What are stem cells and where do they come from?

Stem cells can be isolated from many types of tissues and have the ability to self-renew, maturing into at least one type of specialized cell. Embryonic stem cells (ESCs) are pluripotent and under defined conditions, can replicate indefinitely. It is pluripotency that distinguishes ESCs from adult stem cells (multipotent) found–embryonic stem cells can generate all cell types in the body; adult stem cells can produce only a limited number of cell types. ESCs are useful tools for research and regenerative medicine given their ability to produce endless numbers for ongoing use. Adult stem cells can be isolated from any type of adult tissue. The ease of isolation of adult stem cells depends on the accessibility of the tissue, the prevalence of stem cells in the tissue, the person’s age, presence of markers that aid stem cell isolation and isolation/culture protocols. 

Induced pluripotent stem (iPS) cells are mature adult cells converted into a stem cells by introducing a mixture of transcription factors.