There are two main categories of stem cells: pluripotent stem cells (PSCs) and adult stem cells. Pluripotent stem cells have the ability to differentiate into all of the cells of the adult body. In contrast, adult stem cells are found in a tissue or organ and can differentiate to yield the specialized cell types of that tissue or organ. Two types of embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) have been widely explored for clinical use recently. Human ESCs (hESCs) were first reported by James Thomson’s group in 1998, seventeen years after the generation of mouse ESCs. This prolonged time lag between the creation of mouse and human ESCs was due to substantial differences in morphology and culture conditions, as described later. hESCs have been explored in cell therapies for various diseases and injuries, such as spinal cord injury, age-related macular degeneration, and type 1 diabetes.
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