(B) The levels of IFN- produced in the RTCA assay were quantitated by ELISA; * 0.0001 for all 3 clones versus mock and non-transduced T HOI-07 cells. vivo. These data indicate that novel CAR-T cells utilizing the BCMA 4C8A scFv are effective against multiple myeloma and warrant future clinical development. 0.0001 for BCMA protein versus BCMA and control. (C) Dose-dependent binding of 4C8A mAb to BCMA protein. Dilutions of BCMA mAb 4C8A were incubated in ELISA plates coated with BCMA protein or CD363 unfavorable control protein. * 0.0001 for BCMA protein versus control. (D) BCMA binding to BCMA protein in 293 cells by immunofluorescent staining (IF). BCMA mAb 4C8A was incubated with HEK293 cells, HEK293 cells expressing BCMA, or HEK293 cells expressing unfavorable control protein, CD18. Binding of BCMA mAb 4C8A was detected with Alexa Fluor 488-conjugated anti-mouse IgG. (E) Binding of BCMA monoclonal antibody to BCMA in multiple myeloma cells. BCMA mAb 4C8A, BCMA mAb 19F2 and a mouse IgG1 isotype control mAb were incubated with myeloma lines RPMI8226, H929, and MM1S, as well as Burkitts lymphoma line Raji and the BCMA-negative cell line K562. Binding of the antibodies to HOI-07 the cells was detected by flow cytometry with PE-conjugated anti-mouse IgG. (F) Quantification of binding shown in Physique 1E. To quantitate the binding in panel E, the mean fluorescence intensity (MFI) of each BCMA mAb was divided by the MFI of the isotype control mAb. * 0.05 for BCMA mAb 4C8A versus BCMA mAb 19F2 (MM1S and VEGFA Raji only). (G) BCMA mAb 4C8A binds BCMA in CHO-BCMA cells. BCMA mAb 4C8A, BCMA mAb 19F2, and a mouse IgG1 isotype control mAb were incubated with CHO (Chinese Hamster Ovary) cells stably expressing human BCMA, and binding of the antibodies was detected by flow cytometry with PE-conjugated anti-mouse IgG. 2.2. BCMA Monoclonal 4C8A Antibody Specifically Recognizes BCMA in Multiple Myeloma To detect BCMA monoclonal antibody HOI-07 binding to BCMA in multiple myeloma cells, we performed FACS analysis on several multiple myeloma cell lines: RPMI8226, H929, and MM1S with BCMA antibody 4C8A and also on unfavorable control BCMA-negative K562 cell lines. By flow cytometry, clone 4C8A bound to multiple myeloma lines, as well as Burkitts B-lymphoma Raji cells, but not to BCMA-negative K562 control cells (Physique 1E). Binding was generally greater for clone 4C8A than a commercially-available BCMA mAb, clone 19F2 (Physique 1F). Both mAbs exhibited comparable binding to CHO cells expressing human BCMA protein (Physique 1G) demonstrating high specificity of both antibodies to BCMA. To detect specificity of BCMA in human tissues, the IHC (Immunohistochemistry staining) was performed on several normal tissues. By IHC, clone 4C8A bound to RPMI8226 cells and normal human liver, but not to any other normal human tissues (Physique 2), confirming the specificity of BCMA expression. In addition, we detected positive BCMA staining in primary bone marrow myeloma tissue sample but not in negative control adrenal gland tissue sample (Figure S1) that additionally supports high specificity of BCMA monoclonal antibody to multiple myeloma cells. Open in a separate window Figure 2 Immunohistochemical staining of normal human tissues by BCMA 4C8A mAb. (A) BCMA 4C8A but not the isotype control mAb stained (brown color) RPMI8226 myeloma cells and normal human liver. (B) BCMA 4C8A did not stain any other normal human tissues. Blue color: nucleus counterstain. Original magnification 400. 2.3. CAR-T Cells Generated with BCMA 4C8A Antibody ScFv Recognize BCMA Protein The sequences of clone 4C8As heavy and light chain variable regions were determined and.