Successful lung transplantation in genetic methionyl-tRNA synthetase-related alveolar proteinosis/lung fibrosis without recurrence under methionine supplementation: Medium-term outcome in 4 cases.

Pulmonary alveolar proteinosis (PAP) results from the accumulation of lipoproteinaceous material in the alveoli and alveolar macrophages, and can be associated with pulmonary fibrosis, with a need for lung transplantation (LTx). Causes of PAP are autoimmune (90%-95%), secondary (5%), or hereditary (<1%). Patients with hereditary PAP are generally not considered for isolated LTx, due to the high probability of recurrence after LTx, and only a challenging scenario with sequential LTx followed by hematopoietic stem cell transplantation (HSCT) was reported as successful. Recently, a new genetic cause of PAP linked to mutations in the methionyl-tRNA synthetase (MARS) gene has been reported, with a highly variable clinical presentation. Because clinical correction of the defective MARS activity with methionine supplementation has been reported in nontransplanted children, we reassessed the feasibility of LTx for candidates with MARS-related PAP/fibrosis. We report 3 cases of LTx performed for MARS-related pulmonary alveolar proteinosis-pulmonary fibrosis without recurrence under methionine supplementation, whereas another fourth case transplanted without supplementation had fatal PAP recurrence. These results suggest the effectiveness of methionine in correcting defective MARS activity and also looking for this very rare diagnosis in case of unclassified PAP/fibrosis. It argues for not excluding the feasibility of isolated LTx in patients with MARS mutation.

Refractory Microascus Bronchopulmonary Infection Treated with Olorofim, France.

We report 3 cases of successful treatment of Microascus spp. bronchopulmonary infection in a multiple-traumatized patient and 2 lung transplant recipients in France. We emphasize the promising use of olorofim antifungal therapy in a rising context of intrinsically less-susceptible respiratory infections caused by mold.

Results of Lung Transplantation for Cystic Fibrosis With Selected Donors Over 65 Years Old.

Lung transplantation is limited by the shortage of suitable donors. Many programs have begun to use extended criteria donors. Donors over 65 years old are rarely reported, especially for young cystic fibrosis recipients. This monocentric study was conducted for cystic fibrosis recipients from January 2005 to December 2019, comparing two cohorts according to lung donor age (<65 years or ≥65 years). The primary objective was to assess the survival rate at 3 years using a Cox multivariable model. Of the 356 lung recipients, 326 had donors under 65 years, and 30 had donors over 65 years. Donors' characteristics did not differ significantly in terms of sex, time on mechanical ventilation before retrieval, and partial pressure of arterial oxygen/fraction of inspired oxygen ratio. There were no significant differences in post-operative mechanical ventilation duration and incidence of grade 3 primary graft dysfunction between the two groups. At 1, 3, and 5 years, the percentage of predicted forced expiratory volume in 1 s (p = 0.767) and survival rate did not differ between groups (p = 0.924). The use of lungs from donors over 65 years for cystic fibrosis recipients allows extension of the donor pool without compromising results. Longer follow-up is needed to assess the long-term effects of this practice.

Systems prediction of chronic lung allograft dysfunction: Results and perspectives from the Cohort of Lung Transplantation and Systems prediction of Chronic Lung Allograft Dysfunction cohorts.

Background: Chronic lung allograft dysfunction (CLAD) is the leading cause of poor long-term survival after lung transplantation (LT). Systems prediction of Chronic Lung Allograft Dysfunction (SysCLAD) aimed to predict CLAD. Methods: To predict CLAD, we investigated the clinicome of patients with LT; the exposome through assessment of airway microbiota in bronchoalveolar lavage cells and air pollution studies; the immunome with works on activation of dendritic cells, the role of T cells to promote the secretion of matrix metalloproteinase-9, and subpopulations of T and B cells; genome polymorphisms; blood transcriptome; plasma proteome studies and assessment of MSK1 expression. Results: Clinicome: the best multivariate logistic regression analysis model for early-onset CLAD in 422 LT eligible patients generated a ROC curve with an area under the curve of 0.77. Exposome: chronic exposure to air pollutants appears deleterious on lung function levels in LT recipients (LTRs), might be modified by macrolides, and increases mortality. Our findings established a link between the lung microbial ecosystem, human lung function, and clinical stability post-transplant. Immunome: a decreased expression of CLEC1A in human lung transplants is predictive of the development of chronic rejection and associated with a higher level of interleukin 17A; Immune cells support airway remodeling through the production of plasma MMP-9 levels, a potential predictive biomarker of CLAD. Blood CD9-expressing B cells appear to favor the maintenance of long-term stable graft function and are a potential new predictive biomarker of BOS-free survival. An early increase of blood CD4 + CD57 + ILT2+ T cells after LT may be associated with CLAD onset. Genome: Donor Club cell secretory protein G38A polymorphism is associated with a decreased risk of severe primary graft dysfunction after LT. Transcriptome: blood POU class 2 associating factor 1, T-cell leukemia/lymphoma domain, and B cell lymphocytes, were validated as predictive biomarkers of CLAD phenotypes more than 6 months before diagnosis. Proteome: blood A2MG is an independent predictor of CLAD, and MSK1 kinase overexpression is either a marker or a potential therapeutic target in CLAD. Conclusion: Systems prediction of Chronic Lung Allograft Dysfunction generated multiple fingerprints that enabled the development of predictors of CLAD. These results open the way to the integration of these fingerprints into a predictive handprint.

