Stem cells are undifferentiated cells able to differentiate into specialized cell types. These are used for stem cell treatment, which is an intervention strategy that introduces new adult stem cells into damaged tissue in order to treat disease or injury. For over 30 years, bone marrow and, more recently, umbilical cord blood stem cells have been used to treat cancer patients with leukaemia and lymphoma because during chemotherapy most growing cells are killed, but a donor’s healthy bone marrow reintroduces functional stem cells to replace the cells lost during the treatment. Stem cells are also used to treat brain damage, spinal cord injury, heart damage, blood cell formation, baldness, deafness, blindness and many other illnesses and they are also important for research. If stem cells are so useful then why is there so much controversy about the use of them? The base of the debate is “When does life begin?”
Biology of Stem Cells
A stem cell is a “blank cell”, capable of becoming another more differentiated cell type in the body, such as a skin cell, a muscle cell or a nerve cell. As said, they’re important because they can be used to replace or even heal damaged tissues and cells in the body. Stem cell research started in the mid 1800's with the discovery that some cells could generate other cells. The first real stem cells were discovered in the early 1900's, when it was found that some cells generate blood cells. The first human embryonic stem cell was extracted in 1998.
There are 5 main types of stem cells.
1. Adult (somatic) stem cells: bone marrow and mesenchymal stem cells. 2. Foetal stem cells: stem cells that drive the rapid growth and development of the organs. 3. Cord blood stem cells: used to treat diseases and conditions of the blood or to restore the blood system after treatment for specific cancers. 4. Embryonic stem cells: derived from very early embryos. 5. Induced Pluripotent stem cells: “reprogrammed” cells with a specialized function. The techniques used to make them need to be carefully refined before they can be used to generate iPS cells suitable for safe and effective therapies.
A stem cell possesses two properties:
1. Self-renewal: the ability to go through several cycles of cell division without changing state 2. Potency: the capacity to differentiate into specialized cell types. Stem cells can be:
* Totipotent: able to differentiate in all possible cell types * Pluripotent: able to differentiate in almost all cell types * Multipotent: able to differentiate into a closely related family of cells * Oligopotent: able to differentiate into a few cells
* Unipotent: able to produce cells of the same type but have properties of self-renewal to be called stem cell. As shown in the picture, not all stem cells have the same capabilities. Stem cells extracted from the morula (a four-five day old embryo) are the most capable stem cells, since they’re able to specialize in all possible cell types. Stem cells from the blastocyst (in humans, an embryo of 70-100 cells) are pluripotent. A pluripotent cell can create all cell types except for extra embryonic tissue (placenta), unlike a totipotent cell. Adult stem cells can be multipotent (bone marrow contains stem cells that give rise to all blood cell types but not other cells), oligopotent (a lymphoid stem cell, which can only give rise to blood cells of the lymphatic system) or unipotent.
Adult stem cells can be isolated in many ways, depending on the tissue. Most of them are isolated from bone marrow. Embryonic stem cells are obtained from left over early-stage embryos in assisted fertility treatment, e.g. in vitro fertilization. A remarkable difference between embryonic stem cells and adult stem cells is that the first ones can be grown easily in culture, while adult stem cells are rare in mature...