Latent class analysis identifies distinct phenotypes of primary graft dysfunction after lung transplantation

Lung transplantation: Current insights and outcomes

Until now, the ability to predict or retard immune-mediated rejection events after lung transplantation is still limited due to the lack of specific biomarkers. The pressing need remains to early diagnose or predict the onset of chronic lung allograft dysfunction (CLAD) and its differential phenotypes that is the leading cause of death. Omics technologies (mainly genomics, epigenomics, and transcriptomics) combined with advanced bioinformatic platforms are clarifying the key immune-related molecular routes that trigger early and late events of lung allograft rejection supporting the biomarker discovery. The most promising biomarkers came from genomics. Both unregistered and NIH-registered clinical trials demonstrated that the increased percentage of donor-derived cell-free DNA in both plasma and bronchoalveolar lavage fluid showed a good diagnostic performance for clinically silent acute rejection events and CLAD differential phenotypes. A further success arose from transcriptomics that led to development of Molecular Microscope® Diagnostic System (MMDx) to interpret the relationship between molecular signatures of lung biopsies and rejection events. Other immune-related biomarkers of rejection events may be exosomes, telomer length, DNA methylation, and histone-mediated neutrophil extracellular traps (NETs) but none of them entered in registered clinical trials. Here, we discuss novel and existing technologies for revealing new immune-mediated mechanisms underlying acute and chronic rejection events, with a particular focus on emerging biomarkers for improving precision medicine of lung transplantation field.

Proteomic Analysis of Primary Graft Dysfunction in Porcine Lung Transplantation Reveals Alveolar-Capillary Barrier Changes Underlying the High Particle Flow Rate in Exhaled Breath

Primary graft dysfunction (PGD) remains a challenge for lung transplantation (LTx) recipients as a leading cause of poor early outcomes. New methods are needed for more detailed monitoring and understanding of the pathophysiology of PGD. The measurement of particle flow rate (PFR) in exhaled breath is a novel tool to monitor and understand the disease at the proteomic level. In total, 22 recipient pigs underwent orthotopic left LTx and were evaluated for PGD on postoperative day 3. Exhaled breath particles (EBPs) were evaluated by mass spectrometry and the proteome was compared to tissue biopsies and bronchoalveolar lavage fluid (BALF). Findings were confirmed in EBPs from 11 human transplant recipients. Recipients with PGD had significantly higher PFR [686.4 (449.7-8,824.0) particles per minute (ppm)] compared to recipients without PGD [116.6 (79.7-307.4) ppm, p = 0.0005]. Porcine and human EBP proteins recapitulated proteins found in the BAL, demonstrating its utility instead of more invasive techniques. Furthermore, adherens and tight junction proteins were underexpressed in PGD tissue. Histological and proteomic analysis found significant changes to the alveolar-capillary barrier explaining the high PFR in PGD. Exhaled breath measurement is proposed as a rapid and non-invasive bedside measurement of PGD.

NKG2D receptor activation drives primary graft dysfunction severity and poor lung transplantation outcomes

Clinical outcomes after lung transplantation, a life-saving therapy for patients with end-stage lung diseases, are limited by primary graft dysfunction (PGD). PGD is an early form of acute lung injury with no specific pharmacologic therapies. Here, we present a large multicenter study of plasma and bronchoalveolar lavage (BAL) samples collected on the first posttransplant day, a critical time for investigations of immune pathways related to PGD. We demonstrated that ligands for NKG2D receptors were increased in the BAL from participants who developed severe PGD and were associated with increased time to extubation, prolonged intensive care unit length of stay, and poor peak lung function. Neutrophil extracellular traps (NETs) were increased in PGD and correlated with BAL TNF-α and IFN-γ cytokines. Mechanistically, we found that airway epithelial cell NKG2D ligands were increased following hypoxic challenge. NK cell killing of hypoxic airway epithelial cells was abrogated with NKG2D receptor blockade, and TNF-α and IFN-γ provoked neutrophils to release NETs in culture. These data support an aberrant NK cell/neutrophil axis in human PGD pathogenesis. Early measurement of stress ligands and blockade of the NKG2D receptor hold promise for risk stratification and management of PGD.

