Stem cells are the primordial cells in the human body. The first stem cells occur inside a developing embryo (blastocytes). These stem cells are understood to be totipotent, meaning that they are capable of differentiating into every cell type. They divide, differentiate, and ultimately construct the entire human body.

Stem cell therapy involves the introduction of healthy new stem cells to, potentially, repair, and replace damaged or lost cells. This new technique is being applied to treat a wide range of human conditions, including many types of cancer, infectious diseases, and neurological disorders.