Conversion to belatacept after lung transplantation: Report of 10 cases.

BACKGROUND: Calcineurin inhibitors (CNIs) remain the cornerstone of maintenance immunosuppression (IS) after lung transplantation (LTx), although CNI-related life-threatening toxic effects may occur. Belatacept, a novel immunosuppressant that blocks a T-cell co-stimulation pathway, is a non-nephrotoxic drug indicated as an alternative to CNIs in kidney Tx. In LTx, there are only a few reports of belatacept conversion as a CNI-free or CNI-sparing IS treatment. METHODS: We reviewed a series of 10 LTx recipients with conversion to a CNI-free belatacept IS regimen within the first year post-LTx (n = 7) or a belatacept/low-dose CNI combination after the first year (n = 3). RESULTS: Use of belatacept was triggered by severe renal failure in 9 patients and under-IS with previous other IS-related toxicities in 1 patient. Mean estimated glomerular filtration rate after starting belatacept significantly improved at 6 months after initiation and at the last-follow-up (p = 0.006, and p = 0.002 respectively). The incidence of recurrent and/or severe acute cellular rejection (ACR) episodes was high in patients with CNI-free belatacept-based IS (n = 4/7). Chronic graft allograft dysfunction developed in 2 of 9 recipients under belatacept IS. Belatacept was stopped in 6 patients because of recurrent/severe ACR (n = 3), recurrent opportunistic infections (n = 1), center modified policy (n = 1), or other cause (n = 1). CONCLUSION: Early conversion to CNI-free belatacept-based IS improved renal function in this series but was counterbalanced by a high incidence of recurrent ACR, including life-threatening episodes. Other studies are needed to better determine the indications for its use after LTx, possibly with lower immunological risk IS regimens, such as CNI-sparing belatacept.

First use of imlifidase desensitization in a highly sensitized lung transplant candidate: a case report.

Lung transplant candidates who are highly sensitized against human leucocyte antigen present an ongoing challenge with regards to finding immunologically acceptable donors. Desensitization strategies aimed at reducing preformed donor-specific antibodies have a number of limitations. Imlifidase, an IgG-degrading enzyme derived from Streptococcus pyogenes, is a novel agent that has been used to convert positive crossmatches to negative in kidney transplant candidates, allowing transplantation to occur. We present the first case of imlifidase use for antibody depletion in a highly sensitized lung transplant candidate who went on to undergo a successful bilateral lung transplant.

2022 Update of indications and contraindications for lung transplantation in France.

Lung transplantation (LTx) is a steadily expanding field. The considerable developments have been driven over the years by indefatigable work conducted at LTx centers to improve donor and recipient selection, combined with multifaceted efforts to overcome challenges raised by the surgical procedure, perioperative care, and long-term medical complications. One consequence has been a pruning away of contraindications over time, which has, in some ways, complicated the patient selection process. The Francophone Pulmonology Society (Société de Pneumology de Langue Française, SPLF) set up a task force to produce up-to-date working guidelines designed to assist pulmonologists in managing end-stage respiratory insufficiency, determining which patients may be eligible for LTx, and appropriately timing LTx-center referral. The task force examined the most recent literature and evaluated the risk factors that limit patient survival after LTx. Ideally, the objectives of LTx are to prolong life while also improving quality of life. The guidelines developed by the task force apply to a limited resource and are consistent with the ethical principles described below.

