Gene set enrichment analysis identifies key innate immune pathways in primary graft dysfunction after lung transplantation

Assessment of NLRP3 inflammasome activation in patients with chronic obstructive pulmonary disease before and after lung transplantation

The interplay between purinergic receptors as well as pattern recognition receptors like Toll-like receptors (TLRs) and NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) might have a role in the pathogenesis of chronic obstructive pulmonary disease (COPD). The aim of this study was to determine and compare the concentrations of the damage-associated molecular patterns (DAMPs) heat shock protein 70 (Hsp70) and adenosine triphosphate (ATP), and gene expression of their respective receptors as well as NLRP3 inflammasome-related molecules in the peripheral blood of patients with end-stage COPD before and 1 year after lung transplantation (LT). Lung function was assessed by spirometry and diffusion capacity for carbon monoxide (DLCO). Quantitative polymerase chain reaction (qPCR) was applied for detection of TLR2, TLR4, P2X7R, P2Y2R, IL1B, CASP1, and NLRP3 expression. High-sensitivity ELISA kits were used for extracellular (e) Hsp70 and IL-1β, and luminescence assay for eATP measurements. Concentrations of eHsp70 and eATP as well as IL-1β were significantly increased in the plasma of end-stage COPD patients and significantly decreased after LT. In addition, TLR4, P2Y2R, IL1B, CASP1, and NLRP3 expression was up-regulated in COPD patients before LT, while it was significantly suppressed after LT. In conclusion, it could be assumed that NLRP3 inflammasome is activated in the peripheral blood of end-stage COPD patients and that eHsp70 and eATP could be responsible for its activation through triggering their receptors. On the other hand, previously enhanced pro-inflammatory reactions seem to be suppressed to the healthy population levels in lung recipients without allograft rejection.

Applications of transcriptomics in ischemia reperfusion research in lung transplantation

Ischemia-reperfusion (IR) injury contributes to primary graft dysfunction, a major cause of early mortality after lung transplantation. Transcriptomics uses high-throughput techniques to profile the RNA transcripts within a sample and provides a unique view of the mechanisms underlying various biological processes. This review aims to highlight the applications of transcriptomics in lung IR injury studies, which have thus far revealed inflammatory responses to be the major event activated by IR, identified potential biomarkers and therapeutic targets, and investigated the mechanisms of therapeutic interventions. Ex vivo lung perfusion, together with advanced bioinformatic and transcriptomic techniques, including single-cell RNA-sequencing, microRNA profiling, and multi-omics, continue to expand the capabilities of transcriptomics. In the future, the construction of biospecimen banks and the promotion of international collaborations among clinicians and researchers have the potential to advance our understanding of IR injury and improve the management of lung transplant recipients.

Aging exacerbates murine lung ischemia-reperfusion injury by excessive inflammation and impaired tissue repair response

Donor shortage is a major problem in lung transplantation (LTx), and the use of lungs from elderly donors is one of the possible solutions in a rapidly aging population. However, the utilization of organs from donors aged >65 years has remained infrequent and may be related to a poor outcome. To investigate the molecular events in grafts from elderly donors early after LTx, the left lungs of young and old mice were subjected to 1 hour of ischemia and subsequent reperfusion. The left lungs were collected at 1 hour, 1 day, and 3 days after reperfusion and subjected to wet-to-dry weight ratio measurement, histological analysis, and molecular biological analysis, including RNA sequencing. The lungs in old mice exhibited more severe and prolonged pulmonary edema than those in young mice after ischemia reperfusion, which was accompanied by upregulation of the genes associated with inflammation and impaired expression of cell cycle-related genes. Apoptotic cells increased and proliferating type 2 alveolar epithelial cells decreased in the lungs of old mice compared with young mice. These factors could become conceptual targets for developing interventions to ameliorate lung ischemia-reperfusion injury after LTx from elderly donors, which may serve to expand the old donor pool.

Modeling the Effects of IL-1β-mediated Inflammation During Ex Vivo Lung Perfusion Using a Split Human Donor Model

BACKGROUND

The association between interleukin-1β (IL-1β) concentrations during ex vivo lung perfusion (EVLP) with donor organ quality and post-lung transplant outcome has been demonstrated in several studies. The mechanism underlying IL-1β-mediated donor lung injury was investigated using a paired single-lung EVLP model.

METHODS

Human lung pairs were dissected into individual lungs and perfused on identical separate EVLP circuits, with one lung from each pair receiving a bolus of IL-1β. Fluorescently labeled human neutrophils isolated from a healthy volunteer were infused into both circuits and quantified in perfusate at regular timepoints. Perfusates and tissues were subsequently analyzed, with perfusates also used in functional assays.

RESULTS

Neutrophil numbers were significantly lower in perfusate samples collected from the IL-1β-stimulated lungs consistent with increased neutrophil adhesion ( P = 0.042). Stimulated lungs gained significantly more weight than controls ( P = 0.046), which correlated with soluble intercellular adhesion molecule-1 (R 2 = 0.71, P = 0.0043) and von-Willebrand factor (R 2 = 0.39, P = 0.040) in perfusate. RNA expression patterns for inflammatory genes were differentially regulated via IL-1β. Blockade of IL-1β significantly reduced neutrophil adhesion in vitro ( P = 0.025).

CONCLUSION

These data illustrate the proinflammatory functions of IL-1β in the context of EVLP, suggesting this pathway may be susceptible to therapeutic modulation before transplantation.

Therapeutic reconditioning of damaged lungs by transient heat stress during ex vivo lung perfusion

Ex vivo lung perfusion (EVLP) may serve as a platform for the pharmacologic repair of lung grafts before transplantation (LTx). We hypothesized that EVLP could also permit nonpharmacologic repair through the induction of a heat shock response, which confers stress adaptation via the expression of heat shock proteins (HSPs). Therefore, we evaluated whether transient heat application during EVLP (thermal preconditioning [TP]) might recondition damaged lungs before LTx. TP was performed during EVLP (3 hours) of rat lungs damaged by warm ischemia by transiently heating (30 minutes, 41.5 °C) the EVLP perfusate, followed by LTx (2 hours) reperfusion. We also assessed the TP (30 minutes, 42 °C) during EVLP (4 hours) of swine lungs damaged by prolonged cold ischemia. In rat lungs, TP induced HSP expression, reduced nuclear factor κB and inflammasome activity, oxidative stress, epithelial injury, inflammatory cytokines, necroptotic death signaling, and the expression of genes involved in innate immune and cell death pathways. After LTx, heated lungs displayed reduced inflammation, edema, histologic damage, improved compliance, and unchanged oxygenation. In pig lungs, TP induced HSP expression, reduced oxidative stress, inflammation, epithelial damage, vascular resistance, and ameliorated compliance. Collectively, these data indicate that transient heat application during EVLP promotes significant reconditioning of damaged lungs and improves their outcomes after transplantation.