Lymphocytic Airway Inflammation in Lung Allografts

Lung transplant remains a key therapeutic option for patients with end stage lung disease but short- and long-term survival lag other solid organ transplants. Early ischemia-reperfusion injury in the form of primary graft dysfunction (PGD) and acute cellular rejection are risk factors for chronic lung allograft dysfunction (CLAD), a syndrome of airway and parenchymal fibrosis that is the major barrier to long term survival. An increasing body of research suggests lymphocytic airway inflammation plays a significant role in these important clinical syndromes. Cytotoxic T cells are observed in airway rejection, and transcriptional analysis of airways reveal common cytotoxic gene patterns across solid organ transplant rejection. Natural killer (NK) cells have also been implicated in the early allograft damage response to PGD, acute rejection, cytomegalovirus, and CLAD. This review will examine the roles of lymphocytic airway inflammation across the lifespan of the allograft, including: 1) The contribution of innate lymphocytes to PGD and the impact of PGD on the adaptive immune response. 2) Acute cellular rejection pathologies and the limitations in identifying airway inflammation by transbronchial biopsy. 3) Potentiators of airway inflammation and heterologous immunity, such as respiratory infections, aspiration, and the airway microbiome. 4) Airway contributions to CLAD pathogenesis, including epithelial to mesenchymal transition (EMT), club cell loss, and the evolution from constrictive bronchiolitis to parenchymal fibrosis. 5) Protective mechanisms of fibrosis involving regulatory T cells. In summary, this review will examine our current understanding of the complex interplay between the transplanted airway epithelium, lymphocytic airway infiltration, and rejection pathologies.

A Focused Review on Primary Graft Dysfunction after Clinical Lung Transplantation: A Multilevel Syndrome

Primary graft dysfunction (PGD) is the clinical syndrome of acute lung injury after lung transplantation (LTx). However, PGD is an umbrella term that encompasses the ongoing pathophysiological and -biological mechanisms occurring in the lung grafts. Therefore, we aim to provide a focused review on the clinical, physiological, radiological, histological and cellular level of PGD. PGD is graded based on hypoxemia and chest X-ray (CXR) infiltrates. High-grade PGD is associated with inferior outcome after LTx. Lung edema is the main characteristic of PGD and alters pulmonary compliance, gas exchange and circulation. A conventional CXR provides a rough estimate of lung edema, while a chest computed tomography (CT) results in a more in-depth analysis. Macroscopically, interstitial and alveolar edema can be distinguished below the visceral lung surface. On the histological level, PGD correlates to a pattern of diffuse alveolar damage (DAD). At the cellular level, ischemia-reperfusion injury (IRI) is the main trigger for the disruption of the endothelial-epithelial alveolar barrier and inflammatory cascade. The multilevel approach integrating all PGD-related aspects results in a better understanding of acute lung failure after LTx, providing novel insights for future therapies.

Primary graft dysfunction: what we know

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

Interobserver variability in the evaluation of primary graft dysfunction after lung transplantation: impact of radiological training and analysis of discordant cases

PURPOSE

Radiologic criteria for the diagnosis of primary graft dysfunction (PGD) after lung transplantation are nonspecific and can lead to misinterpretation. The primary aim of our study was to assess the interobserver agreement in the evaluation of chest X-rays (CXRs) for PGD diagnosis and to establish whether a specific training could have an impact on concordance rates. Secondary aim was to analyze causes of interobserver discordances.

MATERIAL AND METHODS

We retrospectively enrolled 164 patients who received bilateral lung transplantation at our institution, between February 2013 and December 2019. Three radiologists independently reviewed postoperative CXRs and classified them as suggestive or not for PGD. Two of the Raters performed a specific training before the beginning of the study. A senior thoracic radiologist subsequently analyzed all discordant cases among the Raters with the best agreement. Statistical analysis to calculate interobserver variability was percent agreement, Cohen's kappa and intraclass correlation coefficient.

RESULTS

A total of 473 CXRs were evaluated. A very high concordance among the two trained Raters, 1 and 2, was found (K = 0.90, ICC = 0.90), while a poorer agreement was found in the other two pairings (Raters 1 and 3: K = 0.34, ICC = 0.40; Raters 2 and 3: K = 0.35, ICC = 0.40). The main cause of disagreement (52.4% of discordant cases) between Raters 1 and 2 was the overestimation of peribronchial thickening in the absence of unequivocal bilateral lung opacities or the incorrect assessment of unilateral alterations.

CONCLUSION

To properly identify PGD, it is recommended for radiologists to receive an adequate specific training.

