Humoral immune responses mediate the development of a restrictive phenotype of chronic lung allograft dysfunction

Maintenance of graft tissue-resident Foxp3+ cells is necessary for lung transplant tolerance in mice

Mechanisms that mediate allograft tolerance differ between organs. We have previously shown that Foxp3+ T cell-enriched bronchus-associated lymphoid tissue (BALT) is induced in tolerant murine lung allografts and that these Foxp3+ cells suppress alloimmune responses locally and systemically. Here, we demonstrated that Foxp3+ cells that reside in tolerant lung allografts differed phenotypically and transcriptionally from those in the periphery and were clonally expanded. Using a mouse lung retransplant model, we showed that recipient Foxp3+ cells were continuously recruited to the BALT within tolerant allografts. We identified distinguishing features of graft-resident and newly recruited Foxp3+ cells and showed that graft-infiltrating Foxp3+ cells acquired transcriptional profiles resembling those of graft-resident Foxp3+ cells over time. Allografts underwent combined antibody-mediated rejection and acute cellular rejection when recruitment of recipient Foxp3+ cells was prevented. Finally, we showed that local administration of IL-33 could expand and activate allograft-resident Foxp3+ cells, providing a platform for the design of tolerogenic therapies for lung transplant recipients. Our findings establish graft-resident Foxp3+ cells as critical orchestrators of lung transplant tolerance and highlight the need to develop lung-specific immunosuppression.

Activation of anti-donor CD8 alloimmune response in clinically diagnosed acute rejection early after living-donor lobar lung transplantation and its impact on outcome

BACKGROUND

The characteristics and prognostic impacts of early graft infiltration after lung transplantation and clinically diagnosed acute rejection remain unclear. Furthermore, the alloimmune response status in lung transplantation remains uninvestigated.

METHODS

In this retrospective cohort study, we evaluated 92 living-donor lobar lung transplantations (LDLLT) to establish the effect of graft infiltration-diagnosed as acute rejection-within one-month post-transplantation (cAR), on chronic lung allograft dysfunction (CLAD)-free LDLLT survival. The alloimmune response was evaluated using the carboxyfluorescein diacetate succinimidyl ester (CFSE)-mixed lymphocyte reaction (MLR) in lymphocytes isolated from donor and recipient blood one week after LDLLT. The anti-donor proliferation of CD4+ and CD8+ T cells was determined using flow cytometry.

RESULTS

cAR was observed in 54 (58.7 %) patients who underwent LDLLT. The median postoperative day of cAR occurrence was 7 days (ranging between 5 and 28 days). Only one episode of cAR occurred in 51 patients (94.4 %). CLAD-free survival was significantly lower in patients who underwent cAR, especially within 2 years after LDLLT (p = 0.016). Thirteen CFSE-MLR assays were performed in seven consecutive LDLLT cases (six bilateral and one unilateral LDLLT). Increased anti-donor proliferation of CD8+ T cells, but not CD4+ T cells, was associated with cAR, irrespective of human leukocyte antigen (HLA) class I mismatch.

CONCLUSION

Early lung graft infiltration after LDLLT increases the risk of the early development of CALD. Augmented anti-donor CD8 + response was also associated with graft infiltration, which could not be predicted from HLA mismatches but could be monitored using MLR in LDLLT.

Chronic Lung Allograft Dysfunction: Clinical Manifestations and Immunologic Mechanisms

The term "chronic lung allograft dysfunction" has emerged to describe the clinical syndrome of progressive, largely irreversible dysfunction of pulmonary allografts. This umbrella term comprises 2 major clinical phenotypes: bronchiolitis obliterans syndrome and restrictive allograft syndrome. Here, we discuss the clinical manifestations, diagnostic challenges, and potential therapeutic avenues to address this major barrier to improved long-term outcomes. In addition, we review the immunologic mechanisms thought to propagate each phenotype of chronic lung allograft dysfunction, discuss the various models used to study this process, describe potential therapeutic targets, and identify key unknowns that must be evaluated by future research strategies.

