Effect of delayed hMSC administration on resolution of lung injury after VILI. Administration of hMSCs at 0.25 and 6 h after VILI restored arterial oxygenation (A), increased static lung compliance (B), had no effect on lung wet:dry weight ratios (C), decreased BAL protein concentrations (D), reduced BAL total cell counts (E), and decreased the proportion of BAL neutrophils (F). hMSC administration at 24 h after VILI did demonstrate reduced efficacy, restoring lung compliance and decreasing alveolar infiltration (n = 8 animals per group). Error bars represent standard deviation. BAL = bronchoalveolar lavage; hMSC = human mesenchymal stromal cell; Vehicle = treatment with vehicle alone; VILI = ventilator-induced lung injury. *Significantly (P < 0.05) different from Vehicle group.