The growing field of xenotransplantation

Currently, there are over 106,000 people on the national list for organ transplants in the United States, with many of them looking for kidney transplants. However, there is a significant shortage of available organs. In 2023, only 27,000 kidney transplants were performed.

In recent years, scientists have been working to advance the field of xenotransplantation, or the transplanting of an organ from one species to another. Using gene-editing techniques, scientists have created animal organs that are less prone to rejection in human bodies.

So far, five patients have received genetically modified pig organs, three of which were kidneys and two of which were hearts. Of these patients, four of them have since passed away after receiving their transplants. 

"When I was on dialysis, [I] couldn't walk long distances without getting short of breath," Looney said. "And now it's like: Go, go, go! It's like a whole new world, a whole different feeling."

"She's doing extraordinarily well," said Robert Montgomery, the director of NYU Langone's Transplant Institute, who led Looney's operation. "If you passed Towana on the street you wouldn't have any idea that she's the only person in the world who's walking around with a functioning pig kidney. That's a big deal."

FDA approves clinical trials of pig organ transplants

So far, xenotransplants of pig organs have only been approved under FDA's compassionate-use program, which allows investigational medical products to be used outside of clinical trials for patients who are critically ill and have few other options.

However, FDA on Monday approved two biotechnology companies, United Therapeutics Corporation and eGenesis, for separate clinical trials that will transplant genetically modified pig organs into patients with kidney failure.

United Therapeutics, which provided the pig kidney in Looney's transplant, is expected to begin its trial midyear. The trial will initially enroll six patients who have been on dialysis for at least six months but don't have any other serious medical issues. There will also be a three-month waiting period between each transplant to allow doctors to learn from the outcomes.

All patients will be monitored for 24 weeks and must agree to regular follow-ups for the rest of their lives. These follow-ups will allow researchers to observe their health and check for any potential pathogens that could be transmitted from pigs to humans.

If the first six transplants are successful, the trial could expand and include up to 50 patients. The trial will be phaseless, combining the traditional Phase 1, 2, and 3 trials, and could lead directly to approval.  

eGenesis is expected to begin its own trial in the second half of the year. The trial will initially include three patients with kidney failure who are unlikely to receive a human transplant within five years. There will be a six-month waiting period between the first and second patient, and a three-month waiting period between the second and the third.

"We're entering a transformative era in organ transplantation," said Mike Curtis, president and CEO of eGenesis.

However, some people have raised concerns about the potential for pathogens in pigs to pass onto humans during the xenotransplantation process.

According to Christopher Bobier, an associate professor at Central Michigan University College of Medicine who specializes in bioethics and health policy, the recipient of an animal organ "could become infected with an undetected pathogen from the porcine source" in the worst-case scenario.

Some medical ethicists have also questioned whether patients can fully consent to xenotransplantation since there are so many unknown risks.

"Saying no would be incredibly difficult" for someone undergoing something as grueling as dialysis, Bobier said. "Fully grasping the lifelong implications of that decision would be even harder."