Clinical predictors for restrictive allograft syndrome: a nested case-control study

Risk factors for restrictive allograft syndrome (RAS), a severe phenotype of chronic lung allograft dysfunction (CLAD) after lung transplantation, are currently not well known. In this retrospective nested case-control-study, we analyzed 69 patients with RAS and 69 matched non-CLAD controls to identify clinical risk factors for RAS. Patients with RAS demonstrated overall higher blood eosinophils (P = .02), increased bronchoalveolar eosinophils (P < .001) and lymphocytes (P = .03), and higher incidence of infections, particularly Pseudomonas species infection (P = .003), invasive fungal disease (P < .001, mainly due to Aspergillus species), SARS-CoV-2 (P < .001), and cytomegalovirus infection (P = .04), compared with non-CLAD controls. Antihuman leukocyte antigen (anti-HLA) antibodies, especially persistent donor-specific antibodies (P < 0.001), specifically targeting HLA-DQ and HLA-DR loci, and antibody-mediated rejection (P < .001), were strongly associated with later RAS. Histopathologic lung injury patterns on transbronchial biopsy (P < .001), and persistent chest computed tomography opacities in absence of pulmonary dysfunction (P < .001) were identified as early indicators of later RAS. Proactive detection and management of these risk factors could help mitigate future decline in allograft function and reduce progression to clinical RAS. Future studies should explore early treatment strategies targeting these modifiable factors to preserve allograft function and improve long-term outcomes for lung transplant recipients.

Update on the immunological mechanisms of primary graft dysfunction and chronic lung allograft dysfunction

PURPOSE OF REVIEW

Primary graft dysfunction (PGD) and chronic lung allograft dysfunction (CLAD) are the leading causes of graft loss in lung transplant recipients. The development of mouse lung transplant models has allowed for the genetic dissection of cellular and molecular pathways that prevent graft survival. This review provides an overview into recent mechanistic insights into PGD and CLAD.

RECENT FINDINGS

Mouse orthotopic lung transplant models and investigations of human lung transplant recipeints have revealed new molecular and cellular targets that promote PGD and CLAD. Donor and recipient-derived innate immune cells promote PGD and CLAD. PGD is driven by communication between classical monocytes and tissue-resident nonclassical monocytes activating alveolar macrophages to release chemokines that recruit neutrophils. Products of cell damage trigger neutrophil NET release, which together with NK cells, antibodies and complement, that further promote PGD. The development of CLAD involves circuits that activate B cells, CD8 + T cells, classical monocytes, and eosinophils.

SUMMARY

Effective targeted management of PGD and CLAD in lung transplant recipient to improve their long-term outcome remains a critical unmet need. Current mechanistic studies and therapeutic studies in mouse models and humans identify new possibilities for prevention and treatment.

Murine orthotopic lung transplant models: A comprehensive overview of genetic mismatch degrees and histopathological insights into chronic lung allograft dysfunction

Currently, lung transplantation outcome remains inferior compared to other solid organ transplantations. A major cause for limited survival after lung transplantation is chronic lung allograft dysfunction. Numerous animal models have been developed to investigate chronic lung allograft dysfunction to discover adequate treatments. The murine orthotopic lung transplant model has been further optimized over the last years. However, different degrees of genetic mismatch between donor and recipient mice have been used, applying a single, minor, moderate, and major genetic mismatch. This review aims to reassess the existing murine mismatch models and provide a comprehensive overview, with a specific focus on their eventual histopathological presentation. This will be crucial to leverage this model and tailor it according to specific research needs.

MNK-driven eIF4E phosphorylation regulates the fibrogenic transformation of mesenchymal cells and chronic lung allograft dysfunction

Tissue fibrosis remains unamenable to meaningful therapeutic interventions and is the primary cause of chronic graft failure after organ transplantation. Eukaryotic translation initiation factor (eIF4E), a key translational regulator, serves as convergent target of multiple upstream profibrotic signaling pathways that contribute to mesenchymal cell (MC) activation. Here, we investigate the role of MAP kinase-interacting serine/threonine kinase-induced (MNK-induced) direct phosphorylation of eIF4E at serine 209 (Ser209) in maintaining fibrotic transformation of MCs and determine the contribution of the MNK/eIF4E pathway to the pathogenesis of chronic lung allograft dysfunction (CLAD). MCs from patients with CLAD demonstrated constitutively higher eIF4E phosphorylation at Ser209, and eIF4E phospho-Ser209 was found to be critical in regulating key fibrogenic protein autotaxin, leading to sustained β-catenin activation and profibrotic functions of CLAD MCs. MNK1 signaling was upregulated in CLAD MCs, and genetic or pharmacologic targeting of MNK1 activity inhibited eIF4E phospho-Ser209 and profibrotic functions of CLAD MCs in vitro. Treatment with an MNK1/2 inhibitor (eFT-508) abrogated allograft fibrosis in an orthotopic murine lung-transplant model. Together these studies identify what we believe is a previously unrecognized MNK/eIF4E/ATX/β-catenin signaling pathway of fibrotic transformation of MCs and present the first evidence, to our knowledge, for the utility of MNK inhibitors in fibrosis.