Primary graft dysfunction after lung transplantation

PURPOSE OF REVIEW

Primary graft dysfunction (PGD) is a clinical syndrome occurring within the first 72 h after lung transplantation and is characterized clinically by progressive hypoxemia and radiographically by patchy alveolar infiltrates. Resulting from ischemia-reperfusion injury, PGD represents a complex interplay between donor and recipient immunologic factors, as well as acute inflammation leading to alveolar cell damage. In the long term, chronic inflammation invoked by PGD can contribute to the development of chronic lung allograft dysfunction, an important cause of late mortality after lung transplant.

RECENT FINDINGS

Recent work has aimed to identify risk factors for PGD, focusing on donor, recipient and technical factors both inherent and potentially modifiable. Although no PGD-specific therapy currently exists, supportive care remains paramount and early initiation of ECMO can improve outcomes in select patients. Initial success with ex-vivo lung perfusion platforms has been observed with respect to decreasing PGD risk and increasing lung transplant volume; however, the impact on survival is not well delineated.

SUMMARY

This review will summarize the pathogenesis and clinical features of PGD, as well as highlight treatment strategies and emerging technologies to mitigate PGD risk in patients undergoing lung transplantation.

The Lung Allograft Microbiome Associates with Pepsin, Inflammation, and Primary Graft Dysfunction

Rationale: Primary graft dysfunction (PGD) is the principal cause of early morbidity and mortality after lung transplantation. The lung microbiome has been implicated in later transplantation outcomes but has not been investigated in PGD. Objectives: To define the peritransplant bacterial lung microbiome and relationship to host response and PGD. Methods: This was a single-center prospective cohort study. Airway lavage samples from donor lungs before organ procurement and recipient allografts immediately after implantation underwent bacterial 16S ribosomal ribonucleic acid gene sequencing. Recipient allograft samples were analyzed for cytokines by multiplex array and pepsin by ELISA. Measurements and Main Results: We enrolled 139 transplant subjects and obtained donor lung (n = 109) and recipient allograft (n = 136) samples. Severe PGD (persistent grade 3) developed in 15 subjects over the first 72 hours, and 40 remained without PGD (persistent grade 0). The microbiome of donor lungs differed from healthy lungs, and recipient allograft microbiomes differed from donor lungs. Development of severe PGD was associated with enrichment in the immediate postimplantation lung of oropharyngeal anaerobic taxa, particularly Prevotella. Elevated pepsin, a gastric biomarker, and a hyperinflammatory cytokine profile were present in recipient allografts in severe PGD and strongly correlated with microbiome composition. Together, immediate postimplantation allograft Prevotella/Streptococcus ratio, pepsin, and indicator cytokines were associated with development of severe PGD during the 72-hour post-transplantation period (area under the curve = 0.81). Conclusions: Lung allografts that develop PGD have a microbiome enriched in anaerobic oropharyngeal taxa, elevated gastric pepsin, and hyperinflammatory phenotype. These findings suggest a possible role for peritransplant aspiration in PGD, a potentially actionable mechanism that warrants further investigation.

Follistatin-like 1 and Biomarkers of Neutrophil Activation Are Associated with Poor Short-Term Outcome after Lung Transplantation on VA-ECMO

The investigation of biomarkers associated with undesired outcome following lung transplantation (LuTX) is essential for a better understanding of the underlying pathophysiology, an earlier identification of susceptible recipients and the development of targeted therapeutic options. We therefore determined the longitudinal perioperative course of putative cytokines related to neutrophil activation (chemokine CC motif ligand 4 (CCL-4), interleukin (IL)-23 and Lipocalin 2 (LCN2)) and a cytokine that has been implicated in graft-versus-host disease (Follistatin-like 1 (FSTL1)) in 42 consecutive patients undergoing LuTX. We plotted receiver-operating curves (ROC) to assess the predictive power of the measured cytokines for short-term outcomes namely primary graft dysfunction (PGD), early complications requiring extracorporeal membrane oxygenation (ECMO), and a high postoperative sequential organ failure assessment (SOFA). All cytokines increased immediately after surgery. ROC analyses determined significant associations between CCL4 and a high SOFA score (area under the curve (AUC) 0.74 (95%CI:0.5−0.9; p < 0.05), between LCN2 and postoperative ECMO support (AUC 0.73 (95%CI:0.5−0.9; p < 0.05), and between FSTL1 and PGD (AUC 0.70 (95%CI:0.5−0.9; p < 0.05). The serum concentrations of the neutrophil-derived cytokines LCN2 and CCL4 as well as FSTL1 were all related to poor outcome after LuTX. The specific predictive power, however, still has to be assessed in larger trials. The potential role of FSTL1 as a biomarker in the development of PGD could be of great interest particularly since this protein appears to play a crucial role in allograft tolerance.

Volatile organic compound profiling to explore primary graft dysfunction after lung transplantation

Primary graft dysfunction (PGD) is a major determinant of morbidity and mortality following lung transplantation. Delineating basic mechanisms and molecular signatures of PGD remain a fundamental challenge. This pilot study examines if the pulmonary volatile organic compound (VOC) spectrum relate to PGD and postoperative outcomes. The VOC profiles of 58 bronchoalveolar lavage fluid (BALF) and blind bronchial aspirate samples from 35 transplant patients were extracted using solid-phase-microextraction and analyzed with comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry. The support vector machine algorithm was used to identify VOCs that could differentiate patients with severe from lower grade PGD. Using 20 statistically significant VOCs from the sample headspace collected immediately after transplantation (< 6 h), severe PGD was differentiable from low PGD with an AUROC of 0.90 and an accuracy of 0.83 on test set samples. The model was somewhat effective for later time points with an AUROC of 0.80. Three major chemical classes in the model were dominated by alkylated hydrocarbons, linear hydrocarbons, and aldehydes in severe PGD samples. These VOCs may have important clinical and mechanistic implications, therefore large-scale study and potential translation to breath analysis is recommended.

