Approximately one in 1,000 babies are born with only one functioning ventricle, compromising the infant’s ability to properly oxygenate and send enough oxygenated blood to the rest of its body. Without surgical repair, infants with this condition have a 70% mortality rate.

The current standard of care is the Fontan operation, which reconfigures the major vessels of the heart to pump blood to the rest of the body. Blood returning from the body passively flows to the lung via a synthetic or tissue-engineered vascular conduit.

A new study by Park et al. from the laboratory of Yibing Qyang, PhD, associate professor of medicine (cardiovascular medicine) and associate professor (pathology and biomedical engineering), published in Cell Stem Cell, reveals a new approach of developing tissue-engineered vascular conduits that offer promising benefits to patients.

Because synthetic conduits are prone to infection and blood clotting, and are incapable of growing with the child, they have limited therapeutic efficacy. Biologic or tissue-engineered conduits, on the other hand, are promising alternatives because they can grow and remodel.

“Because a synthetic graft does not grow with the child, surgical intervention must be repeated over and over,” explained Muhammad Riaz, PhD, MPhil, research scientist (cardiovascular medicine) and co-author of the new paper. “A biological graft can listen to the growth stimulus coming from the body.”

For the study, the team used endothelial cells derived from human induced pluripotent stem cells. The benefit of using these stem cells is threefold: 1) these cells reduce blood clots, 2) they can be produced in the billions, which is the number of cells needed for human grafts, and 3) they support an extracellular environment that allows for further endothelial cell recruitment from the patient.

The research paves the way for the use of fully biologic, endothelialized conduits for single ventricle repair that will not have to be replaced as the child ages.

The most significant and novel methodology presented in this paper is endothelial cell luminal flow training. This involves circulating fluid through the new vessel conduit to mimic the patient’s blood flow.

Interestingly, flow training proved to be the key to the antithrombotic properties of these new vessel conduits. When the human induced pluripotent stem cell-derived endothelial cells were coated onto the vessel conduit without flow training, the conduits still formed a blood clot. When these cells were coated with flow training, no clot formed. Riaz and coauthor Wei Zhang, MBBS, PhD, explained that flow training became an integral part of the story.

“Nobody knew that flow training was going to induce the normal physiologic or antithrombotic function of endothelial cells,” Riaz said. “We now know that flow training is required to properly embed antithrombotic factors into the endothelial cell lumen, though we do not yet understand why.”

Co-author Luke Batty, PhD, former graduate student at the Yale Cardiovascular Research Center, said he was surprised by the black-and-white results when comparing them with and without shear stress groups.

“Research into biological systems is rarely that clean,” he said. “This just goes to show how fundamental this biology is to these types of technology,” he said.

“Findings described in the paper have a high translational impact and are likely to significantly improve the outcomes of pediatric patients with relevant disease,” added Lingfeng Qin, MD, PhD, research scientist and co-author. “As a vascular surgeon, I am very much surprised by the extent to which these endothelialized conduits have undergone adaptive remodeling and perfectly integrate into the native vessel of the recipient. Histological staining, visual observation through a microscope, or even a more sensitive micro-CT scan detecting blood flow changes in the vessels were not able to distinguish the grafted conduit from the native vessel.”

"In our paper, the flow training using a bioreactor showed improved function, such as reducing clotting formation, vascular stenosis, and inflammation after transplantation,” said Jinkyu Park, Ph.D., first author of the paper and now an assistant professor at Hallym University, South Korea. “Endothelialized conduits can be applied not only to single ventricle patients but also to various cases requiring vascular replacement, such as blocked or dysfunctional blood vessels or traumatic vascular injuries."

Riaz, Zhang, and the researchers in the Qyang lab are currently working on many additional projects. One involves striving to better understand how to use a patient’s own cells for development. When the patients’ human induced pluripotent stem cells are used for vessel conduits, they have developmental defects and do not become proper cardiac endothelial cells capable of stopping blood clots. Zhang is studying how to flow train the patient’s human induced pluripotent stem cells to become better vessel conduits.

Another issue the team is exploring is rejection. The patient’s immune system rejects cells from another donor unless they are genetically matched. The Qyang lab would ultimately like to be able to use universal human induced pluripotent stem cell-derived endothelial cells that can be implanted in all patients.

“Our endothelialized engineered vascular conduits are expected to solve urgent, graft stenosis issues in recent clinical trials and set the stage for an off-the-shelf therapy for treating infants born with only one functioning ventricle,” said Qyang, who is a faculty member at the Yale Stem Cell Center and Yale Vascular Biology and Therapeutics Program. “We are excited to continue the investigation of this promising technology."

Park J, Riaz M, Qin L, Zhang W, Batty L, Fooladi S, Kural MH, Li X, Luo H, Xu Z, Wang J, Banno K, Gu SX, Yuan Y, Anderson CW, Ellis MW, Zhou J, Luo J, Shi X, Shin JH, Liu Y, Lee S, Yoder MC, Elder RW, Mak M, Thorn S, Sinusas A, Gruber PJ, Hwa J, Tellides G, Niklason LE, Qyang Y. Fully biologic endothelialized-tissue-engineered vascular conduits provide antithrombotic function and graft patency. Cell Stem Cell. 2024 Dec 3:S1934-5909(24)00406-5. doi: 10.1016/j.stem.2024.11.006. Epub ahead of print. PMID: 39644899.

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