What are human embryonic stem cells?
Six days after fertilisation, a human embryo consists of some hundred cells and is called a blastocyst. A blastocyst
consists of an outer layer of cells, that is called the trophectoderm, and a clump of cells in the middle that is called the inner cell mass. When the embryo develops further in the womb, the cells of the trophectoderm form the placenta while the cells of the inner cell mass will give rise to the actual foetus. In the lab, this inner cell mass can be separated from the trophectoderm and allowed to grow in a Petri dish. If the ICM grows, this will lead to an embryonic stem cell line.
Human embryonic stem cell lines are derived from embryos that are donated by patients undergoing in vitro fertilization and preimplantation genetic diagnosis (PGD), and only after informed consent from the donors. In our lab, we derive stem cells from embryos that are assumed to be genetically normal, e.g. embryos that are surplus to a regular in vitro fertilization cycle. Moreover, we are also interested in deriving stem cells from embryos that are found to be affected after PGD. The stem cell lines will then carry a genetic disease and could possibly represent important tools for research into these diseases.
Embryonic stem cells have two key characteristics that distinguish them from other celltypes. Firstly, these cells can
renew themselves indefinitely when they are kept in a primitive state very
similar to the cells of the early embryo (the undifferentiated state). Secondly, embryonic stem cells are pluripotent, which means that they have the unique ability to differentiate (specialize) into all tissues of an organism, e.g. muscle, brain tissue, lung cells...
Embryonic stem cells are regarded as one of the most promising advances in the field of regenerative medicine and cell and tissue therapy and are also believed to be an indispensable tool to study the early development of humans. Furthermore, differentiated stem cells could provide useful human cell models for basic research and for the testing of drugs or chemicals. In theory, this approach would both reduce the use of laboratory animals and provide better human research models.
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