First kidney transplant from pig to human opens door on big possibilities—and big questions

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In September, surgeons at New York University Langone Health medical center carried out a two-hour operation in which they transplanted a kidney from a genetically altered pig into a human. On Thursday, they provided the first information from this transplant, which they called “a major step forward in potentially utilizing an alternative supply of organs for people facing life-threatening disease.”

This kind of transplant from a source that isn’t human, which is known as a xenotransplantation, offers the possibility to greatly expand the availability of much-needed kidneys as well as other organs that are even more difficult to obtain. While humans can give away one of their kidneys and survive, the same can’t be said of the heart, liver, or other organs that don’t come in handy pairs.

Even so, the actual statics can be surprising. According to the Health Resources and Service Administration, there are over 106,000 Americans currently waiting on an organ to become available for transplant—90,000 of whom are looking for a kidney. Only about 20,000 kidneys become available each year. As a result, 17 people die each day when an organ fails to become available in time. Most of them die from the effects of prolonged kidney failure.

In 2020, 39,000 transplant operations were carried out, but that number could expand greatly—well beyond the current waiting list—if there were a ready source of organs that didn’t make transplants a last, desperate measure. For years, experiments with xenotransplantation—as well as efforts to use a form of 3D printing to create custom replacement organs—have suggested that a new era of transplantation was around the corner, but until September actual experiments had been limited to transplants to primates, not humans. What happened at Langone in September signals that this era and the decisions it requires are drawing very near.

Though the operation was considered successful, don’t expect to see an interview with the first recipient of a pig-sourced kidney. That’s because the operation was preformed on a person who was already brain-dead. The recipient’s body was kept functioning—with the permission of family members—until the organ could be transplanted. Following the operation, the body was kept on a ventilator for a further two and a half days, showing that the kidney was actually functioning.

Other attempts to generate a suitable organ for xenotransplantation have sometimes involved inserting human genes into animals, making them less likely to be rejected by the immune system. This has generated some real concern from scientists and a great deal of media-driven fury about the creation of “chimeras.” In May, Republicans attempted to pass a bill that would have banned “certain types of human-animal chimeras,” and Sen. Mike Braun told horror stories about pigs with human faces. The bill failed along party lines.

However, the pig in the September transplant had a much simpler genetic modification. Rather than inserting any human genes, it had one porcine gene knocked out: the gene that produces a complex polysaccharide known as as alpha-galactose, or more familiarly as “alpha-gal.” The presence of alpha-gal in pigs and most other mammals means that any attempt to transplant their organs usually results in a rapid response by the human immune system. Humans can even become allergic to eating pork, and meat from other mammals, when a tick-borne illness results in alpha-gal syndrome. 

Knocking out alpha-gal doesn’t make a pig organ perfectly compatible. Any recipient of such an organ would have to take immune-suppressing drugs, and the length of the post-operation period wasn’t enough to show that there wouldn’t be consequences, including possible rejection, down the road. However, the transplant surgeons also carried out another step: They transplanted a portion of the pig’s thymus gland along with the kidney. The thymus gland helps “educate” the immune system to prevent it from going after the body’s own organs. The combination of taking out alpha-gal and adding the critical portion of the pig thymus appears to have performed well during the observation period following the surgery.

Every year in America, 100 million pigs are slaughtered for food. Even so, there are people with a strong moral objection to that practice. Raising many more animals expressly so they can be killed to provide back-up organs for humans may seem better—or worse. PETA is already on record as being against the use of any animal for donated organs, and blames the shortage of human organs on selfishness of potential donors.

However, it’s not clear that enough human organs suitable for donation would be available even if signing that spot on your driver’s license were mandatory. After all, humans tend to die from cancer, infectious disease, accidents, and conditions associated with old age, all of which can make organs unsuitable for transplant. They also often die outside the confines of a hospital, making it impossible to preserve organs for transplant. An organ removed from a pig that was bred and prepared for the purpose of providing a xenotransplant could well be better than any available human organ. In addition, smaller pieces of animals, such as heart valves, have long been used in human transplants.

But … the ethics are going to require as much thought as the science. In the near term, expect to see more of these “investigational transplants” carried out in similar circumstances. 

As a reminder, getting to this stage doesn’t mean that everything is going to work out. The first artificial heart was developed in the 1940s and the first one was implanted into a human in 1982, but their use is still far from widespread and the rate of associated problems are still very high. It’s unlikely that transplantation is going to change overnight, or that anyone currently on that long waiting list is going to be assisted by this technology. Still … there’s hope.

And please sign that organ donor card.