Pathologic correlates of bronchiolitis obliterans syndrome in pulmonary retransplant recipients

JAK-STAT activation contributes to cytotoxic T cell-mediated basal cell death in human chronic lung allograft dysfunction

Chronic lung allograft dysfunction (CLAD) is the leading cause of death in lung transplant recipients. CLAD is characterized clinically by a persistent decline in pulmonary function and histologically by the development of airway-centered fibrosis known as bronchiolitis obliterans. There are no approved therapies to treat CLAD, and the mechanisms underlying its development remain poorly understood. We performed single-cell RNA-Seq and spatial transcriptomic analysis of explanted tissues from human lung recipients with CLAD, and we performed independent validation studies to identify an important role of Janus kinase-signal transducer and activator of transcription (JAK-STAT) signaling in airway epithelial cells that contributes to airway-specific alloimmune injury. Specifically, we established that activation of JAK-STAT signaling leads to upregulation of major histocompatibility complex 1 (MHC-I) in airway basal cells, an important airway epithelial progenitor population, which leads to cytotoxic T cell-mediated basal cell death. This study provides mechanistic insight into the cell-to-cell interactions driving airway-centric alloimmune injury in CLAD, suggesting a potentially novel therapeutic strategy for CLAD prevention or treatment.

miR-27a-3p alleviates lung transplantation-induced bronchiolitis obliterans syndrome (BOS) via suppressing Smad-mediated myofibroblast differentiation and TLR4-induced dendritic cells maturation

BACKGROUND

Bronchiolitis obliterans syndrome (BOS), induced by a chronic rejection, remains a significant obstacle for end-stage lung diseases after lung transplantation. We have previously determined that the small non-coding mRNA (miRNA) miR-27a-3p maintained the immature state of dendritic cells (DCs) via the interleukin 10 (IL-10)-dependent regulatory pathway. Such status helped in preventing rejection and alleviating BOS. The present study explored mechanisms how miR-27a-3p may suppress the fibrosis as well as the maturation of DCs, ultimately attenuating BOS in vitro and in vivo.

METHODS/RESULTS

In our tracheal transplantation mouse model, the expression of Smad2, Smad4, and αSMA were significantly decreased in the miR-27a-3p-transfected DCs (p < 0.0001, p = 0.0006, and p = 0.0002 respectively). Moreover, the expression of fibrosis markers (α-SMA, collagen I, and Fn) were potently inhibited in the miR-27a-3p-transfected NIH-3 T3 cells (p < 0.0001, p = 0.00148, and p < 0.0001 respectively). At the same time, reversed results were observed in the inhibitor group (p = 0.0002, p < 0.0001, and p < 0.0001 respectively), indicating that miR-27a-3p could directly inhibit myofibroblast differentiation. Furthermore, in the tracheal transplanted mice, the population of Treg cells was significantly decreased (p < 0.0001). In contrast, Th17 cells were down-regulated in the miR-27a-3p-transfected DCs group (p < 0.0001), accompanied by the decreased IL-17 levels (p = 0.0007) and the induction of TGF-β1 and IL-10 (p < 0.0001 and p = 0.0016 respectively). Further mechanistic studies indicated that miR-27a-3p altered the maturation of DCs by targeting TLR4 and IRAK (p < 0.0001 and p = 0.0002 respectively).

CONCLUSIONS

Our study suggests that miR-27a-3p selectively blocked the TGF-β1/Smad pathways to suppress the myofibroblast differentiation and targeted the TRL4/IRAK4 pathway to restrain DCs maturation, thus attenuating BOS. Our findings suggest that miR-27a-3p is a potential active molecule on BOS management after lung transplantation.

Activation of Humoral Immunity during the Pathogenesis of Experimental Chronic Lung Allograft Dysfunction

Alloreactive and autoreactive antibodies have been associated with the development of chronic lung allograft dysfunction (CLAD), but their pathogenic role is disputed. Orthotopic left lung transplantation was performed in the Fischer-344 to Lewis rat strain combination followed by the application of ciclosporine for 10 days. Four weeks after transplantation, lipopolysaccharide (LPS) was instilled into the trachea. Lungs were harvested before (postoperative day 28) and after LPS application (postoperative days 29, 33, 40, and 90) for histopathological, immunohistochemical, and Western blot analyses. Recipient serum was collected to investigate circulating antibodies. Lung allografts were more strongly infiltrated by B cells and deposits of immunoglobulin G and M were more prominent in allografts compared to right native lungs or isografts and increased in response to LPS instillation. LPS induced the secretion of autoreactive antibodies into the circulation of allograft and isograft recipients, while alloreactive antibodies were only rarely detected. Infiltration of B cells and accumulation of immunoglobulin, which is observed in allografts treated with LPS but not isografts or native lungs, might contribute to the pathogenesis of experimental CLAD. However, the LPS-induced appearance of circulating autoreactive antibodies does not seem to be related to CLAD, because it is observed in both, isograft and allograft recipients.

Secretory Immunoglobulin A Immunity in Chronic Obstructive Respiratory Diseases

Chronic obstructive pulmonary disease (COPD), asthma and cystic fibrosis (CF) are distinct respiratory diseases that share features such as the obstruction of small airways and disease flare-ups that are called exacerbations and are often caused by infections. Along the airway epithelium, immunoglobulin (Ig) A contributes to first line mucosal protection against inhaled particles and pathogens. Dimeric IgA produced by mucosal plasma cells is transported towards the apical pole of airway epithelial cells by the polymeric Ig receptor (pIgR), where it is released as secretory IgA. Secretory IgA mediates immune exclusion and promotes the clearance of pathogens from the airway surface by inhibiting their adherence to the epithelium. In this review, we summarize the current knowledge regarding alterations of the IgA/pIgR system observed in those major obstructive airway diseases and discuss their implication for disease pathogenesis.

