Stem cells are primitive undifferentiated cells that have the capability to form any of the 220 different types of cells in the human body. The embryonic stem cell is found in the embryo and develops into various cells that make a baby. This single cell is capable of forming or specializing to form any kind of cell. During embryonic development the first cell quickly divides to form three embryonic layers namely, the ectoderm, the mesoderm, and the endoderm.

Embryonic stem cell research and the method of cloning led to the development of the famous cloned sheep, Dolly. Cloning essentially involves the duplication of biological material. This is done through a technique called somatic cell nuclear transfer. This method can create a clone as well as be used for producing an embryo from which cells called embryonic stem (ES) cells could be extracted. The advantage of embryonic stem cells is that they can be used to cure several fatal genetic diseases.

Embryonic stem cells possess two major characteristics that make them especially suited for cell therapy. Firstly, being extracted from a very new organism, these cells are at an early stage of development and can be more flexibly used to culture several different kinds of cells. Stem cells that have such a flexibility of development are referred to as pluripotent cells. Also, embryonic stem cells have the ability to remain undifferentiated for long and can divide indefinitely. This makes them self-renewable and they can be used for longer. If transplanted into a patients body, embryonic stem cells are capable of replenishing cells that have been destroyed by ailments like sickle cell anemia, thalesemia, and some forms of cancer.