"White-Out" After Lung Transplantation: A Multicenter Cohort Description of Late Acute Graft Failure

Radiological distribution patterns in restrictive chronic lung allograft dysfunction: Impact on survival across all phenotypes

Background

Restrictive chronic lung allograft dysfunction (CLAD) demonstrates poor outcomes after lung transplantation. However, the impact of radiological patterns on survival within a restrictive CLAD under the new International Society for Heart and Lung Transplantation (ISHLT) criteria remains unclear.

Methods

We analyzed retrospectively 241 bilateral lung transplant recipients between 2005 and 2021. CLAD was diagnosed and classified per the 2019 ISHLT criteria. Restrictive phenotype included restrictive allograft syndrome (RAS) and mixed phenotype. In these cases, RAS-like opacities (RLOs) were evaluated both qualitatively and semiquantitatively on computed tomography at CLAD diagnosis. RLOs were classified into upper-predominant and diffuse/lower-predominant distribution groups. Overall survival after CLAD diagnosis was assessed using Kaplan-Meier method with log-rank test and Cox proportional hazards models.

Results

Eighty-three patients were diagnosed with CLAD after transplantation. Twenty-one (25.3%) had restrictive phenotype, which showed shorter survival compared to bronchiolitis obliterans syndrome (median survival: 19.8 vs 68.1 months; hazard ratio [HR], 4.53; 95% confidence interval [CI], 1.96-10.49; p < 0.001). Within the restrictive phenotype, the upper-predominant group demonstrated longer survival than the diffuse/lower-predominant group (median survival: 61.1 vs 15.5 months; p = 0.008). The diffuse/lower-predominant group had shorter survival compared to any other CLAD phenotype (HR, 8.45; 95% CI, 3.40-21.04; p < 0.001). The extent of RLOs within each distribution pattern was not significantly associated with survival.

Conclusions

In restrictive phenotype CLAD, RLO distribution patterns determined survival outcomes, with diffuse/lower-predominant showing the poorest prognosis, while the extent of RLOs within each pattern did not correlate with prognosis.

The ABC of transplant: ALAD, BLAD, and CLAD: definition and significance

PURPOSE OF REVIEW

Chronic lung allograft dysfunction (CLAD) is a recognized complication after lung transplantation, with a clear definition, although some pitfalls in phenotyping still exist. Recently, new terminologies, such as acute lung allograft dysfunction (ALAD) and baseline lung allograft dysfunction (BLAD) were introduced, but their definitions and real significance are not yet fully established.

RECENT FINDINGS

Based on the existing literature and ongoing discussions within two expert groups of the Advanced Lung Failure & Transplantation Interdisciplinary Network (ALFTx IDN) of the International Society for Heart and Lung Transplantation (ISHLT), we will describe current definitions, prevalence and outcome of these rather new entities, keeping in mind that a lot of uncertainties still exist.

SUMMARY

ALAD and BLAD will be defined, and the currently accepted outcome of these conditions will be summarized. Existing pitfalls in the phenotyping of CLAD will also be discussed.

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.

Chronic Lung Allograft Dysfunction: Evolving Concepts and Therapies

The primary factor that limits long-term survival after lung transplantation is chronic lung allograft dysfunction (CLAD). CLAD also impairs quality of life and increases the costs of medical care. Our understanding of CLAD continues to evolve. Consensus definitions of CLAD and the major CLAD phenotypes were recently updated and clarified, but it remains to be seen whether the current definitions will lead to advances in management or impact care. Understanding the potential differences in pathogenesis for each CLAD phenotype may lead to novel therapeutic strategies, including precision medicine. Recognition of CLAD risk factors may lead to earlier interventions to mitigate risk, or to avoid risk factors all together, to prevent the development of CLAD. Unfortunately, currently available therapies for CLAD are usually not effective. However, novel therapeutics aimed at both prevention and treatment are currently under investigation. We provide an overview of the updates to CLAD-related terminology, clinical phenotypes and their diagnosis, natural history, pathogenesis, and potential strategies to treat and prevent CLAD.

