Human distal airways contain a multipotent secretory cell that can regenerate alveoli

The human lung differs substantially from its mouse counterpart, resulting in a distinct distal airway architecture affected by disease pathology in chronic obstructive pulmonary disease. In humans, the distal branches of the airway interweave with the alveolar gas-exchange niche, forming an anatomical structure known as the respiratory bronchioles. Owing to the lack of a counterpart in mouse, the cellular and molecular mechanisms that govern respiratory bronchioles in the human lung remain uncharacterized. Here we show that human respiratory bronchioles contain a unique secretory cell population that is distinct from cells in larger proximal airways. Organoid modelling reveals that these respiratory airway secretory (RAS) cells act as unidirectional progenitors for alveolar type 2 cells, which are essential for maintaining and regenerating the alveolar niche. RAS cell lineage differentiation into alveolar type 2 cells is regulated by Notch and Wnt signalling. In chronic obstructive pulmonary disease, RAS cells are altered transcriptionally, corresponding to abnormal alveolar type 2 cell states, which are associated with smoking exposure in both humans and ferrets. These data identify a distinct progenitor in a region of the human lung that is not found in mouse that has a critical role in maintaining the gas-exchange compartment and is altered in chronic lung disease.

Development and validation of a prediction model for actionable aspects of frailty in the text of clinicians' encounter notes

OBJECTIVE

Frailty is a prevalent risk factor for adverse outcomes among patients with chronic lung disease. However, identifying frail patients who may benefit from interventions is challenging using standard data sources. We therefore sought to identify phrases in clinical notes in the electronic health record (EHR) that describe actionable frailty syndromes.

MATERIALS AND METHODS

We used an active learning strategy to select notes from the EHR and annotated each sentence for 4 actionable aspects of frailty: respiratory impairment, musculoskeletal problems, fall risk, and nutritional deficiencies. We compared the performance of regression, tree-based, and neural network models to predict the labels for each sentence. We evaluated performance with the scaled Brier score (SBS), where 1 is perfect and 0 is uninformative, and the positive predictive value (PPV).

RESULTS

We manually annotated 155 952 sentences from 326 patients. Elastic net regression had the best performance across all 4 frailty aspects (SBS 0.52, 95% confidence interval [CI] 0.49-0.54) followed by random forests (SBS 0.49, 95% CI 0.47-0.51), and multi-task neural networks (SBS 0.39, 95% CI 0.37-0.42). For the elastic net model, the PPV for identifying the presence of respiratory impairment was 54.8% (95% CI 53.3%-56.6%) at a sensitivity of 80%.

DISCUSSION

Classification models using EHR notes can effectively identify actionable aspects of frailty among patients living with chronic lung disease. Regression performed better than random forest and neural network models.

CONCLUSIONS

NLP-based models offer promising support to population health management programs that seek to identify and refer community-dwelling patients with frailty for evidence-based interventions.

Self-reported poor quality of sleep in solid organ transplant: A systematic review

BACKGROUND

High quality sleep of sufficient duration is vital to overall health and wellbeing. Self-reported poor quality of sleep, sleep reported as irregular in timing, marked by frequent awakenings, or shortened in duration, is common across the solid-organ transplant trajectory.

AIM

This Systematic Review aimed to summarize available literature on rates of self-reported poor quality of sleep among solid organ transplant candidates and recipients.

METHODS

A systematic search of published literature was conducted in PubMed/MEDLINE, Embase, Web of Science, CINHAL, and PsychInfo databases with no date restrictions. Original articles in the English language describing self-reported quality of sleep using standardized questionnaires in adults either waitlisted for, or who received a solid organ transplant (heart, lung, kidney, liver, pancreas, or multi-solid organ) were included.

RESULTS

Of a potential 2054 articles identified, 44 were included (63.6% renal transplant, 20.5% liver transplant, 11.4% lung transplant, and 4.5% included multiple organ transplant populations), with the majority (68.2%) focusing only on post-transplant populations. No included articles focused solely on heart or pancreas transplant populations. On average, the transplant population with the greatest improvement in quality of sleep (reported as poor sleep quality, insomnia, sleep disturbance, or sleep dissatisfaction) from transplant candidacy to post-transplantation were renal transplant (from 53.5% pre, to 38.9% post) followed by liver transplant patients (from 52.8% pre, to 46.3% post), while lung transplant patients remained similar pre- to post-transplantation (55.6% pre, to 52% post). Poor quality of sleep was frequently associated with anxiety and depression, poorer quality of life, restless legs syndrome, and higher comorbidity.

