Cancer-specific cell-surface antigens are ideal targets for monoclonal antibody (mAb)-based immunotherapy but are likely to have previously been identified in transcriptome or proteome analyses. Here, we show that the active conformer of an integrin can serve as a specific therapeutic target for multiple myeloma (MM). We screened >10,000 anti-MM mAb clones and identified MMG49 as an MM-specific mAb specifically recognizing a subset of integrin β molecules. The MMG49 epitope, in the N-terminal region of the β chain, is predicted to be inaccessible in the resting integrin conformer but exposed in the active conformation. Elevated expression and constitutive activation of integrin β conferred high MMG49 reactivity on MM cells, whereas MMG49 binding was scarcely detectable in other cell types including normal integrin β lymphocytes. T cells transduced with MMG49-derived chimeric antigen receptor (CAR) exerted anti-MM effects without damaging normal hematopoietic cells. Thus, MMG49 CAR T cell therapy is promising for MM, and a receptor protein with a rare but physiologically relevant conformation can serve as a cancer immunotherapy target.

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BackgroundRecently, maintaining higher relative dose intensity (RDI) of chemotherapeutic drugs has become a widespread practice in an attempt to achieve better outcomes in the treatment of aggressive lymphoma. The addition of rituximab to chemotherapy regimens has significantly improved outcome in diffuse large B-cell lymphoma (DLBL). However, it is unknown if higher RDI in chemotherapy when combined with rituximab leads to a better outcome in aggressive B-cell lymphoma.MethodsWe retrospectively evaluated the impact of the RDI of initial chemotherapy (consisting of cyclophosphamide, doxorubicin, vincristine and prednisolone with rituximab (R-CHOP) on outcome in 100 newly diagnosed DLBL patients.ResultsA multivariate Cox regression model showed that RDI trended towards a significant association with mortality [hazard ratio per 0.1 of RDI = 0.8; 95% confidence interval 0.6–1.0; P = 0.08]. Additionally, on multivariate logistic analysis, advanced age was a significant factor for reduced RDI.ConclusionOur data suggest that in DLBL patients, mortality was affected by RDI of R-CHOP as the initial treatment, and the retention of a high RDI could therefore be crucial.

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Summary Monoclonal antibody (mAb) drugs are desirable for the improvement of multiple myeloma (MM) treatment. In this study, we found for the first time that CD48 was highly expressed on MM plasma cells. In 22 out of 24 MM patients, CD48 was expressed on more than 90% of MM plasma cells at significantly higher levels than it was on normal lymphocytes and monocytes. CD48 was only weakly expressed on some CD34+ haematopoietic stem/progenitor cells, and not expressed on erythrocytes or platelets. We next examined whether CD48 could serve as a target antigen for mAb therapy against MM. A newly generated in‐house anti‐CD48 mAb induced mild antibody‐dependent cell‐mediated cytotoxicity and marked complement‐dependent cytotoxicity against not only MM cell lines but also primary MM plasma cells in vitro. Administration of the anti‐CD48 mAb significantly inhibited tumour growth in severe combined immunodeficient mice inoculated subcutaneously with MM cells. Furthermore, anti‐CD48 mAb treatment inhibited growth of MM cells transplanted directly into murine bone marrow. Finally and importantly, we demonstrated that the anti‐CD48 mAb did not damage normal CD34+ haematopoietic stem/progenitor cells. These results suggest that the anti‐CD48 mAb has the potential to become an effective therapeutic mAb against MM.