Primary graft dysfunction: what we know

Many advances in lung transplant have occurred over the last few decades in the understanding of primary graft dysfunction (PGD) though effective prevention and treatment remain elusive. This review will cover prior understanding of PGD, recent findings, and directions for future research. A consensus statement updating the definition of PGD in 2016 highlights the growing complexity of lung transplant perioperative care taking into account the increasing use of high flow oxygen delivery and pulmonary vasodilators in the current era. PGD, particularly more severe grades, is associated with worse short- and long-term outcomes after transplant such as chronic lung allograft dysfunction. Growing experience have helped identify recipient, donor, and intraoperative risk factors for PGD. Understanding the pathophysiology of PGD has advanced with increasing knowledge of the role of innate immune response, humoral cell immunity, and epithelial cell injury. Supportive care post-transplant with technological advances in extracorporeal membranous oxygenation (ECMO) remain the mainstay of treatment for severe PGD. Future directions include the evolving utility of ex vivo lung perfusion (EVLP) both in PGD research and potential pre-transplant treatment applications. PGD remains an important outcome in lung transplant and the future holds a lot of potential for improvement in understanding its pathophysiology as well as development of preventative therapies and treatment.

The NLRP3 Inflammasome: Relevance in Solid Organ Transplantation

The NOD, LRR, and pyrin domain-containing 3 (NLRP3) protein has been established as a central component of the inflammasome and regulates the inflammatory response to a myriad of environmental, microbial, and endogenous danger stimuli. Assembly of the NLRP3 inflammasome results in the cleavage and activation of caspase-1, in turn causing release of the pro-inflammatory interleukins 1-beta and 18. This activation response, while crucial to coordinated innate immune defense, can be aberrantly activated by the likes of cell-free DNA, and cause significant autoimmune pathology. Complications of autoimmunity induced by aberrant NLRP3 inflammasome activation have a great degree of mechanistic crossover with alloimmune injury in solid organ transplant, and stratagems to neutralize NLRP3 inflammasome activation may prove beneficial in solid organ transplant management. This article reviews NLRP3 inflammasome biology and the pathology associated with its hyperactivation, as well as the connections between NLRP3 inflammasome activation and allograft homeostasis.

Minimizing Ischemia Reperfusion Injury in Xenotransplantation

The recent dramatic advances in preventing "initial xenograft dysfunction" in pig-to-non-human primate heart transplantation achieved by minimizing ischemia suggests that ischemia reperfusion injury (IRI) plays an important role in cardiac xenotransplantation. Here we review the molecular, cellular, and immune mechanisms that characterize IRI and associated "primary graft dysfunction" in allotransplantation and consider how they correspond with "xeno-associated" injury mechanisms. Based on this analysis, we describe potential genetic modifications as well as novel technical strategies that may minimize IRI for heart and other organ xenografts and which could facilitate safe and effective clinical xenotransplantation.

Obesity-related IL-18 Impairs Treg Function and Promotes Lung Ischemia-reperfusion Injury

RATIONALE

Primary graft dysfunction (PGD) is a severe form of acute lung injury, leading to increased early morbidity and mortality after lung transplantation. Obesity is a major health problem, and recipient obesity is one of the most significant risk factors for developing PGD.

OBJECTIVES

We hypothesized that T-regulatory (Treg) cells are able to dampen early ischemia/reperfusion events and thereby decrease risk of PGD, whereas that action is impaired in obese recipients.

METHODS

We evaluated Treg, T cells and inflammatory markers, plus clinical data, in 79 lung and 41 liver or kidney transplant recipients and studied two groups of mice on high fat diet (HFD), who developed ("inflammatory" HFD) or not ("healthy" HFD) low-grade inflammation with decreased Treg function.

RESULTS

We identified increased levels of IL-18 as a previously unrecognized mechanism that impairs Treg suppressive function in obese individuals. IL-18 decreases levels of FOXP3, the key Treg transcription factor, decreases FOXP3 di- and oligomerization and increases the ubiquitination and proteasomal degradation of FOXP3. IL-18-treated Tregs or Treg from obese mice fail to control PGD, while IL-18 inhibition ameliorates lung inflammation. The IL-18 driven impairment in Treg suppressive function pre-transplant was associated with increased risk and severity of PGD in clinical lung transplant recipients.

CONCLUSION

Obesity-related IL-18 induces Treg dysfunction that may contribute to the pathogenesis of PGD. Evaluation of Treg suppressive function along with IL-18 levels may serve as screening tools to identify pre-transplant obese recipients with increased risk of PGD.

Inhibition of NLRC5 regulates cytokine expression in CD4+ T helper lymphocytes and prolongs murine islet and skin allograft survival

The purpose of this study was to study the effect of inhibiting NLRC5 expression and function on CD4 + T cells, and islet and skin transplantation in mice. A murine skin graft model and islet cell transplantation model were established, and the expression of NLRC5 was compared in rejection and immune tolerance groups. Mice spleen-derived CD4 + T cells were cultured, purified, and enriched in vitro, and transfected with the shRNA lentiviral vector NLRC5-RNAi-GFP. Changes in cytokine secretion were detected to understand changes in immunological function. Murine islet and skin transplantation models were injected with CD4 + T cells transfected with the lentivirus, and the survival time of the grafts and the levels of IFN-γ and IL-10 were compared between groups. The expression of NLRC5 mRNA in islet and skin grafts was significantly increased. In vitro experiments showed that the expression of IL-4 and IL-10 was up-regulated in CD4 + T cells, and T cells differentiation turned to Th2 after inhibition of NLRC5. In vivo experiments showed that inhibition of NLRC5 prolonged islet and skin graft survival. Pathological examination showed that the rejection of transplanted skin and islets in the NLRC5-RNAi group was mild, and there was a correlation between high expression of NLRC5 and rejection of mouse islet and skin grafts. In summary, inhibition of NLRC5 can prolong islet and skin graft survival induce transplant immune tolerance through induction of the secretion of Th2 cytokines by CD4 + T cells.

Early postoperative complications in lung transplant recipients

Lung transplantation has become an established therapy for end-stage lung diseases. Early postoperative complications can impact immediate, mid-term, and long-term outcomes. Appropriate management, prevention, and early detection of these early postoperative complications can improve the overall transplant course. In this review, we highlight the incidence, detection, and management of these early postoperative complications in lung transplant recipients.

Lung Transplantation, Pulmonary Endothelial Inflammation, and Ex-Situ Lung Perfusion: A Review

Lung transplantation (LTx) is the gold standard treatment for end-stage lung disease; however, waitlist mortality remains high due to a shortage of suitable donor lungs. Organ quality can be compromised by lung ischemic reperfusion injury (LIRI). LIRI causes pulmonary endothelial inflammation and may lead to primary graft dysfunction (PGD). PGD is a significant cause of morbidity and mortality post-LTx. Research into preservation strategies that decrease the risk of LIRI and PGD is needed, and ex-situ lung perfusion (ESLP) is the foremost technological advancement in this field. This review addresses three major topics in the field of LTx: first, we review the clinical manifestation of LIRI post-LTx; second, we discuss the pathophysiology of LIRI that leads to pulmonary endothelial inflammation and PGD; and third, we present the role of ESLP as a therapeutic vehicle to mitigate this physiologic insult, increase the rates of donor organ utilization, and improve patient outcomes.

