Chronic Lung Allograft Dysfunction: A Systematic Review of Mechanisms

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.

Triggering receptor expressed on myeloid cells-1 aggravates obliterative bronchiolitis via enhancing the proinflammatory phenotype of macrophages

BACKGROUND

Triggering Receptor Expressed on Myeloid cells-1 (TREM-1) plays an important role in innate immune system. However, whether and how TREM-1 contributes to obliterative bronchiolitis (OB) progression remains unclear.

METHODS

A murine orthotopic tracheal transplantation model was constructed to mimic the pathogenesis of OB. qPCR and immunoblotting were used to measure TREM-1 expression. RNA sequencing was used to investigate the impact of TREM-1 on proinflammatory phenotype of macrophages. Trem-1 knockout mice and Nlrp3 knockout mice were generated to investigate the role of the TREM-1/NLRP3 pathway in the proinflammatory phenotype of macrophages. The infiltration of immune cells within the grafts was quantified using immunofluorescence staining. Flow cytometry was used to detect the proportion of different immune cells in mice spleen and the expression levels of iNOS and co-stimulatory molecules in macrophages.

RESULTS

The expression of TREM-1 was upregulated in the mouse OB model. Genetic ablation or pharmacological inhibition of TREM-1 ameliorated OB, whereas the stimulation of TREM-1 using anti-TREM-1 agonistic antibody exacerbated OB. Moreover, Trem-1 ablation reduced the infiltration of iNOS+ macrophages and limited the T cell responses. In vitro studies revealed that Trem-1 deletion impaired the proinflammatory function and antigen presentation ability of macrophages. Additionally, Trem-1 knockout inhibited the activation of NLRP3 signaling pathway. NLRP3 overexpression restored the proinflammatory phenotype of Trem-1 knockout macrophages.

CONCLUSIONS

These findings indicated that TREM-1 could promote the proinflammatory phenotype of macrophages through NLRP3 inflammasome activation, thereby exacerbating OB progression. These findings indicated that TREM-1 may serve as a therapeutic target for OB treatment.

Relationship between immune cells and the development of chronic lung allograft dysfunction

A major cause of death for lung transplant recipients (LTRs) is the advent of chronic lung allograft dysfunction (CLAD), which has long plagued the long-term post-transplant prognosis and quality of survival of transplant patients. The intricacy of its pathophysiology and the irreversibility of its illness process present major obstacles to the clinical availability of medications. Immunotherapeutic medications are available, but they only aim to slow down the course of CLAD rather than having any therapeutic impact on the disease's development. For this reason, understanding the pathophysiology of CLAD is essential for both disease prevention and proven treatment. The immunological response in particular, in relation to chronic lung allograft dysfunction, has received a great deal of interest recently. Innate immune cells like natural killer cells, eosinophils, neutrophils, and mononuclear macrophages, as well as adaptive immunity cells like T and B cells, play crucial roles in this process through the release of chemokines and cytokines. The present review delves into changes and processes within the immune microenvironment, with a particular focus on the quantity, subtype, and characteristics of effector immune cells in the peripheral and transplanted lungs after lung transplantation. We incorporate and solidify the documented role of immune cells in the occurrence and development of CLAD with the advancements in recent years.

Donor Fractions of Cell-Free DNA Are Elevated During CLAD But Not During Infectious Complications After Lung Transplantation

During the last few years, cell-free DNA (cfDNA) has emerged as a possible non-invasive biomarker for prediction of complications after lung transplantation. We previously published a proof-of-concept study using a digital droplet polymerase chain reaction (ddPCR)-based method for detection of cfDNA. In the current study, we aimed to further evaluate the potential clinical usefulness of detecting chronic lung allograft dysfunction (CLAD) using three different ddPCR applications measuring and calculating the donor fraction (DF) of cfDNA as well as one method using the absolute amount of donor-derived cfDNA. We analyzed 246 serum samples collected from 26 lung transplant recipients. Nine of the patients had ongoing CLAD at some point during follow-up. All four methods showed statistically significant elevation of the measured variable in the CLAD samples compared to the non-CLAD samples. The results support the use of ddPCR-detected cfDNA as a potential biomarker for prediction of CLAD. These findings need to be validated in a subsequent prospective study.

Oversizing lung allografts deteriorates outcomes in patients with pulmonary fibrosis

BACKGROUND

Lung transplantation is the only curative treatment for patients with end-stage pulmonary fibrosis. It is still under debate whether over- or undersizing of lung allografts is preferably performed regarding the postoperative outcome. We therefore analyzed our data using predicted total lung capacity to compare size mismatches.

METHODS

Patient records were retrospectively reviewed. Three groups were formed, 1 including patients with a donor-recipients pTLC ratio (DRPR) of <1.0 (undersized group), the second with a DRPR of ≥1.0 and <1.1 (size-matched group), and the third group with a DRPR of ≥1.1 (oversized group). Outcomes were evaluated using chi-square test and Kruskall-Wallis test as well as Kaplan-Meier analysis, competing risk analysis, and multivariable analysis, respectively.

RESULTS

Between January 2010 and May 2023, among the 1501 patients transplanted at our institution, 422 (28%) patients were included, 26 (2%) patients forming the oversized group (median DRPR: 1.14), 101 (7%) patients forming the size-matched group (median DRPR: 1.03), and 296 (20%) patients forming the undersized group (median DRPR: 0.92). Patients from the oversized group had a higher PGD grade 3 rate at 24 (p < 0.001), 48 (p < 0.001), and 72 (p = 0.039) hours after transplantation as well as a higher in-hospital mortality compared to the undersized group (p = 0.033). The long-term survival was also better in the undersized group compared to the oversized group (p = 0.011) and to the size-matched group (p = 0.01).

CONCLUSIONS

Oversizing lung allografts more than 10% deteriorated early postoperative outcomes and long-term survival in patients with pulmonary fibrosis.

Impact of Transplant Body Mass Index and Post-Transplant Weight Changes on the Development of Chronic Lung Allograft Dysfunction Phenotypes

INTRODUCTION

Chronic lung allograft dysfunction (CLAD) is a lung transplant complication for which four phenotypes are recognized: Bronchiolitis obliterans syndrome (BOS), Restrictive allograft syndrome (RAS), mixed and undefined phenotypes. Weight gain is common after transplant and may negatively impact lung function. Study objectives were to describe post-transplant weight trajectories of patients who developed (or did not) CLAD phenotypes and examine the associations between BMI at transplant, post-transplant changes in weight and BMI, and the risk of developing these phenotypes.

METHODS

Adults who underwent a bilateral lung transplant between 2000 and 2020 at our institution were categorized as having (or not) one of the four CLAD phenotypes based on the proposed classification system. Demographic, anthropometric, and clinical data were retrospectively collected from medical records and analyzed.

RESULTS

Study population included 579 recipients (412 [71.1%] CLAD-free, 81 [14.0%] BOS, 20 [3.5%] RAS, 59 [10.2%] mixed, and 7 [1.2%] undefined phenotype). Weight gains of greater amplitude were seen in recipients with restrictive phenotypes than CLAD-free and BOS patients within the first five years post-transplant. While the BMI category at transplant was not statistically associated with the risk of developing CLAD phenotypes, an increase in weight (Hazard ratio [HR]: 1.04, 95% CI [1.01-1.08]; P = .008) and BMI (HR: 1.13, 95% CI [1.03-1.23]; P = .008) over the post-transplant period was associated with a greater risk of RAS.

CONCLUSION

Post-LTx gain in weight and BMI modestly increased the risk of RAS, adding to the list of unfavorable outcomes associated with weight gain following transplant.

Macrophage and CD8 T cell discordance are associated with acute lung allograft dysfunction progression

BACKGROUND

Acute lung allograft dysfunction (ALAD) is an imprecise syndrome denoting concern for the onset of chronic lung allograft dysfunction (CLAD). Mechanistic biomarkers are needed that stratify risk of ALAD progression to CLAD. We hypothesized that single cell investigation of bronchoalveolar lavage (BAL) cells at the time of ALAD would identify immune cells linked to progressive graft dysfunction.

