'''Adult stem cells''' are pluripotent, semi-differentiated, [[cell]]s that exist in all tissues. "Adult stem cell", however, is not the preferred term used in the field to refer to them—developmental biologists will usually refer to them as a specific cell type (usually referencing genes they express) or as a tissue-specific stem cell. They function to maintain tissue homeostasis by dividing to replace damaged or senescent somatic cells. The two most well-studied examples of adult stem cells are the hematopoietic stem cells, which give rise to blood cells, and the intestinal crypt stem cells, which give rise to the intestinal epithelium.<ref>http://9e.devbio.com/</ref> '''''The use of adult stem cells is opposed by many supporters of [[abortion]], who want to limit stem cell use to harmful [[embryonic stem cells]]'''''.
As pluripotent cells, most adult stem cell types can generate cells of several different types. However, because they are already epigenetically programmed to favor a particular fate, they generally cannot generate cell types outside of their lineage without genetic manipulation.