Types of Stem Cells: Potency

Stem cell potency refers to the potential for certain stem cells to differentiate and become specific types of cells. Stem cells may be obtained from a variety of sources including the embryo (embryonic stem cells), umbilical cord blood and adult or bone marrow stem cell sources. Depending on the source from which they are derived, stem cells may have a particular type of potency.

Stem Cell Potency

The main types of stem cell potency that current stem cell research has focused on include the following:

• totipotent
• pluripotent
• multipotent

These may further be divided into specific categories depending on the types of cells that the stem cells have the potential to become. For instance, stromal stem cells may differentiate to form bone, cartilage, fat and connective tissue cells. Hematopoietic stem cells, on the other hand, will differentiate and form red and white blood cells as well as platelets – although stem cell research has found that this type of stem cell (found in cord blood) does have the potential to become other types of cells.

Totipotent Stem Cells

Totipotent stem cells can be found at the earliest stages of embryonic development within the first few divisions of a fertilized egg. These early stem cells actually comprise the embryo and have the potential to differentiate into embryonic and extraembryonic cells. Totipotent stem cells therefore have the capacity to form completely new embryos that are capable of developing into new organisms.

Pluripotent Stem Cells

Pluripotent stem cells have the ability to differentiate into almost every type of cell found in the human body. There are several sources of pluripotent stem cells, but they are most commonly associated with human embryonic stem cells:

• blastocyst embryonic stem cells: these are embryonic stem cells that are formed seven days after fertilization when the embryo is in the "blastocyst" phase of development
• fetal stem cells: these stem cells may be derived after the eighth week of development when the embryo is referred to as a fetus

Because pluripotent stem cells have the ability to differentiate into a vast variety of human cells, they are often considered of great value to stem cell research.

Multipotent Stem Cells

Multipotent stem cells have the ability to differentiate into limited types of cells in the body that are closely related. For instance hematopoietic stem cells, which produce different types of blood cells, are considered multipotent stem cells.

Multipotent stem cells may be derived from the following sources:

• umbilical cord blood
• adult stem cell sources such as bone marrow or peripheral blood

Unlike pluripotent embryonic stem cells, multipotent stem cells do not have the ability to become a variety of different cell types. However, these types of stem cells are capable of self-replicating in order to repair specific organ tissue.