CONCLUSIONS

Reports of poor quality of sleep are highly prevalent across all solid-organ transplant populations, both pre- and post-transplantation. Future studies should assess quality of sleep longitudinally throughout all phases of the transplantation trajectory, with more research focusing on how to optimize sleep in solid organ transplant populations.

Lung Transplantation Outcomes after Crossing Low-Level Donor Specific Antibodies Without Planned Augmented Immunosuppression

It is unknown whether some donor specific antibodies (DSA) can be crossed at the time of lung transplant without desensitization or augmented induction immunosuppression. This study assessed whether crossing low-level pre-transplant DSA (defined as mean fluorescence intensity (MFI) 1000-6000) without augmented immunosuppression is associated with worse retransplant-free or chronic lung allograft dysfunction (CLAD)-free survival. Of the 458 included recipients, low-level pre-transplant DSA was crossed in 39 (8.6%) patients. The median follow-up time was 2.2 years. There were 15 (38.5%) patients with Class I DSA and 24 (61.5%) with Class II DSA. There was no difference in adjusted overall retransplant-free survival between recipients where pre-transplant DSA was and was not crossed (HR: 0.98 (95% CI = 0.49-1.99), p = 0.96). There was also no difference in CLAD-free survival (HR: 0.71 (95% CI = 0.38-1.33), p = 0.28). There was no difference in Grade 3 PGD at 72 hours (OR: 1.13 (95% CI = 0.52-2.48), p = 0.75) or definite or probable AMR (HR: 2.22 (95% CI = 0.64-7.61), p = 0.21). Lung transplantation in the presence of low-level DSA without planned augmented immunosuppression is not associated with worse overall or CLAD-free survival among recipients with intermediate-term follow-up. This article is protected by copyright. All rights reserved.

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

RATIONALE

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSION

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

The lung microbiome in lung transplantation

Culture-independent study of the lower respiratory tract after lung transplantation has enabled an understanding of the microbiome - that is, the collection of bacteria, fungi, and viruses, and their respective gene complement - in this niche. The lung has unique features as a microbial environment, with balanced entry from the upper respiratory tract, clearance, and local replication. There are many pressures impacting the microbiome after transplantation, including donor allograft factors, recipient host factors such as underlying disease and ongoing exposure to the microbe-rich upper respiratory tract, and transplantation-related immunosuppression, antimicrobials, and postsurgical changes. To date, we understand that the lung microbiome after transplant is dysbiotic; that is, it has higher biomass and altered composition compared to a healthy lung. Emerging data suggest that specific microbiome features may be linked to host responses, both immune and non-immune, and clinical outcomes such as chronic lung allograft dysfunction (CLAD), but many questions remain. The goal of this review is to put into context our burgeoning understanding of the lung microbiome in the postlung transplant patient, the interactions between microbiome and host, the role the microbiome may play in post-transplant complications, and critical outstanding research questions.

Frailty and aging-associated syndromes in lung transplant candidates and recipients

Many lung transplant candidates and recipients are older and frailer compared to previous eras. Older patients are at increased risk for pre- and posttransplant mortality, but this risk is not explained by numerical age alone. This manuscript represents the product of the American Society of Transplantation (AST) conference on frailty. Experts in the field reviewed the latest published research on assessment of elderly and frail lung transplant candidates. Physical frailty, often defined as slowness, weakness, low physical activity, shrinking, and exhaustion, and frailty evaluation is an important tool for evaluation of age-associated dysfunction. Another approach is assessment by cumulative deficits, and both types of frailty are common in lung transplant candidates. Frailty is associated with death or delisting before transplant, and may be associated with posttransplant mortality. Sarcopenia, cognitive dysfunction, depression, and nutrition are other important components for patient evaluation. Aging-associated inflammation, telomere dysfunction, and adaptive immune system senescence may also contribute to frailty. Developing tools for frailty assessment and interventions holds promise for improving patient outcomes before and after lung transplantation.

