Extended ischemic time (>15 hours) using controlled hypothermic storage in lung transplantation: A multicenter experience

Static ice storage has long been the standard-of-care for lung preservation, although freezing injury limits ischemic time (IT). Controlled hypothermic storage (CHS) at elevated temperature could safely extend IT. This retrospective analysis assesses feasibility and safety of CHS with IT > 15 hours. Three lung transplant (LuTx) centers (April-October 2023) included demographics, storage details, IT, and short-term outcome from 13 LuTx recipients (8 male, 59 years old). Donor lungs were preserved in a portable CHS device at 7 (5-9.3)°C. Indication was overnight bridging and/or long-distance transport. IT of second-implanted lung was 17.3 (15.1-22) hours. LuTx were successful, 4/13 exhibited primary graft dysfunction grade 3 within 72 hours and 0/13 at 72 hours. Post-LuTx mechanical ventilation was 29 (7-442) hours. Intensive care unit stay was 9 (5-28) and hospital stay 30 (16-90) days. Four patients needed postoperative extracorporeal membrane oxygenation (ECMO). One patient died (day 7) following malpositioning of an ECMO cannula. This multicenter experience demonstrates the possibility of safely extending IT > 15 hours by CHS.

The nature of chronic rejection after lung transplantation: a murine orthotopic lung transplant study

Introduction

Chronic rejection is a major complication post-transplantation. Within lung transplantation, chronic rejection was considered as airway centred. Chronic Lung Allograft Dysfunction (CLAD), defined to cover all late chronic complications, makes it more difficult to understand chronic rejection from an immunological perspective. This study investigated the true nature, timing and location of chronic rejection as a whole, within mouse lung transplantation.

Methods

40 mice underwent an orthotopic left lung transplantation, were sacrificed at day 70 and evaluated by histology and in vivo µCT. For timing and location of rejection, extra grafts were sacrificed at day 7, 35, 56 and investigated by ex vivo µCT or single cell RNA (scRNA) profiling.

Results

Chronic rejection originated as innate inflammation around small arteries evolving toward adaptive organization with subsequent end-arterial fibrosis and obliterans. Subsequently, venous and pleural infiltration appeared, followed by airway related bronchiolar folding and rarely bronchiolitis obliterans was observed. Ex vivo µCT and scRNA profiling validated the time, location and sequence of events with endothelial destruction and activation as primary onset.

Conclusion

Against the current belief, chronic rejection in lung transplantation may start as an arterial response, followed by responses in venules, pleura, and, only in the late stage, bronchioles, as may be seen in some but not all patients with CLAD.

Controlled Hypothermic Storage for Lung Preservation: Leaving the Ice Age Behind

Controlled hypothermic storage (CHS) is a recent advance in lung transplantation (LTx) allowing preservation at temperatures higher than those achieved with traditional ice storage. The mechanisms explaining the benefits of CHS compared to conventional static ice storage (SIS) remain unclear and clinical data on safety and feasibility of lung CHS are limited. Therefore, we aimed to provide a focus review on animal experiments, molecular mechanisms, CHS devices, current clinical experience, and potential future benefits of CHS. Rabbit, canine and porcine experiments showed superior lung physiology after prolonged storage at 10°C vs. ≤4°C. In recent molecular analyses of lung CHS, better protection of mitochondrial health and higher levels of antioxidative metabolites were observed. The acquired insights into the underlying mechanisms and development of CHS devices allowed clinical application and research using CHS for lung preservation. The initial findings are promising; however, further data collection and analysis are required to draw more robust conclusions. Extended lung preservation with CHS may provide benefits to both recipients and healthcare personnel. Reduced time pressure between procurement and transplantation introduces flexibility allowing better decision-making and overnight bridging by delaying transplantation to daytime without compromising outcome.

The memory of airway epithelium damage in smokers and COPD patients

Chronic obstructive pulmonary disease (COPD), a devastating and irreversible lung disease, causes structural and functional defects in the bronchial epithelium, the (ir)reversibility of which remains unexplored in vitro. This study aimed to investigate the persistence of COPD-related epithelial defects in long-term airway epithelial cultures derived from non-smokers, smokers, and COPD patients. Barrier function, polarity, cell commitment, epithelial-to-mesenchymal transition, and inflammation were evaluated and compared with native epithelium characteristics. The role of inflammation was explored using cytokines. We show that barrier dysfunction, compromised polarity, and lineage abnormalities observed in smokers and COPD persisted for up to 10 wk. Goblet cell hyperplasia was associated with recent cigarette smoke exposure. Conversely, increased IL-8/CXCL-8 release and abnormal epithelial-to-mesenchymal transition diminished over time. These ex vivo observations matched surgical samples' abnormalities. Cytokine treatment induced COPD-like changes in control cultures and reactivated epithelial-to-mesenchymal transition in COPD cells. In conclusion, these findings suggest that the airway epithelium of smokers and COPD patients retains a multidimensional memory of its original state and previous cigarette smoke-induced injuries, maintaining these abnormalities for extended periods.

Ventilatory capacity in CLAD is driven by dysfunctional airway structure

BACKGROUND

Chronic lung allograft dysfunction (CLAD) encompasses three main phenotypes: bronchiolitis obliterans syndrome (BOS), restrictive allograft syndrome (RAS) and a Mixed phenotype combining both pathologies. How the airway structure in its entirety is affected in these phenotypes is still poorly understood.

METHODS

A detailed analysis of airway morphometry was applied to gain insights on the effects of airway remodelling on the distribution of alveolar ventilation in end-stage CLAD. Ex vivo whole lung μCT and tissue-core μCT scanning of six control, six BOS, three RAS and three Mixed explant lung grafts (9 male, 9 female, 2014-2021, Leuven, Belgium) were used for digital airway reconstruction and calculation of airway dimensions in relation to luminal obstructions.

FINDINGS

BOS and Mixed explants demonstrated airway obstructions of proximal bronchioles (starting at generation five), while RAS explants particularly had airway obstructions in the most distal bronchioles (generation >12). In BOS and Mixed explants 76% and 84% of bronchioles were obstructed, respectively, while this was 22% in RAS. Bronchiolar obstructions were mainly caused by lymphocytic inflammation of the airway wall or fibrotic remodelling, i.e. constrictive bronchiolitis. Proximal bronchiolectasis and imbalance in distal lung ventilation were present in all CLAD phenotypes and explain poor lung function and deterioration of specific lung function parameters.

INTERPRETATION

Alterations in the structure of conducting bronchioles revealed CLAD to affect alveolar ventilatory distribution in a regional fashion. The significance of various obstructions, particularly those associated with mucus, is highlighted.

FUNDING

This research was funded with the National research fund Flanders (G060322N), received by R.V.

Computed tomography-based machine learning for donor lung screening before transplantation

BACKGROUND

Assessment and selection of donor lungs remain largely subjective and experience based. Criteria to accept or decline lungs are poorly standardized and are not compliant with the current donor pool. Using ex vivo computed tomography (CT) images, we investigated the use of a CT-based machine learning algorithm for screening donor lungs before transplantation.

METHODS

Clinical measures and ex situ CT scans were collected from 100 cases as part of a prospective clinical trial. Following procurement, donor lungs were inflated, placed on ice according to routine clinical practice, and imaged using a clinical CT scanner before transplantation while stored in the icebox. We trained and tested a supervised machine learning method called dictionary learning, which uses CT scans and learns specific image patterns and features pertaining to each class for a classification task. The results were evaluated with donor and recipient clinical measures.

RESULTS

Of the 100 lung pairs donated, 70 were considered acceptable for transplantation (based on standard clinical assessment) before CT screening and were consequently implanted. The remaining 30 pairs were screened but not transplanted. Our machine learning algorithm was able to detect pulmonary abnormalities on the CT scans. Among the patients who received donor lungs, our algorithm identified recipients who had extended stays in the intensive care unit and were at 19 times higher risk of developing chronic lung allograft dysfunction within 2 years posttransplant.

CONCLUSIONS

We have created a strategy to ex vivo screen donor lungs using a CT-based machine learning algorithm. As the use of suboptimal donor lungs rises, it is important to have in place objective techniques that will assist physicians in accurately screening donor lungs to identify recipients most at risk of posttransplant complications.

