Bone marrow stem cells are supposed to home in on damaged parts of the heart. Once there, they send out signals that help the body repair the injury. There's also evidence, from animal studies, that the stem cells themselves engraft to the heart and help repopulate dead cells with new, living cells.
Now there's evidence from actual patients who suffered heart attacks. It comes from a study led by cardiologist Joshua M. Hare, director of the stem cell institute at the University of Miami Miller School of Medicine, and colleagues at nine other medical centers.
"Stem cell-treated patients had ... significant improvements in heart, lung, and global function,��� Hare said in a news release. "Echocardiography showed improved heart function, particularly in those patients with large amounts of cardiac damage."
It's not the first time heart attack patients have been treated with stem cells. But previous studies used bone marrow cells extracted from the patient and then injected directly into the heart.
Hare's team used an "off-the-shelf" stem cell product -- Prochymal -- containing stem cells harvested from a single healthy donor and grown to large numbers in laboratories. Prochymal is given by intravenous infusion. It's made by Osiris Therapeutics Inc., which sponsored the study, and which currently seeks FDA approval of the product as a treatment for graft-versus-host disease in transplant recipients.
"Many have argued that it’s premature to test stem cells in patients," Hare said. "This trial ... lays the foundation for a brand new cell-based therapy for the human heart."
The Hare study enrolled 53 heart attack patients treated within 10 days of their first heart attack. None of the patients required bypass. A fourth of the patients got infusions of an inactive placebo; the others got various doses of the Prochymal cells.
The main goal of the study was to see if Prochymal was safe. It had been feared that the cells might cause growth of unwanted tissue in the arteries or the lungs; this did not happen. Patients receiving the stem cells had fewer adverse events than those who received placebo.
The secondary goal of the study was to gather some evidence that the treatment actually helped. There was such evidence -- particularly in the patients with the largest infarcts (patches of heart tissue killed during a heart attack).
Why? Emergency signals sent out by wounded heart tissue attract help from stem cells. It's probable that the stronger signal from the more damaged hearts attracted more of the stem cells to the site of injury, suggest Cleveland Clinic researchers Marc S. Penn, MD, PhD, and colleagues in an editorial accompanying the Hare report in the Dec. 8 issue of the Journal of the American College of Cardiology.
Warning that the Hare study is only a first step, Penn and colleagues call the findings "important."
"Many questions remain, but there is excitement in what the future holds with regard to advances in this field," they write.
A phase 2 clinical trial, also sponsored by Osiris, is enrolling heart attack patients.