M1 Macrophage Extracellular Vesicles and TLR3 Agonist Nanoparticles Down‐Regulate Immunosuppression and Metastasis via AKT/TAM in Triple‐Negative Breast Cancer

Metastasis induced by tumor immune escape has been implicated as one of the factors contributing to the aggressiveness of triple-negative breast cancer. Macrophage type 1-derived extracellular vesicles were isolated and combined with PLGA nanoparticles loaded with the TLR3 agonist poly I:C as a therapeutic strategy to investigate their antitumor activity by downregulating tumor immune escape in the tumor microenvironment (TME) of breast cancer in a murine model of orthotopic tumor growth. Tumors were evaluated by qRT-PCR and immunohistochemistry. Cellular uptake and polarization of murine macrophages (RAW 264.7 cells) were analyzed In Vitro by immunofluorescence and flow cytometry, respectively. Furthermore, mouse survival, lymph node involvement, and metastasis were also evaluated. In the animal model, the combination therapy inhibited tumor progression through TME immunomodulation, leading to a reduction in primary tumor size (p < 0.0001) and metastasis, along with an extension in survival of 11 days. Importantly, both innate and adaptive immune responses were enhanced, as indicated by increased CD8 expression (p < 0.0001) and reduced PD-L1 levels in the TME, as well as elevated CD11c expression in lymph nodes (p < 0.0001). Likewise, the combination therapy suppressed tumor progression by reducing AKT1 expression (p < 0.001) and increasing E-cadherin expression (p < 0.01). Based on these findings, the combination therapy functioned as a "vaccine-like immunomodulatory strategy," promoting TME immunomodulation and suppressing metastasis in a murine model of triple-negative breast cancer.