Primary Graft Dysfunction

Primary graft dysfunction (PGD) is a form of acute lung injury after transplantation characterized by hypoxemia and the development of alveolar infiltrates on chest radiograph that occurs within 72 hours of reperfusion. PGD is among the most common early complications following lung transplantation and significantly contributes to increased short-term morbidity and mortality. In addition, severe PGD has been associated with higher 90-day and 1-year mortality rates compared with absent or less severe PGD and is a significant risk factor for the subsequent development of chronic lung allograft dysfunction. The International Society for Heart and Lung Transplantation released updated consensus guidelines in 2017, defining grade 3 PGD, the most severe form, by the presence of alveolar infiltrates and a ratio of PaO₂:FiO₂ less than 200. Multiple donor-related, recipient-related, and perioperative risk factors for PGD have been identified, many of which are potentially modifiable. Consistently identified risk factors include donor tobacco and alcohol use; increased recipient body mass index; recipient history of pulmonary hypertension, sarcoidosis, or pulmonary fibrosis; single lung transplantation; and use of cardiopulmonary bypass, among others. Several cellular pathways have been implicated in the pathogenesis of PGD, thus presenting several possible therapeutic targets for preventing and treating PGD. Notably, use of ex vivo lung perfusion (EVLP) has become more widespread and offers a potential platform to safely investigate novel PGD treatments while expanding the lung donor pool. Even in the presence of significantly prolonged ischemic times, EVLP has not been associated with an increased risk for PGD.

Monocytes promote pyroptosis of endothelial cells during lung ischemia-reperfusion via IL-1R/NF-κB/NLRP3 signaling

In our previous study, we observed that donor pulmonary intravascular nonclassical monocytes play a major role in early PGF, but the specific mechanism remained unclear. In this study, we investigated the mechanistic role of monocytes in inducing pyroptosis of human pulmonary microvascular endothelial cells (HPMECs) during IRI. A murine hilar ligation model of IRI was utilized whereby left lungs underwent 1 h of ischemia and 23 h of reperfusion. Monocyte depletion by intraperitoneal clodronate-liposome treatment on pulmonary edema and pyroptosis activation were determined. In vitro experiments, we performed the co-culture experiments under hypoxia-reoxygenation (H/R) conditions to mimic the IRI environment. We monitored the expression of NLRP3, caspase-1 and IL-1β in co-cultures of monocytes (U937 cells) and HPMECs under H/R conditions. NLRP3, IL-1β and IL-1R siRNA knockdown, caspase-1 and NF-κB pathway inhibitors were employed to elucidate the mechanism modulating HPMEC pyroptosis during H/R. Treatment of mice with clodronate-liposome attenuated IR-induced pulmonary edema, cytokine production and pyroptosis activation. In vitro, NLRP3 knockdown in monocytes reduced caspase-1 and IL-1β secretion in co-cultures of monocytes and HPMECs. Reduced HPMEC pyroptosis was also observed either containing HPMECs with genetically engineered IL-1R knockdown or in co-culture treated with a Triplotide inhibitor that disrupts NF-κB signaling. Monocytes play a vital role in the development of transplant-associated ischemia-reperfusion injury. A potential role is that monocytes secrete IL-1β to induce HPMEC pyroptosis via the IL-1R/NF-κB/NLRP3 pathway.

The NLRP3 inflammasome in macrophages is stimulated by cell-free hemoglobin

Cell‐free hemoglobin (CFH) is associated with severe lung injury in human patients and is sufficient to induce airspace inflammation and alveolar–capillary barrier dysfunction in an experimental model of acute lung injury. The mechanisms through which this occurs are unknown. One key pathway which regulates inflammation during acute lung injury is the NLRP3 inflammasome. Because CFH can act as a damage‐associated molecular pattern, we hypothesized that CFH may activate the NLRP3 inflammasome during acute lung injury. Primary mouse alveolar macrophages and cultured murine macrophages exposed to CFH (0–1 mg/ml) for 24 hr demonstrated robust upregulation of the NLRP3 inflammasome components NLRP3, caspase‐1, and caspase‐11. Maximal induction of the NLRP3 inflammasome by CFH required TLR4. Compared to wild‐type controls, mice lacking NLRP3 developed less airspace inflammation (2.7 × 10⁵ cells/ml in bronchoalveolar lavage fluid versus. 1.1 × 10⁵/ml, p = .006) after exposure to intratracheal CFH. Together, these data demonstrate that CFH can stimulate the NLRP3 inflammasome in macrophages and that this pathway may be important in the pathogenesis of CFH‐induced acute lung injury.

International Society for Heart and Lung Transplantation consensus statement for the standardization of bronchoalveolar lavage in lung transplantation

Bronchoalveolar lavage (BAL) is a key clinical and research tool in lung transplantation (LTx). However, BAL collection and processing are not standardized across LTx centers. This International Society for Heart and Lung Transplantation-supported consensus document on BAL standardization aims to clarify definitions and propose common approaches to improve clinical and research practice standards. The following 9 areas are covered: (1) bronchoscopy procedure and BAL collection, (2) sample handling, (3) sample processing for microbiology, (4) cytology, (5) research, (6) microbiome, (7) sample inventory/tracking, (8) donor bronchoscopy, and (9) pediatric considerations. This consensus document aims to harmonize clinical and research practices for BAL collection and processing in LTx. The overarching goal is to enhance standardization and multicenter collaboration within the international LTx community and enable improvement and development of new BAL-based diagnostics.

NLRP3 inflammasome-mediated pyroptosis contributes to the pathogenesis of non-ischemic dilated cardiomyopathy

Dilated cardiomyopathy (DCM) is one of the most common causes of heart failure, and the underlying mechanism remains largely elusive. Here we investigated whether NLRP3 inflammasome-mediated pyroptosis contributes to non-ischemic DCM and dissected the underlying mechanism. We found that hyper activated NLRP3 inflammasome with pyroptotic cell death of cardiomyocytes were presented in the myocardial tissues of DCM patients, which were negatively correlated with cardiac function. Doxorubicin (Dox)-induced DCM characterization disclosed that NLRP3 inflammasome activation and pyroptosis occurred in Dox-treated heart tissues, but were very marginal in either NLRP3^-/- or caspase-1^-/- mice. Mechanistically, Dox enhanced expressions of NOX1 and NOX4 and induced mitochondrial fission through dynamin-related protein 1 (Drp1) activation, leading to NLRP3 inflammasome-mediated pyroptosis in cardiomyocytes via caspase-1-dependent manner. Conversely, both inhibitions of NOX1 and NOX4 and Drp1 suppressed Dox-induced NLPR3 inflammasome activation and pyroptosis. The alterations of NOX1 and NOX4 expression, Drp1 phosphorylation and mitochondrial fission were validated in DCM patients and mice. Importantly, Dox-induced Drp1-mediated mitochondrial fission and the consequent NLRP3 inflammasome activation and pyroptosis were reversed by NOX1 and NOX4 inhibition in mice. This study demonstrates for the first time that cardiomyocyte pyroptosis triggered by NLRP3 inflammasome activation via caspase-1 causally contributes to myocardial dysfunction progression and DCM pathogenesis.

