The work carried out by Professor Michal Schwartz, at the Weizmann Institute in Israel, demonstrated that spinal nerves, which usually do not regrow after serious injury, can be encouraged to heal by using cells from the immune system that normally promote healing in other parts of the body.
Professor Schwartz said yesterday that the next step would be to try similar work on people who have suffered severe spinal injury that has left them paraplegic. However, she would not put a time-scale on it, or say when clinical trials might begin. Her team has taken 15 years, including three years of experimentation, to reach this stage with rats, she said.
Even so, the results will give hope to paraplegic people including the actor Christopher Reeve, who broke his neck in a horse-riding accident in May 1995. He has vowed to walk again, despite being left paraplegic by the accident. In recent months he has regained some feeling in one leg and can shrug his shoulders and breathe unaided for up to two hours.
Professor Schwartz's work builds on the observation that in lower animals, such as goldfish, the spinal nerves can regenerate themselves, because cells from the immune system called "macrophages" - which react to damage to the body - are able to reach the injured cells and promote regrowth. In higher mammals, including rats and humans, the macrophages are excluded from the central nervous system (CNS). Some scientists have suggested this is because changes to the CNS constitutes memory, andmacrophages would otherwise keep changing the cells back to their original state - wiping out our consciousness.
In the experiments, reported in the journal Nature Medicine, 22 adult rats had their spinal cords severed at the chest. Macrophages which had been activated by separate damage to peripheral nerves were then implanted at the point where the spine was cut. After 20 weeks most of the treated rats were able to move their hind legs and some could put weight on them, though their co-ordination was limited. A "control" group of rats, which had also had their spines severed but received no treatment, showed no improvement.
Yesterday Professor Schwartz said: "The advantage of this method is that it uses the patient's own cells, rather than injecting a foreign body in. It is a very simple manipulation which allows the cells to repair themselves."
Before trying the same technique on humans her team will have to assess how soon after the spinal damage the treatment must be given.