The ex vivo human lung: research value for translational science

A meta-analysis of perfusion parameters affecting weight gain in ex vivo perfusion

BACKGROUND

Ex vivo machine perfusion (EVMP) has been established to extend viability of donor organs. However, EVMP protocols are inconsistent. We hypothesize that there is a significant relationship between specific parameters during EVMP and perfusion outcomes.

METHODS

A meta-analysis of literature was conducted in accordance with the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) Statement. The search encompassed articles published before July 25, 2023. PubMed, Embase, and CENTRAL databases were screened using search terms "ex-vivo," "ex-situ," "machine," and "perfusion." Weight gain, an indicator of organ viability, was chosen to compare outcomes. Extracted variables included perfused organ, warm and cold ischemia time before perfusion, perfusion duration, perfusate flow, pressure, temperature, perfusate composition (presence of cellular or acellular oxygen carrier, colloids, and other supplements) and percent weight change. Data were analyzed using SPSS statistical software.

RESULTS

Overall, 44 articles were included. Red blood cell-based perfusates resulted in significantly lower weight gain compared to acellular perfusates without oxygen carriers (11.3% vs. 27.0%, p < 0.001). Hemoglobin-based oxygen carriers resulted in significantly lower weight gain compared to acellular perfusates (16.5% vs. 27%, p = 0.006). Normothermic perfusion led to the least weight gain (14.6%), significantly different from hypothermic (24.3%) and subnormothermic (25.0%) conditions (p < 0.001), with no significant difference between hypothermic and subnormothermic groups (24.3% vs. 25.0%, p = 0.952). There was a positive correlation between flow rate and weight gain (ß = 13.1, R = 0.390, p < 0.001).

CONCLUSIONS

Oxygen carriers, low flow rates, and normothermic perfusate temperature appear to improve outcomes in EVMP. These findings offer opportunities for improving organ transplantation outcomes.

Feasibility and accuracy of DireCt Lung Ultrasound Evaluation technique to monitor extravascular lung water in porcine lungs

OBJECTIVES

Extravascular lung water precedes deterioration of pulmonary function. Current tools to assess extravascular lung water in a setting of donor lung procurement and ex vivo lung perfusion (EVLP) are either subjective or not feasible. Therefore, a direCt Lung Ultrasound Evaluation (CLUE) has been introduced. This study reassesses the feasibility and accuracy of CLUE by measuring its correlation with lung weight, wet-to-dry ratio (W/D ratio), dynamic compliance and pulmonary vascular resistance (PVR) in a porcine model.

METHODS

CLUE images, lung weight, dynamic compliance and PVR were recorded and lung samples for W/D ratio were taken before and after EVLP. CLUE score was calculated based on B-lines on images taken at each point of the lung using an established equation.

RESULTS

Eighteen porcine lungs were included. Total median of CLUE score, lung weight, W/D ratio and PVR increased significantly, while median of dynamic compliance decreased significantly after EVLP. Total median CLUE score increased significantly in all four surfaces after EVLP with equally high CLUE scores in posterior and diaphragm lines. CLUE score demonstrated a significant strong positive correlation with lung weight (r = 0.825) and W/D ratio (r = 0.837), while CLUE's correlation with dynamic compliance and PVR was significantly moderate to strong (r = -0.669, r = 0.695, respectively).

CONCLUSIONS

CLUE technique is feasible to assess extravascular lung water in donor lungs after procurement and during EVLP. CLUE score correlated significantly with lung weight, W/D ratio, dynamic compliance and PVR. Transplant suitability of a donor lung may not solely depend on CLUE evaluation.

