Chaiwat Subprasom/Reuters/Corbis

Many companies around the world offer stem-cell treatments to patients with heart disease.

An analysis of clinical studies that use adult stem cells to treat heart disease has raised questions about the value of a therapy that many consider inappropriately hyped.

Early-phase clinical trials have reported that adult stem cells are effective in treating heart attack and heart failure, and many companies are moving quickly to tap into this potentially lucrative market. But a comprehensive study that looked at discrepancies in trials investigating treatments that use patients own stem cells, published this week in the journal BMJ (ref. 1), finds that only trials containing flaws, such as design or reporting errors, showed positive outcomes. Error-free trials showed no benefit at all.

The publication comes as two major clinical trials designed to conclusively test the treatments efficacy are recruiting thousands of patients.

The BMJ paper is concerning because the therapeutic approach is already being commercialized, argues stem-cell researcher Paolo Bianco at the Sapienza University of Rome. Premature trials can create unrealistic hopes for patients, and divert resources from the necessary basic studies we need to design more appropriate treatments.

Therapies that use adult stem cells typically involve collecting mesenchymal stem cells from bone marrow taken from the patients hip bone. The cells are then injected back into the patient, to help repair damaged tissue. Original claims that they differentiated into replacement cells have been rejected2, and many clinicians now believe that the cells act by releasing molecules that cause inflammation, with an attendant growth of oxygen-delivering small blood vessels, in the damaged tissue.

The approach has spawned international commercialization of various forms of the therapy, with companies offering treatments for disorders ranging from Parkinsons disease to heart failure. But the effectiveness of such therapies remains unproven.

I have a lot of hope for regenerative medicine, but our results make me fearful.

The BMJ study, led by cardiologist Darrel Francis at Imperial College London, examined 133 reports of 49 randomized clinical trials published up to April last year, involving the treatment of patients who had had a heart attack or heart failure. It included all accessible randomized studies, and looked for discrepancies in design, methodology and reporting of results.

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Doubts over heart stem-cell therapy