Ventilatory capacity in CLAD is driven by dysfunctional airway structure.

BACKGROUND: Chronic lung allograft dysfunction (CLAD) encompasses three main phenotypes: bronchiolitis obliterans syndrome (BOS), restrictive allograft syndrome (RAS) and a Mixed phenotype combining both pathologies. How the airway structure in its entirety is affected in these phenotypes is still poorly understood. METHODS: A detailed analysis of airway morphometry was applied to gain insights on the effects of airway remodelling on the distribution of alveolar ventilation in end-stage CLAD. Ex vivo whole lung µCT and tissue-core µCT scanning of six control, six BOS, three RAS and three Mixed explant lung grafts (9 male, 9 female, 2014-2021, Leuven, Belgium) were used for digital airway reconstruction and calculation of airway dimensions in relation to luminal obstructions. FINDINGS: BOS and Mixed explants demonstrated airway obstructions of proximal bronchioles (starting at generation five), while RAS explants particularly had airway obstructions in the most distal bronchioles (generation >12). In BOS and Mixed explants 76% and 84% of bronchioles were obstructed, respectively, while this was 22% in RAS. Bronchiolar obstructions were mainly caused by lymphocytic inflammation of the airway wall or fibrotic remodelling, i.e. constrictive bronchiolitis. Proximal bronchiolectasis and imbalance in distal lung ventilation were present in all CLAD phenotypes and explain poor lung function and deterioration of specific lung function parameters. INTERPRETATION: Alterations in the structure of conducting bronchioles revealed CLAD to affect alveolar ventilatory distribution in a regional fashion. The significance of various obstructions, particularly those associated with mucus, is highlighted. FUNDING: This research was funded with the National research fund Flanders (G060322N), received by R.V.

COVID-19 Outcomes in Lung Transplant Recipients Following Pre-Exposure Prophylaxis With Tixagevimab-Cilgavimab During the Omicron BA.5 Surge: A Single Center Analysis.

Lung transplant (LTx) recipients are at high risk for COVID-19 related morbidity and mortality. Data regarding pre-exposure prophylaxis (PrEP) with tixagevimab-cilgavimab in this population are scarce. We therefore evaluated COVID-19 breakthrough infections and COVID-19 related complications after PrEP in a retrospective single-center study, including 264 LTx recipients who received PrEP between June 2022 and December 2022, when Omicron BA.5 was the dominant circulating SARS-CoV-2 variant. PrEP was indicated for fully vaccinated patients with poor seroconversion (anti-S <260 BAU/mL). COVID-19 breakthrough infection after PrEP occurred in 11.0% within the first 3 months, increasing to 17.4% within 6 months. Hospitalization rate rose from 27.6% to 52.9% (p = 0.046), while ICU admissions and COVID-19 mortality remained low, respectively occurring in 6.5% and 4.3% of patients with breakthrough infection within 6 months. COVID-19 breakthrough infection and associated hospitalization remained an important problem during the Omicron BA.5 surge in fully vaccinated LTx recipients with deficient seroconversion, despite PrEP with tixagevimab-cilgavimab. However, ICU admissions and COVID-19 mortality were low. Waning of neutralizing effects of PrEP and changing circulating SARS-CoV-2 variants may explain increases in COVID-19 infections and hospitalizations over time after PrEP, highlighting the need for novel, long-term effective PrEP strategies in these high-risk patients.

The Immunopathology of Pulmonary Rejection after Murine Lung Transplantation.

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

Mucosal immune alterations at the early onset of tissue destruction in chronic obstructive pulmonary disease.