Inverted direct allorecognition triggers early donor-specific antibody responses after transplantation.

The generation of antibodies against donor-specific major histocompatibility complex (MHC) antigens, a type of donor-specific antibodies (DSAs), after transplantation requires that recipient's allospecific B cells receive help from T cells. The current dogma holds that this help is exclusively provided by the recipient's CD4+ T cells that recognize complexes of recipient's MHC II molecules and peptides derived from donor-specific MHC alloantigens, a process called indirect allorecognition. Here, we demonstrated that, after allogeneic heart transplantation, CD3ε knockout recipient mice lacking T cells generate a rapid, transient wave of switched alloantibodies, predominantly directed against MHC I molecules. This is due to the presence of donor CD4+ T cells within the graft that recognize intact recipient's MHC II molecules expressed by B cell receptor-activated allospecific B cells. Indirect evidence suggests that this inverted direct pathway is also operant in patients after transplantation. Resident memory donor CD4+ T cells were observed in perfusion liquids of human renal and lung grafts and acquired B cell helper functions upon in vitro stimulation. Furthermore, T follicular helper cells, specialized in helping B cells, were abundant in mucosa-associated lymphoid tissue of lung and intestinal grafts. In the latter, more graft-derived passenger T cells correlated with the detection of donor T cells in recipient's circulation; this, in turn, was associated with an early transient anti-MHC I DSA response and worse transplantation outcomes. We conclude that this inverted direct allorecognition is a possible explanation for the early transient anti-MHC DSA responses frequently observed after lung or intestinal transplantations.

Chronic lung allograft dysfunction is associated with an early increase of circulating cytotoxic CD4+CD57+ILT2+ T cells, selectively inhibited by the immune check-point HLA-G.

BACKGROUND: Survival after lung transplantation (LTx) still remains limited by chronic lung allograft dysfunction (CLAD), thought to represent a form of chronic rejection. We investigated whether the immune checkpoint HLA-G/ILT2 expressed by peripheral T-cell subpopulations could predict CLAD. METHODS: We used data for 150 LTx recipients from COLT (Cohort-For-Lung-Transplantation) cohort with ≥1 available blood sample at 1-, 6-, or 12-months post-Tx. Analysis of T cells by flow cytometry focused on the ILT2 receptor of HLA-G and other markers (CD57, CD25, CD127). T-cell subset analyses compared stable patients and those with CLAD at 3 years post-LTx. RESULTS: With data for 78 stable and 72 CLAD patients, among 21 T-cell subsets expressing ILT2, only CD4+CD57+ILT2+ T cells were associated with outcome. At 1-month post-Tx, low proportion of CD4+CD57+ILT2+ T cells was associated with reduced 3-year incidence of CLAD (CD4+CD57+ILT2+ T cells ≤ first IQR [25%] vs > first IQR, log-rank test, p = 0.028). Furthermore, the incidence of CLAD was higher with >2.6- vs ≤2.6-fold increased proportion of CD4+CD57+ILT2+ T cells over the first year post-LTx (3-year freedom frequencies: 27% [95%CI: 8-50] vs 64% [95%CI: 48-77] (log-rank test, p = 0.014). On multivariable analysis, increased proportion of CD4+CD57+ILT2+ T cells over the first year predicted CLAD (hazard ratio 1.25; 95%CI: 1.09-1.44; p = 0.001). Focusing on CD4+CD57+ILT2+ T cells, we demonstrated ex vivo that they are cytotoxic CD4+ T cells, selectively inhibited by HLA-G. CONCLUSIONS: Our data suggest that an early increase of CD4+CD57+ILT2+ T cells after LTx may be associated with CLAD onset.

Blood Lactate During Double-Lung Transplantation: A Predictor of Grade-3 Primary Graft Dysfunction.

