European researchers report promising results from clinical trials to test whether injections of bone marrow cells can repair heart attack damage.

Bone marrow cells -- a mixture of cells obtained from a patient’s own bone marrow -- are thought by some scientists to contain stem cells that can become heart muscle cells or blood vessel cells.

That hasn't been proved.

But three studies appearing in the Sept. 21 issue of The New England Journal of Medicine show such treatments can offer a benefit to patients -- even if doctors don't yet know how best to use the treatments, in which patients, or at what time.

The trio of studies is an indication of how important this research may one day turn out to be.

Still, one of the trials found no effect when the treatment was given six days after a heart attack.

But another, larger, trial showed that patients who received the bone marrow cells three to seven days after they were given clot-busting treatment did a bit better than patients who got that state-of-the-art treatment alone.

The third trial showed the treatment moderately improved heart function even when given more than six years after a heart attack.

The studies "provide a realistic perspective on this approach while leaving room for cautious optimism and underscoring the need for further study," concludes Harvard Stem Cell Institute researcher Anthony Rosenzweig, MD, in an accompanying editorial.

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"Patients benefited from many established therapies -- including aspirin -- before we understood the underlying mechanisms," Rosenzweig notes. But "even aspirin might not be as effective if it were still being delivered as willow bark."

For the new approach to be fully developed, researchers will have to find out exactly which -- if any -- of the bone marrow cells repair the heart. Until then, Rosenzweig says, patients should receive these treatments only in clinical trials.

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SOURCES: Lunde, K. The New England Journal of Medicine, Sept. 21, 2006; vol 355: pp 1199-1209. Schächinger, V. The New England Journal of Medicine, Sept. 21, 2006; vol 355: pp 1210-1221. Assmus, B. The New England Journal of Medicine, Sept. 21, 2006; vol 355: pp 1222-1232. Rosenzweig, A. The New England Journal of Medicine, Sept. 21, 2006; vol 355: pp 1274-1277. Schwartz, R. The New England Journal of Medicine, Sept. 21, 2006; vol 355: pp 1189-1191.