Stem cells offer promise - not more - for heart disease

Content provided by the Faculty of the Harvard Medical School

Stem cells offer promise - not more - for heart disease

Much as we need a way to fix damaged heart muscle, stem cell therapy isn't just around the corner.

Cardiologists have long thought that damage from a heart attack is permanent, something to be coped with rather than fixed. Some visionaries are aiming to change that, driven by the tantalizing promise of stem cells. They are nudging the notion that humans can regenerate the heart, like a salamander can grow a new tail or leg, away from myth and science fiction toward the doctor's office.

Stem cells are a unique breed of cells with the potential to grow into a variety of different tissues. Some stem cells live in bone marrow, some circulate in the bloodstream, and some even live quietly in the heart. Researchers around the world are trying to figure out how to coax these cells to grow new muscle and blood vessels in damaged or failing hearts.

It won't be happening soon. That's the message from top researchers invited to the third Cardiovascular Cell and Gene Therapy Conference, organized by Dr. Roger J. Hajjar and his colleagues from Massachusetts General Hospital and Harvard Medical School.

An explosion of research since the mid-1990s shows that stem cells can, in theory, regenerate heart tissue. How the theory translates into practice is still very much up in the air. Some small clinical trials show that stem cells can help a damaged heart work better. A few show little or no benefit from adding stem cells. And there are troubling reports from some of these trials that implanted stem cells may interfere with synchronized electrical activity in the heart and lead to serious rhythm problems. At the conference, researchers described other hurdles that must be overcome:

• The number of cardiac stem cells in the heart, which is small to begin with, dwindles with age.

• Stem cells from people with heart disease or diabetes — the very people most likely to need them — don't work nearly as well as those from healthy people.

• Stem cells take up residence and grow into new cardiac tissue in a healthy heart much more readily than they do in one recently damaged by a heart attack.

• Stem cells delivered to the heart may grow and create new cardiac tissue, but it tends to stay physically and electrically separate from the rest of the heart.

By focusing on the hurdles, we don't mean to cast a pall on this exciting field — the odds are good that this research will ultimately pay off. Instead, we want to make the point that stem cell therapy isn't nearly ready for prime time, and that companies offering it as a proven treatment for heart disease are jumping the gun. Some Americans are heeding the pitch ("Heal your heart with your own stem cells") of a company called TheraVitae that offers stem cell therapy in Thailand. As University of Washington researchers Michael LaFlamme and Charles Murry put it, "The heart is not likely to be regenerated in one fell swoop. More likely, we will repair the heart in small steps, perfecting our inventions over many years." Those small steps are being taken in laboratories and clinical trials across the United States and around the world. With that hard work and a little bit of luck, stem cell therapy may someday be part of the heart-healing repertoire.

Last updated:	September 05, 2008