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Stem cell trial wins over skeptical surgeon

By Amos Esty

Powell was skeptical—but pleased by the results.

When it comes to new medical therapies, Richard Powell, M.D., says he tends toward skepticism. But the Dartmouth surgeon was pleasantly surprised by a phase II clinical trial that he led of a potential treatment for critical limb ischemia (CLI).

Fatty: About 750,000 Americans suffer from CLI, an advanced form of peripheral arterial disease, in which a buildup of fatty deposits in arteries severely restricts blood flow. As many as half of those with CLI need a major limb amputation within a year of developing the condition, and the five-year mortality rate is 70%.

In some people with CLI, surgeons can prop the artery open with a stent or bypass the blockage with a graft. But many patients with CLI aren't good candidates for surgery, because the blockage is too extensive or they're too frail.

Flow: In 2007, Powell began a phase II trial of a treatment that uses bone marrow stem cells from an individual patient to try to improve the flow of blood. Patients in the study had bone marrow removed from their hips. The marrow was grown in a lab for two weeks, and the resulting solution was injected back into the patients.

The trial enrolled 86 patients. About two-thirds received the stem-cell treatment, and one-third received a placebo injection. The results, published in the Journal of Vascular Surgery, included outcomes on 46 patients who had been followed for at least six months after treatment. The results from the other 40 patients had not yet been analyzed. The trial was sponsored by Aastrom Biosciences, which paid Powell a fee to lead it.

The primary goal of the study was to determine if the treatment was safe, which it proved to be. But Powell and his colleagues also evaluated the treatment's effectiveness by seeing how long it took before patients' condition worsened significantly.

In the treatment group, only 41% experienced failure.

Failure: Within six months, 79% (11 of 14) of those in the placebo group had experienced "treatment failure," defined as a doubling in the size of a wound, gangrene, an amputation, or death. In the treatment group, only 41% (13 of 32) experienced one of those outcomes.

"It's pretty exciting," Powell says. "The results were a lot better than anybody anticipated." They were so promising, in fact, that a phase III trial is being planned.

Powell wasn't convinced the therapy would work. "You put a stent in the artery, . . . you can tell instantly that you've improved the blood flow," he says. "When you inject all these things in the leg, I'm much more skeptical about how likely that is to work." It's actually not clear exactly how it does work. There are "many unanswered questions," Powell says.

He adds that he'll remain skeptical until a phase III trial is completed, but he's hopeful. "There's no medical treatment now for patients with this problem," he says. "If it turns out to be useful, it's going to be of huge benefit."

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