What are adult stem cells? Adult stem cells come from an existing, specific tissue or cell. They are not pluripotent, but are already developed into a particular category of cell, such as blood cell. The term "adult" doesn't mean they come from human adults; they can be found in babies and adults in specific tissue in the body. Adult stem cells maintain and repair the tissue in which they are found, including the brain, bone marrow, blood, muscle, skin, and liver.