Lung Allograft Rejection Research Articles

P14.01: Cryobiopsy in the Diagnosis of Lung Allograft Rejection: Brazilian Case Series

P14.01: Cryobiopsy in the Diagnosis of Lung Allograft Rejection: Brazilian Case Series

Medical Complications of Lung Transplantation.

Lung transplantation (LT) is now considered as an effective treatment option for end-stage lung diseases that improves the short and long-term survival rates and quality of life. As increasingly many LT procedures are being performed, the medical complications of LT are also increasing in frequency and emerging as a very important issue for transplant clinicians. Although chronic lung allograft dysfunction and infection are major causes of death after LT, many medical complications, several of which result from immunosuppressive treatment, contribute to increased mortality and morbidity. This article reviews the most frequent and important medical complications of LT, accompanied by a review of the literature and studies from South Korea, including lung allograft rejection, infection, and non-allograft organ systemic complications.

Immune processes in the pathogenesis of chronic lung allograft dysfunction: identifying the missing pieces of the puzzle.

Lung transplantation is the optimal treatment for selected patients with end-stage chronic lung diseases. However, chronic lung allograft dysfunction remains the leading obstacle to improved long-term outcomes. Traditionally, lung allograft rejection has been considered primarily as a manifestation of cellular immune responses. However, in reality, an array of complex, interacting and multifactorial mechanisms contribute to its emergence. Alloimmune-dependent mechanisms, including T-cell-mediated rejection and antibody-mediated rejection, as well as non-alloimmune injuries, have been implicated. Moreover, a role has emerged for autoimmune responses to lung self-antigens in the development of chronic graft injury. The aim of this review is to summarise the immune processes involved in the pathogenesis of chronic lung allograft dysfunction, with advanced insights into the role of innate immune pathways and crosstalk between innate and adaptive immunity, and to identify gaps in current knowledge.

Novel approaches for long-term lung transplant survival.

Allograft failure remains a major barrier in the field of lung transplantation and results primarily from acute and chronic rejection. To date, standard-of-care immunosuppressive regimens have proven unsuccessful in achieving acceptable long-term graft and patient survival. Recent insights into the unique immunologic properties of lung allografts provide an opportunity to develop more effective immunosuppressive strategies. Here we describe advances in our understanding of the mechanisms driving lung allograft rejection and highlight recent progress in the development of novel, lung-specific strategies aimed at promoting long-term allograft survival, including tolerance.

Noninvasive monitoring of allograft rejection in a rat lung transplant model: Application of machine learning-based 18F-fluorodeoxyglucose positron emission tomography radiomics.

Standardized uptake values (SUVs) derived from 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography (PET) are valuable but insufficient for detecting lung allograft rejection (AR). Using a rat lung transplantation (LTx) model, we investigated correlations of AR with the SUVmax and PET-derived radiomics and further evaluated the performance of machine learning (ML)-based radiomics for monitoring AR. LTx was performed on 4 groups of rats: isograft, allograft-cyclosporinecontinuous (CsAcont), allograft-CsAdelayed, and allograft-CsA1week. Each rat underwent 18F-FDG PET at week 3 or 6. The SUVmax and radiomic features were extracted from the PET images. Least absolute shrinkage and selection operator regression was used to construct a radiomics score (Rad-score). Ten modeling algorithms with 7 feature selection methods were performed to develop 70 radiomics models (49 ML models and 21 logistic regression models) for monitoring AR, validated using the bootstrap method. In total, 837 radiomic features were extracted from each PET image. The SUVmax and Rad-score showed significant positive correlations with histopathology (p < .05). The area under the curve (AUC) of SUVmax for detecting AR was 0.783. The median AUC of ML models was 0.921, which was superior to that of logistic regression models (median AUC, 0.721). The optimal ML model using a random forest modeling algorithm with random forest feature selection method exhibited the highest AUC of 0.982 (95% confidence interval, 0.875-1.000) in all models. SUVmax provided a good correlation with AR, but ML-based PET radiomics further strengthened the power of 18F-FDG PET functional imaging for monitoring AR in LTx.

