ES-derived cardiomyocytes (green) fix a damaged mouse heart.

Heart cells made from embryonic stem (ES) cells improve the function of injured mouse hearts, report Kolossov et al. (page 2315).

Cell replacement is an attractive therapy for heart failure, which is currently treatable only by organ transplant. But which source of cells makes the best starting material has been a matter of debate. Bone marrow cells were reported to provide some improvement in heart failure patients, but their benefit remains controversial. Kolossov et al. found no improvement of heart function when these cells were injected into mice with ischemic heart injury. Cardiomyocytes derived from ES cells, on the other hand, improved the contractility and blood pumping ability of the injured hearts.

The use of ES cells as starting material for this kind of therapy runs the risk of inducing tumors in the recipient due to small numbers of undifferentiated, pluripotent cells in the population. To limit this risk, Kolossov et al. used genetically engineered ES cells that allowed them to select for a virtually pure population of cardiomyocytes.

This selection trick, however, would have to be modified to be used in humans, as it introduces foreign DNA into the cells. In the meantime, the team plans to see whether similar success is achievable with ES-derived heart cells in larger animals, in which the contractile forces of heart beats are considerably stronger.