Embryonic stem cells (ESCs) are recognized by the general public mainly as a possible source of cellular replacement therapy and transplantation. However, the usefulness of ESCs and ESC-derived tissue cell types for cell-based in vitro test systems in drug screening and toxicity was already recognized early after the discovery of ESCs in the late 1980s.
In the present chapter, the employment of ESCs in cell-based test systems is described in the light of state-of-the-art methods in the field of drug discovery, and the advantages and disadvantages of the applications are discussed. The possible use of ESCs in the drug development process is illustrated by three examples: (1) the use of ESCs for basic research in early developmental biology, (2) the embryonic stem cell test for embryotoxicity, and (3) the use of ESC-derived cardiomyocytes for detection of cardiac toxicity. Potential applications of human ESCs, induced pluripotent stem cells (IPS cells), and personalized medicine are described in the last part.