CD26-inhibition correlates with the absence of chronic lung allograft dysfunction and decreases fibroblast activity in vitro

Abstract Objective Chronic lung allograft dysfunction (CLAD) limits the survival after lung transplantation (Tx). CLAD is characterized by progressive fibrosis of small airways and lung parenchyma. No effective therapy is available that reverses or prevents CLAD. CD26 is a molecule with enzymatic activity also playing a key role in the progression of fibrotic diseases. Here, we analyzed the inhibitory effect of CD26 on fibroblast activity in vitro and the role of CD26-inhibition on allograft rejection in lung transplant patients. Methods Profibrogenic mRNA and protein levels were analyzed in vitro on the CD26-expressing fibroblast cell line Wi-38 using RT-qPCR and Western blot. CD26 was inhibited by Vildagliptin. Migration and proliferation activity of activated fibroblasts were analyzed by Incucyte® and Celltiter-Glo®. Characteristics of patients undergoing lung Tx between 2004 and 2021 were reviewed. Lung biopsies were analyzed by immunohistochemistry (IHC) for CD26. Results In vitro, the expression of profibrogenic genes (αSMA, FAPα, IGFBP7, Collagen 3 and Fibronectin) was significantly reduced in activated lung fibroblasts by Vildagliptin treatment. Also, migration and proliferation activity were attenuated by Vildagliptin. In 221 patients analyzed, CLAD was absent in 34 patients treated with the CD26-inhibitor Sitagliptin vs. an incidence of 18% in patients without Sitagliptin intake (p=0.02). Five-year survival in patients on Sitagliptin was significantly improved vs. patients without CD26-inhibitor intake (80% vs. 58%, p=0.006). Likewise, the incidence of acute cellular rejection (ACR) was significantly reduced in patients on Sitagliptin (7% vs. 35%, p=0.01). IHC of patient lung biopsies showed expression of CD26 in perifibrotic areas of CLAD lesions. Additional clinical data from University Hospital Zurich and from University Hospital Padua confirmed the finding that Sitagliptin intake correlated with the absence of acute and chronic allograft rejection. Conclusion CD26-inhibition attenuates key pro-fibrotic mediators and fibroblast activity in vitro. Impressively, patients on CD26-inhibitor did not show any CLAD. Moreover, ACR was significantly reduced. Gliptins which are in routine clinical use for the treatment of type II diabetes therefore seem to have great potential to be repurposed for a novel clinical application against lung allograft rejection.

Fibrosis of Chronic Lung Allograft Dysfunction After Orthotopic Lung Transplantation is Prevented in the Absence of Secondary Lymphoid Organs in a Mouse Model

<h3>Purpose</h3> It was reported that acute lung allograft rejection occurred without secondary lymphoid organs (SLOs) in a mouse allogenic lung transplantation model. The objective of this study was to investigate the role of SLOs in chronic lung allograft dysfunction (CLAD) after allogenic mouse lung transplantation using splenectomized alymphoplastic (aly/aly) mice as SLOs-deficient recipient. <h3>Methods</h3> Left lung of BALB/c mouse was transplanted into C57BL/6J (B6) or aly/aly mouse with B6 background. Low-dose cyclosporine (10 mg/kg, 3 times/week) and methylprednisolone (1.6 mg/kg, 3 times/week) were given in all the recipient mice until sacrifice. The recipient mice were sacrificed at day 15 (D15, n=4, each group) or day 30 (D30, n=5, each group) to evaluate histology. <h3>Results</h3> Allograft in B6 mice showed A2-3 rejection on D15 and A2-3 rejection with severe peri-airway and peri-vascular fibrosis on D30. On the contrary, allograft in aly/aly mouse showed A1-2 rejection on D15 and D30 without fibrosis (Figure 1). Quantification of peri-airway fibrosis thickness demonstrated significantly less fibrotic change in aly/aly mice than B6 mice on D30 (p = 0.012) (Figure 2). The A grade rejection score was significantly low on D30 in aly/aly mice (median A1, range A1-A2) than B6 mice (median A3, range A2-A3) (p = 0.015). <h3>Conclusion</h3> Fibrotic change with cellular rejection did not occur in the absence of SLOs in a mouse model of CLAD induced by inadequate immunosuppression, which may provide a platform for novel strategy to prevent CLAD.

