Regulatory T cells in lung transplantation--an emerging concept

Donor-Specific Blood Transfusion in Lung Transplantation

Lung transplantation is still hindered by a high rate of chronic rejection necessitating profound immunosuppression with its associated complications. Donor-specific blood transfusion is a pre-transplant strategy aimed at improving graft acceptance. In contrast with standard stored blood or donor-specific regulatory T cells transfusions, this approach utilizes fresh whole blood from the donor prior to allograft transplantation, encompassing all cell types and plasma. The precise mechanisms underlying donor-specific blood transfusion-induced tolerance remain incompletely understood. Associations with regulatory/helper T cells, modulation of mononuclear phagocytic cells or microchimerism have been suggested. While numerous (pre-)clinical studies have explored its application in solid organ transplants like liver, kidney, and intestine, limited attention has been given to the setting of lung transplantation. This comprehensive review summarizes existing knowledge on the mechanisms and outcomes of donor-specific blood transfusion in solid organ transplants both in preclinical and clinical settings. We also address the potential benefits and risks associated with donor-specific blood transfusion in the field of lung transplantation, offering insights into future research directions.

Regulatory T cells: Supporting lung homeostasis and promoting resolution and repair after lung injury

Regulatory T cells, characterized by their expression of the transcription factor Forkhead box P3, are indispensable in maintaining immune homeostasis. The respiratory system is constantly exposed to many environmental challenges, making it susceptible to various insults and infections. Regulatory T cells play essential roles in maintaining homeostasis in the lung and promoting repair after injury. Regulatory T cell function dysregulation can lead to inflammation, tissue damage, or aberrant repair. Research on regulatory T cell mechanisms in the lung has unveiled their influence on lung inflammation and repair mechanisms. In this review, our goal is to highlight the advances in regulatory T cell biology with respect to lung injury and resolution. We further provide a perspective that a deeper understanding of regulatory T cell interactions in the lung microenvironment in health and disease states offers opportunities for therapeutic interventions as treatments to promote lung health.

IL-17A neutralization fails to attenuate airway remodeling and potentiates a proinflammatory lung microenvironment in diacetyl-exposed rats

Bronchiolitis obliterans (BO) is a devastating lung disease that can develop following inhalation exposure to certain chemicals. Diacetyl (DA) is one chemical commonly associated with BO development when inhaled at occupational levels. Previous studies in rats have shown that repetitive DA vapor exposures increased lung CD4+CD25+ T cells and bronchoalveolar (BAL) interleukin-17A (IL-17A) concentrations concurrent with the development of airway remodeling. We hypothesized that IL-17A neutralization would attenuate the severity of airway remodeling after repetitive DA vapor exposures. Sprague-Dawley rats were exposed to 200 parts-per-million DA vapor or filtered air (RA) for 6 h/day × 5 days and monitored for 2 wk postexposure. Treatment with IL-17A neutralization (αIL-17A) or IgG (control) began immediately following exposures and continued twice weekly until study's end. Lungs were harvested for histology, flow cytometry, and BAL analyses. Survival, oxygen saturations, and percent weight change decreased significantly in DA-exposed versus RA-exposed rats, but did not differ significantly between DA + αIL-17A versus DA + IgG. Similarly, the number nor severity of airway lesions did not differ significantly between DA + αIL-17A versus DA + IgG rats despite the percentage of lung regulatory T cells increasing with decreased BAL IL-17A concentrations. Ashcroft scoring of the distal lung parenchyma suggested worse parenchymal remodeling in DA + αIL-17A versus DA + IgG rats with increased expression of tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β), and nuclear factor-kappa B (NF-κB). Collectively, IL-17A neutralization in DA-exposed rats failed to attenuate airway remodeling with increased expression of pro-inflammatory cytokines TNF-α, IL-1β, and NF-κB.NEW & NOTEWORTHY Interleukin-17A (IL-17A) neutralization has shown benefit previously in preclinical models of transplant-associated bronchiolitis obliterans (BO), yet it remains unknown whether IL-17A neutralization has similar benefit for other forms of BO. Here, IL-17A neutralization fails to prevent severe airway remodeling in rats exposed repetitively to the flavoring chemical diacetyl, and instead, promotes a proinflammatory microenvironment with increased expression of TNF-α, IL-1β, and NF-κB within the lung.

