Abstract B058: In silico and in vivo analysis of the Duffy Antigen Receptor for Chemokines (DARC) in the breast tumor microenvironment
Authors: Martini Rachel , Jenkins Brittany , Yates Clayton , Newman Lisa , Manley Nancy , Davis Melissa 
Published: August 2020

Abstract
In clinic, we observe that women of African descent have higher incidence rates of breast cancer (BC). These women are disproportionately diagnosed with the most aggressive subtype of BC, triple-negative BC, compared to women belonging to any other ancestry groups. To investigate factors driving this disparity, our work focuses on the tumor microenvironment (TME), specifically through the lens of an atypical chemokine receptor. The Duffy Antigen Receptor for Chemokines (DARC) is a nonsignaling, atypical chemokine receptor that binds two structural classes of chemokines. DARC modulates chemokine availability in circulation and participates in chemokine transport in tissues, to recruit immune cells back to sites of inflammation. DARC additionally serves as a portal of entry for the malaria-causing parasite Plasmodium vivax. In Sub-Saharan Africa, where malaria is endemic, a regulatory variant arose removing DARC expression from red blood cells (RBCs). This mutation, known as the Duffy-Null allele, was highly beneficial in this population, and quickly rose to fixation. Despite being called Duffy-Null, these individuals retain DARC expression in other cell types, only lacking expression on RBCs. Knowing that the Duffy-Null allele is prevalent in this population of women, we aim to investigate how DARC tumor expression and Duffy-Null status impacts the TME in silico through analysis of The Cancer Genome Atlas (TCGA) data, and in vivo through establishment of mouse models that depict Duffy-Null status in the BC TME. Using TCGA data, we see that DARC tumor gene expression is significantly lower among African-Americans compared to Whites. Using the CIBERSORT online platform, we quantified tumor-associated leukocyte (TAL) abundance in the TME. Overall, we found that tumors with high DARC expression have significantly higher total TAL abundance (p &lt; 0.0001), and that DARC expression and TAL abundance are positively and significantly correlated (R = 0.545, p &lt; 0.0001). Specifically, DARC expression influenced levels of B cell, T cell, monocyte and macrophage population in the TME. In our mouse models, we have utilized the C3(1)Tag BC transgenic mouse model, alongside a DARC knock-out mouse. To better recapitulate the Duffy-Null phenotype in our mouse model, our approach is to generate a BC/Duffy-Null bone marrow derived (BMD) chimera, where a DARC+/-; C3(1)Tag+/0 recipient will receive bone marrow from a DARC -/- donor. The resulting chimera mice will retain DARC expression in all cells, aside from bone marrow-derived cells from the null donor. In the C3(1)Tag line, disease onset is at approximately 12 weeks, at which time we will assess changes in disease progression in our chimeras compared to controls by collecting total number of tumors, tumor location, tumor size and weight, and hematoxylin and eosin staining of tumor sections, and immune cell infiltration quantification.
Citation Format: Rachel Martini, Brittany Jenkins, Clayton Yates, Lisa Newman, Nancy Manley, Melissa Davis. In silico and in vivo analysis of the Duffy Antigen Receptor for Chemokines (DARC) in the breast tumor microenvironment [abstract]. In: Proceedings of the Eleventh AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2018 Nov 2-5; New Orleans, LA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2020;29(6 Suppl):Abstract nr B058.