Beyond Bronchiolitis Obliterans: In-Depth Histopathologic Characterization of Bronchiolitis Obliterans Syndrome after Lung Transplantation

Bronchiolitis obliterans syndrome (BOS) is considered an airway-centered disease, with bronchiolitis obliterans (BO) as pathologic hallmark. However, the histologic spectrum of pure clinical BOS remains poorly characterized. We provide the first in-depth histopathologic description of well-characterized BOS patients and patients without chronic lung allograft dysfunction (CLAD), defined according to the recent consensus guidelines. Explant lung tissue from 52 clinically-defined BOS and 26 non-CLAD patients (collected 1993-2018) was analyzed for histologic parameters, including but not limited to airway lesions, vasculopathy and fibrosis. In BOS, BO lesions were evident in 38 (73%) patients and varied from concentric sub-epithelial fibrotic BO to inflammatory BO, while 10/14 patients without BO displayed 'vanishing airways', defined by a discordance between arteries and airways. Chronic vascular abnormalities were detected in 22 (42%) patients. Ashcroft fibrosis scores revealed a median of 43% (IQR: 23-69) of normal lung parenchyma per patient; 26% (IQR: 18-37) of minimal alveolar fibrous thickening; and 11% (IQR: 4-18) of moderate alveolar thickening without architectural damage. Patchy areas of definite fibrotic damage to the lung structure (i.e., Ashcroft score ≥5) were present in 28 (54%) patients. Fibrosis was classified as bronchocentric (n = 21/28, 75%), paraseptal (n = 17/28, 61%) and subpleural (n = 15/28, 54%). In non-CLAD patients, BO lesions were absent, chronic vascular abnormalities present in 1 (4%) patient and mean Ashcroft scores were significantly lower compared to BOS (p = 0.0038) with 78% (IQR: 64-88) normally preserved lung parenchyma. BOS explant lungs revealed evidence of various histopathologic findings, including vasculopathy and fibrotic changes, which may contribute to the pathophysiology of BOS.

Interleukin 6 trans-signaling is a critical driver of lung allograft fibrosis

Histopathologic examination of lungs afflicted by chronic lung allograft dysfunction (CLAD) consistently shows both mononuclear cell (MNC) inflammation and mesenchymal cell (MC) fibroproliferation. We hypothesize that interleukin 6 (IL-6) trans-signaling may be a critical mediator of MNC-MC crosstalk and necessary for the pathogenesis of CLAD. Bronchoalveolar lavage (BAL) fluid obtained after the diagnosis of CLAD has approximately twofold higher IL-6 and soluble IL-6 receptor (sIL-6R) levels compared to matched pre-CLAD samples. Human BAL-derived MCs do not respond to treatment with IL-6 alone but have rapid and prolonged JAK2-mediated STAT3 Tyr705 phosphorylation when exposed to the combination of IL-6 and sIL-6R. STAT3 phosphorylation within MCs upregulates numerous genes causing increased invasion and fibrotic differentiation. MNC, a key source of both IL-6 and sIL-6R, produce minimal amounts of these proteins at baseline but significantly upregulate production when cocultured with MCs. Finally, the use of an IL-6 deficient recipient in a murine orthotopic transplant model of CLAD reduces allograft fibrosis by over 50%. Taken together these results support a mechanism where infiltrating MNCs are stimulated by resident MCs to release large quantities of IL-6 and sIL-6R which then feedback onto the MCs to increase invasion and fibrotic differentiation.

Chronic lung allograft pathology lesions in two rat strain combinations

Background

Chronic lung allograft dysfunction remains an obstacle to long-term survival after lung transplantation. Two phenotypes have been described: obliterative bronchiolitis and restrictive allograft syndrome. Preclinical models are essential to analyze chronic lung allograft dysfunction pathophysiology.

Methods

Orthotopic lung transplants from 38 Lewis into Fischer 344 (Lew→F344) and 67 Brown-Norway into Lewis (BN→Lew) rats were performed in our center in the last decade. We carefully reviewed and quantified all grafts with chronic rejection (40 cases) (18 Lew→F344, 22 BN→Lew) with the aim to investigate if histological changes of chronic lung allograft dysfunction could be also detected in rat grafts.

Results

All animals showed human reminiscent histological lesions. Early chronic rejection lesions were detected in BN→Lew. End-stage chronic rejection with features of obliterative bronchiolitis was observed in 33% of Lew→F344; end-stage with restrictive allograft syndrome chronic rejection in 67% and 80% of Lew→F344 and BN→Lew, respectively. BN→Lew showed higher grades of endotheliitis, vascular fibrosis, and lower grades of lymphoid aggregates than Lew→F344 (P=0.007, P=0.043, P=0.004, respectively).

Conclusions

Chronic rejection lesions in rat lung allografts mimic those in humans. The frequent occurrence of restrictive allograft syndrome-like lesions in BN→Lew may be related to a higher degree of mismatch in this strain combination. These animal models could allow future mechanistic studies to better understand chronic lung allograft dysfunction pathogenesis.

Spectrum of findings on ventilation‒perfusion lung scintigraphy after lung transplantation and association with outcomes

BACKGROUND

Air trapping (AT) is one of the hallmarks of allograft dysfunction after lung transplantation (LT). Inert gas‒based ventilation‒perfusion (VQ) lung scintigraphy has excellent sensitivity in the detection of AT.

METHODS

We reviewed the charts of patients who underwent single or double LT between January 2012 and December 2014 (N = 193). Patients without a VQ scintigraphy at the first annual visit (n = 16) and those who did not survive till 1 year (n = 26) were excluded (final n = 151, mean age = 55.8 [SD =14] years, male = 85, female = 66). VQ scintigraphy was independently reviewed and reconciled for the presence and severity of AT by 2 investigators blinded to the clinical data (D.F.P. and D.M.). A 3-year post-transplant survival was the primary end-point.

RESULTS

AT was common (n = 73, 48.3%). Patients with obstructive lung diseases as the underlying diagnosis (adjusted odds ratio [OR], 4.36, 95% CI: 1.64‒11.6; p = 0.003) and those with lower body mass index (BMI) (BMI < 25 kg/m² and 25‒30 kg/m²; p < 0.001) had an increased risk of developing AT in the allograft. The presence of AT (adjusted OR, 2.33, 95% CI: 1.01‒5.36; p = 0.04) and peak forced expiratory volume in 1 sec (FEV₁) <60% predicted during the first year after LT were independently associated with 3-year mortality. The association of AT with post-transplant mortality was the strongest among patients with BMI <30 kg/m² and peak FEV₁ <60% predicted.

