Derivation of Human Embryonic Stem Cells. Brief Outline
In order to obtain embryonic stem cells (ES cells) the embryo is destroyed in the blastocyst stage, approximately five days after cell nuclear transfer. The blastocyst consists of an outer cell layer known (trophoblast) that envelops the inner cell mass, from which the stem cells may be obtained. The trophoblast is destroyed either using laser technology or antibodies so as to make it possible to isolate the inner cell mass and transfer it to a culture dish. Once certain growth factors have been introduced these cells can divide any number of times without further differentiation.
Differentiation of the cells into different tissue types only occurs if specific growth factors are added to the culture medium. The benefit that it is hoped can be gained from a therapy using cloned cells is a high level of immunological compatibility due to the genetic identity between the transplanted cells and the recipient.
Aside from cloning techniques embryos (blastocysts) can also be created by in vitro fertilisation (IVF) or through parthenogenesis and subsequently be used for the derivation of embryonic stem cells. See also "In Focus" issue devoted to the research with human embryonic stem cells for a detailed presentation of the different ways of obtaining and using embryonic stem cells: In Focus "Research with Human Embryonic Stem Cells" Online Version.