Abstract 1237: IGM-2644, a CD38xCD3 bispecific IgM T cell engager, shows enhanced anti-tumor activity compared to daratumumab in preclinical models of multiple myeloma

Abstract Multiple myeloma (MM) is a hematologic malignancy characterized by the accumulation of monoclonal plasma cells in the bone marrow. CD38 is an attractive therapeutic target for MM due to its high expression on plasma cells, but it is also expressed on multiple subsets of normal immune cells. Approved therapies including anti-CD38 monoclonal antibodies such as daratumumab are available, however resistance inevitably develops, and toxicities such as reduced immune cell counts put patients at increased risk for infections. To address this and other issues associated with current therapies, we are developing IGM-2644, an engineered high affinity, high avidity bispecific anti-CD38xCD3 IgM T cell engager (TCE) antibody for the treatment of plasma cell disorders. IGM-2644 kills CD38-expressing tumor cells through complement-dependent cytotoxicity (CDC) and T cell-dependent cellular cytotoxicity (TDCC). Live cell imaging of tumor cells in the presence of normal human serum as a source of complement has shown that IGM-2644, compared to daratumumab, has exhibited superior CDC with faster kinetics and higher maximal killing, as well as increased activity on tumor cell lines that express low levels of CD38. IGM-2644 also has displayed enhanced cellular dependent cytotoxicity over daratumumab across tumor cell lines with a range of CD38 expression levels in vitro. In ex vivo assays with MM patient bone marrow mononuclear cells (BMMC), IGM-2644 has shown superior tumor cell depletion compared to daratumumab even with low T cell to tumor cell ratios. Furthermore, IGM-2644 can deplete tumor cells in BMMC from daratumumab-refractory MM patients. Similarly, using in vivo humanized xenograft tumor mouse models with various levels of CD38 expression, greater anti-tumor activity with IGM-2644 over daratumumab was observed. When compared to daratumumab, IGM-2644 demonstrated lower immune cell fratricide in an in vivo xenograft tumor mouse model, suggesting a potentially differentiated safety profile. In summary, IGM-2644 is a bispecific anti-CD38xCD3 IgM TCE antibody that demonstrates superior tumor cell killing when compared to daratumumab in vitro and especially in xenograft tumor models in vivo with low CD38 expression while having low immune cell depletion, potentially reducing the risk of infections. The safety and efficacy of IGM-2644 has been initially studied in a phase 1 clinical trial for relapsed/refractory (r/r) MM. Applicability of IGM-2644 for the treatment of other plasma cell disorders is currently being explored, including autoimmune diseases. Citation Format: Kevin C. Hart, Daniel Santos, Keyu Li, Rui Yun, Min Chai, Andras Kabai, Gene Li, Poonam Yakkundi, Roel P. Funke, Yinghui Guan, Thomas Manley, Liqin Liu, Angus M. Sinclair, Albert F. Candia, Bruce Keyt, Maya F. Kotturi. IGM-2644, a CD38xCD3 bispecific IgM T cell engager, shows enhanced anti-tumor activity compared to daratumumab in preclinical models of multiple myeloma abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 1237.