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

Study on the common mechanisms of gastroesophageal reflux disease and interstitial lung disease

OBJECTIVE

Interstitial lung disease (ILD) and gastroesophageal reflux disease (GERD) have complex interactions and can exacerbate severity of each other. This study aimed to screen shared genes between ILD and GERD and explore their common mechanisms and clinical value.

METHODS

We obtained microarray datasets of ILD and GERD from public databases. Shared genes were screened by differential expression analysis and Venn analysis. Hub genes were screened from shared genes using the protein-protein interaction (PPI) network analysis. The ssGSEA algorithm was utilized to estimate immune infiltration level of ILD and GERD, and correlation of hub genes with immune cell infiltration was studied. Finally, potential drugs that may act on hub genes were screened using DSigDB.

RESULTS

52 shared genes were obtained through Venn analysis. PPI network analysis identified 10 hub genes (BMP4, NT5E, PPARG, EPCAM, DPP4, KLF2, MMP1, AGR2, ADAMTS1, GATA6) that may have diagnostic performance (p < 0.05). The results of immune infiltration showed that hub genes were highly linked to multiple immune cell infiltrations (p < 0.05). In addition, we identified 5 potential drugs. Notably, thioridazine may target 5 hub genes (MMP1, AGR2, KLF2, ADAMTS1, and PPARG) simultaneously (p < 0.05) and had the potential to be a novel therapeutic drug.

CONCLUSION

In summary, we have screened out the hub genes with diagnostic value in ILD and GERD, and also revealed the close relationship between the hub genes and the disease immune microenvironment, providing new research directions for the common mechanism and interaction of the two diseases.

Gastroesophageal Reflux is a Risk Factor for the Development of de novo Donor Specific Antibodies after Lung Transplantation

BACKGROUND

Despite evidence that gastroesophageal reflux (GER) is harmful to the lung allograft, the mechanism of injury remains incompletely defined. We hypothesized that GER induces a humoral alloimmune response and examined the association between GER and de novo donor-specific antibody (DSA) development.

METHODS

508 lung transplant recipients who underwent routine pH-impedance testing at 3 months post-transplant were included. Univariable and multivariable Cox proportional hazards models were used to examine the impact of total GER events on de novo DSA development.

RESULTS

De novo DSA were detected in 230 subjects (45%) at a median of 69 days post-transplant. The highest tertile of GER events (≥19 events) was associated with a significantly increased risk of de novo DSA development compared to the lowest tertile (HR 1.4, 95% CI 1.00-1.91, p=0.05).

CONCLUSION

GER is associated with de novo DSA development, which has implications for monitoring and anti-GER therapy after lung transplant.

Lung allograft dysbiosis associates with immune response and primary graft dysfunction

BACKGROUND

Lower airway enrichment with oral commensals has been previously associated with severe primary graft dysfunction (PGD) after lung transplantation (LT). We aimed to determine whether this dysbiotic signature is present across all PGD severity grades and whether it is associated with a distinct host inflammatory endotype.

METHODS

Lower airway samples from 96 LT recipients were used to evaluate the lung allograft microbiota via 16S rRNA gene sequencing. Bronchoalveolar lavage (BAL) cytokine concentrations and cell differential percentages were compared across PGD grades. In a subset of samples, we evaluated the lower airway host transcriptome using RNA sequencing methods.

RESULTS

Differential analyses demonstrated lower airway enrichment with supraglottic-predominant taxa (SPT) in moderate and severe PGD. Dirichlet multinomial mixtures modeling identified 2 distinct microbial clusters. A greater percentage of subjects with moderate-severe PGD than no PGD were identified within the dysbiotic cluster (C-SPT, 48% and 29%, respectively) though this did not reach statistical significance (p = 0.06). PGD severity associated with increased BAL neutrophil concentration (p = 0.03) and correlated with BAL concentrations of MCP-1/CCL2, IP-10/CXCL10, IL-10, and TNF-α (p < 0.05). Furthermore, signatures of dysbiosis correlated with neutrophils, MCP-1/CCL-2, IL-10, and TNF-α (p < 0.05). C-SPT exhibited differential expression of TNF, SERPINE1, MPO, and MMP1 genes and upregulation of MAPK pathways, host signling associated with neutrophilic inflammation.

