Adult stem cells show little benefit in heart studies

Giving heart attack survivors stem cells from their own bone marrow did little to repair their damaged hearts, according to the three best studies to date of this controversial therapy.

The modest results suggest more study is needed — and, some scientists say, demonstrate the need to lift political limits on using cells from embryos, which offer more promise for turning into heart-repairing tissue.

"The optimal cell type has not been discovered yet," said Dr. Kenneth Chien, director of the Massachusetts General Hospital Cardiovascular Research Center, who had no role in the studies.

Chien said experiments in various laboratories over the past 15 years suggest embryonic stem cells show they can turn into beating cardiac muscle, though it has not been tried in human patients. "This is an area worthy of further pursuit," he said.

The three new studies, reported in Thursday's New England Journal of Medicine, are the largest and most scientific tests yet of whether stem cells derived from adult patients can improve heart function.

Stem cells are blank slates that have the potential to become heart cells or other types of specialized cells. Scientists do not know whether those found in adults have the same potential to specialize as those from embryos.

The studies focused on damage caused by heart attacks, which weaken the heart muscle and reduce its ability to pump blood. Researchers looked at whether stem cells could remedy damage to the main pumping chamber.

In each study, stem cells were infused into the heart through a cardiac catheterization. A tiny balloon momentarily blocked regular blood flow into the heart and stem cells were injected in an attempt to give them a couple of minutes to try to take root.

Success was measured by changes in the amount of blood pumped out with each heartbeat.

• Norwegian researchers gave bone marrow stem cells to 50 patients who'd had heart attacks the previous week and compared them to a similar group who received no such cells. There was no significant improvement six months later.

• German researchers gave stem cell infusions to 101 patients who had suffered a heart attack in the previous week. Another 103 heart attack survivors were given sham infusions. After four months, heart function improved 5.5 percentage points in those who received cell therapy and 3 points in the placebo group.