The differentiated state of somatic cells in an organism is remarkably stable. Cells do not normally change from one differentiation pathway to another. However, adult somatic cells can be experimentally reprogrammed into other cell types, including pluripotent stem cells. By this route, the new cells obtained are genetically equivalent to the cells of origin and, similar to embryonic stem (ES) cells, can be induced to differentiate into any specialised cell type. Nuclear reprogramming (see Glossary) has great potential in terms of its medical application and, for this reason, many efforts have been made to increase its efficiency and to understand the mechanisms by which it occurs. Reprogrammed cells from patients can be used to study diseases in ways not previously possible and to design novel drug screens. Furthermore, reprogrammed cells could also provide a source of patient-matched replacement cells.
