Participants in the study will be randomly selected to receive GM-CSF or a placebo. Participants will undergo baseline testing and will be trained to perform subcutaneous injections and instructed to walk until they develop claudication or symptomatic limitation at least three times a day.
The primary outcome is change in walking performance in the active treatment group after 6 months compared to the placebo group. The secondary outcome includes change in peak walking time at 6 months, changes in circulating progenitor cell levels, ankle brachial index (ABI), walking impairment questionnaire (WIQ) scores, and 36-item Short-Form Health Survey (SF-36) scores. Long-term follow up, by way of a telephone call, will occur with each participant one, two and three years after they enrolled in the study to administer questionnaires and collect adverse event data.