METHODS

We prospectively collected BAL from consenting lung transplant recipients for single cell RNA sequencing. ALAD was defined by a ≥10% decrease in FEV1 not caused by infection or acute rejection and samples were matched to BAL from recipients with stable lung function. We examined cell compositional and transcriptional differences across control, ALAD with decline, and ALAD with recovery groups. We also assessed cell-cell communication.

RESULTS

BAL was assessed for 17 ALAD cases with subsequent decline (ALAD declined), 13 ALAD cases that resolved (ALAD recovered), and 15 cases with stable lung function. We observed broad differences in frequencies of the 26 unique cell populations across groups (p = 0.02). A CD8 T cell (p = 0.04) and a macrophage cluster (p = 0.01) best identified ALAD declined from the ALAD recovered and stable groups. This macrophage cluster was distinguished by an anti-inflammatory signature and the CD8 T cell cluster resembled a Tissue Resident Memory subset. Anti-inflammatory macrophages signaled to activated CD8 T cells via class I HLA, fibronectin, and galectin pathways (p < 0.05 for each). Recipients with discordance between these cells had a nearly 5-fold increased risk of severe graft dysfunction or death (HR 4.6, 95% CI 1.1-19.2, adjusted p = 0.03). We validated these key findings in 2 public lung transplant genomic datasets.

CONCLUSIONS

BAL anti-inflammatory macrophages may protect against CLAD by suppressing CD8 T cells. These populations merit functional and longitudinal assessment in additional cohorts.

The gut microbiome in end-stage lung disease and lung transplantation

Gut dysbiosis has been associated with impaired outcomes in liver and kidney transplant recipients, but the gut microbiome of lung transplant recipients has not been extensively explored. We assessed the gut microbiome in 64 fecal samples from end-stage lung disease patients before transplantation and 219 samples from lung transplant recipients after transplantation using metagenomic sequencing. To identify dysbiotic microbial signatures, we analyzed 243 fecal samples from age-, sex-, and BMI-matched healthy controls. By unsupervised clustering, we identified five groups of lung transplant recipients using different combinations of immunosuppressants and antibiotics and analyzed them in relation to the gut microbiome. Finally, we investigated the gut microbiome of lung transplant recipients in different chronic lung allograft dysfunction (CLAD) stages and longitudinal gut microbiome changes after transplantation. We found 108 species (58.1%) in end-stage lung disease patients and 139 species (74.7%) in lung transplant recipients that were differentially abundant compared with healthy controls, with several species exhibiting sharp longitudinal increases from before to after transplantation. Different combinations of immunosuppressants and antibiotics were associated with specific gut microbial signatures. We found that the gut microbiome of lung transplant recipients in CLAD stage 0 was more similar to healthy controls compared to those in CLAD stage 1. Finally, the gut microbial diversity of lung transplant recipients remained lower than the average gut microbial diversity of healthy controls up to more than 20 years post-transplantation. Gut dysbiosis, already present before lung transplantation was exacerbated following lung transplantation.IMPORTANCEThis study provides extensive insights into the gut microbiome of end-stage lung disease patients and lung transplant recipients, which warrants further investigation before the gut microbiome can be used for microbiome-targeted interventions that could improve the outcome of lung transplantation.

Correlation Between Tacrolimus Levels in Blood Samples Obtained from Central Catheter and Peripheral Venipuncture in Lung Transplant Patients (Ven-Cat Study)

BACKGROUND

Following lung transplantation (LT), receiving immunosuppressive therapy is crucial. Tacrolimus is considered a drug with a narrow therapeutic range and its use requires constant monitoring. This study aimed to evaluate the correlation between tacrolimus levels obtained from central venous catheter and direct venipuncture in adult patients undergoing LT.

METHODS

This prospective study included LT patients hospitalized in conventional ward carrying a central catheter through which no intravenous tacrolimus was administered. Trough samples were obtained through direct puncture and from the central catheter. Pearson correlation coefficient was calculated to quantify the mean difference between the 2 measures.

RESULTS

A total of 54 sample pairs from 16 LT patients were obtained, mostly male (81.3%) and bilateral transplant recipients (93.8%); the transplant procedure was the primary reason for admission (81.3%). The difference in tacrolimus levels between both samples was 0.3 (0.1-0.6) mcg/L, with the measurement for the samples obtained through venipuncture being mostly higher than that for those obtained from the catheter. A strong correlation was observed between the tacrolimus levels in the samples obtained from the catheter and through venipuncture (Pearson correlation coefficient, 0.991; P < 0.001; R2 = 0.982).

CONCLUSIONS

There is an excellent correlation between tacrolimus levels obtained from venipuncture and those obtained from central venous catheter in LT patients undergoing oral tacrolimus therapy.

Higher Molecular Injury at Diagnosis of Acute Cellular Rejection Increases the Risk of Lung Allograft Failure: A Clinical Trial

Rationale: The association of acute cellular rejection (ACR) with chronic lung allograft dysfunction (CLAD) in lung transplant recipients has primarily been described before consensus recommendations incorporating restrictive phenotypes. Furthermore, the association of the degree of molecular allograft injury during ACR with CLAD or death remains undefined. Objectives: To investigate the association of ACR with the risk of CLAD or death and to further investigate if this risk depends on the degree of molecular allograft injury. Methods: This multicenter, prospective cohort study included 188 lung transplant recipients. Subjects underwent serial plasma collections for donor-derived cell-free DNA (dd-cfDNA) at prespecified time points and bronchoscopy. Multivariable Cox proportional-hazards analysis was conducted to analyze the association of ACR with subsequent CLAD or death as well as the association of dd-cfDNA during ACR with risk of CLAD or death. Additional outcomes analyses were performed with episodes of ACR categorized as "high risk" (dd-cfDNA ⩾ 1%) and "low risk" (dd-cfDNA < 1%). Measurements and Main Results: In multivariable analysis, ACR was associated with the composite outcome of CLAD or death (hazard ratio [HR], 2.07 [95% confidence interval (CI), 1.05-4.10]; P = 0.036). Elevated dd-cfDNA ⩾ 1% at ACR diagnosis was independently associated with increased risk of CLAD or death (HR, 3.32; 95% CI, 1.31-8.40; P = 0.012). Patients with high-risk ACR were at increased risk of CLAD or death (HR, 3.13; 95% CI, 1.41-6.93; P = 0.005), whereas patients with low-risk status ACR were not. Conclusions: Patients with ACR are at higher risk of CLAD or death, but this may depend on the degree of underlying allograft injury at the molecular level. Clinical trial registered with www.clinicaltrials.gov (NCT02423070).

Creating superior lungs for transplantation with next-generation gene therapy during ex vivo lung perfusion

Engineering donor organs to better tolerate the harmful non-immunological and immunological responses inherently related to solid organ transplantation would improve transplant outcomes. Our enhanced knowledge of ischemia-reperfusion injury, alloimmune responses and pathological fibroproliferation after organ transplantation, and the advanced toolkit available for gene therapies, have brought this goal closer to clinical reality. Ex vivo organ perfusion has evolved rapidly especially in the field of lung transplantation, where clinicians routinely use ex vivo lung perfusion (EVLP) to confirm the quality of marginal donor lungs before transplantation, enabling safe transplantation of organs originally considered unusable. EVLP would also be an attractive platform to deliver gene therapies, as treatments could be administered to an isolated organ before transplantation, thereby providing a window for sophisticated organ engineering while minimizing off-target effects to the recipient. Here, we review the status of lung transplant first-generation gene therapies that focus on inducing transgene expression in the target cells. We also highlight recent advances in next-generation gene therapies, that enable gene editing and epigenetic engineering, that could be used to permanently change the donor organ genome and to induce widespread transcriptional gene expression modulation in the donor lung. In a future vision, dedicated organ repair and engineering centers will use gene editing and epigenetic engineering, to not only increase the donor organ pool, but to create superior organs that will function better and longer in the recipient.

