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MULTIPLE SCLEROSIS
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06/06/00
31 May/June 2000 Stem cells have the capacity to grow and become any part of the human body, even cells with such diverse and specialized structures and functions as those of the brain, muscle or heart. Stem cells are found in many parts of the body where, in the natural course of events, they are called upon to renew tissues. Best
known are the stem cells of the bone marrow from which red blood cells, white
blood cells and platelets are all derived? After dividing, one `daughter` cell
becomes committed to developing into a certain blood cell, while the other
remains unchanged; returning to the pool of cells is supported by this constant,
self-renewing system. The
great interest in stem cells has arisen because of this ability to produce
limitless numbers of cells which, once `coaxed` into changing to a specific cell
type, could be used to repair or replace damaged or diseased tissue. In theory,
stem cells could be used not only to grow new hearts but also to develop
treatments for diseases like Parkinson’s and MS. Replacing the immune system. Researchers
have a high-risk bone marrow transplantation procedure – one pioneered for
leukaemia patients – to treat people with severe MS. Early results are
promising, but it will take years to see if MS can be stabilized this way. In
MS, the thinking behind bone marrow stem cell transplantation is that by
destroying the existing immune system and allowing it to re-develop `from
scratch`, the replacement immue system may not go on to attack myelin. Stem
cells for bone marrow transplantation can be obtained in two ways. Either they
are taken directly with a sample of bone marrow, or a chemical can be given to
force them into the bloodstream, from which they can be extracted. In either
case they are then temporarily preserved outside the body. In theory, stem cells could be used… to develop treatments for diseases like Parkinson’s and MS.` The next step involves destroying the remaining cells of the immune system within the body by radiotherapy or chemotherapy. The original stem cells are then replaced back into the bone marrow where they regenerate the immune system. However,
as this is still very much an experimental therapy for MS and is associated with
high risk, including death, at the moment it would only be contemplated in the
treatment of people with severe, rapidly progressive disease. Repairing the central nervous system An alternative treatment strategy, aimed at repairing damage and then maintaining healthy myelin, can be achieved using stem cells obtained from three possible sources: ·
Foetal tissue ·
Immortalised cell lines
(derived originally from foetal tissue, but grown in perpetuity in the
laboratory) ·
Cells extracted from
brain tissue biopsies and grown in the laboratory. These cells could be used to repair the damaged central nervous system (CNS), composed of the brain and spinal cord, in one of two ways. Firstly, outside the body in laboratory conditions, stem cells could be induced to become oligodendrocytes (myelin-producing cells). Once transplanted into the brains of people with MS, the hope is that these oligodendrocytes will re-coat the myelin-depleted nerve fibres. `…By destroying the existing immune system and allowing it to re-develop `from scratch`, the replacement immune system may not go on to attack myelin. ` Alternatively, unmanipulated stem cells could be transplanted directly into the brain. In animal models such cells have shown the ability not only to turn any CNS cell type, depending on the stimulus received, but also to actually move towards the area where repair is needed. This treatment, using foetal stem cells, has been used with relative success in Parkinson’s Disease. Although it also has potential in Ms, there are difficulties: ·
Obtaining sufficient
quantities of foetal cells and the ethical issues of this method ·
Getting the stem cells to
change into the correct type of CNS cell (and not subsequently alter to another
cell type) ·
Supporting this
re-population and re-myelination in a controlled manner to avoid excessive
expansion of new cell numbers ·
The auto-immune aspect of MS is
not addressed by this approach. Continued success can only be achieved in
conjunction with therapies to dampen down the immune system in order that new
myelin would not be attacked ·
Identifying and targeting
lesions of relevance to thee specific clinical symptoms seen in individual
patients. Where next? There is potential for the use of stem cells in MS. Clinical trials are already underway in bone marrow transplantation and many neurologists agree that clinical trials of CNS repair are likely within the next five years. Before you see widespread use of these therapies, there are many difficulties to overcome. The
MS Society comments: We
are aware of the controversy surrounding many aspects of MS its treatment and
research on the disease. Work on stem cells is one of these controversial areas
and the Board of Trustees recently discussed support for research in related
fields. While
acknowledging that some people have ethical or religious objections, the Board
felt that it was right for research to proceed subject to strict observance of
the present regulations. The Society’s Constitution requires it to work within the law and we shall
follow this carefully as it evolves. Peter
Cardy MS
Society Chief Executive |
