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MS ExplainedRepairing and replacing myelin

Whilst drugs that alter the action of the immune system or that protect nerves may help to limit the accumulation of damage, neither will reverse the progressive effects of MS. Exploration of processes that might repair areas of damage and thus allow people to recover function that has been lost is another important area of MS research.

From observing areas of the central nervous system that have been damaged by MS it is known that in the earlier stages of the condition the body can to some degree replace lost myelin. If the affected area is no longer being attacked by the immune system, new myelin can be formed, which will repair damage to nerve cells and reverse, at least to a degree, some of the disability caused.

Various strategies for repairing and replacing myelin have been investigated. For instance, chemicals within the immune system have been identified that can accelerate the growth of myelin. Myelin-making cells from the peripheral nervous system (Schwann Cells) have also been transplanted into the central nervous system to see if they will stimulate regrowth. Results have suggested a small effect at best.

Stem cells

Interest has also focussed on the possibility of using stem cells to repair damaged areas in the central nervous system.

Stem cells are unspecialised cells that can develop, or differentiate, into any of the specialised cells of the body, such as those in heart muscle or the insulin-producing cells of the pancreas. Stem cells are the first cells to develop in embryos and allow the foetus to develop the specialised functions and mechanisms that occur in the human body. Stem cells derived from an embryo are capable of developing into all the cell types that make up the tissues and organs, such as the heart, skin and brain.

The use of stem cells from embryos is the cause of much ethical debate. This has also affected the issue of 'hybrid' embryos in which human genetic material is implanted into animal cells that have had most of their own genetic material removed. After six days, stem cells can be extracted for research and the hybrid is destroyed.

Not all stem cell research involves the use of embryos. Stem cells also occur in adults and are used by the body to replace areas of damage. For instance, stem cells in bone marrow produce the different types of blood cells. Although more limited in the types of cells into which they can differentiate, research is now looking at how adult stem cells can be stimulated to turn into oligodendrocyte cells that produce myelin or into nerve cells in sufficient quantity to be used in treatment.

Work is also looking at how best to deliver stem cells so that they go to the appropriate places to carry out repair, and also at ways to ensure that transplanted stem cells do not harm the recipient or grow into unwanted tissue.

Stem cell treatment has been demonstrated for experimental forms of MS and pilot studies in humans - focused principally on safety rather than effectiveness - have started in the UK. If processes can be developed, it opens the possibility that cells destroyed by MS might be replaced and disabilities caused by the loss of nerve pathways reversed.

More information from the MS Trust
Stem cells factsheet
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