Adult bone marrow-derived cells: regenerative potential, plasticity, and tissue commitment.

Reconstitution of infarcted myocardium with functional new cardiomyocytes and vessels, a goal that only a few years ago would have been regarded as extravagant, is now actively pursued in numerous laboratories and clinical centers. Several recent studies in animals as well as humans have shown that transplantation of adult bone marrow-derived cells (BMCs) can improve left ventricular function and halt adverse remodeling after myocardial infarction. Differentiation of adult BMCs into cells of cardiac and vascular lineages has been proposed as a mechanism underlying these benefits and, indeed, differentiation of adult BMCs into cells of non-hematopoietic lineages, including cells of brain, skeletal muscle, heart, liver, and other organs, has been documented repeatedly both in vitro and in vivo. These results are in contrast with conventional definitions and dogma, according to which adult tissue-specific stem cells exhibit only restricted differentiation potential. Thus, these recent studies have sparked intense debate over the ability of adult BMCs to differentiate into non-hematopoietic tissues, and the regeneration of myocardium by differentiation of adult BMCs remains highly controversial. Because of the enormous clinical implications of BMC-mediated cardiac repair, numerous laboratories are currently addressing the feasibility of cardiac regeneration with BMCs and deciphering the mechanism underlying the beneficial effects. The purpose of this review is to critically examine the available evidence regarding the ability of adult BMCs to regenerate non-hematopoietic tissues and their utility in therapeutic cardiac regeneration.