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The cells capable to renew themselves and differentiate in some or all of the specialized cells of the body are known as stem cells. (Weissman, 2000; Lindvall et al., 2004; Singec et al., 2007) They can be found during the first stages of development such as embryonic (ES cells) and fetal stem cells. But they can also be found in adult organisms in specific tissues such as bone marrow, brain, blood, among other tissues and are called adult stem cells or somatic stem cells (Asahara et al., 2000).
Embryonic stem cells are obtained from the inner mass of the blastocysts. ES cells have the pluripotent property of differentiating in cells derived from any of the three germ lines endoderm, ectoderm and mesoderm. (Wobus & Boheker, 2005; Asahara et al., 2000). Whereas adult stem cells do not have such faculty; they are confined to give rise to cells of the particular tissue they are precursors of. Although some adult stem cells of certain organs can generate different kinds of cells within that organ and this is why this kind of stem cells are known to have a multipotent property. (Asahara et al., 2000, Singec et al., 2007).
The ability of these cells of generating specialized and completely functional cells put them under the spotlight all around the world. The first approach with stem cells potential was in the 1960s, when Till, McCulloch, Wu, Becker, and Siminovitch discovered that bone marrow cells could be transformed into blood cells (Weissman, 2000; Geoffrey et al., 2007; Asahara et al., 2000). But the new era of stem cell research started during the 80s and 90s when embryonic stem cells from mouse and human were isolated (Gurtner et al., 2007).
Stem cell therapy: Arguments for and against
Stem cells could be the answer to treat and even cure some or all of the most deathful and disabling diseases humans are affected with. This is because they allow treating diseases not for its symptoms but for the origin of the pathology. They can be genetically modified to produce a particular protein that damaged cells are lacking to produce, or they can be used to regenerate a wounded tissue (Wobus & Boheler, 2005). Considering all this, stem cells have an enormous potential to be used in therapies for any human ailment.
The most efficient way to make stem cells reach the injured tissue is by transplantation. Transplantation of stem cells in a damaged tissue may help in the regeneration of the affected organ (Singec et al., 2007; Asahara et al., 2000). In 1997 Snyder and co-workers (1997; cited by Singec et al., 2007) carried out the first study in the mouse brain that supports the idea that stem cells can reconstitute an adult tissue. And since that study, many others have accepted the efficiency of stem cell transplantation in tissue regeneration of adult specimens (Singec et al., 2007). The problem is that, as in tissue transplantation, immunological reactions may occur against stem cells, unless these cells come from the same individual who is receiving the stem cell therapy which can be achieved by a "therapeutic cloning" (Wobus & Boheler, 2005). Another solution for this problem is to knock down the gene expression of MHC class I and II in the stem cells but this won't guarantee there is not going to be a graft rejection (Wobus & Boheler, 2005).
Another important issue to think about is that genetic modifications of stem cells can cause problems in the host. Though in the body are natural regenerative processes, they might cause a bigger damage in an injured tissue. This is one of the reasons why stem cells are genetically modified in order to retard the side effects that occur while accomplishing regeneration (Asahara et al., 2000). One more motive for modifying stem cells is to make them express a specific molecule necessary to control certain pathology (Asahara et al., 2000). To generate these genetically modified stem cells, they can be subjected to epigenetic modifications and mutations that can make stem cells unsuitable for therapeutics (Wobus & Boheler, 2005).
Stem cells present a coordinate control of cell growth, differentiation and apoptosis but owing to the fact that they have an unlimited proliferative capacity and that they do not need to be bound to something, they are potentially tumourigenic. And as a consequence of that, there is a possibility for benign tumours to appear in the site where stem cells were injected in the patients (Wobus & Boheler, 2005).
The studies that have been done in human and mouse stem cells have revealed a great potential of using this cells to create different types of tissue. And the generation of such a diverse range of tissues makes stem cells a very useful tool of therapeutic value (Wobus & Boheler, 2005).
Even though stem cell therapy is a very promising alternative to treat diseases so far incurable, a lot of research is needed in order to minimize the possible problems that this new therapy could cause in patients. And besides the immunological and tumourigenic complications this treatment could bring, the ethical regulations are other important issue before considering stem cell therapy in humans (Wobus & Boheler, 2005).
Everyday new studies about stem cells are being carried out by researchers all around the globe. And hopefully they can soon get the answer to make stem cell therapy safe enough to be applied in humans. To date, bone marrow cells transplantation has been successfully used to treat leukaemia. So I think it is important to find a way to take advantage of all the properties of stem cells, and use them in benefit of all the ones that suffer an "incurable" illness.
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- Wobus AM, Boheler KR. (2005) Embryonic stem cells: prospects for developmental biology and cell therapy. Physiol Rev. 85(2):635-78.