Interference with CD44 reduces SDF-1–induced migration of human HPCs. Enriched MPB and CB CD34⁺ cells were either untreated (ctrl) or preincubated with antihuman CD44 mAbs (clones BU52 and F10-44-2, as indicated) or mouse isotype control. SDF-1 was added to the lower well in RPMI. Cells were allowed to migrate for 4 hours at 37°C. The average of migration index (percentage of control) in triplicate transwells from at least 3 independent experiments ± SD (^*P < .05) is shown (A). Enriched CB and MPB CD34⁺ cell surface expression of CD44 was analyzed by flow cytometry (B) using mouse antihuman CD44 mAb followed by secondary PE-conjugated donkey antimouse Ab labeling (open area). Cells stained with the secondary antibody alone (gray area) served as control.