Reduction of Immunosuppression Based on Whole Blood EBV-Viral Loads in Lung Transplant Recipients

<h3>Purpose</h3> Post-transplant lymphoproliferative disorder (PTLD) is a rare but serious complication of transplantation affecting 10% of lung transplant recipients with an overall survival of 39%. Reduction of immunosuppression (RIS) for clinically suspected PTLD is included in guidelines for the treatment of PTLD. Pre-emptive RIS based on EBV DNA load is controversial with small scale studies with anecdotal evidence guiding clinical practice. We evaluated our policy of pre-emptive RIS for PTLD incidence, acute rejection, survival and CLAD in a patient control study. <h3>Methods</h3> 26 patients underwent RIS, eight of these patients received prophylactic rituximab. 52 patients were matched for age, date of transplantation, gender, and cystic fibrosis. 26 of these patients were additionally chosen for high EBV-DNA load. Risk of PTLD, acute rejection, overall survival and CLAD was analysed using Kaplan-Meier survival analysis. <h3>Results</h3> EBV DNA loads were different between the groups (p<0.001) with the RIS group having the highest level and more primary EBV infections (table 1). Acute rejection was seen 7.3 years after RIS and 11.7 and 12.3 in the matched groups (p=0,1). Overall CLAD developed earlier in the RIS group but only years after RIS (table 1). Survival and development of PTLD were not different between the groups. Time to PTLD from RIS was also not different (p=0.5, log-rank test). <h3>Conclusion</h3> Pre-emptive RIS based on EBV DNA load did not lead to a concomitant increase in acute rejection episodes, a change in overall survival or a short term increase in chronic lung allograft rejection (CLAD) diagnosis. We conclude that RIS was safe although this analysis cannot prove a reduction in the incidence of PTLD in this high risk PTLD group. A prospective randomized study for EBV DNA guided RIS possibly with pre-emptive rituximab is needed.

Transcriptional Landscape of Chronic Lung Allograft Rejection in Humans

<h3>Purpose</h3> Chronic lung allograft dysfunction (CLAD) remains the main barrier to long-term survival after lung transplant. The main phenotypes of CLAD are bronchiolitis obliterans syndrome (BOS) with small airway fibrosis, and restrictive allograft syndrome (RAS) with extensive lung parenchymal fibrosis. Mechanisms of CLAD and the pathways active in BOS/RAS remain poorly understood. We hypothesized that bulk RNA sequencing (seq) of human CLAD lungs would help uncover pro-fibrotic pathways and phenotype-specific mechanisms. <h3>Methods</h3> At time of retransplantation, we obtained CLAD lung tissue from 27 BOS and 18 RAS. Negative controls included donor lungs (18) and lobectomy samples done for suspected cancers (14); positive controls came from patients with idiopathic pulmonary fibrosis (IPF) (19). RNA was extracted and submitted for bulk RNAseq at a depth of 50 million paired-end 100-base-pair reads. Differentially expressed genes were detected using DESeq2 and NOIseq. <h3>Results</h3> Top differentially expressed genes in CLAD vs. negative controls included genes involved in cell-matrix interactions (COL10A1, ADAM9) and cell proliferation (CST, MDK). Gene Ontology analysis showed higher expression of genes associated with fibrosis and motility, whereas genes involved in defense and immunity were decreased due to immunosuppression in CLAD vs. negative controls. Analyses to compare RAS to BOS are ongoing. As we anticipated an imperfect correlation between clinical phenotypes and transcriptomic endotypes, we performed unsupervised clustering of all samples. A subset of RAS/mixed samples clustered together and in close proximity to IPF, while other distinct clusters appeared independent of clinical phenotypes: These transcriptomic endotypes will merit further exploration. <h3>Conclusion</h3> This large cohort of lung samples allows a detailed analysis of the lung allograft transcriptome in different phenotypes of CLAD, enabling identification of the top differentially expressed genes and pathways in this poorly understood condition.

Transbronchial Cryobiopsy vs Conventional Forceps Biopsy in Lung Transplant Recipients Multicenter Study