OBJECTIVE: Many prognostic factors of grade-3 primary graft dysfunction at postoperative day 3 (PGD3-T72) have been reported, but intraoperative blood lactate level has not been studied. The present retrospective study was done to test the hypothesis that intraoperative blood lactate level (BLL) could be a predictor of PGD3-T72 after double-lung transplantation. DESIGN: Retrospective monocentric cohort study. SETTING: Foch University Hospital, Suresnes, France. PARTICIPANTS: Patients having received a double-lung transplantation between 2012 and 2019. Patients transplanted twice during the study period, having undergone a multiorgan transplantation, or cardiopulmonary bypass, and those under preoperative extracorporeal membrane oxygenation, were excluded. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Analysis was performed on a cohort of 449 patients. Seventy-two (16%) patients had a PGD3-T72. Blood lactate level increased throughout surgery to reach a median value of 2.2 (1.6-3.2) mmol/L in the No-PGD3-T72 group and 3.4 (2.3-5.0) mmol/L in the PGD3-T72 group after second lung implantation. The best predictive model for PGD3-T72 was obtained adding a lactate threshold of 2.6 mmol/L at the end of surgery to the clinical model, and the area under the curve was 0.867, with a sensitivity = 76.9% and specificity = 85.4%. Repeated-measures mixed model of BLL during surgery remained significant after adjustment for covariates (F ratio= 4.22, p < 0.001 for interaction). CONCLUSIONS: Blood lactate level increases during surgery and reaches a maximum after the second lung implantation. A value below the threshold of 2.6 mmol/L at the end of surgery has a high negative predictive value for the occurrence of a grade-3 primary graft dysfunction at postoperative day 3.

Disease progression in patients with the restrictive and mixed phenotype of Chronic Lung Allograft dysfunction-A retrospective analysis in five European centers to assess the feasibility of a therapeutic trial.

BACKGROUND: Chronic Lung Allograft Dysfunction (CLAD) is a major obstacle for long term survival after lung transplantation (LTx). Besides Bronchiolitis Obliterans Syndrome, two other phenotypes of CLAD, restrictive allograft syndrome (RAS) and mixed phenotype, have been described. Trials to test in these conditions are desperately needed and analyzing natural outcome to plan such trials is essential. METHODS: We performed a retrospective analysis of functional outcome in bilateral LTx recipients with RAS and mixed phenotype, transplanted between 2009 and 2018 in five large European centers with follow- up spirometry up to 12 months after diagnosis. Based on these data, sample size and power calculations for randomized therapeutic trial was estimated using two imputation methods for missing values. RESULTS: Seventy patients were included (39 RAS and 31 mixed phenotype), median 3.1 years after LTx when CLAD was diagnosed. Eight, 13 and 25 patients died within 6, 9 and 12 months after diagnosis and a two patients underwent re-transplantation within 12 months leading to a graft survival of 89, 79 and 61% six, nine and 12 months after diagnosis, respectively. Observed FEV1 decline was 451 ml at 6 months and stabilized at 9 and 12 months, while FVC showed continuous decline. Using two methods of imputation, a progressive further decline after 6 months for FEV1 was noted. CONCLUSION: The poor outcome of these two specific CLAD phenotypes suggests the urgent need for future therapeutic randomized trials. The number of missing values in a potential trial seems to be high and most frequently attributed to death. Survival may be used as an endpoint in clinical trials in these distinct phenotypes and imputation techniques are relevant if graft function is used as a surrogate of disease progression in future trials.

COVID-19 in Lung Transplant Recipients: 2 Cases With Acute Respiratory Distress Syndrome Successfully Treated With High-Dose Corticosteroids.

Acute respiratory distress syndrome remains the main cause of death among people with COVID-19. Although many immunomodulatory and antiviral drug therapies have been tested, the only effective therapy against severe COVID-19 pneumonia among the general population is a regimen of high-dose corticosteroids for cases of severe associated inflammation. In solid-organ transplant recipients with long-term immunosuppression, data on disease presentation and evolution are scarce, and the benefit of high-dose corticosteroids remains uncertain for cases of severe COVID-19 pneumonia. Here, we report 2 cases of COVID-19-related acute respiratory distress syndrome that occurred in lung transplant recipients in March and April 2020, respectively. Both cases of acute respiratory distress syndrome occurred in patients with long-term azithromycin treatment prescribed to prevent chronic allograft dysfunction. Acute respiratory distress syndrome was associated with severe inflammation and was cured after early administration of high-dose corticosteroids in both cases, with progressive and complete resolution of lung lesions evidenced on thoracic computed tomography scan. Our findings support the benefit of early high-dose corticosteroids in COVID-19-related acute respiratory distress syndrome with hyperinflammation in patients with long-term immunosuppression such as lung transplant recipients.

A virtual crossmatch-based strategy for perioperative desensitisation in lung transplant recipients with pre-formed donor-specific antibodies: 3-year outcome.

