EPO exposure impedes stromal-derived factor-1–induced migration of UCB CD34⁺cells. (A)The percentage of freshly enriched UCB CD34⁺ cell subsets CD34⁺CD38^– and CD34⁺CD38^– that migrated toward SDF-1 gradient after culture in erythropoietin at 100 and 200 ng/mL concentrations. (B) UCB CD34⁺CD38^– and CD34⁺CD38⁺ populations cell migration toward SDF-1 after incubation with neutralizing EPO (αEPO) and EPOR (αEPOR) antibodies and culture in erythropoietin at 200 ng/mL concentration. (C) The percentage of EPOR-depleted UCB CD34⁺ cells migrated toward SDF-1 in the presence of erythropoietin at 200 ng/mL concentration relative to control (nontransfected UCB CD34⁺ cells) normalized to 100%. Two separate UCB units were examined with 3 experimental replicates per cord. The data are presented as mean ± SEM. Single (*), double (**), and triple (***) asterisks indicate statistical significance when compared with untreated. Single (#) and double (##) hatchmarks indicate statistical significance when compared with isotype control.