This year, the tens of thousands of Americans hoping for a transplant will anxiously await the call telling them that an organ has been found. Some of the patients, with congestive heart failure, will be waiting for a heart. Those with end-stage kidney disease who are on dialysis will be expecting a kidney. Other people with liver disease or failing lungs will also wait their turn. According to the United Network for Organ Sharing, more than 100,000 people are currently on the waiting list for organ transplants. In 2021, only about 41,000 organ transplants were performed – the highest annual figure since at least 1988, according to UNOS. Given the high demand, some patients will continue to wait. Others will eventually die. More than anything else, the problem is the lack of organ donors.
Over the ensuing half century, as surgical techniques have been greatly refined to preserve and transplant solid organs like the heart, kidneys, lungs and liver, some of the greatest advances have spurred the development of new drugs that allow patients to live for many years without the risk of organ rejection. Today, the majority of heart transplant recipients survive at least 10 years.
While the safety and efficiency of transplantation have improved dramatically over the past decades, the supply of donor organs remains a problem. There are multiple barriers to organ donation, including family reluctance and a general lack of social education about the life-saving nature of organ transplantation. The net result is a perpetual shortage of donor organs. The game-changing implication of Mr. Bennett’s recent surgery is not just what it does for heart transplants, but also what it does for organ procurement for transplant surgery as a whole.
Xenotransplantation, the transplant into humans of an organ from a non-human animal, has been attempted unsuccessfully in the past. In 1984, Stephanie Fae Beauclair (who went by the name Baby Fae) was born with hypoplastic left heart syndrome
. In an attempt to save her life, she underwent a heart transplant with the heart of a baboon. She died of organ rejection 21 days after the operation.
For a non-human donor organ to function properly in a human host, it must be anatomically similar (to allow for surgical implantation), function well in the human environment, and not be rejected. (Transplant rejection is a risk that all transplant recipients face, but it’s especially difficult when the donor organ comes from a non-human source.)
Although the heart of an adult pig is anatomically similar to a human heart, for Bennett’s operation, researchers at the University of Maryland modified 10 genes in pigs. Some pig genes have been turned off or “knocked out” to prevent acute rejection. Another gene has been modified to prevent the donor heart from continuing to grow to an unacceptable size after transplantation. Several human genes were given to the pig to prevent clotting abnormalities in the new heart. As is also required for this type of transplant, strong anti-rejection drugs were also administered.
We will know relatively soon if the daring operation restores Bennett’s health. Although his recovery is uncertain and possibly even long, what is certain is that the door to the use of bioengineered non-human organs has been opened – and with it the promise of an almost unlimited supply of donor organs could follow. While the road ahead is surely filled with new physiological, technical and even ethical challenges, we may one day watch this courageous procedure as we now watch Dr. Christaan Barnard’s first heart transplant.