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

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

Potential therapeutic targets for lung repair during human ex vivo lung perfusion

Introduction

The ex vivo lung perfusion (EVLP) technique has been developed to assess the function of marginal donor lungs and has significantly increased donor lung utilisation. EVLP has also been explored as a platform for donor lung repair through injury-specific treatments such as antibiotics or fibrinolytics. We hypothesised that actively expressed pathways shared between transplantation and EVLP may reveal common mechanisms of injury and potential therapeutic targets for lung repair prior to transplantation.

Materials and methods

Retrospective transcriptomics analyses were performed with peripheral tissue biopsies from “donation after brain death” lungs, with 46 pre-/post-transplant pairs and 49 pre-/post-EVLP pairs. Pathway analysis was used to identify and compare the responses of donor lungs to transplantation and to EVLP.

Results

22 pathways were enriched predominantly in transplantation, including upregulation of lymphocyte activation and cell death and downregulation of metabolism. Eight pathways were enriched predominantly in EVLP, including downregulation of leukocyte functions and upregulation of vascular processes. 27 pathways were commonly enriched, including activation of innate inflammation, cell death, heat stress and downregulation of metabolism and protein synthesis. Of the inflammatory clusters, Toll-like receptor/innate immune signal transduction adaptor signalling had the greatest number of nodes and was central to inflammation. These mechanisms have been previously speculated as major mechanisms of acute lung injury in animal models.

Conclusion

EVLP and transplantation share common molecular features of injury including innate inflammation and cell death. Blocking these pathways during EVLP may allow for lung repair prior to transplantation.

Intra-bone bone marrow transplantation from hCD47 transgenic pigs to baboons prolongs chimerism to >60 days and promotes increased porcine lung transplant survival

BACKGROUND

We have recently demonstrated that human-CD47 (hCD47) expressed on endothelial cells of porcine lung xenografts extended median graft survival from 3.5 days to 8.7 days in baboons. Intra-bone bone marrow transplantation (IBBMTx) in a pig-to-baboon model was previously shown to markedly prolong the duration of macrochimerism up to 21 days from 1 to 4 days by intravenous BMTx. We now examined whether the use of hCD47 transgenic (Tg) BM further prolonged the duration of chimerism following IBBMTx. We then tested if lung xenograft survival was prolonged following IBBMTx.

METHODS

Baboons received GalTKO-hCD47/hCD55Tg (n = 5) or -hCD55Tg (n = 1) or -hCD46/HLA-E Tg (n = 1) pig IBBMTx. Macrochimerism, anti-pig T cells and antibody responses were assessed. Animals received lung xenografts from either hCD47+ or hCD47- porcine lungs 1-3 months later.

RESULTS

All baboons that received hCD47Tg porcine IBBM maintained durable macrochimerism >30 days, and two maintained chimerism for >8 weeks. Notably, anti-pig antibody levels decreased over time and anti-pig cellular unresponsiveness developed following IBBMTx. Lungs from hCD47Tg IBBMTx matched pigs were transplanted at day 33 or day 49 after IBBMTx. These animals showed extended survival up to 13 and 14 days, while animals that received lungs from hCD47 negative pigs displayed no prolonged survival (1-4 days).

CONCLUSION

This is the first report demonstrating durable macrochimerism beyond 8 weeks, as well as evidence for B cell tolerance in large animal xenotransplantation. Using hCD47Tg pigs as both IBBMTx and lung donors prolongs lung xenograft survival. However, additional strategies are required to control the acute loss of lung xenografts.

Mitigation of Primary Graft Dysfunction in Lung Transplantation: Current Understanding and Hopes for the Future

Primary graft dysfunction (PGD) is a form of acute lung injury that develops within the first 72 hours after lung transplantation. The overall incidence of PGD is estimated to be around 30%, and the 30-day mortality for grade 3 PGD around 36%. PGD is also associated with the development of bronchiolitis obliterans syndrome, a specific form of chronic lung allograft dysfunction. In this article, we will discuss perioperative strategies for PGD prevention as well as possible future avenues for prevention and treatment.

PAGER 2.0: an update to the pathway, annotated-list and gene-signature electronic repository for Human Network Biology

Integrative Gene-set, Network and Pathway Analysis (GNPA) is a powerful data analysis approach developed to help interpret high-throughput omics data. In PAGER 1.0, we demonstrated that researchers can gain unbiased and reproducible biological insights with the introduction of PAGs (Pathways, Annotated-lists and Gene-signatures) as the basic data representation elements. In PAGER 2.0, we improve the utility of integrative GNPA by significantly expanding the coverage of PAGs and PAG-to-PAG relationships in the database, defining a new metric to quantify PAG data qualities, and developing new software features to simplify online integrative GNPA. Specifically, we included 84 282 PAGs spanning 24 different data sources that cover human diseases, published gene-expression signatures, drug-gene, miRNA-gene interactions, pathways and tissue-specific gene expressions. We introduced a new normalized Cohesion Coefficient (nCoCo) score to assess the biological relevance of genes inside a PAG, and RP-score to rank genes and assign gene-specific weights inside a PAG. The companion web interface contains numerous features to help users query and navigate the database content. The database content can be freely downloaded and is compatible with third-party Gene Set Enrichment Analysis tools. We expect PAGER 2.0 to become a major resource in integrative GNPA. PAGER 2.0 is available at http://discovery.informatics.uab.edu/PAGER/.

Assessment of Postdonation Outcomes in US Living Kidney Donors Using Publicly Available Data Sets

Importance

There are limited resources providing postdonation conditions that can occur in living donors (LDs) of solid-organ transplant. Consequently, it is difficult to visualize and understand possible postdonation outcomes in LDs.

Objective

To assemble an open access resource that is representative of the demographic characteristics in the US national registry, maintained by the Organ Procurement and Transplantation Network and administered by the United Network for Organ Sharing, but contains more follow-up information to help to examine postdonation outcomes in LDs.

