ADAM12 Abrogation Alters Immune Cell Infiltration and Improves Response to Checkpoint Blockade Therapy in the T11 Murine Model of Triple-negative Breast Cancer

Immunosuppressive tumor microenvironment (TME) impedes anti-tumor immune responses and contributes to immunotherapy resistance in triple-negative breast cancer (TNBC). ADAM12, a member of cell surface metalloproteases, is selectively upregulated in mesenchymal/claudin-low TNBCs, where its expression is largely restricted to tumor cells. The role of cancer cell-expressed ADAM12 in modulating the immune TME is not known. We show that knockout in the T11 mouse syngeneic transplantation model of claudin-low TNBC leads to decreased numbers of tumor-infiltrating neutrophils (TINs)/polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) and increased numbers of tumor-infiltrating B cells and T cells. ADAM12 loss in cancer cells increases chemotaxis of B cells and this effect is eliminated by inhibition of CXCR4, a receptor for CXCL12, or anti-CXCL12 blocking antibody. Importantly, ADAM12 loss in T11 cancer cells sensitizes tumors to anti-PD1/anti-CTLA4 combination therapy, although the initial responsiveness is followed by acquired therapy resistance. Depletion of B cells in mice eliminates the improved response to immune checkpoint blockade of knockout T11 tumors. Analysis of gene expression data for claudin-low TNBCs from the METABRIC patient cohort shows significant inverse correlations between and gene expression signatures of several anti-tumor immune cell populations, as well as a significant positive correlation between and gene expression signature of TINs/PMN-MDSCs. Collectively, these results implicate ADAM12 in immunosuppression within the TME in TNBC.