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Utilizing stem cells for research may provide vital clues to the treatment and cure of many of today’s most serious diseases
One of the hottest debates in the media and in Washington are stem cells. We cannot go more than a day without hearing the latest news. We hear who is in favor of research, who thinks we should not allow the use of stem cells, and much more. There are groups strongly advocating both for and against stem cell usage, while other groups attempt to stay neutral as beacons of information.
As the debate rages on, both ethical and moral issues of stem cells rise to the top. Advocates tout the benefits of stem cell research with the promise of curing some of our most dreaded diseases. A pro-research website, “The Why Files Guide to Stem Cells,” declares that, “Once controlled and fathomed, stem cells could make drugs seem as antiquated as horseless carriages.” Yet other groups, such as Do No Harm: The Coalition of Americans for Research Ethics, claims that, “human stem cell research requiring the destruction of human embryos is objectionable on legal, ethical, and scientific grounds.” The media constantly covers these issues, especially the politics. The public is left to ponder the fundamental question underlying the whole issue: What are stem cells?
The plain definition of stem cells are cells that are capable of dividing indefinitely in culture, and give rise to specialized cells. The ability to divide, or to grow, indefinitely in culture, is a very important feature of stem cells. The ability to keep the cells alive continuously makes it possible to conduct a variety of experiments while reducing the variables within an experiment. The second part, giving rise to specialized cells, is key to stem cells’ potential to cure diseases. Stem cells have the ability to develop into bone, muscle, cartilage, or other types of cells. The ability of these cells to develop into almost any cell type could allow for the repair of any damaged or deteriorating tissue, thus they can be used in regenerative medicine. This would be especially valuable to treating diseases such as Parkinson’s, Alzheimer’s, diabetes, and cancer.
Totipotent, Pluripotent, Multipotent
However, to more fully understand stem cells, it is important to view them in the context of human development. At the time of fertilization, when the sperm and egg join, the one cell produced is capable of forming an entire organism. These cells are referred to as totipotent, which means that the potential of the cell is total. For a short while each cell division creates identical totipotent cells. That is to say, any of the cells formed during the first hours after fertilization could be placed in a woman’s uterus and develop into a fetus. By the fourth day, the totipotent cells begin to specialize, forming a blastocyte, or bundle of cells. The outer layer of cells will form the placenta and other necessary tissues required in the uterus for the fetus to develop. However, the inner cluster of cells will continue to develop into nearly all of the tissues of the human body.
Although those inner cells will form virtually every type of tissue in the body, they cannot give rise to the placenta or other supporting tissues for the uterus. Thus, they are unable to form an organism on their own if placed in a woman’s uterus, and are therefore referred to as pluripotent. As the pluripotent cells continue to specialize, they become stem cells that only lead to the development of specific tissues. Thus, some will lead to bone marrow, while some lead to blood or skin, and so on. The stem cells that carry this extra specialization are considered multipotent.
It is clear that multipotent stem cells play a vital role in fetal development; however, multipotent cells can still be found during the course of a person’s adult life. Although usually found in very small quantities, adult stem cells play a critical role in sustaining life. For example, red blood cells are continuously replaced, and the production of new red blood cells is initiated by blood stem cells. Virtually any body function that requires growth involves stem cells. The difference between totipotent, pluripotent, and multipotent cells is essential in understanding stem cells.
Acquiring and Using Pluripotent Stem Cells
There are two initial means of acquiring human pluripotent stem cell lines, each following a protocol used in work with other species. The first method isolates pluripotent stem cells directly from the inner cell mass of the blastocyst. The embryos can be obtained from infertility clinics that use in vitro fertilization (IVF). Excess embryos created for patients can be used, with consent, to harvest the inner cell mass. An alternative means is to culture specific cells from a terminated pregnancy. In this case, the decision to terminate the pregnancy and the consent to use the pluripotent cells are made separately. Each of these techniques yields viable and comparable stem cells.
