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Abstract 4972: Preclinical development of a first-in-class NKp30xBCMA NK cell engager for the treatment of multiple myeloma

Multiple myeloma (MM) is characterized by clonal expansion of malignant plasma cells. Although several new drugs for the treatment of MM have greatly improved survival, many patients are known to relapse and become refractory to all presently available therapies or experience treatment-related toxicities. Therefore, MM remains an unmet medical need and the development of additional novel therapies is required. NK cells play a crucial role in the control of multiple myeloma and accumulating evidence shows the presence of highly cytotoxic NK cells in the bone marrow of MM patients suggesting that targeting NK cells could provide a specific treatment modality to leverage NK cell cytotoxicity in myeloma. Furthermore, NK cells are the first lymphocytes population to reconstitute after autologous stem cell transplant (ASCT) providing an opportunity to target minimal residual disease (MRD) shortly after transplant. B-cell maturation antigen (BCMA) is an excellent target in MM because its restricted expression in normal and malignant plasma cells from untreated and relapsed myeloma patients, but absent in all other main bone marrow cell subsets. Our first-in-class NKp30xBCMA NK cells engager, CTX-4419, binds to BCMA on MM cells and to NKp30 and CD16A (FcγRIIIA) on NK cells, specifically redirecting NK cells towards tumor cells expressing BCMA. We demonstrate here that CTX-4419 retains activity in the presence of high levels of BCMA ligands and serum IgG and induces potent NK cytotoxicity against high and low BCMA expressing cell lines as well as patients (autologous) primary myeloma cells. Moreover, CTX-4419 does not require CD16A binding to kill tumor cells, a unique characteristic that overcomes the reduction or loss of activity of CD16A due to receptor shedding or downregulation in the tumor microenvironment. Furthermore CTX-4419 induces NK proliferation and cytokines/chemokines production by NK cells only in the presence of tumor cells providing sustainable anti-tumor specificity to NK cells. CTX-4419 activates in-vitro cynomolgus NK cells in presence of target cells expressing cynomolgus BCMA and, when given intravenously, CTX-4419 decreases plasma cell counts. CTX-4419 represents a novel class of NK-cell engagers that shows strong potency even in the absence of CD16A engagement and induces NK cell proliferation and lysis of tumor cells expressing low amount of antigen. CTX-4419 has strong activity in an autologous setting when tested in bone marrow samples of MM patients and shows efficacy in a non-human primate model of plasma-cell depletion. These data show that CTX-4419 is strongly differentiated from conventional therapeutic antibodies and is a promising candidate for MM treatment with the potential to be used as monotherapy or in combination with adoptive transfer of NK cells and/or other immuno-therapies. Citation Format: Monia Draghi, Jamie L. Schafer, Allison Nelson, Zach Frye, Amanda Oliphant, Sara Haserlat, jason Lajoie, Kenneth rogers, Francois Villinger, Michael Schmidt, Robert Tighe, Piotr Bobrowicz, Jennifer Watkins-Yoon, Thomas Schuetz. Preclinical development of a first-in-class NKp30xBCMA NK cell engager for the treatment of multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4972.