STEM CELL BASICS
A stem cell is a special kind of cell that has a unique capacity to renew itself and to give rise to specialized cell types. Although most cells of the body, such as heart cells or skin cells, are committed to conduct a specific function, a stem cell is uncommitted and remains uncommitted, until it receives a signal to develop into a specialized cell. Their proliferative capacity combined with the ability to become specialized makes stem cells unique. A stem cell is a special kind of cell that has a unique capacity to renew itself and to give rise to specialized cell types. Although most cells of the body, such as heart cells or skin cells, are committed to conduct a specific function, a stem cell is uncommitted and remains uncommitted, until it receives a signal to develop into a specialized cell. Their proliferative capacity combined with the ability to become specialized makes stem cells unique.
Researchers have for years looked for ways to use stem cells to replace cells and tissues that are damaged or diseased. Recently, stem cells have received much attention.
What is “new” and what has brought stem cell biology to the forefront of science and public policy?
1. What are Cells?
Cells are the fundamental building blocks of the human body. These tiny structures make up the skin, muscles, bones and all of the internal organs. They are the key elements to how our bodies function. Cells serve both a structural and a functional role in the body, performing a wide range of actions to sustain the body’s tissues and organs. There are many different specialized cell types in the adult body. All of these cells perform very specific functions for the tissue or organ they compose. In the case of heart muscle, specialized cells “beat” rhythmically through the conduction of electrical signals, while the cells of the pancreas produce insulin to help the body convert food to energy. These mature cells have been differentiated, or dedicated, to performing their special tasks. Once a cell has become specialized, it cannot be changed into a different type of cell.
2. What are Stem Cells?
Stem cells, also known as progenitor cells, are primitive cells that give rise to other types of cells. There are several kinds of stem cells. Totipotent cells are considered the “master” cells of the body because they contain all the genetic information needed to create all the cells of the body plus the placenta, which nourishes the human embryo. Human cells have this capacity only during the first few divisions of a fertilized egg. After 3 – 4 divisions of totipotent cells, there follows a series of stages in which the cells become increasingly specialized. The next stage of division results in pluripotent cells, which are highly versatile and can give rise to any cell types. At the next stage, cells become multipotent, this mean that they can give rise to several other cell types, but those types are limited in number. An example of multipotent cells is hematopoietic cells-blood stem cells that can develop into several types of blood cells, but cannot develop into brain cells. At the end of the long chain of cell divisions that make up the embryo are “terminally differentiated” cells-cells that are considered to be permanently committed to a specific function.
3. What is an Embryonic Stem Cell?
An embryonic stem cell originates from a group of cells called the inner cell mass, which is part of the early (4 to 5 day) embryo called the blastocyst. Once removed from the blastocyst, the cells of the inner cell mass can be cultured into embryonic stem cells. These embryonic stem cells are not themselves embryos. In fact, evidence is suggesting that these cells do not behave in the laboratory as they would in the developing embryo. The conditions in which these cells develop in culture are likely to differ from those in the developing embryo.
4. What is an Adult Stem Cell?
An adult stem cell is an unspecialized (undifferentiated) cell that occurs in a specialized (differentiated) tissue, renews itself, and becomes specialized to yield all of the specialized cell types of the tissue from which it originated. The most common place to obtain these cells is from the bone marrow. There are many types of stem cells that we can find in the bone marrow, including hematopoietic stem cells, mesenchymal stem cells and angiogenic stem cells. It is known that hematopoietic stem cells form blood; mesenchymal stem cells form bone, cartilage and muscle and angiogenic stem cells form the vascular system (arteries and veins).
5. What are the similarities and differences between Embryonic and Adult Stem Cells?
Adult and embryonic stem cells differ in the number and type of differentiated cell types they can become. Embryonic stem cells can become all cell types of the body because they are pluripotent. Adult stem cells are generally limited to differentiating into different cell types of their tissue of origin. However, some evidence suggests that adult stem cell plasticity may exist, increasing the number of cell types a given adult stem cell can become.
A potential advantage of using adult stem cells is that the patient’s own cells could be expanded in culture and then reintroduced into the patient. The use of the patient’s own adult stem cells would mean that there will not be any risk of immunology rejection. This represents a significant advantage as immune rejection is a difficult problem that can only be circumvented with immunosuppressive drugs. Embryonic stem cells from a donor introduced into a patient could cause transplant rejection.
6. What is Stem Cell Therapy?
Stem Cell therapy can be considered as a group of new techniques, or technologies, that work by replacing diseased or dysfunctional cells with healthy, functioning ones. Our therapeutic treatment harvests the beneficial characteristics of adult stem cells. These new techniques are being applied to a wide range of human diseases, including many types of cancer, neurological diseases such as Parkinson’s and Lou Gehrig’s disease, spinal cord injuries, and heart disease.
7. How does Stem Cell Therapy work?
Even though cells are indispensable in performing many important functions for the body, they can also exist outside the body. They can live and divide in “cultures,” special solutions in test tubes or Petrie dishes. This ability to isolate certain cell types from other cells under controlled conditions has allowed scientists to study them independently of the organ or system they are normally a part of. Through the isolation and targeted manipulation of cells, scientists are researching ways to identify young, regenerating ones that can be used to replace damaged or dead ones in diseased organs. This therapy is similar to the process of organ transplant, but in this case, it’s the transplantation of cells rather than organs.
8. How are Cell Therapies being used today?
Bone marrow transplants are an example of cell therapy in which the stem cells in a donor’s marrow are used to replace the blood cells of the victims of leukemia and other cancers. Cell therapy is also being used in experiments to graft new skin cells to treat serious burn victims, and to grow new corneas for the sight-impaired. Recently, pancreatic cells derived from stem cells were implanted into the body of a diabetic and began to produce insulin.
In all of these applications, the goal is for the healthy cells to become integrated into the body and begin to function like the patient’s own cells. The results of these experiments have far exceeded expectations. Even though cell therapy is a new science, early results have caused great optimism to the medical and healthcare industries.
9. How can I get more information?
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