C646-loaded mesenchymal stromal cell extracellular vesicles alleviate lactate-driven immunoparalysis in sepsis-associated ARDS through the p300-H3K18la-PSMD14 axis.
Sepsis-associated acute respiratory distress syndrome (S-ARDS) is often followed by immunoparalysis, leaving patients vulnerable to secondary infection and adverse outcomes. Lactate is widely used as a severity marker in sepsis, but its direct contribution to immune paralysis remains unclear. We examined lactate-driven immune dysfunction in mouse models, bone marrow-derived macrophages and human CD14+ monocyte-derived macrophages, and tested C646-loaded mesenchymal stromal cell-derived extracellular vesicles (EVs-C646) as an experimental intervention. Lactate elevation blunted cytokine responses after rechallenge, reduced macrophage phagocytosis, shifted macrophages toward an M2-like phenotype, expanded regulatory T cells and decreased interferon-γ (IFN-γ) responses in CD8+ T cells. Mechanistically, lactate activated a p300-histone H3 lysine 18 lactylation (H3K18la) program and upregulated proteasome 26S subunit, non-ATPase 14 (PSMD14). Integrated RNA sequencing, H3K18la chromatin immunoprecipitation sequencing, public sepsis transcriptomic analysis and perturbation experiments identified PSMD14 as a lactylation-linked effector that strengthened AKT/mTOR signalling and promoted macrophage dysfunction. EVs-C646 decreased H3K18la and PSMD14 expression, restored macrophage inflammatory responsiveness, improved bacterial clearance, reduced lung injury and increased survival in experimental S-ARDS-related immunoparalysis models. These findings define a lactate-p300-H3K18la-PSMD14-AKT/mTOR pathway in immunoparalysis and support further preclinical evaluation of lactylation-targeted extracellular vesicle therapy.