By now, you have surely heard of the incredible human/pig heart transplant. The first of its kind surgery is a remarkable medical breakthrough, one that may forever change organ donation and organ transplants.
On January 7, David Bennett, a 57-year-old male patient suffering from terminal congestive heart failure, received a genetically-modified pig heart at the University of Maryland Medical Center (UMMC). The groundbreaking experimental surgery was deemed the patient’s only chance for survival after he was declared unsuitable for a human donor transplant or an artificial heart pump. Having spent months in a hospital bed with no improvement to his condition, Bennett gave his consent to the surgery.
While Bennett is being monitored to see just how long he survives, that he has lived at all is enough to call the surgery “successful,” and regardless of Bennett’s overall survival, it could usher in a whole new approach to the practice of organ transplantation.
This operation is a milestone for xenotransplantation—the transfer of organs from other species to human patients. Prior to this groundbreaking operation, the closest doctors got to successful cross-species transplants were in transplanting modified pig organs into already brain dead patients – just to test the theory. Bennett’s was the first time that such a pig-to-human organ transplant was used to actually sustain a life.
The operation itself received exceptional authorization from America’s Food and Drug Administration under a provision which lets doctors use experimental treatments as a matter of last resort.
The Science Behind the Successful Pig to Human Heart Transplant
For decades, researchers have attempted to tackle xenotransplantation’s fundamental problem. This is that the human body, when it recognizes foreign tissue, will swiftly attach it and reject the transplanted organ. In the case of pigs, the most important marker of “foreignness” is a sugar molecule called galactose-alpha-1,3-galactose (alpha-Gal), which is found on the surfaces of porcine cells. While this molecule does not exist in humans, antibodies to suppress it do. Consequently, no transplant from a pig with alpha-Gal would last more than a couple of minutes in a human body.
In 2003 pigs were produced with a genome modified so as to suppress the enzyme responsible for making alpha-Gal. But the genetic modifications to the pig used in Bennett’s surgery did not stop there. In total, the animal in question had a genome modified in ten ways to optimize the chances of success. Three genes had been removed to reduce the risk of a human antibody rejecting the donor organ. A fourth, a growth gene, had also been knocked out to ensure the heart did not enlarge after transplantation. And six human genes had been added to promote acceptance.
How well Bennett actually does and how long he survives still remains to be seen. Still, supporters of xenotransplantation think its potential to improve lives is huge. In America alone, over 100,000 people are waiting for transplants. In 2020 only a third of the required number of organs became available.
In theory, pigs can be bred to provide humans with any solid organ, though some will be more complex than others. A large part of the heart’s function is mechanical, but other organs have chemical jobs that will be harder to successfully replicate. Moreover, even assuming these barriers can be overcome and successful surgical procedures developed for other organs on transplant waitlists, such as kidneys and livers, most researchers still acknowledge that scaling up xenotransplantation to meet the world’s demand for organs may take decades.
However, regardless of how long Bennett lives with his human-pig heart, the chances that xenotransplantation may eventually become the standard of care for organ transplants have just increased dramatically.