Cell culture refers to the removal of cells from an animal or plant and their subsequent growth in a favorable artificial environment. The cells may be removed from the tissue directly and disaggregated by enzymatic or mechanical means before cultivation, or they may be derived from a cell line or cell strain that has already been established. Stem cells retain the capacity to self-renew as well as to produce progeny with a restricted mitotic potential and restricted range of distinct types of differentiated cell they give rise to.