Obliterative bronchiolitis (OB) is a poorly understood airway disease characterized by the generation of fibrotic bronchiolar occlusions. In the lung transplant setting, OB is a pathological manifestation of bronchiolitis obliterans syndrome (BOS), which is a major impediment to long-term recipient survival. Club cells play a key role in bronchiolar epithelial repair, but whether they promote lung transplant tolerance through preventing OB remains unclear. We determined if OB occurs in mouse orthotopic lung transplants following conditional transgene-targeted club cell depletion. In syngeneic lung transplants club cell depletion leads to transient epithelial injury followed by rapid club cell–mediated repair. In contrast, allogeneic lung transplants develop severe OB lesions that are largely devoid of club cells despite immunosuppression treatment. Lung allograft club cell ablation also triggers the recognition of alloantigens, and pulmonary restricted self-antigens reported associated with BOS development. However, CD8 ⁺ T cell depletion restores club cell reparative responses and prevents OB. In addition, ex vivo analysis reveals a specific role for alloantigen-primed CD8 ⁺ T cells in inhibiting club cell proliferation and maintenance. Taken together, our results demonstrate a vital role for club cells in maintaining lung transplant tolerance and propose a model to identify the underlying mechanisms of OB.

Idiopathic pulmonary fibrosis (IPF) is a progressive, irreversible, and rapidly fatal interstitial lung disease marked by the replacement of lung alveoli with dense fibrotic matrices. Although the mechanisms initiating IPF remain unclear, rare and common alleles of genes expressed in lung epithelia, combined with aging, contribute to the risk for this condition. Consistently, single-cell RNA sequencing (scRNA-seq) studies have identified lung basal cell heterogeneity in IPF that might be pathogenic. We used single-cell cloning technologies to generate “libraries” of basal stem cells from the distal lungs of 16 patients with IPF and 10 controls. We identified a major stem cell variant that was distinguished from normal stem cells by its ability to transform normal lung fibroblasts into pathogenic myofibroblasts in vitro and to activate and recruit myofibroblasts in clonal xenografts. This profibrotic stem cell variant, which was shown to preexist in low quantities in normal and even fetal lungs, expressed a broad network of genes implicated in organ fibrosis and showed overlap in gene expression with abnormal epithelial signatures identified in previously published scRNA-seq studies of IPF. Drug screens highlighted specific vulnerabilities of this profibrotic variant to inhibitors of epidermal growth factor and mammalian target of rapamycin signaling as prospective therapeutic targets. This profibrotic stem cell variant in IPF was distinct from recently identified profibrotic stem cell variants in chronic obstructive pulmonary disease and may extend the notion that inappropriate accrual of minor and preexisting stem cell variants contributes to chronic lung conditions.

The development of donor-specific antibodies (DSA) after lung transplantation is common and results in adverse outcomes. In kidney transplantation, Belatacept has been associated with a lower incidence of DSA, but experience with Belatacept in lung transplantation is limited. We conducted a 2-center pilot randomized controlled trial of de novo immunosuppression with Belatacept after lung transplantation to assess the feasibility of conducting a pivotal trial. Twenty-seven participants were randomized to Control (Tacrolimus, Mycophenolate Mofetil, and prednisone, n = 14) or Belatacept-based immunosuppression (Tacrolimus, Belatacept, and prednisone until day 89 followed by Belatacept, Mycophenolate Mofetil, and prednisone, n = 13). All participants were treated with rabbit anti-thymocyte globulin for induction immunosuppression. We permanently stopped randomization and treatment with Belatacept after 3 participants in the Belatacept arm died compared to none in the Control arm. Subsequently, 2 additional participants in the Belatacept arm died for a total of 5 deaths compared to none in the Control arm (log rank p = 0.016). We did not detect a significant difference in DSA development, acute cellular rejection, or infection between the 2 groups. We conclude that the investigational regimen used in this study is associated with increased mortality after lung transplantation.

