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Basic QuestionsStem cells are a type of cell that can generate many different kinds of mature cells. These cells are the foundation or building block of all tissue in the body. As such they hold the promise of being the body's own essential repair tool. Embryonic stem cells can form any type of cell in the body. In contrast, adult/tissue stem cells are partially specialized and generally only form cells from their tissue of origin. So, blood-forming stem cells can form all types of blood cells, while skin stem cells can form new skin cells. When a stem cell divides, each so-called “daughter” cell has the potential to remain a stem cell or become a cell with a more specialized function, such as a muscle cell, a red blood cell or a brain cell, according to the National Institutes of Health (NIH). Embryonic stem cells can become one of more than 200 specialized cells in the body, thus providing a potentially unlimited source of cells for medical and scientific purposes. They hold the promise of being the body's own essential repair tool. The trick is figuring out how to grow them in a controlled way and to make them take on the exact job needed. The hope is that someday they could treat dozens of diseases and injuries.
Stem cells have two important characteristics that distinguish them from other cells in the body. First, they can replenish themselves for long periods through cell division. Second, after receiving certain chemical signals, they can form specialized cells with specific functions, such as a heart cell or nerve cell.
The easiest way to categorize stem cells is by dividing them into two types: adult/tissue and embryonic. Adult/tissue stem cells are found in specific body tissues during fetal development and throughout adulthood. These so-called “adult” stem cells are also found in the umbilical cord and placenta of newborn babies. Embryonic stem cells (ESCs) are found in the inner cell mass of a five-day-old fertilized embryo called a “blastocyst.” While there are many different varieties of adult/tissue stem cells in different tissues (blood-forming stem cells, skin stem cells, muscle stem cells, nervous system stem cells, etc.), there is only a single type of embryonic stem cell.
Adult/tissue stem cells are present in many different tissues from fetuses, newborn infants, children and adults. Adult/tissue stem cells have been found in most organs of the body including the bone marrow, blood, liver, skin, gastrointestinal tract, nervous system and muscle. Embryonic stem cells are primitive cells that can be generated in a laboratory dish. Scientists isolate stem cells from embryos donated with informed consent of couples who have undergone in vitro fertilization (IVF). These embryos are no longer needed by the donor and would otherwise be discarded. Embryonic stem cells are isolated by transferring the inner cell mass into a plastic laboratory culture dish. Growing embryonic stem cells in the laboratory is known as cell culture. The cells divide and spread over the surface of the culture dish, which is coated with connective tissue cells that have been treated so they will not divide. After stem cells replicate for several days, they crowd the dish. They are removed gently and replated into several fresh culture dishes. Replating the cells is repeated for many months and is called subculturing. After several weeks, those original 30 cells of the inner cell mass yield millions of embryonic stem cells. These cells from a single embryo that have proliferated in a cell culture for six or more months without differentiating – and have normal numbers of chromosomes – are referred to as an embryonic stem cell line.
Once a stem cell line is established, essentially, it can grow forever according to the National Institutes of Health (NIH). 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 apparently indefinitely and cells may be frozen for storage or distribution to other researchers. Stem cell lines carrying genetic defects that cause specific diseases could facilitate the development of new drugs because it would be possible to test new drugs on any human cell type bearing the exact genetic defects that cause disease in patients. Researchers would use the embryonic stem cells to generate the desired mature cells in laboratory dishes, then screen for new drugs that would alleviate disease symptoms.
Embryonic stem cell research represents new hope for millions of Americans. Research on these cells has the potential to lead to new treatments for a range of serious human ailments, including diabetes, cancer, Parkinson's disease, Alzheimer's disease, heart disease, birth defects, spinal cord injury and burns. This extraordinary research is still in its infancy. Research on human embryonic stem cells only began in 1998, while research on adult stem cells has taken place for 40 years. Practical application will only be possible with additional study. No one can say with certainty how long it will take to find a cure for any specific disease using embryonic stem cells. Typically, biomedical research can take 10, 20, even 30 years to produce successful results. But the sooner the research starts, the sooner it can bring new insights and new treatments. The Catholic Church is among the leaders of those who oppose embryonic stem cell research, because they believe that life begins as soon as an egg is fertilized. They maintain that embryonic stem cell research is wrong because harvesting these cells kills the living human embryo. The Catholic Church opposes most forms of in vitro fertilization and the direct destruction of human life for any purpose, including research [Source: Michigan Catholic Conference Focus, February 2005].
Embryonic stem cell research will help to understand the origin of inherited human diseases including birth defects, neurodegenerative diseases and cancer. Stem cells also could be used to develop safer and more effective new drugs. An often overlooked benefit of studying embryonic stem cells is that we currently have no good way of studying early human development. By coaxing embryonic stem cells to form various tissues, we can learn about how genes impact normal development and how development can go wrong.
Cloning is the creation of multiple copies of a single molecule, cell or virus. There are many different kinds of cloning, most of which are now commonplace in science. Cloning has allowed scientists to develop powerful new drugs and to produce insulin and useful bacteria in the lab. It also allows researchers to catch criminals and free innocent people, and produce new plants and livestock to feed an undernourished world population. Therapeutic cloning, or somatic cell nuclear transfer (SCNT), involves removing the nucleus of an unfertilized egg cell, replacing it with the material from the nucleus of a “somatic cell” (a skin cell, for example), and stimulating this new cell to begin dividing. Once the cell begins dividing, stem cells can be extracted five to six days later and used for research. The American Association of Medical Colleges (AAMC) supports ongoing research into SCNT and has endorsed legislation that would allow such research to flourish. Reproductive cloning, on the other hand, is intended to create human beings by cloning human embryos. The AAMC and the National Academy of Sciences recommend a ban on all forms of this type of cloning [Source: American Association of Medical Colleges].
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