Epithelial-Mesenchymal Plasticity is Associated with Immunosuppressive Features in Canine Mammary Carcinomas

Epithelial-mesenchymal plasticity (EMP) is a cellular process activated in carcinoma cells to drive invasiveness, metastasis, and chemoresistance. Recently, we have demonstrated that activation of the EMP program also results in the assembly of an immunosuppressive tumor microenvironment and resistance to immunotherapy in an immunocompetent orthotopic murine model. However, it has yet to be shown whether these findings can be translated to canine carcinomas. Here, we show that in spontaneous canine mammary carcinomas (CMCs), which share similar histopathologic, molecular, and clinical features with human breast cancers, EMP activation is linked to the recruitment of immunosuppressive cells including regulatory T-cells and M2-like macrophages. Additionally, through transcriptomic profiling of CMCs, we identify that the glycoprotein CD109 is associated with EMP-mediated immunosuppression across canine, murine, and human breast cancer models. CD109 has been previously associated with tumorigenicity, but not immunosuppression in cancers of any species. Finally, we identified upregulation of several immunosuppressive paracrine factors across multiple canine carcinomas, including oral squamous cell carcinoma, urothelial carcinoma, and pulmonary carcinoma samples. These findings demonstrate for the first time that the EMP program is associated with immunosuppression in canine carcinomas, with direct translational implications for human breast cancers.