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Monitoring Stem Cell Research 
pharmacological agents and production of vasoactive factors such as 
atrial and brain natriuretic peptides. However, in vivo evidence for 
functional cardiac improvement following transplantation of adult 
bone marrow-derived or ES-derived cardiomyocytes has been 
exceedingly difficult to show to date. In part this may be because 
the signals required for cardiomyocyte differentiation and functional 
regulation are complex and poorly understood. For example, 
phenotypic and functional differentiation of mesenchymal stem cells 
to cardiomyocyte lineage cells in vitro requires culture with 
exogenously added 5-azacytidine Alternatively, the poor 
functional data obtained to date may reflect immune-mediated 
rejection of cells which have been modified during the ex vivo culture 
process or poor viability due to the lack of a sufficient vascular 
supply to the engrafted cells (see below). 
Potential Role For Autologous Skeletal Myoblasts In Myocardial 
Repair. An alternative approach to replacing damaged myocardium 
involves the use of autologous skeletal myoblasts The procedure 
involves harvesting a patient's skeletal muscle cells, expanding the 
cells in a laboratory, and re-injecting the cells into the patient's heart. 
Perceived advantages of the approach include ease of access to the 
cellular source, the fact that immunosuppression is not needed, and 
the lack of ethical dilemmas associated with the use of allogeneic or 
embryonic cells. It has also been argued that using relatively 
ischemia-resistant skeletal myoblasts rather than cardiomyocytes 
might enable higher levels of cell engraftment and survival in 
infarcted regions of the heart, where cardiomyocytes would probably 
perish 
Successful engraftment of autologous skeletal myoblasts into 
injured myocardium has been reported in multiple einimal models of 
cardiac injury. These studies have demonstrated survival and 
engraftment of myoblasts into infarcted or necrotic hearts 
differentiation of the myoblasts into striated cells within the 
damaged myocardium and improved myocardial functional 
performance other studies have shown that the survival of 
transplanted myoblasts can be improved by heat shock pretreatment 
^ , and have confirmed that the benefits of skeletad myoblast transfer 
are additive "with those of conventional therapies, such as 
angiotensin-converting enzyme inhibition More recently, the 
procedure has been reported anecdotally to result in improved 
myocardial function in humans On the basis of these preliminary 
results, clinical trials have begun both in Europe and in the United 
States. In addition to demonstrating functional improvement in 
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