Once these cells are obtained, the use for pluripotent stem cells is varied and vast. At a rudimentary level, these cells can offer insight into human development. Studies could be done that show us how the different cell divisions take place to develop the variety of tissues necessary for human life. Understanding how these events occur could lead to insight on how to prevent diseases, such as cancer, that are a result of mutant cell division.
The pluripotent stem cell potential is perhaps greatest in stem cell therapy. Today, the need for tissue and organ transplant far surpasses the supply. Waiting lists are long and a possible solution lies in pluripotent stem cells and regenerative medicine. Since the stem cells have the ability to develop into most any type of tissue needed, scientists could essentially direct the cells to develop into the specific tissues required. A person needing a liver transplant could perhaps receive a liver grown just for them. This technique of regeneration could be used in virtually every division of medicine and offers hope to patients living with Parkinson’s, Alzheimer’s, a stroke, burns, arthritis, or any number of diseases. The ability doctors would have to treat and cure disease would be unparalleled.
Another use of stem cells is in drug testing. All drugs go through extensive clinical trials before being tested on humans or even being considered for release. Drug testers could use the stem cells to test the drug on a variety of cell types, in addition to testing the drug on human cells that are in early development. Cell lines derived from cancerous cells are used in this manner, but their utility is likely to be inferior to stem cells. By utilizing stem cells initially, animal testing could be reserved for later stages of the drug development, when we already know the drug is safe in human cells. This would reduce costs both in monetary terms and lives.
In addition to the moral and ethical issues that must be addressed, a great deal of research will be needed to realize the full potential of stem cells. It is a large step to go from acquiring stem cells to clinical usage. Understanding the step required for stem cell specialization will be vital to learning how to direct stem cell development. Also, the stem cells acquired will be genetically different than the patient, thus creating another obstacle to overcome. Again, this is work for laboratory scientists.
The Pros and Cons of Adult (Multipotent) Stem Cells
As described earlier, multipotent stem cells is the stage after pluripotent stem cells. That is to say, they have differentiated already but will continue to specialize during development. Since these multipotent cells continue to be found in adults, they are also called adult stem cells. Multipotent cells have not been found for all adult tissues, but there have been and continue to be many discoveries.
The potential for multipotent cells is also quite high. The best use would be in cell transplantations. If adult stem cells can be isolated from an individual and directed to develop into a specific type of tissue, the cells transplanted into the same patient are not likely to be rejected. Additionally, making use of adult stem cells would avoid many of the ethical controversies because aborted fetal tissue or human embryos would no longer be necessary to harvest stem cells.
There exist numerous limitations to adult stem cells, however, that pluripotent stem cells do not possess. The primary issue facing researchers is that it is still unclear if adult stem cells can be coaxed to specialize into a different type of cell than they were initially. Some promise is shown in mice and rat studies, where research has shown that under certain conditions a specialized stem cell could change its specialization. If this redirection works for human cells, blood stem cells could be coaxed to grow into nerve cells, or another needed cell. Further development of this research is an important task facing scientists.
Additionally, adult stem cells have not been found for all tissues of the body. Without having all types of tissues, pluripotent stem cells are left as the means of obtaining certain tissue types. In addition to only some of the tissues having adult stem cells, no tissues have large quantities of stem cells. Obtaining adult stem cells sometimes requires significant procedures of extraction. Plus, isolation and purification of these stem cells is difficult.
Another limitation of adult stem cells is that stem cells from a specific patient will take time to grow up in culture so that there are an adequate number of cells for treatment. This growth may take more time than some patients have available. Other times, especially when the disease has a genetic basis, the adult stem cells would likely carry the genetic error. In general, adult cells are more prone to errors than younger cells. For example, older women have more difficulties with pregnancy—this would be a similar situation.
That’s a Wrap
There are a variety of stem cells. The totipotent stem cells offer little to researchers, however both the pluripotent and multipotent stem cells offer doors to important discoveries. These cells could be used in a variety of manners, all leading toward the treatment of diseases, many of which are currently untreatable. The moral, ethical, and political battle of stem cells will rage on, but the basics of the science stand firm. From a medical perspective, the potential of stem cells is gigantic.
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