Stem cells: These two tiny words are enough to spark heated arguments and ignite fierce passion on all sides of the debate. Why are stem cells so controversial? Since embryonic stem cells were first isolated in 1998 (4), the field of stem cell research has truly excelled. Despite the controversy surrounding this field, stem cell research has been—and will continue to be— essential in the development of treatments for some of the most devastating diseases, disorders, and injuries. Not only have potentially new treatments become available in the last fifteen years, but new methods of obtaining these valuable cells have also been discovered and developed (1,7).
What are stem cells? Every source will have a slightly different definition, but the most basic definition of a stem cell is a cell that can be manipulated to become any type of cell (3). Key properties of stem cells are the ability to self-renew, which means that the cell can divide and produce new copies of itself, and the ability to specialize (4). Stem cells can be one of four types: totipotent, pluripotent, multipotent, or unipotent (4). Totipotent cells are capable of becoming any cell type in the body (4). Without question, these cells are the most prized due to their ability to form any cell that is needed, given the correct chemical signals. However, totipotent stem cells are the most controversial because they are derived from embryos (4). Pluripotent cells have the ability to form any cell type except “extra-embryonic structures (4).” As far as the level of differentiation (i.e. specialization), these are the next best thing to embryonic stem cells (7). Multipotent stem cells are capable of becoming any cell type that is necessary to repair damage to a specific organ or tissue (4). For instance, bone marrow stem cells can form all cells that comprise the blood, but they cannot give rise to other cells, such as nerve cells (4). Unipotent cells can only form one type of cell; an example of this would be spermatogonia only being able to produce sperm cells (4).
The controversy surrounding stem cells most likely comes from the methods used to obtain them. The most infamous method of obtaining stem cells involves the destruction of embryos. However, new methods have been developed recently that could spare embryos from destruction and eliminate the controversy surrounding this vital research. One method of obtaining cells that basically act like totipotent stem cells is through dedifferentiation. Dedifferentiation is a process in which specialized cells become increasingly less specialized until they reach a simpler state (1). According to a 2007 study, researchers have had promising results in the dedifferentiation of muscle, kidney, nerve, and skin cells though the exact mechanism has yet to be identified (1). Another method of acquiring stem cells is through a process called somatic cell nuclear transfer (SCNT). In this process, the nucleus from an egg cell is removed, and it is replaced with the nucleus from an adult cell (7). This method can be used to produce induced pluripotent stem cells (iPSC) (7). Stem cells can also be harvested from umbilical cord blood. Regrettably, these ground-breaking methods have largely been overshadowed by the negativity associated with stem cell research.
To those suffering from debilitating disorders, stem cells might seem like a godsend: a light at the end of a long, dark, and often painful tunnel. To gain a better understanding as to why people suffering from these conditions desperately need stem cell research to continue, one must first understand what these diseases, disorders, and conditions do to the body. Parkinson’s disease occurs when the brain cells that produce dopamine die (6). Classic symptoms of this disease are “tremors and rigidity (6).” Parkinson’s disease is one of the best candidates for stem cell therapy because only one cell type is being lost (4); it is much easier to command a batch of dedifferentiated cells to become one specific cell type than it is to command the cells to become several different types. Another prime candidate for stem cell therapy is diabetes type I. Diabetes type I is an auto-immune disease that can be treated fairly easily with stem cells because only the beta-cell is being lost (4). However, this disease cannot be cured through the use of stem cells because the same underlying condition that killed the original cells would eventually cause the death of the new cells, making multiple transplantations necessary over time (4). A third suitable—perhaps even ideal—candidate for stem cell therapy is macular degeneration, also known as “age-related blindness (4).” This disease is ideal for treatment because it occurs in the eye, which will not reject donor cells, makes it next to impossible for cells to accidentally travel to other parts of the body, and allows the affected eye to be treated without jeopardizing vision in the other eye (4). Diseases and disorders that are more difficult to treat using stem cells include: Alzheimer’s disease, multiple sclerosis (MS), and autism (2, 4, 6). A contributing factor to Alzheimer’s disease is thought to be the build up of proteins that are folded in strange ways; this abnormality interferes with the functions of the cell, eventually leading to its demise (4). In addition, “sticky plaques form on the different nerve cells (4).” Combined, these two characteristics kill many different types of brain