Response of Human CD34 + Cells to CXC,CC,and CX 3 C 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 endothelial cells (HUVECs) or bone marrow-derived endothelial cells (BMECs) were grown to confluence on 3-μm 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 chamber of the culture plates in serum-free conditions. After 24 h, the percentage of transmigrated cells was determined. A mean of 8.5% of unfractionated marrow CD34⁺ populations migrated, and all chemokines tested, with the exception of macrophage inflammatory protein-1α (MIP-1α), had some positive effect on this migration. The greatest effects were seen with stroma-derived factor-1α (SDF-1α) and stroma-derived factor-1β (SDF-1β), with lesser effects noted for other chemokines and cytokines. When the CD34⁺ population was subselected for expression of CD38, a greater fraction of the CD38^- cells migrated as compared to the CD38⁺ fraction. CD34⁺ cells isolated from mobilized peripheral blood and cord blood also migrated in response to chemokines. Chemokines of the CC, CXC, and CX₃C classes as well as other hematopoietic cytokines may modulate the process of stem cell transmigration of endothelial cells. Further understanding of this process may help elucidate the mechanism of stem cell mobilization and homing.