An adult stem cell is an undifferentiated cell found among differentiated cells in a tissue or organ. These cells  can renew themselves  and can differentiate to yield the major specialized cell types of the tissue or organ.

The primary roles of adult stem cells in a living organism are to maintain and repair the tissue in which they are found.

They are also termed as  somatic stem cell. The origin of adult stem cells in mature tissues is unknown.

Adult stem cells have been found in many more tissues than they once thought possible. In right environment, certain kinds of adult stem cells seem to have the ability to differentiate into a number of different cell types, given the right conditions. If this is possible under lab conditions, these cells may become the basis of therapies for many serious common diseases.

About 40 years ago, researchers discovered that the bone marrow contains at least two kinds of stem cells. One population, called hematopoietic stem cells, forms all the types of blood cells in the body. A second population, called bone marrow stromal cells, generate bone, cartilage, fat, and fibrous connective tissue.

There are a very small number of stem cells in each tissue.They may remain non-dividing for many years until they are activated by disease or tissue injury.

The adult tissues reported to contain stem cells include brain, bone marrow, peripheral blood, blood vessels, skeletal muscle, skin and liver.

Struggle, however is to  grow adult stem cells in cell culture and manipulate them to generate specific cell types so they can be used to treat injury or disease.

How To Identify Adult Stem Cells?

One or more of the following three methods are used to identify adult stem cells

1. Labeling the cells in a living tissue with molecular markers and then determining the specialized cell types they generate
2. Removing the cells from a living animal, labeling them in cell culture, and transplanting them back into another animal to determine whether the cells repopulate their tissue of origin
3. Isolating the cells, growing them in cell culture, and manipulating them, often by adding growth factors or introducing new genes, to determine what differentiated cells types they can become.