CONCLUSIONS

The finding of AT on VQ scintigraphy at the first annual visit after LT is independently associated with worse post-transplant mortality. The sub-group of patients who fail to achieve a peak FEV₁ of 60% predicted during the first year after LT appears to be the key driver of this association.

Chronic Lung Allograft Dysfunction: Review of CT and Pathologic Findings

Chronic lung allograft dysfunction (CLAD) is the most common cause of mortality in lung transplant recipients after the 1st year of transplantation. CLAD has traditionally been classified into two distinct obstructive and restrictive forms: bronchiolitis obliterans syndrome and restrictive allograft syndrome. However, CLAD may manifest with a spectrum of imaging and pathologic findings and a combination of obstructive and restrictive physiologic abnormalities. Although the initial CT manifestations of CLAD may be nonspecific, the progression of findings at follow-up should signal the possibility of CLAD and may be present on imaging studies prior to the development of functional abnormalities of the lung allograft. This review encompasses the evolution of CT findings in CLAD, with emphasis on the underlying pathogenesis and pathologic condition, to enhance understanding of imaging findings. The purpose of this article is to familiarize the radiologist with the initial and follow-up CT findings of the obstructive, restrictive, and mixed forms of CLAD, for which early diagnosis and treatment may result in improved survival. Supplemental material is available for this article. © RSNA, 2021.

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.

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.

An update on chronic lung allograft dysfunction

Chronic lung allograft dysfunction (CLAD) remains a significant challenge and the major determinant of morbidity and mortality post lung transplantation (LTx). The definition of CLAD has evolved significantly over the last ten years, reflecting better understanding of pathophysiology and different phenotypes. While there is an agreed consensus approach to CLAD, questions remain regarding the limitations of lung function parameters as well as the role of imaging and histopathology. Here we present a current snapshot of the definition of CLAD, its evolution and future directions.

The histomorphological spectrum of restrictive chronic lung allograft dysfunction and implications for prognosis

Chronic lung allograft dysfunction continues to be the main contributor to poor long-term allograft survival after lung transplantation. The restrictive phenotype of chronic lung allograft dysfunction carries a particularly poor prognosis. Little is known about the pathogenetic mechanisms involved in restrictive chronic lung allograft dysfunction. In this study, we performed histomorphological and immunohistochemical analysis of restrictive chronic lung allograft dysfunction lungs. Explant lung tissue from 21 restrictive chronic lung allograft dysfunction patients was collected and histopathologic patterns of rejection, fibrosis and vascular changes were scored after routine histochemical stains and additional immunohistochemistry for endothelial markers and C4d. In all, 75% of cases showed evidence of acute cellular rejection; lymphocytic bronchiolitis was absent in most lungs, whereas in 55% there was obliterative bronchiolitis. Almost half of the cases showed a pattern consistent with pleuroparenchymal fibro-elastosis (n=10), and a subset showed nonspecific interstitial pneumonia (n=5) or irregular emphysema (n=5). Fibrinous alveolar exudates were frequently seen in association with fibrosis (n=6), but no diffuse alveolar damage was found. Evidence of microvascular damage was present in most cases. An emphysematous pattern of fibrosis was associated with a better survival (P=0.0030), whereas fibrinous exudates were associated with a worse survival (P=0.0007). In addition to the previously described nonspecific interstitial pneumonia and pleuroparenchymal fibro-elastosis patterns in restrictive chronic lung allograft dysfunction, we are the first to describe a pattern of fibrosis-induced subpleural/paraseptal emphysema. This pattern confers a better survival, whereas fibrinous exudates are associated with a worse survival. We believe that our findings offer a pathogenetic theory for pleuroparenchymal fibro-elastosis in restrictive chronic lung allograft dysfunction, and show that restrictive chronic lung allograft dysfunction is an increasingly heterogeneous disease with presumably different mechanisms of subpattern formation.

Chronic lung allograft dysfunction phenotypes and treatment

Chronic lung allograft dysfunction (CLAD) remains a major hurdle limiting long-term survival post lung transplantation. Given the clinical heterogeneity of CLAD, recently two phenotypes of CLAD have been defined [bronchiolitis obliterans syndrome (BOS) vs. restrictive allograft syndrome (RAS) or restrictive CLAD (rCLAD)]. BOS is characterized by an obstructive pulmonary function, air trapping on CT and obliterative bronchiolitis (OB) on histopathology, while RAS/rCLAD patients show a restrictive pulmonary function, persistent pleuro-parenchymal infiltrates on CT and pleuroparenchymal fibro-elastosis on biopsies. Importantly, the patients with RAS/rCLAD have a severely limited survival post diagnosis of 6-18 months compared to 3-5 years after BOS diagnosis. In this review, we will review historical evidence for this heterogeneity and we will highlight the clinical, radiological, histopathological characteristics of both phenotypes, as well as their risk factors. Treatment of CLAD remains troublesome, nevertheless, we will give an overview of different treatment strategies that have been tried with some success. Adequate phenotyping remains difficult but is clearly needed for both clinical and scientific purposes.

What makes a good pediatric transplant lung: Insights from in vivo lung morphometry with hyperpolarized 3 He magnetic resonance imaging

Obtaining information on transplanted lung microstructure is an important part of the current care for monitoring transplant recipients. However, until now this information was only available from invasive lung biopsy. The objective of this study was to evaluate the use of an innovative non-invasive technique, in vivo lung morphometry with hyperpolarized ³He MRI-to characterize lung microstructure in the pediatric lung transplant population. This technique yields quantitative measurements of acinar airways' (alveolar ducts and sacs) parameters, such as acinar airway radii and alveolar depth. Six pediatric lung transplant recipients with cystic fibrosis underwent in vivo lung morphometry MRI, pulmonary function testing, and quantitative CT. We found a strong correlation between lung lifespan and alveolar depth-patients with more shallow alveoli were likely to have a negative outcome sooner than those with larger alveolar depth. Combining morphometric results with CT, we also determined mean alveolar wall thickness and found substantial increases in this parameter in some patients that negatively correlated with DLCO. In vivo lung morphometry uniquely provides previously unavailable information on lung microstructure that may be predictive of a negative outcome and has a potential to aid in lung selection for transplantation.

