Abstract 2689: Mass cytometry analysis of CXCR3 expression in tumor-infiltrated myeloid cells as a predictive biomarker For immunotherapy response

Abstract Monocytes have emerged as important regulators of cancer progression. We have recently found that CXCR3+ circulating monocytes in humans are associated with better response to immunotherapy. Here, we aimed to study the functions and heterogeneity of CXCR3+ monocytes in two different triple negative breast cancer (TNBC) tumors in mice, using either AT3 or EO771 tumor cell lines. AT-3 tumors exhibit higher resistance to anti-PD-1 and anti-CTLA-4 therapy in C57BL/6 breast cancer mouse models compared to EO771 tumors. We evaluated 36 surface protein markers on tumor-infiltrated myeloid cells in tumors isolated from each model using CyTOF mass cytometry. Analysis of monocytes, macrophages and dendritic cells in the tumors using unsupervised clustering identified 13 cell subsets. Significant differences were discovered between the two tumor types in frequencies of nine of 13 identified subsets. However, 3 of these subsets displayed relatively high expression of CXCR3 in EO771 tumors when compared to AT-3 tumors. The significant CXCR3 positive subsets were identified as CXCR3+ early macrophages, CXCR3+ Ly6C+CD11blo classical monocytes and Trem2+ CXCR3+ dendritic cells. We observed higher expression of CXCR4, Trem2, and CCR1 in CXCR3+ myeloid cells when compared to their CXCR3− counterparts in both tumor models. To elucidate the role of these CXCR3+ cells, we performed low-input bulk RNA sequencing of CD115+/CD11b+ cells from blood and spleen of EO771 tumor bearing mice with a wild type or CXCR3KO genotype. Ingenuity Pathway Analysis (IPA) of the differentially expressed genes suggests a significant inhibition of the IL-10 signaling pathway of CXCR3KO cells. These differentially expressed markers and genes suggest a functional importance in this subset in migration to the tumor and antigen presentation, both of which are anti-tumoral functions. Ongoing studies are aimed towards understanding the role of CXCR3+ myeloid cells in regulating response to immunotherapies. Citation Format: Gabriel A. Valentin-Guillama, Nandini Chatterjee, Ahmad Alimadadi, Catherine C. Hedrick. Mass cytometry analysis of CXCR3 expression in tumor-infiltrated myeloid cells as a predictive biomarker For immunotherapy response abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 2689.