Procedural mechanical support for lung transplantation

PURPOSE OF REVIEW

The use of procedural mechanical support during lung transplantation (LTx) varies between centers and the optimal support strategy is still controversially discussed. The two main questions are if cardiopulmonary bypass (CPB) or extracorporeal membrane oxygenation (ECMO) should be preferred and whether mechanical support should be reserved for specific patient groups or a routine use can be recommended.

RECENT FINDINGS

Recent cohort studies have consistently shown that LTx on CPB leads to inferior outcomes when compared to venoarterial (va)-ECMO. Thus, ECMO should be preferred in lung transplantation except for special indications. Despite its higher invasiveness, ECMO offers some pivotal advantages over off-pump lung transplantation. It has been shown to remarkably reduce rates of primary graft dysfunction, supporting the concept of a routine intraoperative ECMO use in LTx.

SUMMARY

Although randomized-controlled trials addressing this question are still lacking, current evidence appears to favor the routine use of ECMO support during lung transplantation.

Preoperative echocardiographic parameters predict primary graft dysfunction following pediatric lung transplantation

The importance of preoperative cardiac function in pediatric lung transplantation is unknown. We hypothesized that worse preoperative right ventricular (RV) systolic and worse left ventricular (LV) diastolic function would be associated with a higher risk of primary graft dysfunction grade 3 (PGD 3) between 48 and 72 hours. We performed a single center, retrospective pilot study of children (<18 years) who had echocardiograms <1 year prior to lung transplantation between 2006 and 2019. Conventional and strain echocardiography parameters were measured, and PGD was graded. Area under the receiver operating characteristic (AUROC) curves and logistic regression were performed. Forty-one patients were included; 14 (34%) developed PGD 3 and were more likely to have pulmonary hypertension (PH) as the indication for transplant (P = .005). PGD 3 patients had worse RV global longitudinal strain (P = .01), RV free wall strain (FWS) (P = .003), RV fractional area change (P = .005), E/e' (P = .01) and lateral e' velocity (P = .004) but not tricuspid annular plane systolic excursion (P = .61). RV FWS (AUROC 0.79, 95% CI 0.62-0.95) and lateral e' velocity (AUROC 0.87, 95% CI 0.68-1.00) best discriminated PGD 3 development and showed the strongest association with PGD 3 (RV FWS OR 3.87 [95% CI 1.59-9.43], P = .003; lateral e' velocity OR 0.10 [95% CI 0.01-0.70], P = .02). These associations remained when separately adjusting for age, weight, primary PH diagnosis, ischemic time, and bypass time. In this pilot study, worse preoperative RV systolic and worse LV diastolic function were associated with PGD 3 and may be modifiable recipient risk factors in pediatric lung transplantation.

Use of donor-derived-cell-free DNA as a marker of early allograft injury in primary graft dysfunction (PGD) to predict the risk of chronic lung allograft dysfunction (CLAD)

BACKGROUND

Primary graft dysfunction (PGD) is a risk factor for chronic lung allograft dysfunction (CLAD). However, the association between PGD and degree of allograft injury remains poorly defined. In this study, we leverage a novel biomarker for allograft injury, percentage donor-derived cell-free DNA (%ddcfDNA), to study the association between PGD, degree of allograft injury, and the development of CLAD.

METHODS

This prospective cohort study recruited 99 lung transplant recipients and collected plasma samples on days 1, 3, and 7 for %ddcfDNA measurements. Clinical data on day 3 was used to adjudicate for PGD. %ddcfDNA levels were compared between PGD grades. In PGD patients, %ddcfDNA was compared between those who developed CLAD and those who did not.

RESULTS

On posttransplant day 3, %ddcfDNA was higher in PGD than in non-PGD patients (median [IQR]: 12.2% [8.2, 22.0] vs 8.5% [5.6, 13.2] p = 0.01). %ddcfDNA correlated with the severity grade of PGD (r = 0.24, p = 0.02). Within the PGD group, higher levels of %ddcfDNA correlated with increased risk of developing CLAD (log OR(SE) 1.38 (0.53), p = 0.009). PGD patients who developed CLAD showed ∼2-times higher %ddcfDNA levels than patients who did not develop CLAD (median [IQR]: 22.4% [11.8, 27.6] vs 9.9% [6.7, 14.9], p = 0.007).

CONCLUSION

PGD patients demonstrated increased early posttransplant allograft injury, as measured by %ddcfDNA, in comparison to non-PGD patients, and these high %ddcfDNA levels were associated with subsequent development of CLAD. This study suggests that %ddcfDNA identifies PGD patients at greater risk of CLAD than PGD alone.

