Introduction to Stem Cells
There are 3 main types of stem cells. They are:
- Prenatal (which include embryonic and fetal)
- Postnatal (which include umbilical cord and placental)
(Although postnatal stem cells are often grouped under the "adult" category, it is useful to define each type separately).
As we shall later describe in more detail, embryonic, fetal and postnatal stem cells are "pluripotent"; adult stem cells, by contrast, have generally been considered to be either "multipotent" or "monopotent", although this belief is changing. (The reader is referred to the section on "Key Terms").
Pluripotent stem cells are capable of differentiating into any other type of cell, whereas multipotent and monopotent stem cells are more limited.
Popular discussions about stem cells usually focus on the differences between embryonic and adult stem cells. It is often pointed out that embryonic stem cells offer a greater potential for treatment, yet critics cite the inherent risks (such as teratomas, nonviability, etc.), as well as the ethical dilemmas surrounding embryonic stem cell research. Even without the ethical controversies, however, embryonic stem cell therapy involves a sufficient amount of scientific problems to qualify as disadvantageous. Adult stem cells, by contrast, while ethically noncontroversial, and without the inherent risks of embryonic stem cells (such as the formation of teratomas, etc.), have heretofore been viewed as restricted in the types of cellular differentiation that they are capable of exhibiting. Additionally, in both embryonic and adult stem cell therapies, immune rejection by the patient is common.
But an alternate answer exists, which is commonly overlooked. Perhaps this answer is so often overlooked because the true nature of the question is overlooked. The key question is not so much a matter of embryonic versus adult stem cells, but rather, the key question is a matter of pluripotent versus multipotent (and monopotent) stem cells.
The answer, therefore, may be found in postnatal stem cells, or more specifically, in umbilical cord and placental stem cells. These stem cells are pluripotent (not multipotent or monopotent, and therefore not limited in their types of cellular differentiation), they carry none of the inherent risks posed by embryonic stem cells (such as teratomas, contamination, etc.), immune rejection has been demonstrated to be very low, and ethically these cells are noncontroversial. Fortuitously, Nature has also provided umbilical cord and placental stem cells in abundance.
Indeed, even the multipotency and monopotency of adult stem cells is now being challenged. New evidence strongly suggests that certain adult stem cells may be capable of as much pluripotency as embryonic stem cells.