Impaired desensitization of truncated CXCR4^m receptors. (A) CXCL12-triggered actin polymerization in CD8⁺-gated (left panels) and CD4⁺-gated (right panels) T cells from WHIM¹⁰¹³ patients P1 (top row, •) and P2 (bottom row, •) or from healthy donors (□). (B) Kinetics of CXCL12-triggered actin polymerization in A0.01 T cells (left panel) or in CD4⁺-gated T lymphocytes (right panel) nontransduced (NT) or transduced with the indicated CXCR4 variants (▵, CXCR4^wt; ▦, CXCR4¹⁰⁰⁰; •, CXCR4¹⁰¹³; □, NT). (A-B) Data are representative of 3 independent experiments. (C) GTPγS binding assays to membranes from HEK-293T cells expressing at similar levels CXCR4^wt (left panel, ○; right panel, □), CXCR4¹⁰⁰⁰ (left panel, ; right panel, ▦), or CXCR4¹⁰¹³ (▪) (geometric MFI for the aforementioned receptors were 11.2, 12.3, and 10.5, respectively). Membranes were treated with the indicated concentrations of CXCL12 (left panel) or left untreated (right panel). Data are mean ± SEM of triplicate determinations. Deduced EC₅₀ values of the experiment of 3 independent determinations were 17 nM for CXCR4^wt, 7 nM for CXCR4¹⁰⁰⁰, and 9 nM for CXCR4¹⁰¹³.