Differential expression of cell adhesion molecules by human hematopoietic progenitor cells from bone marrow and mobilized adult peripheral blood.

The mechanisms responsible for mobilization of hematopoietic progenitor cells (HPC) from the bone marrow into the circulation are unknown. One possibility is that HPC downregulate cell adhesion molecule expression. We studied normal human bone marrow and adult peripheral blood following 4 g/m2 cyclophosphamide and recombinant human granulocyte colony-stimulating factor (rHuG-CSF). Each sample was studied for the coexpression of CD34 and a panel of cell adhesion molecules by dual immunocytometry. Bone marrow HPC express the immunoglobulin gene superfamily members of ICAM-1 (CD54), PECAM-1 (CD31) and LFA-3 (CD58), the integrins VLA-4 (CD49d/CD29), VLA-5 (CD49e/CD29) and LFA-1 (CD11a/CD18), L-Selectin (CD62L), HCAM (CD44) and CD36. Mobilized peripheral blood HPC display less expression of LFA-3 (CD54) and VLA-5 (CD49e). Significant differences in cell adhesion molecule expression do exist between sessile and circulating HPC, but the biological relevance of these observations is currently unclear.