Monitoring regulatory T cells as a prognostic marker in lung transplantation

Lung transplantation is the major surgical procedure, which restores normal lung functioning and provides years of life for patients suffering from major lung diseases. Lung transplant recipients are at high risk of primary graft dysfunction, and chronic lung allograft dysfunction (CLAD) in the form of bronchiolitis obliterative syndrome (BOS). Regulatory T cell (Treg) suppresses effector cells and clinical studies have demonstrated that Treg levels are altered in transplanted lung during BOS progression as compared to normal lung. Here, we discuss levels of Tregs/FOXP3 gene expression as a crucial prognostic biomarker of lung functions during CLAD progression in clinical lung transplant recipients. The review will also discuss Treg mediated immune tolerance, tissue repair, and therapeutic strategies for achieving in-vivo Treg expansion, which will be a potential therapeutic option to reduce inflammation-mediated graft injuries, taper the toxic side effects of ongoing immunosuppressants, and improve lung transplant survival rates.

A Comprehensive Review on the Surgical Aspect of Lung Transplant Models in Mice and Rats

Lung transplantation improves the outcome and quality of life of patients with end-stage pulmonary disease. However, the procedure is still hampered by the lack of suitable donors, the complexity of the surgery, and the risk of developing chronic lung allograft dysfunction. Over the past decades, translational experiments in animal models have led to a better understanding of physiology and immunopathology following the lung transplant procedure. Small animal models (e.g., rats and mice) are mostly used in experiments regarding immunology and pathobiology and are preferred over large animal models due to the ethical aspects, the cost-benefit balance, and the high throughput possibility. In this comprehensive review, we summarize the reported surgical techniques for lung transplantation in rodent models and the management of perioperative complications. Furthermore, we propose a guide to help identify the appropriate species for a given experiment and discuss recent experimental findings in small animal lung transplant models.

γδT17/γδTreg cell subsets: a new paradigm for asthma treatment

Bronchial asthma (abbreviated as asthma), is a heterogeneous disease characterized by chronic airway inflammation and airway hyperresponsiveness. The main characteristics of asthma include variable reversible airflow limitation and airway remodeling. The pathogenesis of asthma is still unclear. Th1/Th2 imbalance, Th1 deficiency and Th2 hyperfunction are classic pathophysiological mechanisms of asthma. Some studies have shown that the imbalance of the Th1/Th2 cellular immune model and Th17/Treg imbalance play a key role in the occurrence and development of asthma; however, these imbalances do not fully explain the disease. In recent years, studies have shown that γδT and γδT17 cells are involved in the pathogenesis of asthma. γδTreg has a potential immunosuppressive function, but its regulatory mechanisms have not been fully elucidated. In this paper, we reviewed the role of γδT17/γδTreg cells in bronchial asthma, including the mechanisms of their development and activation. Here we propose that γδT17/Treg cell subsets contribute to the occurrence and development of asthma, constituting a novel potential target for asthma treatment.