Operating room extubation: A predictive factor for 1-year survival after double-lung transplantation

BACKGROUND

Operating room (OR) extubation has been reported after lung transplantation (LT) in small cohorts. This study aimed to evaluate the prognosis of OR-extubated patients. The secondary objectives were to evaluate the safety of this approach and to identify its predictive factors.

METHODS

This retrospective single-center cohort study included patients undergoing double lung transplantation (DLT) from January 2012 to June 2019. Patients undergoing multiorgan transplantation, repeat transplantation, or cardiopulmonary bypass during the study period were excluded. OR-extubated patients were compared with intensive care unit (ICU)-extubated patients.

RESULTS

Among the 450 patients included in the analysis, 161 (35.8%) were extubated in the OR, and 4 were reintubated within 24 hours. Predictive factors for OR extubation were chronic obstructive pulmonary disease (COPD)/emphysema (p = .002) and cystic fibrosis (p = .005), recipient body mass index (p = .048), and the PaO₂/FiO₂ ratio 10 minutes after second graft implantation (p < .001). OR-extubated patients had a lower prevalence of grade 3 primary graft dysfunction at day 3 (p < .001). Eight (5.0%) patients died within the first year after OR extubation, and 49 (13.5%) patients died after ICU extubation (log-rank test; p = .005). After adjustment for OR extubation predictive factors, the multivariate Cox regression model showed that OR extubation was associated with greater one-year survival (adjusted hazard ratio = 0.40 [0.16-0.91], p = .028).

CONCLUSIONS

OR extubation was associated with a favorable prognosis after DLT, but the association should not be interpreted as causality. This fast-track protocol was made possible by a team committed to developing a comprehensive strategy to enhance recovery.

Ventilation parameters and early graft function in double lung transplantation

BACKGROUND

Currently, the primary graft dysfunction (PGD) score is used to measure allograft function in the early post-lung transplant period. Although PGD grades at later time points (T48 hours and T72 hours) are useful to predict mid- and long-term outcomes, their predictive value is less relevant within the first 24 hours after transplantation. This study aimed to evaluate the capability of PGD grades to predict prolonged mechanical ventilation (MV) and compare it with a model derived from ventilation parameters measured on arrival at the intensive care unit (ICU).

METHODS

A retrospective single-center analysis of 422 double lung transplantations (LTxs) was performed. PGD was assessed 2 hours after arrival at ICU, and grades were associated with length of MV (LMV). In addition, peak inspiratory pressure (P_IP), ratio of the arterial partial pressure of oxygen to fraction of inspired oxygen (P/F ratio), and dynamic compliance (cDyn) were collected, and a logistic regression model was created. The predictive capability for prolonged MV was calculated for both (the PGD score and the model). In a second step, the created model was externally validated using a prospective, international multicenter cohort including 102 patients from the lung transplant centers of Vienna, Toronto, and Budapest.

RESULTS

In the retrospective cohort, a high percentage of extubated patients was reported at 24 hours (35.1%), 48 hours (68.0%), and 72 hours (80.3%) after transplantation. At T0 (time point defined as 2 hours after arrival at the ICU), patients with PGD grade 0 had a shorter LMV with a median of 26 hours (interquartile range [IQR]: 16-47 hours) than those with PGD grade 1 (median: 42 hours, IQR: 27-50 hours), PGD grade 2 (median: 37.5 hours, IQR: 15.5-78.5 hours), and PGD grade 3 (median: 46 hours, IQR: 27-86 hours). However, IQRs largely overlapped for all grades, and the value of PGD to predict prolonged MV was poor. A total of 3 ventilation parameters (P_IP, cDyn, and P/F ratio), determined at T0, were chosen on the basis of clinical reasoning. A logistic regression model including these parameters predicted prolonged MV (>72 hours) with an optimism-corrected area under the curve (AUC) of 0.727. In the prospective validation cohort, the model proved to be stable and achieved an AUC of 0.679.

CONCLUSIONS

The prediction model reported in this study combines 3 easily obtainable variables. It can be employed immediately after LTx to quantify the risk of prolonged MV, an important early outcome parameter.

Comparison of outcomes in lung and heart transplant recipients from the same multiorgan donor

BACKGROUND

Primary graft dysfunction (PGD) and acute cellular rejection (ACR) are important causes of early morbidity and mortality following lung and heart transplantation. While many studies have elucidated donor-related risk factors of PGD and ACR, these complications often occur even with "ideal" donors. Therefore, we investigated potential associations of PGD and ACR between bilateral lung and heart transplant recipients from the same multiorgan donor, respectively.

