Characterization of mouse lymphohematopoietic stem cells lacking spleen colony-forming activity

Abstract

The classical definition of lymphohematopoietic stem cells (LHSC), the most primitive progenitors of all blood cells, requires that they have the capacity for self-renewal and for the long-term production of all blood cell lineages. However, other characteristics of LHSC have been debated. Our previous data suggested that mouse LHSC are very slowly proliferating cells that generate delayed multilineage engraftment, while “radioprotection” (rapid engraftment that will prevent early death from radiation-induced marrow aplasia) results from more committed progenitors. Alternatively, some groups have reported that mouse LHSC are responsible for both radioprotection and long-term repopulation of all blood cell lineages. A possible explanation for this difference is that cells with the capacity for long-term production of all blood cell lineages are biologically heterogeneous. We now show that 10 LHSC can generate all blood cell lineages for the lifetime of the animal. However, these cells lacked radioprotection and spleen colony-forming activity. LHSC were identified and isolated by their small size, their lack of expression of antigens characteristic of mature blood cell lineages, and their high expression of aldehyde dehydrogenase. In addition, these cells were found to express undetectable or low levels of many antigens presumed to mark LHSC, including Thy-1, Ly-6A/E (Sca-1), c-kit, and CD34. There appears to be at least two classes of LHSC with the capacity for long-term production of all blood cell lineages: one that generates both radioprotection and long-term engraftment and one that produces delayed but durable engraftment. Our data suggest that this latter class may represent a very primitive class of LHSC.

Very small embryonic-like stem cells (VSELs) represent a real challenge in stem cell biology: recent pros and cons in the midst of a lively debate

“…In addition to assays based on in vitro cultures, other isolation strategies have also been employed, for example, an interesting population of small cells (ELH stem cells) isolated from murine BM by elutriation (E), lineage depletion (L) and the ability to home (H) to BM has been described, which is able to differentiate into epithelial cells and HSCs. [80][81][82] Another group reported the presence of small cells (known as 'spore-like stem cells') in adult mammalian tissues that are able to differentiate into cells from all germ layers and have been isolated from adult mammalian tissues. 83 Moreover, several recent reports based on fluorescenceactivated cell sorting multiparameter sorting strategies were published that supported the existence of small, primitive VSELs and VSEL-like cells in adult tissues (the most important are listed in Table 1).…”

“…90 Similar small cells isolated by elutriation were reported in the past to give rise to LT-HSCs. 80 Thus, VSELs and VSEL-resembling cells have recently been purified in several laboratories worldwide, and we can expect that the coming years will bring more new information regarding their biology and in vitro and in vivo differentiation potential.…”

“…Give rise to long-term reconstituting hematopoietic stem cells (LT-HSCs) and epithelial cells. [80][81][82] Spore-like stem cells Small cells, B5 mm in diameter, isolated from various murine tissues, resistant to freeze/thawing, expressing Oct-4, and showing broad differentiation. Isolation procedure not revealed.…”

“Small stem cells” in adult tissues: Very small embryonic‐like stem cells stand up!

“…Lin -/ALDH high long-term repopulating HSCs-In the 1990s, Jones et al isolated a population of small long-term repopulating HSCs by employing elutriation followed by FACS based on the high activity of aldehyde dehydrogenase (ALDH high ) and a lack of hematopoietic lineage markers (69,70). The criteria for elutriation were optimized to obtained the fraction of the smallest lymphocytes and separate them from the more mature hematopoietic progenitors (69)(70)(71). Although the size of these cells was not published in the original publication, a recent paper from this group described that these SCs are smaller than 5 μm (72).…”

A Novel View of the Adult Stem Cell Compartment From the Perspective of a Quiescent Population of Very Small Embryonic-Like Stem Cells

“…It is widely accepted that SCs have a distinct morphology (i.e., small size and with a lymphocyte-like appearance), express a distinct panel of surface markers (i.e., CD133 + , CD34 + , CD44 + , Lin − ), show low accumulation of selected metabolic fluorochromes (e.g., Rhodamine 123, Pyronin Y, or Hoe3342), and display differences in activity of certain enzymes (e.g., aldehyde dehydrogenase [ALDH]). All of these traits are helpful in SC identification as well as in purification strategies [21][22][23][24][25] .…”