Quantitative computed tomography assessment of bronchiolitis obliterans syndrome after lung transplantation

BACKGROUND

Bronchiolitis obliterans syndrome (BOS) is a clinical manifestation of chronic allograft rejection following lung transplantation. We examined the quantitative measurements of the proximal airway and vessels and pathologic correlations in subjects with BOS.

METHODS

Patients who received a lung transplant at the Brigham and Women's Hospital between December 1, 2002 and December 31, 2010 were included in this study. We characterized the quantitative CT measures of proximal airways and vessels and pathological changes.

RESULTS

Ninety-four (46.1%) of the 204 subjects were included in the study. There was a significant increase in the airway vessel ratio in subjects who developed progressive BOS compared to controls and non-progressors. There was a significant increase in airway lumen area and decrease in vessel cross-sectional area in patients with BOS compared to controls. Patients with BOS had a significant increase in proximal airway fibrosis compared to controls.

CONCLUSIONS

BOS is characterized by central airway dilation and vascular remodeling, the degree of which is correlated to decrements in lung function. Our data suggest that progressive BOS is a pathologic process that affects both the central and distal airways.

Lung injury pathways: Adenosine receptor 2B signaling limits development of ischemic bronchiolitis obliterans organizing pneumonia

Purpose/Aim of the Study: Adenosine signaling was studied in bronchiolitis obliterans organizing pneumonia (BOOP) resulting from unilateral lung ischemia.

MATERIALS AND METHODS

Ischemia was achieved by either left main pulmonary artery or complete hilar ligation. Sprague-Dawley (SD) rats, Dahl salt sensitive (SS) rats and SS mutant rat strains containing a mutation in the A2B adenosine receptor gene (Adora2b) were studied. Adenosine concentrations were measured in bronchoalveolar lavage (BAL) by HPLC. A2A (A2AAR) and A2B adenosine receptor (A2BAR) mRNA and protein were quantified.

RESULTS

Twenty-four hours after unilateral PA ligation, BAL adenosine concentrations from ischemic lungs were increased relative to contralateral lungs in SD rats. A2BAR mRNA and protein concentrations were increased after PA ligation while miR27a, a negatively regulating microRNA, was decreased in ischemic lungs. A2AAR mRNA and protein concentrations remained unchanged following ischemia. A2BAR protein was increased in PA ligated lungs of SS rats after 7 days, and 4 h after complete hilar ligation in SD rats. SS-Adora2b mutants showed a greater extent of BOOP relative to SS rats, and greater inflammatory changes.

CONCLUSION

Increased A2BAR and adenosine following unilateral lung ischemia as well as more BOOP in A2BAR mutant rats implicate a protective role for A2BAR signaling in countering ischemic lung injury.

Advances in Understanding Bronchiolitis Obliterans After Lung Transplantation

Bronchiolitis obliterans syndrome (BOS) remains a major complication after lung transplantation, causing significant morbidity and mortality in a majority of recipients. BOS is believed to be the clinical correlate of chronic allograft dysfunction, and is defined as an obstructive pulmonary function defect in the absence of other identifiable causes, mostly not amenable to treatment. Recently, it has become clear that BOS is not the only form of chronic allograft dysfunction and that other clinical phenotypes exist; however, we focus exclusively on BOS. Radiologic findings typically demonstrate air trapping, mosaic attenuation, and hyperinflation. Pathologic examination reveals obliterative bronchiolitis lesions and a pure obliteration of the small airways (< 2 mm), with a relatively normal surrounding parenchyma. In this review, we highlight recent advances in diagnosis, pathologic examination, and risk factors, such as microbes, viruses, and antibodies. Although the pathophysiological mechanisms remain largely unknown, we review the role of the airway epithelium and inflammation and the various experimental animal models. We also clarify the clinical and therapeutic implications of these findings. Although significant progress has been made, the exact pathophysiological mechanisms and adequate therapy for posttransplantation BOS remain unknown, highlighting the need for further research to improve long-term posttransplantation BOS-free and overall survival.

[Small airway diseases and immune deficiency]

INTRODUCTION

Innate or acquired immune deficiency may show respiratory manifestations, often characterized by small airway involvement. The purpose of this article is to provide an overview of small airway disease across the major causes of immune deficiency.

BACKGROUND

In patients with common variable immune deficiency, recurrent lower airway infections may lead to bronchiolitis and bronchiectasis. Follicular and/or granulomatous bronchiolitis of unknown origin may also occur. Bronchiolitis obliterans is the leading cause of death after the first year in patients with lung transplantation. Bronchiolitis obliterans also occurs in patients with allogeneic haematopoietic stem cell transplantation, especially in the context of systemic graft-versus-host disease.

VIEWPOINT AND CONCLUSION

Small airway diseases have different clinical expression and pathophysiology across various causes of immune deficiency. A better understanding of small airways disease pathogenesis in these settings may lead to the development of novel targeted therapies.

Current views on chronic rejection after lung transplantation

Chronic lung allograft dysfunction (CLAD) was recently introduced as an overarching term mainly to classify patients with chronic rejection after lung transplantation, although other conditions may also qualify for CLAD. Initially, only the development of a persistent and obstructive pulmonary function defect, clinically identified as bronchiolitis obliterans syndrome (BOS), was considered as chronic rejection, if no other cause could be identified. It became clear in recent years that some patients do not qualify for this definition, although they developed a chronic and persistent decrease in FEV1 , without another identifiable cause. As the pulmonary function decline in these patients was rather restrictive, this was called restrictive allograft syndrome (RAS). In the present review, we will further elaborate on these two CLAD phenotypes, with specific attention to the diagnostic criteria, the role of pathology and imaging, the risk factors, outcome, and the possible treatment options.

