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What are embryonic stem cells?
Embryonic stem cells are undifferentiated cells that are unlike
any specific adult cell. However, they have the ability to form any
adult cell. Because undifferentiated embryonic stem cells can
proliferate indefinitely in culture, they could potentially provide an
unlimited source of specific, clinically important adult cells such as
bone, muscle, liver or blood cells.
Where do embryonic stem cells come from?
Human embryonic stem cells are derived from fertilized embryos
less than a week old. Using 14 blastocysts obtained from donated,
surplus embryos produced by in vitro fertilization, a group of
UW-Madison developmental biologists led by James Thomson established
five independent stem cell lines in November 1998. This was the first
time human embryonic stem cells had been successfully isolated and
cultured.
The cell lines were capable of prolonged, undifferentiated
proliferation in culture and yet maintained the ability to develop into
a variety of specific cell types, including neural, gut, muscle, bone
and cartilage cells.
The embryos used in the work at UW-Madison were originally produced
to treat infertility and were donated specially for this project with
the informed consent of donor couples who no longer wanted the embryos
for implantation.
In virtually every in vitro fertilization clinic in the world,
surplus embryos are discarded if they are not donated to help other
infertile couples or for research. The research protocols were reviewed
and approved by a UW-Madison Institutional Review Board, a panel of
scientists and medical ethicists who oversee such work.
Why are embryonic stem cells important?
Embryonic stem cells are of great interest to medicine and science
because of their ability to develop into virtually any other cell made
by the human body. In theory, if stem cells can be grown and their
development directed in culture, it would be possible to grow cells of
medical importance such as bone marrow, neural tissue or muscle.
The first potential applications of human embryonic stem cell
technology may be in the area of drug discovery. The ability to grow
pure populations of specific cell types offers a proving ground for
chemical compounds that may have medical importance. Treating specific
cell types with chemicals and measuring their response offers a
short-cut to sort out chemicals that can be used to treat the diseases
that involve those specific cell types. Stem cell technology, therefore,
would permit the rapid screening of hundreds of thousands of chemicals
that must now be tested through much more time-consuming processes.
The study of human development also benefits from embryonic stem cell
research. The earliest stages of human development have been difficult
or impossible to study. Human embryonic stem cells offer insights into
developmental events that cannot be studied directly in humans in utero
or fully understood through the use of animal models. Understanding the
events that occur at the first stages of development has potential
clinical significance for preventing or treating birth defects,
infertility and pregnancy loss. A thorough knowledge of normal
development could ultimately allow the prevention or treatment of
abnormal human development. For instance, screening drugs by testing
them on cultured human embryonic stem cells could help reduce the risk
of drug-related birth defects.
How might embryonic stem cells be used to treat disease?
The ability to grow human tissue of all kinds opens the door to
treating a range of cell-based diseases and to growing medically
important tissues that can be used for transplantation purposes. For
example, diseases like juvenile onset diabetes mellitus and Parkinson's
disease occur because of defects in one of just a few cells types.
Replacing faulty cells with healthy ones offers hope of lifelong
treatment. Similarly, failing hearts and other organs, in theory, could
be shored up by injecting healthy cells to replace damaged or diseased
cells.
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