Fibrotic progression from acute cellular rejection is dependent on secondary lymphoid organs in a mouse model of chronic lung allograft dysfunction

Chronic lung allograft dysfunction (CLAD) remains one of the major limitations to long-term survival after lung transplantation. We modified a murine model of CLAD and transplanted left lungs from BALB/c donors into B6 recipients that were treated with intermittent cyclosporine and methylprednisolone postoperatively. In this model, the lung allograft developed acute cellular rejection on day 15 which, by day 30 after transplantation, progressed to severe pleural and peribronchovascular fibrosis, reminiscent of changes observed in restrictive allograft syndrome. Lung transplantation into splenectomized B6 alymphoplastic (aly/aly) or splenectomized B6 lymphotoxin-β receptor-deficient mice demonstrated that recipient secondary lymphoid organs, such as spleen and lymph nodes, are necessary for progression from acute cellular rejection to allograft fibrosis in this model. Our work uncovered a critical role for recipient secondary lymphoid organs in the development of CLAD after pulmonary transplantation and may provide mechanistic insights into the pathogenesis of this complication.

Surgeon-dependent histopathological variations in minor alloantigen-mismatched mouse lung transplantation

Background

The mouse orthotopic single lung transplant (LTx) model is an important scientific tool to explore LTx immunology. C57BL/10J (B10, H-2b) to C57BL/6J (B6, H-2b) minor alloantigen-mismatched LTx exhibits mild acute rejection and chronic fibrosis, mimicking human LTx, where acute rejection is dampened by immunosuppressants and chronic lung allograft dysfunction (CLAD) develops over time. However, we have observed variations in allograft histology across experiments, which were not explained by animal vendor or experimental conditions. The purpose of this study was to evaluate those variations objectively.

Methods

We performed a retrospective review of B10-to-B6 LTx performed in our laboratory 2012-2019. Only LTx without experimental interventions (eg, immunomodulatory agents or genetic modifications) examined at day 28 was eligible for this study. Mice from each surgeon were selected and divided into 3 groups to represent early, middle, and late timepoints in their mouse LTx experience (143 LTx from 5 surgeons). Histology from these LTx was graded in a randomized and blinded manner. Pathological variations and trajectories were graphed; logistic regression analyses were performed for statistical assessment.

Results

Distribution and trajectories of pathological outcomes were significantly different across surgeons. In multivariable logistic regression analyses, surgeon was associated with pathological outcomes whereas case number was not. Longer warm ischemia time was associated with more severe pleural fibrosis.

Conclusions

The B10 to B6 single LTx model can be a powerful tool to recapitulate CLAD-like histology. However, this is a challenging operation and surgeon-dependent variability in histopathological findings needs to be taken into account when designing experimental protocols.

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

Introduction

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

Methods

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

Results

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

Conclusion

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

The 2022 Banff Meeting Lung Report

The Lung Session of the 2022 16th Banff Foundation for Allograft Pathology Conference-held in Banff, Alberta-focused on non-rejection lung allograft pathology and novel technologies for the detection of allograft injury. A multidisciplinary panel reviewed the state-of-the-art of current histopathologic entities, serologic studies, and molecular practices, as well as novel applications of digital pathology with artificial intelligence, gene expression analysis, and quantitative image analysis of chest computerized tomography. Current states of need as well as prospective integration of the aforementioned tools and technologies for complete assessment of allograft injury and its impact on lung transplant outcomes were discussed. Key conclusions from the discussion were: (1) recognition of limitations in current standard of care assessment of lung allograft dysfunction; (2) agreement on the need for a consensus regarding the standardized approach to the collection and assessment of pathologic data, inclusive of all lesions associated with graft outcome (eg, non-rejection pathology); and (3) optimism regarding promising novel diagnostic modalities, especially minimally invasive, which should be integrated into large, prospective multicenter studies to further evaluate their utility in clinical practice for directing personalized therapies to improve graft outcomes.

