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Stem Cells
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What is a stem cell?
A stem cell is essentially a "blank" cell, capable of becoming another differentiated cell type in the body, such as a skin, muscle, or nerve cell.
Why are stem cells important?
Stem cells can be used to replace or heal damaged tissues and cells in
the body.
What are the two broad classes of stem cells?
| Embryonic Stem Cells |
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"Embryonic Type" |
| Embryonic Germ Cells |
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| Umbilical Cord Stem Cells |
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"Adult Type" |
| Placental Stem Cells |
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| Adult Stem Cells |
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Where do embryonic type stem cells come from?
* Embryos - Embryonic stem cells are obtained by harvesting living embryos which are generally 5-7 days old. The removal of embryonic stem cells invariably results in the destruction of the embryo.
* Fetuses - Another kind of stem cell, called an embryonic germ cell, can be obtained from either miscarriages or aborted fetuses.
Where do adult type stem cells come from?
* Umbilical Cords, Placentas and Amniotic Fluid - Adult type stem cells can be derived from various pregnancy-related tissues.
* Adult Tissues - In adults, stem cells are present within various tissues and organ systems. These include the bone marrow, liver, epidermis, retina, skeletal muscle, intestine, brain, dental pulp and elsewhere. Even fat obtained from liposuction has been shown to contain significant numbers of adult type stem cells.
* Cadavers - Neural stem cells have been removed from specific areas in post-mortem human brains as late as 20 hours following death.
How do embryonic and adult stem cells compare?
Embryonic Stem Cell Advantages
1. Flexible - appear to have the potential to make any cell.
2. Immortal - one embryonic stem cell line can potentially provide an endless supply of cells with defined characteristics.
3. Availability - embryos from in vitro fertilization clinics.
Embryonic Stem Cell Disadvantages
1. Difficult to differentiate uniformly and homogeneously into a target tissue.
2. Immunogenic - embryonic stem cells from a random embryo donor
are likely to be rejected after transplantation.
3. Tumorigenic - capable of forming tumors or promoting tumor formation.
4. Destruction of developing human life.
Adult Stem Cell Advantages
1. Special adult type stem cells from bone marrow and from umbilical cords have been isolated recently which appear to be as flexible as the embryonic type.
2. Already somewhat specialized - inducement may be simpler.
3. Not immunogenic - recipients who receive the products of their own stem cells will not experience immune rejection.
4. Relative ease of procurement - some adult stem cells are easy to harvest (skin, muscle, marrow, fat) while others may be more difficult to obtain (brain stem cells). Umbilical and placental stem
cells are likely to be readily available.
5. Non-tumorigenic-tend not to form tumors.
6. No harm done to the donor.
Adult stem cell disadvantages known today do not apply to our treatment.
1. Limited quantity - can sometimes be difficult to obtain in large numbers.
2. Finite - may not live as long as embryonic stem cells in culture.
3. Less flexible (with the exception of #1 above) - may be more difficult to reprogram to form other tissue types.
What are Adult Stem Cells?
An adult stem cell is an undifferentiated cell found among differentiated cells in a tissue or organ, can renew itself, and can differentiate to yield the major specialized cell types of the tissue or organ. The primary roles of adult stem cells in a living organism are to maintain and repair the tissue in which they are found.
The history of research on adult stem cells began in the 1960s when researchers discovered that the bone marrow contains at least two kinds of stem cells. One population, called hematopoietic stem cells, forms all the types of blood cells in the body. A second population, called bone marrow stromal cells, was discovered a few years later. These cells are a mixed cell population that generates bone, cartilage, fat, and fibrous connective tissue.
Why are adult stem cells preferable to embryonic stem cells?
Adult stem cells are a "natural" solution. They naturally exist in our bodies, and they provide a natural repair mechanism for many tissues of our bodies. They belong in the microenvironment of an adult body, while embryonic stem cells belong in the microenvironment of the early embryo, not in an adult body, where they tend to cause tumors and immune system reactions.
Most importantly, adult stem cells have already been successfully used in human therapies for many years. NO therapies in humans have ever been successfully carried out using embryonic stem cells. New therapies using adult type stem cells are being developed all the time. There are many examples of success stories using adult stem cells.
Is Stem Cell Research Ethical?