Technical Advances Targeting Multiday Preservation of Isolated Ex Vivo Lung Perfusion

Indications for ex vivo lung perfusion (EVLP) have evolved from assessment of questionable donor lungs to treatment of some pathologies and the logistics. Yet up to 3 quarters of donor lungs remain discarded across the globe. Multiday preservation of discarded human lungs on EVLP platforms would improve donor lung utilization rates via application of sophisticated treatment modalities, which could eventually result in zero waitlist mortality. The purpose of this article is to summarize advances made on the technical aspects of the protocols in achieving a stable multiday preservation of isolated EVLP. Based on the evidence derived from large animal and/or human studies, the following advances have been considered important in achieving this goal: ability to reposition donor lungs during EVLP; perfusate adsorption/filtration modalities; perfusate enrichment with plasma and/or donor whole blood, nutrients, vitamins, and amino acids; low-flow, pulsatile, and subnormothermic perfusion; positive outflow pressure; injury specific personalized ventilation strategies; and negative pressure ventilation. Combination of some of these advances in an automatized EVLP device capable of managing perfusate biochemistry and ventilation would likely speed up the processes of achieving multiday preservation of isolated EVLP.

Cell-Free Hemoglobin in the Pathophysiology of Trauma: A Scoping Review

OBJECTIVES

Cell-free hemoglobin (CFH) is a potent mediator of endothelial dysfunction, organ injury, coagulopathy, and immunomodulation in hemolysis. These mechanisms have been demonstrated in patients with sepsis, hemoglobinopathies, and those receiving transfusions. However, less is known about the role of CFH in the pathophysiology of trauma, despite the release of equivalent levels of free hemoglobin.

DATA SOURCES

Ovid MEDLINE, Embase, Web of Science Core Collection, and BIOSIS Previews were searched up to January 21, 2023, using key terms related to free hemoglobin and trauma.

DATA EXTRACTION

Two independent reviewers selected studies focused on hemolysis in trauma patients, hemoglobin breakdown products, hemoglobin-mediated injury in trauma, transfusion, sepsis, or therapeutics.

DATA SYNTHESIS

Data from the selected studies and their references were synthesized into a narrative review.

CONCLUSIONS

Free hemoglobin likely plays a role in endothelial dysfunction, organ injury, coagulopathy, and immune dysfunction in polytrauma. This is a compelling area of investigation as multiple existing therapeutics effectively block these pathways.

Perioperative fluid management for lung transplantation is challenging

Lung transplantation is the definitive end-stage treatment for many lung diseases, and postoperative pulmonary oedema severely affects survival after lung transplantation. Optimizing perioperative fluid management can reduce the incidence of postoperative pulmonary oedema and improve the prognosis of lung transplant patients by removing the influence of patient, donor's lung and ECMO factors. Therefore, this article reviews seven aspects of lung transplant patients' pathophysiological characteristics, physiological characteristics of fluids, the influence of the donor lung on pulmonary oedema as well as current fluid rehydration concepts, advantages or disadvantages of intraoperative monitoring tools or types of fluids on postoperative pulmonary oedema, while showing the existing challenges in section 7. The aim is to show the specificity of perioperative fluid management in lung transplant patients and to provide new ideas for individualised fluid management in lung transplantation.

Towards an artificial human lung: modelling organ-like complexity to aid mechanistic understanding

Respiratory diseases account for over 5 million deaths yearly and are a huge burden to healthcare systems worldwide. Murine models have been of paramount importance to decode human lung biology in vivo, but their genetic, anatomical, physiological and immunological differences with humans significantly hamper successful translation of research into clinical practice. Thus, to clearly understand human lung physiology, development, homeostasis and mechanistic dysregulation that may lead to disease, it is essential to develop models that accurately recreate the extraordinary complexity of the human pulmonary architecture and biology. Recent advances in micro-engineering technology and tissue engineering have allowed the development of more sophisticated models intending to bridge the gap between the native lung and its replicates in vitro Alongside advanced culture techniques, remarkable technological growth in downstream analyses has significantly increased the predictive power of human biology-based in vitro models by allowing capture and quantification of complex signals. Refined integrated multi-omics readouts could lead to an acceleration of the translational pipeline from in vitro experimental settings to drug development and clinical testing in the future. This review highlights the range and complexity of state-of-the-art lung models for different areas of the respiratory system, from nasal to large airways, small airways and alveoli, with consideration of various aspects of disease states and their potential applications, including pre-clinical drug testing. We explore how development of optimised physiologically relevant in vitro human lung models could accelerate the identification of novel therapeutics with increased potential to translate successfully from the bench to the patient's bedside.