The Immunopathology of Pulmonary Rejection after Murine Lung Transplantation

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

Intragraft immune cells: accomplices or antagonists of recipient-derived macrophages in allograft fibrosis?

Organ fibrosis caused by chronic allograft rejection is a major concern in the field of transplantation. Macrophage-to-myofibroblast transition plays a critical role in chronic allograft fibrosis. Adaptive immune cells (such as B and CD4⁺ T cells) and innate immune cells (such as neutrophils and innate lymphoid cells) participate in the occurrence of recipient-derived macrophages transformed to myofibroblasts by secreting cytokines, which eventually leads to fibrosis of the transplanted organ. This review provides an update on the latest progress in understanding the plasticity of recipient-derived macrophages in chronic allograft rejection. We discuss here the immune mechanisms of allograft fibrosis and review the reaction of immune cells in allograft. The interactions between immune cells and the process of myofibroblast formulation are being considered for the potential therapeutic targets of chronic allograft fibrosis. Therefore, research on this topic seems to provide novel clues for developing strategies for preventing and treating allograft fibrosis.

The mitigating effect of exogenous carbon monoxide on chronic allograft rejection and fibrosis post-lung transplantation

BACKGROUND

Small airway inflammation and fibrosis or bronchiolitis obliterans (BO) is the predominant presentation of chronic lung allograft dysfunction (CLAD) post-lung transplantation. Carbon monoxide (CO) is a critical endogenous signaling transducer with known anti-inflammatory and anti-fibrotic effects but its therapeutic potential in CLAD remains to be fully elucidated.

METHODS

Here we investigate the effect of inhaled CO in modulating chronic lung allograft rejection pathology in a murine orthotopic lung transplant model of BO (B6D2F1/J→DBA/2J). Additionally, the effects of CO on the activated phenotype of mesenchymal cells isolated from human lung transplant recipients with CLAD were studied.

RESULTS

Murine lung allografts treated with CO (250 ppm × 30 minutes twice daily from days 7 to 40 post-transplantation) demonstrated decreased immune cell infiltration, fibrosis, and airway obliteration by flow cytometry, trichrome staining, and morphometric analysis, respectively. Decreased total collagen, with levels comparable to isografts, was noted in CO-treated allografts by quantitative hydroxyproline assay. In vitro, CO (250 ppm × 16h) was effective in reversing the fibrotic phenotype of human CLAD mesenchymal cells with decreased collagen I and β-catenin expression as well as an inhibitory effect on ERK1/2 MAPK, and mTORC1/2 signaling. Sildenafil, a phosphodiesterase 5 inhibitor, partially mimicked the effects of CO on CLAD mesenchymal cells and was partially effective in decreasing collagen deposition in murine allografts, suggesting the contribution of cGMP-dependent and -independent mechanisms in mediating the effect of CO.

CONCLUSION

These results suggest a potential role for CO in alleviating allograft fibrosis and mitigating chronic rejection pathology post-lung transplant.

Ferret Lung Transplantation Models Differential Lymphoid Aggregate Morphology Between Restrictive and Obstructive Forms of Chronic Lung Allograft Dysfunction

BACKGROUND

Long-term survival after lung transplantation remains limited by chronic lung allograft dysfunction (CLAD). CLAD has 2 histologic phenotypes, namely obliterative bronchiolitis (OB) and restrictive alveolar fibroelastosis (AFE), which have distinct clinical presentations, pathologies, and outcomes. Understanding of OB versus AFE pathogenesis would improve with better animal models.

METHODS

We utilized a ferret orthotopic single-lung transplantation model to characterize allograft fibrosis as a histologic measure of CLAD. Native lobes and "No CLAD" allografts lacking aberrant histology were used as controls. We used morphometric analysis to evaluate the size and abundance of B-cell aggregates and tertiary lymphoid organs (TLOs) and their cell composition. Quantitative RNA expression of 47 target genes was performed simultaneously using a custom QuantiGene Plex Assay.

RESULTS

Ferret lung allografts develop the full spectrum of human CLAD histology including OB and AFE subtypes. While both OB and AFE allografts developed TLOs, TLO size and number were greater with AFE histology. More activated germinal center cells marked by B-cell lymphoma 6 Transcription Repressor, (B-cell lymphoma 6) expression and fewer cells expressing forkhead box P3 correlated with AFE, congruent with greater diffuse immunoglobulin, plasma cell abundance, and complement 4d staining. Furthermore, forkhead box P3 RNA induction was significant in OB allografts specifically. RNA expression changes were seen in native lobes of animals with AFE but not OB when compared with No CLAD native lobes.