METHODS

Between 2011 and 2017, 100 donors contributed 100 bilateral lung transplants and 100 heart transplants performed. Logistic regression analysis for PGD and Cox proportional hazards regression analysis for ACR were used to estimate the relationship of heart and lung transplants.

RESULTS

The incidence of PGD was 33% among lung and 17% among heart transplant recipients. Similarly, the incidence of ACR grade ≥ A2 for lung recipients was 38% (30/80), and the incidence of ACR grade ≥ 2R for heart recipients was 19% (15/80). There was no association between the development of PGD and ACR in lung and heart transplant recipients from the same donor, respectively.

CONCLUSIONS

These findings suggest that inherent donor factors are not critical to the development of PGD and ACR after lung and heart transplantation.

Adipose tissue quantification and primary graft dysfunction after lung transplantation: The Lung Transplant Body Composition study

BACKGROUND

Obesity is associated with an increased risk of primary graft dysfunction (PGD) after lung transplantation. The contribution of specific adipose tissue depots is unknown.

METHODS

We performed a prospective cohort study of adult lung transplant recipients at 4 U.S. transplant centers. We measured cross-sectional areas of subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) on chest and abdominal computed tomography (CT) scans and indexed each measurement to height.2 We used logistic regression to examine the associations of adipose indices and adipose classes with grade 3 PGD at 48 or 72 hours, and Cox proportional hazards models to examine survival. We used latent class analyses to identify the patterns of adipose distribution. We examined the associations of adipose indices with plasma biomarkers of obesity and PGD.

RESULTS

A total of 262 and 117 subjects had available chest CT scans and underwent protocol abdominal CT scans, respectively. In the adjusted models, a greater abdominal SAT index was associated with an increased risk of PGD (odds ratio 1.9, 95% CI 1.02-3.4, p = 0.04) but not with survival time. VAT indices were not associated with PGD risk or survival time. A greater abdominal SAT index correlated with greater pre- and post-transplant leptin (r = 0.61, p < 0.001, and r = 0.44, p < 0.001), pre-transplant IL-1RA (r = 0.25, p = 0.04), and post-transplant ICAM-1 (r = 0.25, p = 0.04). We identified 3 latent patterns of adiposity. The class defined by high thoracic and abdominal SAT had the greatest risk of PGD.

CONCLUSIONS

Subcutaneous, but not visceral, adiposity is associated with an increased risk of PGD after lung transplantation.

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

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

Lung transplantation for pulmonary sarcoidosis

Although relatively few patients with pulmonary sarcoidosis develop advanced disease that progresses to respiratory insufficiency despite receiving best practice pharmacologic interventions, lung transplantation may be the only therapeutic option for such patients to both prolong survival and provide improved quality of life. Lung transplant can be successfully performed for patients with end-stage pulmonary sarcoidosis, and post-transplant survival is similar to that for other transplant indications such as idiopathic pulmonary fibrosis. However, appropriate timing of referral, comprehensive assessment of potential candidates for lung transplant, placement of patients on the lung transplant waiting list when within the transplant window as appropriate, choosing the best procedure (bilateral versus single lung transplant), and optimal peri-operative and post-transplant management are key to successful lung transplant outcomes for patients with sarcoidosis.

Early Graft Dysfunction after Lung Transplantation

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

The Future of Lung Transplantation

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

Primary Graft Dysfunction After Lung Transplantation

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

Update in Chronic Lung Allograft Dysfunction

Chronic lung allograft dysfunction (CLAD) is the major limitation to posttransplant survival. This review highlights the evolving definition of CLAD, risk factors, treatment, and expected outcomes after the development of CLAD.

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

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

Diastolic Dysfunction Increases the Risk of Primary Graft Dysfunction after Lung Transplant

RATIONALE

Primary graft dysfunction (PGD) is a significant cause of early morbidity and mortality after lung transplant and is characterized by severe hypoxemia and infiltrates in the allograft. The pathogenesis of PGD involves ischemia-reperfusion injury. However, subclinical increases in pulmonary venous pressure due to left ventricular diastolic dysfunction may contribute by exacerbating capillary leak.

OBJECTIVES

To determine whether a higher ratio of early mitral inflow velocity (E) to early diastolic mitral annular velocity (é), indicative of worse left ventricular diastolic function, is associated with a higher risk of PGD.

