Session: 651. Multiple Myeloma and Plasma Cell Dyscrasias: Basic and Translational: Poster I
Hematology Disease Topics & Pathways:
Fundamental Science, Plasma Cell Disorders, Diseases, Therapies, Lymphoid Malignancies
[Methods] We designed B-BiTE encoding a single chain fragment variable (scFv) specific for a human IgG-Fc domain and an scFv specific for the CD3ε. B-BiTE and a mAb were mixed at the molar ratio of 1:1 and incubated to generate a mAb/B-BiTE complex prior to administration. An antigen-specific cytokine production by human peripheral blood T cells and NK cells against target cells in the presence or absence of a mAb/B-BiTE complex was analyzed using flow cytometry. Their cytotoxicity against target cells was assessed by 51Cr-release assays. For in vivo experiments, five-week-old NOG mice were irradiated, and subcutaneously or intravenously inoculated with MM1S myeloma cells. After engraftment, fresh and non-stimulated human peripheral blood mononuclear cells were intravenously injected into each mouse. The next day, a mAb alone or a mAb/B-BiTE complex was administered, and tumor sizes of each group were measured to examine anti-tumor efficacy of B-BiTE in vivo.
[Results] Using the CD20-specific mAb, Rituximab as a model, we demonstrated that Rituximab/B-BiTE successfully bound to both CD20+ tumor cells and human T cells simultaneously, and activated human T cells while maintaining antitumor NK-cell activity in vitro. Importantly, B-BiTE did not interfere with NK-cell reactivity induced by an Fc domain of a mAb, which was confirmed by using a much higher molecular concentration of B-BiTE than that of a mAb. In addition, B-BiTE alone or serum immunoglobulin armed with B-BiTE appeared to induce neither T-cell nor NK-cell reactivity to normal cells. Based on these findings, we applied B-BiTE to the CD38-specific mAb, Daratumumab (Dar) and the SLAMF7-specific mAb, Elotuzumab (Elo) to target myeloma cells. In the presence of Dar/B-BiTE and Elo/B-BiTE, human NK cells in addition to human CD8+ T cells and CD4+ T cells proliferated and produced multiple cytokines against both CD38+SLAMF7- and CD38-SLAMF7+ heterogeneous myeloma cells. Importantly, treatment of these lymphocytes appeared to mediate anti-myeloma response without increasing the frequency of regulatory T cells. Their cytotoxic activities against myeloma cells induced by Dar/B-BiTE and Elo/B-BiTE were higher than those induced by Dar and Elo alone in vitro and in vivo. Importantly, both human T cells and NK cells freshly isolated from the patients with MM simultaneously responded to their own myeloma cells in the presence of a mAb/B-BiTE.
[Conclusion] B-BiTE can be a new modality to easily, broadly, and economically generate the stable, safe, and effective bispecific antibodies in combination with clinically available mAbs. This modality can allow us to prepare a panel of next-generation bispecific antibodies which induce both T-cell and NK-cell responses, resulting in further advancement of immunotherapy for RRMM.
Disclosures: Ochi: Grant-in-Aid for Scientific Research (C): Research Funding; Takeda Science Foundation: Research Funding; SENSHIN Medical Research Foundation: Research Funding; Center for Clinical and Translational Research of Kyushu University Hospital: Research Funding. Takenaka: PharmaEssentia Japan KK: Consultancy, Research Funding.
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