cells, which makes the repair work difficult because each brain cell type that has been lost must be produced and then injected at the correct location in order to “integrate properly with the surviving brain tissue (4).” Multiple sclerosis is a neurological disease in which the central nervous system becomes inflamed due to the loss of the myelin sheath (4, 6), which is “a layer of fatty tissue” that insulates the nerves (5). Over time, MS causes its victims to lose control over several basic functions that most people take for granted (6). Utilization of stem cells as a treatment for MS is limited because there is not a way to ensure that the cells “spread throughout the central nervous system and restore all of the lost myelin around nerves (4).” Duchenne muscular dystrophy (DMD) is a fairly common disease that affects mainly skeletal muscles, heart, and respiration muscles (4). DMD is caused by a mutation in the dystrophin gene (4). This is one of the more devastating diseases because its victims are children who barely live to age twenty (4). While a treatment may not be quite ready, scientists have been experimenting with iPSC to develop a human model for this disease (4). Autism is a disorder characterized by communication and social interaction difficulties; the cause is still a mystery (2). However, a 2009 study indicates that stem cell treatments can significantly improve behavior in autistic children (2). In this study, thirty-seven autistic children are split into groups that either receive human cord blood mononuclear cells (CBMNC) and behavioral therapy, human umbilical cord-derived mesenchymal stem cells (UCMSC) and CBMNC combined with behavioral therapy, or are the control group that only receives behavioral therapy (2). The participants’ autism is evaluated and confirmed using three rating systems: Clinical Global Impression (CGI), Childhood Autism Rating Scale (CARS), and Aberrant Behavior Checklist (ABC) (2). At the conclusion of the study, the Combination group (i.e. the group that received UCMSC, CBMNC, and behavioral therapy) seemed to show significant improvement over the other groups (2). Not only can stem cells treat diseases, but they can also repair damaged tissues left behind by a heart attack, stroke, or spinal cord injuries (4). Of these examples, damage left in the wake of a heart attack would be the easiest to fix because only heart muscle cells need to be replaced (4). Repairing the damage from a stroke is more complicated because the affected area of the brain has to essentially be reconstructed (4). Spinal cord injuries are tricky to repair; stem cells have the best chance of healing crush injuries as opposed to injuries where the nerves are completely severed. This is because the “insulating layer of myelin surrounding the nerves has been lost, but the nerves themselves are still intact (4).” However, the stem cell treatment must be administered shortly after the crush injury to the spinal cord is sustained due to the formation of scar tissue. It would be extremely difficult—if not impossible—for stem cells to get past the scar tissue in order to repair the damage (4). Over the past fifteen years, advancements in stem cell research have led to the development of potential treatments for diseases like Parkinson’s and Duchenne’s muscular dystrophy. However, a definitive cure for these catastrophic diseases still evades scientists.
As the characters on the television show Once Upon a Time frequently say, “Magic always comes with a price.” The same is true for therapeutic stem cell transplantation. The price of utilizing stem cells as a treatment option is the risk of tumors rejection, and the transplantation of cells into the body (4). The formation of tumors is most likely to occur when embryonic stem cells are used especially when these cells are cultured in the laboratory (4). This is because embryonic stem cells have the ability to form any kind of cell; therefore, they are more susceptible to mutations (4). The tumors can either be benign or malignant; if the tumor is benign, it is called a teratoma, and if the tumor is malignant, it is a cancer called teratocarcinoma (4). Teratocarcinoma differs from a teratoma in that the tumor contains “undifferentiated stem cells” as well as “differentiated cell types (4).” Like donor organs and tissues after transplantation, donor stem cells carry a risk of being rejected by the recipient’s body (4). Human leukocyte antigen (HLA) proteins—the same proteins responsible for organ and tissue rejections—are capable of causing stem cell transplantations to fail (4). To avoid this complication, the obvious solution would be to harvest the stem cells from the patient’s body or from an identical twin (4). However, the patient’s own cells cannot be used if the disease “is caused by a genetic defect or in an emergency setting (4).” In certain cases, the patient can develop graft-versus-host reaction in which the transplanted cells attack the patient’s cells resulting in sores (4). This “only occurs when the transplant contains antigen-presenting cells and lymphocytes (4).” Curiously, a limited graft-versus-host reaction can be good for a patient because the cells that cause this reaction will kill the remaining cancer cells (4). Another risk associated with stem cell treatments is the transplantation process because that often involves injecting the cells into vital organs such as the brain and the kidneys (4).