BACKGROUND: Pre-formed donor-specific antibodies (DSAs) are associated with worse outcome after lung transplantation (LTx) and might limit access to LTx. A virtual crossmatch-based strategy for perioperative desensitisation protocol has been used for immunised LTx candidates since 2012 at Foch Hospital (Suresnes, France). We compared the outcome of desensitised LTx candidates with high DSA mean fluorescence intensity and those with low or no pre-formed DSAs, not desensitised. METHODS: For all consecutive LTx recipients (January 2012 to March 2018), freedom from chronic lung allograft dysfunction (CLAD) and graft survival were assessed using Kaplan-Meier analysis and Cox multivariate analysis. RESULTS: We compared outcomes for desensitised patients with high pre-formed DSAs (n=39) and those with no (n=216) or low pre-formed DSAs (n=66). The desensitisation protocol decreased the level of immunodominant DSA (class I/II) at 1, 3 and 6 months post-LTx (p<0.001, p<0.01 and p<0.001, respectively). Freedom from CLAD and graft survival at 3 years was similar in the desensitised group as a whole and other groups. Nevertheless, incidence of CLAD was higher with persistent high-level DSAs than cleared high-level (p=0.044) or no DSAs (p=0.014). Conversely, graft survival was better with cleared high DSAs than persistent high-level, low-level and no pre-formed DSAs (p=0.019, p=0.025 and p=0.044, respectively). On multivariate analysis, graft survival was associated with cleared high DSAs (hazard ratio 0.12, 95% CI 0.02-0.85 versus no DSAs; p=0.035) and CLAD with persistent DSAs (3.04, 1.02-9.17 versus no pre-formed DSAs; p=0.048). CONCLUSION: The desensitisation protocol in LTx recipients with high pre-formed DSAs was associated with satisfactory outcome, with cleared high pre-formed DSAs after desensitisation identified as an independent predictor of graft survival.

Pneumocystis pneumonia after lung transplantation: A retrospective multicenter study.

BACKGROUND: Lung transplantation (LT) is an identified risk factor for Pneumocystis pneumonia (PCP). However, PCP management and outcomes remain poorly described in LT recipients and PCP incidence is rarely documented in this population. METHODS: PCP episodes that occurred in 9 French LT centers between January 2010 and October 2017 were included in this analysis. PCP was defined as compatible clinical and radiologic findings associated with fungal identification. RESULTS: Forty-seven PCP were included. The annual incidence rate of PCP was 2.7/1000 patients/year. Patients had a mean age of 53 ± 14 years. Median time from LT was 2.4 ± 3.0 years. Sixty-five percent of patients were not on prophylaxis at the time of PCP while all patients were receiving steroids at the time of PCP. Diagnosis was obtained by bronchoalveolar lavage in 91% (direct examination: 47%, PCR: 62%). The majority of patients were treated with trimethoprim-sulfamethoxazole (78%). Fifty-five percent of patients were hospitalized in ICU for organ failure (for which non-invasive ventilation was used for 21% and mechanical ventilation for 23%). Mortality rate was 15% at day 28 and reached 23% at day 90. Mortality was associated with decreased FEV1, everolimus treatment, Pseudomonas aeruginosa coinfection, fungal coinfection (especially Aspergillus sp.), mechanical ventilation and vasopressors. PCP primary prophylaxis, steroid modification during PCP and the number of immunosuppressive molecules were not associated with mortality. CONCLUSION: PCP is associated with a high mortality in LT. Our data suggest the need for a lifetime PCP prophylaxis in LT recipients. The benefit of adjuvant steroids remains unclear.

Use of CT-SCAN score and volume measures to early identify restrictive allograft syndrome in single lung transplant recipients.

