Mechanisms that regulate homing function of progenitor cells in myocardial infarction.

Cell based therapy has become a new and attractive option for the treatment of cardiac disease and heart failure. Although it has been demonstrated in vitro and in vivo that differentiation of non-differentiated cells (progenitor cells) into cardiomyocytes is able even in adult hearts the potential use of such transdifferentiation processes is limited by the small number of cells that home and engraft in the myocardium and complete the transdifferentiation process. Therefore, cell recruitment to the damaged heart is a major challenge to improve any cell based therapy. This process requires homing and engraftment of stem or progenitor cells. Major strategies to improve stem or progenitor cell homing are based on an improvement of stem or progenitor cell mobilization from the bone marrow. Strategies that have been shown to be successful are those that use granulocyte colony-stimulating factor (G-CSF). But although cell mobilization was indeed successful no major impact on hemodynamics was found. Alternatives are therefore needed and experimental studies use parathyroid hormone, statins, erythropoietin, and others in addition to or as an alternative to G-CSF. Although each of these procedures does have an impact on cell mobilization and homing none of these studies has provided a direct evidence that a major improvement on top of standard pharmacological therapy can be expected from such strategies. In conclusion, improvement of stem cell homing is a major challenge in the development of successful cell based therapies but not yet improved to a clinical relevant status. The underlying concepts of different strategies will be discussed here.