The National Institutes of Health describes stem cells as “unspecialized cells capable of renewing themselves through cell division, which – under certain physiologic or experimental conditions – can be induced to become tissue- or organ-specific cells with special functions.”

Scientists currently work with three types of stem cells:

1. embryonic stem cells derived from embryos donated for research with the informed consent of the donor;

2. non-embryonic somatic (adult) stem cells, which the NIH defines as “a relatively rare undifferentiated cell found in many organs and differentiated tissues with a limited capacity for both self renewal (in the laboratory) and differentiation,” and

3. induced pluripotent stem cells (iPSCs), which are specialized adult cells that have been genetically reprogrammed to operate like a stem cell.