Jamie L. Todd

Bronchiolitis Obliterans Syndrome: The Final Frontier for Lung Transplantation

Bronchiolitis obliterans syndrome (BOS) is a form of chronic lung allograft dysfunction that affects a majority of lung transplant recipients and is the principal factor limiting long-term transplant survival. BOS is characterized by progressive airflow obstruction unexplained by acute rejection, infection, or other coexistent condition. Although BOS is a proven useful clinical syndrome that identifies patients at increased risk for death, its clinical course and underlying causative factors are now recognized to be increasingly heterogeneous. Regardless of the clinical history, the primary pathologic correlate of BOS is bronchiolitis obliterans, a condition of intraluminal airway fibrosis. This article highlights the body of developing research illustrating the mechanisms by which BOS is mediated, including alloimmune reactivity, the emerging roles of humoral and autoimmunity, activation of innate immune cells, and response to nonimmune-related allograft insults, such as infection and aspiration. In addition, we underscore emerging clinical implications and promising future translational research directions that have the potential to advance our knowledge and improve patient outcomes.

Impact of Forced Vital Capacity Loss on Survival after the Onset of Chronic Lung Allograft Dysfunction

RATIONALE Emerging evidence suggests a restrictive phenotype of chronic lung allograft dysfunction (CLAD) exists; however, the optimal approach to its diagnosis and clinical significance is uncertain. OBJECTIVES To evaluate the hypothesis that spirometric indices more suggestive of a restrictive ventilatory defect, such as loss of FVC, identify patients with distinct clinical, radiographic, and pathologic features, including worse survival. METHODS Retrospective, single-center analysis of 566 consecutive first bilateral lung recipients transplanted over a 12-year period. A total of 216 patients developed CLAD during follow-up. CLAD was categorized at its onset into discrete physiologic groups based on spirometric criteria. Imaging and histologic studies were reviewed when available. Survival after CLAD diagnosis was assessed using Kaplan-Meier and Cox proportional hazards models. MEASUREMENTS AND MAIN RESULTS Among patients with CLAD, 30% demonstrated an FVC decrement at its onset. These patients were more likely to be female, have radiographic alveolar or interstitial changes, and histologic findings of interstitial fibrosis. Patients with FVC decline at CLAD onset had significantly worse survival after CLAD when compared with those with preserved FVC (P < 0.0001; 3-yr survival estimates 9% vs. 48%, respectively). The deleterious impact of CLAD accompanied by FVC loss on post-CLAD survival persisted in a multivariable model including baseline demographic and clinical factors (P < 0.0001; adjusted hazard ratio, 2.73; 95% confidence interval, 1.86-4.04). CONCLUSIONS At CLAD onset, a subset of patients demonstrating physiology more suggestive of restriction experience worse clinical outcomes. Further study of the biologic mechanisms underlying CLAD phenotypes is critical to improving long-term survival after lung transplantation.

Thrombolytic Therapy for Acute Pulmonary Embolism: A Critical Appraisal

Pulmonary embolism (PE) is a prevalent condition that may account for > 300,000 deaths annually in the United States alone. Although thrombolytics have been studied as a treatment for acute PE since the 1960s, to date there have been only 11 randomized controlled trials comparing thrombolytic therapy to conventional anticoagulation, and the numbers of patients included in these trials has been small. Many studies confirm that thrombolytic therapy leads to rapid improvement in hemodynamic aberrations associated with PE, and this approach to massive PE with cardiogenic shock is a guideline-based practice. It is widely accepted that acute PE without associated right ventricular (RV) dysfunction or hemodynamic instability can be readily managed with standard anticoagulation. The appropriate therapy for submassive PE (PE associated with RV dysfunction but preserved systemic arterial BP) remains an area of contention, and definitive data proving mortality benefit in this setting are lacking. Further efforts at risk stratification may better determine who is in need of aggressive therapy. This article reviews historical aspects of and current evidence for thrombolytic therapy in acute PE with specific attention to bleeding risk, and data regarding hemodynamic parameters and mortality. We also discuss risk stratification techniques and propose a clinical algorithm for the incorporation of thrombolytic therapy.

Hyaluronan Contributes to Bronchiolitis Obliterans Syndrome and Stimulates Lung Allograft Rejection through Activation of Innate Immunity

