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

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-gamma-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 SpragueDawley rats (n = 8 to 18 per group) underwent intrapulmonary E. coli instillation (5 x 109 colony forming units per kilogram), and were randomized to receive (a) primed mesenchymal stromal cell-derived extracellular vesicles, (b) naive 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 naive mesenchymal stromal cell-derived extracellular vesicles to enhance macrophage bacterial phagocytosis and killing. Results: Survival increased with primed (10 of 11 [ 91%]) and naive (8 of 8 [ 100%]) mesenchymal stromal cell-derived extracellular vesicles compared with vehicle (12 of 18 [ 66.7%], P = 0.038). Primed-but not naive-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 naive-mesenchymal stromal cell-derived extracellular vesicles enhanced endothelial nitric oxide synthase production in the injured lung (endothelial nitric oxide synthase/ss-actin = 0.77 +/- 0.34, 0.25 +/- 0.29, 0.21 +/- 0.33, respectively; P = 0.005). Both primed and naive 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-gamma-primed human umbilical cord mesenchymal stromal cells more effectively attenuated E. coli-induced lung injury compared with extracellular vesicles from naive mesenchymal stromal cells, potentially via enhanced macrophage phagocytosis and killing of E. coli.