Q. Can you tell us what stem cells are? Can they really be the panacea we are looking for?
A. As we all know, humans arise from just a single cell, the fertilized ovum, which is the result of the union of the father's sperm cell and the mother's egg cell. Soon after it has formed, the fertilized ovum multiplies many times over to produce cells called stem cells.
The stem cells that are produced during the first few days of embryonic development are totipotential; they are very versatile cells that can transform to any specialized cell and have unlimited capability to divide and produce exact copies of themselves. But soon after they have been produced, these cells begin to specialize or differentiate, which means they commit themselves to producing only certain cell types, something they need to do to form the various tissues and organs.
As the fetus matures in the womb, its stem cells become more and more specialized such that at birth, their capabilities have markedly reduced. They can no longer produce new organs, but they can still replace those cells in the tissues and organs that die due to physiologic reasons or injury. Stems cells gradually decrease in number and potential as the individual grows older that is why with age, wounds take longer to heal, infections become more difficult to fend-off, etc. But stem cells persist throughout life. They reside in those organs whose existing functional cells they have the capability to replace.
The number and capability of stem cells vary depending on where they are located. In those organs where the lifespan of the functional cells is rather short, they are quite numerous and versatile. For example, the bone marrow has enough stem cells to continuously produce all types of blood cells. Likewise, the gastrointestinal tract and the skin have enough stem cells that can replace cells that are normally shed off or die because of injury.
But in those organs where the functional cells are long-lived such as the brain and muscles, very few stem cells persist to adulthood. Thus, often, nerve cells and muscle cells (such as those in the heart) that are lost are replaced not by functional cells, but by cells that form scar tissue.
Stem cells can be harvested, cultured in the laboratory to increase their number and then introduced to patients to replace damaged, injured or dead cells in, conceivably, any tissue or organ. Are stem cells, therefore, the panacea and fountain of youth that humanity has been seeking for since time immemorial?
Stem cell therapies that are presently being legally performed involve harvesting bone marrow stem cells from the patient to be treated. Bone marrow stem cells can replace bone marrow cells.
Thus, stem cell therapy has proven success in patients with dysfunctional bone marrow, multiple myeloma, leukemias (cancers of the blood) and a few other conditions.
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A primer on Stem Cells