Report: Porcine Virus May Have Killed Heart Transplant Patient

New light may have been shed on the death of a man who died two months after his heart was replaced with that of a pig. New research indicates the heart that David Bennet received was infected with porcine cytomegalovirus, a virus that can cause respiratory and pregnancy complications in pigs.

First reported by MIT Technology Review, the porcine virus has been linked to previous transplant issues. Physicians who have been examining the case of why the transplant failed suggest that Bennet’s death could have been prevented if the virus had been detected. Although porcine cytomegalovirus is not thought to infect humans, previous research on transplanted porcine organs has shown that some organs that were transplanted into baboons and later discovered to have the virus failed.

The pig heart that Bennet received had been genetically altered by Revivicor, a company owned by Maryland-based United Therapeutics. The pig heart had undergone genetic modifications before its birth. It had 10 genes modified to make it a candidate for a potential heart transplant. As BioSpace previously reported, three genes that were likely to trigger a human immune response that would reject the heart were “turned off.” Also, six human genes were added to the pig in order to prevent blood from coagulating in the heart, improve compatibility and further reduce rejection.

Additionally, the pig was also modified to prevent typical growth. At one year old, a pig can weigh about 450 pounds. The gene-edited pig only weighed about 240 pounds when its heart was removed. This modification was made to prevent the animal’s heart from growing too large to be used in a human.

Following his transplant, Bennett was doing well for weeks and there was no sign of rejection. He spent time with his family and participated in physical therapy to help regain strength. However, about two months after the procedure, he took a turn for the worse and ultimately succumbed.

According to the new report, previous xenotransplantation research has shown that pig organs that were discovered to have the porcine cytomegalovirus that was implanted in baboons did not last long. It has been speculated that the immune suppression that occurs in the patient that receives the transplanted organ is unable to keep the virus in check. Also, it is thought that once the organ has been removed from the pig, the virus that may have been under control from a pig’s own natural antibodies is also free to continue infecting cells, Jay Fishman, a specialist in transplant infections at Massachusetts General Hospital, explained to MIT Technology Review.

Joachim Denner of the Institute of Virology at the Free University of Berlin, who conducted some of the early research into how the virus caused the failures in baboon patients, noted that the porcine cytomegalovirus is difficult to detect. However, he speculated that if more thorough testing is done to ensure the latent virus is not found in a pig being genetically altered to provide organs for humans, there is no reason to think that a patient like Bennett could not see sustained life in the future.

While the virus appears to be a likely culprit, Denner added that Bennett himself had been quite ill for a long time and there could be other contributing factors to his death. With Bennett's own heart failing, the transplant was the only thing that could prolong his life.