TUESDAY, July 9, 2002 (HealthDayNews) -- Human neurons cloned from a human cell line have helped repair injured spinal cords in animals, a University of South Florida team reports.

While the use of the neurons for human spinal cord injury is several years away, the researchers say the work is promising.

"This is really the first step," says lead author Samuel Saporta, the associate director of the University of South Florida Center for Aging and Brain Repair. "We might be able to do some human trials in five or six years."

The study appears in the current issue of the Journal of Neurosurgery: Spine.

About 200,000 Americans are living with spinal cord injury, and 11,000 more suffer a spinal cord injury each year, according to the Foundation for Spinal Cord Injury Prevention, Care & Cure.

When the damage occurs, people can lose sensation and, depending on the injury site, control over routine bodily functions. Injuries usually crush thin extensions of the nerve cells called axons, which are surrounded by the vertebrae. Axons carry electrical signals along the spinal cord, sending sensory information and information to control movement. Scientists are still trying to figure out the best way to repair damaged spinal cord tissue.

Saporta's team used hNT neurons, the same type that led to the first transplant to repair brain damage caused by strokes. These hNT neurons, or human neuroteratocarcinoma, are derived from a rare human cancer that includes rapidly dividing cells that can then turn into neurons -- but not back into cancer cells.

Saporta's team evaluated 34 rats in all: one group that received transplants right after the injury; another group that received them two weeks later; and a control group that received no transplants.

"Once transplanted, the cells appear to graft and take the place of the injured cells," Saporta says. All seven animals in the delayed group recovered activity in the neurons that control muscle movement, while only two of the nine in the immediate transplant group recovered. The untreated animals had no improvement.

Delaying the transplant, the researchers speculate, leads to better recovery because the immune system might be less hostile.

"There are basically two strategies in spinal cord repair," Saporta says. "One is to try to get the damaged axons that come from the higher center of the brain to reconnect past the area of injury and reconnect with the motor neurons that cause movement."

"The strategy our research has taken is to form a bridge between the two injured areas of spinal cord, and perhaps we can have the spinal cord relearn with its existing connections how to cause movement. The bridge is the transplanted neurons. We demonstrated the transplanted cells actually engraft, or take up residence, and send out axons and electrically connect," he says.

Other researchers have done the same research with human fetal cells, Saporta adds, but the neurons in the Florida research were derived from a human cell line.

"This cell line is already approved by the [U.S. Food and Drug Administration] for transplant into stroke patients," he says.

The good news for spinal-cord injured patients hoping for treatment?

"We're closer," Saporta says. "The bad news is we don't know how close we are. There are a number of studies that need to be done."

Another expert in the field calls the study "interesting," but also has some caveats.

"The study involves adequate numbers of animals, and the results appear quite dramatic," says Dr. Michael Selzer, a professor of neurology at the University of Pennsylvania School of Medicine.

Selzer is a former consultant for Layton BioScience Inc., which holds the license for hNT neuron transplantation technology, and Saporta is also a consultant.

The caveat, Selzer says, is the authors have not demonstrated adequately exactly how the transplanted cells are functioning.

However, it's a promising cell line, he says: "The spinal cord often doesn't like to accept stem cells [immature, undifferentiated cells], and turn them into neurons. This cell line is already neurons."

What To Do

For information on spinal cord injury, see the Foundation for Spinal Cord Injury Prevention, Care & Cure or the National Institutes of Health.

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