Abstract LB314: Organ-specific roles of CD83+ macrophages in breast cancer

Abstract The purpose of this study is to understand how heterogeneity in organ-specific immune infiltrates can lead to Triple Negative Breast Cancer (TNBC) progression and immunotherapies resistance in metastasis. Both innate and adaptive immune responses are essential for breast cancer progression. Using single-cell multiplexing technology on human and murine models of primary and metastatic breast cancers, we investigated the pattern of immune cell infiltration in bone and lung metastases in a temporal manner. The parallel profiling of metastasis sites revealed a strong involvement of the innate immunity in restraining tumor progression with an acute increase in Mrc1+ Cd83+ tumor-associated macrophages at the early stage of lung colonization. Interestingly, the increase was modest in bone metastasis and remained consistent overtime despite bone metastasis progression. In contrast, we saw an increase in the number of Ly6G+ Lrg1+ granulocytes. Profiling of paired TNBC patient samples from the primary and metastatic sites have shown an immunologically quiescent tumor microenvironment in metastasis as compared to the primary tumors. Hence, to further explore the role of Mrc1+ Cd83+ macrophages on therapeutic resistance, we profiled the orthotopic claudin-low TNBC models, T11 and T12, following their exposure to chemotherapy. While responsive tumors displayed a decreased infiltration of Mrc1+ Cd83+ macrophages, the opposite phenotype was observed in non-responders, suggesting their involvement in tumor progression. Overall, our results suggest differential responses in untreated lung/bone metastases and primary tumors indicating divergent roles for Cd83+ TAMs in restraining or promoting tumor progression, while also indicating some crosstalk between neutrophils and stromal cells that aid in bone metastatic progression. These site-specific differences in immune cell phenotype indicate that there is a great need to thoroughly characterize the tumor immune compartment in both the primary and the metastatic setting to improve treatment responses. Considering the inhibitory effect of macrophages on T cells in these models, this study highlights a tissue-specific reprogramming of immune cells in breast cancer metastasis. Citation Format: Swarnima Singh, Igor Bado. Organ-specific roles of CD83+ macrophages in breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB314.