Immortality – Hype or Hope?

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The lame will walk again

Scientists at Johns Hopkins Hospital in Baltimore, USA have already made paralysed rats walk again and hope to begin human trials within the next five years. In an experiment headed by Dr Douglas Kerr, rats were injected with a virus that infects and damages motor neurons – the nerves that enable movement. The rats were permanently paralysed. But when neural stem cells (cells that can make neurons) were injected into the spinal fluid of the rats, they recovered their ability to walk.

This is an extremely exciting discovery as Dr Kerr explains: 'Most use of neural stem cells so far has been focussed on conditions such as stroke damage or Parkinson's disease which affect a small, specific area. Our study is significant because it's one of the first examples where stem cells may restore function over a broad region of the nervous system.'

Significantly, in Kerr's study, injected neural stem cells migrated to areas of the spinal cord where nerves were damaged. In controls (rats that had no damaged nerves), injected stem cells didn't migrate at all. It's likely then that damaged or dead neurons attract stem cells by emitting a chemical signal – an unexpected finding. Added to that, Kerr has been able to show that the stem cells actually produce new neurons, which function in place of the dead ones. The fact that stem cells can find and replace damaged nerves is of enormous importance and could make potential cures all the more likely.

The targets for this kind of therapy are endless. Parkinson's disease has been one major focus. Last year, a group of scientists grafted neural stem cells into mice that had a 'Parkinson's-type disease'. The mice have shown signs of recovery. Stem cell medicine is also planned for motor neuron disease, Alzheimer's disease, strokes and spinal cord injury – all currently incurable and all now in the throws of research.

This is all very well, except that transferring stem cell technology from animal to human subjects has so far been fraught with problems. In February this year, Woo Suk Hwang from Seoul National University in South Korea was the first to announce success in obtaining stem cells from cloned human embryos. It is a first and an important breakthrough, but the achievement was not all plain sailing. From 30 cloned embryos, Hwang and his team were able to harvest stem cells from only one. Although this one stem cell line will provide important research opportunities there is still a long road to travel before this particular technology becomes routine in humans.

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