Treatment with IL1RAP antibody shows strong in vivo therapeutic effects in the BV173 xenograft model. (A) Cell surface expression of IL1RAP on BV173 cells (black, isotype control; red, IL1RAP). (B-F) NOD/SCID mice were engrafted with BV173 cells and treated biweekly with 500 μg IL1RAP antibody mAb81.2 or a mIgG2a control antibody (n = 10 per group). Treatment started 3 days after transplantation and was continued for a total of 13 doses. Overall survival with mAb81.2 treatment compared with isotype control (median 51 days vs 37 days); treatment days are indicated with blue arrowheads (B). Hematoxylin and eosin–stained BM sections from representative isotype control and mAb81.2-treated mice (bar represents 200 μm; C). Level of leukemic cells in the BM (D) and spleen (E). Spleen weights (F). (G-H) BV173 cells were cultured in the presence of IL1RAP antibodies or isotype control antibodies and analyzed after 48 hours. Total cell number (n = 3; G) and proportions of viable, apoptotic, and dead cells (n = 4; H). Staurosporine (STP) was used as positive control for inducing apoptosis. (I) BV173 cells were used as target cells in an ADCC assay with IL1RAP antibodies or a hIgG1 control antibody using human NK effector cells. Presented is the percentage of BV173 cells killed by ADCC. One representative experiment out of 3 is displayed. (J) BV173 cells were used as target cells in an ADCP assay with IL1RAP antibodies or a hIgG1 control antibody using human macrophages as effector cells. The ADCP effect is presented as the percentages of macrophages with phagocytosed BV173 cells normalized to the isotype control (n = 4).