WHIM-mutant CXCR4 impairs T cell–B cell conjugate stability. (A) Primary CD4⁺ T cells from healthy WT donor or WHIM-patient peripheral blood formed conjugates for 15′ with superantigen (sAg)-pulsed, labeled primary B cells from a healthy allogenic donor. The conjugates were allowed to migrate toward CXCL12 in a transwell filter, allowing the migration of single cells only. The migrated T cells were analyzed by FACS and the number of T cells migrated for each condition is shown. *P < .05 (1-way analysis of variance [ANOVA] and Tukey’s posttest). Experiment performed twice, summary of results (mean ± SEM) shown. (B) Primary CD4⁺ T cells from healthy donor peripheral blood transfected with EGFP-CXCR4 (WT) or EGFP-CXCR4 (WHIM) formed conjugates for 15′ with sAg-pulsed primary B cells from the same donor. The conjugates were allowed to migrate toward CXCL12 in a transwell filter, allowing the migration of single cells only. Migrated EGFP⁺ T cells were analyzed as described in (A). **P < .01 (1-way ANOVA and Tukey’s posttest). The experiment was performed twice, and results (mean ± SEM) from representative experiments are shown.