Heart transplantation is lifesaving for nearly 500 children each year in the US and Canada. Tragically cardiac allograft vasculopathy (CAV) is the leading cause of deaths after the first year in children after heart transplantation. CAV irreversibly destroys the blood vessels of transplanted hearts. The only therapy for CAV is re-transplantation, but given the shortage of donor hearts, this is frequently not possible. The causes of CAV are poorly understood. One contributing cause of CAV is injury during transportation of the donor heart. Reducing this injury likely will reduce CAV. Our goal is to develop a model that contains many key elements of the pediatric heart and we can use to simulate the injury to donor hearts. Proposed is the building of heart tissue from human stem cells complete with its blood vessels formed using highly innovative micro printing techniques. We believe that we can simulate the donor heart injury in “synthetic” heart tissues to better understand the causes of CAV. Ultimately, we hope to investigate strategies and drugs that can be used to prevent and/or reverse CAV and the deaths of children and adults after heart transplantation.

Evidence indicates that cardiac allograft vasculopathy (CAV) begins in the microvasculature (1). This study proposes developing a micro-vascularized endomyocardial tissue (MCT) model for characterizing how ischemia-reperfusion injury (IRI) during organ procurement is linked to CAV.

Aims: We hypothesize that novel 3D bioprinting of etched matrices will guide co-culturing of functional cardiomyocytes (CMs) and endothelial cells (EC) derived from human induced pluripotent stem cells (iPSCs) to form MCT. Aim 1 is to matrix guide ECs to form perfused microvessels. Aim 2 is to matrix guide CMs to synchronously paced contractions (Aim 2A) and, with ECs, to perfused MCT (Aim 2B). Aim 3 is to simulate IRI in MCT.

Further investigation is needed to elucidate the multifactorial pathophysiological process of CAV (2). The nonimmune pathophysiological processes predisposing to CAV all share in common inflammatory injury leading to endothelial dysfunction.(3) Ischemia-reperfusion injury (IRI) is considered a significant nonimmune risk factor both for rejection and in the development of cardiac allograft vasculopathy (CAV) of transplanted pediatric hearts. Given the increasing evidence that CAV begins in the microvasculature as early as the first year post transplant (1), this study focused on the linkage between IRI during organ procurement and early CAV about which there is limited insights due, in part, to the lack of relevant in vitro models. This study proposes developing a human cell-derived model of endomyocardial tissue suitable for simulation of IRI to cardiac microvasculature with a focus on identification of risk factors for CAV.

The MCT developed in this proposed study will have several key features. The genetic background will be human. The ECs and the micro vessels self-assemble with CMs promoting, and responding to, the signaling and cell-cell interactions that occur during normal cardiac tissue development and maturation. The modeling of ischemia will be enhanced by the work of contractions which also serves as a relevant metric to assess the effects of ischemia and reperfusion/recovery for each MCT. The intent is to characterize the expression of putative phenotype changes in the micro vessels induced by IRI screening for changes that have been suspected as increasing the risks for maladaptive innate and alloimmune responses identified in pediatric heart recipients. In Phase II, novel insights from the MCT model studies could be specifically investigated in analyses of endomyocardial biopsies of pediatric recipients with/without the occurrence/progression of CAV.

This study is aligned with the Enduring Hearts priority to fund the development of strategies to prevent or reduce the post-transplant development of rejection, cardiac allograft vasculopathy (CAV) and/or graft failure. CAV is the major cause of late graft loss in pediatric heart transplant patients and ischemia-reperfusion injury is one of the recognized non-immune risk factors of CAV (2, 4). Microvascular dysfunction and loss of contractility are associated with ischemia-reperfusion injury and CAV (5).