Primary Graft Dysfunction

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

The association of post-operative delirium with patient-reported outcomes and mortality after lung transplantation

Post-operative delirium after lung transplantation is common. Its associations with health-related quality of life (HRQL), depression, and mortality remains unknown. In 236 lung transplant recipients, HRQL and depressive symptoms were assessed as part of a structured survey battery before and after transplantation. Surveys included the Geriatric Depressive Scale (GDS) and Short Form 12 (SF12). Delirium was assessed throughout the post-operative intensive care unit (ICU) stay with Confusion Assessment Method for ICU. Delirium and mortality data were extracted from electronic medical records. We examined associations between delirium and changes in depressive symptoms and HRQL using linear mixed effects models and association between delirium and mortality with Cox-proportional hazard models. Post-operative delirium occurred in 34 participants (14%). Delirium was associated with attenuated improvements in SF12-PCS (difference ₋4.0; 95%CI: -7.4, -0.7) but not SF12-MCS (difference 2.2; 95%CI: -0.7,5.7) or GDS (difference ₋0.4; 95%CI: -1.5,0.7). Thirty-two participants died during the study period. Delirium was associated with increased adjusted hazard risk of mortality (HR 17.9, 95%CI: 4.4,72.5). Delirium after lung transplantation identifies a group at increased risk for poorer HRQL and death within the first post-operative year. Further studies should investigate potential causal links between delirium, and poorer HRQL and mortality risk after lung transplantation.

Travelling waves reveal a dynamic seizure source in human focal epilepsy

Treatment of patients with drug-resistant focal epilepsy relies upon accurate seizure localization. Ictal activity captured by intracranial EEG has traditionally been interpreted to suggest that the underlying cortex is actively involved in seizures. Here, we hypothesize that such activity instead reflects propagated activity from a relatively focal seizure source, even during later time points when ictal activity is more widespread. We used the time differences observed between ictal discharges in adjacent electrodes to estimate the location of the hypothesized focal source and demonstrated that the seizure source, localized in this manner, closely matches the clinically and neurophysiologically determined brain region giving rise to seizures. Moreover, we determined this focal source to be a dynamic entity that moves and evolves over the time course of a seizure. Our results offer an interpretation of ictal activity observed by intracranial EEG that challenges the traditional conceptualization of the seizure source.

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.

Mobile health technology to improve emergent frailty after lung transplantation

We evaluated the feasibility, safety, and efficacy of a mHealth-supported physical rehabilitation intervention to treat frailty in a pilot study of 18 lung transplant recipients. Frail recipients were defined by a short physical performance battery (SPPB score ≤7). The primary intervention modality was Aidcube, a customizable rehabilitation mHealth platform. Our primary aims included tolerability, feasibility, and acceptability of use of the platform, and secondary outcomes were changes in SPPB and in scores of physical activity, and disability measured using the Duke Activity Status Index (DASI) and Lung Transplant-Value Life Activities (LT-VLA). Notably, no adverse events were reported. Subjects reported the app was easy to use, usability improved over time, and the app enhanced motivation to engage in rehabilitation. Comments highlighted the complexities of immediate post-transplant rehabilitation, including functional decline, pain, tremor, and fatigue. At the end of the intervention, SPPB scores improved a median of 5 points from a baseline of 4. Physical activity and patient-reported disability also improved. The DASI improved from 4.5 to 19.8 and LT-VLA score improved from 2 to 0.59 at closeout. Overall, utilization of a mHealth rehabilitation platform was safe and well received. Remote rehabilitation was associated with improvements in frailty, physical activity and disability. Future studies should evaluate mHealth treatment modalities in larger-scale randomized trials of lung transplant recipients.

Risk of primary graft dysfunction following lung transplantation in selected adults with connective tissue disease-associated interstitial lung disease

BACKGROUND

Previous studies have reported similarities in long-term outcomes following lung transplantation for connective tissue disease-associated interstitial lung disease (CTD-ILD) and idiopathic pulmonary fibrosis (IPF). However, it is unknown whether CTD-ILD patients are at increased risk of primary graft dysfunction (PGD), delays in extubation, or longer index hospitalizations following transplant compared to IPF patients.