Nanoparticle-assisted Targeting Delivery Technologies for Preventing Organ Rejection

Although organ transplantation is a life-saving medical procedure, the challenge of posttransplant rejection necessitates safe and effective immune modulation strategies. Nanodelivery approaches may have the potential to overcome the limitations of small-molecule immunosuppressive drugs, achieving efficacious treatment options for transplant tolerance without compromising overall host immunity. This review highlights recent advances in biomaterial-assisted formulations and technologies for targeted nanodrug delivery with transplant organ- or immune cell-level precision for treating graft rejection after transplantation. We provide an overview of the mechanism of transplantation rejection, current clinically approved immunosuppressive drugs, and their relevant limitations. Finally, we discuss the targeting principles and advantages of organ- and immune cell-specific delivery technologies. The development of biomaterial-assisted novel therapeutic strategies holds considerable promise for treating organ rejection and clinical translation.

Which strategy is better for lung transplantation: Cardiopulmonary bypass or extracorporeal membrane oxygenation?

Background: In lung transplantation surgery, extracorporeal life support (ECLS) is essential for safety. Various support methods, including cardiopulmonary bypass (CPB) and off-pump techniques, are used, with extracorporeal membrane oxygenation (ECMO) gaining prominence. However, consensus on the best support strategy is lacking.Purpose: This article reviews risks, benefits, and outcomes of different support strategies in lung transplantation. By consolidating knowledge, it aims to clarify selecting the most appropriate ECLS modality.Research Design: A comprehensive literature review examined CPB, off-pump techniques, and ECMO outcomes in lung transplantation, including surgical results and complications.Study Sample: Studies, including clinical trials and observational research, focused on ECLS in lung transplantation, both retrospective and prospective, providing a broad evidence base.Data Collection and/or Analysis: Selected studies were analyzed for surgical outcomes, complications, and survival rates associated with CPB, off-pump techniques, and ECMO to assess safety and effectiveness.Results: Off-pump techniques are preferred, with ECMO increasingly vital as a bridge to transplant, overshadowing CPB. However, ECMO entails hidden risks and higher costs. While safer than CPB, optimizing ECMO postoperative use and monitoring is crucial for success.Conclusions: Off-pump techniques are standard, but ECMO's role is expanding. Despite advantages, careful ECMO management is crucial due to hidden risks and costs. Future research should focus on refining ECMO use and monitoring to improve outcomes, emphasizing individualized approaches for LT recipients.

The Association of Post-Lung Transplant Pulmonary Embolism With the Development of Chronic Lung Allograft Dysfunction

Background

Pulmonary embolism (PE) is a rare yet serious postoperative complication for lung transplant recipients (LTRs). The association between timing and severity of PE and the development of chronic allograft lung dysfunction (CLAD) has not been described.

Methods

A single-center, retrospective cohort analysis of first LTRs included bilateral or single lung transplants and excluded multiorgan transplants and retransplants. PEs were confirmed by computed tomography angiography or ventilation/perfusion (VQ) scans. Infarctions were confirmed on computed tomography angiography by a trained physician. The PE severity was defined by the Pulmonary Embolism Severity Index (PESI) score, a 30-d post-PE mortality risk calculator, and stratified by low I and II (0-85), intermediate III and IV (85-125), and high V (>125). PE and PESI were analyzed in the outcomes of overall survival, graft failure, and chronic lung allograft dysfunction (CLAD).

Results

We identified 57 of 928 patients (6.14%) who had at least 1 PE in the LTR cohort with a median follow-up of 1623 d. In the subset with PE, the median PESI score was 85 (75.8-96.5). Most of the PESI scores (32/56 available) were in the low-risk category. In the CLAD analysis, there were 49 LTRs who had a PE and 16 LTRs (33%) had infarction. When treating PE as time-dependent and adjusting for covariates, PE was significantly associated with death (hazard ratio [HR] 1.8; 95% confidence interval [CI], 1.3-2.5), as well as increased risk of graft failure, defined as retransplant, CLAD, or death (HR 1.8; 95% CI, 1.3-2.5), and CLAD (HR 1.7; 95% CI, 1.2-2.4). Infarction was not associated with CLAD or death. The PESI risk category was not a significant predictor of death or CLAD.

Conclusions

PE is associated with decreased survival and increased hazard of developing CLAD. PESI score was not a reliable predictor of CLAD or death in this lung transplant cohort.

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.

Design and Rationale of Cytokine Filtration in Lung Transplantation (GLUSorb): Protocol for a Multicenter Clinical Randomized Controlled Trial

BACKGROUND

Lung transplantation (LTx) is the only treatment option for end-stage lung disease. Despite improvements, primary graft dysfunction (PGD) remains the leading cause of early mortality and precipitates chronic lung allograft dysfunction, the main factor in late mortality after LTx. PGD develops within the first 72 hours and impairs the oxygenation capacity of the lung, measured as partial pressure of oxygen (PaO2)/fraction of inspired oxygen (FiO2). Increasing the PaO2/FiO2 ratio is thus critical and has an impact on survival. There is a general lack of effective treatments for PGD. When a transplanted lung is not accepted by the immune system in the recipient, a systemic inflammatory response starts where cytokines play a critical role in initiating, amplifying, and maintaining the inflammation leading to PGD. Cytokine filtration can remove these cytokines from the circulation, thus reducing inflammation. In a proof-of-concept preclinical porcine model of LTx, cytokine filtration improved oxygenation and decreased PGD. In a feasibility study, we successfully treated patients undergoing LTx with cytokine filtration (ClinicalTrials.gov; NCT05242289).

OBJECTIVE

The purpose of this clinical trial is to demonstrate the superiority of cytokine filtration in improving LTx outcome, based on its effects on oxygenation ratio, plasma levels of inflammatory markers, PGD incidence and severity, lung function, kidney function, survival, and quality of life compared with standard treatment with no cytokine filtration.

METHODS

This study is a Swedish national interventional randomized controlled trial involving 116 patients. Its primary objective is to investigate the potential benefits of cytokine filtration when used in conjunction with LTx. Specifically, this study aims to determine whether the application of cytokine filtration, administered for a duration of 12 hours within the initial 24 hours following a LTx procedure, can lead to improved patient outcomes. This study seeks to assess various aspects of patient recovery and overall health to ascertain the potential positive impact of this intervention on the posttransplantation course.

RESULTS

The process of patient recruitment for this study is scheduled to commence subsequent to a site initiation visit, which was slated to take place on August 28, 2023. The primary outcome measure that will be assessed in this research endeavor is the oxygenation ratio, a metric denoted as the highest PaO2/FiO2 ratio achieved by patients within a 72-hour timeframe following their LTx procedure.

CONCLUSIONS

We propose that cytokine filtration could enhance the overall outcomes of LTx. Our hypothesis suggests potential improvements in LTx outcome and patient care.

TRIAL REGISTRATION

ClinicalTrials.gov NCT05526950; https://www.clinicaltrials.gov/study/NCT05526950.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

PRR1-10.2196/52553.

CCR5 drives NK cell-associated airway damage in pulmonary ischemia-reperfusion injury

Primary graft dysfunction (PGD) limits clinical benefit after lung transplantation, a life-prolonging therapy for patients with end-stage disease. PGD is the clinical syndrome resulting from pulmonary ischemia-reperfusion injury (IRI), driven by innate immune inflammation. We recently demonstrated a key role for NK cells in the airways of mouse models and human tissue samples of IRI. Here, we used 2 mouse models paired with human lung transplant samples to investigate the mechanisms whereby NK cells migrate to the airways to mediate lung injury. We demonstrate that chemokine receptor ligand transcripts and proteins are increased in mouse and human disease. CCR5 ligand transcripts were correlated with NK cell gene signatures independently of NK cell CCR5 ligand secretion. NK cells expressing CCR5 were increased in the lung and airways during IRI and had increased markers of tissue residency and maturation. Allosteric CCR5 drug blockade reduced the migration of NK cells to the site of injury. CCR5 blockade also blunted quantitative measures of experimental IRI. Additionally, in human lung transplant bronchoalveolar lavage samples, we found that CCR5 ligand was associated with increased patient morbidity and that the CCR5 receptor was increased in expression on human NK cells following PGD. These data support a potential mechanism for NK cell migration during lung injury and identify a plausible preventative treatment for PGD.

