkers in the blood that eventually may be used to detect organ rejection much earlier, before damage could be done.
Although the study is a major step forward, Montgomery said, it involved just one person, so the findings will need to be replicated in others to see whether the reactions are consistent. The researchers just got funding to test immune suppression techniques in 20 additional patients, he said.
‘We’re getting better at this’
In the past year alone, scientist have made enormous progress in understanding how pig kidney transplants work.
The most notable success involved the case of Tim Andrews of New Hampshire, the fourth living person in the US to get a kidney from a genetically modified pig.
Andrews set a record when his pig kidney continued to function for 271 days. Doctors had to remove the organ at the end of October, after they noticed a decline in function. But before that point, the transplant had worked so well that Andrews was able to take long walks and even throw out the first pitch at a Boston Red Sox game.
The kind of research found in the new studies is important for the field, said Dr. Minnie Sarwal, co-director of the Kidney and Pancreas Transplant Program at the University of California San Francisco.
“Sixty-one days of stable renal function is novel proof of concept, and I think it confirms that genetically engineered pig kidneys can sustain physiological function in human circulation,” said Sarwal, who was not involved with the new research. “As a first step, proof of concept, clearly, is very important, because it is bridging the gap between what we were previously worked working on with short lived preclinical models, and we are able to go to true clinical feasibility, even though it’s obviously not long-term. But 61 days is better than, let’s say, hours, or maybe a few days.”
Sarwal, who focuses on therapeutic innovations for immunosuppression drug design, said the new studies also demonstrated that rejection was treatable.
“That part’s not groundbreaking, but I think it’s very comforting that our current treatments would work in that model, which we expected they would, but confirmation is great to see,” she said.
Mapping immune reaction may give researchers other “druggable molecular checkpoints” so they can develop better immunosuppression options for transplant recipients, Sarwal said.
Montgomery thinks his experiment can also give hope that xenotransplantation will be a more viable option someday.
“We’re getting better and better at this, and I think that’s the message that I would like to deliver,” Montgomery said. “There’s going to be ups and downs. Nothing worth doing isn’t fraught with some complications.”
But, he added, “it’s all solveable.”
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