The Immunopathology of Pulmonary Rejection after Murine Lung Transplantation

To improve outcomes following lung transplantation, it is essential to understand the immunological mechanisms that result in chronic graft failure. The associated clinical syndrome is termed chronic lung allograft dysfunction (CLAD), which is known to be induced by alloimmune-dependent (i.e., rejection) and alloimmune-independent factors (e.g., infections, reflux and environmental factors). We aimed to explore the alloimmune-related mechanism, i.e., pulmonary rejection. In this study, we use a murine orthotopic left lung transplant model using isografts and allografts (C57BL/6 or BALB/c as donors to C57BL/6 recipients), with daily immunosuppression (10 mg/kg cyclosporin A and 1.6 mg/kg methylprednisolone). Serial sacrifice was performed at days 1, 7 and 35 post-transplantation (n = 6 at each time point for each group). Left transplanted lungs were harvested, a single-cell suspension was made and absolute numbers of immune cells were quantified using multicolor flow cytometry. The rejection process followed the principles of a classic immune response, including innate but mainly adaptive immune cells. At day 7 following transplantation, the numbers of interstitial macrophages, monocytes, dendritic cells, NK cells, NKT cells, CD4+ T cells and CD8+ T and B cells were increased in allografts compared with isografts. Only dendritic cells and CD4+ T cells remained elevated at day 35 in allografts. Our study provides insights into the immunological mechanisms of true pulmonary rejection after murine lung transplantation. These results might be important in further research on diagnostic evaluation and treatment for CLAD.

The value of point-of-care tests for the detection of SARS-CoV-2 RNA or antigen in bronchoalveolar lavage fluid

BACKGROUND

Transmission of SARS-CoV-2 from donor to recipient is a clinically relevant risk for developing severe COVID-19 after lung transplantation (LTx). This risk of iatrogenic transmission can be reduced by timely detection of viral RNA or antigen in samples of bronchoalveolar lavage (BAL) fluid obtained at the time of lung procurement. We aimed to retrospectively evaluate the detection of SARS-CoV-2 RNA or antigen in BAL fluid samples using three point-of-care tests (POCTs).

METHODS

BAL fluid samples came from patients hospitalized in an intensive care unit during the COVID-19 pandemic. These pandemic samples were scored as positive or negative for SARS-CoV-2 by a RT-qPCR comparator assay for orf1ab. Three commercially available POCTs were then evaluated: cobas SARS-CoV-2 & Influenza A/B assay with the cobas Liat RT-qPCR system (Roche Diagnostics), ID NOW COVID-19 and COVID-19 2.0 (Abbott), and SARS-CoV-2 Rapid Antigen Test (RAT) (Roche Diagnostics). Samples from the pre-pandemic era served as negative controls.

RESULTS

We analyzed a total of 98 BAL fluid samples, each from a different patient: 58 positive pandemic samples (orf1ab Ct<38), 20 putatively negative pandemic samples (orf1ab Ct≥38), and 20 pre-pandemic samples. Univariate logistic regression shows that the probability of detection was highest for cobas Liat, followed by ID NOW, and then RAT. Of clinical relevance, cobas Liat detected SARS-CoV-2 RNA in 30 of the 31 positive pandemic samples that were collected within 10 days after RT-qPCR diagnosis of SARS-CoV-2 infection. None of the 20 pre-pandemic samples had a false-positive result for any POCT.

CONCLUSIONS

POCTs enable the detection of SARS-CoV-2 RNA or antigen in BAL fluid samples and may provide additional information to decide if donor lungs are suitable for transplantation. Detection of respiratory pathogens with POCTs at the time of donor lung procurement is a potential strategy to increase safety in LTx by preventing iatrogenic transmission and severe postoperative infections.

Unagi: Deep Generative Model for Deciphering Cellular Dynamics and In-Silico Drug Discovery in Complex Diseases

Human diseases are characterized by intricate cellular dynamics. Single-cell sequencing provides critical insights, yet a persistent gap remains in computational tools for detailed disease progression analysis and targeted in-silico drug interventions. Here, we introduce UNAGI, a deep generative neural network tailored to analyze time-series single-cell transcriptomic data. This tool captures the complex cellular dynamics underlying disease progression, enhancing drug perturbation modeling and discovery. When applied to a dataset from patients with Idiopathic Pulmonary Fibrosis (IPF), UNAGI learns disease-informed cell embeddings that sharpen our understanding of disease progression, leading to the identification of potential therapeutic drug candidates. Validation via proteomics reveals the accuracy of UNAGI's cellular dynamics analyses, and the use of the Fibrotic Cocktail treated human Precision-cut Lung Slices confirms UNAGI's predictions that Nifedipine, an antihypertensive drug, may have antifibrotic effects on human tissues. UNAGI's versatility extends to other diseases, including a COVID dataset, demonstrating adaptability and confirming its broader applicability in decoding complex cellular dynamics beyond IPF, amplifying its utility in the quest for therapeutic solutions across diverse pathological landscapes.

The hemodynamic interplay between pulmonary ischemia-reperfusion injury and right ventricular function in lung transplantation: a translational porcine model

Lung transplantation (LTx) is a challenging procedure. Following the process of ischemia-reperfusion injury, the transplanted pulmonary graft might become severely damaged, resulting in primary graft dysfunction. In addition, during the intraoperative window, the right ventricle (RV) is at risk of acute failure. The interaction of right ventricular function with lung injury is, however, poorly understood. We aimed to address this interaction in a translational porcine model of pulmonary ischemia-reperfusion injury. Advanced pulmonary and hemodynamic assessment was used, including right ventricular pressure-volume loop analysis. The acute model was based on clamping and unclamping of the left lung hilus, respecting the different hemodynamic phases of a clinical lung transplantation. We found that forcing entire right ventricular cardiac output through a lung suffering from ischemia-reperfusion injury increased afterload (pulmonary vascular resistance from baseline to end experiment P < 0.0001) and induced right ventricular failure (RVF) in 5/9 animals. Notably, we identified different compensation patterns in failing versus nonfailing ventricles (arterial elastance P = 0.0008; stroke volume P < 0.0001). Furthermore, increased vascular pressure and flow produced by the right ventricle resulted in higher pulmonary injury, as measured by ex vivo CT density (correlation: pressure r = 0.8; flow r = 0.85). Finally, RV ischemia as measured by troponin-T was negatively correlated with pulmonary injury (r = -0.76); however, troponin-T values did not determine RVF in all animals. In conclusion, we demonstrate a delicate balance between development of pulmonary ischemia-reperfusion injury and right ventricular function during lung transplantation. Furthermore, we provide a physiological basis for potential benefit of extracorporeal life support technology.NEW & NOTEWORTHY In contrast to the abundant literature of mechanical pulmonary artery clamping to increase right ventricular afterload, we developed a model adding a biological factor of pulmonary ischemia-reperfusion injury. We did not only focus on the right ventricular behavior, but also on the interaction with the injured lung. We are the first to describe this interaction while addressing the hemodynamic intraoperative phases of clinical lung transplantation.

Lymphocyte Depleting and Modulating Therapies for Chronic Lung Allograft Dysfunction

Chronic lung rejection, also called chronic lung allograft dysfunction (CLAD), remains the major hurdle limiting long-term survival after lung transplantation, and limited therapeutic options are available to slow the progressive decline in lung function. Most interventions are only temporarily effective in stabilizing the loss of or modestly improving lung function, with disease progression resuming over time in the majority of patients. Therefore, identification of effective treatments that prevent the onset or halt progression of CLAD is urgently needed. As a key effector cell in its pathophysiology, lymphocytes have been considered a therapeutic target in CLAD. The aim of this review is to evaluate the use and efficacy of lymphocyte depleting and immunomodulating therapies in progressive CLAD beyond usual maintenance immunosuppressive strategies. Modalities used include anti-thymocyte globulin, alemtuzumab, methotrexate, cyclophosphamide, total lymphoid irradiation, and extracorporeal photopheresis, and to explore possible future strategies. When considering both efficacy and risk of side effects, extracorporeal photopheresis, anti-thymocyte globulin and total lymphoid irradiation appear to offer the best treatment options currently available for progressive CLAD patients. SIGNIFICANCE STATEMENT: Effective treatments to prevent the onset and progression of chronic lung rejection after lung transplantation are still a major shortcoming. Based on existing data to date, considering both efficacy and risk of side effects, extracorporeal photopheresis, anti-thymocyte globulin, and total lymphoid irradiation are currently the most viable second-line treatment options. However, it is important to note that interpretation of most results is hampered by the lack of randomized controlled trials.

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.

Off-pump lung re-transplantation avoiding clamshell thoracotomy is feasible and safe: a single-center experience

Background

Lung re-transplantation (re-LTx) is the only therapeutic option for selected patients with advanced allograft dysfunction. This study aims to describe our center's experience to illustrate the feasibility and safety of off-pump re-LTx avoiding clamshell incision.

Methods

We performed a retrospective analysis of 42 patients who underwent bilateral re-LTx between 2007 and 2021. Patients were classified according to their surgical approach and extracorporeal life support (ECLS)-use. Demographics, surgical technique, and short- and long-term outcomes were compared between groups. Continuous data were examined with an independent-sample t-test or non-parametric test. Pearson's chi-squared and Fisher's exact were used to analyze categorical data.

