Stem cell therapy for end-stage heart failure: indispensable role for the cell?

PURPOSE OF REVIEW: For heart failure patients, the urgent need for heart transplantation exceeds the availability of donor hearts. Therefore, cell transplantation has emerged as an interesting and potential solution. This review will focus on the capability of different types of stem cells to regenerate the heart. Moreover, the mechanism for success will be addressed, focusing on the specific (and indispensable?) role of the cells. RECENT FINDINGS: In recent years, many types of stem cells have been described as a possible source for cell transplantation in failing hearts, with mixed outcomes. Cell transplantation is hampered by suboptimal delivery techniques, limited survival of cells, and reduced proliferation and differentiation rates in vivo. Interestingly, the number of injected cells that engrafted the heart successfully cannot explain the observed beneficial effects and, therefore, paracrine effects are suggested for the success in cell therapy. SUMMARY: This review summarizes the current types of stem or progenitor cells used in cardiac cell therapy and beneficial effects on heart function and morphology in preclinical studies. Currently, the observed effects suggest that paracrine effects might be responsible, thereby triggering mobilization and activation of resident (stem) cells, which challenges the classical concept and true regenerative capacity of cell therapy at this point.