Baby receives world’s first combination heart, thymus tissue transplant
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An infant believed to be the first to receive a combination heart transplant and allogeneic processed thymus tissue implant is gaining immune function 6 months after the procedures, potentially reducing the need for antirejection drugs.
The two procedures were performed at Duke University Hospital on Aug. 6, under an expanded access application cleared by the FDA. Researchers called the procedures a milestone in heart transplantation.
The infant, Easton Sinnamon, was aged 6 months when he received his heart transplant. Implantation of the cultured thymus tissue from his heart donor was performed 2 weeks after the heart transplant. Easton was born with severe single-ventricle heart disease as well as thymic deficiency from an unknown cause, causing recurrent infections that prohibited him from being placed on the heart transplant list, according to Joseph W. Turek, MD, PhD, chief of pediatric cardiac surgery at Duke Health.
The successful procedures could lead to expanded viability for transplanted organs in the future, Turek told Healio. Currently, transplanted hearts have an average life span of about 10 to 15 years, Turek said. With durability limited by the toxicity of immune-suppression drugs, other options have long been sought.
“When we perform transplantation for congenital athymia here at Duke, it is only approved for patients aged 9 months or younger,” Turek told Healio. “It helped us to get FDA approval to perform a thymic transplant on Easton because he was 6 months old at the time he received his heart. In the laboratory, we are currently researching what is the age of a thymus that could potentially be potent enough for transplant. This could expand the number of patients who could benefit from this procedure beyond infants — potentially with donors aged 10, 20 and 30 years.”
Heart recognized as ‘self’
Duke researchers received permission from the FDA for the investigational procedures after two important factors lined up: The infant needed a heart transplant and processed thymus tissue implantation independent of one another and he was a patient at Duke, where processed thymus tissue implantation is solely available.
“It was serendipitous in the sense that Easton need both a heart transplant and he also had very poor immune function,” Turek said. “We do each of these operations independently at Duke. We are the only place in the Western Hemisphere that does cultured thymic transplantation for patients with congenital athymia, so we had that expertise in-house. We also perform many heart transplants here. That allowed us to have discussions with FDA and gain approval to try this groundbreaking work in his situation with less risk than we would have otherwise.”
In a media briefing, Turek called the combination of the two procedures “very intriguing” and a longtime goal of Duke researchers, who have performed similar work in animal experiments.
“We thought if we did a thymus and heart transplant on Easton, there is potential that taking both from the same donor would allow that heart to be recognized as ‘self,’” Turek said. “This is a concept known as tolerance, and tolerance has been the holy grail for transplantation. This could be applied to all solid organs down the road if this works.”
The successful combination of procedures could also mean the infant would not reject the heart, even if all immunosuppression medications were withdrawn, Turek said.
Easton, now aged 13 months, continues to take immunosuppression medications, Turek said. In several months, he could be tapered off antirejection drugs if he continues to do well.
The processed thymus tissue implantation method, pioneered at Duke by Louise Markert, MD, uses a proprietary technique to culture and administer processed thymus tissue (Enzyvant Therapeutics GmbH), Duke stated in a press release. The FDA approved allogeneic processed thymus tissue-agdc last fall, indicated for immune reconstitution in pediatric patients with congenital athymia.
Driving future research
During the briefing, Turek said tests show the transplanted processed thymus tissue is functioning and building T cells. Easton’s care team at Duke continues to monitor progress.
“We waited to announce this because we wanted to make sure his immune system was responding,” Turek said. “Sure enough, he is developing his own T cells. We are excited about it.”
Future research will focus on how the two procedures might work for a patient with a competent immune system, Turek said.
“That has been the major obstacle in the research, and we feel we are making progress with this in using this cultured thymus tissue,” Turek said. “With cultured tissue, that allows scaffolding to be created so you don’t have the other cells in the thymus; you can form a brand-new immune system. This organ, whether it is a heart or a liver or whatever it may be, can grow up with that new thymus together and be recognized.”
Easton’s parents, Kaitlyn Sinnamon and Brandon Sinnamon, said their son was placed on extracorporeal membrane oxygenation early in his life as his heart began to fail. They described the day they finally brought him home from the hospital as “amazing.”
“We knew he wanted to be here, and he brought us to our decision to do this transplant,” Kaitlyn Sinnamon said.
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