The information accrued to date regarding embryonic development and stem cells have been accumulated from basic research on mouse embryonic stem cells. Since 1998, researchers have succeeded in culturing human embryonic stem cells under laboratory conditions. Human embryonic stem cell lines have been established from the inner cell mass of human blastocysts that were produced through in vitro fertilization procedures. The techniques for growing human embryonic stem cells as described earlier, are similar to those used for culture of mouse embryonic stem cells. However, human embryonic stem cells must be grown on a mouse embryonic fibroblast feeder layer or in media conditioned by mouse embryonic fibroblasts. Human embryonic stem cell lines can be maintained in culture to generate indefinite numbers of identical stem cells for research. As with mouse embryonic stem cells, culture conditions have been designed to direct differentiation into specific cell types (for example, neural and hematopoietic cells). The applications of stem cell is therapeutic agents are widespread.