CONCLUSIONS

Lower airway dysbiosis within the lung allograft is associated with a neutrophilic inflammatory endotype, an immune profile commonly recognized as the hallmark for PGD. These data highlight a putative role of lower airway microbial dysbiosis in the pathogenesis of this syndrome.

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.

Humoral immunity to lung antigens early post-transplant confers risk for chronic lung allograft dysfunction

BACKGROUND

Autoantibodies and de novo donor HLA-specific antibodies (dnDSA) may contribute to chronic lung allograft dysfunction (CLAD). However, the breadth of reactivities against self-antigens and their association with CLAD has been underexamined. In a single-centre study, we screened lung transplant (LTx) recipients for novel autoantibodies at transplant and 6 months post-LTx, assessed dnDSA exposure, and tested their relationship with CLAD-free survival.

METHODS

Serum samples were collected from 89 crossmatch-negative bilateral lung transplant recipients at the time of LTx and 6 months post-LTx, prior to a CLAD diagnosis, for autoantibody screening using a custom antigen microarray optimized for IgM and IgG detection.

RESULTS

Patients who developed CLAD by 5 years post-LTx demonstrated a decrease in average IgG reactivity, but no decrease in IgM reactivity when measured at 6 months post-LTx. IgG anti-tropoelastin, SP-D, and thyroglobulin autoantibodies were significantly elevated 6 months post-LTx in patients who developed CLAD by 5 years, compared to those who remained CLAD-free at 5 years. In contrast, patients who remained CLAD-free at 5 years had elevated levels of IgG anti-CENP-B at both timepoints and PM/SCL100 at 6 months post-LTx, suggesting these may confer protection. Exposure to autoantibodies against lung-enriched targets, as opposed to ubiquitous antigens, and dnDSA conferred increased CLAD risk.

CONCLUSIONS

We have identified novel autoantibodies associated with CLAD-free survival. Our results bolster the independent relationship between autoantibodies and CLAD. We also identified autoantibody signatures that are associated with a marked increase in CLAD risk. Exposure to lung-enriched targets and dnDSA may have a reciprocal amplifying effect that lies on a tissue-specific mechanistic pathway leading to CLAD.

Interventional anti-reflux management for gastro-oesophageal reflux disease in lung transplant recipients: a systematic review and meta-analysis

INTRODUCTION

Gastroesophageal reflux disease (GORD) and aspiration are risk factors in the development of bronchiolitis obliterans syndrome (BOS) in the lung transplant population. The aim of this study was to investigate if allograft function and survival improved after anti-reflux surgery (ARS) in lung transplant recipients.

METHODS

In accordance with PRISMA guidelines, we conducted a systematic search of MEDLINE, Embase, and the Cochrane library databases from inception until 13/01/2024. Articles reporting outcomes of ARS following lung transplantation were included. A random effects model was used for meta-analysis.

RESULTS

The search identified 20 which were used for quantitative analysis. Overall, FEV1 and rate of change of FEV1 had improved following ARS by 0.141 L/s (95% CI; -02.82, -0.001) and -1.153 mL/d (95% CI; -12.117, -0.188), respectively. Survival hazard ratio post-ARS was 0.39 (95% CI; 0.19, 0.60). Nissen fundoplication was the most effective anti-reflux procedure with the greatest effect on reduction in the rate of change of FEV1, with an improvement of -2.353 mL/d (95% CI; -3.058, -1.649).

CONCLUSION

ARS in lung transplant recipients improves allograft function and survival. Given the increased incidence of GORD in lung transplant recipients, there should be a low threshold for investigation of GORD and subsequent ARS.

