IMGN529 has specific cytotoxicity against CD37⁺ lymphoma cell lines. (A) In vitro cytotoxicity measured by WST-8 assay after 5-day exposure to rituximab (⋄), K7153A antibody (●), IMGN529 (■), or nonbinding huIgG-SMCC-DM1 control conjugate (□). (B) CD37 expression by quantitative flow cytometry expressed as mean ABC values and standard deviation from several independent experiments. (C) EC₅₀ of IMGN529 cytotoxicity plotted against CD37 mean ABC values for the various cell lines listed in panel B. Pearson correlation calculations were performed with 2-tailed P values, and correlation was significant (R² = 0.18; P = .044).