Results

Twenty-six patients (61.9%) underwent re-LTx by anterior thoracotomy without ECLS. Compared to the more invasive approach (thoracotomy with ECLS and clamshell with/without ECLS, n=16, 38.1%), clamshell-avoiding off-pump re-LTx patients had a shorter operative time (471.6±111.2 vs. 704.0±273.4 min, P=0.010) and less frequent grade 3 primary graft dysfunction (PGD-3) at 72 h (7.7% vs. 37.5%, P=0.038). No significant difference was found in PGD-3 incidence within 72 h, mechanical ventilation, intensive care unit (ICU) and hospital stay, and the incidence of reoperation within 90 days between groups (P>0.05). In the long-term, the clamshell-avoiding and off-pump approach resulted in similar 1- and 5-year patient survival vs. the more invasive approach.

Conclusions

Our experience shows that clamshell-avoiding off-pump re-LTx is feasible and safe in selected patients on a case-by-case evaluation.

Mucosal immune alterations at the early onset of tissue destruction in chronic obstructive pulmonary disease

Rationale

COPD is characterized by chronic airway inflammation, small airways changes, with disappearance and obstruction, and also distal/alveolar destruction (emphysema). The chronology by which these three features evolve with altered mucosal immunity remains elusive. This study assessed the mucosal immune defense in human control and end-stage COPD lungs, by detailed microCT and RNA transcriptomic analysis of diversely affected zones.

Methods

In 11 control (non-used donors) and 11 COPD (end-stage) explant frozen lungs, 4 cylinders/cores were processed per lung for microCT and tissue transcriptomics. MicroCT was used to quantify tissue percentage and alveolar surface density to classify the COPD cores in mild, moderate and severe alveolar destruction groups, as well as to quantify terminal bronchioles in each group. Transcriptomics of each core assessed fold changes in innate and adaptive cells and pathway enrichment score between control and COPD cores. Immunostainings of immune cells were performed for validation.

Results

In mildly affected zones, decreased defensins and increased mucus production were observed, along CD8+ T cell accumulation and activation of the IgA pathway. In more severely affected zones, CD68+ myeloid antigen-presenting cells, CD4+ T cells and B cells, as well as MHCII and IgA pathway genes were upregulated. In contrast, terminal bronchioles were decreased in all COPD cores.

Conclusion

Spatial investigation of end-stage COPD lungs show that mucosal defense dysregulation with decreased defensins and increased mucus and IgA responses, start concomitantly with CD8+ T-cell accumulation in mild emphysema zones, where terminal bronchioles are already decreased. In contrast, adaptive Th and B cell activation is observed in areas with more advanced tissue destruction. This study suggests that in COPD innate immune alterations occur early in the tissue destruction process, which affects both the alveoli and the terminal bronchioles, before the onset of an adaptive immune response.

Lung Transplant Outcome From Selected Older Donors (≥70 Years) Equals Younger Donors (<70 Years): A Propensity-matched Analysis

OBJECTIVE

To describe our experience with lung transplantation (LTx) from donors ≥70 years and compare short and long-term outcomes to a propensity-matched cohort of donors <70 years.

BACKGROUND

Although extended-criteria donors have been widely used to enlarge the donor pool, the experience with LTx from older donors (≥70 years) remains limited.

METHODS

All single-center bilateral LTx between 2010 and 2020 were retrospectively analyzed. Matching (1:1) was performed for the donor (type, sex, smoking history, x-ray abnormalities, partial pressure of oxygen/fraction of inspired oxygen ratio, and time on ventilator) and recipient characteristics (age, sex, LTx indication, perioperative extracorporeal life support, and cytomegalovirus mismatch). Primary graft dysfunction grade-3, 5-year patient, and chronic lung allograft dysfunction-free survival were analyzed.

RESULTS

Out of 647 bilateral LTx, 69 were performed from donors ≥70 years. The mean age in the older donor cohort was 74 years (range: 70-84 years) versus 49 years (range: 12-69 years) in the matched younger group. No significant differences were observed in the length of ventilatory support, intensive care unit, or hospital stay. Primary graft dysfunction-3 was 26% in the older group versus 29% in younger donor recipients ( P = 0.85). Reintervention rate was comparable (29% vs 16%; P = 0.10). Follow-up bronchoscopy revealed no difference in bronchial anastomotic complications ( P = 1.00). Five-year patient and chronic lung allograft dysfunction-free survivals were 73.6% versus 73.1% ( P = 0.72) and 51.5% versus 59.2% ( P = 0.41), respectively.

CONCLUSIONS

LTx from selected donors ≥70 years is feasible and safe, yielding comparable short and long-term outcomes in a propensity-matched analysis with younger donors (<70 years).

COVID-19 progression in hospitalized patients using follow-up in vivo CT and ex vivo microCT

BACKGROUND

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes coronavirus disease-19 (COVID-19) which can lead to acute respiratory distress syndrome (ARDS) and evolve to pulmonary fibrosis. Computed tomography (CT) is used to study disease progression and describe radiological patterns in COVID-19 patients. This study aimed to assess disease progression regarding lung volume and density over time on follow-up in vivo chest CT and give a unique look at parenchymal and morphological airway changes in "end-stage" COVID-19 lungs using ex vivo microCT.

METHODS

Volumes and densities of the lung/lobes of three COVID-19 patients were assessed using follow-up in vivo CT and ex vivo whole lung microCT scans. Airways were quantified by airway segmentations on whole lung microCT and small-partition microCT. As controls, three discarded healthy donor lungs were used. Histology was performed in differently affected regions in the COVID-19 lungs.

RESULTS

In vivo, COVID-19 lung volumes decreased while density increased over time, mainly in lower lobes as previously shown. Ex vivo COVID-19 lung volumes decreased by 60% and all lobes were smaller compared to controls. Airways were more visible on ex vivo microCT in COVID-19, probably due to fibrosis and increased airway diameter. In addition, small-partition microCT showed more deformation of (small) airway morphology and fibrotic organization in severely affected regions with heterogeneous distributions within the same lung which was confirmed by histology.

CONCLUSIONS

COVID-19-ARDS and subsequent pulmonary fibrosis alters lung architecture and airway morphology which is described using in vivo CT, ex vivo microCT, and histology.

A Multi-omic Analysis of the Human Lung Reveals Distinct Cell Specific Aging and Senescence Molecular Programs

Age is a major risk factor for lung disease. To understand the mechanisms underlying this association, we characterized the changing cellular, genomic, transcriptional, and epigenetic landscape of lung aging using bulk and single-cell RNAseq (scRNAseq) data. Our analysis revealed age-associated gene networks that reflected hallmarks of aging, including mitochondrial dysfunction, inflammation, and cellular senescence. Cell type deconvolution revealed age-associated changes in the cellular composition of the lung: decreased alveolar epithelial cells and increased fibroblasts and endothelial cells. In the alveolar microenvironment, aging is characterized by decreased AT2B cells and reduced surfactant production, a finding that was validated by scRNAseq and IHC. We showed that a previously reported senescence signature, SenMayo, captures cells expressing canonical senescence markers. SenMayo signature also identified cell-type specific senescence-associated co-expression modules that have distinct molecular functions, including ECM regulation, cell signaling, and damage response pathways. Analysis of somatic mutations showed that burden was highest in lymphocytes and endothelial cells and was associated with high expression of senescence signature. Finally, aging and senescence gene expression modules were associated with differentially methylated regions, with inflammatory markers such as IL1B, IL6R, and TNF being significantly regulated with age. Our findings provide new insights into the mechanisms underlying lung aging and may have implications for the development of interventions to prevent or treat age-related lung diseases.

CT-based Machine Learning for Donor Lung Screening Prior to Transplantation

Background

Assessment and selection of donor lungs remains largely subjective and experience based. Criteria to accept or decline lungs are poorly standardized and are not compliant with the current donor pool. Using ex vivo CT images, we investigated the use of a CT-based machine learning algorithm for screening donor lungs prior to transplantation.

Methods

Clinical measures and ex-situ CT scans were collected from 100 cases as part of a prospective clinical trial. Following procurement, donor lungs were inflated, placed on ice according to routine clinical practice, and imaged using a clinical CT scanner prior to transplantation while stored in the icebox. We trained and tested a supervised machine learning method called dictionary learning , which uses CT scans and learns specific image patterns and features pertaining to each class for a classification task. The results were evaluated with donor and recipient clinical measures.