CONCLUSIONS

The orthotopic ferret single-lung transplant model provides unique opportunities to better understand factors that dispose allografts to OB versus AFE. This will help develop potential immunomodulatory therapies and antifibrotic approaches for lung transplant patients.

Metastasis suppressor NME1 in exosomes or liposomes conveys motility and migration inhibition in breast cancer model systems

Tumor-derived exosomes have documented roles in accelerating the initiation and outgrowth of metastases, as well as in therapy resistance. Little information supports the converse, that exosomes or similar vesicles can suppress metastasis. We investigated the NME1 (Nm23-H1) metastasis suppressor as a candidate for metastasis suppression by extracellular vesicles. Exosomes derived from two cancer cell lines (MDA-MB-231T and MDA-MB-435), when transfected with the NME1 (Nm23-H1) metastasis suppressor, secreted exosomes with NME1 as the predominant constituent. These exosomes entered recipient tumor cells, altered their endocytic patterns in agreement with NME1 function, and suppressed in vitro tumor cell motility and migration compared to exosomes from control transfectants. Proteomic analysis of exosomes revealed multiple differentially expressed proteins that could exert biological functions. Therefore, we also prepared and investigated liposomes, empty or containing partially purified rNME1. rNME1 containing liposomes recapitulated the effects of exosomes from NME1 transfectants in vitro. In an experimental lung metastasis assay the median lung metastases per histologic section was 158 using control liposomes and 15 in the rNME1 liposome group, 90.5% lower than the control liposome group (P = 0.016). The data expand the exosome/liposome field to include metastasis suppressive functions and describe a new translational approach to prevent metastasis.

Single-cell transcriptome mapping identifies a local, innate B cell population driving chronic rejection after lung transplantation

Bronchiolitis obliterans syndrome (BOS) is the main reason for poor outcomes after lung transplantation (LTx). We and others have recently identified B cells as major contributors to BOS after LTx. The extent of B cell heterogeneity and the relative contributions of B cell subpopulations to BOS, however, remain unclear. Here, we provide a comprehensive analysis of cell population changes and their gene expression patterns during chronic rejection after orthotopic LTx in mice. Of 11 major cell types, Mzb1-expressing plasma cells (PCs) were the most prominently increased population in BOS lungs. These findings were validated in 2 different cohorts of human BOS after LTx. A Bhlhe41, Cxcr3, and Itgb1 triple-positive B cell subset, also expressing classical markers of the innate-like B-1 B cell population, served as the progenitor pool for Mzb1⁺ PCs. This subset accounted for the increase in IgG_2c production within BOS lung grafts. A genetic lack of Igs decreased BOS severity after LTx. In summary, we provide a detailed analysis of cell population changes during BOS. IgG⁺ PCs and their progenitors — an innate B cell subpopulation — are the major source of local Ab production and a significant contributor to BOS after LTx.

Bronchiolitis obliterans syndrome after lung or haematopoietic stem cell transplantation: current management and future directions

Bronchiolitis obliterans syndrome (BOS) may develop after either lung or haematopoietic stem cell transplantation (HSCT), with similarities in histopathological features and clinical manifestations. However, there are differences in the contributory factors and clinical trajectories between the two conditions. BOS after HSCT occurs due to systemic graft-versus-host-disease (GVHD), whereas BOS after lung transplantation is limited to the lung allograft. BOS diagnosis after HSCT is more challenging, as the lung function decline may occur due to extrapulmonary GVHD, causing sclerosis or inflammation in the fascia or muscles of the respiratory girdle. Treatment is generally empirical with no established effective therapies. This review provides rare insights and commonalities of both conditions, that are not well elaborated elsewhere in contemporary literature, and highlights the importance of cross disciplinary learning from experts in other transplant modalities. Treatment algorithms for each condition are presented, based on the published literature and consensus clinical opinion. Immunosuppression should be optimised, and other conditions or contributory factors treated where possible. When initial treatment fails, the ultimate therapeutic option is lung transplantation (or re-transplantation in the case of BOS after lung transplantation) in carefully selected candidates. Novel therapies under investigation include aerosolised liposomal cyclosporine, Janus kinase inhibitors, antifibrotic therapies, and (in patients with BOS after lung transplantation) B-cell–directed therapies. Effective novel treatments that have a tangible impact on survival and thereby avoid the need for lung transplantation or re-transplantation are urgently required.

