Metalloproteinase Profiling in Lung Transplant Recipients With Good Outcome and Bronchiolitis Obliterans Syndrome

Blood MMP-9 measured at 2 years after lung transplantation as a prognostic biomarker of chronic lung allograft dysfunction

BACKGROUND

Long-term outcomes of lung transplantation (LTx) remain hampered by chronic lung allograft dysfunction (CLAD). Matrix metalloproteinase 9 (MMP-9) is a secretory endopeptidase identified as a key mediator in fibrosis processes associated with CLAD. The objective of this study was to investigate whether plasma MMP9 levels may be prognostic of CLAD development.

METHODS

Participants were selected from the Cohort in Lung Transplantation (COLT) for which a biocollection was associated. We considered two time points, year 1 (Y1) and year 2 (Y2) post-transplantation, for plasma MMP-9 measurements. We analysed stable recipients at those time points, comparing those who would develop a CLAD within the 2 years following the measurement to those who would remain stable 2 years after.

RESULTS

MMP-9 levels at Y1 were not significantly different between the CLAD and stable groups (230 ng/ml vs. 160 ng/ml, p = 0.4). For the Y2 analysis, 129 recipients were included, of whom 50 developed CLAD within 2 years and 79 remained stable within 2 years. MMP-9 plasma median concentrations were higher in recipients who then developed CLAD than in the stable group (230 ng/ml vs. 118 ng/ml, p = 0.003). In the multivariate analysis, the Y2 MMP-9 level was independently associated with CLAD, with an average increase of 150 ng/ml (95% CI [0-253], p = 0.05) compared to that in the stable group. The Y2 ROC curve revealed a discriminating capacity of blood MMP-9 with an area under the curve of 66%.

CONCLUSION

Plasmatic MMP-9 levels measured 2 years after lung transplantation have prognostic value for CLAD.

Collagen Type IV Alpha 5 Chain in Bronchiolitis Obliterans Syndrome After Lung Transplant: The First Evidence

INTRODUCTION

Bronchiolitis obliterans syndrome (BOS) is the most common form of CLAD and is characterized by airflow limitation and an obstructive spirometry pattern without parenchymal opacities. The protein signature of BOS lesions concerns extracellular matrix organization and aberrant basement membrane composition. In this pilot study, we investigated the presence of COL4A5 in the serum of patients with BOS.

METHODS

41 patients who had undergone LTX were enrolled. Of these, 27 developed BOS and 14 (control group) were considered stable at the time of serum sampling. Of BOS patients, serum samples were analysed at the time of BOS diagnosis and before the clinical diagnosis (pre-BOS). COL4A5 levels were detected through the ELISA kit.

RESULTS

Serum concentrations of COL4A5 were higher in pre-BOS than in stable patients (40.5 ± 13.9 and 24.8 ± 11.4, respectively, p = 0.048). This protein is not influenced by comorbidities, such as acute rejection or infections, or by therapies. Survival analysis also reveals that a higher level of COL4A5 was also associated with less probability of survival. Our data showed a correlation between concentrations of COL4A5 and FEV1 at the time of diagnosis of BOS.

CONCLUSION

Serum concentrations of COL4A5 can be considered a good prognostic marker due to their association with survival and correlation with functional parameters.

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.

Effector immune cells in Chronic Lung Allograft Dysfunction: a Systematic Review

Chronic lung allograft dysfunction (CLAD) remains the major barrier to long‐term survival after lung transplantation and improved insight into its underlying immunological mechanisms is critical to better understand the disease and to identify treatment targets. We systematically searched the electronic databases of PubMed and EMBASE for original research publications, published between January 2000 and April 2021, to comprehensively assess current evidence on effector immune cells in lung tissue and bronchoalveolar lavage fluid from lung transplant recipients with CLAD. Literature search revealed 1351 articles, 76 of which met the criteria for inclusion in our analysis. Our results illustrate significant complexity in both innate and adaptive immune cell responses in CLAD, along with presence of numerous immune cell products, including cytokines, chemokines and proteases associated with tissue remodelling. A clear link between neutrophils and eosinophils and CLAD incidence has been seen, in which eosinophils more specifically predisposed to restrictive allograft syndrome. The presence of cytotoxic and T‐helper cells in CLAD pathogenesis is well‐documented, although it is challenging to draw conclusions about their role in tissue processes from predominantly bronchoalveolar lavage data. In restrictive allograft syndrome, a more prominent humoral immune involvement with increased B cells, immunoglobulins and complement deposition is seen. Our evaluation of published studies over the last 20 years summarizes the complex multifactorial immunopathology of CLAD onset and progression. It highlights the phenotype of several key effector immune cells involved in CLAD pathogenesis, as well as the paucity of single cell resolution spatial studies in lung tissue from patients with CLAD.

