The underlying cause of David Bennett’s death on March 8, two months after he received the heart of a genetically altered pig, remains unknown and is only slightly less mysterious for what can likely be ruled out, suggests a progress report on the case from the director of the cardiac xenotransplantation program where the pioneering surgery took place.
Mr. Bennett died in “diastolic heart failure,” reported Muhammad M. Mohiuddin, MBBS, University of Maryland School of Medicine, Baltimore, “but the mechanism is still under investigation.”
Although the immediate cause could have been single or multiple, evidence so far does not point to immune rejection nor does it support a role for a recently proposed suspect, infection by porcine cytomegalovirus (PCMV), Dr. Mohiuddin observed in front of a standing-room-only audience June 6 at the American Transplant Congress (ATC) in Boston. The congress is a joint meeting of the American Society of Transplant Surgeons (ASTS) and the American Society of Transplantation (AST).
Rocky clinical course
Early characterizations of the patient’s death focused more on his diminished, end-stage clinical condition at the time of the surgery than on immune rejection or other direct effects of the xenograft or on the first-of-its-kind procedure itself.
The 57-year-old Mr. Bennett had presented to the University of Maryland team with nonischemic cardiomyopathy, on multiple inotropes, and requiring an intra-aortic balloon pump, Dr. Mohiuddin said in his ATC presentation. The patient had suffered multiple arrests and resuscitations, and by the time of surgery had been hospitalized for almost 2 months, including 40 days on veno-arterial extracorporeal membrane oxygenation (ECMO).
The transplant procedure itself went as planned until removal of the aortic cross clamp, which triggered a type-A aortic dissection. “We put a graft in the ascending aorta and a stent in the descending aorta. Even after 2 days, we found the dissection extending to the renal artery, so we had to go back and also put a stent in the renal artery,” Dr. Mohiuddin said.
Mr. Bennett also underwent two exploratory laparotomies in the first 10 days after transplantation, after CT imaging revealed signs of possible bowel inflammation and ischemia.
Further, he had to fight back a series of infections that led to major changes to his experimental drug regimen, which included immunosuppressants methylprednisolone and mycophenolate mofetil (MMF), the investigational anti-CD40 antibody KPL-404 (Kiniksa Pharmaceuticals), and the anti-inflammatories etanercept (Enbrel) and tocilizumab (Actemra).
One episode of sepsis, in particular, forced temporary withdrawal of MMF and a reduction in methylprednisolone dosage. It’s unknown whether the 30-day MMF suspension played a role in Mr. Bennett’s ultimate clinical deterioration and death, but it’s “highly possible,” Dr. Mohiuddin said in an interview.
Realistically, Mr. Bennett’s death was likely “multifactorial,” Dr. Mohiuddin said. He was in such poor clinical condition going into the procedure, and afterward confronted so many clinical challenges, that “it’s very difficult to say that one thing caused it.”
That hasn’t lessened speculation that the patient’s heart failed secondary to immunologic rejection or PCMV infection, either in Mr. Bennett or the donor pig.