Design, Setting, and Participants

Cohort study in which the data for the resource and analyses stemmed from the transplant data set derived from 27 clinical studies from the ImmPort database, which is an open access repository for clinical studies. The studies included data collected from 1963 to 2016. Data from the United Network for Organ Sharing Organ Procurement and Transplantation Network national registry collected from October 1987 to March 2016 were used to determine representativeness. Data analysis took place from June 2016 to May 2018. Data from 20 ImmPort clinical studies (including clinical trials and observational studies) were curated, and a cohort of 11 263 LDs was studied, excluding deceased donors, LDs with 95% or more missing data, and studies without a complete data dictionary. The harmonization process involved the extraction of common features from each clinical study based on categories that included demographic characteristics as well as predonation and postdonation data.

Main Outcomes and Measures

Thirty-six postdonation events were identified, represented, and analyzed via a trajectory network analysis.

Results

The curated data contained 10 869 living kidney donors (median [interquartile range] age, 39 [31-48] years; 6175 [56.8%] women; and 9133 [86.6%] of European descent). A total of 9558 living kidney donors with postdonation data were analyzed. Overall, 1406 LDs (14.7%) had postdonation events. The 4 most common events were hypertension (806 [8.4%]), diabetes (190 [2.0%]), proteinuria (171 [1.8%]), and postoperative ileus (147 [1.5%]). Relatively few events (n = 269) occurred before the 2-year postdonation mark. Of the 1746 events that took place 2 years or more after donation, 1575 (90.2%) were nonsurgical; nonsurgical conditions tended to occur in the wide range of 2 to 40 years after donation (odds ratio, 38.3; 95% CI, 4.12-1956.9).

Conclusions and Relevance

Most events that occurred more than 2 years after donation were nonsurgical and could occur up to 40 years after donation. Findings support the construction of a national registry for long-term monitoring of LDs and confirm the value of secondary reanalysis of clinical studies.

Bidirectional transfer of Anelloviridae lineages between graft and host during lung transplantation

Solid organ transplantation disrupts virus-host relationships, potentially resulting in viral transfer from donor to recipient, reactivation of latent viruses, and new viral infections. Viral transfer, colonization, and reactivation are typically monitored using assays for specific viruses, leaving the behavior of full viral populations (the "virome") understudied. Here we sought to investigate the temporal behavior of viruses from donor lungs and transplant recipients comprehensively. We interrogated the bronchoalveolar lavage and blood viromes during the peritransplant period and 6-16 months posttransplant in 13 donor-recipient pairs using shotgun metagenomic sequencing. Anelloviridae, ubiquitous human commensal viruses, were the most abundant human viruses identified. Herpesviruses, parvoviruses, polyomaviruses, and bacteriophages were also detected. Anelloviridae populations were complex, with some donor organs and hosts harboring multiple contemporaneous lineages. We identified transfer of Anelloviridae lineages from donor organ to recipient serum in 4 of 7 cases that could be queried, and immigration of lineages from recipient serum into the allograft in 6 of 10 such cases. Thus, metagenomic analyses revealed that viral populations move between graft and host in both directions, showing that organ transplantation involves implantation of both the allograft and commensal viral communities.

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

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

National Heart, Lung, and Blood Institute and American Association for Thoracic Surgery Workshop Report: Identifying collaborative clinical research priorities in lung transplantation

This report summarizes the discussion and recommendations from the June 2017 NHLBI-AATS Workshop on Identifying Collaborative Clinical Research Priorities in Lung Transplantation.

Early Graft Dysfunction after Lung Transplantation

PURPOSE OF REVIEW

Primary graft dysfunction is an acute lung injury syndrome occurring immediately following lung transplantation. This review aims to provide an overview of the current understanding of PGD, including epidemiology, immunology, clinical outcomes and management.

RECENT FINDINGS

Identification of donor and recipient factors allowing accurate prediction of PGD has been actively pursued. Improved understanding of the immunology underlying PGD has spurred interest in identifying relevant biomarkers. Work in PGD prediction, severity stratification and targeted therapies continue to make progress. Donor expansion strategies continue to be pursued with ex vivo lung perfusion playing a prominent role. While care of PGD remains supportive, ECMO has established a prominent role in the early aggressive management of severe PGD.

SUMMARY

A consensus definition of PGD has allowed marked advances in research and clinical care of affected patients. Future research will lead to reliable predictive tools, and targeted therapeutics of this important syndrome.

GalT-KO pig lungs are highly susceptible to acute vascular rejection in baboons, which may be mitigated by transgenic expression of hCD47 on porcine blood vessels

BACKGROUND

Despite recent progress in survival times of xenografts in non-human primates, there are no reports of survival beyond 5 days of histologically well-aerated porcine lung grafts in baboons. Here, we report our initial results of pig-to-baboon xeno-lung transplantation (XLTx).

METHODS

Eleven baboons received genetically modified porcine left lungs from either GalT-KO alone (n = 3), GalT-KO/humanCD47(hCD47)/hCD55 (n = 3), GalT-KO/hD47/hCD46 (n = 4), or GalT-KO/hCD39/hCD46/hCD55/TBM/EPCR (n = 1) swine. The first 2 XLTx procedures were performed under a non-survival protocol that allowed a 72-hour follow-up of the recipients with general anesthesia, while the remaining 9 underwent a survival protocol with the intention of weaning from ventilation.

RESULTS

Lung graft survivals in the 2 non-survival animals were 48 and >72 hours, while survivals in the other 9 were 25 and 28 hours, at 5, 5, 6, 7, >7, 9, and 10 days. One baboon with graft survival >7 days, whose entire lung graft remained well aerated, was euthanized on POD 7 due to malfunction of femoral catheters. hCD47 expression of donor lungs was detected in both alveoli and vessels only in the 3 grafts surviving >7, 9, and 10 days. All other grafts lacked hCD47 expression in endothelial cells and were completely rejected with diffuse hemorrhagic changes and antibody/complement deposition detected in association with early graft loss.

CONCLUSIONS

To our knowledge, this is the first evidence of histologically viable porcine lung grafts beyond 7 days in baboons. Our results indicate that GalT-KO pig lungs are highly susceptible to acute humoral rejection and that this may be mitigated by transgenic expression of hCD47.

The Future of Lung Transplantation

The field of lung transplant has made significant advances over the last several decades. Despite these advances, morbidity and mortality remain high when compared with other solid organ transplants. As the field moves forward, the speed by which progress can be made will in part be determined by our ability to overcome several stumbling blocks, including donor shortage, proper selection of candidates, primary graft dysfunction, and chronic lung allograft dysfunction. The advances and developments surrounding these factors will have a significant impact on shaping the field within the coming years. In this review, we look at the current climate (ripe for expanding the donor pool), new technology (ex vivo lung perfusion and bioengineered lungs), cutting-edge innovation (novel biomarkers and new ways to treat infected donors), and evidence-based medicine to discuss current trends and predict future developments for what we hope is a bright future for the field of lung transplantation.