Results

Of the 100 lung pairs donated, 70 were considered acceptable for transplantation (based on standard clinical assessment) prior to CT screening and were consequently implanted. The remaining 30 pairs were screened but not transplanted. Our machine learning algorithm was able to detect pulmonary abnormalities on the CT scans. Among the patients who received donor lungs, our algorithm identified recipients who had extended stays in the ICU and were at 19 times higher risk of developing CLAD within 2 years post-transplant.

Conclusions

We have created a strategy to ex vivo screen donor lungs using a CT-based machine learning algorithm. As the use of suboptimal donor lungs rises, it is important to have in place objective techniques that will assist physicians in accurately screening donor lungs to identify recipients most at risk of post-transplant complications.

RIPK1 kinase-dependent inflammation and cell death contribute to the pathogenesis of COPD

RATIONALE

Receptor-interacting protein kinase 1 (RIPK1) is a key mediator of regulated cell death (including apoptosis and necroptosis) and inflammation, both drivers of chronic obstructive pulmonary disease (COPD) pathogenesis.

OBJECTIVE

We aimed to define the contribution of RIPK1 kinase-dependent cell death and inflammation in the pathogenesis of COPD.

METHODS

We assessed RIPK1 expression in single-cell RNA-sequencing data from human and mouse lungs and validated RIPK1 levels in lung tissue of COPD patients via immunohistochemistry. Next, we assessed the consequences of genetic and pharmacological inhibition of RIPK1 kinase activity in experimental COPD, using Ripk1^{S25D /S25D} kinase deficient mice and the RIPK1 kinase inhibitor GSK'547.

MEASUREMENTS AND MAIN RESULTS

RIPK1 expression increased in alveolar type I (AT1), AT2, ciliated and neuroendocrine cells in human COPD. RIPK1 protein levels were significantly increased in airway epithelium of COPD patients, compared to never smokers and smokers without airflow limitation. In mice, exposure to cigarette smoke (CS) increased Ripk1 expression similarly in AT2 cells, and further in alveolar macrophages and T cells. Genetic and/or pharmacological inhibition of RIPK1 kinase activity significantly attenuated airway inflammation upon acute and subacute CS-exposure, as well as airway remodeling, emphysema and apoptotic and necroptotic cell death upon chronic CS-exposure. Similarly, pharmacological RIPK1 kinase inhibition significantly attenuated elastase-induced emphysema and lung function decline. Finally, RNA-sequencing on lung tissue of CS-exposed mice revealed downregulation of cell death and inflammatory pathways upon pharmacological RIPK1 kinase inhibition.

CONCLUSIONS

RIPK1 kinase inhibition is protective in experimental models of COPD and may represent a novel promising therapeutic approach.

Can we attenuate ischaemia-reperfusion injury of allografts in a porcine left lung transplant models by adsorption of cytokines?

OBJECTIVES

Primary graft dysfunction resulting from ischaemia-reperfusion injury remains a major obstacle after lung transplantation (LTx) and is associated with morbidity and mortality. Continuous release of inflammatory cytokines, due to the process of ischaemia and reperfusion, triggers a complex cascade of apoptosis and necrosis resulting in graft dysfunction. Previous studies demonstrated successful graft improvement by cytokine filtration during ex vivo lung perfusion. We hypothesize that plasma cytokine filtration with CytoSorb® during in vivo graft perfusion immediately after implantation may attenuate ischaemia-reperfusion injury after left LTx in a porcine model.

METHODS

Left porcine LTx was performed with allografts preserved for 24 h at 4°C. In the treatment group [T] (n = 7), a veno-venous shunt was created to insert the cytokine filter (CytoSorbents, Berlin, Germany). In the sham group [S] (n = 4), the shunt was created without the filter. Haemodynamic parameters, lung mechanics, blood gases and plasma cytokines were assessed during 6 h in vivo reperfusion.

RESULTS

During 6 h of reperfusion, significant differences in plasma pro-inflammatory cytokine [interferon (IFN)-α, IFN-γ and interleukin (IL)-6] concentrations were observed between [T] and [S], but surprisingly with higher plasma levels in the [T] group. Plasma concentrations of other pro-inflammatory cytokines (IL-1β, IL-12p40, IL-4, IL-6, IL-8, IFN-α, IFN-γ and tumour necrosis factor-α) and anti-inflammatory cytokines (IL-10) did not find any evidence for a difference. Furthermore, our study failed to show meaningful difference in haemodynamics and blood gases. Also, no statistically significant differences were found between [T] and [S] in biopsies and wet-to-dry ratio at the end of the experiment.

CONCLUSIONS

In our porcine left LTx model cytokine filtration did not achieve the intended effect. This is in contrast to previous studies with CytoSorb use during ex vivo lung perfusion as a surrogate LTx model. Our findings might highlight the fact that the theoretical benefit of inserting an additional cytokine adsorber to improve graft function in clinical practice should be critically evaluated with further studies.

Allogeneic Hematopoietic Stem Cell Transplantation After Prior Lung Transplantation for Hereditary Pulmonary Alveolar Proteinosis: A Case Report

Pulmonary alveolar proteinosis (PAP) is a rare, diffuse lung disorder characterized by surfactant accumulation in the small airways due to defective clearance by alveolar macrophages, resulting in impaired gas exchange. Whole lung lavage is the current standard of care treatment for PAP. Lung transplantation is an accepted treatment option when whole lung lavage or other experimental treatment options are ineffective, or in case of extensive pulmonary fibrosis secondary to PAP. A disadvantage of lung transplantation is recurrence of PAP in the transplanted lungs, especially in hereditary PAP. The hereditary form of PAP is an ultra-rare condition caused by genetic mutations in genes encoding for the granulocyte macrophage-colony stimulating factor (GM-CSF) receptor, and intrinsically affects bone marrow derived-monocytes, which differentiate into macrophages in the lung. Consequently, these macrophages typically display disrupted GM-CSF receptor-signaling, causing defective surfactant clearance. Bone marrow/hematopoietic stem cell transplantation may potentially reverse the lung disease in hereditary PAP. In patients with hereditary PAP undergoing lung transplantation, post-lung transplant recurrence of PAP may theoretically be averted by subsequent hematopoietic stem cell transplantation, which results in a graft-versus-disease (PAP) effect, and thus could improve long-term outcome. We describe the successful long-term post-transplant outcome of a unique case of end-stage respiratory failure due to hereditary PAP-induced pulmonary fibrosis, successfully treated by bilateral lung transplantation and subsequent allogeneic hematopoietic stem cell transplantation. Our report supports treatment with serial lung and hematopoietic stem cell transplantation to improve quality of life and prolong survival, without PAP recurrence, in selected patients with end-stage hereditary PAP.

The MUC5B Promoter Polymorphism is Not Associated With Non-ILD Chronic Respiratory Diseases or Post-transplant Outcome

The MUC5B promoter polymorphism (rs35705950) has been associated with interstitial lung disease (ILD) and with prolonged pre-transplant survival in idiopathic pulmonary fibrosis (IPF), but no information is available regarding its prevalence in other respiratory diseases and its influence on post-transplant outcome. We included the Leuven lung transplantation cohort between 1991 and 2015 (n = 801). We assessed the minor allele frequency (MAF) of the MUC5B variant in the entire study cohort and investigated the influence of recipient MUC5B promoter polymorphism on post-transplant outcome in patients who were transplanted after 2004. MUC5B was successfully genotyped in 746 patients. The MAF was significantly higher in ILD (17.6%) compared to chronic obstructive pulmonary disease (COPD)/emphysema (9.3%), cystic fibrosis (CF)/bronchiectasis (BRECT) (7.5%) and pulmonary hypertension (PHT) (7.4%) (p < 0.001). No association was observed between rs35705950 and chronic lung allograft dysfunction (CLAD)/graft loss in the ILD population [CLAD: HR 1.37 95% CI (0.70-2.68); graft loss: HR 1.02 95% CI (0.55-1.89)], nor the entire study cohort [CLAD: HR 0.96 95% CI (0.69-1.34); graft loss: HR 0.97 95% CI (0.70-1.35)]. The MUC5B promoter polymorphism is a very specific predictive factor for the presence of pulmonary fibrosis as it is only associated with pulmonary fibrosis and not with other chronic respiratory diseases. While the MUC5B promoter variant is associated with better pre-transplant survival among IPF patients, recipient MUC5B promoter variant does not play a role in post-transplant outcome.

