Researchers from the National Institutes of Health think thousands of human lives could be saved.
For nearly three years, a pig’s heart has been kept alive, healthy, and beating inside of a baboon’s abdomen, suggesting that cross-species transplants could be coming closer to a reality.
In fact, this cross-species transplant set a new world record for the longest survival yet — so researchers from the National Institutes of Health think that xenotransplantation, or the practice of transplanting organs from one species to another, could save lives.
“People used to think that this was just some wild experiment and it has no implications,” Muhammad Mohiuddin, a cardiac transplant surgeon at National Heart, Lung, and Blood Institute, who led the study, told Science. “I think now we’re all learning that [xenotransplantation in humans] can actually happen.”
In previous xenotransplant experiments, the organs never lived past 500 days in another species. However, in this new study, which is published in the journal Nature Communications, the researchers transplanted pig’s hearts into five baboons by hooking up the organs to the blood vessels in their abdomens.
The baboons still had their own hearts, so they didn’t rely on the pig’s heart for life. However, it’s still extremely impressive that the hearts survived in their abdomens for so long without being destroyed by the baboon’s immune system.
How were the researchers able to pull it off? They genetically modified the organ so that the antibody response in the baboon’s body would be weakened, and the organ would be better suited to survive. They also used a combination of new immune-suppressing drugs to keep the baboon’s immune system from attacking the pig’s heart.
The average survival rate for the hearts was 298 days (about 10 months), but in the record-breaking case, one of the hearts was still beating after an impressive 945 days! The researchers experimented with the immune-suppressing drugs by weaning the baboons off the drugs at varying points throughout the research, and it was only when they reduced the drugs that the hearts began to fail.
This means that there’s still a lot of work to do. Even if the xenotransplants did work in humans, the recipients would have to be on immune-suppressing medications for the rest of their lives, which heightens the risk of infection and cancer.
Plus, further research is needed to determine whether the transplanted hearts would be strong enough to actually keep the recipient alive — the baboons still had their own beating hearts in their bodies.
However, this study is a promising step towards cross-species transplants. According to the US Department of Health & Human Services, 22 people die every day on the organ transplant waiting list, so being able to harvest organs from a new source could be huge — although the ethical concerns about breeding pigs for our own organ needs would definitely need to be smoothed out.
Nonetheless, the findings from this study could be extremely impactful. Baboons are similar to us, so the animals are ideal for researchers to see how humans would respond to the organs from another species. Since pigs are biologically similar to us and we know a lot about their DNA, scientists think using their organs would be the best bet for xenotransplants since it would also be easier to genetically modify the organs.
Next, the team hopes to do a full pig-to-baboon heart transplant in the next few years, and also conduct more animal studies to determine the minimum amount of drugs needed to protect the donated organ.
"This has the potential to really move the field forward," co-author Richard Pierson, a professor of surgery who has studied xenotransplantation for over three decades, said in a press statement. "This new approach clearly made a difference. We obviously have a lot more work to do, but I'm confident that eventually this will be useful to human patients."