Embryonic stem cells hold the blueprint of the entire human or animal.
Discovered in 1998, human embryonic stem cells (hESCs) are the most primitive type of stem cell and can replicate and generate every cell type of the human body.
Human embryonic stem cells are derived from human blastocysts (early stage embryos) that are five to seven days old. In Australia these blastocysts are donated for research with consent from patients who have completed treatment for infertility, and have surplus embryos (see
Fact Sheet 6 - Law and Ethics of Stem Cell Research) . At this stage of development the blastocyst is a hollow ball of about 150 cells and no bigger than a pinhead. The blastocyst comprises a large internal cavity and a small group of approximately 30 cells called the inner cell mass. The outer layer is called the trophectoderm. The inner cell mass is what ultimately becomes the embryo, and the trophectoderm becomes the placenta.
The inner cell mass cells are able to develop into any type of cell in our body and can contribute to all the cells and tissues of the adult organism. These types of cells are called pluripotent and it is this pluripotency that makes them of interest for research and therapy. Embryonic stem cells are isolated from the blastocyst when the inner cell mass is removed and cultured in the laboratory. During this process the blastocyst is destroyed.
Once the cells have been isolated they can be grown continuously in a laboratory culture dish that contains a nutrient-rich culture medium. As the stem cells divide and spread over the surface of the dish some are removed to populate fresh subcultures to form a stem cell line. Because these cells have the ability to keep dividing (self-renewing), large numbers of embryonic stem cells can be grown in the laboratory and also frozen for future use. Therefore, established hESC lines can be maintained in laboratories for research, shared between researchers and maybe ultimately used in cell-based therapies.
For more information see Fact Sheet 1.1 Derivation of Human Embryonic Stem Cells and Fact Sheet 2 - Types of Stem Cells.