For the first time, doctors successfully transplanted a pig kidney into a human
Surgeons in New York successfully attached a kidney grown in a genetically altered pig to a human patient and discovered that the organ functioned normally, a scientific breakthrough that could one day result in a vast new supply of organs for critically ill patients.
Researchers have long sought to grow organs suitable for transplantation into humans in pigs. In recent years, technologies such as cloning and genetic engineering have brought that vision closer to reality, but testing these experimental organs on humans has raised troubling ethical concerns.
So, with the family’s permission, surgeons at New York University Langone Health attached the pig’s kidney to a brain-dead patient who was kept alive on a ventilator, and then monitored the body’s response while measuring the kidney’s function. It is a first-of-its-kind operation.
The researchers only followed the results for 54 hours, and many questions about the long-term effects of such an operation remained unanswered. The procedure will not be available to patients anytime soon due to significant medical and regulatory obstacles that must be overcome.
Nonetheless, experts in the field hailed the surgery as a watershed moment.
“This is a huge breakthrough,” said Dr. Dorry Segev, a transplant surgery professor at the Johns Hopkins School of Medicine who was not involved in the study. “It’s a huge deal.”
A consistent supply of pig organs, which could eventually include hearts, lungs, and livers, would provide a lifeline to the more than 100,000 Americans currently on transplant waiting lists, including the 90,240 who require a kidney. Every day, twelve people on waiting lists die.
An even larger number of Americans with kidney failure — more than 500,000 — rely on arduous dialysis treatments to survive. The vast majority of dialysis patients do not qualify for transplants, which are reserved for those who are most likely to thrive after the procedure, due in large part to the scarcity of human organs.
On October 19, 2021, USA Today broke the news of the surgery. The study hasn’t been peer-reviewed or published in a medical journal yet.
The transplanted kidney came from a pig that had been genetically engineered to produce an organ that would be unlikely to be rejected by the human body. The kidney was attached to blood vessels in the patient’s upper leg, outside the abdomen, in a procedure that closely resembled an actual transplant procedure.
According to Dr. Robert Montgomery, director of the N.Y.U. Langone Transplant Institute, who performed the procedure in September, the organ began functioning normally, producing urine and the waste product creatinine “almost immediately.”
Although the kidney was not implanted in the body, problems with xenotransplants — from animals such as primates and pigs — typically occur at the interface of the blood supply and the organ, where human blood flows through pig vessels, according to experts.
The fact that the organ worked outside the body is a strong indication that it will work inside the body, according to Dr. Montgomery.
“I think it was even better than we expected,” he said. “It looked exactly like any other transplant I’d ever done from a living donor.” A lot of kidneys from deceased people don’t work right away, and it can take days or weeks for them to start working. This worked right away.”
According to the United Network for Organ Sharing, a nonprofit that coordinates the nation’s organ procurement efforts, 39,717 Americans received organ transplants last year, with the majority of them — 23,401 — receiving kidneys.
Dr. Montgomery believes that genetically modified pigs “could potentially be a sustainable, renewable source of organs — the solar and wind of organ availability.”
The prospect of raising pigs to harvest their organs for human consumption is bound to raise concerns about animal welfare and exploitation, despite the fact that an estimated 100 million pigs are killed for food in the United States each year.
“Pigs aren’t spare parts, and they should never be used as such simply because humans are too self-centered to donate their bodies to patients in need of organ transplants,” said People for the Ethical Treatment of Animals, or PETA.
The reactions of transplantation experts ranged from cautiously optimistic to ebullient, but all agreed the procedure represented a paradigm shift.
While some surgeons speculated that genetically engineered pig kidneys could be transplanted into living humans within months, others said there was still much work to be done.
“This is really cutting-edge translational surgery and transplantation that is on the verge of being able to do it in living human beings,” said Dr. Amy Friedman, a former transplant surgeon and chief medical officer of LiveOnNY, the Greater New York area’s organ procurement organization.
The group was involved in the identification and selection of the brain-dead patient who would receive the experimental procedure. Because the organs were unsuitable for transplantation, the patient’s family agreed to allow research to test the experimental transplant procedure.
Dr. Friedman stated that she planned to use pig hearts, livers, and other organs as well. “It’s truly mind-boggling to think of how many transplants we might be able to offer,” she said, adding, “Of course, the pigs would have to be bred.”
Other experts were more reserved, stating that they wanted to see if the results could be replicated and to review data collected by N.Y.U. Langone.
“There’s no doubt this is a tour de force in terms of how difficult it is to do and how many hoops you have to jump through,” said Dr. Jay A. Fishman, associate director of the transplantation center at Massachusetts General Hospital.
“Whether or not this particular study advances the field will depend on what data they collected and whether or not they share it, or whether it is just a step to show they can do it,” Dr. Fishman explained. He urged us to be humble “about what we know.”
Many obstacles remain before the organs of genetically engineered pigs can be used in living humans, according to Dr. David Klassen, chief medical officer of the United Network for Organ Sharing.
While he called the surgery a “watershed moment,” he cautioned that long-term organ rejection occurs even when the donor kidney is well-matched and “even when you’re not attempting to cross species barriers.”
In addition to removing toxins from the blood, the kidney has other functions. There are also concerns about pig viruses infecting recipients, according to Dr. Klassen: “It’s a complicated field, and to imagine that we know everything that will happen and all of the problems that will arise is naive.”
The process of grafting or transplanting organs or tissues between different species, known as xenotransplantation, has a long history. Attempts to use animal blood and skin in humans date back hundreds of years.
Chimpanzee kidneys were transplanted into a small number of human patients in the 1960s. The majority of patients died soon after; the longest a patient lived was nine months. A baboon heart was transplanted into an infant girl named Baby Faye in 1983. She passed away 20 days later.
Pigs outperformed primates in terms of organ procurement because they are easier to raise, mature faster, and reach adult human size in six months. Pig heart valves are routinely transplanted into humans, and pig pancreas cells have been given to some diabetic patients. Pig skin has also been used to make temporary grafts for burn victims.
The marriage of two new technologies, gene editing and cloning, has resulted in genetically modified pig organs. Pig hearts and kidneys have been successfully transplanted into monkeys and baboons, but their use in humans has been ruled out due to safety concerns.
“Up until now, the field has been stuck in the preclinical primate stage, because the transition from primate to living human is perceived as a big jump,” Dr. Montgomery explained.
The kidney used in the new procedure was obtained by deleting a pig gene that codes for a sugar molecule that causes an aggressive human rejection response. Revivicor genetically engineered the pig, which was then approved by the Food and Drug Administration for use as a source of human therapeutics.
Dr. Montgomery and his team also transplanted the pig’s thymus, an immune system gland, in an attempt to prevent immune reactions to the kidney.
After attaching the kidney to blood vessels in the upper leg, the surgeons covered it with a protective shield to observe it and collect tissue samples over the course of the 54-hour study.
Dr. Montgomery and his colleagues discovered that urine and creatinine levels were normal, and no signs of rejection were detected after more than two days of observation.
“There didn’t seem to be any kind of incompatibility between the pig kidney and the human kidney that would prevent it from working,” Dr. Montgomery said. “The kidney was not rejected right away.”
He admitted that the long-term prospects are still unknown. “However, this allowed us to answer a really important question: Is there anything that will happen when we move this from a primate to a human that will be disastrous?”
