Embryonic Stem Cells

ES cell lines cultures (Embryonic stem cell lines) are derived from the inner cell mass (ICM) of an earlier morula stage embryos or blastocyst. An embryo at an early stage of approximately 4 to 5 days old consisting of 50 - 150 cells in humans is known as a blastocyst. In fact embryonic stem cells are termed as pluripotent since they give rise to the development to all derivatives of the three primary germ layers: ectoderm, endoderm and mesoderm.

In other way of speaking, simply each of them can develop into more than 200 cell types of the adult body if a sufficient and necessary stimulation is given for a specific cell type.
   

They are pluripotent cells, which need specific signals for precise and proper differentiation and injecting these ES cells directly to the body is difficult. Moreover just because of their combined ability of unlimited growth and pluripotency, E S cells have remained a theoretically potential source for regeneration and tissue replacement after an injury or a disease. However they do not contribute to the extra-embryonic membranes or the placenta.