Mesenchymal stem cell-derived extracellular vesicles modulate immune activation and preserve microvascular integrity in extrapulmonary sepsis-associated acute lung injury

Sepsis‑induced acute lung injury (ALI) is a major cause of respiratory failure and mortality, driven by immune dysregulation and disruption of the alveolar‑capillary unit. Current management remains largely supportive, with no therapies that directly target the biological mechanisms sustaining lung injury. Mesenchymal stem cell‑derived extracellular vesicles (MSC‑EVs) have emerged as a promising cell‑free therapeutic strategy; however, their effects in polymicrobial sepsis‑associated ALI remain incompletely defined. This study investigated whether MSC‑EVs attenuate sepsis‑associated ALI and modulate immune and endothelial responses in a murine model of extrapulmonary polymicrobial sepsis, and sought to identify transcriptomic mechanisms underlying these effects. A murine cecal slurry model of polymicrobial sepsis was used to induce ALI, with lung histopathology directly compared to human septic lung tissue to establish translational relevance. MSC‑EVs were administered following sepsis induction. Outcomes were assessed through clinical respiratory performance, lung histopathology, immune and endothelial cell profiling, transcriptomic pathway analysis, and microRNA (miRNA) target prediction. MSC‑EV administration significantly improved respiratory status and attenuated alveolar‑capillary injury. These effects were associated with coordinated immune and endothelial remodeling, including reduced neutrophil predominance and activation, expansion of reparative CX3CR1⁺ mononuclear phagocyte populations, attenuation of cytotoxic T‑cell skewing, and preservation of endothelial cell populations. Sepsis‑disrupted inflammatory, immune‑regulatory, and endothelial signaling pathways were reorganized following MSC‑EV treatment. Notably, 54% of suppressed genes were predicted targets of MSC‑EV‑enriched miRNAs, implicating EV miRNA cargo in transcriptional reprogramming. MSC‑EVs mitigate sepsis‑associated ALI through coordinated immune and endothelial reprogramming, with transcriptomic changes consistent with miRNA‑mediated mechanisms. These findings provide mechanistic support for the translational development of MSC‑EVs as a cell‑free, disease‑modifying therapeutic strategy for sepsis‑induced ALI.