Lymphocytic bronchiolitis after lung transplantation is associated with daily changes in air pollution

Prognostic Value of Chest CT Findings at BOS Diagnosis in Lung Transplant Recipients

BACKGROUND

Bronchiolitis obliterans syndrome (BOS) after lung transplantation is characterized by fibrotic small airway remodeling, recognizable on high-resolution computed tomography (HRCT). We studied the prognostic value of key HRCT features at BOS diagnosis after lung transplantation.

METHODS

The presence and severity of bronchiectasis, mucous plugging, peribronchial thickening, parenchymal anomalies, and air trapping, summarized in a total severity score, were assessed using a simplified Brody II scoring system on HRCT at BOS diagnosis, in a cohort of 106 bilateral lung transplant recipients transplanted between January 2004 and January 2016. Obtained scores were subsequently evaluated regarding post-BOS graft survival, spirometric parameters, and preceding airway infections.

RESULTS

A high total Brody II severity score at BOS diagnosis (P = 0.046) and high subscores for mucous plugging (P = 0.0018), peribronchial thickening (P = 0.0004), or parenchymal involvement (P = 0.0121) are related to worse graft survival. A high total Brody II score was associated with a shorter time to BOS onset (P = 0.0058), lower forced expiratory volume in 1 s (P = 0.0006) forced vital capacity (0.0418), more preceding airway infections (P = 0.004), specifically with Pseudomonas aeruginosa (P = 0.002), and increased airway inflammation (P = 0.032).

CONCLUSIONS

HRCT findings at BOS diagnosis after lung transplantation provide additional information regarding its underlying pathophysiology and for future prognosis of graft survival.

Lymphocytic Airway Inflammation in Lung Allografts

Lung transplant remains a key therapeutic option for patients with end stage lung disease but short- and long-term survival lag other solid organ transplants. Early ischemia-reperfusion injury in the form of primary graft dysfunction (PGD) and acute cellular rejection are risk factors for chronic lung allograft dysfunction (CLAD), a syndrome of airway and parenchymal fibrosis that is the major barrier to long term survival. An increasing body of research suggests lymphocytic airway inflammation plays a significant role in these important clinical syndromes. Cytotoxic T cells are observed in airway rejection, and transcriptional analysis of airways reveal common cytotoxic gene patterns across solid organ transplant rejection. Natural killer (NK) cells have also been implicated in the early allograft damage response to PGD, acute rejection, cytomegalovirus, and CLAD. This review will examine the roles of lymphocytic airway inflammation across the lifespan of the allograft, including: 1) The contribution of innate lymphocytes to PGD and the impact of PGD on the adaptive immune response. 2) Acute cellular rejection pathologies and the limitations in identifying airway inflammation by transbronchial biopsy. 3) Potentiators of airway inflammation and heterologous immunity, such as respiratory infections, aspiration, and the airway microbiome. 4) Airway contributions to CLAD pathogenesis, including epithelial to mesenchymal transition (EMT), club cell loss, and the evolution from constrictive bronchiolitis to parenchymal fibrosis. 5) Protective mechanisms of fibrosis involving regulatory T cells. In summary, this review will examine our current understanding of the complex interplay between the transplanted airway epithelium, lymphocytic airway infiltration, and rejection pathologies.

Bronchiolitis obliterans syndrome after lung or haematopoietic stem cell transplantation: current management and future directions

Bronchiolitis obliterans syndrome (BOS) may develop after either lung or haematopoietic stem cell transplantation (HSCT), with similarities in histopathological features and clinical manifestations. However, there are differences in the contributory factors and clinical trajectories between the two conditions. BOS after HSCT occurs due to systemic graft-versus-host-disease (GVHD), whereas BOS after lung transplantation is limited to the lung allograft. BOS diagnosis after HSCT is more challenging, as the lung function decline may occur due to extrapulmonary GVHD, causing sclerosis or inflammation in the fascia or muscles of the respiratory girdle. Treatment is generally empirical with no established effective therapies. This review provides rare insights and commonalities of both conditions, that are not well elaborated elsewhere in contemporary literature, and highlights the importance of cross disciplinary learning from experts in other transplant modalities. Treatment algorithms for each condition are presented, based on the published literature and consensus clinical opinion. Immunosuppression should be optimised, and other conditions or contributory factors treated where possible. When initial treatment fails, the ultimate therapeutic option is lung transplantation (or re-transplantation in the case of BOS after lung transplantation) in carefully selected candidates. Novel therapies under investigation include aerosolised liposomal cyclosporine, Janus kinase inhibitors, antifibrotic therapies, and (in patients with BOS after lung transplantation) B-cell–directed therapies. Effective novel treatments that have a tangible impact on survival and thereby avoid the need for lung transplantation or re-transplantation are urgently required.

