Chronic lung allograft dysfunction: evolving practice

Lung transplantation: Current insights and outcomes

Until now, the ability to predict or retard immune-mediated rejection events after lung transplantation is still limited due to the lack of specific biomarkers. The pressing need remains to early diagnose or predict the onset of chronic lung allograft dysfunction (CLAD) and its differential phenotypes that is the leading cause of death. Omics technologies (mainly genomics, epigenomics, and transcriptomics) combined with advanced bioinformatic platforms are clarifying the key immune-related molecular routes that trigger early and late events of lung allograft rejection supporting the biomarker discovery. The most promising biomarkers came from genomics. Both unregistered and NIH-registered clinical trials demonstrated that the increased percentage of donor-derived cell-free DNA in both plasma and bronchoalveolar lavage fluid showed a good diagnostic performance for clinically silent acute rejection events and CLAD differential phenotypes. A further success arose from transcriptomics that led to development of Molecular Microscope® Diagnostic System (MMDx) to interpret the relationship between molecular signatures of lung biopsies and rejection events. Other immune-related biomarkers of rejection events may be exosomes, telomer length, DNA methylation, and histone-mediated neutrophil extracellular traps (NETs) but none of them entered in registered clinical trials. Here, we discuss novel and existing technologies for revealing new immune-mediated mechanisms underlying acute and chronic rejection events, with a particular focus on emerging biomarkers for improving precision medicine of lung transplantation field.

Thoracic Ultrasound in Lung Transplantation—Insights in the Field

The use of thoracic ultrasound (TUS) is a novel and dynamic diagnostic and monitoring modality that has shown remarkable advances within the last decade, with several published papers investigating its role within the field of lung transplantation. The aim of this current opinion review is to review the existing literature on the role of TUS in all stages of LTx, from in-donor lung evaluation to graft assessment on ex vivo lung perfusion and in the short- and long-term follow-up after LTx.

Immune processes in the pathogenesis of chronic lung allograft dysfunction: identifying the missing pieces of the puzzle

Lung transplantation is the optimal treatment for selected patients with end-stage chronic lung diseases. However, chronic lung allograft dysfunction remains the leading obstacle to improved long-term outcomes. Traditionally, lung allograft rejection has been considered primarily as a manifestation of cellular immune responses. However, in reality, an array of complex, interacting and multifactorial mechanisms contribute to its emergence. Alloimmune-dependent mechanisms, including T-cell-mediated rejection and antibody-mediated rejection, as well as non-alloimmune injuries, have been implicated. Moreover, a role has emerged for autoimmune responses to lung self-antigens in the development of chronic graft injury. The aim of this review is to summarise the immune processes involved in the pathogenesis of chronic lung allograft dysfunction, with advanced insights into the role of innate immune pathways and crosstalk between innate and adaptive immunity, and to identify gaps in current knowledge.

Small airway dilation measured by endoscopic optical coherence tomography correlates with chronic lung allograft dysfunction

SIGNIFICANCE

Chronic lung allograft dysfunction (CLAD) is the leading cause of death in transplant patients who survive past the first year post-transplant. Current diagnosis is based on sustained decline in lung function; there is a need for tools that can identify CLAD onset.

AIM

Endoscopic optical coherence tomography (OCT) can visualize structural changes in the small airways, which are of interest in CLAD progression. We aim to identify OCT features in the small airways of lung allografts that correlate with CLAD status.

APPROACH

Imaging was conducted with an endoscopic rotary pullback OCT catheter during routine bronchoscopy procedures (n  =  54), collecting volumetric scans of three segmental airways per patient. Six features of interest were identified, and four blinded raters scored the dataset on the presence and intensity of each feature.

RESULTS

Airway dilation (AD) was the only feature found to significantly (p  <  0.003) correlate with CLAD diagnosis (R  =  0.40 to 0.61). AD could also be fairly consistently scored between raters (κinter-rater  =  0.48, κintra-rater  =  0.64). There is a stronger relationship between AD and the combined obstructive and restrictive (BOS + RAS) phenotypes than the obstructive-only (BOS) phenotype for two raters (R  =  0.92  ,  0.94).

