People who suffer heart attacks often go on to develop congestive heart failure. This occurs because heart muscle cells, or cardiomyocytes, have a limited capacity to divide; cells that die during an acute coronary event typically are replaced by scar tissue rather than by new healthy cells. A recent study showing that bone marrow stem cells injected into the damaged hearts of living mice differentiated into cardiomyocytes and improved heart function was met with great excitement and prompted clinical trials of the procedure.
Now, data from two independent laboratories raise questions about the earlier mouse study. Using highly sensitive labeling methods to monitor the fate of bone marrow cells injected into damaged or healthy mouse hearts, Murry et al. and Balsam et al. find no evidence that these donor cells differentiate into cardiomyocytes. Although neither study rigorously addresses the therapeutic potential of the procedure, the results indicate that any functional improvements that might be seen in the clinical trials are unlikely to be due the cell differentiation mechanism originally proposed. — PAK
Nature 428, 10.1038/nature02446; 10.1038/nature02460 (2004).