Embryonic stem cells are derived from the inner cell mass of a blastocyst, which is the stage of a human embryo development four to five days after fertilization. The blastocyst is a thin walled structure which has 50 to 150 cells with an inner cell mass and an outer layer of cells. The inner cell mass will develop into the embryo. The outer layer of cells will primarily evolve into the placenta. The National Institutes of Health states “The embryonic stem cells are derived from embryos that develop from eggs fertilized in vitro in an in vitro fertilization clinic and donated for research purposes with the consent of the donor. They are not derived from eggs fertilized inside a woman’s body”.
Embryonic stem cells have the ability to give rise to all types of cells in the body, a term known as pluripotent. Pluripotent of cells could be used to create replacement tissue and cells for medical therapies. According to the National Institutes of Health, “Pluripotent stem cells offer the possibility of a renewable source of replacement cell tissues to treat a myriad of diseases, conditions, and disabilities including Parkinson's disease, amyotrophic lateral sclerosis, spinal cord injury, burns, heart disease, diabetes, and arthritis.” The ability to grow and isolate embryonic stem cells for research has only been possible since 1998. The use of embryonic stem cells to cure and heal illness offers promise, although research is still in the early stages.
The removal of embryonic stem cells kills the embryo from which they are extracted. The cells are foreign to the patient’s body, and they may be rejected. The long term effects of introducing embryonic stem cells into a person’s body are unknown. When embryonic stem cells were injected into mice, the cells had a tendency to develop into a tumor known as a teratoma. According to Blum, Nur, and others, “Teratomas derived from human embryonic stem (hES) cells are unique among oncogenic phenomena as they are polyclonal and develop from apparently normal cells (p 281)”. Researchers have discovered the anti-apoptotic gene survivn which contributes to teratoma formation and are working to inhibit the effect of the gene.
The use of embryonic stem cells for research and treatment of human ailments is a controversial topic. Since the removing cells from a human blastocyte results in the destruction of the embryo, many people view the process as immoral. If life begins at conception, in vitro or otherwise, destroying an embryo could be considered murder.
According to a White House Press release on March 9, 2009, President Obama overturned an order signed by President Bush in 2001 which limited the National Institutes of Health from funding certain studies on embryonic stem cells. Under the new order, the NIH will have greater authority to conduct and support human stem cell research, including embryonic stem cell research. President Obama also stated that he plans to develop guidelines so the research is never used for human cloning for the purpose of reproduction (p 1).
The National Institute of Health defines an adult stem cell is an undifferentiated cell; a cell that has not developed a specialized function. They are found among differentiated cells in a tissue or organ that renews itself, and can differentiate to yield some or all of the major specialized cell types of the tissue or organ. They are also known as somatic stem cells and are found in animals and humans.
Adult stem cells are retrieved primarily from bone marrow, but can also come from a variety of organs and tissues such as brain tissue, blood vessels, skin, teeth and liver. Within each tissue or organ is a certain area known as the stem cell niche in which the undifferentiated adult stem cells are found.
Adult stem cells divide and generate all the cell types of the organs from which they have been extracted. Unlike the embryonic stem cells, an embryo is not destroyed while obtaining the adult stem cells, therefore the technique is not considered controversial. Adult stem cells have been used for years in bone marrow transplants and are easy to extract. Stem cells can also be found in umbilical cord blood. Other adult stem cells, which exist in the stem cell niche in various organs, are relatively small in number, making them difficult to use for research and eventual therapy. Several promising studies have surfaced over the last few years involving adult stem cells. One such study done on rats by Moreno-Monzano, Rodriguez-Jimenez and others used cells that had been transplanted from the lining of the spinal cord in an attempt to reverse some of the paralysis associated with a spinal cord injury. In the study, transplanted cells were found to grow after a spinal cord injury and travel to the injured area. When these cells were transplanted into animals with a spinal cord injury, they regenerated ten times faster than similar cells derived from healthy animals (p 1).
Although there are many advantages to using adult stem cells, there are some limitations. According to the National Institutes of Health, with the exception of bone marrow stem cells and umbilical stem cells, most tissues have a small number of stem cells. When these cells are cultured outside the body, their ability to divide is limited, unlike embryonic stem cells, which can divide prolifically. Scientists in many laboratories are trying to find better ways to grow large quantities of adult stem cells and manipulate them to generate specific cell types.
Cited References
Blum B, Bar-Nur O and others. 2009. The anti-apoptotic gene survivin contributes to teratoma formation by human embryonic cells. In: Nature Biotechnology 27, 281-287 [online database]. c2009 [cited 2009 June 19]. Available from: http://www.nature.com/nbt/journal/v27/n3/abs/nbt.1527.html
Moreno-Manzano and others. 2009. Activated spinal cord ependymal stem cells rescue neurological function. In: Wiley Interscience [online database]. c2009 [cited 2009 June 19]. Available from: http://www3.interscience.wiley.com/journal/121664916/abstract?CRETRY=1&SRETRY=0
Removing barriers to responsible scientific research [online article]. [1 page]. In: Whitehouse Press Office. c2009 [cited 2009 June 19]. Available from: http://www.whitehouse.gov/the_press_office/Removing-Barriers-to-Responsible-Scientific-Research-Involving-Human-Stem-cells/
Stem Cell Basics, Questions and Answers [online article]. National Institutes of Health. In: Stem Cell Information. c2009 [cited 2009 June 19]. Available from: http://stemcells.nih.gov/info/faqs.asp
Stem Cell Basics: What are embryonic stem cells? [online article]. National Institutes of Health. In: Stem Cell Information. c2009 [cited 2009 June 20] Available from: http://stemcells.nih.gov/info/basics/basics3.asp
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