Percentage of low attenuation area on computed tomography detects chronic lung allograft dysfunction, especially bronchiolitis obliterans syndrome, after bilateral lung transplantation

INTRODUCTION

The percentage of low attenuation area (%LAA) on computed tomography (CT) is useful for evaluating lung emphysema, and higher %LAA was observed in patients with chronic lung allograft dysfunction (CLAD). This study investigated the relationship between the %LAA and the development of CLAD after bilateral lung transplantation (LT).

METHODS

We conducted a single-center retrospective study of 75 recipients who underwent bilateral LT; the recipients were divided into a CLAD group (n = 30) and a non-CLAD group (n = 45). The %LAA was calculated using CT and compared between the two groups from 4 years before to 4 years after the diagnosis of CLAD. The relationships between the %LAA and the percent baseline values of the pulmonary function test parameters were also calculated.

RESULTS

The %LAA was significantly higher in the CLAD group than in the non-CLAD group from 2 years before to 2 years after the diagnosis of CLAD (P < .05). In particular, patients with bronchiolitis obliterans syndrome (BOS) exhibited significant differences even from 4 years before to 4 years after diagnosis (P < .05). Significant negative correlations between the %LAA and the percent baseline values of the forced expiratory volume in 1 s (r = -.36, P = .0031), the forced vital capacity (r = -.27, P = .027), and the total lung capacity (r = -.40, P < .001) were seen at the time of CLAD diagnosis.

CONCLUSION

The %LAA on CT was associated with the development of CLAD and appears to have the potential to predict CLAD, especially BOS, after bilateral LT.

Extracorporeal cytokine adsorption reduces systemic cytokine storm and improves graft function in lung transplantation

Objectives

Ischemia-reperfusion injury often coincides with a cytokine storm, which can result in primary graft dysfunction following lung transplantation. Our previous research has demonstrated allograft improvement by cytokine adsorption during ex vivo lung perfusion. The aim of this study was to investigate the effect of in vivo extracorporeal cytokine adsorption in a large animal model.

Materials and Methods

Pig left lung transplantation was performed following 24 hours of cold ischemic storage. Observation period after transplantation was 24 hours. In the treatment group (n = 6), extracorporeal CytoSorb adsorption was started 30 minutes before reperfusion and continued for 6 hours. A control group (n = 3) did not receive adsorber treatment.

Results

During adsorption, we consistently noticed a significant decrease in plasma proinflammatory interleukin (IL)-2, trends of less proinflammatory, tumor necrosis factor- α, IL-1α, and granulocyte-macrophage colony-stimulating factor as well as significantly reduced systemic neutrophils. In addition, a significantly lower peak airway pressure was detected during the 6 hours of adsorption. After 24 hours of observation, when evaluating the left lung allograft independently, we observed significantly improved CO2 removal, partial pressure of oxygen/inspired oxygen fraction ratio, and less acidosis in the treatment group. At autopsy, bronchoalveolar lavage results exhibited significantly lower recruitment of cells and less pro-inflammatory IL-1α, IL-1β, IL-6, and IL-8 in the treatment group. Histologically, the treatment group had a strong trend, indicating less neutrophil invasion into the alveolar space.

Conclusions

Based on our findings, cytokine adsorption during and after reperfusion is a viable approach to reducing posttransplant inflammation following lung transplantation. CytoSorb may increase the acceptance of extended criteria donor lungs, which are more susceptible to ischemia-reperfusion injury.

Mesenchymal Stromal Cell Therapy in Lung Transplantation

Lung transplantation is often the only viable treatment option for a patient with end-stage lung disease. Lung transplant results have improved substantially over time, but ischemia-reperfusion injury, primary graft dysfunction, acute rejection, and chronic lung allograft dysfunction (CLAD) continue to be significant problems. Mesenchymal stromal cells (MSC) are pluripotent cells that have anti-inflammatory and protective paracrine effects and may be beneficial in solid organ transplantation. Here, we review the experimental studies where MSCs have been used to protect the donor lung against ischemia-reperfusion injury and alloimmune responses, as well as the experimental and clinical studies using MSCs to prevent or treat CLAD. In addition, we outline ex vivo lung perfusion (EVLP) as an optimal platform for donor lung MSC delivery, as well as how the therapeutic potential of MSCs could be further leveraged with genetic engineering.

[Chronic lung allograft dysfunction in 2022, past and updates]

INTRODUCTION

While short-term results of lung transplantation have improved considerably, long-term survival remains below that achieved for other solid organ transplants.

CURRENT KNOWLEDGE

The main cause of late mortality is chronic lung allograft dysfunction (CLAD), which affects nearly half of the recipients 5 years after transplantation. Immunological and non-immune risk factors have been identified. These factors activate the innate and adaptive immune system, leading to lesional and altered wound-healing processes, which result in fibrosis affecting the small airways or interstitial tissue. Several phenotypes of CLAD have been identified based on respiratory function and imaging pattern. Aside from retransplantation, which is possible for only small number of patients, no treatment can reverse the CLAD process.

PERSPECTIVES

Current therapeutic research is focused on anti-fibrotic treatments and photopheresis. Basic research has identified numerous biomarkers that could prove to be relevant as therapeutic targets.

CONCLUSION

While the pathophysiological mechanisms of CLAD are better understood than before, a major therapeutic challenge remains.

JAK-STAT activation contributes to cytotoxic T cell-mediated basal cell death in human chronic lung allograft dysfunction

Chronic lung allograft dysfunction (CLAD) is the leading cause of death in lung transplant recipients. CLAD is characterized clinically by a persistent decline in pulmonary function and histologically by the development of airway-centered fibrosis known as bronchiolitis obliterans. There are no approved therapies to treat CLAD, and the mechanisms underlying its development remain poorly understood. We performed single-cell RNA-Seq and spatial transcriptomic analysis of explanted tissues from human lung recipients with CLAD, and we performed independent validation studies to identify an important role of Janus kinase-signal transducer and activator of transcription (JAK-STAT) signaling in airway epithelial cells that contributes to airway-specific alloimmune injury. Specifically, we established that activation of JAK-STAT signaling leads to upregulation of major histocompatibility complex 1 (MHC-I) in airway basal cells, an important airway epithelial progenitor population, which leads to cytotoxic T cell-mediated basal cell death. This study provides mechanistic insight into the cell-to-cell interactions driving airway-centric alloimmune injury in CLAD, suggesting a potentially novel therapeutic strategy for CLAD prevention or treatment.

Systems prediction of chronic lung allograft dysfunction: Results and perspectives from the Cohort of Lung Transplantation and Systems prediction of Chronic Lung Allograft Dysfunction cohorts

Background

Chronic lung allograft dysfunction (CLAD) is the leading cause of poor long-term survival after lung transplantation (LT). Systems prediction of Chronic Lung Allograft Dysfunction (SysCLAD) aimed to predict CLAD.

Methods

To predict CLAD, we investigated the clinicome of patients with LT; the exposome through assessment of airway microbiota in bronchoalveolar lavage cells and air pollution studies; the immunome with works on activation of dendritic cells, the role of T cells to promote the secretion of matrix metalloproteinase-9, and subpopulations of T and B cells; genome polymorphisms; blood transcriptome; plasma proteome studies and assessment of MSK1 expression.

Results

Clinicome: the best multivariate logistic regression analysis model for early-onset CLAD in 422 LT eligible patients generated a ROC curve with an area under the curve of 0.77. Exposome: chronic exposure to air pollutants appears deleterious on lung function levels in LT recipients (LTRs), might be modified by macrolides, and increases mortality. Our findings established a link between the lung microbial ecosystem, human lung function, and clinical stability post-transplant. Immunome: a decreased expression of CLEC1A in human lung transplants is predictive of the development of chronic rejection and associated with a higher level of interleukin 17A; Immune cells support airway remodeling through the production of plasma MMP-9 levels, a potential predictive biomarker of CLAD. Blood CD9-expressing B cells appear to favor the maintenance of long-term stable graft function and are a potential new predictive biomarker of BOS-free survival. An early increase of blood CD4 + CD57 + ILT2+ T cells after LT may be associated with CLAD onset. Genome: Donor Club cell secretory protein G38A polymorphism is associated with a decreased risk of severe primary graft dysfunction after LT. Transcriptome: blood POU class 2 associating factor 1, T-cell leukemia/lymphoma domain, and B cell lymphocytes, were validated as predictive biomarkers of CLAD phenotypes more than 6 months before diagnosis. Proteome: blood A2MG is an independent predictor of CLAD, and MSK1 kinase overexpression is either a marker or a potential therapeutic target in CLAD.