Impact of e-cigarette aerosol on primary human alveolar epithelial type 2 cells

Electronic cigarettes (e-cigarettes) are designed to simulate combustible cigarette smoking and to aid in smoking cessation. Although the number of e-cigarette users has been increasing, the potential health impacts and biological effects of e-cigarettes are still not fully understood. Previous research has focused on the biological effects of e-cigarettes on lung cancer cell lines and distal airway epithelial cells; however, there have been few published studies on the effect of e-cigarettes on primary lung alveolar epithelial cells. The primary purpose of this study was to investigate the direct effect of e-cigarette aerosol on primary human lung alveolar epithelial type 2 (AT2) cells, both alone and in the presence of viral infection. The Melo-3 atomizer caused direct AT2 cell toxicity, whereas the more popular Juul pod's aerosol did not have a detectable cytotoxic effect on AT2 cells. Juul nicotine aerosol also did not increase short-term susceptibility to viral infection. However, 3 days of exposure upregulated genes central to the generation of reactive oxygen species, lipid peroxidation, and carcinogen metabolism and downregulated key innate immune system genes related to cytokine and chemokine signaling. These findings have implications for the potentially injurious impact of long-term use of popular low-power e-cigarette pods on the human alveolar epithelium. Gene expression data might be an important endpoint for evaluating the potential harmful effects of vaping devices that do not cause overt toxicity.

Aerosolized vitamin E acetate causes oxidative injury in mice and in alveolar macrophages

Although vitamin E acetate (VEA) is suspected to play a causal role in the development of electronic-cigarette, or vaping, product use-associated lung injury (EVALI), the underlying biological mechanisms of pulmonary injury are yet to be determined. In addition, no study has replicated the systemic inflammation observed in humans in a murine EVALI model, nor investigated potential additive toxicity of viral infection in the setting of exposure to vaping products. To identify the mechanisms driving VEA-related lung injury and test the hypothesis that viral infection causes additive lung injury in the presence of aerosolized VEA, we exposed mice to aerosolized VEA for extended times, followed by influenza infection in some experiments. We used mass spectrometry to evaluate the composition of aerosolized VEA condensate and the VEA deposition in murine or human alveolar macrophages. Extended vaping for 28 days versus 15 days did not worsen lung injury but caused systemic inflammation in the murine EVALI model. Vaping plus influenza increased lung water compared with virus alone. Murine alveolar macrophages exposed to vaped VEA hydrolyzed the VEA to vitamin E with evidence of oxidative stress in the alveolar space and systemic circulation. Aerosolized VEA also induced cell death and chemokine release and reduced efferocytotic function in human alveolar macrophages in vitro. These findings provide new insights into the biological mechanisms of VEA toxicity.

Donor leukocyte trafficking during human ex vivo lung perfusion

Background

Ex vivo lung perfusion (EVLP) is used to assess and preserve lungs prior to transplantation. However, its inherent immunomodulatory effects are not completely understood. We examine perfusate and tissue compartments to determine the change in immune cell composition in human lungs maintained on EVLP.

Methods

Six human lungs unsuitable for transplantation underwent EVLP. Tissue and perfusate samples were obtained during cold storage and at 1‐, 3‐ and 6‐h during perfusion. Flow cytometry, immunohistochemistry, and bead‐based immunoassays were used to measure leukocyte composition and cytokines. Mean values between baseline and time points were compared by Student's t test.

