GENETICALLY engineered stem cells can help rats’ severed spinal cords grow back together, according to a study published today.

Rats given the treatment, using stem cells taken from rat embryos, could move their legs again after their spines were severed in the lab, said the researchers’ report in the Journal of Neuroscience.

The scientists hope the approach, which generated a new fatty cover for the spinal cord cells called the myelin sheath, also could be shown to work in people.

The key is using the right stem cells and then stimulating them correctly, said the researchers, who were led by Scott Whittemore of the University of Louisville School of Medicine in Kentucky.

“These findings suggest the possibility that transplantation therapy using a subset of neural stem cells and neurotrophic factors might improve functional recovery in human spinal cord injury,” said Dr Michael Selzer, a professor of neurology at the University of Pennsylvania Medical Centre in Philadelphia.

Spinal cord injuries can be caused by accidents or infections and affect 250,000 people a year in the United States alone, costing $US4 billion ($5.25 billion) annually, according to the National Institute of Neurological Disorders.

Whittemore’s team took specific cells from rat embryos called glial restricted precursor cells ? a kind of stem cell or master cell that gives rise to nerve cells.

They genetically engineered these cells to do a little extra work by producing a compound called a growth factor ? in this case, a new one called multineurotrophin. It was designed to coax immature neural stem cells to mature and become specialised cells called oligodendrocytes.

Oligodendrocytes help myelin grow onto nerve fibres, which cannot grow or function without this fatty protective coating.

Two-thirds of the rats in the study regained some hind limb movement, the researchers said.