Extracellular Vesicles from Interferon-&ggr;–primed Human Umbilical Cord Mesenchymal Stromal Cells Reduce Escherichia coli–induced Acute Lung Injury in Rats

What We Already Know about This TopicMesenchymal stromal cells are multipotent adult stem cells with the capacity to differentiate into multiple cell types and have immunomodulatory properties that have been shown to have substantial therapeutic promise in preclinical acute lung injury modelsMesenchymal stromal cells release extracellular vesicles, which are small, spherical membrane fragments comprising distinct populations including both exosomes and microvesicles, which have therapeutic effects in several disease modelsMesenchymal stromal cells are activated or primed by the injury microenvironment, which may be replicated by prior activation of the mesenchymal stromal cells What This Article Tells Us That Is NewIn a rat model of Escherichia coli–induced pneumonia, extracellular vesicles derived from human umbilical cord mesenchymal stromal cells primed with interferon-&ggr; more effectively attenuated E. coli–induced lung injury than did extracellular vesicles from naïve mesenchymal stromal cells, possibly by enhanced macrophage phagocytosis and killing of E. coli bacteria Background: Human umbilical cord mesenchymal stromal cells possess considerable therapeutic promise for acute respiratory distress syndrome. Umbilical cord mesenchymal stromal cells may exert therapeutic effects via extracellular vesicles, while priming umbilical cord mesenchymal stromal cells may further enhance their effect. The authors investigated whether interferon-&ggr;–primed umbilical cord mesenchymal stromal cells would generate mesenchymal stromal cell–derived extracellular vesicles with enhanced effects in Escherichia coli (E. coli) pneumonia. Methods: In a university laboratory, anesthetized adult male Sprague–Dawley rats (n = 8 to 18 per group) underwent intrapulmonary E. coli instillation (5 × 109 colony forming units per kilogram), and were randomized to receive (a) primed mesenchymal stromal cell–derived extracellular vesicles, (b) naïve mesenchymal stromal cell–derived extracellular vesicles (both 100 million mesenchymal stromal cell–derived extracellular vesicles per kilogram), or (c) vehicle. Injury severity and bacterial load were assessed at 48 h. In vitro studies assessed the potential for primed and naïve mesenchymal stromal cell–derived extracellular vesicles to enhance macrophage bacterial phagocytosis and killing. Results: Survival increased with primed (10 of 11 [91%]) and naïve (8 of 8 [100%]) mesenchymal stromal cell–derived extracellular vesicles compared with vehicle (12 of 18 [66.7%], P = 0.038). Primed—but not naïve—mesenchymal stromal cell–derived extracellular vesicles reduced alveolar–arterial oxygen gradient (422 ± 104, 536 ± 58, 523 ± 68 mm Hg, respectively; P = 0.008), reduced alveolar protein leak (0.7 ± 0.3, 1.4 ± 0.4, 1.5 ± 0.7 mg/ml, respectively; P = 0.003), increased lung mononuclear phagocytes (23.2 ± 6.3, 21.7 ± 5, 16.7 ± 5 respectively; P = 0.025), and reduced alveolar tumor necrosis factor alpha concentrations (29 ± 14.5, 35 ± 12.3, 47.2 ± 6.3 pg/ml, respectively; P = 0.026) compared with vehicle. Primed—but not naïve—mesenchymal stromal cell–derived extracellular vesicles enhanced endothelial nitric oxide synthase production in the injured lung (endothelial nitric oxide synthase/&bgr;-actin = 0.77 ± 0.34, 0.25 ± 0.29, 0.21 ± 0.33, respectively; P = 0.005). Both primed and naïve mesenchymal stromal cell–derived extracellular vesicles enhanced E. coli phagocytosis and bacterial killing in human acute monocytic leukemia cell line (THP-1) in vitro (36.9 ± 4, 13.3 ± 8, 0.1 ± 0.01%, respectively; P = 0.0004) compared with vehicle. Conclusions: Extracellular vesicles from interferon-&ggr;–primed human umbilical cord mesenchymal stromal cells more effectively attenuated E. coli–induced lung injury compared with extracellular vesicles from naïve mesenchymal stromal cells, potentially via enhanced macrophage phagocytosis and killing of E. coli.