Results

During the 1st hour of perfusion, perfusate neutrophils increased (+22.2 ± 13.5%, p < 0.05), monocytes decreased (−77.5 ± 8.6%, p < 0.01) and NK cells decreased (−61.5 ± 22.6%, p < 0.01) compared to cold storage. In contrast, tissue neutrophils decreased (−22.1 ± 12.2%, p < 0.05) with no change in monocytes and NK cells. By 6 h, perfusate neutrophils, NK cells, and tissue neutrophils were similar to baseline. Perfusate monocytes remained decreased, while tissue monocytes remained unchanged. There was no significant change in B cells or T cell subsets. Pro‐inflammatory cytokines (IL‐1b, G‐CSF, IFN‐gamma, CXCL2, CXCL1 granzyme A, and granzyme B) and lymphocyte activating cytokines (IL‐2, IL‐4, IL‐6, IL‐8) increased during perfusion.

Conclusions

Early mobilization of innate immune cells occurs in both perfusate and tissue compartments during EVLP, with neutrophils and NK cells returning to baseline and monocytes remaining depleted after 6 h. The immunomodulatory effect of EVLP may provide a therapeutic window to decrease the immunogenicity of lungs prior to transplantation.

Update on the Features and Measurements of Experimental Acute Lung Injury in Animals: An Official American Thoracic Society Workshop Report

Advancements in methods, technology, and our understanding of the pathobiology of lung injury have created the need to update the definition of experimental acute lung injury (ALI). We queried 50 participants with expertise in ALI and acute respiratory distress syndrome using a Delphi method composed of a series of electronic surveys and a virtual workshop. We propose that ALI presents as a "multidimensional entity" characterized by four "domains" that reflect the key pathophysiologic features and underlying biology of human acute respiratory distress syndrome. These domains are 1) histological evidence of tissue injury, 2) alteration of the alveolar-capillary barrier, 3) presence of an inflammatory response, and 4) physiologic dysfunction. For each domain, we present "relevant measurements," defined as those proposed by at least 30% of respondents. We propose that experimental ALI encompasses a continuum of models ranging from those focusing on gaining specific mechanistic insights to those primarily concerned with preclinical testing of novel therapeutics or interventions. We suggest that mechanistic studies may justifiably focus on a single domain of lung injury, but models must document alterations of at least three of the four domains to qualify as "experimental ALI." Finally, we propose that a time criterion defining "acute" in ALI remains relevant, but the actual time may vary based on the specific model and the aspect of injury being modeled. The continuum concept of ALI increases the flexibility and applicability of the definition to multiple models while increasing the likelihood of translating preclinical findings to critically ill patients.

Recent advances in human respiratory epithelium models for drug discovery

The respiratory epithelium is intimately associated with the pathophysiologies of highly infectious viral contagions and chronic illnesses such as chronic obstructive pulmonary disorder, presently the third leading cause of death worldwide with a projected economic burden of £1.7 trillion by 2030. Preclinical studies of respiratory physiology have almost exclusively utilised non-humanised animal models, alongside reductionistic cell line-based models, and primary epithelial cell models cultured at an air-liquid interface (ALI). Despite their utility, these model systems have been limited by their poor correlation to the human condition. This has undermined the ability to identify novel therapeutics, evidenced by a 15% chance of success for medicinal respiratory compounds entering clinical trials in 2018. Consequently, preclinical studies require new translational efficacy models to address the problem of respiratory drug attrition. This review describes the utility of the current in vivo (rodent), ex vivo (isolated perfused lungs and precision cut lung slices), two-dimensional in vitro cell-line (A549, BEAS-2B, Calu-3) and three-dimensional in vitro ALI (gold-standard and co-culture) and organoid respiratory epithelium models. The limitations to the application of these model systems in drug discovery research are discussed, in addition to perspectives of the future innovations required to facilitate the next generation of human-relevant respiratory models.