Impact of Long-Term Atorvastatin Therapy on the Development of Chronic Lung Allograft Dysfunction in Patients with Azithromycin Prophylaxis after Lung Transplantation

OBJECTIVE

To assess the impact of long-term atorvastatin (ATO) therapy on reducing recipient inflammation and immune response, thus lowering the risk of chronic lung allograft dysfunction (CLAD) in lung transplant recipients. This study aimed to investigate the effects of ATO on overall survival, lung function recovery, and its influence on inflammatory factors alongside azithromycin (AZI) prophylaxis.

METHODS

This retrospective single-center study included lung transplant recipients from January 2017 to December 2022. Patients who survival >1 year after lung transplantation and who were receiving AZI prophylaxis for >6 months were selected. Outcome measures involved pulmonary function assessments at various time points after AZI treatment, complete blood cell analysis, and inflammatory factor evaluations.

RESULTS

The incidence of CLAD was significantly lower in the long-term ATO group compared with those not on ATO (P = .011). Long-term ATO treatment significantly delayed CLAD onset after lung transplantation (850 days vs. 630 days; P = .041), with patients showing notably enhanced lung function recovery within 6 months of AZI therapy compared with the non-ATO group. Neutrophil levels decreased in patients with CLAD, and interleukin-6 concentrations significantly decreased in the AZI + ATO group compared with the AZI group. Overall patient survival was significantly better in the AZI+ATO group than in the AZI group (P = .02).

CONCLUSION

In cases where CLAD develops despite AZI prophylaxis, long-term ATO treatment may lead to short-term improvements in lung function. It could also decrease inflammation levels in lung transplant recipients and enhance overall survival. The combination of AZI and long-term ATO therapy may be beneficial for CLAD prevention.

Beyond the organ: lung microbiome shapes transplant indications and outcomes

The lung microbiome plays a crucial role in the development of chronic lung diseases, which may ultimately lead to the need for lung transplantation. Also, perioperative results seem to be connected with altered lung microbiomes and its dynamic changes providing a possible target for optimizing short-term outcome after transplantation. A literature review using MEDLINE, PubMed Central and Bookshelf was performed. Chronic lung allograft dysfunction (CLAD) seems to be influenced and partly triggered by changes in the pulmonary microbiome and dysbiosis, e.g. through increased bacterial load or abundance of specific species such as Pseudomonas aeruginosa. Additionally, the specific indications for transplantation, with their very heterogeneous changes and influences on the pulmonary microbiome, influence long-term outcome. Next to composition and measurable bacterial load, dynamic changes in the allografts microbiome also possess the ability to alter long-term outcomes negatively. This review discusses the "new" microbiome after transplantation and the associations with direct postoperative outcome. With the knowledge of these principles the impact of alterations in the pulmonary microbiome in hindsight to CLAD and possible therapeutic implications are described and discussed. The aim of this review is to summarize the current literature regarding pre- and postoperative lung microbiomes and how they influence different lung diseases on their progression to failure of conservative treatment. This review provides a summary of current literature for centres looking for further options in optimizing lung transplant outcomes and highlights possible areas for further research activities investigating the pulmonary microbiome in connection to transplantation.

