Absence of host tumor necrosis factor receptor 1 attenuates manifestations of idiopathic pneumonia syndrome

A call to arms: a critical need for interventions to limit pulmonary toxicity in the stem cell transplantation patient population

Noninfectious pulmonary toxicity after allogeneic hematopoietic stem cell transplantation (allo-HSCT) causes significant morbidity and mortality. Main presentations are idiopathic pneumonia syndrome (IPS) in the acute setting and bronchiolitis obliterans syndrome (BOS) and cryptogenic organizing pneumonia (COP) at later time point. While COP responds well to corticosteroids, IPS and BOS often are treatment refractory. IPS, in most cases, is rapidly fatal, whereas BOS progresses over time, resulting in chronic respiratory failure, impaired quality of life, and eventually, death. Standard second-line treatments are currently lacking, and current approaches, such as augmented T cell-directed immunosuppression, B cell depletion, TNF blockade, extracorporeal photopheresis, and tyroskine kinase inhibitor therapy, are unsatisfactory with responses in only a subset of patients. Better understanding of underlying pathophysiology hopefully results in the identification of future targets for preventive and therapeutic strategies along with an emphasis on currently underutilized rehabilitative and supportive measures.

An official American Thoracic Society research statement: noninfectious lung injury after hematopoietic stem cell transplantation: idiopathic pneumonia syndrome

RATIONALE

Acute lung dysfunction of noninfectious etiology, known as idiopathic pneumonia syndrome (IPS), is a severe complication following hematopoietic stem cell transplantation (HSCT). Several mouse models have been recently developed to determine the underlying causes of IPS. A cohesive interpretation of experimental data and their relationship to the findings of clinical research studies in humans is needed to better understand the basis for current and future clinical trials for the prevention/treatment of IPS.

OBJECTIVES

Our goal was to perform a comprehensive review of the preclinical (i.e., murine models) and clinical research on IPS.

METHODS

An ATS committee performed PubMed and OVID searches for published, peer-reviewed articles using the keywords "idiopathic pneumonia syndrome" or "lung injury" or "pulmonary complications" AND "bone marrow transplant" or "hematopoietic stem cell transplant." No specific inclusion or exclusion criteria were determined a priori for this review.

MEASUREMENTS AND MAIN RESULTS

Experimental models that reproduce the various patterns of lung injury observed after HSCT have identified that both soluble and cellular inflammatory mediators contribute to the inflammation engendered during the development of IPS. To date, 10 preclinical murine models of the IPS spectrum have been established using various donor and host strain combinations used to study graft-versus-host disease (GVHD). This, as well as the demonstrated T cell dependency of IPS development in these models, supports the concept that the lung is a target of immune-mediated attack after HSCT. The most developed therapeutic strategy for IPS involves blocking TNF signaling with etanercept, which is currently being evaluated in clinical trials.

CONCLUSIONS

IPS remains a frequently fatal complication that limits the broader use of allogeneic HSCT as a successful treatment modality. Faced with the clinical syndrome of IPS, one can categorize the disease entity with the appropriate tools, although cases of unclassifiable IPS will remain. Significant research efforts have resulted in a paradigm shift away from identifying noninfectious lung injury after HSCT solely as an idiopathic clinical syndrome and toward understanding IPS as a process involving aspects of both the adaptive and the innate immune response. Importantly, new laboratory insights are currently being translated to the clinic and will likely prove important to the development of future strategies to prevent or treat this serious disorder.

Translational research efforts in biomarkers and biology of early transplant-related complications

In the time since the first allogeneic hematopoietic stem cell transplantation (HSCT) was performed over 40 years ago, this life-saving procedure has been used increasingly for patients with hematologic, metabolic, and malignant diseases. Despite major advances in our understanding of the immunologic processes (both beneficial and injurious) that are associated with HSCT and improvements in supportive and critical care medicine, successful outcomes are still limited by several serious complications. As such, the establishment of effective therapeutic strategies for these complications will be crucial as increasing numbers of high-risk transplants are performed each year. The development of such approaches is fundamentally dependent upon a basic understanding of pathophysiologic mechanisms of disease and also on our ability to successfully translate these insights back to the bedside. This brief review will highlight breakthroughs in translational research endeavors that have paved the way for the development of novel strategies intended to change the standard of care and optimize outcomes for patients in whom allogeneic HSCT offers the only hope for a cure.

