Potential Clinical Applications of Embryonic Stem Cells

Embryonic stem cells (ESC) have been reported for different mammalian species (i.e. hamster, rat, mink, pig, and cow), but only murine ES cells have successfully transmitted their cell genome through the germline. Recently, interest in stem cell technology has intensified with the reporting of the isolation of primate and human ES cells. In developing this chapter, some conventions have to be established to describe consistently what stem cells are, what characteristics they have, and how they are used in biomedical research. Also, we intend to describe and distinguish the details of foetal and adult stem cells. In between lie important information describing what researchers have discovered about stem cells and a newly developed autologous ES cell–like stem cells, called induced pluripotent stem (iPS) cells. These reprogrammed stem cells (iPS) could be generated from any patient, thus removing both ethical and immunological issues at one time. A stem cell is a special kind of cell that has a unique capacity to renew itself and to give rise to specialized cell types. Although most cells of the body, such as heart or skin cells, are committed to conduct a specific function, a stem cell is uncommitted and remains uncommitted, until it receives a signal to develop into a specialized cell. Their proliferative capacity combined with the ability to become specialized makes stem cells unique. Stem cells can originate from embryonic, foetal, or adult tissue and are broadly categorized accordingly. Embryonic Stem Cells (ESCs) are commonly derived from the inner cell mass (ICM) of a blastocyst, an early (4–5 days) stage of the embryo. Embryonic germ cells (EGCs) are isolated from the gonadal ridge of a 5–10 week foetus. Adult stem cells differ from ESCs and EGCs in that they are found in tissues after birth, and to date, have been found to differentiate into a narrower range of cell types, primarily those phenotypes found in the originating tissue. An adult stem cell is thought to be an undifferentiated cell, found among differentiated cells in a tissue or organ that can renew itself and can differentiate to yield some or all of the major specialized cell types of the tissue or organ. The primary roles of adult stem cells in a living organism are to maintain and repair the tissue in which they are found, because they are able to self-renew and yield differentiated cell types. They are thought to reside in a specific area of each tissue (called a "stem cell niche"). Stem cells may remain quiescent (non-dividing) for long periods of time until they are activated