Abstract B46: Immune characterization of C57BL/6J syngeneic breast cancer mouse models for application in immunotherapy development

Abstract

Abstract Background: Breast cancer is the second leading cause of cancer-related mortality in women worldwide. While immunotherapy has shown success in various solid tumors, it has been largely ineffective in breast cancer. Critical to establishing effective immunotherapies in breast cancer is the development and better characterization of the tumor immunology of immunocompetent syngeneic models. Here, we describe the molecular and in-depth immunological characterization of three C57BL/6J syngeneic breast cancer mouse models: AT3, Py8119 and E0771 cells. Methods: AT3, Py8119, and E0771 cells were obtained from commercial sources. 5x105 cells were implanted orthotopically in 8 weeks old C57BL/6J female mice. Tumors were isolated from mice and breast cancer subtype classification was performed by immunohistochemical (IHC) staining of estrogen receptor alpha (ERα), progesterone receptor (PR) and Erb-B2 Receptor Tyrosine Kinase 2 (ERBB2/HER2). T cell and myeloid cell infiltration patterns of the tumors were determined by CD3 and CD11b IHC staining respectively. Immunophenotyping of splenic immune cell populations and tumor-infiltrating immune cells was performed with multicolor flow cytometry in all three models. Results: Based on the IHC analysis of the orthotopic murine tumors, E0771 and Py8119 tumors fit the histopathological criteria of triple-negative breast cancer models, while AT3 tumors appear to be a model of the HER2-enriched breast cancer subtype. We show significant differences between the AT3, Py8119 and E0771 models regarding the accumulation of myeloid cells (mMDSC, gMDSC, macrophages, dendritic cells) in the tumor and spleen. Furthermore, analysis of tumor-infiltrating CD4 and CD8 T lymphocytes showed high expression levels of PD-1 in all three models, and varying levels of expression of other immune checkpoint molecules (CTLA4, TIM3, LAG3 and PD-L1) that were model specific. Furthermore, flow cytometry analysis also revealed high levels of PD-L1 expression on all three tumor cell types. Conclusion: In summary, we determined the breast cancer molecular subtype, and described the splenic and intratumoral immune landscape of the AT3, Py8119 and E0771 orthotopic C57BL/6J syngeneic breast cancer mouse models. These data will aid the better design of future tumor immunological studies and provide essential knowledge about these preclinical breast cancer models for use in immunotherapy development. Citation Format: Melinda Magna, Marc E Lippman, Barry I Hudson. Immune characterization of C57BL/6J syngeneic breast cancer mouse models for application in immunotherapy development [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy; 2022 Oct 21-24; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2022;10(12 Suppl):Abstract nr B46.