Are All Stem Cells the Same: Pluripotent or Totipotent?

Not only do stem cells come from different sources, but they differ according to their malleability. Stem cells at different developmental stages appear to have different capacities for self-renewal and differentiation. There is some question about whether hES cells are totipotent (able to become any type of tissue in the body) or whether they are pluripotent (able to become some, but not all of the tissue types in the body). It appears that human hES cells can become any of the 200  differentiated cell types in the body, thereby making them totipotent. Some tissue-specific, differentiated stem cells retain pluripotent capacity to generate cells of a more limited number of cell lineages, which some estimate is between six and 10 different types.


The issue of the malleability and potency of different stem cells remains open and controversial. There is a continuing debate over the properties possessed by adult human and hES cells. Many who oppose using human blastocysts to extract hES cells maintain that adult stem cells have the same properties and capabilities for differentiation; however, many researchers maintain that hES cells are the most malleable. Research into adult stem cells continues to evaluate their ability to differentiate. Other researchers assert that we lack evidence to support or refute the claim of equivalent malleability between adult and hES cells, and until such equivalency can be proven, hES research must continue as hES cells appear to be the stronger research tool. Another difference between specialized (adult) stem cells and hES cells is their behaviour  in culture. It is easier to get hES cells to replicate in culture and to keep those cells alive for a very long time, an attribute that is very useful in creating cell lines to study diseases or cell functioning. In contrast, adult stem cells are harder to culture and keep alive. Regardless of their differences, both avenues of research will likely yield valuable and different information for development of clinical therapies.