Embryonic stem cells (ESCs) are pluripotent stem cells that give rise to all cell lineages. They are found in the blastocyst stage of the embryo and can differentiate into different fetal tissues. The cells can be maintained in culture in their pluripotent stage for a long time, and when introduced into an environment, they differentiate into a lineage depending on the external stimuli. This property of embryonic stem cells makes them viable [Page 372]for therapeutic and research purposes. Policies vary from one country to another with respect to isolating embryonic stem cells because of differing philosophical and religious beliefs about the embryo as life. In some countries, use of ESCs is considered unethical because it involves the destruction of an embryo. This section focuses mainly ...