During the past three years, several groups had reported that stem cells found in bone marrow could lodge in the heart and repair muscle damaged by a heart attack. These stem cells normally reside in the bone marrow, where they constantly replenish red blood cells and immune cells. If the earlier findings were correct and the blood-forming stem cells switched their fates, that could reveal an exciting new path for treating heart attack patients.
"We started out attempting to validate and extend those findings," said Leora Balsam, MD, a research fellow working with Robert Robbins, MD, associate professor of cardiothoracic surgery.
Instead of supporting previous findings, however, her experiments contradicted them. She found that in mice, blood-forming stem cells lodge in damaged hearts but retain the form of blood cells rather than transforming into muscle cells. A paper by another research group in the same issue of Nature supports Balsam's findings using slightly different methods.
The question now is why some studies have found that blood-forming stem cells can repair the heart while others show that those adult stem cells retain their blood-forming fate. The question is particularly timely given that human trials are already under way based on the strength of earlier findings refuted by the new research.
"If we are delivering bone marrow to patients with the expectation that it will regenerate the heart, that may not be realistic," Balsam said.