<h3>Purpose</h3> Transbronchial biopsy is considered the gold standard in the diagnosis of acute cellular rejection after lung transplantation. There still remains the discussion in conventional forceps biopsy comparing to cryobiopsy in lung transplant recipients. This study aims to compare the diagnostic yield and potential complications in both procedures. <h3>Methods</h3> In retrospective multicenter study all transbronchial biopsies (TBBs) were evaluated since 2010 till 2019. Surveillance TBBs were performed in 1, 3, 6 and 12 months after lung transplantation. Additional diagnostic bronchoscopies were performed if clinically indicated. Pneumothorax was categorized as none, partial recovered without treatment and pneumothorax required inserting of chest drainage. Bleeding was predefined as none, mild bleeding requiring suction and instillation of cold saline solution and severe bleeding requiring additional instillation of adrenaline. TBBs were graded according to the International Society of Heart and Lung Transplantation (ISHLT) consensus guidelines for the diagnosis of lung allograft rejection. <h3>Results</h3> In 309 patients a total of 448 forceps biopsies and 573 cryobiopsies were performed. The incidence of pneumothorax was significantly (p<0,001) higher after forceps biopsies (9,2 % vs 3,3 %). Bleeding was significantly greater in the cryobiopsy group (cryobiopsy/forceps biopsy: no bleeding 80,4%/96,4%; mild 15,4%/2,4%; severe 4,2%/1.1%; p < 0.001). The mean size of cryo-specimen was five times larger than forceps-group samples. The diagnostic rate of acute rejection using cryobiopsy and forceps biopsy was similar A0 grade 36% vs 39%, A1 grade 46% vs 35%, A2 grade 14% vs 17,5%, A3-A4 grade 4% vs 8,5%. But evidently larger specimens from cryobiopsy catched the presence of bronchiolus in 51% compared with 8% from forceps samples which shows the major significance (p<0,001). <h3>Conclusion</h3> Transbronchial cryobiopsies compared to traditional forceps biopsies provided superior quality of the specimens with significantly higher capture of bronchiolus and lower rate of non-diagnostic samples which also enable potential possibility for futher evaluation of humoral and chronic rejection. Cryobiopsies reduce the number of specimens with acceptable complications.

MNK/eIF4E Ser209 Inhibitor eFT-508 Prevents and Therapeutically Treats Fibrosis in a Murine Model of Restrictive Chronic Lung Allograft Rejection

<h3>Purpose</h3> Lung transplant is limited by poor outcomes due to chronic lung allograft dysfunction, CLAD. A fulminant CLAD phenotype, restrictive allograft syndrome (RAS), with limited therapies underscores the need to understand underlying mechanisms. MNK1 kinase is a key translational regulator of cellular functions via eIF4E serine 209 phosphorylation. Here we investigate the role of MNK/eIF4E Ser209 in mesenchymal cell activation and the therapeutic effectiveness of eFT-508 in a murine model of RAS. <h3>Methods</h3> Human lung allograft derived MCs treated with eFT-508 (10uM x 24h) were immunoblotted for collagen I, alpha smooth muscle actin, CD44, autotaxin. A modified boyden chamber assay was utilized for migration. We recently reported a murine RAS model, B6D2F1/J into C57BL6/J. Mice were administered eFT-508 5mg/kg/daily/gavage in a preventive group days 7-28, or therapeutic group days 14-28. <h3>Results</h3> Human allograft derived MCs from CLAD patients demonstrated 4-fold increase in MNK1 (Thr197/202) and eIF4E Ser209 compared to non-fibrotic MCs. Upon eFT-508 treatment, we observed reduced eIF4E Ser209, collagen I, alpha smooth muscle actin and SPARC expression, and migration (n=7; p<0.05). CD44 and autotaxin protein expression was decreased upon eFT-508 treatment, along with secreted autotaxin activity (n=9; p=0.0005). <i>In vivo</i> preventive treatment with eFT-508 decreased airway fibrosis upon histological examination utilizing trichrome staining. Pleural thickness measurements were also reduced compared to vehicle treated controls. A significant reduction in hydroxyproline content, autotaxin secretion, and activity were also noted in eFT-508 treated transplant lung homogenates (n=7; p<0.001). Therapeutic treatment with eFT-508 reduced hydroxyproline content compared to vehicle treated allografts (n=4; p=0.0252). <h3>Conclusion</h3> MNK/eIF4E Ser209 inhibition reduced fibrotic protein expression and migration, demonstrating a role for this pathway in MC activation. <i>In vivo</i> MNK/eIF4E Ser209 inhibition reduced graft fibrosis by preventive and therapeutic treatment regimens in a murine model of RAS. This data highlights a novel therapeutic option for preventing development and progression of RAS.

Quantitative CT Correlates with Local Inflammation in Lung of Patients with Subtypes of Chronic Lung Allograft Dysfunction.