Nanotraps for the containment and clearance of SARS-CoV-2

SARS-CoV-2 enters host cells through its viral spike protein binding to angiotensin-converting enzyme 2 (ACE2) receptors on the host cells. Here, we show that functionalized nanoparticles, termed "Nanotraps," completely inhibited SARS-CoV-2 infection by blocking the interaction between the spike protein of SARS-CoV-2 and the ACE2 of host cells. The liposomal-based Nanotrap surfaces were functionalized with either recombinant ACE2 proteins or anti-SARS-CoV-2 neutralizing antibodies and phagocytosis-specific phosphatidylserines. The Nanotraps effectively captured SARS-CoV-2 and completely blocked SARS-CoV-2 infection to ACE2-expressing human cell lines and primary lung cells; the phosphatidylserine triggered subsequent phagocytosis of the virus-bound, biodegradable Nanotraps by macrophages, leading to the clearance of pseudotyped and authentic virus in vitro. Furthermore, the Nanotraps demonstrated an excellent biosafety profile in vitro and in vivo. Finally, the Nanotraps inhibited pseudotyped SARS-CoV-2 infection in live human lungs in an ex vivo lung perfusion system. In summary, Nanotraps represent a new nanomedicine for the inhibition of SARS-CoV-2 infection.

In Vitro Lung Models and Their Application to Study SARS-CoV-2 Pathogenesis and Disease

SARS-CoV-2 has spread across the globe with an astonishing velocity and lethality that has put scientist and pharmaceutical companies worldwide on the spot to develop novel treatment options and reliable vaccination for billions of people. To combat its associated disease COVID-19 and potentially newly emerging coronaviruses, numerous pre-clinical cell culture techniques have progressively been used, which allow the study of SARS-CoV-2 pathogenesis, basic replication mechanisms, and drug efficiency in the most authentic context. Hence, this review was designed to summarize and discuss currently used in vitro and ex vivo cell culture systems and will illustrate how these systems will help us to face the challenges imposed by the current SARS-CoV-2 pandemic.

Dose-Dependent Pulmonary Toxicity of Aerosolized Vitamin E Acetate

Electronic-cigarette, or vaping, product use-associated lung injury (EVALI) is a syndrome of acute respiratory failure characterized by monocytic and neutrophilic alveolar inflammation. Epidemiological and clinical evidence suggests a role of vitamin E acetate (VEA) in the development of EVALI, yet it remains unclear whether VEA has direct pulmonary toxicity. To test the hypotheses that aerosolized VEA causes lung injury in mice and directly injures human alveolar epithelial cells, we exposed adult mice and primary human alveolar epithelial type II (AT II) cells to an aerosol of VEA generated by a device designed for vaping oils. Outcome measures in mice included lung edema, BAL analysis, histology, and inflammatory cytokines; in vitro outcomes included cell death, cytokine release, cellular uptake of VEA, and gene-expression analysis. Comparison exposures in both models included the popular nicotine-containing JUUL aerosol. We discovered that VEA caused dose-dependent increases in lung water and BAL protein compared with control and JUUL-exposed mice in association with increased BAL neutrophils, oil-laden macrophages, multinucleated giant cells, and inflammatory cytokines. VEA aerosol was also toxic to AT II cells, causing increased cell death and the release of monocyte and neutrophil chemokines. VEA was directly absorbed by AT II cells, resulting in the differential gene expression of several inflammatory biological pathways. Given the epidemiological and clinical characteristics of the EVALI outbreak, these results suggest that VEA plays an important causal role.