CONCLUSIONS

OCT examination of small AD shows potential as a diagnostic indicator for CLAD and CLAD phenotype and merits further exploration.

Importance of the preoperative prognostic nutritional index score as a predictor of chronic lung allograft dysfunction after lung transplantation: a Japanese single-institution study

PURPOSES

Numerous indicators have been discussed as predictive markers for the incidence of chronic allograft dysfunction (CLAD) after lung transplantation (LTX). The aim of this study was to evaluate whether or not the preoperative prognostic nutrition index (PNI) correlated with the development of CLAD.

METHOD

This study is a single-center and retrospective cohort study. Forty-six patients underwent cadaveric lung transplantation between 2000 and 2016 at our institution. The primary endpoint of this study was the CLAD-free survival of the patients.

RESULT

CLAD was diagnosed in 11 patients (23%) during the follow-up period. Potential risk factors included recipient factors, donor factors, number of HLA mismatches, operation-related factors, and preoperative blood test results, including the preoperative PNI. The patients with a higher PNI showed a longer CLAD-free survival after LTX than those with lower values according to univariate and multivariate analyses (p = 0.01, 0.04, respectively). The 5-year CLAD-free survival rates in the higher-PNI patients and lower-PNI patients were 94% and 62%, respectively.

CONCLUSION

We found that a lower preoperative PNI of the recipient was significantly associated with a higher incidence rate of CLAD. The preoperative PNI may, therefore, be useful as a predictor of the development of CLAD.

Lung Ultrasound to Phenotype Chronic Lung Allograft Dysfunction in Lung Transplant Recipients. A Prospective Observational Study

Background: Bronchiolitis obliterans syndrome (BOS) and restrictive allograft syndrome (RAS) are two distinct phenotypes of chronic lung allograft dysfunction (CLAD) in lung transplant (LTx) recipients. Contrary to BOS, RAS can radiologically present with a pleuroparenchymal fibroelastosis (PPFE) pattern. This study investigates lung ultrasound (LUS) to identify potential surrogate markers of PPFE in order to distinguish CLAD phenotype RAS from BOS. Methods: A prospective cohort study performed at a National Lung Transplantation Center during June 2016 to December 2017. Patients were examined with LUS and high-resolution computed tomography of the thorax (HRCT). Results: Twenty-five CLAD patients (72% males, median age of 54 years) were included, corresponding to 19/6 BOS/RAS patients. LUS-identified pleural thickening was more pronounced in RAS vs. BOS patients (5.6 vs. 2.9 mm) compatible with PPFE on HRCT. LUS-identified pleural thickening as an indicator of PPFE in RAS patients’ upper lobes showed a sensitivity of 100% (95% CI; 54–100%), specificity of 100% (95% CI; 82–100%), PPV of 100% (95% CI; 54–100%), and NPV of 100% (95% CI; 82–100%). Conclusion: Apical pleural thickening detected by LUS and compatible with PPFE on HRCT separates RAS from BOS in patients with CLAD. We propose LUS as a supplementary tool for initial CLAD phenotyping.

[Fibrotic remodeling of the lung following lung and stem-cell transplantation]

Transplantation of solid organs and hematopoietic stem cells represents an important therapeutic option for a variety of end-stage pulmonary diseases, aggressive hematopoietic neoplasms, or severe immunodeficiencies. Although the overall survival following transplantation has generally improved over recent decades, long-time survival of lung and stem-cell transplant recipients is still alarmingly low with an average 5‑year survival rate of only 50-60%. Chronic allo-immunoreactions in general and pulmonary allo-immunoreactions with subsequent fibrosis in particular are major reasons for this poor outcome. Comparable patterns of fibrotic lung remodeling are observed following both lung and hematopoietic stem-cell transplantation. Besides the meanwhile well-established obliterative and functionally obstructive remodeling of the small airways - obliterative bronchiolitis - a specific restrictive subform of fibrosis, namely alveolar fibroelastosis, has been identified. Despite their crucial impact on patient outcome, both entities can be very challenging to detect by conventional histopathological analysis. Their underlying mechanisms are considered overreaching aberrant repair attempts to acute lung injuries with overactivation of (myo-) fibroblasts and excessive and irreversible deposition of extracellular matrix. Of note, the underlying molecular mechanisms are widely divergent between these two morphological entities and are independent of the underlying clinical setting.Further comprehensive investigations of these fibrotic alterations are key to the development of much-needed predictive diagnostics and curative concepts, considering the high mortality of pulmonary fibrosis following transplantation.