BACKGROUND: Restrictive allograft syndrome (RAS) after lung transplantation (LTx) is associated with the poorer graft survival in patients with chronic lung allograft dysfunction (CLAD). Nevertheless, its diagnostic criteria have not been clearly defined after single-LTx (SLTx). Hence, we studied an SLTx cohort with CLAD to investigate the utility of both computed tomography (CT)-score/volume measures and functional spirometric criteria for the early identification of RAS in this population. METHODS: We included 51 patients with SLTx (17 RAS, 17 bronchiolitis obliterans syndrome [BOS], and 17 stable condition). The criteria for RAS diagnosis in SLTx included forced vital capacity (FVC) <80% baseline (BL) or forced expiratory volume in 1 second (FEV1) <80% BL with an FEV1/FVC ratiounchanged or >0.7 and persistent CT-scan-lung opacities. We defined 4 time points (T): T-baseline, T-onset (first CT-scan-opacities), T-follow-up, and T-last. RESULTS: In patients with RAS, the spirometric criteria for RAS at T-onset were reached in only 47% (FVC decline <80% BL [(29%] or FEV1 <80% BL/ratiounchanged or >0.7 [41%]), whereas at the same T-onset date, the graft CT-score increased to 5 (4-6) vs 1 (0-2) at baseline (p < 0.001) (CT - score ≥2 at T-onset in 100% and ΔCT - score ≥2 in 74% of patients with RAS), and the median CT-scan graft volume decreased to 1,722 ml (vs 1,796 ml at T-baseline, p = 0.003) (decreased CT-graft - volume <90% BL in 50% of patients). In contrast, in patients with BOS, CT-score/volume were unchanged at T-onset vs T-baseline (p = 0.8, p = 0.68, respectively). CONCLUSION: Our results suggest that the use of a simple CT-score and to a lesser extent, CT-volume measures, might allow for the early identification and/or prediction of RAS in SLTx rather than functional criteria.

Blood CD9+ B cell, a biomarker of bronchiolitis obliterans syndrome after lung transplantation.

Bronchiolitis obliterans syndrome is the main limitation for long-term survival after lung transplantation. Some specific B cell populations are associated with long-term graft acceptance. We aimed to monitor the B cell profile during early development of bronchiolitis obliterans syndrome after lung transplantation. The B cell longitudinal profile was analyzed in peripheral blood mononuclear cells from patients with bronchiolitis obliterans syndrome and patients who remained stable over 3 years of follow-up. CD24hi CD38hi transitional B cells were increased in stable patients only, and reached a peak 24 months after transplantation, whereas they remained unchanged in patients who developed a bronchiolitis obliterans syndrome. These CD24hi CD38hi transitional B cells specifically secrete IL-10 and express CD9. Thus, patients with a total CD9+ B cell frequency below 6.6% displayed significantly higher incidence of bronchiolitis obliterans syndrome (AUC = 0.836, PPV = 0.75, NPV = 1). These data are the first to associate IL-10-secreting CD24hi CD38hi transitional B cells expressing CD9 with better allograft outcome in lung transplant recipients. CD9-expressing B cells appear as a contributor to a favorable environment essential for the maintenance of long-term stable graft function and as a new predictive biomarker of bronchiolitis obliterans syndrome-free survival.

C4d detection and histological patterns in the diagnosis of antibody-mediated rejection after lung transplantation: a single-centre study.

AIMS: Antibody-mediated rejection (AMR) is an emerging and challenging issue in transplantation. Endothelial deposition of C4d and microvascular inflammation (MI) are reliable markers of AMR in renal and cardiac transplantation, but remain controversial in the lung. Our aim was to assess C4d immunohistochemistry and histological patterns for the diagnosis of lung AMR. METHODS AND RESULTS: We reviewed 158 transbronchial biopsies (TBBs) (n = 85 clinically indicated, and n = 73 surveillance TBBs) from 48 recipients, blinded to clinical and serological data. C4d was scored as 0, 1+ (<10%), 2+ (10-50%) or 3+ (>50%). TBBs were reassessed for MI and acute lung injury (ALI). Donor-specific antibodies (DSAs), acute clinical graft dysfunction and chronic lung allograft graft dysfunction (CLAD) were recorded. C4d3+, C4d2+, C4d1+ and C4d0 occurred respectively in four (2.5%), six (3.8%), 28 (17.7%) and 120 (75.9%) TBBs. MI and ALI were rare but more frequent in C4d1-3+ TBBs than in the absence of C4d. C4d2+ was frequently observed with concomitant infection. Among the surveillance TBBs, only two (2.7%) showed MI. Neither ALI nor C4d3+ was diagnosed on surveillance TBBs. No significant association was found between histopathological findings and DSAs. All four patients with C4d3+ could retrospectively be diagnosed with AMR and developed CLAD. CONCLUSION: Although rare, diffuse C4d deposition appears to be a strong indication of acute clinical AMR in lung transplant patients, whereas intermediate C4d2+ requires more investigations. In stable patients, histopathology and C4d may lack the sensitivity to diagnose subclinical AMR. This emphasises the need for a multidisciplinary evaluation of each suspected AMR case, and the need for complementary diagnostic tools.