Stem cells have two defining capabilities that make them unique: first they are able to generate new copies of themselves (self-renewal) and second, they can differentiate a specific function such as blood cells, brain cells or bone cells. There are different levels of stem cell potency: totipotent (able to give rise to an entirely functional organism), pluripotent (able to give rise to all tissue types) and multipotent (able to differentiate into a limited range of cells within a tissue type).
Multipotent stem cells can be found in adult humans. Adult stem cells play an essential role in the daily health and maintenance of our body - for example 200 billion red blood cells are created each day in the body from haematopoietic stem cells (HSCs) found in the bone marrow.
Recently, a new (artificial) type of stem cell was developed: Induced Pluripotent Stem Cells (IPSC). IPSC's can be derived from adult somatic cells and have similar pluripotent properties to Embryonic Stem Cells (ESC) - without involving the controversial use of embryos. Stem cells may be promising tools for treating diseases in which a cellular and tissue destruction occur. Stem cells could for example provide healthy cells to replace cells that were damaged by a stroke.