RATIONALE Although innate immunity is increasingly recognized to contribute to lung allograft rejection, the significance of endogenous innate ligands, such as hyaluronan (HA) fragments, in clinical or experimental lung transplantation is uncertain. OBJECTIVES To determine if HA is associated with clinical bronchiolitis obliterans syndrome (BOS) in lung transplant recipients, and evaluate the effect of low- or high-molecular-weight HA on experimental lung allograft rejection, including dependence on innate signaling pathways or effector cells. METHODS HA concentrations were measured in bronchoalveolar lavage and plasma samples from lung recipients with or without established BOS. BOS and normal lung tissues were assessed for HA localization and expression of HA synthases. Murine orthotopic lung recipients with established tolerance were treated with low- or high-molecular-weight HA under varied experimental conditions, including Toll-like receptor (TLR) 2/4 and myeloid differentiation protein 88 deficiency and neutrophil depletion. MEASUREMENTS AND MAIN RESULTS HA localized within areas of intraluminal small airways fibrosis in BOS lung tissue. Moreover, transcripts for HA synthase enzymes were significantly elevated in BOS versus normal lung tissues and both lavage fluid and plasma HA concentrations were increased in recipients with BOS. Treatment with low-molecular-weight HA abrogated tolerance in murine orthotopic lung recipients in a TLR2/4- and myeloid differentiation protein 88-dependent fashion and drove expansion of alloantigen-specific T lymphocytes. Additionally, TLR-dependent signals stimulated neutrophilia that promoted rejection. In contrast, high-molecular-weight HA attenuated basal allograft inflammation. CONCLUSIONS These data suggest that accumulation of HA could contribute to BOS by directly activating innate immune signaling pathways that promote allograft rejection and neutrophilia.

Bronchoalveolar Lavage as a Tool to Predict, Diagnose, and Understand Bronchiolitis Obliterans Syndrome

Bronchiolitis obliterans syndrome (BOS), a condition of irreversible small airway fibrosis, is the principal factor limiting long‐term survival after lung transplantation. Bronchoscopy and bronchoalveolar lavage (BAL), techniques central to lung transplant clinical practice, provide a unique opportunity to interrogate the lung allograft during BOS development and identify potential disease mechanisms or biomarkers. Over the past 20 years, numerous studies have evaluated the BAL cellular composition, cytokine profiles and protein constituents in lung transplant recipients with BOS. To date, however, no summative evaluation of this literature has been reported. We developed and applied objective criteria to qualitatively rank the strength of associations between BAL parameters and BOS in order to provide a comprehensive and systematic assessment of the literature. Our analysis indicates that several BAL parameters, including neutrophil count, interleukin‐8, alpha defensins and MMP‐9, demonstrate highly replicable associations with BOS. Additionally, we suggest that considerable opportunity exists to increase the knowledge gained from BAL analyses in BOS through increased sample sizes, covariant adjustment and standardization of the BAL technique. Further efforts to leverage analysis of BAL constituents in BOS may offer great potential to provide additional in‐depth and mechanistic insights into the pathogenesis of this complex disease.

The state of genome-wide association studies in pulmonary disease: a new perspective.

With rapid advances in our knowledge of the human genome and increasing availability of high-throughput investigative technology, genome-wide association (GWA) studies have recently gained marked popularity. As an unbiased approach to identifying genomic regions of importance in complex human disease, the results of such studies have the potential to illuminate novel causal pathways, guide mechanistic research, and aid in prediction of disease risk. The use of a genome-wide approach presents considerable methodological and statistical challenges, and properly conducted studies are essential to avoid false-positive results. A total of 22 GWA studies have been published in pulmonary medicine thus far, implicating several intriguing genomic regions in the determination of pulmonary function measures, onset of asthma, and susceptibility to chronic obstructive pulmonary disease. Many questions remain, however, as most identified genetic variants contribute only nominally to overall disease risk, genetic disease mechanisms remain uncertain, and disease-associated variants are not consistent across studies. Perhaps most fundamentally, the association signals identified have not yet been traced to causal variants. This perspective will review the current state of GWA studies in pulmonary disease. We begin with an introduction to the hypothesis, principles, and limitations of this type of genome-wide approach, highlight key points from available studies, and conclude by addressing future approaches to better understand the genetics of complex pulmonary disease.

Impact of CLAD Phenotype on Survival After Lung Retransplantation: A Multicenter Study

Chronic lung allograft dysfunction (CLAD) remains a major problem after lung transplantation with no definitive treatment except redo lung transplantation (re‐LTx) in selected candidates. However, CLAD is not a homogeneous entity and different phenotypes exist. Therefore, we aimed to evaluate the effect of CLAD phenotypes on survival after re‐LTx for CLAD. Patients who underwent re‐LTx for respiratory failure secondary to CLAD in four LTx centers between 2003 and 2013 were included in this retrospective analysis. Bronchiolitis obliterans syndrome (BOS) and restrictive CLAD (rCLAD) were distinguished using pulmonary function, radiology and explant lung histopathology. Patient variables pre‐ and post‐re‐LTx were collected and analyzed. A total of 143 patients underwent re‐LTx for CLAD resulting in 94 BOS (66%) and 49 rCLAD (34%) patients. Unadjusted and adjusted survival after re‐LTx for rCLAD was worse compared to BOS (HR = 2.60, 1.59–4.24; p < 0.0001 and HR = 2.61, 1.51–4.51; p = 0.0006, respectively). Patients waiting at home prior to re‐LTx experienced better survival compared to hospitalized patients (HR 0.40; 0.23–0.72; p = 0.0022). Patients with rCLAD redeveloped CLAD earlier and were more likely to redevelop rCLAD. Survival after re‐LTx for rCLAD is worse compared to BOS. Consequently, re‐LTx for rCLAD should be critically discussed, particularly when additional peri‐operative risk factors are present.

