The Promise of Stem Cells
We frequently hear about them on the news, they’re controversial, and their application is perhaps one of the most important advances in modern science. But what exactly are stem cells?
Most cells in our body have specialized functions. Red blood cells carry oxygen, heart muscle cells allow the heart to pump blood, bone cells support our skeleton. Stem cells are unspecialized but they do, however, give rise to all of those other cells. After a stem cell divides each new cell can either remain a stem cell or become a different cell with a specialized function, for example, muscle, brain, or liver.
Stem cells come from two sources: embryos, appropriately called embryonic stem cells, and those found in adult tissue, called adult stem cells. Embryonic stem cells come from usually four- or five-day old human embryos, generally obtained from embryos created through in vitro fertilization, a technique that generates more embryos than are needed for implantation into a prospective mother and can be donated by the donor with consent. Basically then, human embryonic stem cells are derived from donated embryos that would otherwise be discarded. Adult stem cells, on the other hand, can be found at all stages of life. These are found amongst many tissues and organs, and their primary role is to maintain and repair the tissues where they are found.
Typically, while embryonic stem cells can become any and all cell types, adult stem cells are limited to generating the cell types of the organ from which they originate, potentially regenerating the entire organ from a few cells. There is no ethical controversy about experimenting with adult stem cells but they are more difficult to isolate because they are rare in mature tissue.
Stem cells are categorized based on their potential to differentiate into other types of cells. Totipotent cells have the ability to differentiate into all possible cell types, pluripotent, the ability to differentiate into almost all cell types, and multipotent, the ability to differentiate into a closely related family of cells.
The study of stem cells, be they adult or embryonic, opens the door for all kinds of applications. Most notable is the potential for tissue regeneration. Currently, we rely on organ donors for transplants, however if stem cells can be engineered to produce new organs, then organ supply would finally meet demand. Stem cells also hold potential for the treatment of cardiovascular disease with embryonic stem cells being investigated as a potential source for regenerating damaged heart tissue.
Drug testing is another potential application. Stem cells can be differentiated into a variety of cell types which can then be used to study the effects of drugs.
Research in this area is progressing quickly. The 2012 Nobel Prize in Physiology or Medicine was awarded to. John Gurdon and Shinya Yamanaka who showed that mature cells can be changed back to embryonic-like states. This is highly significant because the technique can allow for the prolific generation of stem cells which will accelerate research..