Differential cytokine, chemokine and growth factor expression in phenotypes of chronic lung allograft dysfunction

BACKGROUND

Chronic lung allograft dysfunction is a heterogeneous entity limiting long-term survival after lung transplantation. Different clinical phenotypes (bronchiolitis obliterans syndrome [BOS]-neutrophilic BOS-restrictive allograft syndrome [RAS]) have been identified but the mechanisms remain elusive.

METHODS

In this study, we measured 34 different cytokines, chemokines, and growth factors in bronchoalveolar lavage fluid of 20 stable patients, 20 patients suffering from non-neutrophilic BOS, 17 from neutrophilic BOS, and 20 from RAS using classic enzyme-linked immunosorbent assay and multiplex technology.

RESULTS

Total cell count and % neutrophils were elevated in neutrophilic BOS and RAS compared to stable and non-neutrophilic BOS patients, whereas also the % eosinophils was elevated at diagnosis of RAS. Levels of interleukin (IL)-1β (P<0.01), IL-1Rα (P<0.001), IL-6 (P<0.001), IL-8/CXCL8 (P<0.001), IP-10/CXCL10 (P<0.05), MCP-1/CCL2 (P<0.05), macrophage inflammatory protein (MIP)-1α/CCL3 (P<0.001), MIP-1β/CCL4, and vascular endothelial growth factor (VEGF; P<0.05) were differentially regulated in RAS compared to stable, whereas in neutrophilic BOS IL-1β (P<0.001), IL-1Rα (P<0.01), IL-7 (P<0.05), IL-8/CXCL8 (P<0.001), MCP-3/CXCCL7 (P<0.05) and MIP-1α/CCL-3 (P<0.05) were significantly upregulated compared to stable patients. We could not detect any differences between non-neutrophilic BOS and stable patients. Interestingly, bronchoalveolar lavage IL-6, interferon gamma-induced protein (IP)-10/CXCL10 and interferon-inducible T-cell alpha chemoattractant/chemokine (C-X-C motif) ligand 11 (ITAC/CXCL10) were associated with survival after diagnosis in RAS patients.

CONCLUSION

There were major differences in cytokine and chemokine expression in our different study groups. Especially IL-6, but also IP-10/CXCL10, and VEGF may be interesting mediators in RAS.

Restrictive chronic lung allograft dysfunction: Where are we now?

Chronic lung allograft dysfunction (CLAD) remains a frequent and troublesome complication after lung transplantation. Apart from bronchiolitis obliterans syndrome (BOS), a restrictive phenotype of CLAD (rCLAD) has recently been recognized, which occurs in approximately 30% of CLAD patients. The main characteristics of rCLAD include a restrictive pulmonary function pattern with a persistent decline in lung function (FEV1, FVC and TLC), persistent parenchymal infiltrates and (sub)pleural thickening on chest CT scan, as well as pleuroparenchymal fibroelastosis and obliterative bronchiolitis on histopathologic examination. Once diagnosed, median survival is only 6 to 18 months compared with 3 to 5 years with BOS. In this perspective we review the historic evidence for rCLAD and describe the different diagnostic criteria and prognosis. Furthermore, we elaborate on the typical radiologic and histopathologic presentations of rCLAD and highlight risk factors and mechanisms. Last, we summarize some opportunities for further research including the urgent need for adequate therapy. In this perspective we not only assess the current knowledge, but also clarify the existing gaps in understanding this increasingly recognized complication after lung transplantation.

Bronchiolitis obliterans syndrome is not specific for bronchiolitis obliterans in pediatric lung transplant

BACKGROUND

Bronchiolitis obliterans (BO) is the leading cause of mortality beyond the first year after pediatric lung transplant, but the performance of an open lung biopsy is often required for diagnosis. Bronchiolitis obliterans syndrome (BOS) is a clinical diagnosis based on spirometric data that is the accepted standard for staging chronic allograft dysfunction.

METHODS

We determined the sensitivity, specificity, and positive and negative predictive values of BOS for predicting BO in children. A chart review was conducted on 139 open lung biopsies and 43 lung explants performed at our center from 1990 through June 2010 in pediatric recipients of lung transplants. Results were excluded from analysis if insufficient data existed to calculate a stable BOS stage before biopsy/explant.

RESULTS

The criteria for inclusion in the study were met by 67 open lung biopsies and 31 lung explants. The sensitivity, specificity, positive predictive value, and negative predictive value of BOS for predicting BO were 91.0%, 25.8%, 72.6%, and 57.1%.

CONCLUSIONS

We found that early declines in lung function are sensitive, but not specific, for BO. The low specificity of BOS for identifying BO illustrates the challenge facing clinicians in determining the etiology of pulmonary decline after lung transplant.

A new classification system for chronic lung allograft dysfunction

Although survival after lung transplantation has improved significantly during the last decade, chronic rejection is thought to be the major cause of late mortality. The physiologic hallmark of chronic rejection has been a persistent fall in forced expiratory volume in 1 second associated with an obstructive ventilatory defect, for which the term bronchiolitis obliterans syndrome (BOS) was defined to allow a uniformity of description and grading of severity throughout the world. Although BOS was generally thought to be irreversible, recent evidence suggests that some patients with BOS may respond to azithromycin with > 10% improvement in their forced expiratory volume in 1 second. In addition, a restrictive form of chronic rejection has recently been described that does not fit the strict definition of BOS as an obstructive defect. Hence, the term chronic lung allograft dysfunction (CLAD) has been introduced to cover all forms of graft dysfunction, but CLAD has yet to be defined. We propose a definition of CLAD and a flow chart that may facilitate recognition of the different phenotypes of CLAD that can complicate the clinical course of lung transplant recipients.

A relevant experimental model for human bronchiolitis obliterans syndrome

BACKGROUND

The long-term success of human lung transplantation is limited by the development of bronchiolitis obliterans syndrome. Acute rejection episodes and infections are important risk factors and seem to play major pathogenic roles. We established a relevant experimental model that mimics important aspects of human bronchiolitis obliterans syndrome.