Conclusion

Systems prediction of Chronic Lung Allograft Dysfunction generated multiple fingerprints that enabled the development of predictors of CLAD. These results open the way to the integration of these fingerprints into a predictive handprint.

Infection, Rejection, and the Connection

Solid organ transplantation is a life-saving treatment for people with end-stage organ disease. Immune-mediated transplant rejection is a common complication that decreases allograft survival. Although immunosuppression is required to prevent rejection, it also increases the risk of infection. Some infections, such as cytomegalovirus and BK virus, can promote inflammatory gene expression that can further tip the balance toward rejection. BK virus and other infections can induce damage that resembles the clinical pathology of rejection, and this complicates accurate diagnosis. Moreover, T cells specific for viral infection can lead to rejection through heterologous immunity to donor antigen directly mediated by antiviral cells. Thus, viral infections and allograft rejection interact in multiple ways that are important to maintain immunologic homeostasis in solid organ transplant recipients. Better insight into this dynamic interplay will help promote long-term transplant survival.

Diagnostic value of circulating microRNA-21 in chronic lung allograft dysfunction after bilateral cadaveric and living-donor lobar lung transplantation

Background

MicroRNAs (miRNAs) involved in the pathogenesis of pulmonary fibrosis have been shown to be associated with the development of chronic lung allograft dysfunction (CLAD) after lung transplantation (LT). We investigated the role of circulating miRNAs in the diagnosis of CLAD after bilateral LT, including cadaveric LT (CLT) and living-donor lobar LT (LDLLT).

Methods

The subjects of this retrospective study were 37 recipients of bilateral CLT (n = 23) and LDLLT (n = 14), and they were divided into a non-CLAD group (n = 24) and a CLAD group (n = 13). The plasma miRNA levels of the two groups were compared, and correlations between their miRNAs levels and percent baseline forced expiratory volume in 1 s (FEV1), forced vital capacity (FVC), and total lung capacity (TLC) values were calculated from one year before to one year after the diagnosis of CLAD.

Results

The plasma levels of both miR-21 and miR-155 at the time of the diagnosis of CLAD were significantly higher in the CLAD group than in the non-CLAD group (miR-21, P = 0.0013; miR-155, P = 0.042). The miR-21 levels were significantly correlated with the percent baseline FEV1, FVC, and TLC value of one year before and at the time of diagnosis of CLAD (P < 0.05). A receiver operating characteristic curve analysis of the performance of miR-21 levels in the diagnosis of CLAD yielded an area under the curve of 0.89.

Conclusion

Circulating miR-21 appears to be of potential value in diagnosing CLAD after bilateral LT.

Efficacy and safety of total lymphoid irradiation in different chronic lung allograft dysfunction phenotypes

Total lymphoid irradiation (TLI) is an alternative treatment for chronic lung allograft dysfunction (CLAD). However, data regarding its efficacy and tolerance are scarce. This study included patients with CLAD treated with TLI at our center between 2011 and 2018. Clinical characteristics before and after TLI and related complications were analyzed. Forty patients with CLAD (twenty-nine bronchiolitis obliterans syndrome [BOS], nine restrictive allograft syndrome [RAS], and two mixed) were included. Significant attenuation of the forced expiratory volume in 1-sec (FEV₁ ) decline slope was observed in all phenotypes, in both the BOS and RAS. The median FEV₁ 12, 6, and 3 months pre-TLI were as follows: 1980 (IQR 1720-2560), 1665 (IQR 1300-2340) and 1300 (IQR 1040-1740) ml (p < .001), while the median FEV₁ at 3, 6, and 12 months post-TLI was 1110 (IQR 810-1440), 1130 (IQR 860-1470), and 1115 (IQR 865-1490) ml (p = .769). No dropouts due to radiation toxicity were observed. The mean survival according to the Karnofsky Performance Status Scale (KPS) >70 or ≤70 at baseline was 1837 (IQR 259-2522) versus 298 (IQR 128-554) days (p < .0001), respectively. In conclusion, TLI may stop FEV₁ decline in both BOS and RAS. Moreover, a good KPS score may be an important prognostic factor.

Changes in HCMV immune cell frequency and phenotype are associated with chronic lung allograft dysfunction

Background

Human cytomegalovirus (HCMV) infection is common and often severe in lung transplant recipients (LTRs), and it is a risk factor associated with chronic lung allograft dysfunction (CLAD). The complex interplay between HCMV and allograft rejection is still unclear. Currently, no treatment is available to reverse CLAD after diagnosis, and the identification of reliable biomarkers that can predict the early development of CLAD is needed. This study investigated the HCMV immunity in LTRs who will develop CLAD.

Methods

This study quantified and phenotyped conventional (HLA-A2pp65) and HLA-E-restricted (HLA-EUL40) anti-HCMV CD8⁺ T (CD8 T) cell responses induced by infection in LTRs developing CLAD or maintaining a stable allograft. The homeostasis of immune subsets (B, CD4T, CD8 T, NK, and γδT cells) post-primary infection associated with CLAD was also investigated.

Results

At M18 post-transplantation, HLA-EUL40 CD8 T responses were less frequently found in HCMV⁺ LTRs (21.7%) developing CLAD (CLAD) than in LTRs (55%) keeping a functional graft (STABLE). In contrast, HLA-A2pp65 CD8 T was equally detected in 45% of STABLE and 47.8% of CLAD LTRs. The frequency of HLA-EUL40 and HLA-A2pp65 CD8 T among blood CD8 T cells shows lower median values in CLAD LTRs. Immunophenotype reveals an altered expression profile for HLA-EUL40 CD8 T in CLAD patients with a decreased expression for CD56 and the acquisition of PD-1. In STABLE LTRs, HCMV primary infection causes a decrease in B cells and inflation of CD8 T, CD57⁺/NKG2C⁺ NK, and δ2^-γδT cells. In CLAD LTRs, the regulation of B, total CD8 T, and δ2⁺γδT cells is maintained, but total NK, CD57⁺/NKG2C⁺ NK, and δ2^-γδT subsets are markedly reduced, while CD57 is overexpressed across T lymphocytes.

Conclusions

CLAD is associated with significant changes in anti-HCMV immune cell responses. Our findings propose that the presence of dysfunctional HCMV-specific HLA-E-restricted CD8 T cells together with post-infection changes in the immune cell distribution affecting NK and γδT cells defines an early immune signature for CLAD in HCMV⁺ LTRs. Such a signature may be of interest for the monitoring of LTRs and may allow an early stratification of LTRs at risk of CLAD.

Early onset of azithromycin to prevent CLAD in lung transplantation: Promising results of a retrospective single centre experience

INTRODUCTION

Azithromycin (AZI) may be an effective immune modulator in lung transplant (LT) recipients, and can decrease chronic lung allograft dysfunction (CLAD) rates, the leading cause of mortality after the 1st year post-LT. The aim of the study is to assess the effect of AZI initiation and its timing on the incidence and severity of CLAD in LT recipients.

METHODS

Single-center retrospective study, including LT recipients from 01/01/2011 to 30/06/2020. Four groups were established: those who started AZI at the 3rd week post-LT (group A), those who received AZI later than the 3rd week post-LT and had preserved FEV1 (B), those who did not receive AZI (C) and those who started AZI due to a decline in FEV1 (D). The dosage of AZI prescribed was 250 mg three times per week. CLAD was defined and graduated according to the 2019 ISHLT criteria.