Lung Ischaemia-Reperfusion Injury: The Role of Reactive Oxygen Species

Lung ischaemia-reperfusion injury (LIRI) occurs in many lung diseases and during surgical procedures such as lung transplantation. The re-establishment of blood flow and oxygen delivery into the previously ischaemic lung exacerbates the ischaemic injury and leads to increased microvascular permeability and pulmonary vascular resistance as well as to vigorous activation of the immune response. These events initiate the irreversible damage of the lung with subsequent oedema formation that can result in systemic hypoxaemia and multi-organ failure. Alterations in the production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) have been suggested as crucial mediators of such responses during ischaemia-reperfusion in the lung. Among numerous potential sources of ROS/RNS within cells, nicotinamide adenine dinucleotide phosphate (NADPH) oxidases, xanthine oxidases, nitric oxide synthases and mitochondria have been investigated during LIRI. Against this background, we aim to review here the extensive literature about the ROS-mediated cellular signalling during LIRI, as well as the effectiveness of antioxidants as treatment option for LIRI.

Regulation of inside-out β1-integrin activation by CDCP1

Tumor metastasis depends on the dynamic regulation of cell adhesion through β1-integrin. The Cub-Domain Containing Protein-1, CDCP1, is a transmembrane glycoprotein which regulates cell adhesion. Overexpression and loss of CDCP1 have been observed in the same cancer types to promote metastatic progression. Here, we demonstrate reduced CDCP1 expression in high-grade, primary prostate cancers, circulating tumor cells and tumor metastases of patients with castrate-resistant prostate cancer. CDCP1 is expressed in epithelial and not mesenchymal cells, and its cell surface and mRNA expression declines upon stimulation with TGFβ1 and epithelial-to-mesenchymal transition. Silencing of CDCP1 in DU145 and PC3 cells resulted in 3.4-fold higher proliferation of non-adherent cells and 4.4-fold greater anchorage independent growth. CDCP1-silenced tumors grew in 100% of mice, compared to 30% growth of CDCP1-expressing tumors. After CDCP1 silencing, cell adhesion and migration diminished 2.1-fold, caused by loss of inside-out activation of β1-integrin. We determined that the loss of CDCP1 reduces CDK5 kinase activity due to the phosphorylation of its regulatory subunit, CDK5R1/p35, by c-SRC on Y234. This generates a binding site for the C2 domain of PKCδ, which in turn phosphorylates CDK5 on T77. The resulting dissociation of the CDK5R1/CDK5 complex abolishes the activity of CDK5. Mutations of CDK5-T77 and CDK5R1-Y234 phosphorylation sites re-establish the CDK5/CDKR1 complex and the inside-out activity of β1-integrin. Altogether, we discovered a new mechanism of regulation of CDK5 through loss of CDCP1, which dynamically regulates β1-integrin in non-adherent cells and which may promote vascular dissemination in patients with advanced prostate cancer.

Immediate post-operative broncho-alveolar lavage IL-6 and IL-8 are associated with early outcomes after lung transplantation

INTRODUCTION

Previous studies demonstrated that increased cytokine and chemokine levels, either shortly before or after lung transplantation, were associated with post-transplant outcome. However, small patient cohorts were mostly used, focusing on 1 molecule and 1 outcome. In a large single-center cohort, we investigated the predictive value of immediate post-operative broncho-alveolar lavage (BAL) expression of IL-6 and IL-8 on multiple key outcomes, including PGD, CLAD, graft survival, as well as several secondary outcomes.

MATERIAL AND METHODS

All patients undergoing a first lung transplant in whom routine bronchoscopy with BAL was performed during the first 48 hours post-transplantation were included. IL-6 and IL-8 protein levels were measured in BAL via ELISA.

RESULTS

A total of 336 patients were included. High IL-6 levels measured within 24 hours of transplantation were associated with longer time on ICU and time to hospital discharge; and increased prevalence of PGD grade 3. Increased IL-8 levels, measured within 24 hours, were associated with PGD3, more ECMO use, higher donor paO₂ , younger donor age, but not with other short-or long-term outcome. IL-6 and IL-8 measured between 24 and 48 hours of transplantation were not associated with any outcome parameters.

CONCLUSION

Recipient BAL IL-6 and IL-8 within 24 hours post-transplant were associated with an increased incidence of PGD3.

Primary Graft Dysfunction After Lung Transplantation

Primary graft dysfunction is a form of acute injury after lung transplantation that is associated with significant short- and long-term morbidity and mortality. Multiple mechanisms contribute to the pathogenesis of primary graft dysfunction, including ischemia reperfusion injury, epithelial cell death, endothelial cell dysfunction, innate immune activation, oxidative stress, and release of inflammatory cytokines and chemokines. This article reviews the epidemiology, pathogenesis, risk factors, prevention, and treatment of primary graft dysfunction.

Pathophysiology and classification of primary graft dysfunction after lung transplantation

The term primary graft dysfunction (PGD) incorporates a continuum of disease severity from moderate to severe acute lung injury (ALI) within 72 h of lung transplantation. It represents the most significant obstacle to achieving good early post-transplant outcomes, but is also associated with increased incidence of bronchiolitis obliterans syndrome (BOS) subsequently. PGD is characterised histologically by diffuse alveolar damage, but is graded on clinical grounds with a combination of PaO2/FiO2 (P/F) and the presence of radiographic infiltrates, with 0 being absence of disease and 3 being severe PGD. The aetiology is multifactorial but commonly results from severe ischaemia-reperfusion injury (IRI), with tissue-resident macrophages largely responsible for stimulating a secondary 'wave' of neutrophils and lymphocytes that produce severe and widespread tissue damage. Donor history, recipient health and operative factors may all potentially contribute to the likelihood of PGD development. Work that aims to minimise the incidence of PGD in ongoing, with techniques such as ex vivo perfusion of donor lungs showing promise both in research and in clinical studies. This review will summarise the current clinical status of PGD before going on to discuss its pathophysiology, current therapies available and future directions for clinical management of PGD.