METHODS

The Fischer 344-to-Lewis rat strain combination was used for orthotopic left lung transplantation. Isogeneic transplantations were performed in the Lewis rat. Recipients were treated with ciclosporin for 10 days. Lipopolysaccharide or vehicle was instilled into the airways 28 days after transplantation. Grafts were monitored by computed tomography, and recipients were euthanized on Days 28-90. The messenger RNA expression of selected chemokines and their receptors was measured on Days 28, 29, 33, 40 after transplantation. Graft histopathology on Day 90 was compared with lungs from patients who underwent re-transplantation due to end-stage allograft dysfunction.

RESULTS

Lung allografts treated with ciclosporin and vehicle only sporadically displayed tissue remodeling. In contrast, lipopolysaccharide treatment induced severe inflammation. In the long-term, severe vascular remodeling, lung fibrosis, and fibroproliferative remodeling of airways were found that closely resemble the histopathologic changes in grafts from human patients with bronchiolitis obliterans syndrome. Chronic damage was virtually absent from pulmonary isografts and native right lungs. Chemokine (C-C motif) ligand 5 and chemokine (C-X-C motif) ligand 9-11, and their receptors, were over-expressed in allografts.

CONCLUSIONS

Our experimental model mirrors key aspects of human bronchiolitis obliterans syndrome. It will be useful to elucidate its pathogenesis and to develop therapeutic approaches improving the long-term outcome of human lung transplantation.

Lung Transplantation for Idiopathic Pulmonary Fibrosis

Despite advances in the development of novel pharmaceutical agents to treat idiopathic pulmonary fibrosis (IPF), there are no medical therapies known to resolve fibrosis or improve lung function in IPF. Therefore, lung transplantation remains the only life-saving therapy available to treat patients with IPF. However, a shortage of suitable donor organs limits the number of affected individuals who can undergo this procedure, and this shortage highlights the need to allocate donor lungs to those who are in the greatest need of a life-saving therapy yet ensure that those who undergo transplantation will have a reasonable expectation of long-term survival. Still, outcomes remain relatively poor for many patients after lung transplantation, although a sizable minority of patients can enjoy long-term survival after lung transplantation.

Bronchiolitis obliterans syndrome: the Achilles' heel of lung transplantation

Lung transplantation is a therapeutic option for patients with end-stage pulmonary disorders. Unfortunately, chronic lung allograft dysfunction (CLAD), most commonly manifest as bronchiolitis obliterans syndrome (BOS), continues to be highly prevalent and is the major limitation to long-term survival. The pathogenesis of BOS is complex and involves alloimmune and nonalloimmune pathways. Clinically, BOS manifests as airway obstruction and dyspnea that are classically progressive and ultimately fatal; however, the course is highly variable, and distinguishable phenotypes may exist. There are few controlled studies assessing treatment efficacy, but only a minority of patients respond to current treatment modalities. Ultimately, preventive strategies may prove more effective at prolonging survival after lung transplantation, but their remains considerable debate and little data regarding the best strategies to prevent BOS. A better understanding of the risk factors and their relationship to the pathological mechanisms of chronic lung allograft rejection should lead to better pharmacological targets to prevent or treat this syndrome.

Rattus model utilizing selective pulmonary ischemia induces bronchiolitis obliterans organizing pneumonia

Bronchiolitis obliterans organizing pneumonia (BOOP), a morbid condition when associated with lung transplant and chronic lung disease, is believed to be a complication of ischemia. Our goal was to develop a simple and reliable model of lung ischemia in the Sprague-Dawley rat that would produce BOOP. Unilateral ischemia without airway occlusion was produced by an occlusive slipknot placed around the left main pulmonary artery. Studies were performed 7 days later. Relative pulmonary and systemic flow to each lung was measured by injection of technetium Tc 99m macroaggregated albumin. Histological sections were examined for structure and necrosis and scored for BOOP. Apoptosis was detected by immunohistochemistry with an antibody against cleaved caspase 3. Pulmonary artery blood flow to left lungs was less than 0.1% of the cardiac output, and bronchial artery circulation was ∼2% of aortic artery flow. Histological sections from ischemic left lungs consistently showed Masson bodies, inflammation, and young fibroblasts filling the distal airways and alveoli, consistent with BOOP. In quantitative evaluation of BOOP using epithelial changes, inflammation and fibrosis were higher in ischemic left lungs than right or sham-operated left lungs. Apoptosis was increased in areas exhibiting histological BOOP, but there was no histological evidence of necrosis. Toll-like receptor 4 expression was increased in ischemic left lungs over right. An occlusive slipknot around the main left pulmonary artery in rats produces BOOP, providing direct evidence that ischemia without immunomodulation or coinfection is sufficient to initiate this injury. It also affords an excellent model to study signaling and genetic mechanisms underlying BOOP.

Epithelial clara cell injury occurs in bronchiolitis obliterans syndrome after human lung transplantation

Bronchiolitis obliterans syndrome (BOS) is a condition of progressive airflow obstruction that affects a majority of lung transplant recipients and limits long-term posttransplant survival. Although epithelial injury appears central to the development of BOS, little is known regarding the specific epithelial cell types that are affected in this condition. We hypothesized that BOS would involve preferential injury to the secretory Clara cells that function in innate defense and epithelial repair. To test this hypothesis, we assessed tissue transcript, tissue protein and lung fluid protein expression of Clara cell secretory protein (CCSP), a marker for Clara cells, in lung transplant recipients with BOS, BOS-free patients and in donor controls. Our results demonstrate that CCSP tissue transcript and protein expression are significantly reduced in lung transplant recipients with BOS compared to BOS-free or donor controls. In addition, we demonstrate that CCSP protein levels are significantly reduced in the lung fluid of patients with BOS compared to BOS-free controls, in cross-sectional and longitudinal analysis. Collectively, these complementary results illustrate that BOS involves a selective alteration in the distribution and function of bronchiolar Clara cells.

Survival determinants in lung transplant patients with chronic allograft dysfunction

BACKGROUND

Chronic lung allograft dysfunction (CLAD) remains the leading cause of mortality after lung transplantation.

METHODS

In this retrospective single-center study, we aimed to identify different phenotypes of and risk factors for mortality after CLAD diagnosis using univariate and multivariate Cox proportional hazard survival regression analysis.