Lung Transplant Pathology: An Overview on Current Entities and Procedures

Alloimmune reactions are, besides various infections, the major cause for impaired lung allograft function following transplant. Acute cellular rejection is not only a major trigger of acute allograft failure but also contributes to development of chronic lung allograft dysfunction. Analogous to other solid organ transplants, acute antibody-mediated rejection has become a recognized entity in lung transplant pathology. Adequate sensitivity and specificity in the diagnosis of alloimmune reactions in the lung can only be achieved by synoptic analysis of histopathologic, clinical, and radiological findings together with serologic and microbiologic findings.

Noninvasive methods for detection of chronic lung allograft dysfunction in lung transplantation

Lung transplantation (LTx) is the only therapeutic option for end-stage lung diseases. Chronic lung allograft dysfunction (CLAD), which manifests as airflow restriction and/or obstruction, is the primary factor limiting the long-term survival of patients after surgery. According to histopathological and radiographic findings, CLAD comprises two phenotypes, bronchiolitis obliterans syndrome and restrictive allograft syndrome. Half of all lung recipients will develop CLAD in 5 years, and this rate may increase up to 75% 10 years after surgery owing to the paucity in accurate and effective early detection and treatment methods. Recently, many studies have presented noninvasive methods for detecting CLAD and improving diagnosis and intervention. However, the significance of accurately detecting CLAD remains controversial. We reviewed published studies that have presented noninvasive methods for detecting CLAD to highlight the current knowledge on clinical symptoms, spirometry, imaging examinations, and other methods to detect the disease.

Bone Marrow-derived Mesenchymal Stem Cells and Chronic Allograft Disease in a Bronchiolitis Obliterans Animal Model

INTRODUCTION

Bronchiolitis obliterans (BO) is the most common expression of chronic allograft dysfunction in lung transplantation. Moreover, BO represents the major cause of death in the long-term after this procedure. On the other hand, mesenchymal stem cells have been tested in animal models of BO aiming to interfere in its development. The aim of this experimental study is to explore the role of bone-marrow derived stem cells (BMSCs) as a preventive intervention of BO occurrence.

MATERIALS AND METHODS

This an experimental randomized study. A bronchiolitis obliterans animal model in rats was reproduced: heterotopical tracheal transplant model in lung parenchyma. Five of these animals were used as control group. After setting up the model, individuals were divided in 3 groups of treatment (n=15), in which BMSCs were administered in 3 different time points after the tracheal transplant (tracheal transplantation and BMSCs administration occurred the same day, group G0; after 7 days, group G7; after 14 days, group G14. In addition, within each group, BMSCs were administered through 3 different routes: endotracheally, endovascular and topically in the lung parenchyma). Animals were sacrificed at 21 days. Histology, fluorescence in situ hybridization and immunohistochemistry techniques were performed for identifying stem cells.

RESULTS

Compared to control group, animals receiving BMSCs showed large neovessels in a loose fibrous matrix. Group G7 showed less fibrosis (p<0.033) and edema (p<0.028). Moreover, G7 animals receiving stem cells endotracheally showed no fibrosis (p<0.008). Alveolar-like patches of tissue were observed among all groups (53.4%, 46.7% and 40% in G0, G7 and G14 respectively), consisting of cells expressing both stem and alveolar cells biomarkers.

CONCLUSION

BMSCs modify the course of bronchiolitis obliterans and differentiate into alveolar cells. Endotracheal administration of BMSCs 7 days after the heterotopical tracheal transplant might be considered an effective way to prevent BO in this animal model.

