German doctors have found that their method of using bone marrow stem cells to repair tissue damaged by heart attacks did not work in a major clinical trial. The German researchers at the German Heart Centre in Munich gave patients a factor which stimulated stem cell activity. This worked as planned, but there was no difference in the amount of heart damage or in the heart-pumping ability of patients who got the treatment and of those who did not.

Nonetheless, researchers in the field are not discouraged. “The field is so complex at this time and there is limited understanding of which cells are most important, how many cells are needed to have a desired effect and what is the best vehicle to deliver them to the site of a myocardial infarction [heart attack],” said Dr Robert A. Kloner in an editorial in the Journal of the American Medical Association.

“I, for one, am not ready to give up on this technology,” he wrote. “The basic concept that stem cells may someday be used to treat heart attacks is exciting.”

Several human trials are under way, Kloner said. “Some studies are using stem cells injected directly into the heart muscle, some use intracoronary artery injection, some use bone marrow stem cells. What we need now are larger, well-controlled studies.” It will take four or five years for the technique to prove its worth, he said.