Embryonic stem cells are derived from blastocysts — embryos that are about a week old. At this stage, the blastocyst has about 100 cells. Human blastocysts like this have been donated to research from in vitro fertilization clinics. In order to get embryonic stem cell lines, scientists remove cells from the inner cell mass region. These cells have the potential to develop into any type of cell in the body. Once the cells are removed, they are placed on a culture plate with nutrients and growth factors. The blastocyst is destroyed in this process. An embryonic cell line is established when these cells multiply and divide. Under the right conditions, these cell lines can be maintained indefinitely. By adding different growth factors, it is possible to induce these embryonic stem cells into developing into different cell types. These cells could someday be used in therapies to replace damaged cells and organs.