Controlling cell proliferation and tissue formation for myocardial repair

The repair of myocardial infarction by implantation of exogenous cells holds substantial promise for the prevention and treatment of heart failure. Unfortunately, small and highly variable cell-graft size limits the functional benefit of this therapy. This work seeks to control intracardiac graft size by developing innovative technologies to (1) increase graft cell proliferation through the modulation of intracellular signaling, and (2) improve cell seeding efficiency and survival by engineering the formation of three-dimensional cardiac tissue.;To control graft cell proliferation, we genetically encoded skeletal myoblasts to express a chimeric drug-responsive growth factor receptor. Drug administration activated the chimeric receptor and stimulated the proliferation of genetically modified skeletal myoblasts in vitro. After injection of these cells into infarcted mouse hearts, systemic drug delivery doubled intracardiac graft size. Importantly, dose-dependent increases in myoblast graft size were associated with corresponding reductions in adverse ventricular dilation following myocardial infarction. Since skeletal muscle cannot electromechanically couple with host cardiomyocytes after implantation in the hearts, a chimeric receptor system to control the proliferation of human cardiomyocytes derived from embryonic stem cells was next developed. Human cardiomyocytes genetically expressing this receptor proliferated in response to drug in a variable fashion. Further development of this system is ongoing.;A system to control three-dimensional cell aggregation was next developed in order to create scaffold-free human cardiac tissue patches. Extended culture time and media optimization yielded patches that were highly pure for viable and proliferative cardiomyocytes. Further addition of endothelial cells and fibroblasts to these patches resulted in the formation of an endothelial cell network morphologically resembling a rudimentary vascular plexus. "Tri-cell" patches containing cardiomyocytes, endothelial cells, and fibroblasts were also stiffer than those containing only cardiomyocytes, suggesting that they contained a connective tissue element. After implantation into infarcted rat hearts, tri-cell human cardiac tissue patches formed long-term and stable grafts of human myocardium as well as microvessels that anastomosed to the host coronary circulation. Taken together, these technologies address several critical challenges associated with cell grafting for the repair of human heart disease.