A systematic review of the evidence so far suggests stem cells derived from bone marrow moderately improves heart function after a heart attack. But the authors say larger trials are needed before we can devise guidelines for therapy practice, or draw conclusions about the long-term benefit of the treatment, such as whether it extends life.

The review, about to be published in the Cochrane Library, updates one done in 2008 that reviewed 13 trials; the new one takes into account another 20 more recent trials. Even though these later trials had longer follow ups, it was still not possible to draw firm conclusions about the long term benefits.

Lead author Enca Martin-Rendon, of the Stem Cell Research laboratory, NHS Blood and Transplant at the John Radcliffe Hospital in Oxford, UK, told the press that they found it hard to compare the 33 studies because they used so many different approaches:

“Larger trials with standardised treatment procedures would help us to know whether this treatment is really effective,” said Martin-Rendon.

In order to pump blood around the body, the heart also needs its own constant supply of blood. If this supply is cut off by a blocked artery, it can cause a heart attack and damage the muscle tissue in the affected part of the heart, causing the cells to start dying, a process known as necrosis.

In the days and weeks after a heart attack, the necrosis can spread, eventually leaving a large part of the heart muscle unable to perform the job of contracting and pumping as well as it ought to. This increases the risk of further heart problems.

Stem cells are precursor cells that have the potential to mature into any cell in the body, including heart muscle cells. For this review, the researchers looked only at treatments that use stem cells derived from bone marrow. At present, such treatments are only available at centres that do research.

Another recently published study described a treatment that used stem cells derived from the patient’s own heart tissue to repair heart attack damage.

For the review, Martin-Rendon and colleagues pooled data on a total of 1,765 patients from 33 trials. All the patients had already undergone the conventional treatment, angioplasty, where a balloon is inflated in the blocked artery to open it up and restore blood flow.

They concluded that stem cell therapy using bone marrow-derived stem cells (BMSCs) can result in a moderate long-term improvement in heart function, that lasts for up to 5 years. But there was not enough data to enable them to say anything firm about the effect on survival rates.

Martin-Rendon said:

“This new treatment may lead to moderate improvement in heart function over standard treatments,” adding that:

“Stem cell therapy may also reduce the number of patients who later die or suffer from heart failure, but currently there is a lack of statistically significant evidence based on the small number of patients treated so far.”

The authors said it was still to early to compile guidelines for standard practice, and further work would be needed before anyone can do this. For instance, more information is needed to establish cell dosage, the timing of transplantation and how best to measure heart function.

One large trial, called BAMI, is already under way. The European Society of Cardiology for Stem Cells and Cardiac Repair is conducting the trial, which is funded by the European Union Seventh Framework Programme for Research and Innovation (EU FP7-BAMI).

Anthony Mathur, a co-author of this latest Cochrane review, and principal investigator of the BAMI trial, said:

”The BAMI trial will be the largest stem cell therapy trial in patients who have suffered heart attacks and will test whether this treatment prolongs the life of these patients.”

Written by Catharine Paddock PhD