STEM CELLS are very important not for what they are but for what they can become. They can transform into all the 200-odd cell types found in the human body and finding ways to control this transformation has become a crucial topic in biological science.
Scientists believe that if they can control the way a stem cell transforms, they can use them to treat diseases such as Parkinson'sand multiple sclerosis. Treatments are some years away, however, as much remains to be learned about how stem cells work. The research is made more complex because not all stem cells are the same. Some can become any tissue type. Others can only transform into a restricted family of tissue types – for example, those associated with blood cells or with the brain.
For this reason, researchers working with stem cells tend to stream into groups depending on which stem-cell typethey are studying. Each has its own technological challenges and each has its own ethical concerns.
EMBRYONIC STEM CELLS
These are the "gold standard" of stem cells because they are "pluripotent", able to transform into the widest possible range of tissue types. Using them causes ethical dilemmas, however because they are harvested from a living embryo, a process which destroys the embryo. Those who argue that life begins at the moment of conception refuse to accept embryonic stem-cell research for this reason, even to the point of rejecting the use of self-perpetuating stem-cell lines because of their source.
ADULT STEM CELLS
These are found in mature tissues such as bone marrow, liver or the brain. They provide essential replacement cells, but can only transform into a limited range of tissue types associated with where they are found. They are rare, but can be harvested from these tissues and their use poses few ethical issues.
INDUCED PLURIPOTENT STEM CELLS
These are the most exciting advance made since the discovery of stem cells in 1981. In November 2007, scientists announced that they had taken human adult skin cells and “re-programmed” them to behave like true embryonic stem cells. They are still under study, but in time could provide a source of pluripotent stem cells but with no ethical problems because no embryo is destroyed to make them. The problem is that the only way to ensure that these induced cells act and grow the same as the embryonic cells is comparative testing, something that will still require research that destroys embryos.
Dick Ahlstrom