Gene Editing photo

She’s got the heart of a pig—and that’s a good thing. Researchers are reporting that a baboon is still alive after receiving a heart transplanted from a pig, The Telegraph reports. The baboon has lived with the heart in its abdomen for more than a year.

Its longevity is a milestone. Previously, when researchers tried to transplant pig hearts into primates, the primates’ bodies would reject the transplants within six months, The Telegraph reports. Ultimately, researchers want to make pig hearts transplantable into humans. Pigs could provide a larger supply of the organ than human donors can, closing the tragic gap between supply and demand. In the U.S., about 3,000 people are on the waiting list for a heart transplant, but only about 2,000 hearts become available each year, according to the U.S. National Heart, Lung and Blood Institute, which conducted the baboon study. Those who are waiting can use mechanical devices, but those aren’t perfect, the institute says.

Pig hearts are promising because they’re close enough to human hearts in anatomy. Doctors also already use heart valves taken from pigs and cows in human surgeries. It seems pig hearts are just a little too foreign for primate bodies to accept easily, however. In previous studies, the hearts would trigger a massive immune response in the primates they were transplanted into. Such responses can be deadly and they’ve been a major barrier to developing pig heart transplants, The Telegraph reports. It will be years before pig hearts are ready for human patients, if they ever are.

The team specially engineered its pigs to have some human genes and to lack some pig genes.

To make hearts that baboons—and, in the future, humans—won’t reject, the National Heart, Lung and Blood Institute team specially engineered its pigs to have some human genes and to lack some pig genes. The researchers also gave their baboons drugs to suppress their immune systems. (Human patients take immunosuppressant drugs when they get organ transplants, so that’s not unusual.)

It seems what made the transplants work was just the right balance of genetic engineering and immune system-suppressing drugs. In an abstract the team submitted to a meeting of heart and torso surgeons, the team reports that when it tried other drug regimens, their baboons died in less than a year. Baboons who received hearts from un-genetically modified pigs rejected the hearts within a day.

Now that the team has shown pig hearts are able to hang around inside primates safely, the next step will be to actually replace baboons’ hearts with pig hearts, The Telegraph reports. The baboon in this study has a pig heart in its body alongside its own heart, which is doing all the work.

This baboon study hasn’t been published in a peer-reviewed journal yet, but its authors presented it yesterday at the annual meeting of the American Association for Thoracic Surgery.

The Telegraph