RESULTS

We included 358 LT recipients: 139 (38.83%) were in group A, 94 (26.25%) in group B, 91 (25.42%) in group C, and 34 (9.50%) in group D. Group A experienced the lowest CLAD incidence and severity at 1 (p = .01), 3 (p < .001), and 5 years post-LT, followed by Group B. Groups C and D experienced a higher incidence and severity of CLAD (p = .015). Initiation of AZI prior to FEV1 decline (Groups A and B) proved to be protective against CLAD after adjusting for differences between the treatment groups.

CONCLUSIONS

Early initiation of AZI in LT recipients could have a role in decreasing the incidence and severity of CLAD. In addition, as long as FEV1 is preserved, initiating AZI at any time could also be useful to prevent the incidence of CLAD and reduce its severity.

Lung Allograft Microbiome Association with Gastroesophageal Reflux, Inflammation, and Allograft Dysfunction

Rationale: It remains unclear how gastroesophageal reflux disease (GERD) affects allograft microbial community composition in lung transplant recipients and its impact on lung allograft inflammation and function. Objectives: Our objective was to compare the allograft microbiota in lung transplant recipients with or without clinically diagnosed GERD in the first year after transplant and assess associations between GERD, allograft microbiota, inflammation, and acute and chronic lung allograft dysfunction (ALAD and CLAD). Methods: A total of 268 BAL samples were collected from 75 lung transplant recipients at a single transplant center every 3 months after transplant for 1 year. Ten transplant recipients from a separate transplant center provided samples before and after antireflux Nissen fundoplication surgery. Microbial community composition and density were measured using 16S ribosomal RNA gene sequencing and quantitative polymerase chain reaction, respectively, and inflammatory markers and bile acids were quantified. Measurements and Main Results: We observed a range of allograft community composition with three discernible types (labeled community state types [CSTs] 1-3). Transplant recipients with GERD were more likely to have CST1, characterized by high bacterial density and relative abundance of the oropharyngeal colonizing genera Prevotella and Veillonella. GERD was associated with more frequent transitions to CST1. CST1 was associated with lower inflammatory cytokine concentrations than pathogen-dominated CST3 across the range of microbial densities observed. Cox proportional hazard models revealed associations between CST3 and the development of ALAD/CLAD. Nissen fundoplication decreased bacterial load and proinflammatory cytokines. Conclusions: GERD was associated with a high bacterial density, Prevotella- and Veillonella-dominated CST1. CST3, but not CST1 or GERD, was associated with inflammation and early development of ALAD and CLAD. Nissen fundoplication was associated with a reduction in microbial density in BAL fluid samples, especially the CST1-specific genus, Prevotella.

Elevated cell-free DNA in respiratory viral infection and associated lung allograft dysfunction

Respiratory viral infection (RVI) in lung transplant recipients (LTRs) is a risk for chronic lung allograft dysfunction (CLAD). We hypothesize that donor-derived cell-free DNA (%ddcfDNA), at the time of RVI predicts CLAD progression. We followed 39 LTRs with RVI enrolled in the Genomic Research Alliance for Transplantation for 1 year. Plasma %ddcfDNA was measured by shotgun sequencing, with high %ddcfDNA as ≥1% within 7 days of RVI. We examined %ddcfDNA, spirometry, and a composite (progression/failure) of CLAD stage progression, re-transplant, and death from respiratory failure. Fifty-nine RVI episodes, 38 low and 21 high %ddcfDNA were analyzed. High %ddcfDNA subjects had a greater median %FEV₁ decline at RVI (-13.83 vs. -1.83, p = .007), day 90 (-7.97 vs. 0.91, p = .04), and 365 (-20.05 vs. 1.09, p = .047), compared to those with low %ddcfDNA and experienced greater progression/failure within 365 days (52.4% vs. 21.6%, p = .01). Elevated %ddcfDNA at RVI was associated with an increased risk of progression/failure adjusting for symptoms and days post-transplant (HR = 1.11, p = .04). No difference in %FEV₁ decline was seen at any time point when RVIs were grouped by histopathology result at RVI. %ddcfDNA delineates LTRs with RVI who will recover lung function and who will experience sustained decline, a utility not seen with histopathology.

Transition from BOS to RAS impairs prognosis after lung transplantation-CLAD subtype analysis by CT volumetry

Background

Chronic lung allograft dysfunction (CLAD), subclassified into bronchiolitis obliterans syndrome (BOS) or restrictive allograft syndrome (RAS), limits survival after lung transplantation. Information concerning transition from BOS to RAS is limited. We aimed to characterize the lung volume change after BOS diagnosis by computed tomography (CT) volumetry and to determine the incidence, risk factors and clinical significance of BOS to RAS transition.

Methods

CT volumetry measurements were performed from 63 patients with CLAD initially classified as BOS by CT volumetry. BOS patients with lung volume remaining >85% of baseline were classified as persistent BOS, whereas BOS patients whose lung volume permanently decreased to ≤85% of baseline were classified as BOS to RAS transition.

Results

During follow-up (median 9.8 years) eight patients (12.7%) were classified as BOS to RAS transition, which decreased recipient (p = 0.004) and graft survival (p = 0.020) in comparison to patients with persistent BOS. Opacities on chest imaging preceded BOS to RAS transition in 88% of patients. Opacities on chest imaging at BOS diagnosis and early CLAD diagnosis after transplantation were risk factors for transition.

Conclusion

Based on lung volume decrease measured by CT volumetry, a small proportion of BOS patients transitioned to RAS which had an adverse effect on recipient and graft survival.

Pyroptosis and respiratory diseases: A review of current knowledge

Pyroptosis is a relatively newly discovered programmed cell death accompanied by an inflammatory response. In the classical view, pyroptosis is mediated by caspases-1,-4,-5,-11 and executed by GSDMD, however, recently it was demonstrated that caspase-3 and-8 also participate in the process of pyroptosis, by cleaving GSDMD/E and GSDMD respectively. Different from autophagy and apoptosis, many pores are formed on the cell membrane during pyroptosis, which makes the cell membrane lose its integrity, eventually leading to the release of cytokines interleukin(IL)-1β and IL-18. When the body is infected with pathogens or exposed to some stimulations, pyroptosis could play an immune defense role. It is found that pyroptosis exists widely in infectious and inflammatory respiratory diseases such as acute lung injury, bronchial dysplasia, chronic obstructive pulmonary disease, and asthma. Excessive pyroptosis may accompany airway inflammation, tissue injury, and airway damage, and induce an inflammatory reaction, leading to more serious damage and poor prognosis of respiratory diseases. This review summarizes the relationship between pyroptosis and related respiratory diseases.

Characterization of Immunopathology and Small Airway Remodeling in Constrictive Bronchiolitis

Rationale: Constrictive bronchiolitis (ConB) is a relatively rare and understudied form of lung disease whose underlying immunopathology remains incompletely defined. Objectives: Our objectives were to quantify specific pathological features that differentiate ConB from other diseases that affect the small airways and to investigate the underlying immune and inflammatory phenotype present in ConB. Methods: We performed a comparative histomorphometric analysis of small airways in lung biopsy samples collected from 50 soldiers with postdeployment ConB, 8 patients with sporadic ConB, 55 patients with chronic obstructive pulmonary disease, and 25 nondiseased control subjects. We measured immune and inflammatory gene expression in lung tissue using the NanoString nCounter Immunology Panel from six control subjects, six soldiers with ConB, and six patients with sporadic ConB. Measurements and Main Results: Compared with control subjects, we found shared pathological changes in small airways from soldiers with postdeployment ConB and patients with sporadic ConB, including increased thickness of the smooth muscle layer, increased collagen deposition in the subepithelium, and lymphocyte infiltration. Using principal-component analysis, we showed that ConB pathology was clearly separable both from control lungs and from small airway disease associated with chronic obstructive pulmonary disease. NanoString gene expression analysis from lung tissue revealed T-cell activation in both groups of patients with ConB with upregulation of proinflammatory pathways, including cytokine-cytokine receptor interactions, NF-κB (nuclear factor-κB) signaling, TLR (Toll-like receptor) signaling, T-cell receptor signaling, and antigen processing and presentation. Conclusions: These findings indicate shared immunopathology among different forms of ConB and suggest that an ongoing T-helper cell type 1-type adaptive immune response underlies airway wall remodeling in ConB.