Regulatory and Effector Cell Disequilibrium in Patients with Acute Cellular Rejection and Chronic Lung Allograft Dysfunction after Lung Transplantation: Comparison of Peripheral and Alveolar Distribution

Background: The immune mechanisms occurring during acute rejection (AR) and chronic lung allograft dysfunction are a challenge for research and the balance between effector and regulatory cells has not been defined completely. In this study, we aimed to elucidate the interaction of effector cells, mainly Th17, Th1 and Th2, and regulatory cells including (CD4⁺CD25⁺CD127^low/−) T reg cells and phenotypes of B regs, CD19⁺CD24^hiCD38^hi, CD19⁺CD24^hiCD27^hi and CD19⁺CD5⁺CD1d⁺. Methods: Bronchoalveolar lavage cells (BAL) and peripheral blood mononuclear cells (PBMCs) from stable lung transplanted (LTx )subjects (n = 4), AR patients (n = 6) and bronchiolitis obliterans syndrome (BOS) (n = 6) were collected at the same time. Cellular subsets were detected through flow cytometry. Results: A predominance of Th17 cells subtypes in the PBMCs and BAL and a depletion of Tregs, that resulted in decrease Treg/Th17 ratio, was observed in the AR group. CD19⁺CD24^hiCD38^hi Bregs resulted increased in BAL of AR patients. Th1 cells predominance and a reduction of Tregs cells was observed in BAL from AR patients. Moreover, multivariate analysis showed interdependences within studied variables revealing that effector cells and regulatory cells can effectively discriminate patients’ immunological status. Conclusions: In AR, BOS and stable lung transplant, regulatory and effector cells clearly demonstrated different pathways of activation. Understanding of the balance of T cells and T and B regulatory cells can offers insights into rejection.

Combined low-dose everolimus and low-dose tacrolimus after Alemtuzumab induction therapy: a randomized prospective trial in lung transplantation

BACKGROUND

Long-term outcomes of lung transplantation are severely affected by comorbidities and development of chronic rejection. Among the comorbidities, kidney insufficiency is one of the most frequent and it is mainly caused by the cumulative effect of calcineurin inhibitors (CNIs). Currently, the most used immunosuppression protocols worldwide include induction therapy and a triple-drug maintenance immunosuppression, with one calcineurin inhibitor, one anti-proliferative drug, and steroids. Our center has pioneered the use of alemtuzumab as induction therapy, showing promising results in terms of short- and long-term outcomes. The use of alemtuzumab followed by a low-dose double drug maintenance immunosuppression, in fact, led to better kidney function along with excellent results in terms of acute rejection, chronic lung allograft dysfunction, and survival (Benazzo et al., PLoS One 14(1):e0210443, 2019). The hypothesis driving the proposed clinical trial is that de novo introduction of low-dose everolimus early after transplantation could further improve kidney function via a further reduction of tacrolimus. Based on evidences from kidney transplantation, moreover, alemtuzumab induction therapy followed by a low-dose everolimus and low-dose tacrolimus may have a permissive action on regulatory immune cells thus stimulating allograft acceptance.

METHODS

A randomized prospective clinical trial has been set up to answer the research hypothesis. One hundred ten patients will be randomized in two groups. Treatment group will receive the new maintenance immunosuppression protocol based on low-dose tacrolimus and low-dose everolimus and the control group will receive our standard immunosuppression protocol. Both groups will receive alemtuzumab induction therapy. The primary endpoint of the study is to analyze the effect of the new low-dose immunosuppression protocol on kidney function in terms of eGFR change. The study will have a duration of 24 months from the time of randomization. Immunomodulatory status of the patients will be assessed with flow cytometry and gene expression analysis.

DISCUSSION

For the first time in the field of lung transplantation, this trial proposes the combined use of significantly reduced tacrolimus and everolimus after alemtuzumab induction. The new protocol may have a twofold advantage: (1) further reduction of nephrotoxic tacrolimus and (2) permissive influence on regulatory cells development with further reduction of rejection episodes.

TRIAL REGISTRATION

EUDRACT Nr 2018-001680-24. Registered on 15 May 2018.

Nlrp3 Inflammasome Inhibitor MCC950 Ameliorates Obliterative Bronchiolitis by Inhibiting Th1/Th17 Response and Promoting Treg Response After Orthotopic Tracheal Transplantation in Mice

BACKGROUND

Obliterative bronchiolitis (OB) remains the major complication limiting long-term survival of patients after lung transplantation. We aimed to explore the effects of the selective NACHT, LRR, and PYD domains-containing protein 3 (Nlrp3) inflammasome inhibitor MCC950 on the pathogenesis of OB.

