Tissue Engineering Strategies to Improve Post-MI Engraftment of hESC-Derived Cardiomyocytes

Abstract

Transplantation of stem cell-derived cardiomyocytes is a promising strategy for repairing damaged cardiac muscle following a myocardial infarction. Our group and others have demonstrated both long-term engraftment and increased cardiac function after implantation in preclinical models using rodents and large animals. Despite this progress, there are still significant limitations to address in order to facilitate successful clinical translation of this therapy. Firstly, multiple delivery methods have been used to transplant stem cell-derived cardiomyocytes (hESC-cardiomyocytes) in rodents, including injecting cell suspensions and implanting engineered tissues. However, the ability of human cardiomyocytes to electrically and mechanically integrate with rodent myocardium using these delivery methods is not well understood. Secondly, current transplantation methods only retain a small fraction of implanted cells, leading to small graft size and an excess of cells needed for transplant. Here, we first conducted a comparative study to assess the engraftment and electromechanical integration of hESC-cardiomyocytes in the infarcted rat myocardium. This research demonstrated for the first time that human cardiomyocytes electrically integrate with the rat myocardium and beat in synchrony to rates over 6 Hz. We demonstrated that intramyocardially delivered cells (injected as a cell suspension or as cardiac micro-tissues) were electrically coupled to the host tissue, compared to no observed coupling when delivered as epicardial patches. All implant methods resulted in human myocardial grafts, however there was no improvement in graft area using these scaffold-free tissue engineering approaches compared to cell suspensions. To address this limitation, we designed an approach to improve engraftment and limit the number of cells required for implantation by promoting cardiomyocyte proliferation after transplantation. We developed a collagen-based hydrogel with the immobilized Notch ligand Delta-1, which was used in vitro to promote Notch signaling and increase cardiomyocyte proliferation by over 2-fold in engineered cardiac tissues. The optimized Notch-signaling hydrogel was then translated in vivo and used as a delivery vehicle for hESC-cardiomyocytes in the infarcted rat myocardium. This resulted in a 3-fold increase in cardiomyocyte proliferation and a 3-fold increase in graft size compared to controls. Taken collectively, the research in this dissertation highlights the potential of tissue engineering strategies to improve implantation of stem cell-derived cardiomyocytes, by promoting electromechanical integration and cell proliferation in preclinical models of myocardial infarction.