Rationale: COPD is characterized by chronic airway inflammation, small airways changes, with disappearance and obstruction, and also distal/alveolar destruction (emphysema). The chronology by which these three features evolve with altered mucosal immunity remains elusive. This study assessed the mucosal immune defense in human control and end-stage COPD lungs, by detailed microCT and RNA transcriptomic analysis of diversely affected zones. Methods: In 11 control (non-used donors) and 11 COPD (end-stage) explant frozen lungs, 4 cylinders/cores were processed per lung for microCT and tissue transcriptomics. MicroCT was used to quantify tissue percentage and alveolar surface density to classify the COPD cores in mild, moderate and severe alveolar destruction groups, as well as to quantify terminal bronchioles in each group. Transcriptomics of each core assessed fold changes in innate and adaptive cells and pathway enrichment score between control and COPD cores. Immunostainings of immune cells were performed for validation. Results: In mildly affected zones, decreased defensins and increased mucus production were observed, along CD8+ T cell accumulation and activation of the IgA pathway. In more severely affected zones, CD68+ myeloid antigen-presenting cells, CD4+ T cells and B cells, as well as MHCII and IgA pathway genes were upregulated. In contrast, terminal bronchioles were decreased in all COPD cores. Conclusion: Spatial investigation of end-stage COPD lungs show that mucosal defense dysregulation with decreased defensins and increased mucus and IgA responses, start concomitantly with CD8+ T-cell accumulation in mild emphysema zones, where terminal bronchioles are already decreased. In contrast, adaptive Th and B cell activation is observed in areas with more advanced tissue destruction. This study suggests that in COPD innate immune alterations occur early in the tissue destruction process, which affects both the alveoli and the terminal bronchioles, before the onset of an adaptive immune response.

Prognostic Value of Chest CT Findings at BOS Diagnosis in Lung Transplant Recipients.

BACKGROUND: Bronchiolitis obliterans syndrome (BOS) after lung transplantation is characterized by fibrotic small airway remodeling, recognizable on high-resolution computed tomography (HRCT). We studied the prognostic value of key HRCT features at BOS diagnosis after lung transplantation. METHODS: The presence and severity of bronchiectasis, mucous plugging, peribronchial thickening, parenchymal anomalies, and air trapping, summarized in a total severity score, were assessed using a simplified Brody II scoring system on HRCT at BOS diagnosis, in a cohort of 106 bilateral lung transplant recipients transplanted between January 2004 and January 2016. Obtained scores were subsequently evaluated regarding post-BOS graft survival, spirometric parameters, and preceding airway infections. RESULTS: A high total Brody II severity score at BOS diagnosis (P = 0.046) and high subscores for mucous plugging (P = 0.0018), peribronchial thickening (P = 0.0004), or parenchymal involvement (P = 0.0121) are related to worse graft survival. A high total Brody II score was associated with a shorter time to BOS onset (P = 0.0058), lower forced expiratory volume in 1 s (P = 0.0006) forced vital capacity (0.0418), more preceding airway infections (P = 0.004), specifically with Pseudomonas aeruginosa (P = 0.002), and increased airway inflammation (P = 0.032). CONCLUSIONS: HRCT findings at BOS diagnosis after lung transplantation provide additional information regarding its underlying pathophysiology and for future prognosis of graft survival.

COVID-19 progression in hospitalized patients using follow-up in vivo CT and ex vivo microCT.

Background: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes coronavirus disease-19 (COVID-19) which can lead to acute respiratory distress syndrome (ARDS) and evolve to pulmonary fibrosis. Computed tomography (CT) is used to study disease progression and describe radiological patterns in COVID-19 patients. This study aimed to assess disease progression regarding lung volume and density over time on follow-up in vivo chest CT and give a unique look at parenchymal and morphological airway changes in "end-stage" COVID-19 lungs using ex vivo microCT. Methods: Volumes and densities of the lung/lobes of three COVID-19 patients were assessed using follow-up in vivo CT and ex vivo whole lung microCT scans. Airways were quantified by airway segmentations on whole lung microCT and small-partition microCT. As controls, three discarded healthy donor lungs were used. Histology was performed in differently affected regions in the COVID-19 lungs. Results: In vivo, COVID-19 lung volumes decreased while density increased over time, mainly in lower lobes as previously shown. Ex vivo COVID-19 lung volumes decreased by 60% and all lobes were smaller compared to controls. Airways were more visible on ex vivo microCT in COVID-19, probably due to fibrosis and increased airway diameter. In addition, small-partition microCT showed more deformation of (small) airway morphology and fibrotic organization in severely affected regions with heterogeneous distributions within the same lung which was confirmed by histology. Conclusions: COVID-19-ARDS and subsequent pulmonary fibrosis alters lung architecture and airway morphology which is described using in vivo CT, ex vivo microCT, and histology.

