The version used in Maryland came from a pig with 10 genetic modifications developed by Revivicor, a subsidiary of United Therapeutics.
After promising tests of these pig organs on baboons, three U.S. transplant teams launched the first human studies in late 2021. Surgeons from New York University and the University of Alabama have joined forces. pig kidneys to people with brain death, but the University of Maryland went there. a step further when Griffith sewed a pig’s heart on Bennett’s chest in early January.
Transferring swine viruses to humans has been a concern: some fear that xenotransplantation could trigger a pandemic if a virus spreads inside a patient’s body and then spreads to doctors and nurses. The concern could be severe enough to require lifelong monitoring of patients.
However, the specific type of virus found in Bennett’s donor’s heart is not believed to be capable of infecting human cells, says Jay Fishman, a transplant infection specialist at Massachusetts General Hospital. Fishman believes that “there is no real risk to humans” of its spread.
In contrast, the problem is that swine cytomegalovirus is associated with reactions that can damage the organ and the patient, with catastrophic results. Two years ago, for example, German researchers reported that pig hearts transplanted into baboons would only last a couple of weeks if the virus was present, while infection-free organs could survive for more than half a year.
These researchers said they found “surprisingly high” virus levels in pig hearts removed from baboons. They believe the virus could be undone not only because the baboons’ immune system was suppressed with drugs, but also because the pig’s immune system was no longer there to keep the virus under control. “It seems very likely that the same thing happens in humans,” they warned at the time.
Joachim Denner of the Institute of Virology at the Free University of Berlin, who led the study, says the solution to the problem is more accurate evidence. The U.S. team appears to have tested the pig’s snout to detect the virus, but it often hides deeper in the tissues.
“It’s a latent virus that is difficult to detect,” says Denner. “But if you test the animal better, it will not pass. The virus can be easily detected and eliminated from pig populations, but unfortunately they did not use a good test and did not detect the virus, and that was the reason. donor became infected and the virus was transmitted by transplantation “.
Denner says he still believes the experiment was a “great success.” For example, the first human-to-human heart transplant, in 1967, lasted only 18 days, and two years later, one in Germany lasted only 27 hours.
Denner says Bennett’s death can’t be attributed to the virus alone. “This patient was very, very, very ill. Don’t forget,” he said. “Maybe the virus contributed, but it wasn’t the only reason.”
Cause of death?
The cause of Bennett’s death is important, because if his heart failed as a result of the immune rejection, researchers may have to return to the drawing board. Instead, companies like United Therapeutics and eGenesis, or academics who work with them, are now expected to start clinical trials of their pig organs in a year or two.
Bennett was offered a pig heart after Griffith applied for special permission from the U.S. Food and Drug Administration to test an animal organ in a single transplant. He was considered a good candidate for the daring attempt because he was on the verge of dying of heart failure and was not eligible for a sparse human heart transplant due to a history of disregarding medical advice.