METHODS

We performed a retrospective cohort study of patients in the Lung Transplant Outcomes Group who underwent bilateral lung transplant at our institution between 2004 and 2014 for interstitial lung disease, chronic obstructive pulmonary disease, or pulmonary arterial hypertension. Transthoracic echocardiograms obtained during evaluation for transplant listing were analyzed for E/é and other measures of diastolic function. PGD was defined as PaO2/FiO2 less than or equal to 200 with allograft infiltrates at 48 or 72 hours after reperfusion. The association between E/é and PGD was assessed with multivariable logistic regression.

MEASUREMENTS AND MAIN RESULTS

After adjustment for recipient age, body mass index, mean pulmonary arterial pressure, and pretransplant diagnosis, higher E/é and E/é greater than 8 were associated with an increased risk of PGD (E/é odds ratio, 1.93; 95% confidence interval, 1.02-3.64; P = 0.04; E/é >8 odds ratio, 5.29; 95% confidence interval, 1.40-20.01; P = 0.01).

CONCLUSIONS

Differences in left ventricular diastolic function may contribute to the development of PGD. Future trials are needed to determine whether optimization of left ventricular diastolic function reduces the risk of PGD.

Protein Quantitative Trait Loci Analysis Identifies Genetic Variation in the Innate Immune Regulator TOLLIP in Post-Lung Transplant Primary Graft Dysfunction Risk

The authors previously identified plasma plasminogen activator inhibitor-1 (PAI-1) level as a quantitative lung injury biomarker in primary graft dysfunction (PGD). They hypothesized that plasma levels of PAI-1 used as a quantitative trait could facilitate discovery of genetic loci important in PGD pathogenesis. A two-stage cohort study was performed. In stage 1, they tested associations of loci with PAI-1 plasma level using linear modeling. Genotyping was performed using the Illumina CVD Bead Chip v2. Loci meeting a p < 5 × 10(-4) cutoff were carried forward and tested in stage 2 for association with PGD. Two hundred ninety-seven enrollees were evaluated in stage 1. Six loci, associated with PAI-1, were carried forward to stage 2 and evaluated in 728 patients. rs3168046 (Toll interacting protein [TOLLIP]) was significantly associated with PGD (p = 0.006). The increased risk of PGD for carrying at least one copy of this variant was 11.7% (95% confidence interval 4.9-18.5%). The false-positive rate for individuals with this genotype who did not have PGD was 6.1%. Variants in the TOLLIP gene are associated with higher circulating PAI-1 plasma levels and validate for association with clinical PGD. A protein quantitative trait analysis for PGD risk prioritizes genetic variations in TOLLIP and supports a role for Toll-like receptors in PGD pathogenesis.

Primary Graft Dysfunction and Mortality Following Lung Transplantation: A Role for Proadrenomedullin Plasma Levels

Primary graft dysfunction (PGD) after lung transplantation (LT) is a heterogeneous syndrome that comprises clinical presentations with diverse grades of severity. Proadrenomedullin (proADM) levels may be associated with PGD and may enhance its relationship with outcomes. We prospectively included 100 LT recipients. Plasma levels of proADM were measured at 24, 48 and 72 h after admission to the intensive care unit (ICU). We assessed their relationship with PGD grade and ICU mortality. Fifty patients (50%) presented grade 3 PGD at ICU admission. Twenty-two patients (22%) developed grade 3 PGD at 72 h, the only grade associated with higher mortality (odds ratio 6.84, 95% confidence interval [CI] 1.47-38.44). ProADM levels measured at 24 h (3.25 vs. 1.61 nmol/L; p = 0.016) and 72 h (2.17 vs. 1.35 nmol/L; p = 0.011) were higher in these patients than the rest of the population. When we added the individual predictive utility of grade 3 PGD at 72 h for ICU mortality (area under the curve [AUC] 0.72, 95% CI 0.53-0.90) to that of ProADM at 72 h, the predictive value of the model improved (AUC 0.81, 95% CI 0.65-0.97). Higher levels of proADM measured following LT are associated with grade 3 PGD at 72 h. ProADM enhances the association of this entity with mortality.