Impact of human leukocyte antigen mismatch on lung transplant outcome

OBJECTIVES

Human leucocyte antigen (HLA) mismatch between donor and recipient has a differential impact on the outcome after transplant (Tx) among transplantable solid organs. Although the lung is considered a highly antigenic organ, the impact of HLA matching between the donor and the recipient has been shown to be heterogeneous on lung Tx outcome. To provide further evidence that HLA matching should be considered in the decision process prior to lung Tx, we evaluated the impact of donor/recipient HLA mismatch on the outcome after lung Tx at our institution.

METHODS

All patients who underwent lung Tx were analysed in this retrospective single-cohort study between 1994 and 2013 for HLA (-A, -B or -DR) matching between the donor and the recipient and their association with overall survival, the incidence of acute cellular rejection (ACR) and the development of chronic lung allograft dysfunction (CLAD).

RESULTS

In total, 371 (197 men) patients were included. Of these, 117 patients had no HLA match (0/6), 143 had a 1/6 match, 77 had 2/6 matches, 28 had 3/6 matches and 6 had 4/6 matches. One hundred and twenty-two (33%) patients experienced at least 1 episode of ACR and 172 (46%) patients developed CLAD. Univariate analysis showed a significant correlation between HLA mismatch and the development of CLAD, whereas multivariate analysis revealed that the number of HLA matches (hazard ratio 0.76; P = 0.002), antibodies to cytomegalovirus in either donors or recipients (hazard ratio 1.52; P = 0.036) and donor age (hazard ratio 1.03; P < 0.001) were independent risk factors for the development of CLAD. On the other hand, HLA matches did not correlate with the incidence of ACR and with the overall survival rate.

CONCLUSIONS

The number of HLA mismatches between donors and recipients after lung Tx did not correlate with ACR or with the overall survival. In contrast, HLA mismatch correlated with the development of CLAD and should therefore be considered a risk factor.

Pulmonary complications of influenza infection: a targeted narrative review

Severe influenza infection represents a leading cause of global morbidity and mortality. Several clinical syndromes that involve a number of organs may be associated with Influenza infection. However, lower respiratory complications remain the most common and serious sequel of influenza infection. These include influenza pneumonia, superinfection with bacteria and fungi, exacerbation of underlying lung disease and ARDS. This review analyzes the available literature on the epidemiology and clinical considerations of these conditions. It also provides an overview of the effects of type of influenza, antiviral therapy, vaccination and other therapies on the outcome of these complications.

Precision medicine: integration of genetics and functional genomics in prediction of bronchiolitis obliterans after lung transplantation

PURPOSE OF REVIEW

Lung transplantation (LTx) can be a life saving treatment in end-stage pulmonary diseases, but survival after transplantation is still limited. Posttransplant development of chronic lung allograft dysfunction with bronchiolits obliterans syndrome (BOS) as the major subphenotype, is the main cause of morbidity and mortality. Early identification of high-risk patients for BOS is a large unmet clinical need. In this review, we discuss gene polymorphisms and gene expression related to the development of BOS.

RECENT FINDINGS

Candidate gene studies showed that donor and recipient gene polymorphisms affect transplant outcome and BOS-free survival after LTx. Both selective and nonselective gene expression studies revealed differentially expressed fibrosis and apoptosis-related genes in BOS compared with non-BOS patients. Significantly, recent microarray expression analysis of blood and broncho-alveolar lavage suggest a role for B-cell and T-cell responses prior to the development of BOS. Furthermore, 6 months prior to the development of BOS differentially expressed genes were identified in peripheral blood cells.

SUMMARY

Genetic polymorphisms and gene expression changes are associated with the development of BOS. Future genome wide studies are needed to identify easily accessible biomarkers for prediction of BOS toward precision medicine.

Cell-Free DNA and CXCL10 Derived from Bronchoalveolar Lavage Predict Lung Transplant Survival