Impact of anastomosis time during lung transplantation on primary graft dysfunction

Primary graft dysfunction (PGD) is a major obstacle after lung transplantation (LTx), associated with increased early morbidity and mortality. Studies in liver and kidney transplantation revealed prolonged anastomosis time (AT) as an independent risk factor for impaired short- and long-term outcomes. We investigated if AT during LTx is a risk factor for PGD. In this retrospective single-center cohort study, we included all first double lung transplantations between 2008 and 2016. The association of AT with any PGD grade 3 (PGD3) within the first 72 h post-transplant was analyzed by univariable and multivariable logistic regression analysis. Data on AT and PGD was available for 427 patients of which 130 (30.2%) developed PGD3. AT was independently associated with the development of any PGD3 ≤72 h in uni- (odds ratio [OR] per 10 min 1.293, 95% confidence interval [CI 1.136-1.471], p < .0001) and multivariable (OR 1.205, 95% CI [1.022-1.421], p = .03) logistic regression analysis. There was no evidence that the relation between AT and PGD3 differed between lung recipients from donation after brain death versus donation after circulatory death donors. This study identified AT as an independent risk factor for the development of PGD3 post-LTx. We suggest that the implantation time should be kept short and the lung cooled to decrease PGD-related morbidity and mortality post-LTx.

The molecular and cellular mechanisms associated with the destruction of terminal bronchioles in COPD

RATIONALE

Peripheral airway obstruction is a key feature of chronic obstructive pulmonary disease (COPD), but the mechanisms of airway loss are unknown. This study aims to identify the molecular and cellular mechanisms associated with peripheral airway obstruction in COPD.

METHODS

Ten explanted lung specimens donated by patients with very severe COPD treated by lung transplantation and five unused donor control lungs were sampled using systematic uniform random sampling (SURS), resulting in 240 samples. These samples were further examined by micro-computed tomography (CT), quantitative histology and gene expression profiling.

RESULTS

Micro-CT analysis showed that the loss of terminal bronchioles in COPD occurs in regions of microscopic emphysematous destruction with an average airspace size of ≥500 and <1000 µm, which we have termed a "hot spot". Based on microarray gene expression profiling, the hot spot was associated with an 11-gene signature, with upregulation of pro-inflammatory genes and downregulation of inhibitory immune checkpoint genes, indicating immune response activation. Results from both quantitative histology and the bioinformatics computational tool CIBERSORT, which predicts the percentage of immune cells in tissues from transcriptomic data, showed that the hot spot regions were associated with increased infiltration of CD4 and CD8 T-cell and B-cell lymphocytes.

INTERPRETATION

The reduction in terminal bronchioles observed in lungs from patients with COPD occurs in a hot spot of microscopic emphysema, where there is upregulation of IFNG signalling, co-stimulatory immune checkpoint genes and genes related to the inflammasome pathway, and increased infiltration of immune cells. These could be potential targets for therapeutic interventions in COPD.

Microbial Community Composition in Explanted Cystic Fibrosis and Control Donor Lungs

To date, investigations of the microbiota in the lungs of people with Cystic Fibrosis (PWCF) have primarily focused on microbial community composition in luminal mucus, with fewer studies observing the microbiota in tissue samples from explanted lung tissue. Here, we analysed both tissue and airway luminal mucus samples extracted from whole explanted lungs of PWCF and unused donor lungs. We determined if the lung microbiota in end-stage CF varied within and between patients, was spatially heterogeneous and related to localized structural damage. Microbial community composition was determined by Illumina MiSeq sequencing and related to the CF-Computed Tomography (CT) score and features of end-stage lung disease on micro-CT. Ninety-eight CF tissue (n=11 patients), 20 CF luminal mucus (n=8 patients) and 33 donor tissue (n=4 patients) samples were analysed. Additionally, we compared 20 paired CF tissue and luminal mucus samples that enabled a direct “geographical” comparison of the microbiota in these two niches. Significant differences in microbial communities were apparent between the 3 groups. However, overlap between the three groups, particularly between CF and donor tissue and CF tissue and CF luminal mucus was also observed. Microbial diversity was lower in CF luminal mucus compared to CF tissue, with dominance higher in luminal mucus. For both CF and donor tissue, intra- and inter-patient variability in ecological parameters was observed. No relationships were observed between ecological parameters and CF-CT score, or features of end-stage lung disease. The end-stage CF lung is characterised by a low diversity microbiota, differing within and between individuals. No clear relationship was observed between regional microbiota variation and structural lung damage.

A Focused Review on Primary Graft Dysfunction after Clinical Lung Transplantation: A Multilevel Syndrome

Primary graft dysfunction (PGD) is the clinical syndrome of acute lung injury after lung transplantation (LTx). However, PGD is an umbrella term that encompasses the ongoing pathophysiological and -biological mechanisms occurring in the lung grafts. Therefore, we aim to provide a focused review on the clinical, physiological, radiological, histological and cellular level of PGD. PGD is graded based on hypoxemia and chest X-ray (CXR) infiltrates. High-grade PGD is associated with inferior outcome after LTx. Lung edema is the main characteristic of PGD and alters pulmonary compliance, gas exchange and circulation. A conventional CXR provides a rough estimate of lung edema, while a chest computed tomography (CT) results in a more in-depth analysis. Macroscopically, interstitial and alveolar edema can be distinguished below the visceral lung surface. On the histological level, PGD correlates to a pattern of diffuse alveolar damage (DAD). At the cellular level, ischemia-reperfusion injury (IRI) is the main trigger for the disruption of the endothelial-epithelial alveolar barrier and inflammatory cascade. The multilevel approach integrating all PGD-related aspects results in a better understanding of acute lung failure after LTx, providing novel insights for future therapies.

A Comprehensive Review on the Surgical Aspect of Lung Transplant Models in Mice and Rats

Lung transplantation improves the outcome and quality of life of patients with end-stage pulmonary disease. However, the procedure is still hampered by the lack of suitable donors, the complexity of the surgery, and the risk of developing chronic lung allograft dysfunction. Over the past decades, translational experiments in animal models have led to a better understanding of physiology and immunopathology following the lung transplant procedure. Small animal models (e.g., rats and mice) are mostly used in experiments regarding immunology and pathobiology and are preferred over large animal models due to the ethical aspects, the cost-benefit balance, and the high throughput possibility. In this comprehensive review, we summarize the reported surgical techniques for lung transplantation in rodent models and the management of perioperative complications. Furthermore, we propose a guide to help identify the appropriate species for a given experiment and discuss recent experimental findings in small animal lung transplant models.

Lung Microenvironments and Disease Progression in Fibrotic Hypersensitivity Pneumonitis

Rationale: Fibrotic hypersensitivity pneumonitis (fHP) is an interstitial lung disease caused by sensitization to an inhaled allergen. Objectives: To identify the molecular determinants associated with progression of fibrosis. Methods: Nine fHP explant lungs and six unused donor lungs (as controls) were systematically sampled (4 samples/lung). According to microcomputed tomography measures, fHP cores were clustered into mild, moderate, and severe fibrosis groups. Gene expression profiles were assessed using weighted gene co-expression network analysis, xCell, gene ontology, and structure enrichment analysis. Gene expression of the prevailing molecular traits was also compared with idiopathic pulmonary fibrosis (IPF). The explant lung findings were evaluated in separate clinical fHP cohorts using tissue, BAL samples, and computed tomography scans. Measurements and Main Results: We found six molecular traits that associated with differential lung involvement. In fHP, extracellular matrix and antigen presentation/sensitization transcriptomic signatures characterized lung zones with only mild structural and histological changes, whereas signatures involved in honeycombing and B cells dominated the transcriptome in the most severely affected lung zones. With increasing disease severity, endothelial function was progressively lost, and progressive disruption in normal cellular homeostatic processes emerged. All six were also found in IPF, with largely similar associations with disease microenvironments. The molecular traits correlated with in vivo disease behavior in a separate clinical fHP cohort. Conclusions: We identified six molecular traits that characterize the morphological progression of fHP and associate with in vivo clinical behavior. Comparing IPF with fHP, the transcriptome landscape was determined considerably by local disease extent rather than by diagnosis alone.