Interleukin-18: A Novel Participant in the Occurrence, Development, and Drug Therapy of Obliterative Bronchiolitis Postlung Transplantation

Background

Obliterative bronchiolitis (OB) was a main cause of deterioration of long-term prognosis in lung transplant recipients after the first posttransplant year. Proinflammatory cytokine interleukin-18 (IL-18) strengthened both the natural immunity and acquired immunity and played an important role in organ transplantation. The roles of IL-18 in the occurrence, development, and drug treatment of OB remained unclear.

Methods

Small interfering RNA (siRNA) against mouse IL-18 (siRNA-IL-18) was used to silence IL-18 expression. Mouse heterotopic tracheal transplantation model was used to simulate OB. Recipient mice were divided into 5 groups (n = 12) according to donor mouse strains and drug treatment: isograft group, allograft group, allograft+tacrolimus group, allograft+azithromycin group, and allograft+tacrolimus+azithromycin group. The luminal obliteration rates were pathological evaluation. Expressions of cytokines and MMPs were detected by real-time PCR, western blot, and enzyme chain immunosorbent assay (ELISA).

Results

The luminal obliteration rates of IL-18 of the siRNA-IL-18 group were significantly lower than those of the negative control group (p < 0.0001) and the blank control group (p = 0.0002). mRNA expressions of IFN-γ, EMMPRIN, MMP-8, and MMP-9 of the siRNA-IL-18 group were significantly lower than those of the negative and blank control groups. No tracheal occlusion occurred in grafts of the isograft group. The rates of tracheal occlusion of the allograft group, allograft+tacrolimus group, allograft+azithromycin group, and allograft+tacrolimus+azithromycin group were 72.17 ± 4.66%, 40.33 ± 3.00%, 38.50 ± 2.08%, and 23.33 ± 3.24%, respectively. There were significant differences between the 4 groups (p < 0.001). Serum protein expressions of IL-17 (p = 0.0017), IL-18 (p = 0.0036), IFN-γ (p = 0.0102), and MMP-9 (p = 0.0194) were significantly decreased in the allograft+tacrolimus+azithromycin group compared to the allograft group.

Conclusions

IL-18 could be a novel molecular involved in the occurrence, development, and drug treatment of OB.

Potential novel biomarkers for chronic lung allograft dysfunction and azithromycin responsive allograft dysfunction

Chronic Lung Allograft Dysfunction (CLAD), manifesting as Bronchiolitis Obliterans Syndrome (BOS) or Restrictive Allograft Syndrome (RAS), is the main reason for adverse long-term outcome after Lung Transplantation (LTX). Until now, no specific biomarkers exist to differentiate between CLAD phenotypes. Therefore, we sought to find suitable cytokines to distinguish between BOS, RAS and Azithromycin Responsive Allograft Dysfunction (ARAD); and reveal potential similarities or differences to end-stage fibrotic diseases. We observed significantly increased Lipocalin-2 serum concentrations in RAS compared to BOS patients. In addition, in RAS patients immunohistochemistry revealed Lipocalin-2 expression in bronchial epithelium and alveolar walls. Patients with ARAD showed significantly lower Activin-A serum concentrations compared to Stable-LTX and BOS patients. Further, increased serum concentrations of Lipocalin-2 and Activin-A were predictors of worse freedom-from-CLAD in Stable-LTX patients. These biomarkers serve as promising serum biomarkers for CLAD prediction and seem suitable for implementation in clinical practice.

