Abstract P2-21-09: Detailed analyses of pro-metastatic and anti-metastatic microenvironments of murine breast tumors in syngeneic mice

Abstract Despite the advances in early diagnostics and therapeutics, women with metastatic breast cancer have limited treatment options. Women with TNBC, who constitute 15-20% of breast cancer patients, are often diagnosed with aggressive/metastatic disease. Advanced studies implicated immunosuppressive tumor microenvironment (TME) in aggressive/metastatic properties of TNBC subtype. Alternatively activated immature myeloid cells including tumor-associated macrophages (TAM), tumor-associated neutrophils (TAN), tumor-associated dendritic cells (TADC) and myeloid derived suppressor cells (MDSC) constitute a major component of TME. However, anti-tumorigenic microenvironment is also reported and that may have clinical relevance in early TNBC patients. Therefore, our hypothesis is that myeloid cells polarize to become immunosuppressive and infiltrate tumors and pre-metastatic niches in patients with advanced disease, while patients with early TNBCs may elicit anti-tumor immune response eliminating disseminated tumor cells (DTC). The utilization of syngeneic immunocompetent mouse models has contributed to our current understanding of immunosuppressive or immunomodulatory TME. Using these models, we have demonstrated that tumor dissemination and growth at metastatic sites is facilitated by MDSC’s. Emerging technologies; single cell RNA sequencing (scRNA-Seq), mass cytometry (CyTOF) or cellular indexing of transcriptomes and epitopes sequencing (CITE-Seq) has been powerful platforms for detailed characterization of tumors and TME compartments. We performed scRNA-Seq and CyTOF analyses of the myeloid cell populations of tumors and spleens from metastatic 4T1 and non-invasive EMT6 tumor-bearing mice. Tumors and spleens from 4T1 tumor-bearing mice exhibited a marked expansion of myeloid cell subsets that are characterized by the expression of immunosuppressive as well as progenitor markers. On the contrary, indicated tissues from EMT6 mice were enriched in NK cells, T and B lymphocytes and they were lacking immunosuppressive myeloid cell subsets. Furthermore, we identified a distinct differentiation pattern of immature myeloid cell subsets from neutrophil progenitors (NP) in 4T1 tumor-bearing mice. Using the murine TNBC models in syngeneic mice, we provide evidence that early TNBC tumors may elicit anti-tumor immune responses and thus the survival outcome in those patients is substantially increased after complete surgical resection of the primary tumors. Whereas immunosuppressive tumor microenvironment contributes to the poor overall survival in patients with advanced TNBCs. Therefore, identifying an anti-tumor immune signature in early TNBC patients may be utilized as a clinical biomarker before surgical intervention as well as improve the survival outcome. Citation Format: Fulya Alkan, Justin D. Wilson, Nika Shekastehband, Catherine HEDRICK, Alicia Arnold, Roni Bollag, Huidong Shi, Hasan Korkaya. Detailed analyses of pro-metastatic and anti-metastatic microenvironments of murine breast tumors in syngeneic mice [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-21-09.