Stem Cells
Stem cells are undifferentiated, multipotential somatic cells from which other, specialized cells arise by differentiation. Stem cells are cells which have the ability to divide infinitely, and to develop into the huge variety of specialized cells required for the creation of an organism. Most cells have a specific function (e.g., liver cells, skin cells, brain cells, etc.) and once they have taken on this function, in a process called differentiation, they cannot be adapted for any other function. Stem cells, however, have not gone through the differentiation process.
By isolating stem cells in a laboratory, scientists theoretically could grow new heart cells to repair damage from heart attacks, new liver cells to treat hepatitis, or new red blood cells for cancer patients. As of 2001 the methods by which customize stem cells with respect to function is as yet unknown.
A number of different types of stem cells have been identified. Totipotent (Total Potency) stem cells represent the cell created during the fusion of sperm and egg in conception, and the cells created in the next few cell division cycles. Every cell contains all the genetic information necessary to create an entire being. With time these totipotent cells begin to specialize into pluripotent cells, that have the potential to create many but not all of the types of tissue necessary for the development of the entire being.
Pluripotent stem cells develop into more specialized stem cells committed to the generation of a specific cell line (examples include skin stem cell, liver stem cell, blood stem cell, nerve stem cell). Specialization is a one-way process and a specific stem cell line cannot become less specialized.
Human pluripotent stem cells are important to science and to advances in health care. At the most fundamental level, stem cells could further the understanding of the myriad complex events that occur during human development. Of primary importance would be the identification of factors involved in the cellular decision-making process that results in cell specialization. Conditions such as cancer and birth defects are due to abnormal cell specialization and cell division. A better understanding of normal cell processes will allow scientists to better understand the fundamental errors that cause these diseases.
Stem cell research could also change the way drugs are developed and tested. Testing in animals and humans could be reduced, as stem cell lines could be used in the initial screening of therapeutic agents. Only those showing potential would be carried through to animal or human testing.
The most far-reaching potential of human pluripotent stem cells is the generation of cells and tissue that could be used for so-called cell therapies. Many diseases and disorders result from disruption of cellular function or destruction of tissues of the body. The organs and tissues available for transplantation is far outnumbered by the number of people in need. Stem cells, stimulated to develop into specialized cells, offer the possibility of a renewable source of replacement cells and tissue to treat diseases and conditions such as Parkinson's disease, Alzheimer's disease, spinal cord injury, stoke, burns, heart disease, diabetes, osteoarthritis and rheumatoid arthritis.
Blood stem cells are capable of differentiating into red blood cells, platelets, and the many types of white blood cells necessary for the immune system. Stem cells have been utilized to treat cancer patients whose immune systems have been destroyed by chemotherapy.
Another stem cell therapeutic procedure involves the administration of bone marrow cells. Anticancer strategies that target the rapidly growing cancerous cells also compromise other fast growing cells, such as bone marrow cells. Transplantation of bone marrow cells, themselves a type of stem cells, or a peripheral blood stem cell transplant, can restore the vital functions lost by the therapeutic destruction of the original marrow population.
In early 1999, there were several reports of the successful laboratory growth and differentiation of stem cells into multiple cell lines. Such a strategy could provide a ready supply of transplantation and material. However, ethical concerns over the embryonic source of the stem cells need to be addressed before the potential of this stem cell technology can be fully realized. Adult stem cells do exist. However, their small number would require cell culture techniques to increase their numbers to therapeutically useful levels. The time required to do this might not allow for fully effective therapy.
More generally, the potential of stem cell transplantation therapy will require a solution to the problem of immune rejection. Because pluripotent stem cells obtained from embryos or fetal tissue would be genetically different from the recipient, future research would need to focus on modifying human stem cells to minimize tissue incompatibility or to create tissue banks with the most common tissue-type profiles.
This is the complete article, containing 769 words
(approx. 3 pages at 300 words per page).