The foregut in cystic fibrosis

The aerodigestive organs share a kindred embryologic origin that allows for a more complete explanation as to how the foregut can remain a barrier to normalcy in people with cystic fibrosis (pwCF). The structures of the aerodigestive tract include the nasopharynx, the oropharynx, the hypopharynx, the esophagus, the stomach, as well as the supraglottic, glottic, and subglottic tubular airways (including the trachea). Additional gastrointestinal (GI) luminal/alimentary organs of the foregut include the duodenum. Extraluminal foregut structures include the liver, the gall bladder, the biliary tree, and the pancreas. There are a variety of neurologic controls within these complicated anatomic compartments to separate the transit of food and liquid from air. These structures share the same origin from the primitive foregut/mesenchyme. The vagus nerve is a critical structure that unites respiratory and digestive functions. This article comments on the interconnected nature of cystic fibrosis and the GI tract. As it relates to the foregut, this has been typically treated as simple "reflux" as the cause of worsened lung function in pwCF. That terms like gastroesophageal reflux (GER), gastroesophageal reflux disease (GERD), heartburn, and regurgitation are used interchangeably to reflect pathology further complicates matters; we offer a more physiologically accurate term called "GI-related aspiration" or "GRASP." Broadly, this term reflects that aspiration of foregut contents from the duodenum through the stomach to the esophagus, into the pharynx and the respiratory tree in pwCF. As a barrier to normalcy in pwCF, GRASP is fundamentally two disease processes-GERD and gastroparesis-that likely contribute most to the deterioration of lung disease in pwCF. In the modulator era, successful GRASP management will be critical, particularly in those post-lung transplantation (LTx), only through successful management of both GERD and gastroparesis. Standardization of clinical management algorithms for GRASP in CF-related GRASP is a key clinical and research gap preventing normalcy in pwCF; what exists nearly exclusively addresses surgical evaluations or offers guidance for the management of GI symptoms alone (with unclear parameters for respiratory disease considerations). We begin first by describing the result of GRASP damage to the lung in various stages of lung disease. This is followed by a discussion of the mechanisms by which the digestive tract can injure the lungs. We summarize what we anticipate future research directions will be to reduce the impact of GRASP as a barrier to normalcy in pwCF.

Longitudinal Lower Airway Microbial Signatures of Acute Cellular Rejection in Lung Transplantation

Rationale: Acute cellular rejection (ACR) after lung transplant is a leading risk factor for chronic lung allograft dysfunction. Prior studies have demonstrated dynamic microbial changes occurring within the allograft and gut that influence local adaptive and innate immune responses. However, the lung microbiome's overall impact on ACR risk remains poorly understood. Objectives: To evaluate whether temporal changes in microbial signatures were associated with the development of ACR. Methods: We performed cross-sectional and longitudinal analyses (joint modeling of longitudinal and time-to-event data and trajectory comparisons) of 16S rRNA gene sequencing results derived from lung transplant recipient lower airway samples collected at multiple time points. Measurements and Main Results: Among 103 lung transplant recipients, 25 (24.3%) developed ACR. In comparing samples acquired 1 month after transplant, subjects who never developed ACR demonstrated lower airway enrichment with several oral commensals (e.g., Prevotella and Veillonella spp.) than those with current or future (beyond 1 mo) ACR. However, a subgroup analysis of those who developed ACR beyond 1 month revealed delayed enrichment with oral commensals occurring at the time of ACR diagnosis compared with baseline, when enrichment with more traditionally pathogenic taxa was present. In longitudinal models, dynamic changes in α-diversity (characterized by an initial decrease and a subsequent increase) and in the taxonomic trajectories of numerous oral commensals were more commonly observed in subjects with ACR. Conclusions: Dynamic changes in the lower airway microbiota are associated with the development of ACR, supporting its potential role as a useful biomarker or in ACR pathogenesis.

The Oral-Lung Microbiome Axis in Connective Tissue Disease-Related Interstitial Lung Disease

Connective tissue disease-related interstitial lung disease (CTD-ILD) is a frequent and serious complication of CTD, leading to high morbidity and mortality. Unfortunately, its pathogenesis remains poorly understood; however, one intriguing contributing factor may be the microbiome of the mouth and lungs. The oral microbiome, which is a major source of the lung microbiome through recurrent microaspiration, is altered in ILD patients. Moreover, in recent years, several lines of evidence suggest that changes in the oral and lung microbiota modulate the pulmonary immune response and thus may play a role in the pathogenesis of ILDs, including CTD-ILD. Here, we review the existing data demonstrating oral and lung microbiota dysbiosis and possible contributions to the development of CTD-ILD in rheumatoid arthritis, Sjögren's syndrome, systemic sclerosis, and systemic lupus erythematosus. We identify several areas of opportunity for future investigations into the role of the oral and lung microbiota in CTD-ILD.