Molecular mechanisms of neuroendocrine differentiation in prostate cancer progression

Background

Rapid evolution of the therapeutic management of prostate cancer, especially in in second-generation androgen inhibitors, has increased the opportunity of transformation from prostate cancer (PCa) to neuroendocrine prostate cancer (NEPC). NEPC still lacks effective diagnostic and therapeutic interventions. Researches into the molecular characteristics of neuroendocrine differentiation is undoubtedly crucial to the discovery of new target genes for accurate diagnostic and therapeutic targets.

Purpose

In this review, we focus on the relevant genes and molecular mechanisms that have contributed to the transformation in the progression of PCa and discuss the potential targeted molecule that might improve diagnostic accuracy and therapeutic effectiveness.

Methods

The relevant literatures from PubMed have been reviewed for this article.

Conclusion

Several molecular characteristics influence the progression of neuroendocrine differentiation of prostate cancer which will provide a novel sight for accurate diagnosis and target therapeutic intervention for patients with NEPC.

Sustained Club Cell Injury in Mice Induces Histopathologic Features of Deployment-Related Constrictive Bronchiolitis

Histopathologic evidence of deployment-related constrictive bronchiolitis (DRCB) has been identified in soldiers deployed to Southwest Asia. While inhalational injury to the airway epithelium is suspected, relatively little is known about the pathogenesis underlying this disabling disorder. Club cells are local progenitors critical for repairing the airway epithelium after exposure to various airborne toxins, and a prior study using an inducible transgenic murine model reported that 10 days of sustained targeted club cell injury causes constrictive bronchiolitis. To further understand the mechanisms leading to small airway fibrosis, a murine model was employed to show that sustained club cell injury elicited acute weight loss, caused increased local production of proinflammatory cytokines, and promoted accumulation of numerous myeloid cell subsets in the lung. Transition to a chronic phase was characterized by up-regulated expression of oxidative stress-associated genes, increased activation of transforming growth factor-β, accumulation of alternatively activated macrophages, and enhanced peribronchiolar collagen deposition. Comparative histopathologic analysis demonstrated that sustained club cell injury was sufficient to induce epithelial metaplasia, airway wall thickening, peribronchiolar infiltrates, and clusters of intraluminal airway macrophages that recapitulated key abnormalities observed in DRCB. Depletion of alveolar macrophages in mice decreased activation of transforming growth factor-β and ameliorated constrictive bronchiolitis. Collectively, these findings implicate sustained club cell injury in the development of DRCB and delineate pathways that may yield biomarkers and treatment targets for this disorder.

Graft dysfunction and rejection of lung transplant, a review on diagnosis and management

Introduction

Lung transplantation has proven to be an effective treatment option for end‐stage lung disease. However, early and late complications following transplantation remain significant causes of high mortality.

Objectives

In this review, we focus on the time of onset in primary graft dysfunction and rejection complications, as well as emphasize the role of imaging manifestations and pathological features in early diagnosis, thus assisting clinicians in the early detection and treatment of posttransplant complications and improving patient quality of life and survival.

Data source

We searched electronic databases such as PubMed, Web of Science, and EMBASE. We used the following search terms: lung transplantation complications, primary graft dysfunction, acute rejection, chronic lung allograft dysfunction, radiological findings, and diagnosis and treatment.

Conclusion

Primary graft dysfunction, surgical complications, immune rejection, infections, and neoplasms represent major posttransplant complications. As the main posttransplant survival limitation, chronic lung allograft dysfunction has a characteristic imaging presentation; nevertheless, the clinical and imaging manifestations are often complex and overlap, so it is essential to understand the temporal evolution of these complications to narrow the differential diagnosis for early treatment to improve prognosis.

Early and late complications after lung transplantation remain essential causes of high mortality. In this review, we focus on the timing of the onset of primary graft dysfunction and rejection complications and highlight the role of imaging manifestations and clinicopathologic features in early diagnosis, thus assisting clinicians in the early detection and treatment of posttransplant complications and improving patient quality of life and survival.