Most types of stem cell research are morally acceptable and laudable. Only research using embryonic stem cells raise insuperable moral objections. An ethical overview:
* Embryonic Stem Cells - always morally objectionable, because the human embryo must be destroyed in order to harvest its stem cells.
* Embryonic Germ Cells - morally objectionable when utilizing fetal tissue derived from elective abortions, but morally acceptable when utilizing material from spontaneous abortions (miscarriages) if the parents give informed consent.
* Umbilical Cord Stem Cells - morally acceptable, since the umbilical cord is no longer required once the delivery has been completed.
* Placentally-Derived Stem Cells - morally acceptable, since the afterbirth is no longer required after the delivery has been completed.
* Adult Stem Cells - morally acceptable.
Isn't it a matter of religious belief as to when human beings begin?
It is not a matter of religious belief, but a matter of biology. A human embryo is a human being, a being that is clearly and unmistakably human. Each of us was once an embryo, and this affirmation does not depend on religion, belief systems, or imposing anything on anyone. It depends only on a grasp of basic biology. Once you are constituted a human being (which always occurs at fertilization or at an event that mimics fertilization, as in cloning), aren't you a new member of the human race who must be protected?
Why is the destruction of human embryos wrong?
The well-known moral principle that good ends do not justify immoral means applies directly here. Once you are a being who is human, you are the bearer of human rights and you should never be violated for any reason. We know that the human embryo is a human being because it possesses an internal code for self-actualization and is an organism with an independent and inherent teleology (goal-directedness) to develop into an adult, and is physiologically alive and genetically human. Should human embryos be depersonalized or instrumentalized for research purposes?
Great Media Myths in the Debate Over Stem Cell Research
Myth 1. Stem cells can only come from embryos. In fact, as mentioned above, stem cells can be taken from umbilical cords, the placenta, amniotic fluid, adult tissues and organs such as bone marrow, fat from liposuction, regions of the nose, and even from cadavers up to 20 hours after death.
Myth 2. Christians are against stem cell research. There are four categories of stem cells: embryonic stem cells, embryonic germ cells, umbilical cord stem cells, and adult stem cells. Given that germ cells can come from miscarriages that involve no deliberate interruption of pregnancy, Christians in general oppose the use of only one of these four categories, i.e., embryonic stem cells. In other words, most Christians approve of three of the four possible types of stem cell research.
Myth 3. Embryonic stem cell research has the greatest promise. Up to now, no human being has ever been cured of a disease using embryonic stem cells. Adult stem cells, on the other hand, have already cured thousands. For example, bone marrow cells from the hipbone have repaired scar tissue on the heart after heart attacks. Research using adult cells is 20-30 years ahead of embryonic stem cell research and holds greater promise. This is in part because stem cells are part of the natural repair mechanisms of an adult body, while embryonic stem cells do not belong in an adult body (where they are likely to form tumors, and to be rejected as foreign tissue by the recipient). Rather, embryonic stem cells really belong only within the specialized microenvironment of a rapidly growing embryo, which is a radically different setting than an adult body.
Myth 4. Therapeutic cloning and reproductive cloning are fundamentally different from each other. The creation of cloned embryos, either to make a baby or to harvest cells, occurs by the same series of technical steps. The only difference is what will be done with the cloned human embryo that is produced.
Myth 5. Somatic nuclear cell transfer is different from cloning. In fact "somatic cell nuclear transfer" is simply cloning by a different name. The end result is still a cloned embryo.
Myth 6. By doing somatic cell nuclear transfer, we can directly produce tissues or organs without having to clone an embryo. At the present stage of research, scientists are unable to bypass the creation of an embryo in the production of tissues or organs. In the future it may be possible to inject elements from the cytoplasm of a woman's ovum into a somatic cell to "reprogram" it into a stem cell. This is called "de-differentiation". If so, there would be no fundamental moral objection to this approach to getting stem cells.
Myth 7. Every body cell, or somatic cell, is somehow an embryo and thus a human life. People sometimes argue: "Every cell in the body has the potential to become an embryo. Does that mean that every time we wash our hands and are shedding thousands of cells, we are killing life?" A normal skin cell will only give rise to more skin cells when it divides, while an embryo will give rise to the entire adult organism. Skin cells are not potential adults. Skin cells are potentially only more skin cells. Only embryos are potential adults.
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