Abstract 607: Humanized mice model for efficacy and toxicity evaluation of drugs targeting CD47-SIRPα-PD1-PD-L1 axes
Authors: Liang Juan , Ju Cunxiang , Li Song , Yu Weiwei , Sun Hongyan , Chen Santi Suryani , Zhao Jing , Gao Xiang , Moore Mark 
Published: June 2022

Abstract
CD47 is widely expressed on the surface of cells. CD47 interacts with inhibitory receptor signaling protein alpha (SIRPα) to mediate a series of activities such as apoptosis, proliferation, and immune response. Tumor cells can escape the immune surveillance of macrophages through the CD47-SIRPa signaling pathway. Blocking CD47-SIRPα interactions has been shown to promote the destruction of cancer cells by phagocytes. Furthermore, there is growing evidence that targeting of the CD47-SIRPα axis may also promote antigen-presenting cell function. These identify the CD47-SIRPα axis as a promising innate immune checkpoint in cancer. We have generated humanized SIRPα and double humanized CD47/SIRPα mice model for drug efficacy and toxicity evaluation. The humanized mice with human extracellular domain and mouse cytoplasmic fragment of target protein showed similar immune cell population compared with wild type mice. The anti-CD47 antibody, Magrolimab (5F9) analog, displayed anti-tumor effect when administrated to humanized SIRPα mice bearing MC38-hCD47 (MC38 cells engineered to express human CD47) tumor cells. The tumor regression was also observed when treating humanized CD47/SIRPα mice bearing MC38-hCD47 with tested anti-CD47 antibody. Dual checkpoint blockade of CD47 and PD-L1 or PD1 have been reported as a synergistic therapy that activates both innate and adaptive immune response against tumors.We also generated humanized PD1/SIRPα and PD1/PDL1/SIRPα/CD47 mice model for efficacy and toxicity evaluation of drugs targeting for CD47/SIRPα-PD1/PD-L1 axes. Treatment with anti-CD47, anti-SIRPα and anti-PD-L1 alone showed tumor regression efficacy, and combination of anti-PD-L1 and anti-SIRPα or anti-CD47 showed improved anti-tumor effect compared with alone treatment. Those data suggested the humanized syngeneic mice model are useful for the efficacy evaluation of drugs targeting of axes.However, the administration of anti-CD47 blocking antibodies may cause haematotoxicity, including anaaemia and thrombocytopenia, because of the ubiquitous expression of CD47.In vitro Erythrocyte binding activity analysis showed that red blood cells(RBC) collected from humanized CD47/SIRPα mice could bind with Magrolimab analog, while another anti-CD47 antibody has low affinity with RBC. Furthermore, treatment with Magrolimab analog in CD47/SIRPα humanized mice caused haemagglutination and Hemolysis of human RBCs, which were not observed when treating with tested anti-CD47 antibody. Thus, the humanized CD47 and double humanized CD47/SIRPα mice are also suitable for CD47 antibody toxicity evaluation. In conclusion, humanized CD47/SIRPα and quadruple humanized PD1/PDL1/SIRPα/CD47 mice model provide a validated preclinical mouse model to interrogate new therapeutic agents targeting SIRPα-PD1 axes in immune oncology therapy.
Citation Format: Juan Liang, Cunxiang Ju, Song Li, Weiwei Yu, Hongyan Sun, Santi Suryani Chen, Jing Zhao, Xiang Gao, Mark Moore. Humanized mice model for efficacy and toxicity evaluation of drugs targeting CD47-SIRPα-PD1-PD-L1 axes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 607.