Standard methods for detecting chronic lung allograft dysfunction (CLAD) and rejection have poor sensitivity and specificity and have conventionally required bronchoscopies and biopsies. Plasma cell-free DNA (cfDNA) has been shown to be increased in various types of allograft injury in transplant recipients and CXCL10 has been reported to be increased in the lung tissue of patients undergoing CLAD. This study used a novel cfDNA and CXCL10 assay to evaluate the noninvasive assessment of CLAD phenotype and prediction of survival from bronchoalveolar lavage (BAL) fluid. A total of 60 BAL samples (20 with bronchiolitis obliterans (BOS), 20 with restrictive allograft syndrome (RAS), and 20 with stable allografts (STA)) were collected from 60 unique lung transplant patients; cfDNA and CXCL10 were measured by the ELISA-based KIT assay. Median cfDNA was significantly higher in BOS patients (6739 genomic equivalents (GE)/mL) versus STA (2920 GE/mL) and RAS (4174 GE/mL) (p < 0.01 all comparisons). Likelihood ratio tests revealed a significant association of overall survival with cfDNA (p = 0.0083), CXCL10 (p = 0.0146), and the interaction of cfDNA and CXCL10 (p = 0.023) based on multivariate Cox proportional hazards regression. Dichotomizing patients based on the median cfDNA level controlled for the mean level of CXCL10 revealed an over two-fold longer median overall survival time in patients with low levels of cfDNA. The KIT assay could predict allograft survival with superior performance compared with traditional biomarkers. These data support the pursuit of larger prospective studies to evaluate the predictive performance of cfDNA and CXCL10 prior to lung allograft failure.

Long-Term Outcomes of Adult Lung Transplantation Recipients: A Single-Center Experience in South Korea

Background

Recently, the number of lung transplants in South Korea has increased. However, the long-term outcome data is limited. In this study, we aimed to investigate the long-term outcomes of adult lung transplantation recipients.

Methods

Among the patients that underwent lung transplantation at a tertiary referral center in South Korea between 2008 and 2017, adults patient who underwent deceased-donor lung transplantation with available follow-up data were enrolled. Their medical records were retrospectively reviewed.

Results

Through eligibility screening, we identified 60 adult patients that underwent lung (n=51) or heart-lung transplantation (n=9) during the observation period. Idiopathic pulmonary fibrosis (46.7%, 28/60) was the most frequent cause of lung transplantation. For all the 60 patients, the median follow-up duration for post-transplantation was 2.6 years (range, 0.01–7.6). During the post-transplantation follow-up period, 19 patients (31.7%) died at a median duration of 194 days. The survival rates were 75.5%, 67.6%, and 61.8% at 1 year, 3 years, and 5 years, respectively. Out of the 60 patients, 8 (13.3%) were diagnosed with chronic lung allograft dysfunction (CLAD), after a mean duration of 3.3±2.8 years post-transplantation. The CLAD development rate was 0%, 17.7%, and 25.8% at 1 year, 3 years, and 5 years, respectively. The most common newly developed post-transplantation comorbidity was the chronic kidney disease (CKD; 54.0%), followed by diabetes mellitus (25.9%).

Conclusion

Among the adult lung transplantation recipients at a South Korea tertiary referral center, the long-term survival rates were favorable. The proportion of patients who developed CLAD was not substantial. CKD was the most common post-transplantation comorbidity.

Recent advances in lung transplantation

Lung transplantation can improve quality of life and prolong survival for individuals with end-stage lung disease, and many advances in the realms of both basic science and clinical research aspects of lung transplantation have emerged over the past few decades. However, many challenges must yet be overcome to increase post-transplant survival. These include successfully bridging patients to transplant, expanding the lung donor pool, inducing tolerance, and preventing a myriad of post-transplant complications that include primary graft dysfunction, forms of cellular and antibody-mediated rejection, chronic lung allograft dysfunction, and infections. The goal of this manuscript is to review salient recent and evolving advances in the field of lung transplantation.

Montelukast for bronchiolitis obliterans syndrome after lung transplantation: A randomized controlled trial

