updated 9/20/2006 5:00:13 PM ET 2006-09-20T21:00:13

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.

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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.

Largest studies to date
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.
  • Another study in Germany focused on patients who had had heart attacks at least three months earlier — on average more than six years previously. Researchers gave 28 patients an infusion of bone marrow stem cells, 24 an infusion of stem cells from circulating blood and 23 no infusions. Three months after treatment, bone marrow recipients had a 3 percentage point gain in pumping ability compared with the others.

No difference in length or quality of life
These small improvements made no difference in patients feeling better or living longer, although some experts noted the studies were not designed to measure that.

It’s not clear why one study found no effect and two found modest benefits. The explanation may be differences in how many stem cells were used, or in how the cells were handled and prepared, said Dr. Warren Sherman, a Columbia University cardiologist with stem cell expertise.

Five researchers were co-authors on both of the German studies. After the articles were accepted for publication, two researchers notified the journal that they had founded t2cure, a company developing cell therapies for heart disease.

In a commentary in the medical journal, a deputy editor, Dr. Robert Schwartz, lamented that dozens of companies promise cures that involve adult or cord-blood stem cells, though there’s no clear proof that this works.

“These three clinical trials probably will not stop the exploitation of patients,” Schwartz wrote.

The Bush Administration has restricted research that involves the destruction of embryos. But Schwartz and others said the three new studies illustrate the need to pursue embryonic stem cell research.

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