Before stem cells become a routine treatment option in the medical field, several obstacles—such as the limited capability to produce the right types of cells, the high costs associated with this therapy, and the raging battle over ethics—must be overcome. The nature of the stem cell and the fact that scientists have yet to unlock the technology to mass produce stem cells limits the possible beneficiaries. For example, adult stem cells have not been able to grow in the laboratory long enough to produce large numbers of cells (4). This limits the number of patients that are able to receive stem cell treatments. One reason for the high cost of stem cell therapy is the basic economic principle of supply and demand: when there are sufficient supplies, demand remains balanced and prices stay relatively low. However, limited supplies and increasing demand lead to higher prices. Currently, there are not enough stem cells available to meet the overwhelming demand. Another reason for the expense of stem cell therapy is due to “the level of quality control and of hygiene required of cells to be transplanted together with the use of special clinical grade culture reagents (4).” While the production of a sufficient supply of cells and the high costs of therapy are difficult obstacles to overcome, the major hurdle to clear before stem cells are incorporated into routine medical care is the ethics debate. The only aspect of the argument that ever seems to get publicity is whether or not this research can be considered murder. However, there are more debates taking place over issues that are just as serious. An example of one of these often ignored questions could be: is it possible to develop one uniform set of regulations for the world to follow regarding the sources of stem cells (4)? It would be extremely difficult, for example, to persuade Germany, which has strict policies regarding the source of stem cells, to relax these regulations and be more like the United Kingdom, Sweden, and Belgium, which have the least restrictive policies regarding this extremely sensitive topic (4).
What is something that even the federal government absolutely refuses to spend money on and is enough to inspire ordinary people to fight to the bitter end on either side of a distinct line of demarcation? The answer is stem cells. Simply put, a stem cell is a cell that can become any type of cell (3). These cells come in four varieties: totipotent, pluripotent, multipotent, and unipotent (4). While stem cells are capable of treating devastating diseases like Duchenne’s muscular dystrophy, Alzheimer’s disease, and multiple sclerosis, they carry the risk of tumor development and rejection along with the transplantation itself (4). Despite the risks and challenges, the future of stem cells research looks promising.
Literature Cited
1. Cai, S., Fu, X., and Sheng, Z. 2007. Dedifferentiation: a new approach in stem cell research. BioScience [Internet] 2007 [cited 2013 Sept 15]; 57 (8): 655-662. Available from http://www.jstor.org/stable/10.1641/B570805.
2. Lv et al.: Transplantation of human cord blood mononuclear cells and umbilical cordderived mesenchymal stem cells in autism. Journal of Translational Medicine 2013 11:196
3. Mandal, A. What are stem cells [Internet]. [cited 2013 Sept 15]. Available from www.news-medical.net/health/What-are-stem-cells.aspx.
4. Mummery, C., Wilmut, I., van de Stolpe, A., Roelen, B.A.J. 2011. Stem Cells Scientific Facts and Fiction, 1st ed. Elsevier Inc., Burlington, MA, pp. 46, 50, 135-136, 140-142, 146-147, 147-148, 150, 151, 157, 152, 156-157, 159-162, 165, 169, 283, 286, 298.
5. Myers, D.G. 2005. Psychology Tenth Edition in Modules, 10th ed. Worth Publishers, NY, pp. 48.
6. Schwartz, P.H., Bryant, P.J. 2008. Therapeutic uses of stem cells. In: Fundamentals of the Stem Cell Debate The Scientific, Religious, Ethical & Political Issues (K. Monroe, R. Miller, and J. Tobis, eds.), University of California Press, Berkeley, CA, pp. 37-61.
7. Weidong, H., Yali, Z., and Xiaobing, F. 2010. Induced pluripotent stem cells: the dragon awakens. BioScience [Internet] 2010 [cited 2013 Oct 8]; 60 (4): 278-285. Available from http://www.jstor.org/stable/10.1525/bio.2010.60.4.6
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