RESULTS

CLAD was diagnosed in 71 of 294 patients (24.2%) at 30.9±22.8 months after transplantation. Pulmonary function was obstructive in 51 (71.8%) of the CLAD patients, restrictive in 20 (28.2%) patients, of whom 17 had persistent parenchymal infiltrates on pulmonary computer tomography (CAT) scan. In univariate analysis, previous development of neutrophilic reversible allograft dysfunction (NRAD, P=0.012) and a restrictive pulmonary function (P=0.0024) were associated with a worse survival, whereas there was a strong trend for early development of CLAD and persistent parenchymal infiltrates on CAT scan (P=0.067 and 0.056, respectively). In multivariate analysis, early development of CLAD (P=0.0067), previous development of NRAD (P=0.0016), and a restrictive pulmonary function pattern (P=0.0005) or persistent parenchymal infiltrates on CAT scan (P=0.0043) remained significant.

CONCLUSION

Although most CLAD patients develop an obstructive pulmonary function, 28% develop a restrictive pulmonary function, compatible with the recently defined restrictive allograft syndrome phenotype. Early-onset CLAD, previous development of NRAD, and the development of restrictive allograft syndrome are associated with worse survival after CLAD has been diagnosed.

Stromal activation and formation of lymphoid-like stroma in chronic lung allograft dysfunction

BACKGROUND

Lymphoid neogenesis is associated with the development of chronic lung allograft dysfunction (CLAD). Activation of stromal resident cells may be an important mechanism of lymphoid neogenesis.

METHODS

Twenty CLAD lungs explanted for retransplantation were immunohistochemically examined for lymphoid neogenesis, ectopic lymphoid chemokines, and dendritic cells (DCs). Formation of peripheral lymph node addressin (PNAd)+ high endothelial venule (HEV)-like vessels was examined in 134 transbronchial biopsies taken over 2 years posttransplant from 20 consecutive lung transplant recipients.

RESULTS

CLAD lungs were characterized by higher grades of CXCL12 in alveolar (P=0.002) and airway epithelial cells (P=0.001), CCL21+ lymph vessels (P=0.01), and infiltration of DC-specific intercellular adhesion molecule-grabbing nonintegrin+ immature DCs (P=0.056) than normal control lungs. Activation of stromal resident cells in CLAD lungs was highlighted by formation of lymphoid-like stroma including expression of CCL21 and CXCL13, fibroblastic reticular-like cells and DC-specific lysosome-associated membrane protein+ mature DCs in association with a significantly larger number of lymphoid aggregates (P<0.001) with lymphangitc distribution compared with normal lungs. A larger number of PNAd+ HEV-like vessels were also observed outside of lymphoid aggregates with a lymphangitic distribution (P<0.001). HEV-like vessels in transbronchial biopsies were more graded in lungs that eventually developed CLAD (n=7) than those that did not (n=13) by 3 years after transplantation (P=0.001).

CONCLUSION

Lymphoid neogenesis associated with CLAD accompanies activation of stromal resident cells and formation of lymphoid-like stroma. Induction of PNAd+ HEV-like vessels occurs before the manifestation of CLAD.

A review of bronchiolitis obliterans syndrome and therapeutic strategies

Lung transplantation is an important treatment option for patients with advanced lung disease. Survival rates for lung transplant recipients have improved; however, the major obstacle limiting better survival is bronchiolitis obliterans syndrome (BOS). In the last decade, survival after lung retransplantation has improved for transplant recipients with BOS. This manuscript reviews BOS along with the current therapeutic strategies, including recent outcomes for lung retransplantation.

Chronic allograft dysfunction

Chronic, progressive, and irreversible loss of lung function is the major medium-term and long-term complication after lung transplantation and the leading cause of death. Over the past decade, progress has been made in understanding the pathogenesis of bronchiolitis obliterans. Alloimmune factors and nonalloimmune factors may contribute to its development. Understanding the precise mechanism of each type of chronic allograft dysfunction may open up the field for new preventive and therapeutic interventions. This article reviews major new insights into the clinical aspects, pathophysiology, risk factors, diagnosis, and management of chronic allograft dysfunction after lung transplantation.

Restrictive allograft syndrome (RAS): a novel form of chronic lung allograft dysfunction

BACKGROUND

Bronchiolitis obliterans syndrome (BOS) with small-airway pathology and obstructive pulmonary physiology may not be the only form of chronic lung allograft dysfunction (CLAD) after lung transplantation. Characteristics of a form of CLAD consisting of restrictive functional changes involving peripheral lung pathology were investigated.

METHODS

Patients who received bilateral lung transplantation from 1996 to 2009 were retrospectively analyzed. Baseline pulmonary function was taken as the time of peak forced expiratory volume in 1 second (FEV(1)). CLAD was defined as irreversible decline in FEV(1) < 80% baseline. The most accurate threshold to predict irreversible decline in total lung capacity and thus restrictive functional change was at 90% baseline. Restrictive allograft syndrome (RAS) was defined as CLAD meeting this threshold. BOS was defined as CLAD without RAS. To estimate the effect on survival, Cox proportional hazards models and Kaplan-Meier analyses were used.

RESULTS

Among 468 patients, CLAD developed in 156; of those, 47 (30%) showed the RAS phenotype. Compared with the 109 BOS patients, RAS patients showed significant computed tomography findings of interstitial lung disease (p < 0.0001). Prevalence of RAS was approximately 25% to 35% of all CLAD over time. Patient survival of RAS was significantly worse than BOS after CLAD onset (median survival, 541 vs 1,421 days; p = 0.0003). The RAS phenotype was the most significant risk factor of death among other variables after CLAD onset (hazard ratio, 1.60; confidential interval, 1.23-2.07).

CONCLUSIONS

RAS is a novel form of CLAD that exhibits characteristics of peripheral lung fibrosis and significantly affects survival of lung transplant patients.

