(A) CLL B cells that migrated into the stromal cell layer have lower CXCR4- and higher CD49d (VLA-4)-surface expression than input CLL B cells. CLL cells from 3 representative patients that migrated into the MSC layer were stained with anti-CD19 and anti-CXCR4 or anti-CD49d MoAbs. An aliquot of the input CLL cells before addition to the assay was stained for comparison. The bold lines represent the staining for the specific MoAb, while the thin lines show the isotype control staining of the respective sample. The numbers indicate the mean fluorescence intensity for CXCR4 or CD49d, respectively. (B) Pseudoemperipolesis of CLL cells was significantly inhibited by anti-CXCR4 MoAb, pretreatment with 200 ng/mL SDF-1, and pertussis toxin, while preincubation with an isotype-matched MoAb to an irrelevant antigen had no inhibitory effect. The bars represent the number of CLL B cells that had migrated into the stromal cell layer after 2 hours (1 × 10⁷ input cells), relative to the nontreated controls (100%) and are the means (±SD) of 6 different CLL patients tested in 3 independent experiments. The stars indicate significant differences with P < .05, using Bonferroni’st-test.