View Abstract

A7539 - PD-1 Inhibition Promotes Th1 Inflammation and Alters Lymphocyte Activation in Mice After LPS-Lung Injury
Author Block: K. Gibbs, L. D. Purcell, C. Liu, D. Files; Pulmonary, Critical Care, Allergy, and Immunology, Wake Forest, Winston-Salem, NC, United States.
Rationale: The development of effective immunotherapies targeting the checkpoint co-inhibitor Programmed Death-1 (PD-1) has revolutionized the treatment of non-small cell lung cancer (NSCLC). PD-1 is a surface receptor that blunts T cell-mediated inflammation, acting through both pro- and anti-inflammatory T cell lineages. Although an important mediator of immune homeostasis in health, PD-1 activation in cancer patients promotes tumor escape. Recent clinical trials have demonstrated that anti-PD-1 monoclonal antibodies improve survival in NSCLC; however, the accompanying disruption of normal immune regulation increases immune-related adverse events (irAEs). Among the most dangerous irAEs is PD-1 inhibitor pneumonitis. Severe PD-1 pneumonitis is radiographically and histologically indistinguishable from Acute Respiratory Distress Syndrome (ARDS) and is associated with high mortality. Despite the clinical importance of PD-1 pneumonitis, the mechanisms underlying this immunopathology are largely unknown. We hypothesize that PD-1 inhibition worsens lung injury by enhancing effector T (Teff) inflammation and impairing regulatory T cell (Treg)-mediated immune resolution.
Methods: Adult (8 week old) male C57Bl6J mice were treated with either anti-PD-1 antibody (BioXcell, 200 ug/mouse) or isotype control via intraperitoneal injection on day -3, 0, and +3 relative to intratracheal lipopolysaccharide (IT-LPS, 3 ug/gm) instillation. Lung injury markers (cell count and differential) were assessed on day 3 and day 7 and weight changes were measured daily. On day 7, bronchoalveolar lavage (BAL) cells and parenchymal lung cells were collected and stimulated using Phorbol 12-Myristate 13-Acetate/ionomycin (Leukocyte activation cocktail, BD Biosciences) for 4 hours. Analysis of lymphocyte subsets, activation state and cytokine production was performed using flow cytometry.
Results: Anti-PD-1 treated and isotype treated mice had similar injury severity by BAL cell count and differential at peak (day 3) and late injury (day 7). Weight loss and recovery was also similar between the two groups. Despite having similar degrees of inflammation, PD-1 inhibition resulted in distinct lymphocyte phenotypes: Anti-PD-1 therapy increased CD4 Teff expression of TNFa (p= 0.018) and CD8 cell expression of TNFa (p=0.002) and interferon y (p=0.026) in lung single cell suspension. Lungs from anti-PD-1 animals had fewer memory/effector CD44+, CD62L- Tregs (p=0.001). In the BAL, a higher percentage of CD8 cells expressed TNFa (p=0.014)in anti-PD-1 treated mice. Interestingly, we also found that Tregs comprised a significantly larger fraction of CD4 cells within the BAL in these animals (6.8% vs 4.6%, p = 0.0241)
Conclusion: PD-1 inhibition increases Th1 cytokine production and impairs Treg maturation after IT-LPS lung injury.