Airway Natural Killer Cells and Bacteria in Health and Disease

Natural killer (NK) cells are innate lymphoid cells at the interface between innate and adaptive immunity and mostly studied for their important roles in viral infections and malignant tumors. They can kill diseased cells and produce cytokines and chemokines, thereby shaping the adaptive immune response. Nowadays, NK cells are considered as a strong weapon for cancer immunotherapy and can for example be transduced to express tumor-specific chimeric antigen receptors or harnessed with therapeutic antibodies such as the so-called NK engagers. Whereas a large body of literature exists about the antiviral and antitumoral properties of NK cells, their potential role in bacterial infections is not that well delineated. Furthermore, NK cells are much more heterogeneous than previously thought and have tissue-characteristic features and phenotypes. This review gives an overview of airway NK cells and their position within the immunological army dressed against bacterial infections in the upper and predominantly the lower respiratory tracts. Whereas it appears that in several infections, NK cells play a non-redundant and protective role, they can likewise act as rather detrimental. The use of mouse models and the difficulty of access to human airway tissues for ethical reasons might partly explain the divergent results. However, new methods are appearing that are likely to reduce the heterogeneity between studies and to give a more coherent picture in this field.

The endogenous capacity to produce proinflammatory mediators by the ex vivo human perfused lung

Background

The ex vivo human perfused lung model has enabled optimizing donor lungs for transplantation and delineating mechanisms of lung injury. Perfusate and airspace biomarkers are a proxy of the lung response to experimental conditions. However, there is a lack of studies evaluating biomarker kinetics during perfusion and after exposure to stimuli. In this study, we analyzed the ex vivo-perfused lung response to three key perturbations: exposure to the perfusion circuit, exogenous fresh whole blood, and bacteria.

Results

Ninety-nine lungs rejected for transplantation underwent ex vivo perfusion. One hour after reaching experimental conditions, fresh whole blood was added to the perfusate (n = 55). Two hours after reaching target temperature, Streptococcus pneumoniae was added to the perfusate (n = 42) or to the airspaces (n = 17). Perfusate and airspace samples were collected at baseline (once lungs were equilibrated for 1 h, but before blood or bacteria were added) and 4 h later. Interleukin (IL)-6, IL-8, angiopoietin (Ang)-2, and soluble tumor necrosis factor receptor (sTNFR)-1 were quantified. Baseline perfusate and airspace biomarker levels varied significantly, and this was not related to pre-procurement P_aO₂:FiO₂ ratio, cold ischemia time, and baseline alveolar fluid clearance (AFC). After 4 h of ex vivo perfusion, the lung demonstrated a sustained production of proinflammatory mediators. The change in biomarker levels was not influenced by baseline donor lung characteristics (cold ischemia time, baseline AFC) nor was it associated with measures of experimental epithelial (final AFC) or endothelial (percent weight gain) injury. In the presence of exogenous blood, the rise in biomarkers was attenuated. Lungs exposed to intravenous (IV) bacteria relative to control lungs demonstrated a significantly higher rise in perfusate IL-6.

Conclusions

The ex vivo-perfused lung has a marked endogenous capacity to produce inflammatory mediators over the course of short-term perfusion that is not significantly influenced by donor lung characteristics or the presence of exogenous blood, and only minimally affected by the introduction of systemic bacteremia. The lack of association between biomarker change and donor lung cold ischemia time, final alveolar fluid clearance, and experimental percent weight gain suggests that the maintained ability of the human lung to produce biomarkers is not merely a marker of lung epithelial or endothelial injury, but may support the function of the lung as an immune cell reservoir.

A CLUE for better assessment of donor lungs: Novel technique in clinical ex vivo lung perfusion

BACKGROUND

The direCt Lung Ultrasound Evaluation (CLUE) technique was proven to be an accurate method for monitoring extravascular lung water in donor lungs during ex vivo lung perfusion (EVLP) in an experimental model. The aim of this study was to examine the application of CLUE in the clinical setting.

METHODS

Lungs were evaluated using acellular EVLP protocol. Ultrasound images were obtained directly from the lung surface. Images were graded according to the percentage of B-lines seen on ultrasound. CLUE scores were calculated at the beginning and end of EVLP for the whole lung, each side, and lobe based on the number (No.) of images in each grade and the total No. of images taken and evaluated retrospectively.