METHODS

We performed a multicenter retrospective cohort study of CTD-ILD and IPF patients enrolled in the Lung Transplant Outcomes Group registry who underwent lung transplantation between 2012 and 2018. We utilized mixed effects logistic regression and stratified Cox proportional hazards regression to determine whether CTD-ILD was independently associated with increased risk for grade 3 PGD or delays in post-transplant extubation and hospital discharge compared to IPF.

RESULTS

A total of 32.7% (33/101) of patients with CTD-ILD and 28.9% (145/501) of patients with IPF developed grade 3 PGD 48-72 hours after transplant. There were no significant differences in odds of grade 3 PGD among patients with CTD-ILD compared to those with IPF (adjusted OR 1.12, 95% CI 0.64-1.97, p = 0.69), nor was CTD-ILD independently associated with a longer post-transplant time to extubation (adjusted HR for first extubation 0.87, 95% CI 0.66-1.13, p = 0.30). However, CTD-ILD was independently associated with a longer post-transplant hospital length of stay (median 23 days [IQR 14-35 days] vs17 days [IQR 12-28 days], adjusted HR for hospital discharge 0.68, 95% CI 0.51-0.90, p = 0.008).

CONCLUSION

Patients with CTD-ILD experienced significantly longer postoperative hospitalizations compared to IPF patients without an increased risk of grade 3 PGD.

Impact of the elimination of the donation service area on United States lung transplant practices and outcomes at high and low competition centers

In November 2017, the donation service area (DSA) was removed as the primary unit of US donor lung allocation. Our primary objective was to evaluate the effect of this change on recipient characteristics, the use of pretransplant extracorporeal membrane oxygenation (ECMO), and on index hospitalization length of stay (LOS) and early posttransplant complications. We also assessed whether these outcomes differed in high and low competition centers, as defined by the Herfindahl-Hirschman Index. Following DSA removal, there was a 9-day decrease in median waitlist time (P = .001) and an increase in median lung allocation score (40 vs 42, P < .0001) but no difference in the need for pretransplant ECMO (incidence rate ratio = 1.16, P = .12). Median LOS increased from 17 to 19 days in the post-DSA era (P = .01). There was no difference in posttransplant outcomes, including prolonged ventilation, new dialysis, or early survival, in the general cohort or between competition groups. High competition centers saw an 18.5-minute increase in ischemic time compared to low competition centers (P = .04) but did not differentially increase single lung transplants or pretransplant ECMO utilization. Overall, DSA elimination was associated with increased posttransplant LOS but no significant differences in pretransplant ECMO or other posttransplant outcomes. Effects were largely similar at low and high competition centers.

The impact of HLA-DR mismatch status on retransplant-free survival and bronchiolitis obliterans syndrome‒free survival among sensitized lung transplant recipients

INTRODUCTION

Donor‒recipient HLA-DR locus matching may be protective against bronchiolitis obliterans syndrome (BOS) in lung transplant recipients. It is unknown whether this benefit is more significant among sensitized (calculated panel reactive antibodies (CPRAs) of >0%) and highly sensitized (CPRAs of ≥80%) recipients who may be at a higher risk for BOS.

METHODS

This was a retrospective cohort study of adults in the Scientific Registry of Transplant Recipients who underwent lung transplantation between May 5, 2005 and May 31, 2019. Retransplant-free survival and BOS-free survival were compared among recipients with 0 vs ≥1 DR mismatches, grouped according to sensitization.

