The NIH lists three types of stem cells: embryonic (derived from the inner cell mass of blastocysts), adult (derived from anything later, including aborted fetuses), and iPSCs. They differ in several ways:

  • Plasticity
    • Embryonic: pluripotent, since they can produce all cell types of an adult body, but not all cell types of a human embryo (i.e. cannot produce trophoblast, because they are taken from the inner cell mass).
    • Adult: multipotent, limited to the cell types of their tissue of origin. However, evidence suggests that adult stem cell plasticity may exist, increasing the number of cell types a given adult stem cell can become.
    • iPSCs: pluripotent.
  • Available quantity (large numbers of cells are needed for effective stem cell replacement therapies)
    • Embryonic: large numbers can be relatively easily grown in culture
    • Adult: rare in mature tissues; methods for expanding their numbers in cell culture have not yet been worked out.
    • iPSCs: supply is limited by transformable somatic cells (large limit).
  • HLA matching
    • Embryonic: identical if cloned, variable otherwise.
    • Adult: identical if the patient’s own cells are expanded in culture and  reintroduced into the patient.
    • iPSCs: identical if the patient’s own cells are reprogrammed.