(A) RT-PCR analysis for CXCR4 mRNA in CLL samples from 12 different patients. The specific 1,058-bp PCR fragment is visible in 12 representative B-CLL samples (lanes 1 through 12). The arrow points to the 1,018-bp marker of the 1-Kb control DNA ladder shown in the lanes flanking the test samples. (B) Logarithmic fluorescence histograms depicting the expression of CXCR4 on mononuclear blood cells of a representative patient with CLL (left panel) and Nalm-6 (center) or Reh cells (right panel). The left panel depicts the logarithmic red fluorescence of electronically-gated CD3⁺ T cells (bold line) or the CD19⁺ CLL cells (shaded) stained with the anti-CXCR4–PE MoAb or with a PE-labeled isotype control antibody (thin lined histogram). The center and right histograms depict the Nalm-6 or Reh cells, respectively, stained with the anti-CXCR4–PE MoAb (shaded) or isotype control antibody (open histogram).