Bronchiolitis obliterans syndrome (BOS) remains the major problem which precludes long-term survival after lung transplantation. Previously, an open label pilot study from our group demonstrated a possible beneficial effect of montelukast in progressive BOS patients with low airway neutrophilia (<15%), and already on azithromycin treatment, in whom the further decline in pulmonary function was attenuated. This was, however, a non-randomized and non-placebo controlled trial. The study design is a single center, prospective, interventional, randomized, double blind, placebo-controlled trial, with a two arm parallel group design and an allocation ratio of 1:1. Randomization to additional montelukast (10 mg/day, n = 15) or placebo (n = 15) was performed from 2010 to 2014 at the University Hospitals Leuven (Leuven, Belgium) in all consecutive patients with late-onset (>2years posttransplant) BOS ≥1. Primary end-point was freedom from graft loss 1 year after randomization; secondary end-points were acute rejection, lymphocytic bronchiolitis, respiratory infection rate; and change in FEV₁, airway and systemic inflammation during the study period. Graft loss at 1 y and 2y was similar in both groups (respectively p = 0. 981 and p = 0.230). Montelukast had no effect on lung function decline in the overall cohort. However, in a post-hoc subanalysis of BOS stage 1 patients, montelukast attenuated further decline of FEV₁ during the study period, both in absolute (L) (p = 0.008) and % predicted value (p = 0.0180). A linear mixed model confirmed this association. Acute rejection, lymphocytic bronchiolitis, respiratory infections, systemic and airway inflammation were comparable between groups over the study period. This randomized controlled trial showed no additional survival benefit with montelukast compared to placebo, although the study was underpowered. The administration of montelukast was associated with an attenuation of the rate of FEV₁ decline, however, only in recipients with late-onset BOS stage 1.

Prevention of chronic rejection after lung transplantation

Long-term survival after lung transplantation (LTx) is limited by chronic rejection (CR). Therapeutic strategies for CR have been largely unsuccessful, making prevention of CR an important and challenging therapeutic approach. In the current review, we will discuss current clinical evidence regarding prevention of CR after LTx.

Multivariate modeling using quantitative CT metrics may improve accuracy of diagnosis of bronchiolitis obliterans syndrome after lung transplantation

BACKGROUND

To assess how quantitative CT (qCT) metrics compare to pulmonary function testing (PFT) and semi-quantitative image scores (SQS) to diagnose bronchiolitis obliterans syndrome (BOS), manifestation of chronic lung allograft dysfunction after lung transplantation (LTx), according to the type of LTx (unilateral or bilateral).

METHODS

Paired inspiratory-expiratory CT scans and PFTs of 176 LTx patients were analyzed retrospectively, and separated into BOS (78) and non-BOS (98) cohorts. SQS were assessed by 2 radiologists and graded (0-3) for features including mosaic attenuation and bronchiectasis. qCT metrics included lung volumes and air trapping volumes. Multivariate logistic regression (MVLR) and support vector machines (SVM) were used for the classification task.

RESULTS

MVLR and SVM models using PFT metrics demonstrated highest accuracy for bilateral LTx (max AUC 0.771), whereas models using qCT metrics-only outperformed models using SQS or PFTs in unilateral LTx (max AUC 0.817), to diagnose BOS. Adding PC (principal components) from qCT on top of PFT improved model diagnostic accuracy for all transplant types.

CONCLUSIONS

Combinations of qCT metrics augment the diagnostic performance of PFTs, are superior to SQS to predict BOS status, and outperform PFTs in the unilateral LTx group. This suggests that latent information on paired volumetric CT may allow early diagnosis of BOS in LTx patients, particularly in unilateral LTx.

Comparison of extracorporeal photopheresis and alemtuzumab for the treatment of chronic lung allograft dysfunction

BACKGROUND

Survival after lung transplantation is limited by chronic lung allograft dysfunction (CLAD). Immunomodulatory therapies such as extracorporeal photopheresis (ECP) and alemtuzumab (AL) have been described for refractory CLAD, but comparative outcomes are not well defined.

METHODS

We retrospectively reviewed spirometric values and clinical outcomes after therapy with ECP, AL, or no treatment (NT) in patients with CLAD who underwent transplant between January 2005 and December 2014. We used inverse probability-weighted regression adjustment (IPWRA) to adjust for potential confounders affecting treatment choice.