Reduction of primary graft dysfunction using cytokine adsorption during organ preservation and after lung transplantation

Despite improvements, lung transplantation remains hampered by both a scarcity of donor organs and by mortality following primary graft dysfunction (PGD). Since acute respiratory distress syndrome (ARDS) limits donor lungs utilization, we investigated cytokine adsorption as a means of treating ARDS donor lungs. We induced mild to moderate ARDS using lipopolysaccharide in 16 donor pigs. Lungs were then treated with or without cytokine adsorption during ex vivo lung perfusion (EVLP) and/or post-transplantation using extracorporeal hemoperfusion. The treatment significantly decreased cytokine levels during EVLP and decreased levels of immune cells post-transplantation. Histology demonstrated fewer signs of lung injury across both treatment periods and the incidence of PGD was significantly reduced among treated animals. Overall, cytokine adsorption was able to restore lung function and reduce PGD in lung transplantation. We suggest this treatment will increase the availability of donor lungs and increase the tolerability of donor lungs in the recipient.

Lung transplantation is hindered by the scarcity of organs and by mortality following primary graft dysfunction. Here, the authors show that cytokine absorption can be used in donor lungs during ex vivo lung perfusion and post-transplant, and leads to restored lung function and reduced primary graft dysfunction in animal models.

Chronic Lung Allograft Dysfunction Is Associated with Increased Levels of Cell-Free Mitochondrial DNA in Bronchoalveolar Lavage Fluid of Lung Transplant Recipients

Chronic Lung Allograft Dysfunction (CLAD) is a life-threatening complication that limits the long-term survival of lung transplantation patients. Early diagnosis remains the basis of efficient management of CLAD, making the need for distinctive biomarkers critical. This explorative study aimed to investigate the predictive power of mitochondrial DNA (mtDNA) derived from bronchoalveolar lavages (BAL) to detect CLAD. The study included 106 lung transplant recipients and analyzed 286 BAL samples for cell count, cell differentiation, and inflammatory and mitochondrial biomarkers, including mtDNA. A receiver operating curve analysis of mtDNA levels was used to assess its ability to detect CLAD. The results revealed a discriminatory pro-inflammatory cytokine profile in the BAL fluid of CLAD patients. The concentration of mtDNA increased in step with each CLAD stage, reaching its highest concentration in stage 4, and correlated significantly with decreasing FEV1. The receiver operating curve analysis of mtDNA in BAL revealed a moderate prediction of CLAD when all stages were grouped together (AUROC 0.75, p-value < 0.0001). This study has found the concentration mtDNA in BAL to be a potential predictor for the early detection of CLAD and the differentiation of different CLAD stages, independent of the underlying pathology.

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.

Lung transplantation and severe coronary artery disease: results from a single-centre experience

OBJECTIVES

The management of severe coronary artery disease at the time of lung transplantation remains a challenge. We analyzed the short- and long-term-outcomes of lung transplant recipients with severe coronary artery disease.

METHODS

Records of adult patients transplanted at our institution between April 2010 and February 2021 were retrospectively reviewed. Severe coronary artery disease was defined by coronary stenosis ≥70% (main stem ≥50%) at the coronary angiography performed before or at the time of listing. Patient characteristics, perioperative- and long-term-outcomes were compared between patients with and without severe coronary artery disease.

RESULTS

Among 896 lung-transplanted patients who had undergone a coronary angiography before transplantation, 77 (8.5%) showed severe coronary artery disease, the remaining 819 (91.5%) did not. Patients with severe coronary artery disease were older (p < 0.0001), more often male (p < 0.0001) and were transplanted more often for pulmonary fibrosis (p = 0.0007). The median (interquartile range) follow-up was 46 (20-76) months. At the Cox multivariable analysis severe coronary artery disease was not associated with mortality. Patients with pretransplant percutaneous transluminal coronary angioplasty and patients with coronary artery bypass graft surgery concomitant to transplantation had equivalent survival compared to patients without severe coronary artery disease (p = 0.513, p = 0.556).

CONCLUSIONS

Severe coronary artery disease was not associated with decreased survival after lung transplantation. Concomitant coronary artery bypass graft surgery and pretransplant percutaneous transluminal coronary angioplasty can be used for revascularization.

The role of mechanical ventilation in primary graft dysfunction in the postoperative lung transplant recipient: A single center study and literature review

Background

Primary graft dysfunction (PGD) is still a major complication in patients undergoing lung transplantation (LTx). Much is unknown about the effect of postoperative mechanical ventilation on outcomes, with debate on the best approach to ventilation.

Aim/Purpose

The goal of this study was to generate hypotheses on the association between postoperative mechanical ventilation settings and allograft size matching in PGD development.

Method

This is a retrospective study of LTx patients between September 2011 and September 2018 (n = 116). PGD was assessed according to the International Society of Heart and Lung Transplantation (ISHLT) criteria. Data were collected from medical records, including chest x‐ray assessments, blood gas analysis, mechanical ventilator parameters and spirometry.

Results

Positive end‐expiratory pressures (PEEP) of 5 cm H₂O were correlated with lower rates of grade 3 PGD. Graft size was important as tidal volumes calculated according to the recipient yielded greater rates of PGD when low volumes were used, a correlation that was lost when donor metrics were used.

Conclusion

Our results highlight a need for greater investigation of the role donor characteristics play in determining post‐operative ventilation of a lung transplant recipient. The mechanical ventilation settings on postoperative LTx recipients may have an implication for the development of acute graft dysfunction. Severe PGD was associated with the use of a PEEP higher than 5 and lower tidal volumes and oversized lungs were associated with lower long‐term mortality. Lack of association between ventilatory settings and survival may point to the importance of other variables than ventilation in the development of PGD.

Markers of rejection of a lung allograft: state of the art

Chronic lung allograft dysfunction (CLAD) affects approximately 50% of all lung transplant recipients by 5 post-operative years and is the leading cause of death in lung transplant recipients. Early CLAD diagnosis or ideally prediction of CLAD is essential to enable early intervention before significant lung injury occurs. New technologies have emerged to facilitate biomarker discovery, including epigenetic modification and single-cell RNA sequencing. This review examines new and existing technologies for biomarker discovery and the current state of research on biomarkers for identifying lung transplant rejection.

Novel role for tumor suppressor gene, liver kinase B1, in epithelial-mesenchymal transition leading to chronic lung allograft dysfunction

Epithelial-mesenchymal transition (EMT) has been implicated to play a role in chronic lung allograft dysfunction (CLAD). Liver kinase B1 (LKB1), a tumor suppressor gene, can regulate EMT. However, its role in CLAD development following lung transplantation remains unknown. Using qRT-PCR, biopsies from lung transplant recipients with bronchiolitis obliterans syndrome (BOS) demonstrated significant downregulation of LKB1 (p = .0001), compared to stable biopsies. To determine the role of LKB1 in EMT development, we analyzed EMT in human bronchial epithelial cell line BEAS-2B. Knockdown of LKB1 by siRNA significantly dysregulated mesenchymal markers expression in BEAS-2B cells. Following incubation of human primary bronchial epithelial cell or BEAS-2B cells with exosomes isolated from BOS or stable lung transplant recipients, LKB1 expression was inhibited when incubated with BOS-exosome. Incubation with BOS-exosomes also decreased LKB1 expression and induced EMT markers in air-liquid interface culture method. Our results provide novel evidence that exosomes released from transplanted lungs undergoing chronic rejection are associated with inactivated tumor suppressor gene LKB1 and this loss induces EMT leading to the pathogenesis of CLAD following human lung transplantation.

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

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

Multi-omics profiling predicts allograft function after lung transplantation

RATIONALE

Lung transplantation is the ultimate treatment option for patients with end-stage respiratory diseases but bears the highest mortality rate among all solid organ transplantations due to chronic lung allograft dysfunction (CLAD). The mechanisms leading to CLAD remain elusive due to an insufficient understanding of the complex post-transplant adaptation processes.