Chronic Lung Allograft Dysfunction

Chronic lung allograft dysfunction (CLAD) is a syndrome of progressive lung function decline, subcategorized into obstructive, restrictive, and mixed phenotypes. The trajectory of CLAD is variable depending on the phenotype, with restrictive and mixed phenotypes having more rapid progression and lower survival. The mechanisms driving CLAD development remain unclear, though allograft injury during primary graft dysfunction, acute cellular rejection, antibody-mediated rejection, and infections trigger immune responses with long-lasting effects that can lead to CLAD months or years later. Currently, retransplantation is the only effective treatment.

Ambient Air Pollution and Adverse Waitlist Events Among Lung Transplant Candidates

BACKGROUND

Air pollution is associated with cardiopulmonary disease and death in the general population. Fine particulate matter (PM2.5) is particularly harmful due to its ability to penetrate into areas of gas exchange within the lungs. Persons with advanced lung disease are believed to be particularly susceptible to PM2.5 exposure, but only a few studies have examined the effect of exposure on this population. Here we investigate the association between PM2.5 exposure and adverse waitlist events among lung transplant (LT) candidates.

METHODS

US registry data were used to identify LT candidates listed between January 1, 2010 and December 31, 2016. Annual PM2.5 concentration at year of listing was estimated for each candidate's ZIP Code using National Aeronautics and Space Administration's (NASA) Socioeconomic Data and Applications Center Global Annual PM2.5 Grids. We estimated crude and adjusted hazard ratios for adverse waitlist events, defined as death or removal, using Cox proportional hazards regression.

RESULTS

Of the 15 075 included candidates, median age at listing was 60, 43.8% were female individuals, and 81.7% were non-Hispanic White. Median ZIP Code PM2.5 concentration was 9.06 µg/m3. When compared with those living in ZIP Codes with lower PM2.5 exposure (PM2.5 <10.53 µg/m3), candidates in ZIP Codes in the highest quartile of PM2.5 exposure (≥10.53 µg/m3) had 1.14-fold (95% confidence interval, 1.04-1.25) risk of adverse waitlist events. The result remained significant after adjusting for demographics, education, insurance, smoking, lung allocation score, body mass index, and blood type (hazard ratio, 1.17; 95% confidence interval, 1.07-1.29).

CONCLUSIONS

Elevated ambient PM2.5 concentration was associated with adverse waitlist events among LT candidates. These findings highlight the impact of air pollution on clinical outcomes in this critically ill population.

Acute Rejection in the Modern Lung Transplant Era

Acute cellular rejection (ACR) remains a common complication after lung transplantation. Mortality directly related to ACR is low and most patients respond to first-line immunosuppressive treatment. However, a subset of patients may develop refractory or recurrent ACR leading to an accelerated lung function decline and ultimately chronic lung allograft dysfunction. Infectious complications associated with the intensification of immunosuppression can also negatively impact long-term survival. In this review, we summarize the most recent evidence on the mechanisms, risk factors, diagnosis, treatment, and prognosis of ACR. We specifically focus on novel, promising biomarkers which are under investigation for their potential to improve the diagnostic performance of transbronchial biopsies. Finally, for each topic, we highlight current gaps in knowledge and areas for future research.

Chronic Lung Allograft Dysfunction: Evolving Concepts and Therapies

The primary factor that limits long-term survival after lung transplantation is chronic lung allograft dysfunction (CLAD). CLAD also impairs quality of life and increases the costs of medical care. Our understanding of CLAD continues to evolve. Consensus definitions of CLAD and the major CLAD phenotypes were recently updated and clarified, but it remains to be seen whether the current definitions will lead to advances in management or impact care. Understanding the potential differences in pathogenesis for each CLAD phenotype may lead to novel therapeutic strategies, including precision medicine. Recognition of CLAD risk factors may lead to earlier interventions to mitigate risk, or to avoid risk factors all together, to prevent the development of CLAD. Unfortunately, currently available therapies for CLAD are usually not effective. However, novel therapeutics aimed at both prevention and treatment are currently under investigation. We provide an overview of the updates to CLAD-related terminology, clinical phenotypes and their diagnosis, natural history, pathogenesis, and potential strategies to treat and prevent CLAD.

