​By definition, stem cells are cells that can produce other cells and tissue as well as renew themselves. Stem cells grown in laboratories allow us to study the development of disease using a patient's own cells. Using external factors, skin cells derived from patients can be transformed into stem cells, called induced pluripotent stem cells (iPSC), which we can afterwards re-differentiate into different specific tissues, such as nerve cells, liver cells, heart cells etc. This makes it possible for us to study disease mechanisms and test treatments without involving the patient directly, and it may be possible to repair damaged cells which can further be used to treat patients.