“ The adult stem cell, ” says the National Institutes of Health (NIH) in the United States, “is an undifferentiated (unspecialized) cell that is found in a differentiated (specialized) tissue, ” such as bone marrow, blood and blood vessels, the skin, the spinal cord, the liver, the gastrointestinal tract, and the pancreas.
USA Riikliku Tervishoiuinstituudi teatel on „täiskasvanud tüvirakk diferentseerumata (spetsialiseerumata) rakk, mida võib leida diferentseerunud koest ”, näiteks luuüdist, verest ja veresoontest, nahast, seljakeelikust, maksast, seedekulglast ning kõhunäärmest.