Clinical outcomes associated with long-term exposure to airborne particulate pollution in kidney transplant recipients

BACKGROUND

Researchers have yet to investigate the specific association between 10-μm particulate matter (PM10) levels and the risk of graft failure, kidney disease, or the functional decline of transplanted kidneys, in kidney transplant recipients (KTRs). Furthermore, we know very little about the association between PM10 levels and the development of allograft rejection in transplanted kidneys. Identification of air pollution as a potential contributor to kidney disease could help reduce future disease burden, stimulate policy discussions on the importance of reducing air pollution with respect to health and disease, and increase public awareness of the hazards of air pollution. We aimed to evaluate the relationship of PM10 with the risk of graft failure, mortality, and decline of graft function in KTRs.

METHODS

Air pollutant data were obtained from the Korean National Institute of Environmental Research. We then investigated potential associations between these data and the clinical outcomes of 1532 KTRs who underwent kidney transplantation in a tertiary hospital between 2001 and 2015. Survival models were used to evaluate the association between PM10 concentrations and the risk of death-censored graft failure (DCGF), all-cause mortality, and biopsy-proven rejection (BPR), over a median follow-up period of 6.31 years.

RESULTS

The annual mean PM10 exposure after kidney transplantation was 27.1 ± 8.0 μg/m3. Based on 1-year baseline exposure, 1 μg/m3 increase in PM10 concentration was associated with an increased risk of DCGF (hazard ratio (HR): 1.049; 95% confidence interval (CI): 1.014-1.084) and BPR (HR: 1.053; 95% CI: 1.042-1.063). Fully adjusted models showed that all-cause mortality was significantly associated with 1-year average PM10 concentrations (HR, 1.09; 95% CI, 1.043 to 1.140).

CONCLUSIONS

Long-term PM10 exposure is significantly associated with BPR, DCGF, and all-cause mortality in KTRs.

Chronic lung allograft dysfunction small airways reveal a lymphocytic inflammation gene signature

Chronic lung allograft dysfunction (CLAD) is the major barrier to long-term survival following lung transplantation, and new mechanistic biomarkers are needed. Lymphocytic bronchitis (LB) precedes CLAD and has a defined molecular signature. We hypothesized that this LB molecular signature would be associated with CLAD in small airway brushings independent of infection. We quantified RNA expression from small airway brushings and transbronchial biopsies, using RNAseq and digital RNA counting, respectively, for 22 CLAD cases and 27 matched controls. LB metagene scores were compared across CLAD strata by Wilcoxon rank sum test. We performed unbiased host transcriptome pathway and microbial metagenome analysis in airway brushes and compared machine-learning classifiers between the two tissue types. This LB metagene score was increased in CLAD airway brushes (p = .002) and improved prediction of graft failure (p = .02). Gene expression classifiers based on airway brushes outperformed those using transbronchial biopsies. While infection was associated with decreased microbial alpha-diversity (p ≤ .04), neither infection nor alpha-diversity was associated with LB gene expression. In summary, CLAD was associated with small airway gene expression changes not apparent in transbronchial biopsies in this cohort. Molecular analysis of airway brushings for diagnosing CLAD merits further examination in multicenter cohorts.

The role of innate immunity in the long-term outcome of lung transplantation

Long-term survival after lung transplantation remains suboptimal due to chronic lung allograft dysfunction (CLAD), a progressive scarring process affecting the graft. Although anti-donor alloimmunity is central to the pathogenesis of CLAD, its underlying mechanisms are not fully elucidated and it is neither preventable nor treatable using currently available immunosuppression. Recent evidence has shown that innate immune stimuli are fundamental to the development of CLAD. Here, we examine long-standing assumptions and new concepts linking innate immune activation to late lung allograft fibrosis.

Gene signatures common to allograft rejection are associated with lymphocytic bronchitis

Lymphocytic bronchitis (LB) precedes chronic lung allograft dysfunction. The relationships of LB (classified here as Endobronchial or E-grade rejection) to small airway (A- and B-grade) pathologies are unclear. We hypothesized that gene signatures common to allograft rejection would be present in LB. We studied LB in two partially overlapping lung transplant recipient cohorts: Cohort 1 included large airway brushes (6 LB cases and 18 post-transplant referents). Differential expression using DESeq2 was used for pathway analysis and to define an LB-associated metagene. In Cohort 2, eight biopsies for each pathology subtype were matched with pathology-free biopsies from the same subject (totaling 48 samples from 24 subjects). These biopsies were analyzed by multiplexed digital counting of immune transcripts. Metagene score differences were compared by paired t tests. Compared to referents in Cohort 1, LB demonstrated upregulation of allograft rejection pathways, and upregulated genes in these cases characterized an LB-associated metagene. We observed statistically increased expression in Cohort 2 for this LB-associated metagene and four other established allograft rejection metagenes in rejection vs paired non-rejection biopsies for both E-grade and A-grade subtypes, but not B-grade pathology. Gene expression-based categorization of allograft rejection may prove useful in monitoring lung allograft health.