Pulmonary hypertension (PH) comprises a diverse group of disorders that share a common pathway of pulmonary vascular remodeling leading to right ventricular failure. Development of anti-remodeling strategies is an emerging frontier in PH therapeutics that requires a greater understanding of the interactions between vascular wall cells and their extracellular matrices. The ubiquitous matrix glycan, hyaluronan (HA), is markedly elevated in lungs from patients and experimental models with PH. Herein, we identified HA synthase-2 (HAS2) in the pulmonary artery smooth muscle cell (PASMC) layer as a predominant locus of HA dysregulation. HA upregulation involves depletion of NUDT21, a master regulator of alternative polyadenylation, resulting in 3'UTR shortening and hyper-expression of HAS2. The ensuing increase of HAS2 and hyper-synthesis of HA promoted bioenergetic dysfunction of PASMC characterized by impaired mitochondrial oxidative capacity and a glycolytic shift. The resulting HA accumulation stimulated pro-remodeling phenotypes such as cell proliferation, migration, apoptosis-resistance, and stimulated pulmonary artery contractility. Transgenic mice, mimicking HAS2 hyper-synthesis in smooth muscle cells, developed spontaneous PH, whereas targeted deletion of HAS2 prevented experimental PH. Pharmacological blockade of HAS2 restored normal bio-energetics in PASMC, ameliorated cell remodeling phenotypes, and reversed experimental PH in vivo. In summary, our results uncover a novel mechanism of HA hyper-synthesis and downstream effects on pulmonary vascular cell metabolism and remodeling. (c) 2022 The Authors. Published by Elsevier B.V.

Idiopathic pulmonary fibrosis (IPF) is a fatal disease with limited treatment options. The role of the developmental transcription factor Sine oculis homeobox homolog 1 (SIX1) in the pathophysiology of lung fibrosis is not known. IPF lung tissue samples and IPF-derived alveolar type II cells (AT2) showed a significant increase in SIX1 mRNA and protein levels, and the SIX1 transcriptional coactivators EYA1 and EYA2 were elevated. Six1 was also upregulated in bleomycin-treated (BLM-treated) mice and in a model of spontaneous lung fibrosis driven by deletion of Telomeric Repeat Binding Factor 1 ( Trf1 ) in AT2 cells. Conditional deletion of Six1 in AT2 cells prevented or halted BLM-induced lung fibrosis, as measured by a significant reduction in histological burden of fibrosis, reduced fibrotic mediator expression, and improved lung function. These effects were associated with increased macrophage migration inhibitory factor (MIF) in lung epithelial cells in vivo following SIX1 overexpression in BLM-induced fibrosis. A MIF promoter–driven luciferase assay demonstrated direct binding of Six1 to the 5′-TCAGG-3′ consensus sequence of the MIF promoter, identifying a likely mechanism of SIX1-driven MIF expression in the pathogenesis of lung fibrosis and providing a potentially novel pathway for targeting in IPF therapy.

Bronchiolitis obliterans syndrome (BOS) is a major cause of morbidity and mortality in lung transplantation and allogeneic hematopoietic stem cell transplantation (allo-HSCT) recipients. Clinical guidelines recommend lung function monitoring to aid early identification of BOS, but real-world rates of pulmonary function testing (PFT) have not been studied. The purpose of this study was to quantify PFT rates in lung transplantation and allo-HSCT recipients. This longitudinal retrospective study used US data from the IQVIA PharMetrics Plus commercial claims database (January 1, 2006-September 30, 2018) and the Medicare Limited Data Set (January 1, 2010-December 31, 2018). Study recipients had no evidence of transplantation 12 months before transplantation, which was identified by using diagnosis and procedure codes. PFTs were identified by using procedure codes. Outcomes were percentage of recipients who received ≥1 PFT in each follow-up year, including spirometry, lung diffusion capacity, lung function volume test, and plethysmography, including the average number of total and specific tests per recipient. The study identified 367 commercially insured and 1776 Medicare recipients who underwent lung transplantation; 92% and 86% received ≥1 lung function test in the first year after transplantation, respectively. Among recipients observable 3 years after transplant, 85% and 83% received ≥1 PFT. Among 2187 commercially insured and 1864 Medicare recipients who underwent allo-HSCT, 44% and 36% received ≥1 lung function test in the first posttransplant year. In the third year after transplant, only 31% and 26% of observable allo-HSCT recipients underwent any PFT. Morbidity and mortality from BOS remain high in lung transplant and allo-HSCT recipients, but lung function testing in the first posttransplant year is not universal, with substantially lower rates among allo-HSCT recipients. Furthermore, testing rates in all cohorts declined over time. Increased and sustained monitoring could lead to earlier detection of BOS and earlier intervention and treatment.