METHODS

Mouse orthotopic tracheal transplants were performed to mimic OB. MCC950 (50 mg/kg) or saline was intraperitoneally injected daily. The luminal occlusion rate and collagen deposition were evaluated by hematoxylin and eosin and Masson's trichrome staining, respectively. Infiltration of CD4+, CD8+ T cells, and neutrophils was detected with immunohistochemical staining. The frequencies of T helper 1 cell (Th1), T helper 17 cell (Th17), and regulatory T cells (Treg) were measured by flow cytometry. Cytokine levels were measured by ELISA kits.

RESULTS

MCC950 treatment significantly inhibited Nlrp3 inflammasome activation after allogeneic tracheal transplant and markedly decreased the luminal occlusion rate and collagen deposition in the allograft. The numbers of infiltrating CD4+, CD8+ T cells, and neutrophils in the allograft were also significantly reduced by MCC950 treatment. MCC950 dramatically decreased the frequencies of Th1/Th17 cells and the levels of interferon gamma/interleukin (IL)-17A and increased the Treg cell frequencies and IL-10 level; however, these effects were abolished by the addition of IL-1β and IL-18 both in vitro and in vivo. OB was also rescued by the addition of IL-1β and/or IL-18.

CONCLUSIONS

Blocking Nlrp3 inflammasome activation with MCC950 ameliorates OB lesions. The mechanistic analysis showed that MCC950 regulated the balance of Th1/Th17 and Treg cells and that this process is partially mediated by inhibition of IL-1β and IL-18. Therefore, targeting the Nlrp3 inflammasome is a promising strategy for controlling OB after lung transplantation.

[Predictors for the Bronchiolitis Obliterans Syndrome in Lung Transplant Patient]

肺移植是治疗终末期肺病的有效方法。目前，肺移植术后1年生存率已达到80%，由于闭塞性细支气管炎综合症（bronchiolitis obliterans syndrome, BOS）的发生，5年生存率维持在50%左右。BOS是一个纤维化的过程，最终导致不可逆的气道闭塞。缺血-再灌注损伤、感染、氧化应激以及急性排斥反应等多个因素参与了BOS的发生。研究证实BOS的早期诊断与预后良好相关。因此，寻找灵敏、特异的BOS预测标记物对于提高肺移植患者长期生存具有重要的科学和临床意义。本文就与BOS发生发展相关的免疫调节细胞、分泌性蛋白质、细胞膜蛋白等指标的变化在BOS早期诊断中的作用进行综述。

Precision medicine: integration of genetics and functional genomics in prediction of bronchiolitis obliterans after lung transplantation

PURPOSE OF REVIEW

Lung transplantation (LTx) can be a life saving treatment in end-stage pulmonary diseases, but survival after transplantation is still limited. Posttransplant development of chronic lung allograft dysfunction with bronchiolits obliterans syndrome (BOS) as the major subphenotype, is the main cause of morbidity and mortality. Early identification of high-risk patients for BOS is a large unmet clinical need. In this review, we discuss gene polymorphisms and gene expression related to the development of BOS.

RECENT FINDINGS

Candidate gene studies showed that donor and recipient gene polymorphisms affect transplant outcome and BOS-free survival after LTx. Both selective and nonselective gene expression studies revealed differentially expressed fibrosis and apoptosis-related genes in BOS compared with non-BOS patients. Significantly, recent microarray expression analysis of blood and broncho-alveolar lavage suggest a role for B-cell and T-cell responses prior to the development of BOS. Furthermore, 6 months prior to the development of BOS differentially expressed genes were identified in peripheral blood cells.

