CXCR4 pepducins enhance rituximab-mediated cytotoxicity in leukemic cells from patients with CLL. Leukemic cells isolated from 5 patients with CLL were treated overnight with vehicle (0.3% DMSO), PZ-218, PZ-210, or plerixafor (AMD) in the absence or presence of rituximab (20 μg/mL). Samples were stained with annexin V–FITC, and evaluated for apoptotic cells by flow cytometry. Data represent means ± SEM (n = 5). *P < .05 compared with rituximab-treated controls.