CAN THE DOCTOR WHO MADE PARALYZED RATS WALK AGAIN DO THE SAME FOR HUMANS? "60 MINUTES" SUNDAY

The doctor who injected human stem cells into paralyzed rats and saw them walk again knows he may not be able to duplicate the feat in humans. But the walking rats give Hans Keirstead and the millions who could benefit from his research the hope that something positive will come out of human clinical trials he hopes will take place. Keirstead is featured in an Ed Bradley report on stem cell therapies to be broadcast on 60 MINUTES Sunday, Feb. 26 (7:00-8:00 PM, ET/PT) on the CBS Television Network.

Keirstead believes that embryonic stem cells -- cells culled from a fertilized human egg that can grow into any type of cell in the body -- are a medical milestone seen only every 100 years. "I have never seen in my career a biological tool as powerful as the stem cells. It addresses every single human disease," says Keirstead.

So when he injected them into the spine of a paralyzed rat, they replaced the damaged spinal cells that were causing the paralysis. The rat walked again, but Keirstead knows it's a huge leap to expect a human to do that. "The fears of giving someone false hope are real," Keirstead tells Bradley. "We're not trying to come up with something to take people from zero capabilities to 100 percent. These are incremental advances and it's experimental," he says. "I think we could call this a dazzling success if we saw the smallest improvement in the ability of a human to do anything that they could not do. If they could move a single finger, I would call that a raving success. Let's hope it's a lot more."

Keirstead has his critics who say he is trying to rush the treatment into humans, in whom the side effects from stem cells are unknown and could include the formation of tumors or other abnormal cells. "I am very concerned and I'll be losing sleep, no doubt, when this first gets into humans," says Keirstead. "There is a potential for harm. This is a risky endeavor, like any clinical trial," he tells Bradley.

Some, including President Bush, who believe life starts in the fertilized egg, think harm is already being done because when the stem cells are taken from a human embryo, the embryo dies. The federal government for this reason has restricted funds for stem cell research. People like Keirstead raise funds privately and some states have begun to pass laws to make funds available for the research.

Keirstead says he is doing good, pointing out that the embryos being used were created for in-vitro fertilization and because they are no longer needed, fertility clinics often discarded them. "I think the use of embryonic stem cells is an ethical and responsible thing to do with tissue that would have been destroyed," he tells Bradley. "If you think that [the embryo] is a holy thing, then value it�.Use it for research and the betterment of lives. Don't throw it away," says Keirstead.