Characterization of CD34+ subsets derived from bone marrow, umbilical cord blood and mobilized peripheral blood after stem cell factor and interleukin 3 stimulation

We characterized CD34(+) cells purified from bone marrow (BM), mobilized peripheral blood (PB) and cord blood (CB) and we tried to establish correlations between the cell cycle kinetics of the CD34(+)CD38(-) and CD34(+)CD38(+) subpopulations, their sensitivity to SCF and IL-3 and their expression of receptors for these two CSFs. At day 0, significantly fewer immature CD34(+)CD38(-) cells from CB and mobilized PB are in S + G2M phases of the cell cycle (respectively 2.0 +/- 0.4 and 0.9 +/- 0.3 %) than their BM counterpart (5.6 +/- 1.2%). A 48-h incubation with SCF + IL-3 allows a significant increase in the percentage of carding CD34(+)CD38(-) cells in CB (19.2 +/- 2.2%, P < 0.0002) and PB (14.1 +/- 5.5%, P<0.05) while the proliferative potential of BM CD34(+)CD38(-) progenitors remains constant (8.6 +/- 1.0%, NS). CD123 (IL-3 receptor) expression is similar in the three sources of hematopoietic cells at day 0 and after 48-h culture. CD117 (SCF receptor) expression, although very heterogeneous according to the subpopulations and the sources of progenitors evaluated, seems not to correlate with the difference of progenitor cell sensitivity to SCF nor with their proliferative capacity. Considering the importance of the c-kit/SCF complex in the adhesion of stem cells to the microenvironment, several observations are relevant. The density of CD117 antigen expression (expressed in terms of mean equivalent soluble fluorescence, MESF) is significantly lower on fresh PB cells than on their BM (P < 0.017) and CB (P < 0.004) counterparts, particularly in the immature CD34(+)CD38(-) population (560 +/- 131, 2121 +/- 416 and 1192 +/-129 MESF respectively); moreover, when PB and BM CD34(+)CD38(-) cells are stimulated for 48 h with SCF + IL-3, the CD117 expression decreases by 1.5- and 1.66-fold, respectively. This reduction could modify the functional capacities of ex vivo PB and BM manipulated immature progenitor cells.