Understanding Stem Cells
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Every day it seems as if there are new information—and new controversies— being reported about stem cells. What many people do not know is that there are actually two types of stem cells: embryonic stem cells and adult stem cells. Both may have applications in diabetes research as well as many other diseases.
Embryonic Stem Cells
Embryonic stem cells (ES cells, or fetal stem cells) are taken from fertilized human eggs at a very early stage. They have two key qualities: They can divide indefinitely, and they can form into a variety of cell types (a process called differentiation). For example, ES cells might differentiate into brain cells, blood cells, pancreatic cells or other cell types. In the diabetes field, one highly contested study claimed that ES cells could be coaxed into forming insulin-secreting beta cells, but several other studies dispute these findings.
Though we hear so much about embryonic stem cells in the news, ES cell research is literally in its infancy. There is still much basic research to be done on embryonic stem cells. One holdup is the difficulty of producing stable cell lines in the laboratory (“in culture”). While ES cells can be turned into healthy cell types in culture, they also can turn into highly undesirable cells, including tumor cells.
There are no federal restrictions on the use of mouse embryonic stem cells, so work with ES cells from mice is progressing both in the United States and worldwide.
Adult Stem Cells
The term “adult stem cell” is somewhat misleading. Adult stem cells can be found in people of any age—infants, adolescents or adults. What makes these cells “adult stem cells” is that they are undifferentiated cells (cells with the ability to mature into any of a variety of cell types) that come from differentiated tissue (tissue that is specialized, such as brain tissue or heart tissue).
For example, adult stem cells found in the bone marrow or blood (called hematopoietic adult stem cells) can become red blood cells or any of several types of white blood cells. There are at least 11 known tissues in humans containing adult stem cells.
Research with adult stem cells is further advanced than the research with ES cells. Adult stem cells are currently being used for therapies in the areas of Parkinson’s research, heart tissue regeneration, spinal cord injury, tissue regrowth, restoring blood flow, regrowing corneas, curing sickle-cell anemia and treating multiple sclerosis and lupus.
Adult stem cells are inherently more stable than ES cells, but they, too, present hurdles that researchers must overcome. Adult stem cells can neither form whole organisms, nor can they form all types of tissues and cells.
The application of adult stem cell research is underway in animal models of type 1 diabetes. At least seven published studies over the past eight years have found different types of adult islet stem cells in animals or humans.
In terms of islet regeneration, research is most advanced with hematopoietic stem cells from bone marrow, which may directly benefit islet regeneration. However, the possibility of turning adult hematopoietic stem cells into islet cells has drawbacks. This stem cell population may not be robust enough, meaning that of the harvested cells, only an insufficiently small amount will mature into islets. Other adult stem cells also located in the bone marrow may have the potential to form into islet cells, but again, researchers are not sure if it is possible to harvest enough of these cells to produce sufficient insulin to change the course of disease in diabetes.
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