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Stem cells are cells that have the remarkable potential to develop into many
different cell types in the body. There are three classes of stem cells:
totipotent, multipotent, and pluripotent.
A fertilized egg is considered totipotent, meaning that its potential is total;
it gives rise to all the different types of cells in the body.
Multipotent stem cells (Umbilical Cord stem cells) that can give rise to a
small number
of different cell types.
Pluripotent stem cells (Embryonic stem cells) can give rise to any type of cell
in the
body except those needed to develop a fetus.
Pluripotent stem cells (Embryonic stem cells) are isolated from human embryos
that are a few days old. Cells from these embryos can be used to create
pluripotent stem cell "lines." These are cell cultures that can be grown
indefinitely in the laboratory. Pluripotent stem cell lines have also been
developed from fetal tissue obtained from fetal tissue (older than 8 weeks of
development). Pluripotent stem cells, while having great therapeutic potential,
face formidable technical challenges. First, scientists must learn how to
control their development into all the different types of cells in the body.
Second, the cells now available for research are likely to be rejected by a
patient's immune system. Finally, the idea of using stem cells from human
embryos or human fetal tissue troubles many people on ethical grounds.
Conversely, multipotent stem cells (Umbilical Cord stem cells), such as
blood-forming stem cells in bone marrow (called hematopoietic stem cells, or
HSCs) are currently the only type of stem cell commonly being used to treat
human diseases. Doctors have been transferring HSCs in bone marrow transplants
for years. More advanced techniques of collecting, or "harvesting", HSCs are
now used in order to treat leukemia, lymphoma and several inherited blood
disorders. The clinical potential of Umbilical Cord stem cells has also been
demonstrated in the treatment of other human diseases. However, these newer
uses have involved studies with a very limited number of patients. Until
recently, there was little evidence that multipotent, Umbilical Cord stem cells
could change course and provide the flexibility that researchers need in order
to address all the medical diseases and disorders they would like to. New
findings in animals, however, suggest that even after a stem cell has begun to
specialize, it may be more flexible than previously thought. There are
currently several limitations to using Umbilical Cord stem cells, too. Although
many different kinds of multipotent stem cells have been identified, Umbilical
Cord stem cells that could give rise to all cell and tissue types have not yet
been found.
Thus, although human Embryonic stem cells are thought to have much greater
developmental potential, umbilical cord blood stem cells have already been used
successfully in the treatment of many diseases and disorders, and without the
ethical concerns surrounding Embryonic stem cell use.
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