Peripheral Blood Gene Expression Changes Associated With Primary Graft Dysfunction After Lung Transplantation

Recipient responses to primary graft dysfunction (PGD) after lung transplantation may have important implications to the fate of the allograft. We therefore evaluated longitudinal differences in peripheral blood gene expression in subjects with PGD. RNA expression was measured throughout the first transplant year in 106 subjects enrolled in the Clinical Trials in Organ Transplantation-03 study using a panel of 100 hypothesis-driven genes. PGD was defined as grade 3 in the first 72 posttransplant hours. Eighteen genes were differentially expressed over the first year based on PGD development, with significant representation from innate and adaptive immunity genes, with most differences identified very early after transplant. Sixteen genes were overexpressed in the blood of patients with PGD compared to those without PGD within 7 days of allograft reperfusion, with most transcripts encoding innate immune/inflammasome-related proteins, including genes previously associated with PGD. Thirteen genes were underexpressed in patients with PGD compared to those without PGD within 7 days of transplant, highlighted by T cell and adaptive immune regulation genes. Differences in gene expression present within 2 h of reperfusion and persist for days after transplant. Future investigation will focus on the long-term implications of these gene expression differences on the outcome of the allograft.

The Selective JAK1/3-Inhibitor R507 Mitigates Obliterative Airway Disease Both With Systemic Administration and Aerosol Inhalation

BACKGROUND

The efficacy of selective Janus kinase 1/3 inhibitor R507 to prevent obliterative airway disease was analyzed in preclinical airway transplantation models.

METHODS

Orthotopic trachea transplantations were performed between Lewis donors and Brown Norway rat recipients. Oral everolimus (4 mg/kg once per day) or oral respective inhaled R507 (60 mg/kg twice per day, each) was used for immunosuppression. Grafts were retrieved after 6 or 60 days. Toxicity and anti-inflammatory effects of R507 were analyzed on human airway epithelial cells.

RESULTS

In 6-day animals, oral and inhaled R507 more potently diminished mononuclear graft infiltration than everolimus and preserved ciliated pseudostratified columnar respiratory epithelium. Everolimus and R507 similarly suppressed systemic cellular and humoral immune activation. In untreated rats, marked obliterative airway disease developed over 60 days. Oral and inhaled R507 was significantly more effective in reducing airway obliteration and preserved the morphology of the airway epithelium. Luciferase-positive donors revealed that a substantial amount of smooth muscle cells within the obliterative tissue was of donor origin. Only everolimus but not R507, adversely altered kidney function and lipid profiles. The R507 aerosol did not show airway toxicity in vitro but effectively suppressed activation of inflammatory signaling pathways induced by IL-1β.

CONCLUSIONS

The Janus kinase 1/3 inhibitor R507 is a very well-tolerated immunosuppressant that similarly diminished obliterative airway disease with systemic or inhaled administration.

Inflammasomes and IL-1 biology in the pathogenesis of allograft dysfunction

Inflammasomes are high-molecular-weight cytosolic complexes that mediate the activation of caspases. There are many inflammasomes, and each is influenced by a unique pattern-recognition receptor response. Two signals are typically involved in the inflammasome pathways. Signal one involves recognition of pathogen-associated molecular patterns (PAMPs), such as LPS or other colonizing/invading microbes, that interact with TLRs, which induce the downstream production of pro-IL-1β. This is followed by signal two, which involves recognition of PAMPs or damage-associated molecular patterns (DAMPs), such as uric acid or ATP, via NLRP3, which leads to caspase-1-dependent cleavage of pro-IL-1β to active IL-1β and pyroptosis. Ultimately, these two signals cause the release of multiple proinflammatory cytokines. Both PAMPs and DAMPs can be liberated by early insults to the allograft, including ischemia/reperfusion injury, infections, and rejection. The consequence of inflammasome activation and IL-1 expression is the upregulation of adhesion molecules and chemokines, which leads to allograft neutrophil sequestration, mononuclear phagocyte recruitment, and T cell activation, all of which are key steps in the continuum from allograft insult to chronic allograft dysfunction.

The Perioperative Lung Transplant Virome: Torque Teno Viruses Are Elevated in Donor Lungs and Show Divergent Dynamics in Primary Graft Dysfunction

Primary graft dysfunction (PGD) is a principal cause of early morbidity and mortality after lung transplantation, but its pathogenic mechanisms are not fully clarified. To date, studies using standard clinical assays have not linked microbial factors to PGD. We previously used comprehensive metagenomic methods to characterize viruses in lung allografts >1 mo after transplant and found that levels of Anellovirus, mainly torque teno viruses (TTVs), were significantly higher than in nontransplanted healthy controls. We used quantitative polymerase chain reaction to analyze TTV and shotgun metagenomics to characterize full viral communities in acellular bronchoalveolar lavage from donor organs and postreperfusion allografts in PGD and non-PGD lung transplant recipient pairs. Unexpectedly, TTV DNA levels were elevated 100-fold in donor lungs compared with healthy adults (p = 0.0026). Although absolute TTV levels did not differ by PGD status, PGD cases showed a smaller increase in TTV levels from before to after transplant than did control recipients (p = 0.041). Metagenomic sequencing revealed mainly TTV and bacteriophages of respiratory tract bacteria, but no viral taxa distinguished PGD cases from controls. These findings suggest that conditions associated with brain death promote TTV replication and that greater immune activation or tissue injury associated with PGD may restrict TTV abundance in the lung.

Mechanisms of graft rejection after lung transplantation

PURPOSE OF REVIEW

To date, outcomes after lung transplantation are far worse than after transplantation of other solid organs. New insights into mechanisms that contribute to graft rejection and tolerance after lung transplantation remain of great interest. This review examines the recent literature on the role of innate and adaptive immunity in shaping the fate of lung grafts.

RECENT FINDINGS

Innate and adaptive immune cells orchestrate allograft rejection after transplantation. Innate immune cells such as neutrophils are recruited to the lung graft early after reperfusion and subsequently promote allograft rejection. Although it is widely recognized that CD4 T lymphocytes in concert with CD8 T cells promote graft rejection, regulatory Foxp3 CD4 T, central memory CD8 T cells, and natural killer cells can facilitate tolerance.

SUMMARY

This review highlights interactions between innate and adaptive immune pathways and how they contribute to lung allograft rejection. These findings lay a foundation for the design of new therapeutic strategies that target both innate and adaptive immune responses.

Protein biomarkers associated with primary graft dysfunction following lung transplantation

Severe primary graft dysfunction affects 15-20% of lung transplant recipients and carries a high mortality risk. In addition to known donor, recipient, and perioperative clinical risk factors, numerous biologic factors are thought to contribute to primary graft dysfunction. Our current understanding of the pathogenesis of lung injury and primary graft dysfunction emphasizes multiple pathways leading to lung endothelial and epithelial injury. Protein biomarkers specific to these pathways can be measured in the plasma, bronchoalveolar lavage fluid, and lung tissue. Clarification of the pathophysiology and timing of primary graft dysfunction could illuminate predictors of dysfunction, allowing for better risk stratification, earlier identification of susceptible recipients, and development of targeted therapies. Here, we review much of what has been learned about the association of protein biomarkers with primary graft dysfunction and evaluate this association at different measurement time points.