MiR-223 is increased in lungs of patients with COPD and modulates cigarette smoke-induced pulmonary inflammation

Since microRNA (miR)-223-3p modulates inflammatory responses and COPD is associated with amplified pulmonary inflammation, we hypothesized that miR-223-3p plays a role in COPD pathogenesis. Expression of miR-223-3p was measured in lung tissue of 2 independent cohorts with COPD GOLD stage II-IV patients, never smokers and smokers without COPD. The functional role of miR-223-3p was studied in deficient mice and upon overexpression in airway epithelial cells from COPD and controls. We observed higher miR-223-3p levels in patients with COPD stage II-IV compared to (non)-smoking controls, and levels were associated with higher neutrophil numbers in bronchial biopsies of COPD patients. MiR-223-3p expression was also increased in lungs and bronchoalveolar lavage of cigarette smoke (CS)-exposed mice. CS-induced neutrophil and monocyte lung infiltration was stronger in miR-223 deficient mice upon acute (5 days) exposure, but attenuated upon sub-chronic (4 weeks) exposure. Additionally, miR-223 deficiency attenuated acute and sub-chronic CS-induced lung infiltration of dendritic cells and T lymphocytes. Finally, in vitro overexpression of miR-223-3p in non-COPD airway epithelial cells suppressed CXCL8 and GM-CSF secretion and gene expression of the pro-inflammatory transcription factor TRAF6. Importantly, this suppressive effect of miR-223-3p was compromised in COPD-derived cultures. In conclusion, we demonstrate that miR-223-3p is increased in lungs of COPD patients and CS-exposed mice, and is associated with neutrophilic inflammation. In vivo data indicate that miR-223 acts as negative regulator of acute CS-induced neutrophilic and monocytic inflammation. In vitro data suggests that miR-223-3p does so by suppressing pro-inflammatory airway epithelial responses, which is less effective in COPD epithelium.

Diagnostic Yield of 18F-FDG PET After Lung Transplantation: A Single-center, Retrospective Cohort Study

BACKGROUND

To investigate the diagnostic yield of 18F-fluorodeoxyglucose positron emission tomography (18F-FDG PET) in lung transplant recipients.

METHODS

A single-center, retrospective cohort study including 234 18F-FDG PET examinations in 199 lung transplant recipients. Indication for PET referral, 18F-FDG PET diagnosis/findings and final clinical diagnosis were classified into 3 groups: malignancy, infection/inflammation not otherwise specified, and chronic lung allograft dysfunction with restrictive allograft syndrome phenotype. Sensitivity/specificity analysis was performed to determine accuracy of 18F-FDG PET in each group.

RESULTS

Sensitivity of 18F-FDG PET for malignancy was 91.4% (95% confidence interval, 82.5%-96.0%) and specificity was 82.3% (95% confidence interval, 74.5%-88.1%). Infection/inflammation not otherwise specified and restrictive allograft syndrome as indication for 18F-FDG PET comprised relatively small groups (14 and 31 cases, respectively). In addition, 18F-FDG PET revealed clinically relevant incidental findings in 15% of cases.

CONCLUSIONS

Referral for 18F-FDG PET after lung transplantation mainly occurred to confirm or rule out malignancy. In this specific setting, 18F-FDG PET has a high diagnostic yield. Accuracy of 18F-FDG PET for other indications is less clear, given small sample sizes. Clinically relevant diagnoses, unrelated to the primary indication for 18F-FDG PET, are found relatively often in this immunocompromised cohort.

Early protein expression profile in bronchoalveolar lavage fluid and clinical outcomes in primary graft dysfunction after lung transplantation

OBJECTIVES

Primary graft dysfunction (PGD) remains a major post-transplant complication and is associated with increased morbidity and mortality. Mechanisms evoking PGD are not completely clear, but inflammation plays a central role. We investigated the association between PGD and inflammatory proteins present in immediate postoperative bronchoalveolar lavage.

METHODS

All double-lung recipients transplanted at our institution from 2002 to 2018 were included in our study. We retrospectively selected 80 consecutive lung transplant recipients with different PGD grades (n = 20 for each PGD grades 0-1 to 2-3). In bronchoalveolar lavage performed within the first 24 h after donor aortic cross-clamping following lung transplantation, concentrations of 30 cytokines, chemokines and growth factors were assessed by enzyme-linked immunosorbent assay (ELISA) and correlated with donor and recipient demographics and outcomes. For analysis, 2 groups were defined: 'mild' PGD (grade 0-1) and 'severe' PGD (grades 2-3).

RESULTS

Significant differences between mild and severe PGD were found in 8 biomarkers [interleukin (IL)-6, IL-10, IL-13, eotaxin, granulocyte colony-stimulating factor, interferon γ, macrophage inflammatory protein 1α, surfactant protein D (SP-D); P < 0.05]. Increased IL-10 and IL-13, but none of the other proteins, were associated with short-term outcome (longer time to extubation; P = 0.005 and P < 0.0001; increased intensive care unit stay; P = 0.012 and P < 0.0001; and hospital stay; P = 0.041 and P = 0.002). There were no significant differences in donor and recipient characteristics between the groups.

CONCLUSIONS

Expression profiles of key inflammatory mediators in bronchoalveolar lavage fluid differed significantly between lung transplant recipients with severe versus mild PGD and correlated with clinical outcome variables. Further research should focus on the early mechanisms leading to PGD.

Connective Tissue Growth Factor Is Overexpressed in Explant Lung Tissue and Broncho-Alveolar Lavage in Transplant-Related Pulmonary Fibrosis

Background

Connective tissue growth factor (CTGF) is an important mediator in several fibrotic diseases, including lung fibrosis. We investigated CTGF-expression in chronic lung allograft dysfunction (CLAD) and pulmonary graft-versus-host disease (GVHD).

Materials and Methods

CTGF expression was assessed by quantitative real-time polymerase chain reaction (qPCR) and immunohistochemistry in end-stage CLAD explant lung tissue (bronchiolitis obliterans syndrome (BOS), n=20; restrictive allograft syndrome (RAS), n=20), pulmonary GHVD (n=9). Unused donor lungs served as control group (n=20). Next, 60 matched lung transplant recipients (BOS, n=20; RAS, n=20; stable lung transplant recipients, n=20) were included for analysis of CTGF protein levels in plasma and broncho-alveolar lavage (BAL) fluid at 3 months post-transplant, 1 year post-transplant, at CLAD diagnosis or 2 years post-transplant in stable patients.

Results

qPCR revealed an overall significant difference in the relative content of CTGF mRNA in BOS, RAS and pulmonary GVHD vs. controls (p=0.014). Immunohistochemistry showed a significant higher percentage and intensity of CTGF-positive respiratory epithelial cells in BOS, RAS and pulmonary GVHD patients vs. controls (p<0.0001). BAL CTGF protein levels were significantly higher at 3 months post-transplant in future RAS vs. stable or BOS (p=0.028). At CLAD diagnosis, BAL protein content was significantly increased in RAS patients vs. stable (p=0.0007) and BOS patients (p=0.042). CTGF plasma values were similar in BOS, RAS, and stable patients (p=0.74).

Conclusions

Lung CTGF-expression is increased in end-stage CLAD and pulmonary GVHD; and higher CTGF-levels are present in BAL of RAS patients at CLAD diagnosis. Our results suggest a potential role for CTGF in CLAD, especially RAS, and pulmonary GVHD.

The transition from normal lung anatomy to minimal and established fibrosis in idiopathic pulmonary fibrosis (IPF)

BACKGROUND

The transition from normal lung anatomy to minimal and established fibrosis is an important feature of the pathology of idiopathic pulmonary fibrosis (IPF). The purpose of this report is to examine the molecular and cellular mechanisms associated with this transition.

METHODS

Pre-operative thoracic Multidetector Computed Tomography (MDCT) scans of patients with severe IPF (n = 9) were used to identify regions of minimal(n = 27) and established fibrosis(n = 27). MDCT, Micro-CT, quantitative histology, and next-generation sequencing were used to compare 24 samples from donor controls (n = 4) to minimal and established fibrosis samples.

FINDINGS

The present results extended earlier reports about the transition from normal lung anatomy to minimal and established fibrosis by showing that there are activations of TGFBI, T cell co-stimulatory genes, and the down-regulation of inhibitory immune-checkpoint genes compared to controls. The expression patterns of these genes indicated activation of a field immune response, which is further supported by the increased infiltration of inflammatory immune cells dominated by lymphocytes that are capable of forming lymphoid follicles. Moreover, fibrosis pathways, mucin secretion, surfactant, TLRs, and cytokine storm-related genes also participate in the transitions from normal lung anatomy to minimal and established fibrosis.

INTERPRETATION

The transition from normal lung anatomy to minimal and established fibrosis is associated with genes that are involved in the tissue repair processes, the activation of immune responses as well as the increased infiltration of CD4, CD8, B cell lymphocytes, and macrophages. These molecular and cellular events correlate with the development of structural abnormality of IPF and probably contribute to its pathogenesis.

Genome-wide CRISPR screening identifies TMEM106B as a proviral host factor for SARS-CoV-2

The ongoing COVID-19 pandemic has caused a global economic and health crisis. To identify host factors essential for coronavirus infection, we performed genome-wide functional genetic screens with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and human coronavirus 229E. These screens uncovered virus-specific as well as shared host factors, including TMEM41B and PI3K type 3. We discovered that SARS-CoV-2 requires the lysosomal protein TMEM106B to infect human cell lines and primary lung cells. TMEM106B overexpression enhanced SARS-CoV-2 infection as well as pseudovirus infection, suggesting a role in viral entry. Furthermore, single-cell RNA-sequencing of airway cells from patients with COVID-19 demonstrated that TMEM106B expression correlates with SARS-CoV-2 infection. The present study uncovered a collection of coronavirus host factors that may be exploited to develop drugs against SARS-CoV-2 infection or future zoonotic coronavirus outbreaks.

