Blocking of transendothelial migration. CD34⁺ cells were either preincubated with the respective blocking MoAb, an isotype matched IgG1, or PBS/BSA 1% alone (control without antibody), and added to the upper chamber of the transmigration system. The number of transmigrated cells was measured after 24 hours. Transmigration was expressed as percent of the control without antibody pretreatment, *P < .05.