Embryonic and adult stem cells: types, sources, and medical potential

Stem Cell

Stems Cells are the source of all body tissues. Growth and development of the human body arises from the stem cell and is maintained by it. Although all cells can divide or copy themselves, stem cells are unique because of their ability to replicate and create all other types of cells. This ability of the stem cell makes it a powerful tool for biological research and medicine. Scientists believe that stem cell research has the potential to finding cures for several previously incurable diseases. Despite this exciting potential, progress in stem cell research has so far been hampered by serious technical, ethical, and political issues. This paper discusses the types of stem cells and their sources, the potential of stem cell use in medical science, and the issues that are holding back rapid progress in stem cell research.

Types of Stem Cell

There are basically two types of stem cells: the embryonic stem cells and the adult stem cells.

Embryonic Stem Cell: Embryonic stem cells are 'precursor cells' that have the capacity to divide for indefinite periods of time in culture and to give rise to virtually any type of specialized cell in the body. They are derived from the inner cell mass of a blastocyst before the cells have started to specialize and the embryo is transformed into a fetus. (Shapiro, 2006, p. 205). Embryonic stem cells were first discovered when scientists managed to derive stem cells from the embryo of a mouse more than 20 years ago, while the ability to isolate stem cells from the human embryo was discovered in 1998. ("Stem Cells Basic," 2006)

Adult Stem Cells: Adult stem cells are present in the tissues of human beings such as the nerve, blood, skin, and muscle cells and perform the function of growth, repair and maintenance of these tissues in our life times. The main difference between the adult stem cells and the embryonic stem cells is that the former typically generate only the cell types of the tissue in which they reside while the latter can be induced to produce all types of cells. A blood-forming adult stem cell in the bone marrow, for example, is used to get the different types of blood cells such as red blood cells, white blood cells and platelets. Recent research has also shown that it is possible to grow other types of tissues from some adult stem cells as well, although adult stem are certainly not as versatile in their replicating characteristic as the embryonic stem cells. ("Stem Cells: Basics, 2006).

Sources of Stem Cells

Embryonic stem cells are almost always derived from embryos developed from eggs fertilized during fertility treatment in clinics. In the process of in vitro fertilization, eggs removed surgically from a female ovary are fertilized with sperms in a lab for subsequent implant in a woman's uterus. Numerous fertility clinics fuse more than one egg with sperm as a routine in order to try another implant if the first one does not work. Hence, thousands of such "left-over" embryos are stored in liquid nitrogen freezers in the United States and other countries where in vitro clinics exist, which can be used for stem cell research.

Although, these 'left-over' embryos from in vitro fertilization clinics are the most common source for the stem cells used in research, other more controversial sources for embryonic stem cell also exist. These include aborted fetuses, cloned human embryos, or specially fertilized eggs for creating stem cell cultures. Adult stem cells can be isolated from a tissue sample obtained from an adult and the richest sources of adult stem cells are bone marrow and cord blood obtained from the umbilical cord and placenta (Wagner, 2007).

Potential Uses of Stem Cells

Although bone marrow stem cells have been used to treat cancer patients for several decades now, most of their potential uses are yet to be developed. Most scientists agree that due to the ability of embryonic stern cells for self-renewal and their capacity to develop into a wide variety of cell types, potential applications of embryonic stem cells are almost limitless.

Nervous System Diseases: Perhaps the most exciting potential of stem cell is in the possible use of stem cells for curing currently incurable "nervous system" diseases that result from loss of nerve cells such as Parkinson's disease, Alzheimer's, ALS, and multiple sclerosis. For example, nerve cells that make the chemical dopamine could conceivably be created from stem cells for individuals with Parkinson's disease (Shapiro, 2006).

Type I Diabetes: Type I diabetes is an autoimmune disease in which the cells of the pancreas that normally produce insulin are destroyed by the patient's own immune system. Stem cell research indicates that it may be possible to direct human embryonic stem cells in cell culture to 'differentiate' into forming insulin-producing cells; these could then be transplanted into diabetic patients who are unable to produce their own insulin. (Ibid.)

Heart Disease: Stem cell research also holds the promise of generating healthy heart muscle cells in the laboratory and then transplanting those cells into patients with chronic heart disease. Already, research in mice and other animals has shown that bone marrow stem cells, transplanted into a damaged heart, can generate heart muscle cells and successfully replace damaged heart tissue. ("Stem Cells: Basics, 2006)

Prior Testing of Drugs: Apart from their potential therapeutic applications, stem cells also have the potential to significantly change the way pharmaceutical drugs are tested now. New medications could be tested initially on cells or tissues developed from stem cells, and only those drugs initially found to be safe and effective could be cleared for further testing on humans.

Therapeutic cloning: One of the major problems with stem cell therapy is that of rejection by the body, which recognizes the stem cells as a foreign body and attacks them. The procedure (also known as 'somatic cell nuclear transfer') has the potential to overcome rejection risks. It involves removal of the nucleus of an unfertilized egg cell and replacing it with the nucleus of a 'somatic cell.' The stem cells extracted from such an egg cell in its blastocyst stage share the individual's genetic information and would be less likely to be rejected when used in therapy. (Shapiro, 2006).

Conclusion

Stem cells that have the unique ability to replicate and develop into other types of specialized cells hold enormous therapeutic promise. However, as we discussed in this essay, stem cell research is still in its infancy and has to overcome several formidable ethical, political, and technical barriers before it can realize its potential and deliver the promised 'miracle cures' for a number of dilapidating diseases.