The transplant surgeon announced last month that the 57-year-old patient, who survived two months after undergoing a pig heart transplant, had died of a pig virus.
In January, David Bennett, a handyman who had suffered from heart failure, underwent a highly experimental surgery at the University of Maryland Medical Center in which doctors implanted a genetically modified pig heart.
Shortly after undergoing the surgery, Mr. Bennett died in March. The hospital simply said his condition worsened over a few days but did not provide an exact cause of death.
Last month, Mr. Bennett’s transplant surgeon, Bartley Griffith, revealed that the pig’s heart was infected with a swine virus known as cytomegalovirus in pigs, which may have contributed to Mr. Bennett’s death. In a webinar hosted by the American Transplant Society on April 20, Dr. Griffiths described the virus and doctors’ attempts to treat it, the MIT Technology Review first reported on Wednesday.
“We are starting to find out why he died,” Dr. Griffiths said, adding that[The virus] Perhaps it was the actor, or it could be the actor, who caused all this.”
According to experts, the transplant was a “key test for an external organ transplant,” a process that involves transferring tissue between different species. They believe the experiment may have been derailed by an “unintentional error,” as pigs bred to supply organs are supposed to be virus-free.
“If this is an infection, we can potentially prevent it in the future,” Dr. Griffiths said during the webinar.
The biggest challenge in animal-to-human transplants is the resilience of the human immune system, as it can attack foreign cells in a process called rejection and trigger a response that will eventually destroy the transplanted organ or tissue.
As a result, companies are bioengineering pigs by removing and adding different genes to help mask their tissues from potential immune attacks. The heart used in Mr. Bennett’s case came from a pig that had undergone 10 genetic modifications made by Revivicor, a biotech company.
Despite concerns that an organ transplant could lead to a pandemic if the virus adapts within the human body and spreads to others, experts believe the specific type of virus in donor Mr. Bennett’s heart is unable to infect human cells.
According to Jay Fishman, who specializes in transplant infections at Massachusetts General Hospital, “there is no real risk to humans” from spreading it to others. Instead, the concern stems from the ability of CMV in pigs to provoke reactions that can damage and destroy not only the organ, but also the patient.
Experts are reluctant to attribute Bennett’s death entirely to the virus. According to Joachim Diener, a researcher at the Institute of Virology at the Free University of Berlin, “This patient was very, very, very ill. Don’t forget that? The virus may have contributed but it wasn’t the only cause.”
Two years ago, Diener led a study in which researchers reported that pig hearts transplanted into baboons only last several weeks if they contained CMV in pigs. On the other hand, hearts that were free of infection were able to live over a period of six months.
Shortly after Mr. Bennett’s surgery, Dr. Griffiths and his team frequently monitored his recovery through various blood tests. In one test, doctors checked Mr. Bennett’s blood for traces of several viruses and bacteria and found a “small dot” indicating the presence of CMV in pigs. However, because his levels were so low, the doctors assumed the result might be wrong.
Dr. Griffiths also revealed that because the private blood test was taking nearly 10 days to perform, doctors were unable to tell that the virus was actually starting to multiply quickly. As a result, this may have triggered a reaction that Dr. Griffiths now thinks was likely a “cytokine blast,” a storm of an exaggerated immune response that can cause serious problems.
On day 43 of the experiment, doctors discovered that Mr. Bennett was breathing hard and warm to the touch. “He looked really funky. Something happened to him. He looked injured,” Dr. Griffith said, adding, “He’s lost his attention and won’t talk to us.”
In an effort to fight Mr. Bennett’s infection while keeping his immune system in check, doctors provided him with intravenous immunoglobulin as well as cidofovir, a drug sometimes used in AIDS patients. Mr. Bennett showed signs of recovery after 24 hours before his condition deteriorated again.
“I personally suspect that he developed a capillary leak in response to his inflammatory burst, which filled his heart with edema, edema turned into fibrous tissue, and went into acute diastolic heart failure,” Dr. Griffiths said at the webinar. – guardian