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4 thoughts on “Stem Cells versus Progenitors”

  1. I hate to see useful distinctions being eroded. I know that the funding has led to “every cell that divides being called a stem cell”, as Austin Smith once put it, but there really is a useful distinction to be made here.
    Of course no definition is accepted by everyone, but a reasonable majority consider stem cells to be cells that survive for the life of the organism which both reproduce themselves and generate differentiated progeny. Progenitor cells are those which turn into something else after a period of time short compared to the lifespan.
    This means that all cells of the early embryo are progenitors and not stem cells. Embryonic stem cells behave like stem cells in culture but their putative counterparts in the embryo are not stem cells because they soon turn into something else.
    In the haematopoietic system, where the development of stem cells has been carefully studied, they are known to arise about E10.5 in the mouse, based on the ability to reconstitute the bone marrow of a lethally irradiated host. So we have the apparent paradox that early embryo cells are not stem cells, but some of their offspring are. This is not really a paradox and it does illustrate nicely that we have two distinct entities here that deserve different names.
    Actually you can get funding for “progenitor cells” too. I am a member of a Consortium of the NHLBI devoted to “Heart, Blood and Lung Progenitor Cells”.

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  2. In hematopoietic system (the most well studies adult stem cell system) there is a clear distinction between stem and progenitor cells. It based not only on lifespan, which is important characteristic, but mostly on ability to self-renew. In mouse we can passage hematopoietic stem cell serially many generations (from mouse to mouse) during few years. Progenitors aren’t self-renew and characterized by very short lifespan.

    I think, it’s important to separate assay-based definitions of progenitors and stem cells, especially for biologists. Defining the difference is important also for physicians and cell product developers. Otherwise the public and business executives will call “stem cell” as any cell. This trend you can see now.

    Unfortunately “stem cell” is becoming a label, that you can use to get fund or capital for cell product development. If academic funding organizations still ok about both – progenitors or stem cell (I agree with Jonathan), investors and Wall Street want to hear only “stem cell”. That’s why any “cell therapy” currently accepted as an equivalent of “stem cell therapy”. Many people call hepatocyte or chondrocyte transplantation as “stem cell therapy”. Whatever works for money! Whatever sells. The label “stem cell” is current bestseller.

    I’d agree with Jonathan that there is a debate about definition of embryonic stem cell and progeny. What Jonathan was talking about was amazingly described here –
    http://www.nature.com/stemcells/2009/0906/090625/full/stemcells.2009.90.html

    I think, the right terminology and definition is not just matter of semantics, it’s matter of basic science.

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  3. I understand Jonathan’s point but I would side with Teisha – these definitions could really be “splitting hairs” or becoming increasingly redundant. For example, what definitions do we use when stem cell behaviour (lasting throughout life and generating progeny) is the result of the probabilistic behviour of a population of cells? In these cases it appears impossible to distinguish a priori which cells will be the stem cells and which the progenitors. Do we call them all stem cells? Indeed there may not be a distinction between these two types of cells, beyond the vagaries of probability, and one would argue that “stemness” and “progenitorness” are properties of the population and not individual cells.

    (See work by Ben Simons and others for more on this type of stem cell behaviour. Nice review in Cell Stem Cell. 2007 Oct 11;1(4):371-81.)

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