Targeting immunosuppression for enhanced focused ultrasound efficacy in triple negative breast cancer.

Abstract Immunologic rejection of triple-negative breast cancer (TNBC) is rare. Focused Ultrasound (FUS) promotes anti-tumor immunity by inducing tissue destruction and inflammation. We hypothesized that thermally-ablative FUS (tFUS) would increase the immune response to TNBC. However, TNBC is commonly accompanied by the expansion of immunosuppressive myeloid cells. By implanting a metastasizing TNBC cell line, 4T1, into BALB/c mice, we showed that a combinatorial therapy of tFUS and Gemcitabine (GEM), a myeloablative chemotherapy, was able to control primary tumor growth and reduce mortality. This response is dependent on T cell-mediated immunity. While this treatment remarkably resulted in some cures, the effects were not durable in every case; suggesting immunosuppression may be re-established. We hypothesize GEM is synergizing with FUS to immunologically control tumor growth by either depleting myeloid derived suppressor cells (MDSCs) or inducing tumor cell death. To discriminate between these possibilities, we will use a Ly6G-specific 1A8 antibody to deplete the MDSC population. In parallel, we are interrogating the ability of GEM to induce immunogenic cell death in this model. Current studies are focused on understanding alterations and the role of CD4 and CD8 T cells in tumor control after FUS+GEM therapy. Finally, RNAseq analysis has been performed on treated samples to develop hypotheses to explain the effectiveness of dual therapy. Notably, similar therapeutic approaches are now ongoing as a clinical trial at our institution. We expect our studies to reveal the mechanistic basis in which FUS and GEM are eliciting an immunological response resulting in primary tumor growth control and an overall survival advantage. Supported by grants from NIH (R01 164985 101 GB10846 41017)