Abstract 5444: ImmuMab® mice enable efficient development of antibody therapeutics by unparalleled diversity across multiple formats

Abstract This study highlights the latest advancements of ImmuMab® gene-edited mouse platform, engineered with human immunoglobulin germlines to facilitate efficient antibody therapeutic development across diverse formats, including canonical, heavy-chain-only (HCO), common-light-chain (CLC), or combinations thereof. Utilizing massive-fragment across species in situ replacement technology, these mice underwent Mb-scale humanization of immunoglobulin gene fragments in single-step operations, circumventing the cumulative cellular damage associated with traditional transgenic approaches. These new mice all deliver distinguished immune dynamic profiles featuring rapid initial immune responses and compelling titer plateaus. Since their introductions, the ImmuMab® mouse suite (HK, HKL, HL, HCO, CLC) has consistently delivered highly diversified repertoires across 35+ antibody discovery programs, with no failures due to suboptimal immune responses. Designed for canonical antibody generation, the ImmuMab HK, HKL and HL mice (the latter two newly introduced), feature up to over 3.2 Mb human Immunoglobulin variable region genes. The ImmuMab HK mice in different project had deliver stable median titers ranging from 72.9k to 656.1k by the third dose, with some maximum titers approaching 1968.3k. Their immune responses exhibit robust resilience against challenging targets, including seven-transmembrane receptors and antigens with over 99% human-mouse homology. Notably, in one hybridoma screening against hROR1, the primary clone positivity rate (OD450 > 0.5) exceeded 33%. Selected monoclonal antibodies demonstrating affinities ranging from 0.001 to 1 nM (by BLI) and internalization rates of 20%-90% (Temperature-dependent). Some antibodies further demonstrated superior cytotoxic efficacy (MMAE-conjugated) compared to benchmark antibody-drug conjugates (ADC). Additionally, one discovery program with ImmuMab Light® (CLC) mice by rapid immunization (1-week intervals) yielded seven candidate antibodies with picomolar EC50 values (EC50 < 5 × 10-10 M, ELISA) within a single screening cycle. Furthermore, the ImmuMab Heavy® (HCO) mouse enabled rapid heavy-chain-only immune response, reaching titers of 218.7k∼656.1k within four weeks and identifying nanomolar heavy-chain-only antibodies with low single-digit nanomolar EC50 values for both human and cynomolgus monkey antigens. The ImmuMab® mouse platform enables efficient development of antibody therapeutics across multiple formats. Its robust immune responses and high repertoire diversity make it a powerful tool for generating high-quality candidates, even against challenging targets. Citation Format: Yuan Li, Wenbao Wu, Yu Wei, Yingjun Zhao, Yu Zhang, Jiwei Zhang. ImmuMab® mice enable efficient development of antibody therapeutics by unparalleled diversity across multiple formats [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 5444.