Quantitative Proteomics of Bronchoalveolar Lavage Fluid in Idiopathic Pulmonary Fibrosis

The proteomic analysis of bronchoalveolar lavage fluid (BALF) can give insight into pulmonary disease pathology and response to therapy. Here, we describe the first gel-free quantitative analysis of BALF in idiopathic pulmonary fibrosis (IPF), a chronic and fatal scarring lung disease. We utilized two-dimensional reversed-phase liquid chromatography and ion-mobility-assisted data-independent acquisition (HDMSE) for quantitation of >1000 proteins in immunodepleted BALF from the right middle and lower lobes of normal controls and patients with IPF. Among the analytes that were increased in IPF were well-described mediators of pulmonary fibrosis (osteopontin, MMP7, CXCL7, CCL18), eosinophil- and neutrophil-derived proteins, and proteins associated with fibroblast foci. For additional discovery and targeted validation, BALF was also screened by multiple reaction monitoring (MRM), using the JPT Cytokine SpikeMix library of >400 stable isotope-labeled peptides. A refined MRM assay confirmed the robust expression of osteopontin, and demonstrated, for the first time, upregulation of the pro-fibrotic cytokine, CCL24, in BALF in IPF. These results show the utility of BALF proteomics for the molecular profiling of fibrotic lung diseases and the targeted quantitation of soluble markers of IPF. More generally, this study addresses critical quality control measures that should be widely applicable to BALF profiling in pulmonary disease.

Spirometrically Significant Acute Rejection Increases the Risk for BOS and Death after Lung Transplantation

Acute rejection (AR) is a common complication following lung transplantation and is an established risk factor for bronchiolitis obliterans syndrome (BOS). AR clinical presentation varies considerably and is sometimes associated with an acute decrease in forced expiratory volume in 1 s (FEV1). We hypothesized that lung transplant recipients who experience such spirometrically significant AR (SSAR), as defined by a ≥10% decline in FEV1 relative to the prior pulmonary function test, are subsequently at increased risk for BOS and worse overall survival. In a large single center cohort (n = 339), SSAR occurred in 79 subjects (23%) and significantly increased the risk for BOS (p < 0.0001, HR = 3.2, 95% CI 2.3–4.6) and death (p = 0.0001, HR = 2.3, 95% CI 1.5–3.5). These effects persisted after multivariate adjustment for pre‐BOS AR and lymphocytic bronchiolitis burden. An analysis of the subset of patients who experienced severe SSAR (≥20% decline in FEV1) resulted in even greater hazards for BOS and death. Thus, we demonstrate a novel physiological measure that allows discrimination of patients at increased risk for worse posttransplant outcomes. Further studies are needed to determine mechanisms of airflow impairment and whether aggressive clinical interventions could improve post‐SSAR outcomes.

An Exome Sequencing Study to Assess the Role of Rare Genetic Variation in Pulmonary Fibrosis

Rationale: Idiopathic pulmonary fibrosis (IPF) is an increasingly recognized, often fatal lung disease of unknown etiology. Objectives: The aim of this study was to use whole‐exome sequencing to improve understanding of the genetic architecture of pulmonary fibrosis. Methods: We performed a case‐control exome‐wide collapsing analysis including 262 unrelated individuals with pulmonary fibrosis clinically classified as IPF according to American Thoracic Society/European Respiratory Society/Japanese Respiratory Society/Latin American Thoracic Association guidelines (81.3%), usual interstitial pneumonia secondary to autoimmune conditions (11.5%), or fibrosing nonspecific interstitial pneumonia (7.2%). The majority (87%) of case subjects reported no family history of pulmonary fibrosis. Measurements and Main Results: We searched 18,668 protein‐coding genes for an excess of rare deleterious genetic variation using whole‐exome sequence data from 262 case subjects with pulmonary fibrosis and 4,141 control subjects drawn from among a set of individuals of European ancestry. Comparing genetic variation across 18,668 protein‐coding genes, we found a study‐wide significant (P < 4.5 × 10−7) case enrichment of qualifying variants in TERT, RTEL1, and PARN. A model qualifying ultrarare, deleterious, nonsynonymous variants implicated TERT and RTEL1, and a model specifically qualifying loss‐of‐function variants implicated RTEL1 and PARN. A subanalysis of 186 case subjects with sporadic IPF confirmed TERT, RTEL1, and PARN as study‐wide significant contributors to sporadic IPF. Collectively, 11.3% of case subjects with sporadic IPF carried a qualifying variant in one of these three genes compared with the 0.3% carrier rate observed among control subjects (odds ratio, 47.7; 95% confidence interval, 21.5‐111.6; P = 5.5 × 10−22). Conclusions: We identified TERT, RTEL1, and PARN—three telomere‐related genes previously implicated in familial pulmonary fibrosis—as significant contributors to sporadic IPF. These results support the idea that telomere dysfunction is involved in IPF pathogenesis.