Impact of Allograft Injury Time of Onset on the Development of Chronic Lung Allograft Dysfunction After Lung Transplantation

The impact of allograft injury time of onset on the risk of chronic lung allograft dysfunction (CLAD) remains unknown. We hypothesized that episodes of late-onset (≥6 months) allograft injury would produce an augmented CXCR3/ligand immune response, leading to increased CLAD. In a retrospective single-center study, 1894 transbronchial biopsy samples from 441 lung transplant recipients were reviewed for the presence of acute rejection (AR), lymphocytic bronchiolitis (LB), diffuse alveolar damage (DAD), and organizing pneumonia (OP). The association between the time of onset of each injury pattern and CLAD was assessed by using multivariable Cox models with time-dependent covariates. Bronchoalveolar lavage (BAL) CXCR3 ligand concentrations were compared between early- and late-onset injury patterns using linear mixed-effects models. Late-onset DAD and OP were strongly associated with CLAD: adjusted hazard ratio 2.8 (95% confidence interval 1.5-5.3) and 2.0 (1.1-3.4), respectively. The early-onset form of these injury patterns did not increase CLAD risk. Late-onset LB and acute rejection (AR) predicted CLAD in univariable models but lost significance after multivariable adjustment for late DAD and OP. AR was the only early-onset injury pattern associated with CLAD development. Elevated BAL CXCR3 ligand concentrations during late-onset allograft injury parallel the increase in CLAD risk and support our hypothesis that late allograft injuries result in a more profound CXCR3/ligand immune response.

Modeling the Effect of the Aryl Hydrocarbon Receptor on Transplant Immunity

Background

Exposure to pollutants through inhalation is a risk factor for lung diseases including cancer, asthma, and lung transplant rejection, but knowledge of the effects of inhaled pollutants on pathologies outside of the lung is limited.

Methods

Using the minor-mismatched model of male C57BL/6J (B6) to female B6 skin grafts, recipient mice were treated with an inhaled urban dust particle sample every 3 days before and after grafting. Graft survival time was determined, and analysis of the resulting immune response was performed at time before rejection.

Results

Significant prolongation of male skin grafts occurred in recipient female mice treated with urban dust particles compared with controls and was found to be dependent on aryl hydrocarbon receptor (AHR) expression in the recipient mouse. T cell responses to the male histocompatibility antigen (H-Y) Dby were not altered by exposure to pollutants. A reduction in the frequency of IFNγ-producing CD4 T cells infiltrating the graft on day 7 posttransplant was observed. Flow cytometry analysis revealed that AHR expression is upregulated in IFNγ-producing CD4 T cells during immune responses in vitro and in vivo.

Conclusions

Surprisingly, inhalation of a pollutant standard was found to prolong graft survival in a minor-mismatched skin graft model in an AHR-dependent manner. One possible mechanism may be an effect on IFNγ-producing CD4 T cells responding to donor antigen. The increased expression of AHR in this CD4 T cell subset suggests that AHR ligands within the particulate matter may be directly affecting the type 1 T helper cell response in this model.

Chronic effects of air pollution on lung function after lung transplantation in the Systems prediction of Chronic Lung Allograft Dysfunction (SysCLAD) study

An irreversible loss in lung function limits the long-term success in lung transplantation. We evaluated the role of chronic exposure to ambient air pollution on lung function levels in lung transplant recipients (LTRs).The lung function of 520 LTRs from the Cohort in Lung Transplantation (COLT) study was measured every 6 months. The levels of air pollutants (nitrogen dioxide (NO₂), particulate matter with an aerodynamic cut-off diameter of x µm (PM_x) and ozone (O₃)) at the patients' home address were averaged in the 12 months before each spirometry test. The effects of air pollutants on forced expiratory volume in 1 s (FEV₁) and forced vital capacity (FVC) in % predicted were estimated using mixed linear regressions. We assessed the effect modification of macrolide antibiotics in this relationship.Increased 12-month levels of pollutants were associated with lower levels of FVC % pred (-2.56%, 95% CI -3.86--1.25 for 5 µg·m^-3 of PM₁₀; -0.75%, 95% CI -1.38--0.12 for 2 µg·m^-3 of PM_2.5 and -2.58%, 95% CI -4.63--0.53 for 10 µg·m^-3 of NO₂). In patients not taking macrolides, the deleterious association between PM and FVC tended to be stronger and PM₁₀ was associated with lower FEV₁Our study suggests a deleterious effect of chronic exposure to air pollutants on lung function levels in LTRs, which might be modified with macrolides.