The Lung Microbiome Predicts Mortality and Response to Azithromycin in Lung Transplant Recipients with Chronic Rejection

Rationale: Chronic lung allograft dysfunction (CLAD) is the leading cause of death after lung transplant, and azithromycin has variable efficacy in CLAD. The lung microbiome is a risk factor for developing CLAD, but the relationship between lung dysbiosis, pulmonary inflammation, and allograft dysfunction remains poorly understood. Whether lung microbiota predict outcomes or modify treatment response after CLAD is unknown. Objectives: To determine whether lung microbiota predict post-CLAD outcomes and clinical response to azithromycin. Methods: Retrospective cohort study using acellular BAL fluid prospectively collected from recipients of lung transplant within 90 days of CLAD onset. Lung microbiota were characterized using 16S rRNA gene sequencing and droplet digital PCR. In two additional cohorts, causal relationships of dysbiosis and inflammation were evaluated by comparing lung microbiota with CLAD-associated cytokines and measuring ex vivo P. aeruginosa growth in sterilized BAL fluid. Measurements and Main Results: Patients with higher bacterial burden had shorter post-CLAD survival, independent of CLAD phenotype, azithromycin treatment, and relevant covariates. Azithromycin treatment improved survival in patients with high bacterial burden but had negligible impact on patients with low or moderate burden. Lung bacterial burden was positively associated with CLAD-associated cytokines, and ex vivo growth of P. aeruginosa was augmented in BAL fluid from transplant recipients with CLAD. Conclusions: In recipients of lung transplants with chronic rejection, increased lung bacterial burden is an independent risk factor for mortality and predicts clinical response to azithromycin. Lung bacterial dysbiosis is associated with alveolar inflammation and may be promoted by underlying lung allograft dysfunction.

Gastroesophageal Reflux Revealed by 18 F-MFBG PET/CT

ABSTRACT

A 56-year-old woman who had a lung transplant 4 months ago presented frequent vomiting for 1 month. Barium meal and 99m Tc gastroesophageal scintigraphy showed no gastroesophageal reflux. The patient was enrolled in a clinical trial and underwent 18 F-MFBG PET/CT dynamic imaging. At the seventh minute of dynamic imaging, the images revealed reflux from the cardia into the esophagus and reached the oral cavity.

Oesophageal stasis is a risk factor for chronic lung allograft dysfunction and allograft failure in lung transplant recipients

Background

Morbidity and mortality in lung transplant recipients are often triggered by recurrent aspiration events, potentiated by oesophageal and gastric disorders. Previous small studies have shown conflicting associations between oesophageal function and the development of chronic lung allograft dysfunction (CLAD). Herein, we sought to investigate the relationship between oesophageal motility disorders and long-term outcomes in a large retrospective cohort of lung transplant recipients.

Methods

All lung transplant recipients at the Toronto Lung Transplant Program from 2012 to 2018 with available oesophageal manometry testing within the first 7 months post-transplant were included in this study. Patients were categorised according to the Chicago Classification of oesophageal disorders (v3.0). Associations between oesophageal motility disorders with the development of CLAD and allograft failure (defined as death or re-transplantation) were assessed.

Results

Of 487 patients, 57 (12%) had oesophagogastric junction outflow obstruction (OGJOO) and 47 (10%) had a disorder of peristalsis (eight major, 39 minor). In a multivariable analysis, OGJOO was associated with an increased risk of CLAD (HR 1.71, 95% CI 1.15-2.55, p=0.008) and allograft failure (HR 1.69, 95% CI 1.13-2.53, p=0.01). Major disorders of peristalsis were associated with an increased risk of CLAD (HR 1.55, 95% CI 1.01-2.37, p=0.04) and allograft failure (HR 3.33, 95% CI 1.53-7.25, p=0.002). Minor disorders of peristalsis were not significantly associated with CLAD or allograft failure.

Conclusion

Lung transplant recipients with oesophageal stasis characterised by OGJOO or major disorders of peristalsis were at an increased risk of adverse long-term outcomes. These findings will help with risk stratification of lung transplant recipients and personalisation of treatment for aspiration prevention.

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

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