AbstractWhat We Already Know about This TopicWhat This Article Tells Us That Is NewBackgroundHuman mesenchymal stromal cells demonstrate promise for acute respiratory distress syndrome, but current studies use highly heterogenous cell populations. We hypothesized that a syndecan 2 (CD362)–expressing human mesenchymal stromal cell subpopulation would attenuate Escherichia coli–induced lung injury and enhance resolution after ventilator-induced lung injury.MethodsIn vitro studies determined whether CD362+ human mesenchymal stromal cells could modulate pulmonary epithelial inflammation, wound healing, and macrophage phagocytosis. Two in vivo rodent studies determined whether CD362+ human mesenchymal stromal cells attenuated Escherichia coli–induced lung injury (n = 10/group) and enhanced resolution of ventilation-induced injury (n = 10/group).ResultsCD362+ human mesenchymal stromal cells attenuated cytokine-induced epithelial nuclear factor kappa B activation, increased epithelial wound closure, and increased macrophage phagocytosis in vitro. CD362+ human mesenchymal stromal cells attenuated Escherichia coli–induced injury in rodents, improving arterial oxygenation (mean ± SD, 83 ± 9 vs. 60 ± 8 mmHg, P < 0.05), improving lung compliance (mean ± SD: 0.66 ± 0.08 vs. 0.53 ± 0.09 ml · cm H2O−1, P < 0.05), reducing bacterial load (median [interquartile range], 1,895 [100–3,300] vs. 8,195 [4,260–8,690] colony-forming units, P < 0.05), and decreasing structural injury compared with vehicle. CD362+ human mesenchymal stromal cells were more effective than CD362− human mesenchymal stromal cells and comparable to heterogenous human mesenchymal stromal cells. CD362+ human mesenchymal stromal cells enhanced resolution after ventilator-induced lung injury in rodents, restoring arterial oxygenation (mean ± SD: 113 ± 11 vs. 89 ± 11 mmHg, P < 0.05) and lung static compliance (mean ± SD: 0.74 ± 0.07 vs. 0.45 ± 0.07 ml · cm H2O−1, P < 0.05), resolving lung inflammation, and restoring histologic structure compared with vehicle. CD362+ human mesenchymal stromal cells efficacy was at least comparable to heterogenous human mesenchymal stromal cells.ConclusionsA CD362+ human mesenchymal stromal cell population decreased Escherichia coli–induced pneumonia severity and enhanced recovery after ventilator-induced lung injury.