Scientists are transplanting a purified form of subjects' own adult stem cells into their legs that have severely blocked arteries. The goal is to grow new small blood vessels and restore circulation.

The first two subjects in the 20-site national trial recently underwent the stem cell transplant process at Northwestern Memorial Hospital.

Scientists at the university's Feinberg School of Medicine who are leading the study said severely blocked arteries in the leg and sharply diminished blood flow can result in wounds that don't heal, tissue breakdown and gangrene. That condition, called critical limb ischemia, results in the amputation of more than 100,000 limbs annually in the United States.

The research targets patients who have exhausted all other medical options including angioplasty, stents and bypass surgery to repair blocked circulation in their legs.

"They're at the end of the therapeutic road and they're ultimately facing potential amputation," said Dr. Douglas Losordo, the study's principal national investigator. "This is hopefully a way to help them avoid that."