The two core features that characterize stem cells are the capacity for self-renewal and differentiation into specialty cell types. By origin, stem cells are classified as embryonic stem cells (ESC) and adult stem cells (ASC). ESCs are pluripotent, meaning they are capable of differentiating into all cell types (more than 200 cell types in the human body). ASC, by contrast, are typically multipotent with a limited range of the types of cells they can differentiate into. An example of ASC is hematopoietic stem cells (HSC), which originate in the bone marrow and are capable of becoming red blood cells, white blood cells, and platelets. As for the source of ASC, it could be the umbilical cord, bone marrow, or peripheral blood.
Stem cells come in different varieties. These include:
- Embryonic stem cells which are capable of becoming any cell type
- Adult stem cells (also called somatic stem cells) are found in assorted tissues whose differentiation is confined within the specific tissue type that harbors the adult stem cells
- Mesenchymal stem cells that differentiate into bone cells, fat cells, and muscle cells
- Neural stem cells that form brain cells, such as astrocytes and neurons
- Hematopoietic stem cells that develop into all types of blood cells, including red blood cells, white blood cells, and platelets
