Abstract 6165: DARC/ACKR1 expression is associated with immune landscape changes among triple negative breast tumors
Authors: Martini Rachel , Telesford Kiel , Lord Brittany , Ravichandran Hiranmayi , Elemento Olivier , Manley Nancy , Monteil Michele , Newman Lisa , Manne Upender , Yates Clayton , Davis Melissa B. 
Published: June 2022

Abstract
Recent work defining the immune landscape across breast cancer (BC) subtypes have revealed that TNBC tumors have increased immunogenicity, and these increases in immune cell infiltration are associated with better prognosis and outcomes.
Our recent work has proposed the Duffy Antigen Receptor for Chemokines (DARC), as a potential driver of immune regulation in breast tumors. DARC/ACKR1 is an atypical chemokine receptor that promiscuously binds both pro-inflammatory CC and pro-angiogenic CXC class chemokines and plays a role in chemokine gradient establishment both in circulation, and at sites of inflammation via chemokine transcytosis. In the BC context, we and others have reported DARC/ACKR1 protein expression on breast tumor epithelial cells by IHC and have also shown a range of gene expression in breast tumors from bulk RNAseq data in the TCGA cohort. Specifically, alongside CIBERSORT deconvolution of tumor associated immune cell populations, we have shown a strong positive correlation between DARC/ACKR1 gene expression and total tumor-associated leukocyte (TAL) abundance across all BC subtypes.
To investigate the role of DARC/ACKR1 specifically in the TNBC tumor microenvironment (TME), we have analyzed (1) in silico bulk RNAseq data from two independent TNBC cohorts, (2) imaging mass cytometry data from TNBC patients and (3) murine model of DARC/ACKR1 BC progression in a basal-like BC transgenic mouse model.
Our in silico data shows strong positive correlation of DARC/ACKR1 expression and TAL abundance, when DARC/ACKR1 expression is both dichotomized and analyzed as a continuous variable. Immune cell populations increasing with DARC/ACKR1 expression include B cell, T cell, monocyte and macrophage populations, which was consistent with our previous findings across all BC subtypes. IMC analysis of TNBC FFPE sections to determine protein expression of various immune and structural markers on the single-cell level between DARC/ACKR1 high or low expressing tumors show cells from DARC/ACKR1 high expressing tumors clustered distinctly from DARC/ACKR1 low expressing tumors. Image analysis also revealed increased infiltration among our DARC/ACKR1 high tumors. Finally, our murine model of DARC/ACKR1 in TNBC, shows that tumor development followed similar disease progression as human BC, following early through late-stage disease. DARC/ACKR1 deficient mice were found to have larger tumor volume and more palpable tumors, where DARC/ACKR1 expressing mice show co-localization of DARC and immune cell expression.
This is the first work to describe the role of DARC/ACKR1 in the TNBC TME in bulk tumor transcriptomic data, spatial single-cell protein level data, and murine BC tumor model. Further investigation of factors that drive immune response in TNBC tumors, like DARC/ACKR1, may lead the way to novel therapeutic options or biomarkers for better outcomes for women with TNBC.
Citation Format: Rachel Martini, Kiel Telesford, Brittany Lord, Hiranmayi Ravichandran, Olivier Elemento, Nancy Manley, Michele Monteil, Lisa Newman, Upender Manne, Clayton Yates, Melissa B. Davis. DARC/ACKR1 expression is associated with immune landscape changes among triple negative breast tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6165.