RESULTS

Of 267 patients, 31 received immunomodulatory therapies for CLAD, and 78 received NT. The slope of forced expiratory volume in 1 second (FEV₁) decline significantly improved after treatment with AL and with ECP compared with pre-treatment FEV₁ slope; however, there was no significant change in slope of forced vital capacity (FVC). Comparison with NT was limited because of clinical differences in treatment groups. After IPWRA, we found no significant difference in mean difference of FEV₁ slope (ml/month) when comparing treatment with NT, suggesting stabilization of lung function in the treatment group. We found no difference between the 2 immunomodulatory therapies 1, 3, and 6 months post-treatment (-49.9 [95% CI -581.8, +482.0], p = 0.85; +27.7 [95% CI -167.6, +223.0], p = 0.78; -9.6 [95% CI -167.5, +148.2], p = 0.91). We found no difference in mean FVC slope or differences between ECP and AL in infection rates or survival after treatment.

CONCLUSIONS

Immunomodulatory therapy for CLAD with ECP or AL was associated with a significant change in FEV₁ slope post-treatment compared with pre-treatment slope, with minimal effect on FVC. There was no difference between the 2 therapies in their effect on pulmonary function.

Comparative analysis of morphological and molecular motifs in bronchiolitis obliterans and alveolar fibroelastosis after lung and stem cell transplantation

Chronic lung allograft dysfunction (CLAD) remains the major obstacle to long‐term survival following lung transplantation (LuTx). Morphologically CLAD is defined by obliterative remodelling of the small airways (bronchiolitis obliterans, BO) as well as a more recently described collagenous obliteration of alveoli with elastosis summarised as alveolar fibroelastosis (AFE). Both patterns are not restricted to pulmonary allografts, but have also been reported following haematopoietic stem cell transplantation (HSCT) and radio chemotherapy (RC). In this study we performed compartment‐specific morphological and molecular analysis of BO and AFE lesions in human CLAD (n = 22), HSCT (n = 29) and RC (n = 6) lung explants, utilising conventional histopathology, laser‐microdissection, PCR techniques and immunohistochemistry to assess fibrosis‐associated gene and protein expression. Three key results emerged from our analysis of fibrosis‐associated genes: (i) generally speaking, “BO is BO”. Despite the varying clinical backgrounds, the molecular characteristics of BO lesions were found to be alike in all groups. (ii) “AFE is AFE”. In all groups of patients suffering from restrictive changes to lung physiology due to AFE there were largely – but not absolutely ‐ identical gene expression patterns. iii) BO concomitant to AFE after LuTx is characterised by an AFE‐like molecular microenvironment, representing the only exception to (i). Additionally, we describe an evolutionary model for the AFE pattern: a non‐specific fibrin‐rich reaction to injury pattern triggers a misguided resolution attempt and eventual progression towards manifest AFE. Our data point towards an absence of classical fibrinolytic enzymes and an alternative fibrin degrading mechanism via macrophages, resulting in fibrous remodelling and restrictive functional changes. These data may serve as diagnostic adjuncts and help to predict the clinical course of respiratory dysfunction in LuTx and HSCT patients. Moreover, analysis of the mechanism of fibrinolysis and fibrogenesis may unveil potential therapeutic targets to alter the course of the eventually fatal lung remodelling.

Airway remodelling in the transplanted lung

Following lung transplantation, fibrotic remodelling of the small airways has been recognized for almost 5 decades as the main correlate of chronic graft failure and a major obstacle to long-term survival. Mainly due to airway fibrosis, pulmonary allografts currently show the highest attrition rate of all solid organ transplants, with a 5-year survival rate of 58 % on a worldwide scale. The observation that these morphological changes are not just the hallmark of chronic rejection but rather represent a manifestation of a multitude of alloimmune-dependent and -independent injuries was made more recently, as was the discovery that chronic lung allograft dysfunction manifests in different clinical phenotypes of respiratory impairment and corresponding morphological subentities. Although recent years have seen considerable advances in identifying and categorizing these subgroups on the basis of clinical, functional and histomorphological changes, as well as susceptibility to medicinal treatment, this process is far from over. Since the actual pathophysiological mechanisms governing airway remodelling are still only poorly understood, diagnosis and therapy of chronic lung allograft dysfunction presents a major challenge to clinicians, radiologists and pathologists alike. Here, we review and discuss the current state of the literature on chronic lung allograft dysfunction and shed light on classification systems, corresponding clinical and morphological changes, key cellular players and underlying molecular pathways, as well as on emerging diagnostic and therapeutic approaches.

