Human embryonic stem cells (HESCs) are derived from the inner cell mass of the early embryo; the cells are genetically normal and retain in vitro both the ability to self renew and also to differentiate into each of the cell types found in the adult body. Such a system offers an in vitro model of human embryogenesis. Thus, a powerful resource now exists for the investigation of human developmental biology, the testing of candidate drugs for toxicology and efficacy and ultimately, tissue engineering for regenerative medicine.
The sensitivity of HESCs to biologically active factors and their developmental plasticity are attributes that confer upon them such great potential, but also present significant obstacles to their exploitation.