Chronic lung allograft dysfunction post-lung transplantation: The era of bronchiolitis obliterans syndrome and restrictive allograft syndrome

Chronic lung allograft dysfunction (CLAD) following lung transplantation limits long-term survival considerably. The main reason for this is a lack of knowledge regarding the pathological condition and the establishment of treatment. The consensus statement from the International Society for Heart and Lung Transplantation on CLAD in 2019 classified CLAD into two main phenotypes: Bronchiolitis obliterans syndrome and restrictive allograft syndrome. Along with this clear classification, further exploration of the mechanisms and the development of appropriate prevention and treatment strategies for each phenotype are desired. In this review, we summarize the new definition of CLAD and update and summarize the existing knowledge on the underlying mechanisms of bronchiolitis obliterans syndrome and restrictive allograft syndrome, which have been elucidated from clinicopathological observations and animal experiments worldwide.

Chronic lung allograft dysfunction: light at the end of the tunnel?

PURPOSE OF REVIEW

Chronic lung allograft dysfunction (CLAD) has been recently introduced as an umbrella-term encompassing all forms of chronic pulmonary function decline posttransplant with bronchiolitis obliterans syndrome and restrictive allograft syndrome as the most important subtypes. Differential diagnosis and management, however, remains complicated.

RECENT FINDINGS

Herein, we provide an overview of the different diagnostic criteria (pulmonary function, body plethysmography and radiology) used to differentiate bronchiolitis obliterans syndrome and restrictive allograft syndrome, their advantages and disadvantages as well as potential problems in making an accurate differential diagnosis. Furthermore, we discuss recent insights in CLAD management and treatment and advances in the search for accurate biomarkers of CLAD.

SUMMARY

Careful dissection of CLAD phenotypes is of utmost importance to assess patient prognosis, but uniform diagnostic criteria are desperately needed. There is a long way ahead, but the first steps towards this goal are now taken; tailored individualized therapy will be the golden standard to treat CLAD in the future, but randomized placebo-controlled and multicentre trials are needed to identify new and powerful therapeutic agents.

Bronchiolitis obliterans syndrome and restrictive allograft syndrome after lung transplantation: why are there two distinct forms of chronic lung allograft dysfunction?

Bronchiolitis obliterans syndrome (BOS) had been considered to be the representative form of chronic rejection or chronic lung allograft dysfunction (CLAD) after lung transplantation. In BOS, small airways are affected by chronic inflammation and obliterative fibrosis, whereas peripheral lung tissue remains relatively intact. However, recognition of another form of CLAD involving multiple tissue compartments in the lung, termed restrictive allograft syndrome (RAS), raised a fundamental question: why there are two phenotypes of CLAD? Increasing clinical and experimental data suggest that RAS may be a prototype of chronic rejection after lung transplantation involving both cellular and antibody-mediated alloimmune responses. Some cases of RAS are also induced by fulminant general inflammation in lung allografts. However, BOS involves alloimmune responses and the airway-centered disease process can be explained by multiple mechanisms such as external alloimmune-independent stimuli (such as infection, aspiration and air pollution), exposure of airway-specific autoantigens and airway ischemia. Localization of immune responses in different anatomical compartments in different phenotypes of CLAD might be associated with lymphoid neogenesis or the de novo formation of lymphoid tissue in lung allografts. Better understanding of distinct mechanisms of BOS and RAS will facilitate the development of effective preventive and therapeutic strategies of CLAD.

Surveillance for acute cellular rejection after lung transplantation

Acute cellular rejection (ACR) is a common complication following lung transplantation (LTx), affecting almost a third of recipients in the first year. Established, comprehensive diagnostic criteria exist but they necessitate allograft biopsies which in turn increases clinical risk and can pose certain logistical and economic problems in service delivery. Undermining these challenges further, are known problems with inter-observer interpretation of biopsies and uncertainty as to the long-term implications of milder or indeed asymptomatic episodes. Increased risk of chronic lung allograft dysfunction (CLAD) has long been considered the most significant consequence of ACR. Consensus is lacking as to whether this applies to mild ACR, with contradictory evidence available. Given these issues, research into alternative, minimal or non-invasive biomarkers represents the main focus of research in ACR. A number of potential markers have been proposed, but none to date have demonstrated adequate sensitivity and specificity to allow translation from bench to bedside.