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1603 Development of a New Fc/CD3 Bispecific T-Cell Engager to Advance Anti-Myeloma Immunotherapy

Program: Oral and Poster Abstracts
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
Saturday, December 11, 2021, 5:30 PM-7:30 PM

Tatsuya Konishi1*, Toshiki Ochi, MD, PhD1,2*, Masaki Maruta, MD, PhD1*, Kazushi Tanimoto, MD, PhD1*, Takashi Saitou, PhD3*, Takeshi Imamura, MD, PhD3*, Masaki Yasukawa, MD, PhD2,4* and Katsuto Takenaka, MD, PhD1

1Department of Hematology, Clinical Immunology and Infectious Diseases, Ehime University Graduate School of Medicine, Ehime, Japan
2Division of Immune Regulation, Proteo-Science Center, Ehime University, Ehime, Japan
3Department of Molecular Medicine for Pathogenesis, Ehime University Graduate School of Medicine, Ehime, Japan
4Ehime Prefectural University of Health Sciences, Ehime, Japan

[Background] Immunotherapy using monoclonal antibodies (mAbs) has significantly improved clinical outcomes of patients with multiple myeloma (MM). Nevertheless, most of the patients eventually relapse, and relapsed/refractory MM (RRMM) still has a dismal prognosis probably due to the heterogeneity of myeloma cells, highlighting the need for the development of novel therapeutic approaches. Recently, new antibody-based modalities have been developed, and tested in clinical trials for RRMM. Among them, bispecific T-cell engager (BiTE) has been expected to have a potential to treat RRMM. To enhance its anti-tumor efficacy, following concerns need to be overcome. First, conventional BiTE lacks an Fc domain which is necessary to induce NK-cell response. Second, conventional BiTE needs to be administered continuously to maintain its blood concentration achieving sufficient antitumor effects because of its low molecular weight. Third, conventional BiTE can target only one antigen expressed by tumor cells, suggesting the difficulty to totally kill myeloma cells with antigenic heterogeneity. To overcome these concerns, we have developed a novel BiTE-based modality, named as Bridging-BiTE (B-BiTE), which can endow a series of clinically available mAbs with NK-cell as well as T-cell activation capacity. In this study, we have investigated the efficacy, universality, and safety of mAbs armed with B-BiTE for the treatment of MM.

[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.

*signifies non-member of ASH