Novel anti-ROR1 antibody clone huXBR1-402 binds specifically to human ROR1 overexpressed on leukemic B cells. (A) Antibody competitive binding assay showing results from ROR1⁺ Mino, JeKo-1 cells, and ROR1^– MEC1 cells. Cells were preincubated with either huXBR1-402, 2A2, trastuzumab (negative), or a no-block control indicated immediately below the x-axis. Cells are then probed with fluorescence-conjugated ROR1 antibodies (2A2-PE, monoclonal ROR1 antibody; ROR1-PE, polyclonal ROR1 antibody) indicated below the x-axis legends. n = 3 independent experiments. (B) huXBR1-402 primary antibody-stained CLL patient–derived PBMCs detected with AF647 conjugated secondary antibody against human Fc region. Staining is shown for CD19⁺/CD5⁺ CLL B cells and matched CD3⁺ T cells. n = 14 patients with CLL, n = 8 matched T-cell samples. (C) Quantification of surface ROR1 expression in primary CLL PBMCs. Quantification is shown for CLL B cells and matched T cells. n = 14 patients with CLL, n = 8 matched T-cell samples. (D) ROR1 staining expression in B cells from CLL and healthy donor PBMCs normalized to matched T cells. n = 8 patients with CLL, n = 7 normal donors. Data were analyzed by flow cytometry, and statistical significance was analyzed via Student t tests. MFI, mean fluorescence intensity. Error bars indicate ± SE.