Researchers are reporting that a type of stem cell therapy called granulocyte-macrophage colony-stimulating factor (GM-CSF) did not improve walking ability in people with peripheral artery disease (PAD), a condition in which plaque builds up in the arteries of the legs, causing pain and weakness when walking. In a clinical trial (the PROPEL Randomized Clinical Trial) of 210 people with PAD, the researchers tested the effects of GM-CSF either alone or in combination with exercise to treat walking impairment. Neither treatment improved walking. Exercise alone, however, lead to significant improvements. "Although this trial showed no added benefit of stem cell mobilization by GM-CSF in individuals with PAD, it yet again confirmed the benefits of exercise on walking capacity that have been observed in previous studies," said Dr. Diane Reid, a National Heart, Lung and Blood Institute (NHLBI) project officer for the study and a medical officer in the NHLBI Vascular Biology and Hypertension Branch. "Prompt reporting of negative clinical trial results, as done here, provides valuable information to guide the future directions of research on potential new therapeutics." The study, published in the Journal of the American Medical Association, was partly funded by NHLBI.