An association of particulate air pollution and traffic exposure with mortality after lung transplantation in Europe

Air pollution from road traffic is a serious health risk, especially for susceptible individuals. Single-centre studies showed an association with chronic lung allograft dysfunction (CLAD) and survival after lung transplantation, but there are no large studies.13 lung transplant centres in 10 European countries created a cohort of 5707 patients. For each patient, we quantified residential particulate matter with aerodynamic diameter ≤10 µm (PM₁₀) by land use regression models, and the traffic exposure by quantifying total road length within buffer zones around the home addresses of patients and distance to a major road or freeway.After correction for macrolide use, we found associations between air pollution variables and CLAD/mortality. Given the important interaction with macrolides, we stratified according to macrolide use. No associations were observed in 2151 patients taking macrolides. However, in 3556 patients not taking macrolides, mortality was associated with PM₁₀ (hazard ratio 1.081, 95% CI 1.000-1.167); similarly, CLAD and mortality were associated with road lengths in buffers of 200-1000 and 100-500 m, respectively (hazard ratio 1.085- 1.130). Sensitivity analyses for various possible confounders confirmed the robustness of these associations.Long-term residential air pollution and traffic exposure were associated with CLAD and survival after lung transplantation, but only in patients not taking macrolides.

Environmental Exposures-The Missing Link in Immune Responses After Transplantation

In transplantation, immunosuppression has been directed at controlling acute responses, but treatment of chronic rejection has been ineffective. It is possible that factors that have previously been unaccounted for, such as exposure to inhaled pollution, ultraviolet light, or loss of the normal equilibrium between the gut immune system and the outside environment may be responsible for shifting immune responses to an effector/inflammatory phenotype, which leads to loss of self-tolerance and graft acceptance, and a shift towards autoimmunity and chronic rejection. Cells of the immune system are in a constant balance of effector response, regulation, and quiescence. Endogenous and exogenous signals can shift this balance through the aryl hydrocarbon receptor, which serves as a thermostat to modulate the response one way or the other, both at mucosal surfaces of interface organs to the outside environment, and in the internal milieu. Better understanding of this balance will identify a target for maintenance of self-tolerance and continued graft acceptance in patients who have achieved a "steady state" after transplantation.

Chronic lung allograft dysfunction: evolving practice

PURPOSE OF REVIEW

Chronic lung allograft dysfunction (CLAD) was recently introduced as an overarching term covering different phenotypes of chronic allograft dysfunction, including obstructive CLAD (bronchiolitis obliterans syndrome), restrictive CLAD (restrictive allograft syndrome) and graft dysfunction due to causes not related to chronic rejection. In the present review, we will highlight the latest insights and current controversies regarding the new CLAD terminology, underlying pathophysiologic mechanisms, diagnostic approach and possible treatment options.

RECENT FINDINGS

Different pathophysiological mechanisms are clearly involved in clinically distinct phenotypes of chronic rejection, as is reflected by differences in histology, allograft function and imaging. Therefore, not all CLAD patients may equally benefit from specific therapies.

SUMMARY

The recent introduction of CLAD importantly changed the clinical practice in lung transplant recipients. Given the relative low accuracy of the current diagnostic tools, future research should focus on specific biomarkers, more sensitive pulmonary function parameters and imaging techniques for timely CLAD diagnosis and phenotyping. Personalized or targeted therapeutic options for adequate prevention and treatment of CLAD are required.

Air pollution and the development of posttransplant chronic lung allograft dysfunction

Chronic lung allograft dysfunction (CLAD) is the leading cause of mortality following lung transplantation. We conducted a retrospective cohort study including 397 bilateral lung recipients transplanted in from 1996 to 2009 to determine the association between ambient air pollution, CLAD and mortality. Pollution exposure was assessed using satellite-based estimates of nitrogen dioxide, distance to major roadway and total length of roadways around a patient's home. Cumulative exposures to ozone and particulate matter were estimated from concentrations measured at fixed-site stations near patients' homes using inverse distance weighted interpolation. Cox proportional hazards models were used to estimate the associations of CLAD with air pollution exposure, adjusting for various individual and neighborhood characteristics. During the follow-up, 185 patients developed CLAD (47%) and 101 patients died (25%). Fifty-four deaths (53%) were due to CLAD. We observed an association between CLAD development and road density within 200 m of a patient's home (HR 1.30 [95% CI 1.07-1.58]). Although based on a subgroup of 14 patients, living within 100 m of a highway was associated with a high risk for developing CLAD (HR 4.91 [95% CI 2.22, 10.87]). These data suggest that exposure to traffic-related air pollution is associated with development of CLAD among lung transplant recipients.