RESULTS

A total of 23 EVLP cases were performed resulting in 13 lung transplants (LTxs) with no hospital mortality. Primary graft dysfunction (PGD) occurred in only 1 recipient (PGD3, no PGD2). Significant differences were found between suitable and non-suitable lungs in CLUE scores (1.03 vs 1.85, p < 0.001), unlike the partial pressure of oxygen/fraction of inspired oxygen ratio. CLUE had the highest area under the receiver operating characteristic curve (0.98) compared with other evaluation parameters. The initial CLUE score of standard donor lungs was significantly better than marginal lungs. The final CLUE score in proned lungs showed improvement when compared with initial CLUE score, especially in the upper lobes.

CONCLUSIONS

The CLUE technique shows the highest accuracy in evaluating donor lungs for LTx suitability compared with other parameters used in EVLP. CLUE can optimize the outcomes of LTx by guiding the decision making through the whole process of clinical EVLP.

The ex vivo perfused human lung is resistant to injury by high-dose S. pneumoniae bacteremia

Few patients with bacteremia from a nonpulmonary source develop acute respiratory distress syndrome (ARDS). However, the mechanisms that protect the lung from injury in bacteremia have not been identified. We simulated bacteremia by adding Streptococcus pneumoniae to the perfusate of the ex vivo perfused human lung model. In contrast to a pneumonia model in which bacteria were instilled into the distal air spaces of one lobe, injection of high doses of S. pneumoniae into the perfusate was not associated with alveolar epithelial injury as demonstrated by low protein permeability of the alveolar epithelium, intact alveolar fluid clearance, and the absence of alveolar edema. Unexpectedly, the ex vivo human lung rapidly cleared large quantities of S. pneumoniae even though the perfusate had very few intravascular phagocytes and lacked immunoglobulins or complement. The bacteria were cleared in part by the small number of neutrophils in the perfusate, alveolar macrophages in the airspaces, and probably by interstitial pathways. Together, these findings identify one mechanism by which the lung and the alveolar epithelium are protected from injury in bacteremia.

Bioengineering of Pulmonary Epithelium With Preservation of the Vascular Niche

The shortage of transplantable donor organs directly affects patients with end-stage lung disease, for which transplantation remains the only definitive treatment. With the current acceptance rate of donor lungs of only 20%, rescuing even one half of the rejected donor lungs would increase the number of transplantable lungs threefold, to 60%. We review recent advances in lung bioengineering that have potential to repair the epithelial and vascular compartments of the lung. Our focus is on the long-term support and recovery of the lung ex vivo, and the replacement of defective epithelium with healthy therapeutic cells. To this end, we first review the roles of the lung epithelium and vasculature, with focus on the alveolar-capillary membrane, and then discuss the available and emerging technologies for ex vivo bioengineering of the lung by decellularization and recellularization. While there have been many meritorious advances in these technologies for recovering marginal quality lungs to the levels needed to meet the standards for transplantation – many challenges remain, motivating further studies of the extended ex vivo support and interventions in the lung. We propose that the repair of injured epithelium with preservation of quiescent vasculature will be critical for the immediate blood supply to the lung and the lung survival and function following transplantation.

Acute respiratory distress syndrome subphenotypes and therapy responsive traits among preclinical models: protocol for a systematic review and meta-analysis

BACKGROUND

Subphenotypes were recently reported within clinical acute respiratory distress syndrome (ARDS), with distinct outcomes and therapeutic responses. Experimental models have long been used to mimic features of ARDS pathophysiology, but the presence of distinct subphenotypes among preclinical ARDS remains unknown. This review will investigate whether: 1) subphenotypes can be identified among preclinical ARDS models; 2) such subphenotypes can identify some responsive traits.

