Genetically engineered macrophages reverse the immunosuppressive tumor microenvironment and improve immunotherapeutic efficacy in TNBC.

The main challenges in current immunotherapy for triple-negative breast cancer (TNBC) lie in the immunosuppressive tumor microenvironment (TME). Considering tumor-associated macrophages (TAMs) are the most abundant immune cells in the TME, resetting TAMs is a promising strategy for ameliorating the immunosuppressive TME. Here, we developed genetically engineered macrophages (GEMs) with gene-carrying adenoviruses, to maintain the M1-like phenotype and directly deliver the immune regulators interleukin-12 and CXCL9 into local tumors, thereby reversing the immunosuppressive TME. In tumor-bearing mice, GEMs demonstrated targeted enrichment in tumors and successfully reprogramed TAMs to M1-like macrophages. Moreover, GEMs significantly enhanced the accumulation, proliferation, and activation of CD8+ T cells, mature dendritic cells, and natural killer cells within tumors, while diminishing M2-like macrophages, immunosuppressive myeloid-derived suppressor cells, and regulatory T cells. This treatment efficiently suppressed tumor growth. In addition, combination therapy with GEMs and anti-programmed cell death protein 1 further improved interferon-γ+CD8+ T cell percentages and tumor inhibition efficacy in an orthotopic murine TNBC model. Therefore, this study provides a novel strategy for reversing the immunosuppressive TME and improving immunotherapeutic efficacy through live macrophage-mediated gene delivery.