Can stem cells 'mend broken hearts'? Studies raise both hope and doubt

Two major reviews of clinical trials using stem cells to treat advanced heart disease have found a positive effect of the stem cell treatment, but caution against overstating this effect until more trials are carried out. One of the studies highlights worrying 'discrepancies' in data from some of the most successful trials.

The first review was published by The Cochrane Library: an organisation that reviews clinical evidence in almost every field of medicine. By analysing results across several studies, their reviews hope to provide a truer idea of whether a particular treatment works.

For this review researchers analysed data from 23 randomised controlled trials involving 1,255 patients. They found there were fewer deaths among heart disease patients receiving both stem cell treatment and standard treatment, compared to those undergoing standard treatment alone. However, the improvements were not as strong as those seen in patients recovering from heart attacks.

Dr Enca Martin-Rendon, a stem cell researcher at the University of Oxford, and a review co-author, said: 'This is encouraging evidence that stem cell therapy has benefits for heart disease patients. However, it is generated from small studies and it is difficult to come to any concrete conclusions until larger clinical trials that look at longer-term effects are carried out'.

The need for further trials was echoed in a second review, published in the BMJ, which reported on 133 studies from 49 different clinical trials. These trials used bone marrow stem cells - like those analysed by Cochrane - in patients with heart disease, and used ejection fraction (the amount of blood pumped with each heart beat) as their measure of success.

This review concluded there was a small positive effect to stem cell treatment, but at the same time raised issues over discrepancies in some of the trials. Researchers found a strong link between discrepancies and reported benefits - the more discrepancies in the data, the more likely it was for a positive effect to be reported.

No discrepancies were noted for five of the clinical trials in the review. They all reported no benefit from stem cell therapy.

Dr Stephen Epstein, director of translational and vascular biology research at the MedStar Heart Institute in the USA, who was not involved in the study, told Forbes magazine: 'The results and conclusions are shocking, profoundly disappointing and, from a personal perspective, very sad. I’ve been aware of investigators presenting results as more positive than they actually were, or even indicating a negative trial was "positive" by emphasizing the effects on one of several secondary endpoints despite the primary endpoint showing no effect'.