Do pig-to-human transplants work? Here are the risks you face

If you are interested in the developments in medical technology or organ transplants, the chances are you've heard of pig-to-human transplants. For those unfamiliar, researchers have been conducting some experiments on transplanting organs from genetically modified pigs to humans in recent years to deal with the acute shortage of donor organs.

Besides the patient who recently died two months after being transplanted with a pig heart at the beginning of this year, two patients were also transplanted with pig kidneys. 

Despite the fact that the kidneys from pigs that had been genetically modified to have human-like immune systems appeared to function well, some scientists still dispute the efficacy of the experiments, according to a report published in Nature.

The testing process

Before experimenting on humans, pig organs have been transplanted into nonhuman primates. For example, one baboon lived with a genetically modified pig heart for more than two years. However, as might be expected, there are some critical differences between baboons and humans.

First of all, baboons' immunological and metabolic systems are different from those of humans. Secondly, some particular immunosuppressive drugs that have been used in human organ transplants do not work in nonhuman primates, according to Robert Montgomery, a transplant surgeon at New York University (NYU) who also led the experiments. Montgomery also suggests that the death of a patient is “the closest thing we’re going to get to a living human without the risk of harm.”

Transplant tests were conducted in September and November 2021, and then Montgomery and his team utilized pigs that had been genetically modified to lack a gene called alpha-1,3-galactosyltransferase (αGal), which triggers the human immune system and leads to the rejection of xenotransplants.

The researchers also transplanted a pig thymus with each kidney, an organ that helps the body accept foreign organs by producing immune cells.

Later on, the team tested these “thymokidneys” on two people, who had been confirmed as dead one or two days earlier, to monitor both how the kidneys functioned and how the immune system of the human body responded to the transplanted organs.

Risks of a later immune reaction

According to a paper published in The New England Journal of Medicine on May 19th, the researchers stated that the patients hadn't shown any acute immunological reactions to the organs. Though Montgomery finds this “very reassuring,” he also believes that if the patients had been maintained on life support for months, a later immunological response might have developed.

Though the research team is speaking positively of their experiments, some researchers are still skeptical and concerned about the possible reactions that can develop later on.

“It’s a pig that’s not relevant to what we need to know,” says David Cooper, a transplant surgeon at Massachusetts General Hospital in Boston.

Paige Porrett, a transplant surgeon at the University of Alabama at Birmingham, and her team have conducted another study. They removed both kidneys from a dead person to test whether the patient’s antibodies would attack the pig organ, and they monitored the patient for 74 hours. Similar to the experiment of Montogomery's team, the results Porrett’s team got have shown little immunological reactivity to the organs. 

However, while producing urine, the pig kidneys did not process creatinine, which may indicate that the organs were not functioning correctly. However, there is a fact to be regarded that the patient had been dead for five days. Therefore, Porrett is reported to suspect that the patient's metabolic processes may be shutting down. She claims that her team has transplanted pig kidneys into several more persons who have been certified brain dead and that the results will be published soon.

On the other hand, David Cooper, a transplant surgeon at Massachusetts General Hospital in Boston, expresses his suspicion by asking if the human immune system will attack the organ months later and whether the organ will continue to function. “I personally don’t think we’ll get definitive data from doing studies in brain-dead patients,” he says.

Time will tell if animal-to-human transplants will be safe one day, while disputes on this topic seem to continue longer in the science world. On the other hand, suspicions shed light on some critical risks, which may lead to complications and death in the future, and are to be taken seriously.