Stem cell



Stem cells are cells which are not terminally differentiated and are
therefore able to produce cells of other types. Medical researchers hope
they can be used to repair specific tissues or to grow organs from scratch.
There are three types of stem cells: totipotent, pluripotent, and
multipotent. A single totipotent stem cell can grow into an entire organism.
Pluripotent stem cells cannot grow into a whole organism, but they can
become any other type of cell in the body. Multipotent stem cells can only
become particular types of cells: e.g. blood cells, or bone cells.

Adult stem cells

Stem cells can be found in adult human beings. Adult stem cells reproduce
daily to provide certain specialized cells - for example 200 billion red
blood cells are created each day in the body. Until recently it was thought
that each of these cells could produce just one particular type of cell -
this is called differentiation (see Morphogenesis). However in the past few
years, evidence has been gathering of stem cells that can form in to several
different forms. Bone marrow stem cells are known to be able to transform in
to liver, nerve, muscle and kidney cells.

Adult stem cells may be even more versatile than this. Researchers at the
New York University School of Medicine have extracted stem cells from the
bone-marrow of mice which are they say are pluripotent. Turning one type of
stem cell in to another is called transdifferentiation.

Embryonic stem cells

Stem cells which originate from embryos are seen to have the most potential
because of their totipotent properties - they are able to grow in to any of
the 200 cell types in the body. Embryonic stem cells can be obtained from a
cloned embryo, created by fusing a denucleated egg-cell with a patient's
cell. The embryo produced is allowed to grow, and stem cells are then
extracted. Because they are obtained from a clone, they are genetically
compatible with the patient.

As well as having the largest medical potential, they are also the most
controversial type of stem cell because their utilization involves the
destruction of human embryos. Some people believe that these embryos are
human beings, and therefore destroying them for any reason is effectively
murder. This belief is also the basis for 'Pro-life' opposition to abortion.
Many scientists defend the destruction of embryos citing all the medical
benefits that it is possible to achieve with them, and saying that many
would have been destroyed anyway. 'Pro-life' groups respond that it would be
possible to achieve the same benefits from the use of adult stem cells -
although most scientists agree that we are further from using these in the
same way hoped for embryonic stem cells.

Another controversy in the use of embryonic stem cells is the use of
therapeutic cloning. This involves the cloning of early embryos from which
stem cells are harvested, providing a larger source of the cells. Many see
this as encouraging human cloning, which they think could be dangerous or unethical.

Current treatments

For over 30 years, bone marrow stem cells have been used to treat cancer
patients with conditions such as leukemia and lymphoma. These are detroyed
in some chemotherapy treatments, but if they are removed before the process
and then reinjected, the cells produce large amounts of red and white blood
cells, to keep the body healthy and help to fight infection.

Since the 1980s stem cells have been taken from the blood instead of the
bone-marrow, making the procedure safer for older people. Although normally
scarce, the number of 'Peripheral blood cells' can be increased by a course
of drugs, which release the stem cells from the bone-marrow. These are
removed before chemotherapy, which kills most of them, and then re-injected.

Potential treatments

Research injecting neural (adult) stem cells in to the brains of rats can be
astonishingly successful in treating cancerous tumours. With traditional
techniques brain cancer can be almost impossible to treat because it spreads
so rapidly. Researchers at the Harvard Medical School injected cells
genetically engineered to convert a separately injected non-toxic substance
in to a cancer-killing agent. Within days the cells had migrated in to the
cancerous area end the injected substance was able to reduce tumour mass by
80 per cent.

Stem cells are also apparently able to repair muscle damaged after heart
attacks. Heart attacks are due to the coronary artery being blocked,
starving tissue of oxygen and nutrients. Days after the attack is over, the
cells try to 'remodel' themselves so they can pump harder. However, because
of the decreased blood flow this attempt is futile and results even more
muscle cells to weaken and die. Researchers at Columbia-Presbyterian found
that injecting bone-marrow stem cells in to mice which had had heart attacks
induced in them resulted in an improvement of 33 per cent in the functioning
of the heart. The damaged tissue had regrown by 68 per cent. Clinical trials
in humans are hoped for by 2003.

Sources of stem cells

Blood from the placenta and unbilical cord of new-born babies is a useful
source of adult stem cells. Since 1988 these 'cord blood' stem cells have
been used to treat Gunther's disease, Hunter syndrome, Hurler syndrome,
acute lymphocytic leukemia and many more problems mostly in children. It is
collected by removing the umbilical cord, cleansing it and withdrawing blood
from the umbilical vein. This blood is then immediately analysed for
infectious agents and the tissue-type is determined. Cord blood is stored in
liquid nitrogen for later use, when it is thawed and injected through a vein
in to the patient. This kind of treatment where the stem cells are collected
from another donor is called allogenic treatment. When the cells are
collected from the same patient they will be used on it is called
autologous.

In fact, useful sources of adult stem cells are being found in organs all
over the body. Research at McGill University in Montreal have extracted stem
cells from skin able to differentiate in to many types of tissue including
neurones, smooth muscle cells and fat-cells. These were found in 'dermis' -
a layer of tissue beneath the skin.

In the same way that organs can be transplanted from cadavers researchers at
the Salk Insitute in California have found that these could be used as a
source of stem cells as well. Taking stem cells from the brains of corpses
they were able to coax them in to dividing in to valuable neurons. However
whether they will function correctly when used in treatment has not yet been
determined.

In May of 2003, researchers announced that they had successfully used
embryonic stem cells to produce human egg cells. Spokespersons stated that
these egg cells could be used in turn to produce new stem cells. If research
and testing proved that artifically created egg cells could be a viable
source for embryonic stem cells, they noted, then this would remove the
necessity of harvesting human embryos. Thus, the controversy over donating
human egg cells and embryos would be largely dismissed.

Legal situation

Due to the controversy surrounding embryonic stem cells, in November 2001
the US National Institutes of Health announced a list of 72 approved human
embryonic cell lines which researchers are to be allowed to work with.
However some scientists declared problems they had with the list - that some
cell lines are less useful to work with than others. Also other scientists
are not convinced that the list actually contains 72 different lines - they
think some are derivations of a single line.

Controversy over ethical implications

Ethicists, philosophers, theologians and clergy are all very concerned with
the ethical implications of stem cell research. In the U.S. most Christian
groups have come out strongly against all forms of this research as they
view it as a form of abortion, which they see as murder. Jewish groups, of
all denominations, have come out in favor of this research, as they do not
view an early stage embryo as a human being. Many Humanists,
Unitarian-Universalists, and many Muslim clerics have come out in favor of
stem cell research.

In spite of this and his own personal views on the subject, US President
George W. Bush announced on August 9, 2001 that he would support federal
funding of limited research on embryonic stem cells.

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