Three new studies published in the New England Journal of Medicine (NEJM) reveal contradictory results following the use of bone marrow-derived stem cells to treat heart attack patients. Two of reports found that injections of a patient's own bone marrow cells can improve heart function after a heart attack, while a third study showed no effect. An accompanying editorial by deputy NEJM editor Dr Robert Schwartz warns that these inconclusive results 'will probably not stop the exploitation of patients with promises that bone marrow (or cord blood) can cure almost any chronic disease'.
Heart attacks damage the heart muscle and associated blood vessels, which stop it working effectively. Previous research suggested that injections of stem cells derived from bone marrow can trigger the growth of new heart muscle, although scientists do not clearly understand how this happens. According to cardiologist Andreas Zeiher of the University of Frankfurt - and leader of two of the trials - the '$100 million question' is whether certain types of bone marrow cell are more effective at cardiac repair than others.
In one of the trials, Zeiher and his colleagues studied 204 volunteers who had suffered a heart attack within the previous week, and a further 75 who had been affected more than six years earlier. Half of the new patients were given an injection of their own bone marrow into the affected artery, while the others received a placebo injection. Four months after treatment, the heart-pumping capacity (measured as 'left ventricular ejection fraction') of the treated participants was 2.5 per cent better than the control group's. A year later, two of the treated patients had died, but none had suffered another heart attack, compared to six deaths and five further heart attacks in the control group.
The study of patients who had suffered heart attacks more than six years previously showed that patients given an injection of bone marrow cells had an improved pumping efficiency of 4.1 per cent. Another group who received injections of blood cells, rather than bone marrow, showed no benefit. A third study, published by scientists based at the Rikshospitalet in Oslo, Norway, also showed no beneficial effect. However, the study was not designed to pick up differences in pumping efficiency of less than five per cent - the minimum improvement team leader Ketil Lunde felt was necessary to justify the invasive procedure.
Zeiher is now planning a trial of a further 1200 patients. Commenting on the recent studies, US cardiologist Joshua Hare told the journal Science: 'I don't think the data's strong enough to say we should start doing this to everybody', adding, 'but it clearly substantiates that we should move ahead'. In his editorial, Dr Schwartz praised the researchers for carrying out 'very difficult studies', but also cautioned that the studies provided no evidence that the injected cells actually became cardiac myocytes (heart muscle cells).