Migration of ZAP-70⁺ CLL cells toward CCL19 and CCL21, but not CXCL12, is increased when compared with ZAP-70^– CLL cells. PB CLL cells were assayed in the bare filter chemotaxis assay for migration in response to CCL19, CCL21 (1 μg/mL), or CXCL12 (100 ng/mL). CLL cell migration is expressed as a migration index as described in “Patients, materials, and methods” under “Chemotaxis assay.” The concentration of the chemokines were those that induced maximal migration.¹⁸  Input and transmigrated cells were stained with anti-CD19 and anti-CD5 antibodies to determine the percentages of input CLL B cells that migrated into the lower chambers. Results for each chemokine are the mean ± SEM of 5 independent experiments. Student 2-sample 2-tailed t test. N/S indicates not significant.