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What
are human embryonic stem cells? Stem cells are cells that
have the remarkable potential to develop into many different cell
types in the body. Serving as a sort of repair system for the body,
they can theoretically divide without limit to replenish other cells
for as long as the person or animal is still alive. When a stem cell
divides, each "daughter" cell has the potential to either remain a
stem cell or become another type of cell with a more specialized
function, such as a muscle cell, a red blood cell, or a brain cell.
A more detailed primer on stem cells can be found at
http://stemcells.nih.gov/info/basics.
What classes of stem cells are there?
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.
- Stem cells that can give rise to a small number of different
cell types are generally called multipotent.
- Pluripotent stem cells can give rise to any type of cell in
the body except those needed to develop a fetus.
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 Where do stem cells come from?
Pluripotent 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" -- cell cultures that can be grown
indefinitely in the laboratory. Pluripotent stem cell lines have
also been developed from cells obtained from fetal tissue (older
than 8 weeks of development).
Why do scientists want to use stem cell lines?
Once a stem cell line is established from a cell in the body, it
is essentially immortal, no matter how it was derived. That is, the
researcher using the line will not have to go through the rigorous
procedure necessary to isolate stem cells again. Once established, a
cell line can be grown in the laboratory indefinitely, and cells may
be frozen for storage or distribution to other researchers.
Stem cell lines grown in the lab provide scientists with the
opportunity to "engineer" them for use in transplantation or
treatment of diseases. For example, before scientists can use any
type of tissue, organ or cell for transplantation, they must
overcome attempts by a patient's immune system to reject the
transplant. In the future, scientists may be able to modify human
stem cell lines in the laboratory by using gene therapy or other
techniques to overcome this immune rejection. Scientists might also
be able to replace damaged genes or add new genes to stem cells in
order to give them characteristics that can ultimately treat
diseases.
[National
Institutes of Health] |
