Abstract 2167: A novel humanized mouse model for preclinical assessment of anti-CD47 and anti-SIRPΑtherapeutics.

Abstract Background: CD47, a ubiquitously expressed "don't eat me" molecular signal, mediates the evasion of tumor cells from phagocytic clearance through specific interaction with signal regulatory protein alpha (SIRPΑ) expressed on the surface of macrophages and dendritic cells. Therapeutic agents targeting the CD47-SIRPΑ pathway promote tumor cell eradication through two well-characterized mechanisms: 1. Blocking antibodies, including monoclonal and bispecific antibodies, interfere with the CD47-SIRPΑ interaction to enhance macrophage-driven phagocytosis of tumor cells; 2. The Fc domain mediates antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC). These biological processes further strengthen dendritic cell-mediated antigen presentation and initiate anti-tumor adaptive immune responses, which collectively establishes the CD47-SIRPΑ axis as a high-priority target in immuno-oncology. Methods: To support the translational assessment of CD47-targeted therapies, GemPharmatech developed a BALB/c-derived double humanized hCD47/hSIRPα knock-in mouse model, in which the extracellular domains of human CD47 and SIRPΑ were expressed. Successful model construction was verified by detecting the protein expression levels of hCD47 and hSIRPΑ in BALB/c-hCD47/hSIRPΑ mice. This model was used to evaluate the anti-tumor efficacy of the anti-hCD47 antibody Magrolimab (5F9) using a CT26-hCD47 colorectal tumor model—established by engrafting CT26 overexpressing human CD47 into BALB/c-hCD47/hSIRPΑ mice. Given the well-documented toxicity of CD47 blockade, anti-SIRPΑ antibodies were also tested to explore an alternative targeting strategy. Additionally, the anti-tumor efficacy of the hSIRPΑ × hClaudin18.2 bispecific antibody (BsAb) was evaluated in BALB/c-hCD47/hSIRPΑ mice bearing the EMT6-hCD47-hClaudin18.2 triple-negative breast tumor model, where EMT6 cells overexpress both human CD47 and human Claudin18.2. Results: Expression of hCD47 and hSIRPΑ in BALB/c-hCD47/hSIRPΑ mice was successfully verified. Administration of the anti-hCD47 antibody induced dose-dependent tumor regression in the established colorectal tumor model. Notably, the hSIRPΑ×hClaudin18.2 bispecific antibody (BsAb) exerted a significant anti-tumor effect in BALB/c-hCD47/hSIRPΑ knock-in mice implanted with EMT6-hCD47-hClaudin18.2 tumor cells. Conclusions: The BALB/c-hCD47/hSIRPΑ mouse model serves as a clinically relevant tool for evaluating therapeutics targeting the CD47-SIRPΑ pathway within an immuocompetent model. Notably, it addresses key limitations of traditional immunocompromised murine models while providing critical insights into the mechanisms underlying CD47 pathway-mediated tumor clearance, toxicity management, and immune activation. Citation Format: Hongyan Sun, Shaotong Ma, Yujing Zhang, Huixin Yang, Xiang Gao. A novel humanized mouse model for preclinical assessment of anti-CD47 and anti-SIRPΑtherapeutics [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 2167.