Cardiac progenitor cells: In vitro and in vivo characterization

The adult human heart contains small populations of resident progenitor cells capable of repairing a limited amount of damage. A method to expand cardiac progenitors in culture would allow for the readministration of cardiac progenitors to bolster the endogenous response after injury. Cardiac progenitor cells were grown from percutaneous endomyocardial biopsy specimens taken from 70 adults using the cardiosphere culture method. Cardiosphere-derived cells (CDCs) were immunophenotyped and subjected to differentiation assays in vitro. CDCs were found to contain populations of cardiac progenitor cells, cardiac mesenchymal cells, endothelial precursors, and cardiomyocyte precursors. CDCs formed tube-like networks when subjected to an endothelial differentiation assay, while CDCs co-cultured with neonatal cardiomyocytes cycled calcium in sync with neighboring cells and demonstrated electrophysiological properties of cardiomyocytes. Furthermore, CDC-conditioned media restored tube-formation capacity to growth factor-starved human umbilical vein endothelial cells and protected neonatal cardiomyocytes from undergoing hypoxia-induced apoptosis. To assess in vivo therapeutic potential, acute myocardial infarcts (MIs) were created in immunodeficient mice and human CDCs were injected into the infarct border zone. Echocardiographic left ventricular function and multiple cell-tracking techniques served as endpoints. Optical imaging revealed that CDCs were located only within the heart for up to 1 week post-MI. Western blot revealed that CDCs secreted hepatocyte growth factor, insulin-like growth factor 1, and vascular endothelial growth factor in vivo for up to 3 weeks post-MI. Histology revealed that CDCs stably engrafted for up to 6 weeks and could be found distributed throughout the infarct, border zone, and remote myocardium. After 6 weeks, CDCs within the infarct had formed small cardiomyocytes, while CDCs within the remote myocardium had formed large cardiomyocytes with well-defined sarcomeric organization. Cell fusion did not play a significant role in the formation of CDC-derived cardiomyocytes as determined by fluorescence in situ hybridization. CDC-treated animals maintained left ventricular function better than control animals treated with dermal fibroblasts or injection solution, and better than animals treated with cardiac progenitors or cardiac mesenchymal cells alone. Left ventricular remodeling was also attenuated in CDC-treated animals. We conclude that human CDCs are capable of cardiac regeneration. Autologous CDCs offer an attractive source for cellular cardiomyoplasty.