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Stem cell repair of infarcted myocardium: an overview for clinicians.

Under appropriate cell culture conditions, stem cells are capable of differentiating into cardiac myocytes and endothelial cells (Table 1). If these results can be reproduced in vivo, it may be possible to use stem cells to impede progressive deterioration into heart failure or even to restore cardiac function in patients with acutely or chronically damaged myocardium. In this article, we will provide for the clinical cardiologist a brief overview of the conceptual basis for stem cell therapy and review the current laboratory evidence supporting its potential value. We will describe the clinical options in stem cell treatment of damaged myocardium and the potential limitations that need to be assessed in randomized clinical trials. 

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TABLE 1. Glossary of Terms Used in This Article 



### The Conceptual Basis of Stem Cell Therapy

Stem cells share the following two defining characteristics: the capacity to differentiate into a spectrum of different cell types and the capacity to renew themselves.1 The biological principle that underlies stem cell therapy is tissue-directed differentiation. For example, adult stem cells isolated from liver tissue and reinjected into liver become hepatocytes, whereas the same cells injected into myocardium become myocytes.2 Stem cells have been engrafted into a broad spectrum of tissues, including regenerating bone, neural tissue, dystrophic skeletal muscle, and injured skeletal muscle.3

The classification of stem cells, based on a large number of cell markers, is still in evolution, and interested readers are referred to excellent reviews in the basic science literature.4,5 The primary distinction is between embryonic and adult stem cells. Most cardiovascular research has used adult stem cells derived from the bone marrow. Within the bone marrow, a simplified distinction is between CD34+ hematopoietic stem cells, which are precursors of blood and endothelial cells, and CD34− mesenchymal stem cells, which are precursors of stromal cells, including fibroblasts and osteocytes. …