Pulmonary function changes in experimental graft-versus-host disease of the lung

Pulmonary graft-versus-host disease (p-GVHD) is a serious complication after allogeneic stem cell transplantation (allo-SCT) of high morbidity and high mortality. We characterized breathing patterns and pulmonary function changes in correlation to lung histopathology and survival by using a well-established murine model of p-GVHD. Lethally irradiated B6D2F1 mice received SCT from either syngeneic B6D2F1 or allogeneic C57BL/6 animals. Within 6 weeks, severe p-GVHD developed in allogeneic recipients characterized by progressive interstitial, alveolar, peribronchial, and periluminal inflammatory cell infiltration, whereas in syngeneic recipients lung histology remained normal. Allogeneic recipients demonstrated decreased minute ventilation (MV), reduced peak inspiratory and expiratory flow rates as early as 1 week after SCT. In addition, allo-SCT resulted in restrictive pulmonary function changes as early as 7 days after transplantation and in progressive airflow obstruction within 6 weeks. Decreased breathing abilities and pulmonary function changes of allogeneic recipients were associated with increased mortality and the severity of acute graft-versus-host disease (aGVHD). These findings show that p-GVHD can be characterized by changes in pulmonary function and functional respiratory insufficiency. Furthermore, our data strengthen the understanding, that the lung is a critical target organ of aGVHD.

Simultaneous absence of surfactant proteins A and D increases lung inflammation and injury after allogeneic HSCT in mice

The relative contributions of the hydrophilic surfactant proteins (SP)-A and -D to early inflammatory responses associated with lung dysfunction after experimental allogeneic hematopoietic stem cell transplantation (HSCT) were investigated. We hypothesized that the absence of SP-A and SP-D would exaggerate allogeneic T cell-dependent inflammation and exacerbate lung injury. Wild-type, SP-D-deficient (SP-D(-/-)), and SP-A and -D double knockout (SP-A/D(-/-)) C57BL/6 mice were lethally conditioned with cyclophosphamide and total body irradiation and given allogeneic bone marrow plus donor spleen T cells, simulating clinical HSCT regimens. On day 7, after HSCT, permeability edema progressively increased in SP-D(-/-) and SP-A/D(-/-) mice. Allogeneic T cell-dependent inflammatory responses were also increased in SP-D(-/-) and SP-A/D(-/-) mice, but the altered mediators of inflammation were not identical. Compared with wild-type, bronchoalveolar lavage fluid (BALF) levels of nitrite plus nitrate, GM-CSF, and MCP-1, but not TNF-alpha and IFN-gamma, were higher in SP-D-deficient mice before and after HSCT. In SP-A/D(-/-) mice, day 7 post-HSCT BALF levels of TNF-alpha and IFN-gamma, in addition to nitrite plus nitrate and MCP-1, were higher compared with mice lacking SP-D alone. After HSCT, both SP-A and SP-D exhibited anti-inflammatory lung-protective functions that were not completely redundant in vivo.

Interferon-gamma regulates idiopathic pneumonia syndrome, a Th17+CD4+ T-cell-mediated graft-versus-host disease

RATIONALE

Pulmonary complications of hematopoietic stem cell transplantation include infections and graft-versus-host diseases, such as idiopathic pneumonia syndrome (IPS). Conflicting data exist regarding the role of the interferon (IFN)-gamma-producing Th1 CD4(+) T-cell subset and IL-17A in IPS.

OBJECTIVES

To determine the role of IFN-gamma and IL-17A in the establishment of pulmonary graft-versus-host disease.

METHODS

A semiallogeneic murine model based on C57BL/6 x BALB/c as recipients with transplantation of BALB/c RAG2(-/-) bone marrow and transfer of different genetic knockout T cells (T-bet(-/-), IFN-gamma(-/-), IFN-gammaR(-/-)) on a BALB/c background. Lung tissue was examined for parenchymal changes and infiltrating cells by histology and fluorescence-activated cell sorter analysis.