Once daily tacrolimus conversion in lung transplantation: A prospective study on safety and medication adherence

BACKGROUND

Lung transplantation (LTx) requires a calcineurin inhibitor-based immunosuppressive regimen. A once daily (QD) tacrolimus regimen was developed to increase medication adherence. However, data concerning its safety and efficacy in LTx are lacking.

METHODS

In this prospective study, stable LTx patients were consecutively converted from twice daily (BID) tacrolimus to QD tacrolimus on a 1 mg:1 mg basis. Trough level (C_min), renal function, cholesterol, fasting glucose, potassium and lung function were monitored six months before and up to one year after conversion. Adherence and its barriers were assessed by self-reported questionnaires (Basel Assessment of Adherence to Immunosuppressive Medications Scale (BAASIS) and Identification of Medication Adherence Barriers questionnaire (IMAB)) and blood-based assays (mean C_min and coefficient of variation (CV)).

RESULTS

We included 372 patients, in whom we observed a decrease in tacrolimus C_min of 18.5% (p < 0.0001) post-conversion, requiring subsequent daily dose adaptations in both cystic fibrosis (CF) (n = 72) and non-CF patients (n = 300). We observed a small decrease in eGFR one year post-conversion (p = 0.024). No significant changes in blood creatinine, potassium, fasting glucose, cholesterol or rate of lung function decline were observed. In a subgroup of 166 patients, significantly fewer patients missed doses (8.4% vs. 19.3%, p = 0.016) or had irregular intake post-conversion (19.3% vs. 32.5%, p = 0.019). Mean C_min and CV, as well as the total number of barriers, also decreased significantly post-conversion.

CONCLUSIONS

In LTx, conversion from BID to QD tacrolimus (1 mg:1 mg) requires close monitoring of tacrolimus C_min. QD tacrolimus after transplantation is safe with respect to renal function, metabolic parameters and allograft function and improves LTx recipient adherence.

Real life experience with mTOR-inhibitors after lung transplantation

Mammalian target of rapamycin inhibitors (mTORi) are increasingly used after lung transplantation as part of a calcineurin inhibitor sparing regimen, aiming to preserve renal function. The aim of our study was to determine whether immunosuppressive therapy using mTORi in lung transplant recipients (LTR) is feasible in practice, or limited by intolerance and adverse events. Data were retrospectively assessed for all LTR transplanted between July 1991 and January 2020. Patients ever receiving mTORi (monotherapy or in combination with calcineurin inhibitor) as treatment of physicians' choice were included. 149/1184 (13%) of the LTR ever received mTORi. Main reasons to start were renal insufficiency (67%) and malignancy (21%). In 52% of the patients, mTORi was stopped due to side effects or drug toxicity after a median time of 159 days. Apart from death, main reasons for discontinuation were infection (19%) and edema (14%). Early discontinuation (<90 days) was mainly due to edema or gastrointestinal intolerance. As mTORi was stopped due to adverse events or drug intolerance in 52% of LTR, cautious consideration of advantages and disadvantages when starting mTORi is recommended.

Profibrotic epithelial TGF-β1 signaling involves NOX4-mitochondria cross talk and redox-mediated activation of the tyrosine kinase FYN

Idiopathic pulmonary fibrosis (IPF) is characterized by a disturbed redox balance and increased production of reactive oxygen species (ROS), which is believed to contribute to epithelial injury and fibrotic lung scarring. The main pulmonary sources of ROS include mitochondria and NADPH oxidases (NOXs), of which the NOX4 isoform has been implicated in IPF. Non-receptor SRC tyrosine kinases (SFK) are important for cellular homeostasis and are often dysregulated in lung diseases. SFK activation by the profibrotic transforming growth factor-β (TGF-β) is thought to contribute to pulmonary fibrosis, but the relevant SFK isoform and its relationship to NOX4 and/or mitochondrial ROS in the context of profibrotic TGF-β signaling is not known. Here, we demonstrate that TGF-β1 can rapidly activate the SRC kinase FYN in human bronchial epithelial cells, which subsequently induces mitochondrial ROS (mtROS) production, genetic damage shown by the DNA damage marker γH2AX, and increased expression of profibrotic genes. Moreover, TGF-β1-induced activation of FYN involves initial activation of NOX4 and direct cysteine oxidation of FYN, and both FYN and mtROS contribute to TGF-β-induced induction of NOX4. NOX4 expression in lung tissues of IPF patients is positively correlated with disease severity, although FYN expression is down-regulated in IPF and does not correlate with disease severity. Collectively, our findings highlight a critical role for FYN in TGF-β1-induced mtROS production, DNA damage response, and induction of profibrotic genes in bronchial epithelial cells, and suggest that altered expression and activation of NOX4 and FYN may contribute to the pathogenesis of pulmonary fibrosis.

Flow-controlled ventilation during EVLP improves oxygenation and preserves alveolar recruitment

BACKGROUND

Ex vivo lung perfusion (EVLP) is a widespread accepted platform for preservation and evaluation of donor lungs prior to lung transplantation (LTx). Standard lungs are ventilated using volume-controlled ventilation (VCV). We investigated the effects of flow-controlled ventilation (FCV) in a large animal EVLP model. Fourteen porcine lungs were mounted on EVLP after a warm ischemic interval of 2 h and randomized in two groups (n = 7/group). In VCV, 7 grafts were conventionally ventilated and in FCV, 7 grafts were ventilated by flow-controlled ventilation. EVLP physiologic parameters (compliance, pulmonary vascular resistance and oxygenation) were recorded hourly. After 6 h of EVLP, broncho-alveolar lavage (BAL) was performed and biopsies for wet-to-dry weight (W/D) ratio and histology were taken. The left lung was inflated, frozen in liquid nitrogen vapors and scanned with computed tomography (CT) to assess regional distribution of Hounsfield units (HU).

RESULTS

All lungs endured 6 h of EVLP. Oxygenation was better in FCV compared to VCV (p = 0.01) and the decrease in lung compliance was less in FCV (p = 0.03). W/D ratio, pathology and BAL samples did not differ between both groups (p = 0.16, p = 0.55 and p = 0.62). Overall, CT densities tended to be less pronounced in FCV (p = 0.05). Distribution of CT densities revealed a higher proportion of well-aerated lung parts in FCV compared to VCV (p = 0.01).

CONCLUSIONS

FCV in pulmonary grafts mounted on EVLP is feasible and leads to improved oxygenation and alveolar recruitment. This ventilation strategy might prolong EVLP over time, with less risk for volutrauma and atelectrauma.

Peripheral Blood Eosinophilia Is Associated with Poor Outcome Post-Lung Transplantation

Eosinophils play a role in many chronic lung diseases. In lung transplantation (LTx), increased eosinophils in bronchoalveolar lavage (BAL) was associated with worse outcomes. However, the effect of peripheral blood eosinophilia after LTx has not been investigated thoroughly. A retrospective study was performed including all LTx patients between 2011-2016. Chronic lung allograft dysfunction (CLAD)-free and graft survival were compared between patients with high and low blood eosinophils using an 8% threshold ever during follow-up. A total of 102 patients (27.1%) had high blood eosinophils (≥8%) (45 before CLAD and 17 after, 40 had no CLAD) and 274 (72.9%) had low eosinophils (<8%). Patients with high blood eosinophils demonstrated worse graft survival (p = 0.0001) and CLAD-free survival (p = 0.003) compared to low eosinophils. Patients with both high blood and high BAL (≥2%) eosinophils ever during follow-up had the worst outcomes. Within the high blood eosinophil group, 23.5% had RAS compared to 3% in the group with low eosinophils (p < 0.0001). After multivariate analysis, the association between high blood eosinophils and graft and CLAD-free survival remained significant (p = 0.036, p = 0.013) independent of high BAL eosinophils and infection at peak blood eosinophilia, among others. LTx recipients with ever ≥8% blood eosinophils demonstrate inferior graft and CLAD-free survival, specifically RAS, which requires further prospective research.

