Chemotherapy coupled to macrophage inhibition leads to B cell-mediated T cell memory activation and durable triple negative breast cancer regression

Immunosuppressive elements within the tumor microenvironment such as Tumor Associated Macrophages (TAMs) can present a barrier to successful anti-tumor responses by cytolytic T cells. We employed preclinical syngeneic p53 null mouse models of TNBC to develop a treatment regimen that harnessed the immunostimulatory effects of low-dose chemotherapy coupled with the pharmacologic inhibition of TAMs. Combination therapy was used to successfully treat several highly aggressive, claudin-low murine mammary tumors and lung metastasis. Long-term responders developed tertiary lymphoid structures co-infiltrated by T and B cells at the treatment site. Mechanistically, CD86+ antigen-experienced T cells exhibited polyclonal expansion and resulted in exceptional responses upon tumor rechallenge. Combination treatment also eliminated lung metastases. High dimensional transcriptomic data for CD45+ immune cells lead to the identification of an aberrant developmental trajectory for TAMs that were resistant to treatment. Signatures derived from these TAM populations were predictive of patient response to our therapy. This study illustrates the complexity of tumor infiltrating myeloid cells and highlights the importance of personalized immuno-genomics to inform therapeutic regimens.