Azithromycin and the treatment of lymphocytic airway inflammation after lung transplantation

Lymphocytic airway inflammation is a major risk factor for chronic lung allograft dysfunction, for which there is no established treatment. We investigated whether azithromycin could control lymphocytic airway inflammation and improve allograft function. Fifteen lung transplant recipients demonstrating acute allograft dysfunction due to isolated lymphocytic airway inflammation were prospectively treated with azithromycin for at least 6 months (NCT01109160). Spirometry (FVC, FEV1 , FEF25-75 , Tiffeneau index) and FeNO were assessed before and up to 12 months after initiation of azithromycin. Radiologic features, local inflammation assessed on airway biopsy (rejection score, IL-17(+)  cells/mm(2) lamina propria) and broncho-alveolar lavage fluid (total and differential cell counts, chemokine and cytokine levels); as well as systemic C-reactive protein levels were compared between baseline and after 3 months of treatment. Airflow improved and FeNO decreased to baseline levels after 1 month of azithromycin and were sustained thereafter. After 3 months of treatment, radiologic abnormalities, submucosal cellular inflammation, lavage protein levels of IL-1β, IL-8/CXCL-8, IP-10/CXCL-10, RANTES/CCL5, MIP1-α/CCL3, MIP-1β/CCL4, Eotaxin, PDGF-BB, total cell count, neutrophils and eosinophils, as well as plasma C-reactive protein levels all significantly decreased compared to baseline (p < 0.05). Administration of azithromycin was associated with suppression of posttransplant lymphocytic airway inflammation and clinical improvement in lung allograft function.

The aryl hydrocarbon receptor meets immunology: friend or foe? A little of both

The aryl hydrocarbon receptor (AHR) has long been studied by toxicologists as a ligand-activated transcription factor that is activated by dioxin and other environmental pollutants such as polycyclic aromatic hydrocarbons (PAHs). The hallmark of AHR activation is the upregulation of the cytochrome P450 enzymes that metabolize many of these toxic compounds. However, recent findings demonstrate that both exogenous and endogenous AHR ligands can alter innate and adaptive immune responses including effects on T-cell differentiation. Kynurenine, a tryptophan breakdown product, is one such endogenous ligand of the AHR. Expression of indoleamine 2,3-dioxygenase by dendritic cells causes accumulation of kynurenine and results in subsequent tolerogenic effects including increased regulatory T-cell activity. At the same time, PAHs found in pollution enhance Th17 differentiation in the lungs of exposed mice via the AHR. In this perspective, we will discuss the importance of the AHR in the immune system and the role this might play in normal physiology and response to disease.

Pre-transplant impedance measures of reflux are associated with early allograft injury after lung transplantation

BACKGROUND

Acid reflux has been associated with poorer outcomes after lung transplantation. Standard pre-transplant reflux assessment has not been universally adopted. Non-acid reflux may also induce a pulmonary inflammatory cascade, leading to acute and chronic rejection. Esophageal multichannel intraluminal impedance and pH testing (MII-pH) may be valuable in standard pre-transplant evaluation. We assessed the association between pre-transplant MII-pH measures and early allograft injury in lung transplant patients.

METHODS

This was a retrospective cohort study of lung transplant recipients who underwent pre-transplant MII-pH at a tertiary center from 2007 to 2012. Results from pre-transplant MII-pH, cardiopulmonary function testing, and results of biopsy specimen analysis of the transplanted lung were recorded. Time-to-event analyses were performed using Cox proportional hazards and Kaplan-Maier methods to assess the associations between MII-pH measures and development of acute rejection or lymphocytic bronchiolitis.

RESULTS

Thirty patients (46.7% men; age, 54.2 years) met the inclusion criteria. Pre-transplant cardiopulmonary function and pulmonary diagnoses were similar between outcome groups. Prolonged bolus clearance (hazard ratio [HR], 4.11; 95% confidence interval [CI], 1.34-12.57; p = 0.01), increased total distal reflux episodes (HR, 4.80; 95% CI, 1.33-17.25; p = 0.02), and increased total proximal reflux episodes (HR, 4.43; 95% CI, 1.14-17.31; p = 0.03) were significantly associated with decreased time to early allograft injury. Kaplan-Meier curves also demonstrated differences in time to rejection by prolonged bolus clearance (p = 0.01) and increased total distal reflux episodes (p = 0.01). Sub-group analysis including only patients with MII-pH performed off proton pump inhibitors (n = 24) showed similar results.

