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According to one study, around 128 million Americans are affected by diseases for which researchers look to stem cell
technology for promise of treatment. What they currently know indicates that adult stem cells have a limited ability
to differentiate into useful tissues, fetal stem cells have a greater capacity to do so, and ES cells are thought to
be able to differentiate into any other kind of cell.
The different types of cells all have promising applications; here is an overview:
Childhood-Onset Diabetes: In Type 1 Diabetes, the cells in the pancreas that produce
insulin are attacked by the immune system. There have been attempts to treat it by
transplanting pancreatic cells, but the immunosuppressive drugs required to perform the
transplant are hard for the body to handle, and the number of transplants available is very small.
Stem cells could be engineered to differentiate into the beta cells responsible for insulin production,
and they could be manipulated to minimize the possibility of an immune response that usually impairs transplants.
Nervous System Diseases: There are certain cells in the body that reach maturation and no longer actively
divide. Nerve cells are an example of such cells. Therefore, if these cells are damaged or destroyed, there
is no repair or replenishment occurring. This is one deterrent from using drugs; they are known to damage and
kill cells of the nervous system. Unfortunately, people afflicted with certain traumas or diseases to of the
nervous system such as multiple sclerosis, Alzheimer's disease, Parkinson's disease, do not have a choice.
Researchers see stem cells as a potential treatment to such diseases. For example, participants
in Parkinson's studies have shown some progress after fetal cell implantation in preliminary trials.
Studies on rodents have also produced desirable results when subjected to similar conditions. Perhaps a
treatment for such debilitating diseases and injuries is in our future.
Even in cases where actively dividing cells are damaged, stem cell treatment is desired. In diseases and
injuries of the bones and cartilage, if differentiated stem cells could be transplanted into patients,
perhaps long-term damage could be alleviated. Examples are arthritis, bone fractures, and chondrodysplasia.
Immunodeficiency Diseases: Not only have stem cells shown promise in nervous system traumas and diseases,
but also they could potentially be used in treatment of primary (congenital) and secondary (acquired)
immunodeficiency diseases. These diseases arise when an immune function is underdeveloped, suppressed,
or absent. Examples of such diseases are Thymic aplasia (DiGeorge syndrome), Wiskott-Aldrich syndrome,
and AIDS. If pluripotent stem cells could be transplanted to patients with autoimmune diseases, they may be
able to direct the immune system to function normally.
Cancer: Finally, if stem cells can be manipulated into becoming bone marrow stem cells.
Such cells are currently used in treating patients with deficiencies, such as post-chemotherapy
cancer patients with some effectiveness. Future studies are aimed at developing treatments,
which are more successful in hopes of lowering side affects from chemotherapy.
But, quite frankly this subject is not that easy as there are many legal, human
and technical difficulties before researchers, scientists and medical experts. In
fact there are many ways in which human stem cells can be used in basic research and
in clinical research. However, there are many technical hurdles between the promise of stem
cells and the realization of these uses, which will only be overcome by continued intensive stem cell research.
Studies of human embryonic stem cells (ES cells) may yield information about the complex
events that occur during human development. A primary goal of this work is to identify how
undifferentiated stem cells become differentiated. Scientists know that turning genes on and
off is central to this process. A significant hurdle to this use and most uses of stem cells
is that scientists do not yet fully understand the signals that turn specific genes on and off
to influence the differentiation of the stem cell.
Human stem cells could also be used to test new drugs. For example, new medications could be
tested for safety on differentiated cells generated from human pluripotent cell lines. Other kinds of
cell lines are already used in this way. Cancer cell lines, for example, are used to screen potential
anti-tumor drugs. But, the availability of pluripotent stem cells would allow drug testing in a wider
range of cell types.
However, to screen drugs effectively, the conditions must be identical when comparing
different drugs. Therefore, scientists will have to be able to precisely control the differentiation
of stem cells into the specific cell type on which drugs will be tested. Current knowledge of the signals
controlling differentiation fall well short of being able to mimic these conditions precisely to consistently
have identical differentiated cells for each drug being tested.
Perhaps the most important potential application of human stem cells is the generation of cells and tissues
that could be used for cell-based therapies. Today, donated organs and tissues are often used to replace
ailing or destroyed tissue, but the need for transplantable tissues and organs far outweighs the available
supply. Stem cells, directed to differentiate into specific cell types, offer the possibility of a renewable
source of replacement cells and tissues to treat diseases including Parkinson's and Alzheimer's diseases,
spinal cord injury, stroke, burns, heart disease, diabetes, osteoarthritis, and rheumatoid arthritis.
To be useful for transplant purposes, stem cells must be reproducibly made to:
- Proliferate extensively and generate sufficient quantities of tissue.
- Differentiate into the desired cell type(s).
- Survive in the recipient after transplant.
- Integrate into the surrounding tissue after transplant.
- Function appropriately for the duration of the recipient's life.
- Avoid harming the recipient in any way.
- Also, to avoid the problem of immune rejection, scientists are experimenting with different research strategies to generate tissues that will not be rejected.
Advances in stem cell technology have illuminated their thereapeutic potential, but these advances come
with equally significant ethical dilemmas. Though some experiments have shown that adult stem cells can be
useful, the most promising results come from embryonic stem cells derived from a 5-7 day embryo and embryonic
germ cells, derived from aborted fetuses. Each of the sources of stem cells poses their own ethical questions.
The controversies in stem cell research represent broader concerns about biotechnology and human life.
Manipulating the basic components of life, and determining whether an embryo has rights that science is bound
to respect, are difficult questions, by any measure. To summarize, the promise of stem cell therapies is an exciting
one, but significant technical hurdles remain that will only be overcome through years of intensive research and a
broader approach.
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