Stem Cells Used for Research: Types and Implications

Stem cells are classified according to their potency. "Potency" is a term that describes how many types of cells a stem cell can become.

Totipotent stem cells are cells that have not begun differentiating at all. They are capable of developing into any other type of body cell. Pluripotent cells are almost as potent as totipotent stem cells. They have barely started differentiating and can develop into almost any other type of cell.

Multipotent stem cells are stem cells that have begun differentiating into a general type of cell. They are capable of developing into one of several cell types in a given "family" of cell types. For example, a blood stem cell (hematopoietic stem cell) can become any of the many types of blood cell (red blood cells, white blood cells, platelets, etc.), but cannot become a muscle cell or a nerve cell.

Oligopotent stem cells can differentiate into only a few types of cell. For example, a lymphoid stem cell can become any of the blood cells found in the lymphatic system (T cells, B cells, and plasma cells), but not a different kind of blood cell, such as a red blood cell or platelet.

Unipotent stem cells can only become one type of cell — their own. They are considered stem cells because they can reproduce indefinitely. An example is skin cells, which can renew themselves indefinitely, but which cannot become any other type of cell.

Stem cells are found in embryos, in the umbilical cord, and in many tissues of the fully developed body, most notably the bone marrow. Stem cells may be classified according to their origin.

Totipotent cells are found only in a newly-fertilized embryo after the first few cell divisions, before the embryo develops any kind of structure. Once the embryo begins to develop structure (through a process called gastrulation), the cells are considered pluripotent.

Embryonic stem cells are cells derived by removing the inner cell mass of an embryo that is a few days old, a procedure that kills the embryo. Embryonic stem cells are pluripotent.

Adult stem cells are any stem cells derived from a more mature tissue, such as the umbilical cord, bone marrow, or skin. Despite the name, adult stem cells do not necessarily come from adults; they can come from fetuses, newborns, and children as well. Adult stem cells are usually multipotent, oligopotent, or unipotent.

Totipotent cells are found only in a newly-fertilized embryo after the first few cell divisions, before the embryo develops any kind of structure. Once the embryo begins to develop structure (through a process called gastrulation), the cells are considered pluripotent.

Horst Ibelgauft. Cytokines and Cells Online Pathfinder Encyclopedia (COPE). Available at http://www.copewithcytokines.de/