Researchers have kept a pig heart alive and ticking in a baboon for 945 days. The heart, from a genetically modified pig, was designed to function in a primate. The next step is pig-to-human transplants.
Interspecies transplants, or xenotransplantation, come with one big problem: rejection. Transplants are rejected even between humans, so the pigs have to be genetically modified to make them more compatible. Pigs are a good place to start because their organs are more or less the right size, and companies like Revivicor, which supplied the pig heart for the baboon, keep tweaking the genes to fine-tune the organs for human use. The goal, Revivicor founder and co-CEO Martine Rothblatt told MIT Technology Review, is to make a successful pig-to-human lung transplant within the next few years.
The biggest hurdle is what’s called hyperacute rejection. Hyperacute rejection “is a reaction to the ‘foreign’ organ or cell by the body’s normal immune system,” says Revivicor. It’s caused by sugars on the surfaces of cells, which humans don’t have, so our immune systems reject them. Switching off the right gene knocks out the enzyme that produces these sugars, but right now, antirejection drugs are still needed.
The pig heart in the baboon was transplanted by surgeon and researcher Muhammad Mohiuddin, at the National Heart, Lung, and Blood Institute, in Bethesda, Maryland. The baboon kept its own heart to pump blood–the purpose of the transplant was to see if the pig heart could survive.
“We believe it could have gone on forever,” Mohiuddin told MIT Technology Review. “I would say 60 percent of the improvement was due to the organ, and 40 percent due to better drugs.” The pig heart only stopped working when Mohiuddin stopped using his improved drugs.
Morally, this is unknown territory. Yet growing pigs for organs doesn’t seem such a stretch from growing them for food. And Rothblatt’s own goal of putting pig lungs in humans is also personal–her own daughter may need a lung transplant one day.