[Predictors for the Bronchiolitis Obliterans Syndrome in Lung Transplant Patient]

肺移植是治疗终末期肺病的有效方法。目前，肺移植术后1年生存率已达到80%，由于闭塞性细支气管炎综合症（bronchiolitis obliterans syndrome, BOS）的发生，5年生存率维持在50%左右。BOS是一个纤维化的过程，最终导致不可逆的气道闭塞。缺血-再灌注损伤、感染、氧化应激以及急性排斥反应等多个因素参与了BOS的发生。研究证实BOS的早期诊断与预后良好相关。因此，寻找灵敏、特异的BOS预测标记物对于提高肺移植患者长期生存具有重要的科学和临床意义。本文就与BOS发生发展相关的免疫调节细胞、分泌性蛋白质、细胞膜蛋白等指标的变化在BOS早期诊断中的作用进行综述。

FK506 combined with GM6001 prevents tracheal obliteration in a mouse model of heterotopic tracheal transplantation

BACKGROUND

Obliterative bronchiolitis (OB) is the major complication limiting the long-term survival of allografts after lung transplantation. In this study, we investigated the effect of tacrolimus (FK506) combined with GM6001，a matrix metalloproteinase (MMP) inhibitor， on the formation of OB using a mouse heterotopic tracheal transplantation model.

METHODS

Syngeneic tracheal grafts were transplanted heterotopically from BALB/c mice to BALB/c mice. Allografts from C57BL/6 mice were transplanted to BALB/c mice. Isograft group, allograft group, allograft+FK506 group, allograft +GM6001 group and allograft+FK506 + GM6001 group was given respectively intraperitoneal injection of saline, saline, FK506, GM6001 and FK506 + GM6001 once a day. At 28 day after transplantation, OB incidence was determined by hematoxylin-eosin staining and the expressions of MMPs and cytokines were assessed using enzyme linked immunosorbent assay, immunohistochemical assays and western blot assay.

RESULTS

The tracheal occlusion rates of isograft group, allograft group, allograft+FK506 group, allograft+GM6001 group and allograft+FK506 + GM6001 group were 0, 74.1 ± 9.79%, 34.4 ± 6.04%, 40.3 ± 8.77% and 26.5 ± 5.73% respectively. There were significant differences between the latter two groups (P < .001). The serum MMP-8 and MMP-9 levels of allograft group were significantly higher than those of isograft group (P < .05) and had no significant decrease when treated by FK506. The serum MMP-8 and MMP-9 levels of allograft+FK506 + GM6001 group were significantly lower than those of allograft+FK506 group (P < .05). MMP-8 and MMP-9 protein expression in the grafts of allograft+FK506 + GM6001 group were lower than those of allograft+FK506 group verified by immunohistochemical staining and western blotting.

CONCLUSION

FK506 combined with GM6001 could alleviate tracheal obliteration in mouse heterotopic tracheal transplantation model, due to its inhibitory effect on MMPs.

Bronchiolitis obliterans murine model induced by nitric acid aerosol inhalation: An economical and reproducible model

PURPOSE

Bronchiolitis obliterans (BO) is a highly debilitative and fatal syndrome associated with a series of severe lower airway disorders. The pathogenesis of BO is complicated and not entirely understood. An appropriate animal model of BO may aid research into its pathogenesis. Here, we establish a mouse model of BO to provide insight into this disease.

MATERIALS AND METHODS

6-8 week old BABL/c mice were exposed to 5% nitric acid (NA) aerosol through a nebulizer for 3 hours, and controls were exposed to distilled water instead. Symptoms, airway resistance and pathological process were observed dynamically. The levels of matrix metalloproteinase-2 (MMP-2), MMP-9, tissue inhibitor of metalloproteinase-1 (TIMP-1), 8-isoprostane and myeloperoxidase (MPO) in lung tissue and bronchoalveolar lavage fluids (BLAF) were determined by ELISA on day 3, 7, 14, 28 and 56 after the aerosol nebulization.

RESULTS

Typical BO lesions were observed in NA nebulized mice characterized histologically by initial necrotizing bronchiolitis and final airway fibrosis at day 28 after the aerosol nebulization. NA nebulized mice also exhibited labored breathing and significantly increased airway resistance. Expression of MMP-2, MMP-9, TIMP-1, 8-isoprostane and MPO were significantly elevated in NA nebulized mice in different time frame.

CONCLUSION

A murine BO model was established by NA aerosol inhalation. It provides an easy, economic, and reproducible mice model for BO research.

Double lung, unlike single lung transplantation might provide a protective effect on mortality and bronchiolitis obliterans syndrome

Background

Survival after lung transplantation (LTx) is often limited by bronchiolitis obliterans syndrome (BOS).