Lymphocyte Depleting and Modulating Therapies for Chronic Lung Allograft Dysfunction.

Chronic lung rejection, also called chronic lung allograft dysfunction (CLAD), remains the major hurdle limiting long-term survival after lung transplantation, and limited therapeutic options are available to slow the progressive decline in lung function. Most interventions are only temporarily effective in stabilizing the loss of or modestly improving lung function, with disease progression resuming over time in the majority of patients. Therefore, identification of effective treatments that prevent the onset or halt progression of CLAD is urgently needed. As a key effector cell in its pathophysiology, lymphocytes have been considered a therapeutic target in CLAD. The aim of this review is to evaluate the use and efficacy of lymphocyte depleting and immunomodulating therapies in progressive CLAD beyond usual maintenance immunosuppressive strategies. Modalities used include anti-thymocyte globulin, alemtuzumab, methotrexate, cyclophosphamide, total lymphoid irradiation, and extracorporeal photopheresis, and to explore possible future strategies. When considering both efficacy and risk of side effects, extracorporeal photopheresis, anti-thymocyte globulin and total lymphoid irradiation appear to offer the best treatment options currently available for progressive CLAD patients. SIGNIFICANCE STATEMENT: Effective treatments to prevent the onset and progression of chronic lung rejection after lung transplantation are still a major shortcoming. Based on existing data to date, considering both efficacy and risk of side effects, extracorporeal photopheresis, anti-thymocyte globulin, and total lymphoid irradiation are currently the most viable second-line treatment options. However, it is important to note that interpretation of most results is hampered by the lack of randomized controlled trials.

Aspergillus-Specific IgG Antibodies are Associated With Fungal-Related Complications and Chronic Lung Allograft Dysfunction After Lung Transplantation.

Fungal exposure and sensitization negatively affect outcomes in various respiratory diseases, however, the effect of fungal sensitization in lung transplant (LTx) recipients is still unknown. We performed a retrospective cohort study of prospectively collected data on circulating fungal specific IgG/IgE antibodies, and their correlation with fungal isolation, chronic lung allograft dysfunction (CLAD) and overall survival after LTx. 311 patients transplanted between 2014 and 2019 were included. Patients with elevated Aspergillus fumigatus or Aspergillus flavus IgG (10%) had more mold and Aspergillus species isolation (p = 0.0068 and p = 0.0047). Aspergillus fumigatus IgG was specifically associated with Aspergillus fumigatus isolation in the previous or consecutive year (AUC 0.60, p = 0.004 and AUC 0.63, p = 0.022, respectively). Elevated Aspergillus fumigatus or Aspergillus flavus IgG was associated with CLAD (p = 0.0355), but not with death. Aspergillus fumigatus, Aspergillus flavus or Aspergillus niger IgE was elevated in 19.3% of patients, but not associated with fungal isolation, CLAD or death. Mold isolation and Aspergillus species isolation from respiratory cultures were associated with CLAD occurrence (p = 0.0011 and p = 0.0005, respectively), and Aspergillus species isolation was also associated with impaired survival (p = 0.0424). Fungus-specific IgG could be useful in long-term follow-up post-LTx, as a non-invasive marker for fungal exposure, and thus a diagnostic tool for identifying patients at risk for fungal-related complications and CLAD.

Acute Rejection and Chronic Lung Allograft Dysfunction: Obstructive and Restrictive Allograft Dysfunction.

Lung transplantation is an established treatment of well-selected patients with end-stage respiratory diseases. However, lung transplant recipients have the highest rates of acute and chronic rejection among transplanted solid organs. Owing to ongoing alloimmune recognition and associated immune-driven airway/vascular remodeling, precipitated by multifactorial, endogenous or exogenous, post-transplant injuries to the bronchovascular axis of the secondary pulmonary lobule, most lung transplant recipients will suffer from a pathophysiological decline of their allograft, either functionally and/or structurally. This review discusses current knowledge, barriers, and gaps in acute cellular rejection and chronic lung allograft dysfunction-the greatest impediment to long-term post-transplant survival.