Chronic rejection of lung allografts has two major subtypes, bronchiolitis obliterans syndrome (BOS) and restrictive allograft syndrome (RAS), which present radiologically either as air trapping with small airways disease or with persistent pleuroparenchymal opacities. Parametric response mapping (PRM), a computed tomography (CT) methodology, has been demonstrated as an objective readout of BOS and RAS and bears prognostic importance, but has yet to be correlated to biological measures. Using a topological technique, we evaluate the distribution and arrangement of PRM-derived classifications of pulmonary abnormalities from lung transplant recipients undergoing redo-transplantation for end-stage BOS (N = 6) or RAS (N = 6). Topological metrics were determined from each PRM classification and compared to structural and biological markers determined from microCT and histopathology of lung core samples. Whole-lung measurements of PRM-defined functional small airways disease (fSAD), which serves as a readout of BOS, were significantly elevated in BOS versus RAS patients (p = 0.01). At the core-level, PRM-defined parenchymal disease, a potential readout of RAS, was found to correlate to neutrophil and collagen I levels (p < 0.05). We demonstrate the relationship of structural and biological markers to the CT-based distribution and arrangement of PRM-derived readouts of BOS and RAS.

Risk Factors for Bile Aspiration and its Impact on Clinical Outcomes.

INTRODUCTION:Bile reflux may cause for lung allograft rejection, yet there are no studies that determine (i) the relationship between gastric and lung bile concentrations, (ii) whether bile is present in lungs of nontransplant patients, (iii) the relationship between gastric dysmotility and lung bile, (iv) the impact of reflux therapies on lung bile, and (v) whether lung bile worsens outcomes in nontransplant patients. This study will address these gaps in the literature.METHODS:We prospectively recruited lung transplant (LTX) patients and nontransplant patients with respiratory symptoms (RP) and collected paired gastric and lung samples. Bile concentration and composition of samples was assessed using liquid chromatography–mass spectrometry. Bile results were compared with clinical parameters, including the presence of esophagitis, gastric dysmotility, and/or pathologic gastroesophageal reflux.RESULTS:Seventy patients (48 RP and 22 LTX) were recruited. Overall, 100% of gastric and 98% of bronchoalveolar lavage samples contained bile. The mean gastric bile concentrations in RP and LTX patients were 280 ± 703 nmol/L and 1,004 ± 1721 nmol/L, respectively (P = 0.02). There was no difference in lung bile concentrations between RP (9 ± 30 nmol/L) and LTX (11 ± 15 nmol/L, P = 0.7). Patients with delayed gastric emptying had higher lung bile concentrations (15.5 ± 18.8 nmol/L) than patients with normal gastric emptying (4.8 ± 5.7 nmol/L, P = 0.05) independently of reflux burden. Proton pump inhibitor use increased the proportion of unconjugated gastric bile acids. High lung bile concentrations were associated with an increased risk of hospitalization and longer hospital stays in RP patients (P < 0.05).DISCUSSION:Lung bile is almost universally present in symptomatic patients, and higher concentrations are associated with poorer respiratory outcomes.

Blocking hyaluronan synthesis alleviates acute lung allograft rejection.

Lung allograft rejection results in the accumulation of low–molecular weight hyaluronic acid (LMW-HA), which further propagates inflammation and tissue injury. We have previously shown that therapeutic lymphangiogenesis in a murine model of lung allograft rejection reduced tissue LMW-HA and was associated with improved transplant outcomes. Herein, we investigated the use of 4-Methylumbelliferone (4MU), a known inhibitor of HA synthesis, to alleviate acute allograft rejection in a murine model of lung transplantation. We found that treating mice with 4MU from days 20 to 30 after transplant was sufficient to significantly improve outcomes, characterized by a reduction in T cell–mediated lung inflammation and LMW-HA content and in improved pathology scores. In vitro, 4MU directly attenuated activation, proliferation, and differentiation of naive CD4+ T cells into Th1 cells. As 4MU has already been demonstrated to be safe for human use, we believe examining 4MU for the treatment of acute lung allograft rejection may be of clinical significance.