Lung cancer: a rare indication for, but frequent complication after lung transplantation

Lung transplantation is an effective and safe therapy for carefully selected patients suffering from a variety of end-stage pulmonary diseases. Lung cancer negatively affects prognosis, particularly in patients who are no longer candidates for complete resection. Lung transplantation can be considered for carefully selected and well staged lung cancer patients with proven, lung-limited, multifocal, (minimally invasive) adenocarcinoma in situ (AIS) (previously called bronchioloalveolar cell carcinoma) causing respiratory failure. Despite a substantial risk of tumour recurrence (33-75%), lung transplantation may offer a survival benefit (50% at 5 years) with best palliation of their disease. Reports on lung transplantation for other low-grade malignancies are rare. Lung transplant candidates at higher risk for developing lung cancer [mainly previous smokers with chronic obstructive lung disease (COPD) and idiopathic pulmonary fibrosis (IPF) or older patients] should be thoroughly and repeatedly screened for lung cancer prior to listing, and preferably also during waiting list time if longer than 1 year, including the use of PET-CT scan and EBUS-assisted bronchoscopy in case of undefined, but suspicious pulmonary abnormalities. Double-lung transplantation should now replace single-lung transplantation in these high-risk patients because of a 6-9% prevalence of lung cancer developing in the remaining native lung. Patients with unexpected, early stage bronchial carcinoma in the explanted lung may have favourable survival without recurrence. Early PET-CT (at 3-6 months) following lung transplantation is advisable to detect early, subclinical disease progression. Donor lungs from (former) smokers should be well examined at retrieval. Suspicious nodules should be biopsied to avoid grafting cancer in the recipient. Close follow-up with regular visits and screening test in all recipients is needed because of the increased risk of developing a primary or secondary cancer in the allograft from either donor or recipient origin.

Clinical utility of CD4+ function assessment (ViraCor-IBT ImmuKnow test) in lung recipients

The ImmuKnow assay measures cell-mediated immunity, quantifying ATP production from peripheral blood CD4+T-cells in solid-organ transplant patients who undergo immunosuppressive therapy. We aimed to measure functional immunity in lung transplant recipients and correlate Immuknow values with immunosuppression levels, presence of chronic lung allograft dysfunction (CLAD) and infections. We evaluated 61 lung recipients who underwent follow-up for lung transplantation between 2010 and 2014. Rejection and infection were retrospectively analyzed. The association between over-immunosuppression and a number of predictors was assessed by means of univariate and multivariate logistic regression models. 71 out of 127 samples (56%) showed an over-immunosuppression with an ImmuKnow assay mean level of 112.92ng/ml (SD±58.2), vs. 406.14ng/ml (SD±167.7) of the rest of our cohort. In the over-immunosuppression group we found 51 episodes of infection (71%) (OR 2.754, 95% CI 1.40-5.39; P-value 0.003). In the other group, only 25 samples (44%) were taken during an infectious episode. The mean absolute ATP level was significantly different between patients with or without infection (202.38±139.06ng/ml vs. 315.51±221.60ng/ml; P<0.001). RAS (Restrictive allograft syndrome) was associated to low ImmuKnow level (P<0.001). These results were confirmed by the multivariate analysis. The ImmuKnow assay levels were significantly lower in infected lung transplant recipients compared with non-infected recipients and in RAS patients.

Special considerations for the use of lung transplantation in pediatrics

Lung transplantation has become an accepted therapy in infants, children and adolescents suffering from end-stage lung diseases, an impaired quality of life as well as a reduced life expectancy. Within Europe, pediatric lung transplantation is largely performed in predominantly adult centers due to a relatively low overall case volume. Children do represent a specific and challenging cohort facing a transplant procedure, where the selection of potential candidates becomes a crucial step to maximize net survival benefit. Therefore, interdisciplinary evaluation and early listing in view of current indications and contraindications, adequate preoperative education of the child and family members, discussion of possibly required bridging procedures in case of deterioration, appropriate technical planning of the operation, adherence to postoperative medical treatment and follow-up are all crucial steps in this demanding puzzle. In this article, the authors review recent advances in the field of pediatric lung transplantation and outline challenges in the future.