SUMMARY

Genetic polymorphisms and gene expression changes are associated with the development of BOS. Future genome wide studies are needed to identify easily accessible biomarkers for prediction of BOS toward precision medicine.

Splenocyte Infusion and Whole-Body Irradiation for Induction of Peripheral Tolerance in Porcine Lung Transplantation: Modifications of the Preconditioning Regime for Improved Clinical Feasibility

BACKGROUND

Preoperative low-dose whole-body irradiation (IRR) with 1.5 and 7 Gy thymic IRR of the recipient, combined with a perioperative donor splenocyte infusion lead to reliable donor specific peripheral tolerance in our allogeneic porcine lung transplantation model. To reduce the toxicity of this preconditioning regime, modifications of the IRR protocol and their impact on allograft survival were assessed.

METHODS

Left-sided single lung transplantation from major histocompatibility complex and sex mismatched donors was performed in 14 adult female minipigs. Recipient animals were exposed to 3 different protocols of nonmyeloablative IRR within 12 hours before transplantation. All animals were administered a donor splenocyte infusion on the day of lung transplantation. Intravenous pharmacologic immunosuppression was withdrawn after 28 postoperative days. Allograft survival was monitored by chest radiographs and bronchoscopy.

RESULTS

IRR prolonged transplant survival in a dose- and field-dependent manner. Shielding of the bone marrow from IRR (total lymphoid IRR at 1.5 and 7 Gy thymic IRR) significantly reduced protocol toxicity defined as thrombocytopenia and consecutive increased bleeding propensity, but had a less effective impact on graft survival. Whole-body IRR at 0.5 and 7 Gy thymic IRR proved to be ineffective for reliable tolerance induction. Eventually, high levels of circulating CD4⁺CD25^high regulatory T cells were present in long-term survivors.

CONCLUSIONS

These data show that the infusion of donor-specific alloantigen in combination with IRR is efficient once a threshold dose is exceeded.

Association of Higher CD4+ CD25high CD127low , FoxP3+ , and IL-2+ T Cell Frequencies Early After Lung Transplantation With Less Chronic Lung Allograft Dysfunction at Two Years

Regulatory T cells (Treg) can regulate alloantigens and may counteract chronic lung allograft dysfunction (CLAD) in lung transplantation. We analyzed Treg in peripheral blood prospectively and correlated percentages of subpopulations with the incidence of CLAD at 2 years. Among lung-transplanted patients between January 2009 and July 2011, only patients with sufficient Treg measurements were included into the study. Tregs were measured immediately before lung transplantation, at 3 weeks and 3, 6, 12, and 24 months after transplantation and were defined as CD4⁺ CD25^high T cells and further analyzed for CTLA4, CD127, FoxP3, and IL-2 expressions. Between January 2009 and July 2011, 264 patients were transplanted at our institution. Among the 138 (52%) patients included into the study, 31 (22%) developed CLAD within 2 years after transplantation. As soon as 3 weeks after lung transplantation, a statistically significant positive association was detected between Treg frequencies and later absence of CLAD. At the multivariate analysis, increasing frequencies of CD4⁺ CD25^high CD127^low , CD4⁺ CD25^high FoxP3⁺ and CD4⁺ CD25^high IL-2⁺ T cells at 3 weeks after lung transplantation emerged as protective factors against development of CLAD at 2 years. In conclusion, higher frequencies of specific Treg subpopulations early after lung transplantation are protective against CLAD development.

