The Basics of Stem Cells
Stem cells have been a hot (and hot-button) topic since researchers began to successfully isolate and develop lines of them in the late 1990s. Usually the controversy surrounding their sources has overshadowed the actual research and advances (if any) in the field, but recent reports that research using adult stem cell lines has moved ahead of similar research employing embryonic cells, have given both researchers and politicians hope that the science of, as opposed to the controversy of stem cells, can come to the fore.
Stem cells have the ability to renew themselves through mitotic cell division while remaining undifferentiated (self-renewal), and they have the capacity to differentiate into a broad range of specialized cell types (potency). These attributes have given rise to the hope that stem cells can be used therapeutically to repair or regenerate many kinds of damaged tissue, especially those types (like central nervous system cells) that do not replicate once a critical age has been reached.
Research on stem cells dates back to studies and experiments involving bone marrow and umbilical cord blood in the 1960s and ‘70s, but it wasn’t until 1981 that scientists at Cambridge University and the University of California–San Francisco successfully extracted mouse embryonic cells.
Human embryonic cells would have to wait another 17 years until researchers at the University of Wisconsin–Madison isolated them. Ironically adult stem cell isolation occurred only a few years later, most notably in 2003 at the National Institutes of Health (NIH).
Adult Stem Cells
Adult stem cells are able to self-renew indefinitely, and have the potential to grow into an entire organ from a small group of that organ’s cells. In addition there is promising research that shows the potential for adult stem cells to grow into other cell types as well. Currently, however, adult stem therapies require a source from a specific line, which makes culturing and harvesting sufficient cells challenging.
These cells can theoretically be derived from any adult cell, including bone marrow, hair follicles, nerves, and a class of cells called Mesenchymal stem cells (MSC) that appear to differentiate into a variety of tissues (referred to as multipotent). Additional research is being done involving cells from umbilical cord blood which are also more adaptable than typical adult cells.
Adult stem cell therapies have been used successfully for many years to treat leukemia and related bone/blood cancers, and recent advances in orthopedic treatments (regeneration of cartilage) and organ transplants involving stem-cell-grown tissue show great promise.
Embryonic Stem Cells
These cells are derived from the inner cell mass of an early-stage embryo known as a blastocyst, and this extraction leads to the destruction of the embryo, causing much of the ethical controversy surrounding stem cells in general. Embryonic stem cells pluripotent, that is they can differentiate into nearly all cells, as opposed to the majority of adult-derived cells that are usually limited to the organ/tissue from which they came.
This is ability is a double-edged sword: the potential exists for therapies to be developed that would allow this class of stem cells to repair or regenerate any tissue in any patient, but it also means that uncontrolled, undifferentiated masses can form, akin to cancer. As a result, and due to restrictions in several countries on embryonic stem cell production (notably the U.S.), there are no approved therapies using this type of cell yet. But the potential is great, and research continues, though at a diminished pace.