Lung Transplantation

The therapeutic options for patients with advanced pulmonary parenchymal or vascular disorders are currently limited. Lung transplantation remains one of the few viable interventions, but on account of the insufficient donor pool only a minority of these patients actually undergo the procedure each year. Following transplantation there are a number of early and late allograft complications such as primary graft dysfunction, allograft rejection, infection, post-transplant lymphoproliferative disorder and late injury that is now classified as chronic lung allograft dysfunction. The pathologist plays an essential role in the diagnosis and classification of these myriad complications. Although the transplant procedures are performed in selected centers patients typically return to their local centers. When complications arise it is often the responsibility of the local pathologist to evaluate specimens. Therefore familiarity with the pathology of lung transplantation is important.

Primary graft dysfunction: lessons learned about the first 72 h after lung transplantation

PURPOSE OF REVIEW

In 2005, the International Society for Heart and Lung Transplantation published a standardized definition of primary graft dysfunction (PGD), facilitating new knowledge on this form of acute lung injury that occurs within 72 h of lung transplantation. PGD continues to be associated with significant morbidity and mortality. This article will summarize the current literature on the epidemiology of PGD, pathogenesis, risk factors, and preventive and treatment strategies.

RECENT FINDINGS

Since 2011, several manuscripts have been published that provide insight into the clinical risk factors and pathogenesis of PGD. In addition, several transplant centers have explored preventive and treatment strategies for PGD, including the use of extracorporeal strategies. More recently, results from several trials assessing the role of extracorporeal lung perfusion may allow for much-needed expansion of the donor pool, without raising PGD rates.

SUMMARY

This article will highlight the current state of the science regarding PGD, focusing on recent advances, and set a framework for future preventive and treatment strategies.

Objective Estimates Improve Risk Stratification for Primary Graft Dysfunction after Lung Transplantation

Primary graft dysfunction (PGD) is a major cause of early mortality after lung transplant. We aimed to define objective estimates of PGD risk based on readily available clinical variables, using a prospective study of 11 centers in the Lung Transplant Outcomes Group (LTOG). Derivation included 1255 subjects from 2002 to 2010; with separate validation in 382 subjects accrued from 2011 to 2012. We used logistic regression to identify predictors of grade 3 PGD at 48/72 h, and decision curve methods to assess impact on clinical decisions. 211/1255 subjects in the derivation and 56/382 subjects in the validation developed PGD. We developed three prediction models, where low-risk recipients had a normal BMI (18.5-25 kg/m(2) ), chronic obstructive pulmonary disease/cystic fibrosis, and absent or mild pulmonary hypertension (mPAP<40 mmHg). All others were considered higher-risk. Low-risk recipients had a predicted PGD risk of 4-7%, and high-risk a predicted PGD risk of 15-18%. Adding a donor-smoking lung to a higher-risk recipient significantly increased PGD risk, although risk did not change in low-risk recipients. Validation demonstrated that probability estimates were generally accurate and that models worked best at baseline PGD incidences between 5% and 25%. We conclude that valid estimates of PGD risk can be produced using readily available clinical variables.

Lung transplantation: a treatment option in end-stage lung disease

BACKGROUND

Lung transplantation is the final treatment option in the end stage of certain lung diseases, once all possible conservative treatments have been exhausted. Depending on the indication for which lung transplantation is performed, it can improve the patient's quality of life (e.g., in emphysema) and/ or prolong life expectancy (e.g., in cystic fibrosis, pulmonary fibrosis, and pulmonary arterial hypertension). The main selection criteria for transplant candidates, aside from the underlying pulmonary or cardiopulmonary disease, are age, degree of mobility, nutritional and muscular condition, and concurrent extrapulmonary disease. The pool of willing organ donors is shrinking, and every sixth candidate for lung transplantation now dies while on the waiting list.

METHOD

We reviewed pertinent articles (up to October 2013) retrieved by a selective search in Medline and other German and international databases, including those of the International Society for Heart and Lung Transplantation (ISHLT), Eurotransplant, the German Institute for Applied Quality Promotion and Research in Health-Care (Institut für angewandte Qualitätsförderung und Forschung im Gesundheitswesen, AQUA-Institut), and the German Foundation for Organ Transplantation (Deutsche Stiftung Organtransplantation, DSO).

RESULTS

The short- and long-term results have markedly improved in recent years: the 1-year survival rate has risen from 70.9% to 82.9%, and the 5-year survival rate from 46.9% to 59.6%. The 90-day mortality is 10.0%. The postoperative complications include acute (3.4%) and chronic (29.0%) transplant rejection, infections (38.0%), transplant failure (24.7%), airway complications (15.0%), malignant tumors (15.0%), cardiovascular events (10.9%), and other secondary extrapulmonary diseases (29.8%). Bilateral lung transplantation is superior to unilateral transplantation (5-year survival rate 57.3% versus 47.4%).

