CSL362 mediates specific, dose-dependent NK cell–induced cell lysis of CD123-positive leukemia cell lines and of CD34⁺ CML patient cells. (A) CD123-overexpressing TF-1 erythroleukemia cells (CD123/TF-1) and MOLM-1, a BC-CML cell line, were incubated for 4 hours with healthy donor NK cells at an E:T of 10:1 in the presence of increasing concentrations (as indicated) of CSL362 or CSL360 (negative control because it lacks ADCC activity). The percentage of antibody-dependent target cell lysis measured in at least 3 independent LDH assays is shown. (B) Percent lysis of individual CP- and BC-CML patients’ CD34⁺ cells during CSL362-induced ADCC was determined as described for panel A, and the number of remaining committed CP-CML (C) and BC-CML (D) progenitors was assessed by CFU assay. (E-F) CSL362-mediated ADCC selectively depletes CD123-expressing CML CD34⁺ and CD34⁺/CD38^– cells. CD34⁺ cells of CP- and BC-CML patients subjected to CSL362-mediated ADCC as in panel A were analyzed by flow cytometry using antibodies against CD34, CD38, and CD123 (binding to a distinct epitope to CSL362). (E) Representative density and dot plots of CP-CML CD34⁺ cells are shown. (F) Quantitative analysis of the respective CD123-expressing populations. *P < .05; ***P < .001 (indicate significant differences by unpaired Student t test between control and CSL362-treated conditions).