MM-derived exosomes promote M2 macrophage polarization and immunosuppressive microenvironment: therapeutic opportunities.

Multiple myeloma (MM) progression involves extensive immunosuppressive remodeling of the bone marrow microenvironment. In this study, we performed a comprehensive mass spectrometry-based proteomic analysis of exosomes derived from MM cells (MM-Exos), revealing that these exosomal proteins are predominantly enriched in pathways associated with immune regulation. We demonstrated that MM-Exos effectively drive macrophage polarization toward the M2 phenotype, thereby facilitating the establishment and maintenance of an immunosuppressive tumor microenvironment. Mechanistically, we identified the ERK1/2 signaling pathway as a critical mediator of MM-Exo-induced macrophage polarization. Importantly, we found that simvastatin, a widely used inhibitor of cholesterol biosynthesis, effectively impaired exosome secretion from MM cells and subsequently reduced M2 macrophage polarization. Collectively, our study reveals a novel mechanism of immune evasion in MM, in which MM-Exos promote the polarization of macrophages toward the M2 phenotype via ERK1/2 pathway activation. These findings underscore the therapeutic potential of targeting exosome-mediated intercellular communication within the MM bone marrow microenvironment to improve clinical outcomes.