A research network led by a Mayo Clinic physician found that stem cells obtained from bone marrow delivered two to three weeks after a person has a heart attack did not improve heart function. This is the first study to systematically examine the timing and method of stem cell delivery and provides vital information for the field of cell therapy.
The results were presented this morning at the 2011 Scientific Sessions of the American Heart Association Meeting in Orlando, Fla.
They also will be published online in JAMA to coincide with the presentation.
"Some data suggests that stem cell therapy is helpful within the first week after a heart attack," says Robert Simari, M.D., cardiologist at Mayo Clinic and chairman of the Cardiovascular Cell Therapy Research Network (CCTRN). The network includes five clinics and other sites supported by the National Heart, Lung, and Blood Institute, part of the National Institutes of Health. "Our study helps identify the limits of when stem cell therapy might be beneficial. We now know that this therapy should not be extended two to three weeks after a heart attack. While it is safe to do so, we did not find any benefit to heart function after six months."
Between July 2008 and February 2011, 87 people with heart attacks and moderate to severe left ventricular dysfunction received their own bone marrow mononuclear stem cells (BMCs) or placebo. The study, called LateTIME, developed a standardized method of processing the BMCs and was the first such trial to provide a uniform dose to each participant.
The researchers assessed heart function through a cardiac MRI by measuring the ejection fraction, or what percentage of blood is pumped out of the left ventricle during each contraction. No significant differences were found in the cardiac function readings between baseline and six months in the BMC group (from 48.7 percent to 49.2 percent) or the placebo group (from 45.3 percent to 48.8 percent).
Dr. Simari says that earlier studies suggest patients with severe heart attacks benefit most from stem cell therapy. The researchers were interested in studying the two- to three-week period because many people who have severe heart attacks are not well enough or stable enough to receive cells right after their heart attacks. "Many are on life support or other systems, and we didn't think that studying them that early was the best way to assess the benefits to the sickest patients," Dr. Simari says.
The LateTIME study offers a cautionary lesson for people who have had heart attacks and are considering going overseas to seek stem cell treatment. "We would suggest that individuals not seek treatment outside of the U.S. for therapies that aren't proven effective," Dr. Simari says. The researchers think that the heart may be less receptive to such therapies two to three weeks after a heart attack, or that a person's stem cells are less potent at that time.
Jay Traverse, M.D., lead author of the study and a cardiologist at the Minneapolis Heart Institute at Abbott Northwestern Hospital, says patients will be followed clinically for two years in the LateTIME study.
"There may still be other benefits to stem cell therapy that may be uncovered over time," Dr. Traverse says. "We observed that patients who received the cell therapy had fewer adverse events such as placement of defibrillators or repeat revascularization compared to patients who got the placebo, consistent with observations in some of the European trials. This therapy may provide hidden safety measures that reduce adverse events and that's something we will follow closely."
LateTIME is one of three heart stem cell trials being conducted by CCTRN. The other trials will explore the effectiveness of stem cell therapy delivered at three days and seven days following a heart attack, and the usefulness of stem cell therapy in people with chronic heart failure.
The research was funded by the National Heart, Lung, and Blood Institute and supported in part by the Molecular and Cellular Therapeutics Facility at the University of Minnesota and the Cell Processing Facility at Baylor College of Medicine.
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