Response of human CD34(+) cells to CXC, CC, and CX3C chemokines: Implications for cell migration and activation

Ultrastructural studies of marrow and examination of the in vivo processes of stem cell homing and mobilization show that multipotential hematopoietic progenitors are able to traverse endothelial cells. The regulation of this process by various classes of chemokines was studied in this report, using an in vitro model of transendothelial migration. Human umbilical vein endo thelial cells (HU-VECs) or bone marrow-derived endothelial cells (BMECs) we re grown to confluence on 3-mum microporous membrane inserts and placed in 24-well culture plates. CD34(+) cells isolated from normal volunteer donor marrow by immunoadsorption or magnetic bead selection techniques were added to the inserts and various individual chemokines were added to the lower c hamber of the culture plates in serum-free conditions. After 24 h, the perc entage of transmigrated cells was determined. A mean of 8.5% of unfractiona ted marrow CD34(+) populations migrated, and all chemokines tested, with th e exception of macrophage inflammatory protein-1 alpha (MIP-1 alpha), had s ome positive effect on this migration. The greatest effects were seen with stroma-derived factor-1 alpha (SDF-1 alpha) and stroma-derived factor-1 bet a (SDF-1 beta), with lesser effects noted for other chemokines and cytokine s. When the CD34(+) population was subselected for expression of CD38, a gr eater fraction of the CD38(-) cells migrated as compared to the CD38(+) fra ction. CD34(+) cells isolated from mobilized peripheral blood and cord bloo d also migrated in response to chemokines. Chemokines of the CC, CXC, and C X3C classes as well as other hematopoietic cytokines may modulate the proce ss of stem cell transmigration of endothelial cells. Further understanding of this process may help elucidate the mechanism of stem cell mobilization and homing.