Innate immune activation by the viral PAMP poly I:C potentiates pulmonary graft-versus-host disease after allogeneic hematopoietic cell transplant

Respiratory viral infections cause significant morbidity and increase the risk for chronic pulmonary graft-versus-host disease (GVHD) after hematopoietic cell transplantation (HCT). Our overall hypothesis is that local innate immune activation potentiates adaptive alloimmunity. In this study, we hypothesized that a viral pathogen-associated molecular pattern (PAMP) alone can potentiate pulmonary GVHD after allogeneic HCT. We, therefore, examined the effect of pulmonary exposure to polyinosinic:polycytidylic acid (poly I:C), a viral mimetic that activates innate immunity, in an established murine HCT model. Poly I:C-induced a marked pulmonary T cell response in allogeneic HCT mice as compared to syngeneic HCT, with increased CD4+ cells in the lung fluid and tissue. This lymphocytic inflammation persisted at 2 weeks post poly I:C exposure in allogeneic mice and was associated with CD3+ cell infiltration into the bronchiolar epithelium and features of epithelial injury. In vitro, poly I:C enhanced allospecific proliferation in a mixed lymphocyte reaction. In vivo, poly I:C exposure was associated with an early increase in pulmonary monocyte recruitment and activation as well as a decrease in CD4+FOXP3+ regulatory T cells in allogeneic mice as compared to syngeneic. In contrast, intrapulmonary poly I:C did not alter the extent of systemic GVHD in either syngeneic or allogeneic mice. Collectively, our results suggest that local activation of pulmonary innate immunity by a viral molecular pattern represents a novel pathway that contributes to pulmonary GVHD after allogeneic HCT, through a mechanism that includes increased recruitment and maturation of intrapulmonary monocytes.

Should lung transplantation be performed for patients on mechanical respiratory support? The US experience

OBJECTIVE

The study objectives were to (1) compare survival after lung transplantation in patients requiring pretransplant mechanical ventilation or extracorporeal membrane oxygenation with that of patients not requiring mechanical support and (2) identify risk factors for mortality.

METHODS

Data were obtained from the United Network for Organ Sharing for lung transplantation from October 1987 to January 2008. A total of 15,934 primary transplants were performed: 586 in patients on mechanical ventilation and 51 in patients on extracorporeal membrane oxygenation. Differences between nonsupport patients and those on mechanical ventilation or extracorporeal membrane oxygenation support were expressed as 2 propensity scores for use in comparing risk-adjusted survival.

RESULTS

Unadjusted survival at 1, 6, 12, and 24 months was 83%, 67%, 62%, and 57% for mechanical ventilation, respectively; 72%, 53%, 50%, and 45% for extracorporeal membrane oxygenation, respectively; and 93%, 85%, 79%, and 70% for unsupported patients, respectively (P < .0001). Recipients on mechanical ventilation were younger, had lower forced vital capacity, and had diagnoses other than emphysema. Recipients on extracorporeal membrane oxygenation were also younger, had higher body mass index, and had diagnoses other than cystic fibrosis/bronchiectasis. Once these variables, transplant year, and propensity for mechanical support were accounted for, survival remained worse after lung transplantation for patients on mechanical ventilation and extracorporeal membrane oxygenation.

CONCLUSION

Although survival after lung transplantation is markedly worse when preoperative mechanical support is necessary, it is not dismal. Thus, additional risk factors for mortality should be considered when selecting patients for lung transplantation to maximize survival. Reduced survival for this high-risk population raises the important issue of balancing maximal individual patient survival against benefit to the maximum number of patients.

[Medical complications of lung transplantation]

In 2010, lung transplantation is a valuable therapeutic option for a number of patients suffering from of end-stage non-neoplastic pulmonary diseases. The patients frequently regain a very good quality of life, however, long-term survival is often hampered by the development of complications such as the bronchiolitis obliterans syndrome, metabolic and infectious complications. As the bronchiolitis obliterans syndrome is the first cause of death in the medium and long term, an intense immunosuppressive treatment is maintained for life in order to prevent or stabilize this complication. The immunosuppression on the other hand induces a number of potentially severe complications including metabolic complications, infections and malignancies. The most frequent metabolic complications are arterial hypertension, chronic renal insufficiency, diabetes, hyperlipidemia and osteoporosis. Bacterial, viral and fungal infections are the second cause of mortality. They are to be considered as medical emergencies and require urgent assessment and targeted therapy after microbiologic specimens have been obtained. They should not, under any circumstances, be treated empirically and it has also to be kept in mind that the lung transplant recipient may present several concomitant infections. The most frequent malignancies are skin cancers, the post-transplant lymphoproliferative disorders, Kaposi's sarcoma and some types of bronchogenic carcinomas, head/neck and digestive cancers. Lung transplantation is no longer an exceptional procedure; thus, the pulmonologist will be confronted with such patients and should be able to recognize the symptoms and signs of the principal non-surgical complications. The goal of this review is to give a general overview of the most frequently encountered complications. Their assessment and treatment, though, will most often require the input of other specialists and a multidisciplinary and transversal approach.

Indicators for steroid response in biopsy proven acute graft rejection after lung transplantation

OBJECTIVE

Acute rejection (AR) after lung transplantation (LTx) requires prompt intervention. Most episodes respond to steroid pulse therapy. The aim of this study was to evaluate clinical indicators for non-response to steroid treatment in biopsy proven AR after the early postoperative period.

METHODS

We prospectively analysed 85 patients more than 6 months after LTx with symptomatic biopsy proven AR (>or=grade A1) from Jan. 2005 until Nov. 2007 in a single centre. In 47 patients, AR was steroid-sensitive (group 1), 38 patients did not respond to steroid pulse therapy (group 2). All AR episodes were associated with clinical symptoms. Fifty-seven (67%) were low-grade rejections (ISHLT A1).

RESULTS

Independent clinical predictors for steroid response vs. non-steroid response in biopsy proven AR were "days after transplantation" (p=0.01, adjusted hazard ratio (HR) 1.2), "decline in home spirometry slope" (p=0.03, HR 0.97), "adherence to home spirometry" (p=0.05, HR 0.98) and "serum CRP" (p=0.02, HR 0.87). Eight patients (21%) of group 2 developed BOS during the following 6 months.

CONCLUSIONS

Early detection of deterioration in graft function seems to be crucial for effective treatment of AR. Home spirometry seems to be useful in detecting early changes in graft function and surveillance protocols could be potentially helpful in predicting patients likely to demonstrate a steroid response.