Acute lung injury (ALI) is characterized by rapid alveolar injury, inflammation, cytokine induction, and neutrophil accumulation. Although early events in the pathogenesis of ALI have been defined, the mechanisms underlying resolution are unknown. As a model of ALI, we administered intratracheal (i.t.) LPS to mice and observed peak lung injury 4 days after the challenge, with resolution by day 10. Numbers of alveolar lymphocytes increased as injury resolved. To examine the role of lymphocytes in this response, lymphocyte-deficient Rag-1 -/-and C57BL/6 WT mice were exposed to i.t. LPS. The extent of injury was similar between the groups of mice through day 4, but recovery was markedly impaired in the Rag-1 -/-mice. Adoptive transfer studies revealed that infusion of CD4 + CD25 + Foxp3 + Tregs as late as 24 hours after i.t. LPS normalized resolution in Rag-1 -/-mice. Similarly, Treg depletion in WT mice delayed recovery. Treg transfer into i.t. LPS-exposed Rag-1 -/-mice also corrected the elevated levels of alveolar proinflammatory cytokines and increased the diminished levels of alveolar TGF-β and neutrophil apoptosis. Mechanistically, Treg-mediated resolution of lung injury was abrogated by TGF-β inhibition. Moreover, BAL of patients with ALI revealed dynamic changes in CD3 + CD4 + CD25 hi CD127 lo Foxp3 + cells. These results indicate that Tregs modify innate immune responses during resolution of lung injury and suggest potential targets for treating ALI, for which there are no specific therapies currently available.

Aggarwal NR, King LS, D'Alessio FR. Diverse macrophage populations mediate acute lung inflammation and resolution.

Checkpoint inhibitor pneumonitis (CIP) is an immunerelated adverse event that can occur after initiation of anti-programmed death 1/programmed death ligand 1 immune checkpoint inhibitor (ICI) therapy for the treatment of multiple malignancies, including NSCLC. However, the incidence of CIP has not been previously examined in a population that included both trial-enrolled and non-trialenrolled patients with advanced NSCLC. Furthermore, risk factors and other clinical characteristics associated with CIP severity are not known. In this study, we retrospectively examined clinical characteristics, incidence, and risk factors for CIP in a cohort of 205 patients with NSCLC, all of whom received anti-programmed death 1/programmed death ligand 1 ICIs. Our results demonstrate a higher incidence of CIP (19%) than previously reported in clinical trials (3%-5%). Our data also suggest that tumor histologic type may be a risk factor for CIP development. We observed a wide range of time to onset of CIP (median 82 days), with high morbidity and mortality associated with higher-grade CIP regardless of degree of immunosuppression. Our data provide new insight into the epidemiology and clinical