<i>In Situ</i> Remodeling of Tumor Microenvironment via Specific Cancer-Associated Fibroblasts Subtype Engineering to Boost Antitumor Immunity

Cancer-associated fibroblasts (CAFs) are heterogeneous and critical drivers of tumor progression, yet engineering tumor-promoting CAF subtypes <i>in situ</i> offers an untapped therapeutic opportunity. Herein, we verify that the FAP+αSMA+ CAFs subtype in the 4T1 murine model effectively recapitulates its counterpart in human triple-negative breast cancer (TNBC), demonstrating strong tumor-promoting activity. We specifically engineer these CAFs <i>in situ</i> to enhance antitumor immunity using an innovative nanodrug, IL-15 plasmid-loaded FAP-sensitive MgCa/z-Gly-Pro-pamidronate acid nanoparticles (PN/MCG NPs). PN/MCG NPs can reverse the tumor-promoting phenotype of FAP⁺ αSMA⁺ CAFs and engineer FAP⁺ αSMA⁺ CAFs to sustain IL-15 expression. These engineered FAP⁺ αSMA⁺ CAFs significantly reduce the tumor immune suppression. Gene set enrichment analysis (GSEA) reveals enhanced immune cell proliferation and activation. Furthermore, we also prove that FAP⁺ αSMA⁺ human mammary fibroblast cells (FAP⁺ αSMA⁺ HMFs) also can be engineered by PN/MCG NPs <i>in vitro</i>. Our findings demonstrate that <i>in situ</i> CAF engineering is a promising strategy to remodel the tumor microenvironment and enhance immunotherapy in TNBC.