Method

Survey of 278 recipients who underwent LTx. The endpoint used was BOS (BOS grade ≥ 2), death or Re-lung transplantation (Re-LTx) assessed by competing risk regression analyses.

Results

The incidence of BOS grade ≥ 2 among double LTx (DLTx) recipients was 16 ± 3% at 5 years, 30 ± 4% at 10 years, and 37 ± 5% at 20 years, compared to single LTx (SLTx) recipients whose corresponding incidence of BOS grade ≥ 2 was 11 ± 3%, 20 ± 4%, and 24 ± 5% at 5, 10, and 20 years, respectively (p > 0. 05). The incidence of BOS grade ≥ 2 by major indications ranked in descending order: other, PF, CF, COPD, PH and AAT1 (p < 0. 05). The mortality rate by major indication ranked in descending order: COPD, PH, AAT1, PF, Other and CF (p < 0. 05).

Conclusion

No differences were seen in the incidence of BOS grade ≥ 2 regarding type of transplant, however, DLTx recipients showed a better chance of survival despite developing BOS compared to SLTx recipients. The highest incidence of BOS was seen among CF, PF, COPD, PH, and AAT1 recipients in descending order, however, CF and PF recipients showed a better chance of survival despite developing BOS compared to COPD, PH, and AAT1 recipients.

T Cells Promote Bronchial Epithelial Cell Secretion of Matrix Metalloproteinase-9 via a C-C Chemokine Receptor Type 2 Pathway: Implications for Chronic Lung Allograft Dysfunction

Chronic lung allograft dysfunction (CLAD) is the major limitation of long-term survival after lung transplantation. CLAD manifests as bronchiolitis obliterans syndrome (BOS) or restrictive allograft syndrome (RAS). Alloimmune reactions and epithelial-to-mesenchymal transition have been suggested in BOS. However, little is known regarding the role of allogenicity in epithelial cell differentiation. Primary human bronchial epithelial cells (BECs) were treated with activated T cells in the presence or absence of transforming growth factor (TGF)-β. The expression of epithelial and mesenchymal markers was investigated. The secretion of inflammatory cytokines and matrix metalloproteinase (MMP)-9 was measured in culture supernatants and in plasma from lung transplant recipients (LTRs): 49 stable, 29 with BOS, and 16 with RAS. We demonstrated that C-C motif chemokine 2 secreted by T cells supports TGF-β-induced MMP-9 production by BECs after binding to C-C chemokine receptor type 2. Longitudinal investigation in LTRs revealed a rise in plasma MMP-9 before CLAD onset. Multivariate analysis showed that plasma MMP-9 was independently associated with BOS (odds ratio [OR] = 6.19, p = 0.002) or RAS (OR = 3.9, p = 0.024) and predicted the occurrence of CLAD 12 months before the functional diagnosis. Thus, immune cells support airway remodeling through the production of MMP-9. Plasma MMP-9 is a potential predictive biomarker of CLAD.

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.

Molecular Profiling in Lung Biopsies of Human Pulmonary Allografts to Predict Chronic Lung Allograft Dysfunction

Chronic lung allograft dysfunction (CLAD) is the main reason for poor long-term outcome of lung transplantation, with bronchiolitis obliterans (BO) representing the predominant pathological feature. BO is defined as a progressive fibrous obliteration of the small airways, thought to be triggered by a combination of nonimmune bronchial injury and alloimmune and autoimmune mechanisms. Because biopsy samples are too insensitive to reliably detect BO and a decline in lung function test results, which is clinically used to define CLAD, does not detect early stages, there is need for alternative biomarkers for early diagnosis. Herein, we analyzed the cellular composition and differential expression of 45 tissue remodeling-associated genes in transbronchial lung biopsy specimens from two cohorts with 18 patients each: patients who did not develop CLAD within 3 years after transplantation (48 biopsy specimens) and patients rapidly developing CLAD within the first 3 postoperative years (57 biopsy specimens). Integrating the mRNA expression levels of the five most significantly dysregulated genes from the transforming growth factor-β axis (BMP4, IL6, MMP1, SMAD1, and THBS1) into a score, patient groups could be confidently separated and the outcome predicted (P < 0.001). We conclude that overexpression of fibrosis-associated genes may be valuable as a tissue-based molecular biomarker to more accurately diagnose or predict the development of CLAD.