Allogeneic Hematopoietic Stem Cell Transplantation After Prior Lung Transplantation for Hereditary Pulmonary Alveolar Proteinosis: A Case Report.

Pulmonary alveolar proteinosis (PAP) is a rare, diffuse lung disorder characterized by surfactant accumulation in the small airways due to defective clearance by alveolar macrophages, resulting in impaired gas exchange. Whole lung lavage is the current standard of care treatment for PAP. Lung transplantation is an accepted treatment option when whole lung lavage or other experimental treatment options are ineffective, or in case of extensive pulmonary fibrosis secondary to PAP. A disadvantage of lung transplantation is recurrence of PAP in the transplanted lungs, especially in hereditary PAP. The hereditary form of PAP is an ultra-rare condition caused by genetic mutations in genes encoding for the granulocyte macrophage-colony stimulating factor (GM-CSF) receptor, and intrinsically affects bone marrow derived-monocytes, which differentiate into macrophages in the lung. Consequently, these macrophages typically display disrupted GM-CSF receptor-signaling, causing defective surfactant clearance. Bone marrow/hematopoietic stem cell transplantation may potentially reverse the lung disease in hereditary PAP. In patients with hereditary PAP undergoing lung transplantation, post-lung transplant recurrence of PAP may theoretically be averted by subsequent hematopoietic stem cell transplantation, which results in a graft-versus-disease (PAP) effect, and thus could improve long-term outcome. We describe the successful long-term post-transplant outcome of a unique case of end-stage respiratory failure due to hereditary PAP-induced pulmonary fibrosis, successfully treated by bilateral lung transplantation and subsequent allogeneic hematopoietic stem cell transplantation. Our report supports treatment with serial lung and hematopoietic stem cell transplantation to improve quality of life and prolong survival, without PAP recurrence, in selected patients with end-stage hereditary PAP.

Pulmonary graft-versus-host disease and chronic lung allograft dysfunction: two sides of the same coin?

Allogeneic haematopoietic stem-cell transplantation (HSCT) and lung transplantation are both established life-saving treatment options for carefully selected patients with various haematological disorders or end-stage lung diseases, respectively. However, long-term survival after allogeneic HSCT is severely limited by chronic graft-versus-host disease (cGVHD)-of which pulmonary cGVHD in particular has a very poor prognosis-and long-term survival after lung transplantation is hampered by chronic lung allograft dysfunction (CLAD). Both pulmonary cGVHD and CLAD are characterised by similar underlying immunopathology, which results in transplant-related pulmonary fibrosis and structural lung remodelling, leading to respiratory dysfunction. Accurate clinical identification and appropriate management is of utmost importance to allow for timely diagnosis, to further optimise current preventive and treatment strategies of pulmonary cGVHD and CLAD, and to ameliorate quality of life and long-term outcomes after allogeneic HSCT and lung transplantation. In this Review, we provide a unique state-of-the-art perspective of both entities for respiratory care practitioners.

Antifibrotic drugs in lung transplantation and chronic lung allograft dysfunction: a review.

This review aims to provide an overview of pre-transplant antifibrotic therapy on peri-transplant outcomes and to address the possible role of antifibrotics in lung transplant recipients with chronic lung allograft dysfunction.Lung transplantation is an established treatment modality for patients with various end-stage lung diseases, of which idiopathic pulmonary fibrosis and other progressive fibrosing interstitial lung diseases are growing indications. Theoretically, widespread use of antifibrotics prior to lung transplantation may increase the risk of bronchial anastomotic complications and impaired wound healing.Long-term graft and patient survival are still hampered by development of chronic lung allograft dysfunction, on which antifibrotics may have a beneficial impact.Antifibrotics until the moment of lung transplantation proved to be safe, without increasing peri-transplant complications. Currently, best practice is to continue antifibrotics until time of transplantation. In a large multicentre randomised trial, pirfenidone did not appear to have a beneficial effect on lung function decline in established bronchiolitis obliterans syndrome. The results of antifibrotic therapy in restrictive allograft syndrome are eagerly awaited, but nonrandomised data from small case reports/series are promising.

