CELL CYCLE-RELATED CHANGES IN REPOPULATING CAPACITY OF HUMAN MOBILIZED PERIPHERAL-BLOOD CD34(-DEFICIENT MICE() CELLS IN NONOBESE DIABETIC SEVERE COMBINED IMMUNE)

Most primitive hematopoietic progenitor cells reside in vivo within th e G(0)/G(1) phase of the cell cycle. By simultaneous DNA/RNA staining it is possible to distinguish G(0) and G(1) states and to isolate cell s in defined phases of the cell cycle. We report here the use of cell cycle fractionation to separate human mobilized peripheral blood (MPB) CD34(+) cells capable of repopulating the bone marrow (BM) of non-obe se diabetic/severe combined immune-deficient (NOD/SCID) mice. In fresh ly isolated MPB, repopulating cells were predominant within the G(0) p hase, because transplantation of CD34(+) cells residing in G(0) (G(0)C D34(+)) resulted on average in a 16.6- +/- 3.2-fold higher BM chimeris m than infusion of equal numbers of CD34(+) cells isolated in G(1). We then investigated the effect of ex vivo cell cycle progression, in th e absence of cell division, on engraftment capacity. Freshly isolated G(0)CD34(+) cells were activated by interleukin-3 (IL-3), stem cell fa ctor (SCF), and flt3-ligand (FL) for a 36-hour incubation period durin g which a fraction of cells progressed from G(0) into G(1) but did not complete a cell cycle. The repopulating capacity of stimulated cells was markedly diminished compared with that of unmanipulated G(0)CD34() cells. Cells that remained in G(0) during the 36-hour incubation per iod and those that traversed into G(1) were sorted and assayed separat ely in NOD/SCID recipients. The repopulating ability of cells remainin g in G(0) was insignificantly reduced compared with that of unstimulat ed G(0)CD34(+) cells. On the contrary, CD34(+) cells traversing from G (0) into G(1) were largely depleted of repopulating capacity. Similar results were obtained when G(0)CD34(+) cells were activated by the com bination of thrombopoietin-SCF-FL. These studies provide direct eviden ce of the quiescent nature of cells capable of repopulating the BM of NOD/SCID mice. Furthermore, these data also demonstrate that G(0)-G(1) progression in vitro is associated with a decrease in engraftment cap acity. (C) 1998 by The American Society of Hematology.