A decline in club cell secretory proteins in lung transplantation is associated with release of natural killer cells exosomes leading to chronic rejection

In human lung transplant recipients, a decline in club cell secretory protein (CCSP) in bronchoalveolar lavage fluid has been associated with chronic lung allograft dysfunction (CLAD) as well as the induction of exosomes and immune responses that lead to CLAD. However, the mechanisms by which CCSP decline contributes to CLAD remain unknown. To define the mechanisms leading to CCSP decline and chronic rejection, we employed two mouse models: 1) chronic rejection after orthotopic single lung transplantation and 2) anti-major histocompatibility complex (MHC) class I-induced obliterative airway disease. In the chronic rejection mouse model, we detected circulating exosomes with donor MHC (H2b) and lung self-antigens and also development of antibodies to H2b and lung self-antigens and then a decline in CCSP. Furthermore, DBA2 mice that received injections of these exosomes developed antibodies to donor MHC and lung self-antigens. In the chronic rejection mouse model, natural killer (NK) and CD8 T cells were the predominant graft-infiltrating cells on day 14 of rejection followed by exosomes containing NK cell-associated and cytotoxic molecules on day 14 and 28. When NK cells were depleted, exosomes with NK cell-associated and cytotoxic molecules as well as fibrosis decreased. Induction of exosomes led to immune responses to donor MHC and lung self-antigens, resulting in CCSP decline, leading to NK cell infiltration and release of exosomes from NK cells. These results suggest a novel role for exosomes derived from NK cells in the pathogenesis of chronic lung allograft rejection.

Impact of COVID-19 on Lung Allograft and Clinical Outcomes in Lung Transplant Recipients: A Case-control Study.

The impacts of COVID-19 on lung allograft function, rejection, secondary infection, and clinical outcomes in lung transplant recipients (LTRs) remain unknown. A 1:2 matched case-control study was performed to evaluate rehospitalization, lung allograft function, and secondary infections up to 90 d after COVID-19 diagnosis (or index dates for controls). Twenty-four LTRs with COVID-19 (cases) and 48 controls were identified. Cases and controls had similar baseline characteristics and lung allograft function. LTRs with COVID-19 had higher incidence of secondary bacterial infection (29.2% versus 6.3%, P = 0.008), readmission (29.2% versus 10.4%, P = 0.04), and for-cause bronchoscopy (33.3% versus 12.5%, P = 0.04) compared with controls. At d 90, mortality in cases versus controls was 8.3% versus 2.1% (P = 0.21), incidence of invasive fungal infections in cases versus controls was 20.8% versus 8.3% (P = 0.13) and forced expiratory volume in 1 s (FEV1) decline ≥10% from baseline occurred in 19% of cases versus 12.2% of controls (P = 0.46). No acute cellular rejection, acute antibody-mediated rejection, or new donor-specific anti-HLA antibodies were observed among cases or controls within 90 d post index date. We found LTRs with COVID-19 were at risk to develop secondary infections and rehospitalization post COVID-19, compared with controls. While we did not observe post viral acute cellular rejection or antibody-mediated rejection, further studies are needed to understand if LTRs with COVID-19 who did not recover baseline lung function within 90 d have developed chronic lung allograft dysfunction stage progression.

Immune Checkpoints Expression in Chronic Lung Allograft Rejection.

Chronic lung allograft dysfunction (CLAD) is the main cause of poor survival and low quality of life of lung transplanted patients. Several studies have addressed the role of dendritic cells, macrophages, T cells, donor specific as well as anti-HLA antibodies, and interleukins in CLAD, but the expression and function of immune checkpoint molecules has not yet been analyzed, especially in the two CLAD subtypes: BOS (bronchiolitis obliterans syndrome) and RAS (restrictive allograft syndrome). To shed light on this topic, we conducted an observational study on eight consecutive grafts explanted from patients who received lung re-transplantation for CLAD. The expression of a panel of immune molecules (PD1/CD279, PDL1/CD274, CTLA4/CD152, CD4, CD8, hFoxp3, TIGIT, TOX, B-Cell-Specific Activator Protein) was analyzed by immunohistochemistry in these grafts and in six control lungs. Results showed that RAS compared to BOS grafts were characterized by 1) the inversion of the CD4/CD8 ratio; 2) a higher percentage of T lymphocytes expressing the PD-1, PD-L1, and CTLA4 checkpoint molecules; and 3) a significant reduction of exhausted PD-1-expressing T lymphocytes (PD-1pos/TOXpos) and of exhausted Treg (PD-1pos/FOXP3pos) T lymphocytes. Results herein, although being based on a limited number of cases, suggest a role for checkpoint molecules in the development of graft rejection and offer a possible immunological explanation for the worst prognosis of RAS. Our data, which will need to be validated in ampler cohorts of patients, raise the possibility that the evaluation of immune checkpoints during follow-up offers a prognostic advantage in monitoring the onset of rejection, and suggest that the use of compounds that modulate the function of checkpoint molecules could be evaluated in the management of chronic rejection in LTx patients.

