Cardiosphere-derived cells (CDCs) were grown from rat hearts and percutaneous endomyocardial adult human biopsy specimens. Rat CDCs plated as single cells formed clones with a doubling time of 42.2 ± 0.7 hours (n = 9). Clones from rat CDCs divided steadily for 27 days before proliferation spontaneously slowed and morphological changes occurred in most cells. After 56 days, rat clonal populations contained a small fraction of c-Kit
+
cells as determined by flow cytometry, and large subsets of cells expressing cardiac troponin I, α-smooth muscle actin, and von Willebrand factor as determined by immunofluorescence, indicative of their multipotentiality
in vitro
. To assess therapeutic potential, acute myocardial infarcts (MIs) were created in immunodeficient mice and actively proliferating polyclonal human CDCs were injected into the border zone. Echocardiographic left ventricular function, histological examination, and immunofluorescence served as endpoints. CDC-injected animals showed no significant deterioration in ejection fraction (EF) from 2 days (EF = 45.2 ± 4.8%) to 6 weeks post-MI (EF = 40.2 ± 4.5%, n = 7, p = NS), in contrast to fibroblast-injected control animals (EF = 42.8 ± 4.3% at 2 days vs 27.3 ± 4.0% at 6 weeks, p < 0.01). At the 6 week endpoint, the CDC group had thicker infarct walls as measured histologically compared to the fibroblast group (0.26 ± 0.03mm vs 0.12 ± 0.01mm, n = 5, p < 0.01). CDC engraftment was determined by immunofluorescence using a human-specific antibody. CDCs stably engrafted for up to 6 weeks and could be found distributed primarily throughout the infarct (57 ± 3% of engrafted CDCs, n = 5 animals), as well as the border zone (30 ± 5%) and viable tissue (13 ± 3%). After 6 weeks, CDCs within the infarct had formed small myocytes with little cytoplasmic cardiac troponin I, while CDCs within the viable myocardium had formed large myocytes with well-defined sarcomeric organization. We conclude that CDCs are clonogenic and spontaneously multipotent
in vitro
and capable of preserving heart function in a mouse infarct model. Functional preservation is presumably due in part to maintenance of infarct wall thickness, likely secondary to stable CDC engraftment within the infarct, as well as the formation of morphologically mature myocytes throughout the non-infarcted tissue.
Absence of auto-antibodies against cardiac troponin I predicts improvement of left ventricular function after acute myocardial infarction