MEASUREMENTS AND MAIN RESULTS

After transfer of semiallogeneic bone marrow together with donor CD4(+) T cells lacking IFN-gamma or T-bet-a T-box transcription factor controlling Th1 commitment-we found severe inflammation in the lungs, but no enhancement in other organs. In contrast, wild-type donor CD4(+) T cells mediated minimal inflammation only, and donor CD8(+) T cells were not required for IPS development. Mechanistically, the absence of IFN-gamma or IFN-gamma signaling in pulmonary parenchymal cells promoted expansion of IL-17A-producing CD4(+) T cells and local IL-17A release. In vivo depletion of IL-17A reduced disease severity.

CONCLUSIONS

One mechanism of IFN-gamma protection against IPS is negative regulation of the expansion of pathogenic IL-17A-producing CD4(+) T cells through interaction with the IFN-gamma receptor on the pulmonary parenchymal cell population.

A role for TNF receptor type II in leukocyte infiltration into the lung during experimental idiopathic pneumonia syndrome

Idiopathic pneumonia syndrome (IPS) is a frequently fatal complication following allogeneic stem cell transplantation (allo-SCT). Experimental models have revealed that TNF-alpha contributes to pulmonary vascular endothelial cell (EC) apoptosis, and modulates the infiltration of donor leukocytes into the lung parenchyma. The inflammatory effects of TNF-alpha are mediated by signaling through the type I (TNFRI) or type II (TNFRII) TNF receptors. We investigated the relative contribution of TNFRI and TNFRII to leukocyte infiltration into the lung following allo-SCT by using established murine models. Wild-type (wt) B6 mice or B6 animals deficient in either TNFRI or TNFRII were lethally irradiated and received SCT from allogeneic (LP/J) or syngeneic (B6) donors. At week 5 following SCT, the severity of IPS was significantly reduced in TNFRII-/- recipients compared to wt controls, but no effect was observed in TNFRI-/- animals. Bronchoalveolar lavage fluid (BALF) levels of RANTES and pulmonary ICAM-1 expression in TNFRII-/- recipients were also reduced, and correlated with a reduction of CD8(+) cells in the lung. Pulmonary inflammation was also decreased in TNFRII-/- mice using an isolated MHC class I disparate model (bm1 --> B6), and in bm1 wt mice transplanted with B6 TNF-alpha-/- donor cells. Collectively, these data demonstrate a role for TNF-alpha signaling through TNFRII in leukocyte infiltration into the lung following allo-SCT, and suggest that disruption of the TNF-alpha:TNFRII pathway may be an effective tool to prevent or treat IPS.

Regulation of caveolin-1 expression, nitric oxide production and tissue injury by tumor necrosis factor-alpha following ozone inhalation

Alveolar macrophages (AM) and inflammatory mediators including nitric oxide and peroxynitrite contribute to ozone-induced lung injury. The generation of these mediators is regulated, in part, by the transcription factor NF-kappaB. We previously demonstrated a critical role for NF-kappaB p50 in ozone-induced injury. In the present studies mechanisms regulating NF-kappaB activation in the lung after ozone inhalation were analyzed. Treatment of wild type (WT) mice with ozone (0.8 ppm, 3 h) resulted in a rapid increase in NF-kappaB binding activity in AM, which persisted for at least 12 h. This was not evident in mice lacking TNFalpha which are protected from ozone-induced injury; there was also no evidence of nitric oxide or peroxynitrite production in lungs from these animals. These data demonstrate that TNFalpha plays a role in NF-kappaB activation and toxicity. TNFalpha signaling involves PI-3-kinase (PI3K)/protein kinase B (PKB), and p44/42 MAP kinase (MAPK) which are important in NF-kappaB activation. Ozone Inhalation resulted in rapid and transient increases in p44/42 MAPK and PI3K/PKB in AM from WT mice, which was evident immediately after exposure. Caveolin-1, a transmembrane protein that negatively regulates PI3K/PKB and p44/42 MAPK signaling, was downregulated in AM from WT mice after ozone exposure. In contrast, ozone had no effect on caveolin-1, PI3K/PKB or p44/42 MAPK expression in AM from TNFalpha knockout mice. These data, together with our findings that TNFalpha suppressed caveolin-1 expression in cultured AM, suggest that TNFalpha and downstream signaling mediate activation of NF-kappaB and the regulation of inflammatory genes important in ozone toxicity, and that this process is linked to caveolin-1.

