Adult (Somatic) stem cells are unspecialized cells that are found in different parts of the body and, depending on the source tissue, have different properties. Adult stem cells are capable of self-renewal and give rise to daughter cells that are specialized to form the cell types found in the original body part.

Adult stem cells are multipotent, meaning that they appear to be limited in the cell types that they can produce based on current evidence. However, recent scientific studies suggest that adult stem cells may have more plasticity than originally thought. Stem cell plasticity is the ability of a stem cell from one tissue to generate the specialized cell type(s) of another tissue. For example, bone marrow stromal cells are known to give rise to bone cells, cartilage cells, fat cells and other types of connective tissue (which is expected), but they may also differentiate into cardiac muscle cells and skeletal muscle cells (this was not initially thought possible).

Hematopoietic stem cells that give rise to all blood and immune cells are today the most understood of the adult stem cells. Hematopoietic stem cells from bone marrow have been providing lifesaving cures for leukemia and other blood disorders for over 40 years. Hematopoietic stem cells are primarily found in the bone marrow but have also been found in the peripheral blood in very low numbers. Compared to adult stem cells from other tissues, hematopoietic stem cells are relatively easy to obtain.

Mesenchymal stem cells are also found in the bone marrow. Mesenchymal stem cells are a mixed population of cells that can form fat cells, bone, cartilage and ligaments, muscle cells, skin cells and nerve cells.

Hematopoietic and stromal stem cell differentiation:4

Umbilical cord blood from newborns is a rich source of hematopoietic stem cells. Research has found that these stem cells are less mature than other adult stem cells, meaning that they are able to proliferate longer in culture and may contribute to a broader range of tissues. Research is ongoing to determine whether umbilical cord stem cells are pluripotent or multipotent and the extent of their plasticity.

Cord blood, which traditionally has been discarded, has emerged as an alternative source of hematopoietic stem cells for the treatment of leukemia, lymphoma and other lethal blood disorders. It has also been used as a life-saving treatment for children with infantile Krabbes disease, a lysosomal storage disease that produces progressive neurological deterioration and death in early childhood.

Regardless of the adult stem cells' source bone marrow, umbilical cord blood or other tissues these cells are present in minute quantities. This makes identification, isolation and purification challenging. Scientists are currently trying to determine how many kinds of adult stem cells exist and where they are located in the body.

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Cell Therapy and Regenerative Medicine

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