Embryonic stem cells have not yet differentiated into specific cell types such as nerve cells, muscle cells, bone cells, blood cells, etc. They are "pluripotent" meaning that they have the potential to develop into many different types of body cells. Because of this they can be harvested from a blastocyst that as previously stated results in its destruction and coaxed into developing into specific types of cells. Stem cells occur in humans and in embryos but only embryonic stem cells are pluripotent. Adult stem cells can produce only a certain sort of cell, for example blood cells in adults can produce only new blood cells, spermatogonia can give rise only to sperm cells. Because Embryonic Stem Cells are pluripotent however they can be used in the treatment of disease. Scientists believe that they can be used to treat a wide range of diseases, including Alzheimer's Parkinson's, cancer, and diabetes. John Gearhart of John's Hopkins University and James Thomson of the University of Wisconsin were the first to create immortalized embryonic stem cell lines. By the term "immortalized" is intended the ability of an Embryonic Stem Cell to multiply indefinitely while still retaining its pluropotence. So we can now create from a single embryo a line of stem cells that will continue to multiply indefinitely and from which scientists can create body cells of many different types.
