Engineering a strategy for the preservation and rehabilitation of living allogenic heart valves

PROJECT SUMMARY/ABSTRACT Despite the global need, there is no heart valve replacement with long-term durability or growth potential. Such need is most critical for pediatric patients born with congenital heart defects, as continued growth and remodeling of the implanted valve is essential for avoiding multiple surgeries, which are the current standard of care. Living allogenic valve transplantation (LAVT) has recently been introduced as a means of delivering a valve replacement with physiologic growth and self-repair mechanisms. Nevertheless, LAVT suffers from limitations regarding i) availability, ii) ex vivo viability, iii) the cost, time and resource constraints related to minimizing tissue ischemic time, and iv) immunogenicity. What remains lacking is a living valvular allograft that can be transplanted off-the-shelf. Therefore, this project seeks to develop a strategy for the preservation of living valvular allografts for at least 3 weeks ex vivo. The central hypothesis is that environmental control of the key factors inducing valve degradation, combined with biomimetic physical stimuli, will enable maintenance of valve viability, microarchitecture, and function. To inform the design of this storage strategy, pathologic processes in failed cryopreserved homografts (the historic gold-standard) will be characterized (Aim 1). The rationale is that the mechanisms underlying failure of currently-available homografts will serve as the blueprint for developing a storage technique capable of overcoming these same adverse outcomes (Aim 2). Patterns of cell infiltration and cell phenotype, pathologic shifts in the extracellular matrix, and immunologic rejection will be investigated. Aim 2 will be carried out in integrated fashion with Aim 1. Aims 2.1 and 2.2 identify the temperature and biochemical cues required to preserve valvular allograft physiology ex vivo, respectively. Aim 2.3 will be executed in parallel, and focuses on development of a bioreactor which continuously exposes valvular allografts to open/close cycles at a physiologic rate. Taken together, the project’s success would enable ex vivo valve preservation, significantly enhancing the clinical availability and logistic-ease of LAVT. The living nature of these tissues is particularly relevant to the pediatric field, where it is imperative that implanted grafts grow with the patient. Furthermore, this study has focus on the environmental elements required to maintain valvular homeostasis. This offers unique insights in valve tissue physiology, and how the absence of key bio-instructive factors can contribute to valvular disease. This study will be carried out as a collaborative effort between the labs of Dr. Gordana Vunjak-Novakovic (University Professor at Columbia) and Dr. David Kalfa (Congenital Heart Surgeon and Director of the Pediatric Heart Valve Center at Columbia), both located on the Columbia University Medical Center Campus. The proposed fellowship applies tools of cell and tissue engineering towards developing living-tissue valve replacements for clinical use, synergizing translational research with clinical experience. The labs collectively bring expertise in cardiac valve engineering, tissue engineering, stem cells, valve physiology, and cardiothoracic surgery – synergizing these skills towards developing a living valve replacement for young patients.