Cell delivery and tracking in post-myocardial infarction cardiac stem cell therapy: an introduction for clinical researchers.

Stem cell-based therapy for patients with post-infarct heart failure is a relatively new and revolutionary concept in cardiology. Despite the encouraging results from pre-clinical studies, outcomes from most clinical trials remain moderately positive while the clinical benefits are largely attributed to transplanted cell-associated paracrine effects in stimulating angiogenesis and protecting endogenous cardiomyocytes. This scenario indicates that there may be a considerably protracted iterative process of conceptual and procedural refinement before true clinical benefits can be fully materialized. At present, many pressing questions regarding cell therapy remain unanswered. In addition to the primary interest in determining the ideal type of stem cells with best cardiogenic potential in vitro and in vivo, there are growing concerns on the impact of the host cardiac milieu on the transplanted cells, including their survival, migration, engraftment, and trans-differentiation as well as contribution to left ventricular function. Effective cell delivery and tracking methods are central to the unraveling of these questions. To date, cell-delivery modalities are yet to be optimized and strategies for safe and effective assessment of cells transplanted in the recipients are to be established. In this review, we discuss cell delivery and tracking modalities that are adopted in the current pre-clinical and clinical studies. We further discussed emerging technologies that are poised to impact the success of cell therapy.