Pathological Comparisons of Paraseptal and Centrilobular Emphysema in Chronic Obstructive Pulmonary Disease

Rationale: Although centrilobular emphysema (CLE) and paraseptal emphysema (PSE) are commonly identified on multidetector computed tomography (MDCT), little is known about the pathology associated with PSE compared with that of CLE.Objectives: To assess the pathological differences between PSE and CLE in chronic obstructive pulmonary disease (COPD).Methods: Air-inflated frozen lung specimens (n = 6) obtained from patients with severe COPD treated by lung transplantation were scanned with MDCT. Frozen tissue cores were taken from central (n = 8) and peripheral (n = 8) regions of each lung, scanned with micro-computed tomography (microCT), and processed for histology. The core locations were registered to the MDCT, and a percentage of PSE or CLE was assigned by radiologists to each of the regions. MicroCT scans were used to measure number and structural change of terminal bronchioles. Furthermore, microCT-based volume fractions of CLE and PSE allowed classifying cores into mild emphysema, CLE-dominant, and PSE-dominant.Measurements and Main Results: The percentages of PSE measured on MDCT and microCT were positively associated (P = 0.015). The number of terminal bronchioles per milliliter of lung and cross-sectional lumen area were significantly lower and wall area percentage was significantly higher in CLE-dominant regions compared with mild emphysema and PSE-dominant regions (all P < 0.05), whereas no difference was found between PSE-dominant and mild emphysema samples (all P > 0.5). Immunohistochemistry showed significantly higher infiltration of neutrophils (P = 0.002), but not of macrophages, CD4, CD8, or B cells, in PSE compared with CLE regions.Conclusions: The terminal bronchioles are relatively preserved, whereas neutrophilic inflammation is increased in PSE-dominant regions compared with CLE-dominant regions in patients with COPD.

Small airway loss in the physiologically ageing lung: a cross-sectional study in unused donor lungs

BACKGROUND

Physiological lung ageing is associated with a gradual decline in dynamic lung volumes and a progressive increase in residual volume due to diminished elastic recoil of the lung, loss of alveolar tissue, and lower chest wall compliance. However, the effects of ageing on the small airways (ie, airways <2·0 mm in diameter) remain largely unknown. By using a combination of ex-vivo conventional CT (resolution 1 mm), whole lung micro-CT (resolution 150 μm), and micro-CT of extracted cores (resolution 10 μm), we aimed to provide a multiresolution assessment of the small airways in lung ageing in a large cohort of never smokers.

METHODS

For this cross-sectional study, we included donor lungs collected from 32 deceased never-smoking donors (age range 16-83 years). Ex-vivo CT and whole lung high-resolution CT (micro-CT) were used to determine total airway numbers, stratified by airway diameter. Micro-CT was used to assess the number, length, and diameter of terminal bronchioles (ie, the last generation of conducting airways); mean linear intercept; and surface density in four lung tissue cores from each lung, extracted using a uniform sampling approach. Regression β coefficients are calculated using linear regression and polynomial models.

FINDINGS

Ex-vivo CT analysis showed an age-dependent decrease in the number of airways of diameter 2·0 mm to less than 2·5 mm (β coefficient per decade -0·119, 95% CI -0·193 to -0·045; R²=0·29) and especially in airways smaller than 2·0 mm in diameter (-0·158, -0·233 to -0·084; R²=0·47), between 30 and 80 years of age, but not of the larger (≥2·5 mm) diameter airways (-0·00781, -0·04409 to 0·02848; R²=0·0007). In micro-CT analysis of small airways, the total number of terminal bronchioles per lung increased until the age of 30 years, after which an almost linear decline in the number of terminal bronchioles was observed (β coefficient per decade -2035, 95% CI -2818 to -1252; R²=0·55), accompanied by a non-significant increase in alveolar airspace size (6·44, -0·57 to 13·45, R²=0·10). Moreover, this decrease in terminal bronchioles was associated with the age-related decline of pulmonary function predicted by healthy reference values.

INTERPRETATION

Loss of terminal bronchioles is an important structural component of age-related decline in pulmonary function of healthy, non-smoking individuals.

FUNDING

Research Foundation-Flanders, KU Leuven, Parker B Francis Foundation, UGent, Canadian Institutes for Health.

Late-onset "acute fibrinous and organising pneumonia" impairs long-term lung allograft function and survival

Acute fibrinous and organising pneumonia (AFOP) after lung transplantation is associated with a rapid decline in pulmonary function. However, the relation with chronic lung allograft dysfunction (CLAD) remains unclear. We investigated the association between detection of AFOP in lung allograft biopsies with clinically important endpoints.We reviewed lung allograft biopsies from 468 patients who underwent lung transplantation at the University Hospitals Leuven (2011-2017). AFOP was categorised as early new-onset (≤90 days post-transplant) or late new-onset (>90 days post-transplant); and associated with CLAD-free survival, graft survival, donor-specific antibodies, airway and blood eosinophilia.Early and late AFOP was detected in 24 (5%) and 30 (6%) patients, respectively. CLAD-free survival was significantly lower in patients with late AFOP (median survival 2.42 years; p<0.0001) compared with patients with early or without AFOP and specifically associated with development of restrictive allograft syndrome (OR 28.57, 95% CI 11.34-67.88; p<0.0001). Similarly, graft survival was significantly lower in patients with late AFOP (median survival 4.39 years; p<0.0001) compared with patients with early AFOP or without AFOP. Late AFOP was furthermore associated with detection of circulating donor-specific antibodies (OR 4.75, 95% CI 2.17-10.60; p=0.0004) compared with patients with early or without AFOP, and elevated airway and blood eosinophilia (p=0.043 and p=0.045, respectively) compared with early AFOP patients.Late new-onset AFOP is associated with a worse prognosis and high risk of CLAD development, specifically restrictive allograft syndrome. Our findings indicate that late new-onset AFOP might play a role in the early pathogenesis of restrictive allograft syndrome.

Histopathologic and radiologic assessment of nontransplanted donor lungs

Donor organ shortage results in significant waiting list mortality. Donor lung assessment is currently based on donors' history, gas exchange, chest X-ray, bronchoscopy findings, and ultimately in situ inspection but remains subjective. We correlated histopathology and radiology in nontransplanted donor lungs with the clinical indications to decline the offered organ. Sixty-two donor lungs, not used for transplantation (2010-2019), were procured, air-inflated, frozen, scanned with computed tomography, systematically sampled, and histologically and radiologically assessed. Thirty-nine (63%) lungs were declined for allograft-related reasons. In 13/39 (33%) lungs, histology could not confirm the reason for decline, in an additional 8/39 (21%) lungs, histologic abnormalities were only considered mild. In 16/39 (41%) lungs, radiology could not confirm the reason for decline. Twenty-three (37%) donor lungs were not transplanted due to extrapulmonary causes, of which three (13%) lungs displayed severe histologic abnormalities (pneumonia, n = 2; emphysema, n = 1), in addition to mild emphysema in 9 (39%) lungs and minor bronchopneumonia in 1 (4%). Radiology revealed ground-glass opacities in 8/23 (35%) and emphysema in 4/23 (17%) lungs. Histopathologic and radiologic assessment of nontransplanted donor lungs revealed substantial discrepancy with the clinical reason for decline. Optimization of donor lung assessment is necessary to improve current organ acceptance rates.

Successful Pseudomonas aeruginosa eradication improves outcomes after lung transplantation: a retrospective cohort analysis

Long-term survival after lung transplantation (LTx) is hampered by development of chronic lung allograft dysfunction (CLAD). Pseudomonas aeruginosa is an established risk factor for CLAD. Therefore, we investigated the effect of P. aeruginosa eradication on CLAD-free and graft survival.

Patients who underwent first LTx between July, 1991, and February, 2016, and were free from CLAD, were retrospectively classified according to P. aeruginosa presence in respiratory samples between September, 2011, and September, 2016. P. aeruginosa-positive patients were subsequently stratified according to success of P. aeruginosa eradication following targeted antibiotic treatment. CLAD-free and graft survival were compared between P. aeruginosa-positive and P. aeruginosa-negative patients; and between patients with or without successful P. aeruginosa eradication. In addition, pulmonary function was assessed during the first year following P. aeruginosa isolation in both groups.

CLAD-free survival of P. aeruginosa-negative patients (n=443) was longer compared with P. aeruginosa-positive patients (n=95) (p=0.045). Graft survival of P. aeruginosa-negative patients (n=443, 82%) was better compared with P. aeruginosa-positive patients (n=95, 18%) (p<0.0001). Similarly, P. aeruginosa-eradicated patients demonstrated longer CLAD-free and graft survival compared with patients with persistent P. aeruginosa. Pulmonary function was higher in successfully P. aeruginosa-eradicated patients compared with unsuccessfully eradicated patients (p=0.035).

P. aeruginosa eradication after LTx improves CLAD-free and graft survival and maintains pulmonary function. Therefore, early P. aeruginosa detection and eradication should be pursued.