Granulocyte colony-stimulating factor and lineage-independent modulation of VLA-4 expression on circulating CD34+ cells

Although the use of allogeneic transplants of peripheral blood stem/progenitor cells (PBSCs) is increasing, the precise mechanism of PBSC mobilization has not yet been fully clarified. We examined the expression of some adhesion molecules on CD34+ cells from steady-state bone marrow (BM), granulocyte colony-stimulating factor (G-CSF)-mobilized PBSCs, and cytotoxic drugs plus G-CSF-mobilized PBSCs. Irrespective of mobilization method, very late antigen (VLA)-4 expression on circulating CD34+ cells was significantly lower than on steady-state BM CD34+ cells. To elucidate the influence of lineage commitment on VLA-4 expression of circulating CD34+ cells, we analyzed VLA-4 expression on different subsets of CD34+ cells with or without CD33, CD38, CD5, or CD10 antigens, or Glycophorin A in G-CSF-mobilized PBSCs and steady-state BM from related donors, using 3-color flow cytometry. VLA-4 on circulating CD34+ subsets was less expressed than on each corresponding subset of steady-state BM CD34+ cells. Furthermore, VLA-4 positive rates showed no significant difference among the CD34+ subsets. Finally, the data comparing CD34+ cells from steady-state and G-CSF-mobilized PBSCs revealed no differences in terms of VLA-4 expression. These data suggest that reduced expression of VLA-4 may be a result of peripheralization of CD34+ cells from bone marrow, which occurs in a G-CSF- and lineage-independent fashion.