Friday, October 13, 2006

Biology 101: An explanation of stem cells and cloning

The following are commonly asked questions about stem-cell research and human cloning. Answers have been provided by Dr. Richard A. Chole of Washington University School of Medicine and Barbara Quigley, executive director of the St. Louis Center for Bioethics and Culture. Both also serve on the board of directors of Missourians Against Human Cloning.

Why all the fuss about stem cells?

The human body is made of millions of cells. When some cells are injured, missing or not working properly, individuals experience problems or diseases. Scientists have found that one way to treat some diseases is to substitute healthy cells for those that are unable to work properly. Stem cells have the ability to transform into other cells and can sometimes serve as these replacements.

What are stem cells?

Stem cells are cells that do not have specific functions but can develop into other cells that have specific roles in the body, that is, any type of body cell. Some stem cells are "totipotent" — they can develop into any type of cell. Other stem cells are "unipotent" or "multipotent" and can develop into only one type of cell or a limited number of other types of cells.

Are all stem cells the same?

No. There are many types of stem cells but they can be classified into two basic groups: "adult" stem cells, also known as "somatic" cells (cells taken from body tissues) and "embryonic" stem cells, which are taken from an embryo.

What is wrong with taking stem cells from an embryo?

In order for stem cells to be harvested from an embryo the embryo is destroyed. A human embryo is the earliest stage of human life.

What is an embryo?

After fertilization of the egg, a zygote is formed. The zygote is the earliest form of the embryo. Over time the zygote grows as it continues to develop by cell division. In about five days the embryo has about 200 cells and is called a blastocyst.

Where do the embryonic stem cells come from?

Embryonic stem cells (ES cells) come from the inner cell mass of the blastocyst. These are the cells that will develop into all of the different tissues of the body.

What is so special about embryonic stem cells?

ES cells can develop into any type of cell depending on the conditions in which they are cultivated: nerve cells, muscle cells, etc. Furthermore, when cultivated in the laboratory, they continue to divide and reproduce themselves indefinitely.

Why haven’t embryonic cells been used to treat chronic diseases in people?

The only reported use of human ES cells to treat human disease was an attempt to cure Parkinson’s disease. This study showed some promise but many of the patients developed abnormal movements that could not be controlled with medicines. Some patients actually became worse. These studies were stopped and no further human uses of ES cells have been reported. Although scientists believe that embryonic stem cells may someday be useful in medical treatments, knowledge of the behavior of ES cells is incomplete. When implanted in experimental animals, ES cells continue to replicate and often develop into tumors called teratomas.

Are there ethical concerns in the use of adult (or somatic) stem cells?

No. Somatic stem cells are obtained from body tissues such as bone marrow, umbilical cord blood, fat cells, etc. Adult (somatic) stem cells can be obtained without damaging the donor and they cannot develop into an embryo.

Can adult stem cells be used for treatment of medical diseases?

Yes. Although adult stem cells may not be as flexible as embryonic stem cells, adult stem cells have been used for years to treat and cure human diseases. Every week scientists discover new ways to use adult stem cells to treat chronic diseases. Examples are sickle cell anemia and leukemia. Studies in animals have shown that there are possible cures for diabetes, heart disease and neurological diseases with adult stem cells

What is cloning?

In cloning, an egg (ovum) from a woman is surgically removed from her body and taken to the laboratory where the nucleus is removed. A body cell (somatic cell) is removed from any part of the body, commonly skin cells, and its nucleus is taken to the laboratory where it is inserted into the "empty" egg. The cell that is formed is a cloned zygote which then develops spontaneously into a cloned blastocyst, or cloned embryo.

What is SCNT?

SCNT (Somatic Cell Nuclear Transfer) is the scientific term for cloning. The term SCNT is sometimes confusing because it sounds like "somatic stem cell," but actually refers to the transfer of the nucleus from the somatic cell to the ovum (egg). SCNT results in a cloned embryo.

Are there concerns about removing eggs from healthy women?

Yes. Even women’s groups that support ES research have concerns about SCNT. Judy Norsigian wrote in the Boston Globe on February 25, 2005: "There is a disturbing lack of attention to the risks to women’s health posed by the advent of embryo cloning ... Omitted from the polarized debate is any discussion of the thousands of women who will need to undergo egg extraction procedures for such embryo cloning. A primary concern is the substantial risks to women’s health posed by the extraction procedure and the inability to obtain true informed consent from egg donors given the current lack of adequate safety data." Since women are paid to donate their eggs, some people believe that this process would exploit poor young women.

Can a cloned embryo continue to develop?

We know that cloned embryos of mice, cats, sheep and cattle have been allowed to develop into adult animals. As far as we know, no human cloned embryo has ever been allowed to develop beyond a blastocyst, but one could assume that what has been successful in other mammals could also work in humans. Further development would require implantation into a uterus and this has never been attempted, as far as we know.

Are cloned embryos genetically identical to the donor of the somatic cell?

Actually, no. While the nucleus of the donor somatic cell contains most of the genes, there are some genes outside the nucleus (mitochondrial genes) which are carried along with the transplanted nucleus (blue dots below). The egg with its nucleus removed also carries some mitochondrial genes (green dots below). The resulting cloned zygote contains nuclear genes from the donor somatic cell and mitochondrial genes from both the donor somatic cell and the egg. This combination of mitochondrial DNA from two individuals does not occur in nature.

Is it appropriate to regulate scientific research in the United States?

Yes. Modern society has appropriately restricted research in many ways. Since the atrocities in Nazi Germany, society has adopted rules about research on humans (the Nuremberg Code). Scientists left to their own discretion have not always done the right thing. In Tuskegee, Ala., black men were infected with syphilis and left untreated to see what happened. In Willowbrook, N.Y., retarded children were infected with hepatitis to see how the disease spread. In Germany, Jews were tortured and killed in medical experiments to test the limits of human physiology. By "dehumanizing" these groups of people (black men, retarded children, Jews) scientists of the time saw no ethical problem in doing these experiments.

Moreover, the promise of future benefit from the research was used to help justify the experiments. If a scientist does not consider the human embryo to be human, destroying it poses no moral or ethical problems. It is the right and responsibility of society to limit or regulate scientific research that is morally or ethically unacceptable.

A quick summary

Stem cells offer the potential for significant medical treatment. The use of adult stem cells has led to many medical breakthroughs and poses no ethical problem. However the production and destruction of human embryos required for embryonic stem cell research is a significant ethical and moral problem. Human beings, even the tiniest developing human beings, should not be used in experiments which result in their death.


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