CONCLUSION

Seamless integration of the various components of treatment will be essential for further improvements in outcome. In particular, the follow-up care of transplant recipients should always be provided in close cooperation with the transplant center.

Heterogeneous phenotypes of acute respiratory distress syndrome after major trauma

RATIONALE

Acute respiratory distress syndrome (ARDS) is a heterogeneous syndrome that can develop at various times after major trauma.

OBJECTIVES

To identify and characterize distinct phenotypes of ARDS after trauma, based on timing of syndrome onset.

METHODS

Latent class analyses were used to identify patterns of ARDS onset in a cohort of critically ill trauma patients. Identified patterns were tested for associations with known ARDS risk factors and associations were externally validated at a separate institution. Eleven plasma biomarkers representing pathophysiologic domains were compared between identified patterns in the validation cohort.

MEASUREMENTS AND MAIN RESULTS

Three patterns of ARDS were identified; class I (52%) early onset on Day 1 or 2, class II (40%) onset on Days 3 and 4, and class III (8%) later onset on Days 4 and 5. Early-onset ARDS was associated with higher Abbreviated Injury Scale scores for the thorax (P < 0.001), lower lowest systolic blood pressure before intensive care unit admission (P = 0.003), and a greater red blood cell transfusion requirement during resuscitation (P = 0.030). In the external validation cohort, early-onset ARDS was also associated with a higher Abbreviated Injury Scale score for the thorax (P = 0.001) and a lower lowest systolic blood pressure before intensive care unit enrollment (P = 0.006). In addition, the early-onset phenotype demonstrated higher plasma levels of soluble receptor for advanced glycation end-products and angiopoietin-2.

CONCLUSIONS

Degree of hemorrhagic shock and severity of thoracic trauma are associated with an early-onset phenotype of ARDS after major trauma. Lung injury biomarkers suggest a dominant alveolar-capillary barrier injury pattern in this phenotype.

Update in lung transplantation 2013

Research in pulmonary transplantation is actively evolving in quality and scope to meet the challenges of a growing population of lung allograft recipients. In 2013, research groups leveraged large publicly available datasets in addition to multicenter research networks and single-center studies to make significant contributions to our knowledge and clinical care in the areas of donor use, clinical transplant outcomes, mechanisms of rejection, infectious complications, and chronic allograft dysfunction.

Subphenotypes in acute respiratory distress syndrome: latent class analysis of data from two randomised controlled trials

BACKGROUND

Subphenotypes have been identified within heterogeneous diseases such as asthma and breast cancer, with important therapeutic implications. We assessed whether subphenotypes exist within acute respiratory distress syndrome (ARDS), another heterogeneous disorder.

METHODS

We used data from two ARDS randomised controlled trials (ARMA trial and ALVEOLI trial), sponsored by the National Heart, Lung, and Blood Institute. We applied latent class modelling to identify subphenotypes using clinical and biological data. We modelled data from both studies independently. We then tested the association of subphenotypes with clinical outcomes in both cohorts and with the response to positive end-expiratory pressure (PEEP) in the ALVEOLI cohort.

FINDINGS

We analysed data for 1022 patients: 473 in the ARMA cohort and 549 in the ALVEOLI cohort. Independent latent class models indicated that a two-class (ie, two subphenotype) model was the best fit for both cohorts. In both cohorts, we identified a hyperinflammatory subphenotype (phenotype 2) that was characterised by higher plasma concentrations of inflammatory biomarkers, a higher prevalence of vasopressor use, lower serum bicarbonate concentrations, and a higher prevalence of sepsis than phenotype 1. Participants in phenotype 2 had higher mortality and fewer ventilator-free days and organ failure-free days in both cohorts than did those in phenotype 1 (p<0·007 for all). In the ALVEOLI cohort, the effects of ventilation strategy (high PEEP vs low PEEP) on mortality, ventilator-free days and organ failure-free days differed by phenotype (p=0·049 for mortality, p=0·018 for ventilator-free days, p=0·003 for organ-failure-free days).

INTERPRETATION

We have identified two subphenotypes within ARDS, one of which is categorised by more severe inflammation, shock, and metabolic acidosis and by worse clinical outcomes. Response to treatment in a randomised trial of PEEP strategies differed on the basis of subphenotype. Identification of ARDS subphenotypes might be useful in selecting patients for future clinical trials.

FUNDING

National Institutes of Health.