GM-CSF-mobilized peripheral blood CD34⁺ cells differ from steady-state bone marrow CD34⁺ cells in adhesion molecule expression

To determine the effect of growth factor mobilization on the expression of adhesion molecules, we compared CD34⁺ progenitor cell (PC) populations from steady-state bone marrow (BM) with granulocyte-macrophage colony-stimulating factor (GM-CSF)-mobilized apheresis products (peripheral blood stem cell (PSC)) using flow cytometry. To increase the accuracy of this analysis, CD34⁺ cells were enriched (MiniMACS) before cytometric analysis. A significantly lower expression of very late antigen-4 (VLA-4), leukocyte function antigen-1 (LFA-1) and LFA-3 were observed on PSC compared to BM CD34⁺ cells. In addition, significantly lower mean fluorescence intensity (MFI) of VLA-4, VLA-5, intercellular adhesion molecule-1 (ICAM-1), and sialyl Lewis(x) were observed on PSC as compared to BM CD34⁺ cells. Significantly higher levels of L-selectin and CD44 expression were observed on PSC as compared to BM CD34⁺ cells based on frequency and MFI (P ≤ 0.05). In addition, the duration of GM-CSF administration or number of prior aphereses had no effect on adhesion molecule expression. These data suggest that decreased expression of adhesion molecules including VLA-4, LFA-1, ICAM-1 and LFA-3 play a role in PC mobilization. Based on these studies, we suggest that PC mobilization occurs as a stochastic process and is associated with the selection of CD34⁺ cells with low adhesion molecule expression.