IFNgamma differentially controls the development of idiopathic pneumonia syndrome and GVHD of the gastrointestinal tract

Although proinflammatory cytokines are key mediators of tissue damage during graft-versus-host disease (GVHD), IFNgamma has previously been attributed with both protective and pathogenic effects. We have resolved this paradox by using wild-type (wt), IFNgamma(-/-), and IFNgammaR(-/-) mice as donors or recipients in well-described models of allogeneic stem cell transplantation (SCT). We show that donor-derived IFNgamma augments acute GVHD via direct effects on (1) the donor T cell to promote T helper 1 (Th1) differentiation and (2) the gastrointestinal (GI) tract to augment inflammatory cytokine generation. However, these detrimental effects are overwhelmed by a protective role of IFNgamma in preventing the development of idiopathic pneumonia syndrome (IPS). This is the result of direct effects on pulmonary parenchyma to prevent donor cell migration and expansion within the lung. Thus, IFNgamma is the key cytokine differentially controlling the development of IPS and gastrointestinal GVHD after allogeneic SCT.

Pulmonary complications of haematopoietic cell transplantation in children

Paediatric haematopoietic cell transplantation has experienced significant advances in the last few decades. However, pulmonary complications are an important limitation to the efficacy of this intervention, contributing to post-transplantation morbidity and mortality. Such complications persist even in experienced centres and occur in adult and paediatric recipients. This review identifies the paediatric pulmonary complications that are commonly seen following haematopoietic cell transplantation and addresses both infectious and non-infectious aetiologies and their clinical manifestations, evaluation, and potential therapy. Ultimately, improvement in outcomes will require attention to immunosuppression as well as traditional diagnostic procedures and treatment. This article aims to review the current state of pulmonary complications post-transplantation, to examine the impact of our recent advances and changes in treatment, and to identify potential future therapies and hypothesise what role these might have on long-term survival.

Inflammatory cytokines and the development of pulmonary complications after allogeneic hematopoietic cell transplantation in patients with inherited metabolic storage disorders

Patients with inherited metabolic storage disorders are at a higher risk of developing pulmonary complications after hematopoietic cell transplantation (HCT). This single-center prospective study of 48 consecutive inherited metabolic storage disorder patients was performed to identify risk factors for the development of pulmonary complications after HCT. Before HCT, subjects underwent bronchoalveolar lavage (BAL) for cell count, culture, nitrite levels, and analysis of proinflammatory cytokines and chemokines. The overall incidence of pulmonary complications was 52% (infectious, 23%; noninfectious, 29%) over a period of 4 years. Diffuse alveolar hemorrhage was the most frequent noninfectious complication and occurred in 19% of patients, all of whom had a diagnosis of mucopolysaccharidosis (Hurler and Maroteaux-Lamy syndromes). Levels of interleukin (IL)-1beta, IL-6, IL-8, tumor necrosis factor alpha, macrophage inflammatory protein 1alpha, and granulocyte colony-stimulating factor in BAL fluid samples obtained before HCT were higher in patients with mucopolysaccharidoses than in patients with leukodystrophies. In addition, levels of IL-1beta, IL-6, IL-8, and granulocyte colony-stimulating factor were increased in the BAL fluid of patients who developed noninfectious pulmonary complications compared with those who did not develop pulmonary complications. It is interesting to note that most noninfectious pulmonary complications occurred in patients with mucopolysaccharidoses, especially diffuse alveolar hemorrhage, which occurred exclusively in patients with mucopolysaccharidoses. Higher levels of bronchial proinflammatory cytokines and chemokines may be predictive of the development of subsequent posttransplantation noninfectious complications in patients with mucopolysaccharidoses, especially those with Hurler syndrome. Larger studies will be required to further elucidate etiologic mechanisms and predictive factors.