Can Stem Cells Cure Heart Disease?

So far, clinical studies have produced mixed results, but a new set of trials aim to sort out the best approaches to therapy.

It's a tantalizing thought: injecting stem cells isolated from a person's own blood into an ailing heart in hopes of repairing years of accumulated decay. But so far, human trials testing cell therapies for heart attacks have yielded mixed results, creating controversy over various aspects of the treatment: the types of cells that are used, the way they are delivered, and when in the course of the disease they are given. With the next round of trials, scientists hope to nail down the precise set of conditions needed to effectively heal a sickly heart.

Healing hearts: Scientists are testing new stem-cell therapies that could help heal the ailing heart.

"If it works, it could revolutionize cardiology," says Amish Raval, a cardiologist at the University of Wisconsin, Madison, who is running a stem-cell trial for heart failure.

Nearly five million people in the United States have heart failure caused by damage to the heart that interferes with its ability to pump blood, and nearly a million people suffer heart attacks each year. And despite a series of advances in cardiovascular care over the past decades, heart disease accounts for one in every 2.8 deaths in the United States. "In the past, we've relied on medication or mechanical therapies to open blood vessels and improve heart function," says Raval. "But there are still people who fail those therapies. Stem cells may have the potential to improve on that."

In terms of the clinical testing of stem-cell therapies, heart disease is arguably the furthest along of the common diseases. But cell-based therapies are proving trickier to test than traditional drugs and medical devices are. They seem to require the perfect combination of ingredients and execution. Scientists must determine the best cells to transplant, the best way to prepare cells, and when and how they should be delivered.

The largest stem-cell trials for heart disease to date--three were published last year and one in 2005--used cells derived from the patients' own bone marrow to treat myocardial infarction, or heart attack. The results were mixed: some studies found moderate improvements in a few measures of heart function, but none were able to show a clear health benefit. "Are you living longer or having less heart failure? Those are questions that are still out there," says Stefan Janssens, head of the cardiac clinic at the University Hospital Gasthuisberg, in Belgium.

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Janssens and others suspect that variability comes from different methods used to purify the stem cells. So he and others in Europe are planning a larger trial, testing 1,000 to 2,000 patients, in which the researchers will specifically assess the numbers and function of cells transplanted into each patient. The goal? To determine if stem-cell therapy can actually save lives.

One unknown concerning cell therapies for heart disease is related to the fact that bone marrow contains two types of stem cells: blood-forming stem cells, which give rise to blood cells, and mesenchymal stem cells, which can form muscle and bone. While previous trials have used a mixture of these two types of cells, some scientists think that isolating one or the other of the cell types from the mix will boost healing power. "Benefits noted in previous trials weren't sustained, so selecting cells with therapeutic potential is a better idea," says Raval.