CONCLUSIONS

Prolonged bolus clearance, increased total distal reflux episodes, and increased total proximal reflux episodes on pre-transplant MII-pH were associated with decreased time to early allograft injury after lung transplantation. Routine pre-transplant MII-pH may provide clinically relevant data regarding transplant outcomes and peri-transplant care.

Three-year results of an investigator-driven multicenter, international, randomized open-label de novo trial to prevent BOS after lung transplantation

BACKGROUND

Chronic lung allograft dysfunction (CLAD), predominantly manifest as bronchiolitis obliterans syndrome (BOS), is the primary cause of morbidity and death after lung transplantation. We assessed the efficacy and safety of 2 de novo immunosuppression protocols to prevent BOS.

METHODS

This was a multicenter, prospective, international, randomized (1:1) open-label superiority study of de novo enteric-coated mycophenolate sodium (MPS) vs delayed-onset everolimus (RAD), both arms in combination with cyclosporine (CsA) monitored by 2-hour post-dose (C2) levels, and corticosteroids. Target C2 levels were lower in the RAD group because RAD is known to potentiate CsA nephrotoxicity. Cytolytic induction therapy was not used. Patients were stratified at entry for cystic fibrosis. Confirmation of anastomotic healing was required for randomization. Primary efficacy was freedom from BOS Grade 1 on intention-to-treat (ITT) analysis. Secondary efficacy parameters were patient and graft survival and severity of rejection. Treatment failure was defined by graft loss, patient death, drug cessation, or need for other therapy.

RESULTS

The 3-year freedom from BOS Grade 1 was 70% for MPS (n = 80) vs 71% for RAD (n = 84; p = 0.95 by log-rank) in ITT but was lower in the RAD arm of the per-protocol population (p = 0.03). The 3-year survival was 84% (MPS) vs 76% (RAD; p = 0.19 by log-rank). Thirteen patients switched from MPS vs 31 from RAD (p < 0.01). Days on MPS were greater than days on RAD (p < 0.01). Rejection events proven by biopsy specimen were more common on MPS (p = 0.02), as were leucopenia (p < 0.01), diarrhea (p < 0.01), and cytomegalovirus infection (p = 0.04). Venous thromboembolism was more frequent on RAD (p = 0.02). Creatinine at 3 years was 160 ± 112 μmol/1iter in MPS patients vs 152 ± 98 μmol/1iter in RAD patients (p = 0.67).

CONCLUSIONS

This 3-year ITT analysis found no significant difference between arms but was underpowered to accept the null hypothesis that RAD and MPS have equivalent efficacy in preventing BOS or death after lung transplantation.

CXCR3 ligands are associated with the continuum of diffuse alveolar damage to chronic lung allograft dysfunction

RATIONALE

After lung transplantation, insults to the allograft generally result in one of four histopathologic patterns of injury: (1) acute rejection, (2) lymphocytic bronchiolitis, (3) organizing pneumonia, and (4) diffuse alveolar damage (DAD). We hypothesized that DAD, the most severe form of acute lung injury, would lead to the highest risk of chronic lung allograft dysfunction (CLAD) and that a type I immune response would mediate this process.

OBJECTIVES

Determine whether DAD is associated with CLAD and explore the potential role of CXCR3/ligand biology.

METHODS

Transbronchial biopsies from all lung transplant recipients were reviewed. The association between the four injury patterns and subsequent outcomes were evaluated using proportional hazards models with time-dependent covariates. Bronchoalveolar lavage (BAL) concentrations of the CXCR3 ligands (CXCL9/MIG, CXCL10/IP10, and CXCL11/ITAC) were compared between allograft injury patterns and "healthy" biopsies using linear mixed-effects models. The effect of these chemokine alterations on CLAD risk was assessed using Cox models with serial BAL measurements as time-dependent covariates.

MEASUREMENTS AND MAIN RESULTS

There were 1,585 biopsies from 441 recipients with 62 episodes of DAD. An episode of DAD was associated with increased risk of CLAD (hazard ratio, 3.0; 95% confidence interval, 1.9-4.7) and death (hazard ratio, 2.3; 95% confidence interval, 1.7-3.0). There were marked elevations in BAL CXCR3 ligand concentrations during DAD. Furthermore, prolonged elevation of these chemokines in serial BAL fluid measurements predicted the development of CLAD.

CONCLUSIONS

DAD is associated with marked increases in the risk of CLAD and death after lung transplantation. This association may be mediated in part by an aberrant type I immune response involving CXCR3/ligands.

