The University of Maryland School of Medicine reached a medical milestone this year when it transplanted a genetically-engineered pig heart into a human for the first time. David Bennett Sr., the pig heart recipient, survived for two months after the transplant. Doctors suspect he may have lived longer had the pig heart not been infected with porcine cytomegalovirus.
Porcine cytomegalovirus, a herpes virus, is a preventable virus in pigs that rarely causes symptoms in these animals.
Revivicor, the biotechnology company that raised the pigs, engineered the pigs to make their organs less likely to be rejected when transplanted into the human body. This engineering process was also meant to produce pigs that were pathogen-free. Revivicor has yet to comment about the virus.
Bartley Griffith, the surgeon who transplanted the heart into Bennett, said he believes the virus could have contributed to Bennett's death. "If this was an infection, we can likely prevent it in the future," Griffith commented further.
Known as xenotransplantation, the process of transplanting animal organs into humans could theoretically spark a pandemic if an animal virus in an organ were to infect a human recipient who could then infect other people. Fortunately, porcine cytomegalovirus is believed to be incapable of infecting human cells, according to Jay Fishman, a transplant infections specialist at Massachusetts General Hospital.
The potential for porcine cytomegalovirus to damage transplanted organs has been a concern. German researchers found in studies where baboons received pig hearts that hearts infected with the virus extended life by only a couple of weeks whereas pathogen-free transplanted organs extended life by more than half a year. These researchers believed the virus was able to damage the pig heart in baboon transplant recipients once the pig's immune system was no longer present to keep the virus in check and because the baboons' immune systems were suppressed by medications. At that time, those researchers warned of this happening in humans.
The transplant team reportedly tested the donor pig's snout for the virus prior to transplantation, but the virus can apparently be present in deeper tissues instead. The lead of the German study looking at transplants in baboons, Joachim Denner, states, "It's a latent virus and hard to detect. But if you test the animal better, it will not happen. The virus can be detected and easily removed from pig populations, but unfortunately, they didn't use a good assay and didn’t detect the virus, and this was the reason. The donor pig was infected, and the virus was transmitted by the transplant."
The medical community still considers this pig to human transplant a success. After all, the first human to human heart transplant lasted an even shorter period at only 18 days.
Researchers are investigating Bennett's death further in search for answers over the exact cause of his death, still uncertain if it may have been a result of his body rejecting the transplant. No signs of immune rejection were found, however, about a month after the transplantation.
Sources: MIT Technology Review, The Pig Site, Sci Rep