Selection Criteria for Lung Transplantation: Controversies and New Developments.

Lung transplantation is an accepted therapeutic option for end-stage lung diseases. The imbalance between limited availability and vast need of donor organs necessitates careful selection of recipient candidates, ensuring the best possible utilization of the scarce resource of organs. Nonetheless, possible lung transplant candidates who could experience a meaningful improvement in survival and quality of life should not be excluded solely based on the complexity of their case. In this review, controversial issues or difficult limitations for lung transplantation, and new developments in recipient selection criteria, are discussed, which may help broaden recipient eligibility for lung transplantation without compromising long-term outcomes.

Antifungal Prophylaxis After Lung Transplantation: Where Are We Now?

BACKGROUND: Lung transplantation is an important treatment option for various end-stage lung diseases. However, survival remains limited due to graft rejection and infections. Despite that fungal infections are frequent and carry a bad prognosis, there is currently no consensus on efficacy, optimal drug, route, or duration of antifungal prophylaxis. This narrative review summarizes current strategies for antifungal prophylaxis after lung transplantation. METHODS: English language articles in Embase, Pubmed, UptoDate, and bibliographies were used to assess the efficacy and safety of available antifungal agents for prophylaxis in adult lung transplant recipients. RESULTS: Overall, there are limited high-quality data. Universal prophylaxis is more widely used and may be preferable over targeted prophylaxis. Both formulations of inhaled amphotericin B and systemic azoles are effective at reducing fungal infection rates, yet with their own specific advantages and disadvantages. The benefit of combination regimens has yet to be proven. Considering the post-transplant timing of the onset of fungal infections, postoperative prophylaxis during the first postoperative months seems indicated for most patients. CONCLUSIONS: Based on existing literature, universal antifungal prophylaxis with inhaled amphotericin B and systemic voriconazole for at least 3-6 mo after lung transplantation may be advisable, with a slight preference for amphotericin B because of its better safety profile.

Free Airway C4d after Lung Transplantation - A Quantitative Analysis of Bronchoalveolar Lavage Fluid.

In recent years, the utility of vascular complement factor 4d (C4d) deposition as diagnostic tool for antibody mediated rejection (AMR) after lung transplantation, has become a controversial issue. We aimed to pinpoint the problematic nature of C4d as biomarker with a simple experiment. We quantified C4d in broncho-alveolar lavage (BAL) of lung transplant patients with diverse post-transplant complications in 3 different settings of clinically clear cases of: 1/ chronic lung allograft dysfunction (CLAD); 2/ acute complications acute rejection (AR), lymphocytic bronchiolitis (LB), antibody-mediated rejection (AMR) and respiratory infection (INF); 3/ patients with parallel C4d immunostaining and Anti-HLA. All groups were compared to BAL of stable patients. C4d was measured via standard ELISA. C4d was increased in CLAD, predominantly in RAS (p = 0.0026) but not in BOS (p = 0.89). C4d was increased in all acute events, AR (p = 0.0025), LB (p < 0.0001), AMR (p = 0.0034), infections (p < 0.0001). In patients with parallel C4d immunostaining and serum HLA antibodies, C4d was increased in C4d-/HLA- (p = 0.0011); C4d-/HLA+ (p = 0.013); HLA+/C4d + (p = 0.0081). A correlation of systemic C-reactive protein (CRP) with C4d was found in all patients (r = 0.49; p < 0.0001). We hypothesize that free C4d in BAL may only be representative of a general immune response in the transplanted lung.

Total lymphoid irradiation in progressive bronchiolitis obliterans syndrome after lung transplantation: a single-center experience and review of literature.