METHODS

We will include comparative preclinical (in vivo and ex vivo) ARDS studies published between 2009 and 2019 in which pre-specified therapies were assessed (interleukin (IL)-10, IL-2, stem cells, beta-agonists, corticosteroids, fibroblast growth factors, modulators of the receptor for advanced glycation end-products pathway, anticoagulants, and halogenated agents) and outcomes compared to a control condition. The primary outcome will be a composite of the four key features of preclinical ARDS as per the American Thoracic Society consensus conference (histologic evidence of lung injury, altered alveolar-capillary barrier, lung inflammatory response, and physiological dysfunction). Secondary outcomes will include the single components of the primary composite outcome, net alveolar fluid clearance, and death. MEDLINE, Embase, and Cochrane databases will be searched electronically and data from eligible studies will be extracted, pooled, and analyzed using random-effects models. Individual study reporting will be assessed according to the Animal Research: Reporting of In Vivo Experiments guidelines. Meta-regressions will be performed to identify subphenotypes prior to comparing outcomes across subphenotypes and treatment effects.

DISCUSSION

This study will inform on the presence and underlying pathophysiological features of subphenotypes among preclinical models of ARDS and should help to determine whether sufficient evidence exists to perform preclinical trials of subphenotype-targeted therapies, prior to potential clinical translation.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO (ID: CRD42019157236).

Recent advances in chronic obstructive pulmonary disease pathogenesis: from disease mechanisms to precision medicine

Chronic obstructive pulmonary disease (COPD) is a devastating lung disease with a high personal and societal burden. Exposure to toxic particles and gases, including cigarette smoke, is the main risk factor for COPD. Together with smoking cessation, current treatment strategies of COPD aim to improve symptoms and prevent exacerbations, but there is no disease-modifying treatment. The biggest drawback of today's COPD treatment regimen is the 'one size fits all' pharmacological intervention, mainly based on disease severity and symptoms and not the individual's disease pathology. To halt the worrying increase in the burden of COPD, disease management needs to be advanced with a focus on personalized treatment. The main pathological feature of COPD includes a chronic and abnormal inflammatory response within the lungs, which results in airway and alveolar changes in the lung as reflected by (small) airways disease and emphysema. Here we discuss recent developments related to the abnormal inflammatory response, ECM and age-related changes, structural changes in the small airways and the role of sex-related differences, which are all relevant to explain the individual differences in the disease pathology of COPD and improve disease endotyping. Furthermore, we will discuss the most recent developments of new treatment strategies using biologicals to target specific pathological features or disease endotypes of COPD. © 2020 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Implementation of an experimental isolated lung perfusion model on surgically resected human lobes

Isolated lung perfusion (ILP) is an ideal model to study treatment effects on a variety of pathologies. As published research mostly relies on rejected donor lungs or animal organs, this study investigates the use of surgically resected human lobes as an alternative and novel model for personalized experimental research. Ten surgically resected lobes were perfused in acellular and normothermic condition. The indication for surgery was lung cancer. Perfusion and ventilation were adapted to the size of the lobes and both functional and metabolic parameters were assessed during ILP. Patients (age 67.5 y (59–81)|♀n = 3|♂n = 7) underwent anatomic pulmonary lobectomy. Ischemic time between arterial ligation and ILP was 226 minutes (161–525). Median duration of ILP was 135 (87–366) minutes. Gas exchange and mechanical respiratory parameters remained steady during ILP (pulmonary venous pO₂ 196(151–219) mmHg | peak AWP: 14.5(11–22) cmH₂O). Metabolism stayed constant during ILP (Glucose consumption: 1.86 mg/min/L_TLC (95%CI: −2.09 to −1.63) | lactate production: 0.005 mmol/min/ L_TLC (95%CI: 0.004 to 0.007)). ILP of surgically resected human lobes is a feasible and promising method. By maintaining a near physiological setting, this model may pave the way for future experimental lung research including cancer research, transplantation, physiology, pharmacology and mechanical ventilation.