Microbiota in heart and lung transplantation: implications for innate-adaptive immune interface

PURPOSE OF REVIEW

Transplantation continues to be the only treatment option for end-stage organ failure when other interventions have failed. Although short-term outcomes have improved due to advances in perioperative care, long-term outcomes continue to be adversely affected by chronic rejection. Little is known about the role microbiota play in modulating alloimmune responses and potentially contributing to graft failure. Initial data have identified a correlation between specific changes of the recipient and/or donor microbiota and transplant outcomes. In this review, we will focus on recent findings concerning the complex interplay between microbiota and the innate immune system after heart and lung transplantation.

RECENT FINDINGS

Gut microbiome derangements in heart failure promote an inflammatory state and have lasting effects on the innate immune system, with an observed association between increased levels of microbiota-dependent metabolites and acute rejection after cardiac transplantation. The lung allograft microbiome interacts with components of the innate immune system, such as toll-like receptor signalling pathways, NKG2C+ natural killer cells and the NLRP3 inflammasome, to alter posttransplant outcomes, which may result in the development of chronic rejection.

SUMMARY

The innate immune system is influenced by alterations in the microbiome before and after heart and lung transplantation, thereby offering potential therapeutic targets for prolonging allograft survival.

Transcription factor FOXF1 identifies compartmentally distinct mesenchymal cells with a role in lung allograft fibrogenesis

In this study, we demonstrate that forkhead box F1 (FOXF1), a mesenchymal transcriptional factor essential for lung development, was retained in a topographically distinct mesenchymal stromal cell population along the bronchovascular space in an adult lung and identify this distinct subset of collagen-expressing cells as key players in lung allograft remodeling and fibrosis. Using Foxf1-tdTomato BAC (Foxf1-tdTomato) and Foxf1-tdTomato Col1a1-GFP mice, we show that Lin-Foxf1+ cells encompassed the stem cell antigen 1+CD34+ (Sca1+CD34+) subset of collagen 1-expressing mesenchymal cells (MCs) with a capacity to generate CFU and lung epithelial organoids. Histologically, FOXF1-expressing MCs formed a 3D network along the conducting airways; FOXF1 was noted to be conspicuously absent in MCs in the alveolar compartment. Bulk and single-cell RNA-Seq confirmed distinct transcriptional signatures of Foxf1+ and Foxf1- MCs, with Foxf1-expressing cells delineated by their high expression of the transcription factor glioma-associated oncogene 1 (Gli1) and low expression of integrin α8 (Itga), versus other collagen-expressing MCs. FOXF1+Gli1+ MCs showed proximity to Sonic hedgehog-expressing (Shh-expressing) bronchial epithelium, and mesenchymal expression of Foxf1 and Gli1 was found to be dependent on paracrine Shh signaling in epithelial organoids. Using a murine lung transplant model, we show dysregulation of epithelial-mesenchymal SHH/GLI1/FOXF1 crosstalk and expansion of this specific peribronchial MC population in chronically rejecting fibrotic lung allografts.

Interleukin 6 trans-signaling is a critical driver of lung allograft fibrosis

Histopathologic examination of lungs afflicted by chronic lung allograft dysfunction (CLAD) consistently shows both mononuclear cell (MNC) inflammation and mesenchymal cell (MC) fibroproliferation. We hypothesize that interleukin 6 (IL-6) trans-signaling may be a critical mediator of MNC-MC crosstalk and necessary for the pathogenesis of CLAD. Bronchoalveolar lavage (BAL) fluid obtained after the diagnosis of CLAD has approximately twofold higher IL-6 and soluble IL-6 receptor (sIL-6R) levels compared to matched pre-CLAD samples. Human BAL-derived MCs do not respond to treatment with IL-6 alone but have rapid and prolonged JAK2-mediated STAT3 Tyr705 phosphorylation when exposed to the combination of IL-6 and sIL-6R. STAT3 phosphorylation within MCs upregulates numerous genes causing increased invasion and fibrotic differentiation. MNC, a key source of both IL-6 and sIL-6R, produce minimal amounts of these proteins at baseline but significantly upregulate production when cocultured with MCs. Finally, the use of an IL-6 deficient recipient in a murine orthotopic transplant model of CLAD reduces allograft fibrosis by over 50%. Taken together these results support a mechanism where infiltrating MNCs are stimulated by resident MCs to release large quantities of IL-6 and sIL-6R which then feedback onto the MCs to increase invasion and fibrotic differentiation.