Comparative efficacy and mechanism of action of cardiac progenitor cells after cardiac injury.

Successful cell therapy requires cells to resist the hostile ischemic myocardium, be retained to continue secreting cardioprotective growth factors/exosomes, and resist immunological host responses. Clinically relevant stem/progenitor cells in a rodent model of acute myocardial infarction (MI) demonstrated that neonatal cardiac mesenchymal stromal cells (nMSCs) provide the most robust cardiac functional recovery. Transplanted nMSCs significantly increased the number of tissue reparative macrophages and regulatory T-cells and decreased monocyte-derived inflammatory macrophages and neutrophils in the host myocardium. mRNA microarray and single-cell analyses combined with targeted depletion studies established CD47 in nMSCs as a key molecule responsible for cell retention in the myocardium through an antiphagocytic mechanism regulated by miR34a-5p. Gain and loss-of-function studies demonstrated that miR34a-5p also regulated the production of exosomes and cardioprotective paracrine factors in the nMSC secretome. In conclusion, miR34a-5p and CD47 play an important role in determining the composition of nMSCs' secretome and immune evasion, respectively.