Exposure to atmospheric particulate matter enhances Th17 polarization through the aryl hydrocarbon receptor

Lung diseases, including asthma, COPD, and other autoimmune lung pathologies are aggravated by exposure to particulate matter (PM) found in air pollution. IL-17 has been shown to exacerbate airway disease in animal models. As PM is known to contain aryl hydrocarbon receptor (AHR) ligands and the AHR has recently been shown to play a role in differentiation of Th17 T cells, the aim of this study was to determine whether exposure to PM could impact Th17 polarization in an AHR-dependent manner. This study used both cell culture techniques and in vivo exposure in mice to examine the response of T cells to PM. Initially experiments were conducted with urban dust particles from a standard reference material, and ultimately repeated with freshly collected samples of diesel exhaust and cigarette smoke. The readout for the assays was increased T cell differentiation as indicated by increased generation of IL-17A in culture, and increased populations of IL-17 producing cells by intracellular flow cytometry. The data illustrate that Th17 polarization was significantly enhanced by addition of urban dust in a dose dependent fashion in cultures of wild-type but not AHR^-/- mice. The data further suggest that polycyclic aromatic hydrocarbons played a primary role in this enhancement. There was both an increase of Th17 cell differentiation, and also an increase in the amount of IL-17 secreted by the cells. In summary, this paper identifies a novel mechanism whereby PM can directly act on the AHR in T cells, leading to enhanced Th17 differentiation. Further understanding of the molecular mechanisms responsible for pathologic Th17 differentiation and autoimmunity seen after exposure to pollution will allow direct targeting of proteins involved in AHR activation and function for treatment of PM exposures.

Bronchiolitis obliterans syndrome and restrictive allograft syndrome: do risk factors differ?

BACKGROUND

Chronic rejection is the major problem hampering long-term survival after lung transplantation. Recently, it became clear that patients may develop an obstructive (bronchiolitis obliterans syndrome [BOS]) or a restrictive lung function defect (restrictive allograft syndrome [RAS]), for which specific risk factors are unknown.

METHODS

A retrospective analysis of our lung transplantation cohort was performed (n=380). Patients with an irreversible decline in forced expiratory volume in 1 second were identified and classified as BOS or RAS. Patient characteristics, bronchoalveolar lavage (BAL) cellularity, rates of respiratory tract infection, colonization, acute rejection, and lymphocytic bronchiolitis were compared between BOS, RAS, and stable patients.

RESULTS

There were 103 patients suffering from chronic rejection, of which 79 had BOS and 24 were diagnosed with RAS. There were more patients with infection and pseudomonal colonizations in BOS and RAS compared with control (P=0.0090 and P=0.0034, respectively). More patients ever experienced acute and severe acute rejections (A≥2; both P<0.0001) and lymphocytic bronchiolitis (P=0.0006) in BOS and RAS versus control. There were more patients experiencing severe lymphocytic bronchiolitis in RAS compared with BOS (P=0.031). BAL neutrophilia in BOS and RAS were elevated at days 360, 540, and 720 versus control. BOS, but especially RAS patients, experienced more frequent episodes of increased BAL eosinophilia (≥2%; P<0.0001).

CONCLUSION

Acute rejection, lymphocytic bronchiolitis, colonization with pseudomonas, infection, and BAL eosinophilia and neutrophilia are risk factors for the later development not only of RAS but also of BOS.

The aryl hydrocarbon receptor: a novel target for immunomodulation in organ transplantation

The aryl hydrocarbon receptor (AHR), which has been central to studies in toxicology for years as the receptor for the toxicant dioxin, is rapidly gaining interest in immunology based on its ability to influence T-cell differentiation. Multiple studies have documented that binding of this receptor with certain ligands favors T-cell differentiation toward regulatory T cells, and paradoxically, binding of this same receptor with different ligands enhances Th17 effector cell differentiation. This finding has been confirmed in both in vitro and in vivo models, where different ligands are able to either ameliorate or conversely aggravate autoimmunity in experimental autoimmune encephalomyelitis. The AHR has both an endogenous role that is important in development and normal physiology and an exogenous role as a receptor for manmade toxicants, with their binding leading to transcription of cytochrome P450 enzymes that metabolize these same ligands. Based on recent reports that will be summarized in this overview, we will consider the role that the AHR might play as a sensor to the outside environment, leading to alteration of the acquired immune system that might have relevance in transplantation or other medical conditions. In addition to describing the data in normal physiology and T-cell differentiation, we will present examples of the importance of this receptor in preclinical models of disease and highlight specific ligands that target the AHR and will have efficacy in treating transplant rejection and in tolerance protocols.