OBJECTIVES

To better understand these lung adaptation processes after transplantation and to investigate their association with future changes in allograft function.

METHODS

We performed an exploratory cohort study of bronchoalveolar lavage samples from 78 lung recipients and donors. We analysed the alveolar microbiome using 16S rRNA sequencing, the cellular composition using flow cytometry, as well as metabolome and lipidome profiling.

MEASUREMENTS AND MAIN RESULTS

We established distinct temporal dynamics for each of the analysed data sets. Comparing matched donor and recipient samples, we revealed that recipient-specific as well as environmental factors, rather than the donor microbiome, shape the long-term lung microbiome. We further discovered that the abundance of certain bacterial strains correlated with underlying lung diseases even after transplantation. A decline in forced expiratory volume during the first second (FEV1) is a major characteristic of lung allograft dysfunction in transplant recipients. By using a machine learning approach, we could accurately predict future changes in FEV1 from our multi-omics data, whereby microbial profiles showed a particularly high predictive power.

CONCLUSION

Bronchoalveolar microbiome, cellular composition, metabolome and lipidome show specific temporal dynamics after lung transplantation. The lung microbiome can predict future changes in lung function with high precision.

CTOTC-08: A multicenter randomized controlled trial of rituximab induction to reduce antibody development and improve outcomes in pediatric lung transplant recipients

We conducted a randomized, placebo-controlled, double-blind study of pediatric lung transplant recipients, hypothesizing that rituximab plus rabbit anti-thymocyte globulin induction would reduce de novo donor-specific human leukocyte antigen antibodies (DSA) development and improve outcomes. We serially obtained clinical data, blood, and respiratory samples for at least one year posttransplant. We analyzed peripheral blood lymphocytes by flow cytometry, serum for antibody development, and respiratory samples for viral infections using multiplex PCR. Of 45 subjects enrolled, 34 were transplanted and 27 randomized to rituximab (n = 15) or placebo (n = 12). No rituximab-treated subjects versus five placebo-treated subjects developed de novo DSA with mean fluorescence intensity >2000. There was no difference between treatment groups in time to the primary composite outcome endpoint (death, bronchiolitis obliterans syndrome [BOS] grade 0-p, obliterative bronchiolitis or listing for retransplant). A post-hoc analysis substituting more stringent chronic lung allograft dysfunction criteria for BOS 0-p showed no difference in outcome (p = .118). The incidence of adverse events including infection and rejection episodes was no different between treatment groups. Although the study was underpowered, we conclude that rituximab induction may have prevented early DSA development in pediatric lung transplant recipients without adverse effects and may improve outcomes (Clinical Trials: NCT02266888).

Soluble factors of mesenchimal stem cells (FS-MSC) as a potential tool to reduce inflammation in donor's lungs after hypovolemic shock

OBJECTIVE

The shortage of viable lungs is still a major obstacle for transplantation. Trauma victims who represent potential lung donors commonly present hypovolemic shock leading to pulmonary inflammation and deterioration and rejection after transplantation. Seeking to improve lung graft, new approaches to donor treatment have been tested. This study focuses on treatment with mesenchymal stem cells (MSCs) or soluble factors produced by MSCs (FS-MSC) using a rat model for lung donors after hemorrhagic shock.

METHODS

Forty-eight rats were divided into four groups: Sham (n=12), animals without induction of hypovolemic shock; Shock (n=12), animals submitted to hypovolemic shock (mean arterial pressure 40 mmHg); MSC (n=12), animals submitted to hypovolemic shock and treated with MSCs, and FS (n=12), animals submitted to hypovolemic shock and treated with FS-MSC. The animals were subjected to a 50-minute hypovolemic shock (40 mmHg) procedure. The treated animals were monitored for 115 minutes. We performed histopathology of lung tissue and quantification of inflammatory markers (TNF-α, IL-1β, IL-6, IL-10, iCAM and vCAM) in lung tissue and peripheral blood leukocytes (PBLs).

RESULTS

Hemorrhagic shock resulted in higher PBLs and neutrophil infiltrate in the lungs. FS animals had lower neutrophil density comparing with Shock and MSC animals (p<0.001). No differences in the cytokine levels in lung tissue were observed between the groups.

CONCLUSIONS

The lungs of rats submitted to hemorrhagic shock and treated with FS-MSC showed reduced inflammation indicated in a decrease in lung neutrophil infiltrate.

COMP: A Potential Early Biomarker of RAS After Lung Transplantation

Chronic rejection, defined as chronic lung allograft dysfunction (CLAD), is the major factor limiting long-term survival after lung transplantation (LTx). A specific subgroup of CLAD is restrictive allograft syndrome (RAS). CLAD’s pathogenesis is largely unknown, but previous findings suggest that it is associated with increased fibrosis in the transplanted lung. Cartilage oligomeric matrix protein (COMP) has been associated with multiple fibrotic conditions. The current study aimed to explore the relation between COMP serum levels and development of CLAD, and RAS in particular, in a retrospective cohort of LTx patients.

Emphysematous changes and lower levels of plasma irisin are associated with bronchiolitis obliterans syndrome after bilateral living-donor lobar lung transplantation

PURPOSE

Decreased irisin levels may be associated with the development of emphysema. Similarly, emphysematous changes may develop in patients with chronic lung allograft dysfunction (CLAD) after living-donor lobar lung transplantation (LDLLT). We investigated the severity of emphysematous changes and the relationship between irisin levels and CLAD after bilateral LDLLT and cadaveric lung transplantation (CLT).

METHODS

The subjects of this retrospective study were 59 recipients of bilateral LDLLT (n = 31) or CLT (n = 28), divided into a non-CLAD group (n = 41), a LDLLT-CLAD group (n = 11), and a CLT-CLAD group (n = 7). We compared the severity of emphysematous changes, the skeletal muscle mass, and the plasma irisin levels among the groups.

RESULTS

The emphysematous changes were significantly more severe in the LDLLT-CLAD and CLT-CLAD groups (p = 0.046 and 0.036), especially in patients with bronchiolitis obliterans syndrome (BOS), than in the non-CLAD group. Although the skeletal muscle mass was similar in all the groups, the plasma irisin levels were significantly lower in the LDLLT-CLAD group (p = 0.022), especially in the patients with BOS after LDLLT, than in the non-CLAD group.

CONCLUSION

Emphysematous changes and lower levels of plasma irisin were associated with CLAD, especially in patients with BOS, after bilateral LDLLT.

Overexpression of the MSK1 Kinase in Patients With Chronic Lung Allograft Dysfunction and Its Confirmed Role in a Murine Model

BACKGROUND

Chronic lung allograft dysfunction (CLAD) and its obstructive form, the obliterative bronchiolitis (OB), are the main long-term complications related to high mortality rate postlung transplantation. CLAD treatment lacks a significant success in survival. Here, we investigated a new strategy through inhibition of the proinflammatory mitogen- and stress-activated kinase 1 (MSK1) kinase.

METHODS

MSK1 expression was assessed in a mouse OB model after heterotopic tracheal allotransplantation. Pharmacological inhibition of MSK1 (H89, fasudil, PHA767491) was evaluated in the murine model and in a translational model using human lung primary fibroblasts in proinflammatory conditions. MSK1 expression was graded over time in biopsies from a cohort of CLAD patients.

RESULTS

MSK1 mRNA progressively increased during OB (6.4-fold at D21 posttransplantation). Inhibition of MSK1 allowed to counteract the damage to the epithelium (56% restoration for H89), and abolished the recruitment of MHCII+ (94%) and T cells (100%) at the early inflammatory phase of OB. In addition, it markedly decreased the late fibroproliferative obstruction in allografts (48%). MSK1 inhibitors decreased production of IL-6 (whose transcription is under the control of MSK1) released from human lung fibroblasts (96%). Finally, we confirmed occurrence of a 2.9-fold increased MSK1 mRNA expression in lung biopsies in patients at 6 months before CLAD diagnosis as compared to recipients with stable lung function.

CONCLUSIONS

These findings suggest the overall interest of the MSK1 kinase either as a marker or as a potential therapeutic target in lung dysfunction posttransplantation.