In a groundbreaking experiment, scientists connected genetically modified pig kidney to a human patient and observed that the organ successfully filtered waste from the body.

According to the New York Times, the experiment was carried out on a brain-dead patient who was a registered organ donor and his family agreed to the operation. During the 54-hour experiment, the kidney stayed outside the patient's body, where the surgeon could observe the organ and collect tissue samples. Although the kidney is not implanted in the body, this process still allows the team to see whether the organ will be rejected immediately; experts told the New York Times that the problem of animal-to-human transplantation usually occurs where human blood contacts animal tissues, such as blood vessels. middle.

Compared with primate organs, pig organs have many advantages in transplantation. For example, according to the Associated Press (AP) report, pigs have been raised as food, produce many litters in a short gestation period, and grow organs that are surprisingly similar to humans. But there is a major obstacle: pig tissue carries a gene that encodes a sugar molecule called alpha-gal, which can drive the human immune system into a frenzy and cause organ rejection. (Live Science previously reported that in people who are allergic to rare red meat, α-gal can trigger a life-threatening allergic reaction.)

Related: How long can an organ stay outside the body before transplantation? 

Therefore, in the transplantation experiment conducted last month, the research team used kidneys from genetically engineered pigs lacking this sugar-producing gene. To prepare for transplantation, the team modified the kidney in another way: they transplanted pig thymus (a small gland that helps train immune cells to fight infection) into the kidney. Dr. Robert Montgomery is NYU Langone Health Explained at a press conference held on October 21. 

Montgomery said that previous primate transplant studies have shown that by transferring the thymus of the donor animal to the transplant recipient, this can help "re-educate" the recipient's immune system so that the body can receive long-term transplants. This is why in future long-term trials with living participants, the team plans to use pig kidneys equipped with thymus, which is why they used the same kidneys in this shorter experiment. 

In other words, in the 54-hour experiment, the team is observing a more direct immune response to the kidney, where antibodies in the human blood supply will attack the organ when it enters the organ. Fortunately, such an attack did not occur. On the contrary, the kidneys began to produce large amounts of urine within a few minutes after being inserted into the patient's blood vessel.

"It functions absolutely normal," Montgomery told the Associated Press. Once it attaches to the blood vessels in the patient's thigh, the pig kidney begins to filter creatine (a waste product of muscle cell function) from the blood and quickly reduces the creatine level to the normal range. "It was not immediately rejected as we feared."

Given the promising results, this experiment may represent a big step forward for xenotransplantation-transplantation from animals to humans, but there are still many problems.   

"We need to learn more about the lifespan of organs," Dr. Dory Segoff, professor of transplant surgery at the Johns Hopkins School of Medicine, told the New York Times, who was not involved in the study. The chief medical officer of the United States, Dr. David Krassen, said that “even if you don’t try to cross the species barrier,” kidney rejection will occur long after transplantation. Therefore, it is necessary to carefully evaluate the durability of pig-to-human transplantation. The Organ Sharing Network told the New York Times .

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However, if pig-to-human transplantation can be more widely used, "it is incredible to think about how many transplants we might be able to provide," former transplant surgeon and chief medical officer Amy Friedman ( Dr. Amy Friedman, the head of LiveOnNY, an organ procurement organization based in New York, told the New York Times. According to The Times, 23,401 U.S. residents underwent a kidney transplant last year, and 90,240 Americans are currently waiting for a kidney transplant. Many patients with renal failure cannot be included in the list, partly because of the scarcity of available kidneys.

Pig kidney may allow more people to undergo transplantation, but "of course, you have to breed pigs," Friedman said.

Revavicor, a subsidiary of United Therapeutics, developed genetically modified pigs for recent transplants; according to the Associated Press report in December 2020, the company's so-called GalSafe pigs were approved by the U.S. Food and Drug Administration for medical use and consumption last year. Revivicor has no immediate plans to sell these pigs as food, but the product may be attractive, for example, to people who are allergic to alpha-gal.

Live Science previously reported that in the future, the gene editing tool CRISPR could also make pig organ transplantation safer. At the same time, some laboratories have taken a completely different approach to the transplant problem: cultivating human tissues and organs in pigs for later harvesting for transplantation. In theory, because organs are made up of human cells, they are less likely to be rejected. However, the development of this human-pig chimera is still in its early stages and has raised many ethical issues.

Read more about transplant experiments in The New York Times and The Associated Press. 

Editor's note: This story was updated on October 21 and clarified how pig thymus was used in the study based on detailed information shared by Dr. Robert Montgomery at a press conference held on the same day. The original story was published on October 20.

Originally published on Live Science. 

Nicoletta Lanese is a full-time writer for Live Science, covering health and medicine, as well as various biological, animal, environmental and climate stories. She has a degree in neuroscience and dance from the University of Florida, and a graduate certificate in science communication from the University of California, Santa Cruz. Her work has appeared in media such as Scientist Magazine, Science News, San Jose Mercury News, and Mongabay.

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