Low CXCR4 membrane expression on CD34+ cells characterizes cells mobilized to blood

In this work, association between the presence and membrane density of CXCR4 and the effectiveness of mobilization was studied. Ninety G-CSF mobilized PBPC and 28 native BM (nBM) preparations obtained from healthy individuals for transplantation and BM obtained after G-CSF mobilized PBPC collection in 10 donors were investigated. Positivity for CD34, HLA-DR and CXCR4 were analysed in the three colour fluorescence. The cellular pro. le of PBPC differed from nBM preparations with respect to lower: (i) proportion of CD34+ cells (0.64% +/- 0.04 vs 0.92 +/- 0.07) and CD34+ CXCR4+ cells (0.30% +/- 0.02 vs 0.61 +/- 0.07); (ii) contribution of CXCR4+ cells to CD34+ cells (52.2% +/- 2.5 vs 62.2% +/- 4.2); (iii) CXCR4 epitope density in CD34+ cells (48.9 +/- 5.5 vs 94.7 +/- 10.4). PBPC yield for CD34+ cells was correlated with the content of CD34+ cells lacking CXCR4 in the leukapheresis product (R = 0.38). In contrast, nBM harvested for transplantation was poor in CD34+ cells if these cells were frequently CXCR4 (R = -0.49). The present study shows that CD34+ cells mobilized to blood were characterized with a low proportion of CXCR4 and this associated with CD34+ cell content in PBPC.