Revivicor's genetically modified pig heart is first successfully transplanted in human patient

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Several genes in a donor pig, developed by United Therapeutics subsidiary Revivicor, were inactivated to prevent rejection of a transplant, while another six human genes were added to the pig’s genome. (Photo by shalamov/iStock/Getty Images Plus/Getty Images)

Once as improbable an idea as seeing pigs fly, the xenotransplantation of organs from animals to humans is becoming an increasingly viable option as the science of genetic editing improves and organ donor waitlists continue to lengthen.

The latest promising update in humans’ quest to harvest life-saving organs from our four-legged, porcine friends saw a team of surgeons at the University of Maryland Medical Center successfully implant a heart taken from a genetically modified pig into the body of 57-year-old Maryland resident David Bennett.

This marks the first time that a pig’s heart has been successfully transplanted into a human. The operation was granted emergency authorization by the FDA on Dec. 31 through the agency’s “compassionate access” provision.

According to University of Maryland Medicine, Bennett has end-stage heart disease and opted into the experimental treatment after exhausting his other options. Three days after the eight-hour procedure, though he remained on a heart-lung bypass machine, Bennett’s body appeared to be responding well to the porcine heart, his doctors reported.

“It’s working, and it looks normal,” Bartley Griffith, M.D., who led the surgical team, told The New York Times. “We are thrilled, but we don’t know what tomorrow will bring us. This has never been done before.”

The procedure required some “clever plastic surgery” because of the “squirrelly” anatomical challenges that come with placing a pig organ into a human body, Griffith said, but once connected to Bennett’s blood supply, “the heart fired right up.”

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The donor pig was genetically modified by United Therapeutics subsidiary Revivicor. The Virginia-based company reportedly made 10 alterations: Four of the pig’s genes were inactivated, and six human genes were inserted into its genome. Nine of the edits were made to reduce the chances that Bennett’s body would reject the new heart post-transplant, while the last was made to stop excessive growth of the pig tissue once implanted.

Those chances were further helped by an experimental drug co-developed by Muhammad Mohiuddin, M.D., director of the University of Maryland School of Medicine’s cardiac xenotransplantation program, who helped conduct the pre-transplant research. The drug, made by Kiniksa Pharmaceuticals, is designed to suppress the human immune system, preventing the body from immediately fighting back against the foreign implant.

The heart was preserved before the surgery in XVIVO Perfusion’s XVIVO Heart Box, which provides hypothermic, non-ischemic perfusion to keep donor organs healthy until they’re ready to be implanted. The system is still under development but was awarded the FDA’s breakthrough-device designation in 2019.

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Though Bennett’s procedure was certainly groundbreaking, the surgeons warned that it won’t spark an immediate flood of xenotransplants, since it will take much more research and time to make the therapy widely available.

Still, this marks the second significant achievement in the realm of porcine transplants in just the last few months. In September, a surgical team at NYU Langone Health took a kidney from another of Revivicor’s genetically modified pigs—this time, with only one genetic edit—and successfully attached it to a human patient’s blood vessels.

In that case, the patient was already brain-dead, and the kidney was kept outside the body for observation. However, the surgeons said the procedure was the first in which the animal donor organ wasn’t immediately rejected by and didn’t cause a major immune response in the body of its human recipient.