The Basics - What Exactly Is A Stem Cell?

A very common question happens to be one that goes back to the basics - what is a stem cell?

Stem cells are essentially building blocks that are found in all multicellular organisms.  These cells can divide (through a process called mitosis), self renew, and differentiate into many different cell types.

Again, the classic definition of a stem cell requires that it possess the following properties:

• Self-renewal: the ability to go through continued cycles of cell division while maintaining the undifferentiated state.
• Potency: the ability to differentiate into specialized cell types.

These properties make these cells so special and important.  It is the ability to renew throughout a person's life that allows our bodies to continually repair and heal.  And the differentiation allows for healing of all types of tissues throughout the body.

In general, there are two broad types of stem cells: embryonic, which are isolated from blastocysts (a product of early gestation that leads to the development of the embryo), and adult stem cells, found in various tissues throughout the body. In the developing embryo, stem cells can differentiate into all specialized cells (these are called pluripotent cells) and also maintain the normal turnover of regenerative organs/tissues, such as blood, skin, or intestinal tissues.  In adults, stem cells serve as the repair system for the body, replenishing adult tissues after injury or through the normal process of aging.  Adult stem cells are multipotent, meaning they can differentiate into many cell types, but not all.

There are three readily-accessible sources of  autologous (meaning from one's own body) adult stem cells in humans:
1. Bone marrow - requires extraction by drilling into bone (typically the iliac crest)
2. Adipose tissue (fat) - requires extraction by liposuction
3. Blood - requires extraction through the process of pheresis, wherein blood is drawn from the donor, passed through a machine that extracts the stem cells, then returns other portions of the blood back to the donor

Stem cells can also be found in umbilical cord blood just after birth.

Autologous harvesting involves the least risk when working with stem cells, as the cells are obtained from the patient's own body.  Thus, there is no chance of an auto-immune reaction or tissue rejection.  This also eliminates the risk of acquring an infection from another person.