RESULTS

Among all 20,355 included recipients, 0 DR mismatch status was associated with improved retransplant-free survival (hazard ratio [HR] = 0.83, 95% CI = 0.74-0.93, p = 0.002) and BOS-free survival (HR = 0.86, 95% CI = 0.77-0.96, p = 0.007). Among sensitized recipients, 0 DR mismatch status was also associated with improved retransplant-free survival (HR = 0.79, 95% CI = 0.65-0.97, p = 0.02) and BOS-free survival (HR = 0.82, 95% CI = 0.67-1.00, p = 0.04). There was however no difference in retransplant-free or BOS-free survival between sensitized and non-sensitized recipients with 0 DR mismatches. Among highly sensitized recipients, 0 DR mismatch status was not associated with retransplant-free or BOS-free survival. Among sensitized and highly sensitized recipients, 0 DR mismatch status was not associated with reduced use of plasmapheresis or reduced biopsy-proven, treated acute cellular rejection compared with non-sensitized recipients.

CONCLUSIONS

HLA-DR matching is associated with a similar improvement in retransplant-free and BOS-free survival among non-sensitized and sensitized lung transplant recipients. DR matching does not confer a more substantial retransplant-free or BOS-free survival benefit to highly sensitized recipients than to non-sensitized recipients.

Local complement activation is associated with primary graft dysfunction after lung transplantation

BACKGROUND

The complement system plays a key role in host defense but is activated by ischemia/reperfusion injury (IRI). Primary graft dysfunction (PGD) is a form of acute lung injury occurring predominantly due to IRI, which worsens survival after lung transplantation (LTx). Local complement activation is associated with acute lung injury, but whether it is more reflective of allograft injury compared with systemic activation remains unclear. We proposed that local complement activation would help identify those who develop PGD after LTx. We also aimed to identify which complement activation pathways are associated with PGD.

METHODS

We performed a multicenter cohort study at the University of Pennsylvania and Washington University School of Medicine. Bronchoalveolar lavage (BAL) and plasma specimens were obtained from recipients within 24 hours after LTx. PGD was scored based on the consensus definition. Complement activation products and components of each arm of the complement cascade were measured using ELISA.

RESULTS

In both cohorts, sC4d and sC5b-9 levels were increased in BAL of subjects with PGD compared with those without PGD. Subjects with PGD also had higher C1q, C2, C4, and C4b, compared with subjects without PGD, suggesting classical and lectin pathway involvement. Ba levels were higher in subjects with PGD, suggesting alternative pathway activation. Among lectin pathway–specific components, MBL and FCN-3 had a moderate-to-strong correlation with the terminal complement complex in the BAL but not in the plasma.

CONCLUSION

Complement activation fragments are detected in the BAL within 24 hours after LTx. Components of all 3 pathways are locally increased in subjects with PGD. Our findings create a precedent for investigating complement-targeted therapeutics to mitigate PGD.

FUNDING

This research was supported by the NIH, American Lung Association, Children’s Discovery Institute, Robert Wood Johnson Foundation, Cystic Fibrosis Foundation, Barnes-Jewish Hospital Foundation, Danish Heart Foundation, Danish Research Foundation of Independent Research, Svend Andersen Research Foundation, and Novo Nordisk Research Foundation.

Substantial differences between local and systemic complement activation in lung transplant recipients who develop primary graft dysfunction are identified in two independent cohorts.

Emerging biomarkers in chronic lung allograft dysfunction

Introduction: Lung transplantation remains an important treatment for patients with end stage lung disease. Chronic lung allograft dysfunction (CLAD) remains the greatest limiting factor for long term survival. As the diagnosis of CLAD is based on pulmonary function tests, significant lung injury is required before a diagnosis is feasible, likely when irreversible damage has already occurred. Therefore, research is ongoing for early CLAD recognition, with biomarkers making up a substantial amount of this research.Areas covered: The purpose of this review is to describe available biomarkers, focusing on those which aid in predicting CLAD and distinguishing between different CLAD phenotypes. We describe biomarkers presenting in bronchial alveolar lavage (BAL) as well as circulating in peripheral blood, both of which offer an appealing alternative to lung biopsy.Expert opinion: Development of CLAD involves complex, multiple immune and nonimmune mechanisms. Therefore, evaluation of potential CLAD biomarkers serves a dual purpose: clinically, the goal remains early detection and identification of patients at increased risk. Simultaneously, biomarkers offer insight into the different mechanisms involved in the pathophysiology of CLAD, leading to the development of possible interventions. The ultimate goal is the development of both preventive and early intervention strategies for CLAD to improve the overall survival of our lung transplant recipients.