Cytokine expansion culture of cord blood CD34+ cells induces marked and sustained changes in adhesion receptor and CXCR4 expressions

Recent studies have demonstrated defective bone marrow homing of hematopoietic stem cells after cytokine expansion culture. Adhesion receptors (ARs) are essential to the homing process, and it is possible that cytokine culture modulates AR expression. We studied changes in expression of very late antigen-4 (VLA-4), VLA-5, L-selectin, leukocyte function-associated antigen-1 (LFA-1), CD44, and the stromal cell-derived factor-1 (SDF-1) receptor, CXCR4, during cytokine culture of cord blood (CB) CD34(+) cells. Expression of ARs was studied by flow cytometry on CB CD34(+) cells in whole blood, after purification and during culture for up to 10 days. Cells were cultured with stem cell factor (SCF), thrombopoietin (TPO), Flt3-ligand (Flt3), and G-CSF. Results showed that 80% or more of uncultured CD34(+) cells were positive for VLA-4, L-selectin, LFA-1, CD44, and CXCR4 while 50% were positive for VLA-5. Purification of CD34(+) cells did not affect AR expression, but cytokines increased expression three- to nine-fold throughout the 10-day culture period. In contrast, expression of CXCR4 decreased. Expression changes of ARs and CXCR4 on CD34(+)/CD38(-) cells mirrored those of the total CD34(+) population. The results indicate that cytokine culture significantly increases AR expression on CB CD34(+) cells, which may be related to the decrease in homing of cytokine-cultured hematopoietic stem cells.