Antibody-Mediated Rejection and Lung Transplantation.

Antibody-mediated rejection (AMR) is now a widely recognized form of lung allograft rejection, with mounting evidence for AMR as an important risk factor for the development of chronic lung allograft dysfunction and markedly decreased long-term survival. Despite the recent development of the consensus diagnostic criteria, it remains a challenging diagnosis of exclusion. Furthermore, even after diagnosis, treatment directed at pulmonary AMR has been nearly exclusively derived from practices with other solid-organ transplants and other areas of medicine, such that there is a significant lack of data regarding the efficacy for these in pulmonary AMR. Lastly, outcomes after AMR remain quite poor despite aggressive treatment. In this review, we revisit the history of AMR in lung transplantation, describe our current understanding of its pathophysiology, discuss the use and limitations of the consensus diagnostic criteria, review current treatment strategies, and summarize long-term outcomes. We conclude with a synopsis of our most pressing gaps in knowledge, introduce recommendations for future directions, and highlight promising areas of active research.

Lung Transplantation: CT Assessment of Chronic Lung Allograft Dysfunction (CLAD).

Chronic lung allograft rejection remains one of the major causes of morbi-mortality after lung transplantation. The term Chronic Lung Allograft Dysfunction (CLAD) has been proposed to describe the different processes that lead to a significant and persistent deterioration in lung function without identifiable causes. The two main phenotypes of CLAD are Bronchiolitis Obliterans Syndrome (BOS) and Restrictive Allograft Syndrome (RAS), each of them characterized by particular functional and imaging features. These entities can be associated (mixed phenotype) or switched from one to the other. If CLAD remains a clinical diagnosis based on spirometry, computed tomography (CT) scan plays an important role in the diagnosis and follow-up of CLAD patients, to exclude identifiable causes of functional decline when CLAD is first suspected, to detect early abnormalities that can precede the diagnosis of CLAD (particularly RAS), to differentiate between the obstructive and restrictive phenotypes, and to detect exacerbations and evolution from one phenotype to the other. Recognition of early signs of rejection is crucial for better understanding of physiopathologic pathways and optimal management of patients.

IL-17 Receptor on Donor Cells Regulates Acute and Chronic Lung Allograft Rejection Potentiated by Repeated Endotoxin Inhalations

<h3>Purpose</h3> Chronic lung allograft dysfunction is a major complication after lung transplantation (LTx). Excessive IL17 receptor A (IL17RA) signaling has been recognized as a key factor; however, its precise mechanism is unclear. In a mouse minor alloantigen mismatched LTx model (C57BL/10 [B10, H-2^b] → C57BL/6 [B6. H-2^b]), we found that repeated airway endotoxin (lipopolysaccharide, LPS) challenge augments airway epithelial damage, acute and chronic rejection with airway obliteration, together with increased IL17A transcription in allografts but not isografts. We hypothesized that both donor and recipient cell responses to IL17A are important in mediating these processes. We therefore investigated the role of IL17RA on donor and recipient cells in the context of chronic rejection. <h3>Methods</h3> B10→B6 LTx and B6→B10 LTx were performed with or without intratracheal LPS administration (5 ug LPS/50 ul PBS, Day 3, 7, 10, 14, 17, 21). B6 IL17RA^−/− mice were used as donors or recipients. Grafts were assessed with micro CT scans on days 3 and 27; histological scoring and quantitative PCR were performed 28 days after LTx. <h3>Results</h3> Without LPS, neither donor nor recipient IL17RA deficiency modified histological scores or lung graft volume or density by CT scan. LPS-treated IL17RA^−/− recipients showed a similar degree of lung radiographic change and histological acute rejection compared to IL17RA^+/+ recipients; however airway obliteration was attenuated (Figure A). In contrast, recipients of IL17RA^−/− donor lungs showed reduced gain of graft density on CT, and diminished acute rejection and peri-airway fibrosis (Figure B-C). IL17RA^−/− donor grafts had fewer CXCL1 (a neutrophil chemoattractant) transcripts (Figure D). <h3>Conclusion</h3> IL17RA signaling on donor cells regulates acute and chronic rejection in LTx recipients experiencing airway inflammation.