Limited results about treatment with total lymphoid irradiation (TLI) in lung transplant (LTx) recipients suffering from progressive bronchiolitis obliterans syndrome (BOS) have been reported. We performed a retrospective analysis of all LTx recipients undergoing TLI for progressive BOS in our center, focusing on long-term outcomes regarding overall survival and lung allograft function. Treatment with TLI (2004-2017, n = 20, 1 BOS stage 1, 6 BOS stage 2, and 13 BOS stage 3) resulted in significant attenuation of the FEV1 -decline in the majority of patients, mainly in those with a rapid decline (P = 0.0005). This allowed bridging to redo-transplantation in five patients. However, three patients progressed from BOS to RAS following prior TLI. Overall patient survival was 44% at 2 years post-TLI and 38% after 17 years. Generally, TLI was well tolerated, with limited side effects and no serious adverse events. TLI may attenuate the decline in FEV1 of LTx recipients with rapid progressive BOS and could thus help to bridge selected patients to redo-transplantation.

Mortality after lung transplantation: a single-centre cohort analysis.

Detailed data on postoperative death in lung transplant (LTx) recipients are lacking. Therefore, we investigated all deaths after LTx in a large, single-centre, 25-year follow-up cohort. Prevalence, time, place and cause of death (COD) were retrospectively analysed for all patients undergoing primary LTx between July 1991 and December 2015 in our centre. Over subsequent years, postoperative survival significantly improved, with proportionally more patients surviving to 1-year post-LTx (P < 0.0001). A total of 347 (38.9%) LTx recipients died, of which 53.6% expired within 3 years post-LTx [median time to death 910 (236-2447) days]. Autopsy was performed in 34.8% of deaths. COD included CLAD in 27.1% (BOS 63.8% vs. RAS 36.2%); infection (26.5%); malignancy (15.6%); postoperative complication (11.2%); cardiovascular disease (4.6%) or other causes (6.9%). In 8.1%, no clear COD could be determined. COD significantly differed between the various LTx indications (P = 0.047). With longer follow-up, infection becomes a less prevalent COD, but CLAD and malignancies a more important COD. The majority of patients died on the intensive care unit (40.6%) or hospital ward (29.1%), but place of death varied depending on the underlying COD. The current study provides insights into the postoperative deaths of LTx recipients.

Myeloid-Derived Suppressor Cells in Lung Transplantation.

Myeloid-derived suppressor cells (MDSC) are a heterogeneous group of immune cells from the myeloid lineage. MDSCs expand in pathological situations, such as chronic infection, cancer, autoimmunity, and allograft rejection. As chronic lung allograft dysfunction (CLAD) limits long-term survival after lung transplantation (LTx), MDSCs may play a role in its pathophysiology. We assessed phenotype and frequency of MDSCs in peripheral blood from lung transplant recipients and its relationship to post-transplant complications and immunosuppression. Granulocytic (G)-MDSC were identified and quantified by flow cytometry of blood from 4 control subjects and 20 lung transplant patients (stable n = 6, infection n = 5; CLAD n = 9). G-MDSC functionality was assessed in vitro by their capability to block CD4 and CD8 T cell proliferation. More G-MDSC could be assessed using EDTA tubes compared to heparin tubes (p = 0.004). G-MDSC were increased in stable lung transplant recipients vs. non-transplant controls (52.1% vs. 9.4%; p = 0.0095). The infection or CLAD groups had lower G-MDSCs vs. stable recipients (28.2%p = 0.041 and 33.0%; p = 0.088, respectively), but were not different among CLAD phenotypes. G-MDSC tended to correlate with cyclosporine A and tacrolimus levels (r2 = 0.18; r2 = 0.17). CD4 and CD8 cells proliferation decreased by 50 and 80% if co-cultured with MDSCs (1:6 and 1:2 MDSC:T-cell ratio, respectively). In conclusion, circulating MDSCs are measurable, functional and have a G-MDSC phenotype in lung transplant patients. Their frequency is increased in stable patients, decreased during post-transplant complications, and related to level of immunosuppression. This study may pave the way for further investigations of MDSC in the context of lung transplantation.