In the process of homing, CD34+ hematopoietic progenitor cells migrate across the bone marrow endothelium in response to stromal cell-derived factor (SDF)-1. To develop more efficient stem cell transplantation procedures, it is important to define the adhesion molecules involved in the homing process. Here, we identified the adhesion molecules that control the migration of primary human CD34+ cells across human bone marrow endothelial cells.
Migration of CD34+ cells is enhanced across interleukin 1β prestimulated bone marrow endothelium, suggesting an important role for the endothelium in adhesion and formation of the chemotactic gradient. Under these conditions, 30-100 ng/ml SDF-1 induced a rapid and efficient migration of CD34+ cells (± 46% migration in 4 h). In contrast, 600-1,000 ng/ml SDF-1 were required for optimal migration across fibronectin-coated filters. Subsequent studies revealed that transendothelial migration of CD34+ cells is mediated by β1- and β2-integrins and PECAM-1 (CD31) but not by CD34 or E-selectin. Whereas these antibodies individually blocked migration for 25%-35%, migration was reduced by 68% when the antibodies were combined. Thus, these adhesion molecules play specific and independent roles in the transmigration process. Finally, O-glycosylated proteins appeared to play a role, since SDF-1-induced migration of CD34+ cells (treated with a glycoprotease from Pasteurella haemolytica) across endothelial cells was clearly inhibited.
In conclusion, we show that efficient SDF-1-induced migration of primary human CD34+ cells across bone marrow endothelium is mediated by β1-integrins, β2-integrins, CD31 and O-glycosylated proteins.