First Human Heart Stem Cell Trial Shows Promise

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(Updated) For the first time, doctors were able to improve heart function and reverse tissue damage in heart failure patients, using stem cells taken from the patients’ own heart tissue.

Experts hailed the findings, which were simultaneously published on Monday in the journal The Lancet and presented at the American Heart Association’s annual meeting in Orlando, as potentially groundbreaking. “Every once in a while there’s a landmark study in medicine,” Dr. Josh Hare, chief of cardiology and director of the Interdisciplinary Stem Cell Institute at University of Miami, told ABC News. “I think this is a landmark in medicine. It reaches the level of when the first heart transplant was done.”

The clinical trial, led by University of Louisville researchers, involved 23 patients with severe heart failure, a chronic condition that is both debilitating and fatal, commonly caused by heart disease or heart attack. Blockages in heart vessels cause heart muscle tissue to die, which in turn weakens the heart’s ability to pump blood. Patients with heart failure suffer from fatigue, shortness of breath and swelling, and many are severely impaired in day-to-day life.

Bypass surgery to treat heart failure can improve blood flow and prevent further damage, but it can’t restore the loss of heart tissue. That’s why doctors have been hoping to use stem cells to regrow healthy muscle tissue.

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The new study is the first to use cardiac stem cells in humans. Sixteen of the patients were infused with stem cells purified from their own heart tissue, which was taken during coronary artery bypass surgery. The other seven patients in the study received standard care after bypass surgery. Each infusion of about 1 million cardiac stem cells, delivered through a catheter to the heart about 100 days after surgery, was estimated to generate about 4 trillion new heart muscle cells.

The small clinical trial was designed to test the safety of the technique, but the researchers found unexpected improvements in their patients’ heart function. Of the patients who were infused with stem cells, 14 showed significant gains in blood-pumping efficiency, from 30% to nearly 39%, at a four-month follow-up; the control group showed no change. A year after treatment, the stem cell recipients were still showing improvement, with blood-pumping efficiency increasing to 43% in eight of the patients. What’s more, in half of the patients who received stem cells, MRI scans revealed that areas of dead muscle tissue were progressively healing at 4 months and 1 year after treatment.

In terms of patients’ quality of life, those numbers can be considerable. Study author Dr. John H. Loughran of the University of Louisville told WebMD:

The improvement we have seen in patients is quite encouraging. … Michael Jones, our first patient, could barely walk 30 feet [before treatment]. I saw him this morning. He says he plays basketball with his granddaughter, works on his farm, and gets on the treadmill for 30 minutes three times a week. It is stories like that that makes these results really encouraging.

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The new study was published on the same day as a study in the Journal of the American Medical Association, which found that using stem cells derived from patients’ bone marrow failed to improve heart function in heart attack patients after six months. The researchers are still studying whether re-injecting patients with these cells earlier, within a week after heart attack (rather than the two to three weeks researchers waited in the JAMA study), could help.

Although cardiac stem cells are much more difficult to retrieve than bone marrow stem cells, the new Lancet study suggests they may result in significant long-term benefits.

“What is really exciting about the use of cardiac stem cells is we think we’re attacking the fundamental problem: replacing dead tissue with new cardiac muscle,” lead author Dr. Roberto Bolli, director of cardiology at University of Louisville, told ABC News. “Again, if these results are confirmed, this would be a true revolution in medicine; one of the biggest advances in cardiology in my lifetime.”

Correction [3:35 p.m.]: The original version of this story misstated that the Lancet study was led by Harvard researchers. It was led by scientists at the University of Louisville, working with researchers at Harvard Medical School.

Meredith Melnick is a reporter at TIME. Find her on Twitter at @MeredithCM. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.

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