Effects of mouse anti-HM1.24 MoAb and human IgG on ADCC activity mediated by humanized anti-HM1.24 MoAb.⁵¹Cr-labeled RPMI 8226 cells were incubated with PBMCs from healthy donors (E/T ratio, 50) and humanized anti-HM1.24 MoAb (1 μg/mL) in the presence of mouse anti-HM1.24 MoAb (□), heat-aggregated human IgG (•), or monomeric human IgG (○). Effector cells were preincubated for 15 minutes at room temperature with monomeric or heat-aggregated IgG. Data represent the mean ± SD of triplicates. *P < .05 or †P < .005, compared with the data in the absence of mouse anti-HM1.24 MoAb or human IgG preparations.