Both CD34(+)38(+) and CD34(+)38(-) cells home specifically to the bone marrow of NOD/LtSZ scid/scid mice but show different kinetics in expansion

Human hemopoietic stem cells (HSC) have been shown to engraft, differentiat e, and proliferate in the hemopoietic tissues of sublethally irradiated NOD /LtSZ scid/scid (NOD/SCID) mice. We used this model to study homing, surviv al, and expansion of human HSC populations from different sources or phenot ype. We observed that CD34(+) cells homed specifically to bone marrow (BM) and spleen, but by 3 days after injection, survived only in the BM. These B M-homed CD34(+) cells proliferated intensively and gave rise to a 12-fold, 5.5-fold, and 4-fold expansion in 3 days for umbilical cord blood, adult mo bilized peripheral blood, and adult BM-derived cells, respectively. By inje ction of purified subpopulations, it was demonstrated that both CD34(+)38() and CD34(+)38(-) umbilical cord blood HSC homed to the BM and expanded. I mportantly, kinetics of expansion were different: CD34(+)38(+) cells starte d to increase in cell number from day 3 onwards, and by 4 wk after injectio n, virtually all CD34(+) cells had disappeared. In contrast, CD34(+)38(-) c ells remained quiescent during the first week and started to expand intensi vely from the third week on. In this paper, we have shown that homing, surv ival, and expansion of stem cells are three independent phenomena important in the early phase of BM engraftment and that kinetics of engraftment diff er between CD34(+)38(+) and CD34(+)38(-) cells.