CD37 is expressed in patients with MCL and MCL cell lines, and CD37-SMIP treatment is cytotoxic in MINO. (A) Representative medium-power (20× original magnification) view of normal tonsil control tissue showing CD37 expression by the B cells of a B-cell follicle and lack of expression in the interfollicular lymphocytes. The intensity of membranous and cytoplasmic staining is greater in the B cells found within the mantle zone compared with those in the germinal center. (B) Representative high-power (40×) and low-power (10×, inset) view of a 2-mm MCL core from a tissue microarray. Images were captured with an Olympus DP25 digital camera using DP2-BSW Version 1.3 software mounted on an Olympus BX41 microscope with 10×/0.30, 20×/0.40, and 40×/0.65 objectives. Images were resized without color or contrast manipulation in Adobe Photoshop CS2 Version 9.0.2. (C) CD37 expression assessed by AQUA of immunofluorescence in CD20⁺ B cells from cases of MCL and benign lymphoid tissue represented on a tissue microarray. Column indicates average from 28 tissue cores representing 14 cases of MCL and 14 tissue cores from 8 cases of benign lymphoid tissue (6 lymph node and 2 tonsil); bars, 1 SD 2-tailed, unpaired t test, P < .001. (D) Flow cytometric assessment of CD37 surface expression in 6 MCL cell lines with fluorescein isothiocyanate (FITC)–conjugated anti-CD37 antibody and IgG1 isotype control antibody. (E) Viability of MINO cells 72 hours after treatment with CD37-SMIP, rituximab, and trastuzumab in the presence of a cross-linking, Fc-specific, goat anti–human IgG. Viability was measured by Annexin V/propidium iodide staining and normalized to control. Data are representative of 3 separate experiments.