Basic Questions
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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 here.
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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 fetal tissue obtained from fetal
tissue (older than 8 weeks of development).
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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.
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Healthcare Questions
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Why are doctors and
scientists so excited about human embryonic stem cells?
Stem cells have potential in many different areas of health and
medical research. To start with, studying stem cells will help us to
understand how they transform into the dazzling array of specialized
cells that make us what we are. Some of the most serious medical
conditions, such as cancer and birth defects, are due to problems
that occur somewhere in this process. A better understanding of
normal cell development will allow us to understand and perhaps
correct the errors that cause these medical conditions.
Another potential application of
stem cells is making cells and tissues for medical therapies. Today,
donated organs and tissues are often used to replace those that are
diseased or destroyed. Unfortunately, the number of people needing a
transplant far exceeds the number of organs available for
transplantation. Pluripotent stem cells offer the possibility of a
renewable source of replacement cells and tissues to treat a myriad
of diseases, conditions, and disabilities including Parkinson's and
Alzheimer's diseases, spinal cord injury, stroke, burns, heart
disease, diabetes, osteoarthritis and rheumatoid arthritis.
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Have human embryonic stem
cells been used successfully to treat any human diseases yet?
Scientists have only been able to do experiments with human
embryonic stem cells (hESC) since 1998, when a group led by Dr.
James Thomson at the University of Wisconsin developed a technique
to isolate and grow the cells. Moreover, federal funds to support
hESC research have only been available since August 9, 2001, when
President Bush announced his decision on federal funding for hESC
research. Because many academic researchers rely on federal funds to
support their laboratories, they are just beginning to learn how to
grow and use the cells. Thus, although hESC are thought to offer
potential cures and therapies for many devastating diseases,
research using them is still in its early stages.
Adult 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
used to treat human diseases. Doctors have been transferring HSCs in
bone marrow transplants for over 40 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 adult stem
cells has also been demonstrated in the treatment of other human
diseases that include diabetes and advanced kidney cancer. However,
these newer uses have involved studies with a very limited number of
patients.
-
What will be the best type
of stem cell to use for therapy?
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. Another serious
consideration is that the idea of using stem cells from human
embryos or human fetal tissue troubles many people on ethical
grounds.
Until recently, there was little
evidence that multipotent adult 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 adult stem cells. Although many different kinds
of multipotent stem cells have been identified, adult stem cells
that could give rise to all cell and tissue types have not yet been
found. Adult stem cells are often present in only minute quantities
and can therefore be difficult to isolate and purify. There is also
evidence that they may not have the same capacity to multiply as
embryonic stem cells do. Finally, adult stem cells may contain more
DNA abnormalities—caused by sunlight, toxins, and errors in making
more DNA copies during the course of a lifetime. These potential
weaknesses might limit the usefulness of adult stem cells.
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I have Parkinson’s
Disease. Is there a clinical trial that I can participate in that
uses stem cells as therapy?
The public may search a database of NIH-sponsored clinical trials at
www.clinicaltrials.gov.
Enter the search terms of interest (in this case, Parkinson's
Disease and stem cells) to search for applicable clinical
trials.
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Where can I donate umbilical
cord stem cells?
NIH cannot accept donated umbilical cord stem cells from the general
public. The National Marrow Donor Program maintains a Web page on
donating cord blood at http://www.marrow.org/NMDP/cord_blood_bank_list.html,
and the International Cord Blood Society has one at http://www.cordblood.org/.
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Research and Policy Questions
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Which research is best to
pursue?
The development of stem cell lines that can produce many tissues of
the human body is an important scientific breakthrough. This
research has the potential to revolutionize the practice of medicine
and improve the quality and length of life. Given the enormous
promise of stem cells therapies for so many devastating diseases,
NIH believes that it is important to simultaneously pursue all lines
of research and search for the very best sources of these cells.
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Why not use adult stem cells
instead of using human embryonic stem cells in research?
Human embryonic stem cells are thought to have much greater
developmental potential than adult stem cells. This means that
embryonic stem cells may be pluripotent—that is, able to give rise
to cells found in all tissues of the embryo except for germ cells
rather than being merely multipotent—restricted to specific
subpopulations of cell types, as adult stem cells are thought to be.
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What are the NIH Guidelines
on the utilization of stem cells derived from human fetal tissue
(embryonic germ cells)?
The Federal Register Announcement National
Institutes of Health Guidelines for Research Using Human Pluripotent
Stem Cells (230k PDF; get
Adobe Reader), published August 25, 2000, was
"superceded as it pertains to embryonic stem cell
research" on November
14, 2001). However, Section II. B, titled
"Utilization of Human Pluripotent Stem Cells Derived from Human
Fetal Tissue," still governs human embryonic germ cell
research. In addition, Section III, titled "Areas of Research
Involving Human Pluripotent Stem Cells That Are Ineligible for NIH
Funding," governs both human embryonic stem cell and human
embryonic germ cell research.
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May individual states pass
laws to permit human embryonic stem cell research?
Individual states have the authority to pass laws to permit human
embryonic stem cell research using state funds. Unless Congress
passes a law that bans it, states may pay for research using human
embryonic stem cell lines that are not eligible for federal funding.
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Where can I find information
about patents obtained for stem cells?
The U.S. Patent and Trademark Office offers a full-text
search of issued patents and published applications. Try
searching for "stem cell" or "stem cells."
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