Abstract PD9-01: Stromal mediators of lymphocyte exclusion and dysfunction in triple negative breast cancer

Abstract

Abstract Triple negative breast cancer (TNBC) is the most aggressive breast cancer subtype with poor prognosis and limited treatment options. One of the mechanisms contributing to this is the ability of TNBC tumors to evade anti-tumour response, limiting the success of immune-checkpoint therapy. In recent studies of the tumor microenvironment, stromal cells have emerged as potential important mediators of lymphocyte function in TNBC. Multi-omics studies from our group and others have elucidated the heterogeneity of stromal cells and their interactions with immune cells in TNBC. However, the clinical relevance and functional characteristics of these relationships remain poorly explored. Our previous work revealed functionally distinct subpopulations of stromal cells in breast cancer: endothelial cells, myofibroblast-like cancer-associated fibroblasts (myCAFs), inflammatory-CAFs (iCAFs), and perivascular-like cells which resemble pericyte and smooth muscle cells in immature and differentiated states (imPVLs; dPVLs), respectively. Here we directly explored the clinical relevance of these stromal subpopulations and their association with immune evasion in a large independent TNBC cohort with long-term survival data. Using markers derived from our single-cell multi-omics studies, we performed multiplex immunofluorescence using the OPAL9 platform on tumor microarrays from 222 TNBC patients to mark myCAFs, iCAFs, dPVLs, endothelial cells, CD8 and/or PD1 positive T-cells. Digital imaging analysis (QuPath) revealed a significant negative correlation between the abundance of stromal cells and CD8 T cells. This cytotoxic T-cell exclusion is primarily driven by smooth muscle dPVLs. Parallel to this T-cell exclusion, our functional studies demonstrate that stromal cells suppress T-cell proliferation. Using multiple ex vivo co-culture models of primary TNBC CAFs and peripheral blood mononuclear cells (PBMCs) from healthy and matched donors, we show that CAFs suppress the proliferative capability of CD4 and CD8 T-cells. ScRNA-seq of these co-culture models demonstrate that CAF educated T cells are driven into a LAG3+ exhausted state enriched for canonical pathways of immunosuppressive cytokine signaling. Our findings suggest that manipulation of these stromal subpopulations could elicit a more effective immune response in a subset of patients through inhibiting T-cell dysfunction and exclusion. Citation Format: Julia Chen, Sunny Wu, Travis Ruan, Iveta Slapetova, Ewan Millar, Elgene Lim, Alex Swarbrick. Stromal mediators of lymphocyte exclusion and dysfunction in triple negative breast cancer [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 PD9-01.