Airway remodelling in the transplanted lung

Following lung transplantation, fibrotic remodelling of the small airways has been recognized for almost 5 decades as the main correlate of chronic graft failure and a major obstacle to long-term survival. Mainly due to airway fibrosis, pulmonary allografts currently show the highest attrition rate of all solid organ transplants, with a 5-year survival rate of 58 % on a worldwide scale. The observation that these morphological changes are not just the hallmark of chronic rejection but rather represent a manifestation of a multitude of alloimmune-dependent and -independent injuries was made more recently, as was the discovery that chronic lung allograft dysfunction manifests in different clinical phenotypes of respiratory impairment and corresponding morphological subentities. Although recent years have seen considerable advances in identifying and categorizing these subgroups on the basis of clinical, functional and histomorphological changes, as well as susceptibility to medicinal treatment, this process is far from over. Since the actual pathophysiological mechanisms governing airway remodelling are still only poorly understood, diagnosis and therapy of chronic lung allograft dysfunction presents a major challenge to clinicians, radiologists and pathologists alike. Here, we review and discuss the current state of the literature on chronic lung allograft dysfunction and shed light on classification systems, corresponding clinical and morphological changes, key cellular players and underlying molecular pathways, as well as on emerging diagnostic and therapeutic approaches.

[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.

Inducible costimulatory molecule deficiency induced imbalance of Treg and Th17/Th2 delays rejection reaction in mice undergoing allogeneic tracheal transplantation

OBJECTIVE

This study aimed to investigate the role of inducible costimulatory molecule (ICOS) pathway in the rejection reaction of mice undergoing allogeneic tracheal transplantation.

METHODS

The bronchus was separated from wide-type (WT) BalB/c mice and transplanted into WT BalB/c mice, C57 mice and icos(-/-) mice to prepare the obliterative bronchiolitis (OB) animal model. The transplanted bronchus was pathologically examined; flow cytometry was done to detect the T cell subsets and activity of the bronchus and spleen of recipient mice.

RESULTS

21 d after transplantation, evident rejection reaction was observed and the proportion of Th2 and Th17 cells increased significantly in the bronchus and spleen in C57 mice receiving allogeneic tracheal transplantation when compared with mice with autologous transplantation, but the proportion of Treg cells was comparable between them. When compared with WT BalB/c mice, the proportion of Th2, Th17 and Treg cells reduced markedly and rejection reaction was attenuated in icos(-/-) mice receiving tracheal transplantation, although rejection reaction was still noted.

CONCLUSION

icos knockout may delay the rejection reaction after tracheal transplantation, which might be ascribed to the imbalance among Th2, Th17 and Treg cells.

An international ISHLT/ATS/ERS clinical practice guideline: diagnosis and management of bronchiolitis obliterans syndrome

Bronchiolitis obliterans syndrome (BOS) is a major complication of lung transplantation that is associated with poor survival. The International Society for Heart and Lung Transplantation, American Thoracic Society, and European Respiratory Society convened a committee of international experts to describe and/or provide recommendations for 1) the definition of BOS, 2) the risk factors for developing BOS, 3) the diagnosis of BOS, and 4) the management and prevention of BOS. A pragmatic evidence synthesis was performed to identify all unique citations related to BOS published from 1980 through to March, 2013. The expert committee discussed the available research evidence upon which the updated definition of BOS, identified risk factors and recommendations are based. The committee followed the GRADE (Grading of Recommendation, Assessment, Development and Evaluation) approach to develop specific clinical recommendations. The term BOS should be used to describe a delayed allograft dysfunction with persistent decline in forced expiratory volume in 1 s that is not caused by other known and potentially reversible causes of post-transplant loss of lung function. The committee formulated specific recommendations about the use of systemic corticosteroids, cyclosporine, tacrolimus, azithromycin and about re-transplantation in patients with suspected and confirmed BOS. The diagnosis of BOS requires the careful exclusion of other post-transplant complications that can cause delayed lung allograft dysfunction, and several risk factors have been identified that have a significant association with the onset of BOS. Currently available therapies have not been proven to result in significant benefit in the prevention or treatment of BOS. Adequately designed and executed randomised controlled trials that properly measure and report all patient-important outcomes are needed to identify optimal therapies for established BOS and effective strategies for its prevention.

Adaptive and innate immune responses in a rat orthotopic lung transplant model of chronic lung allograft dysfunction

Acute rejection and respiratory infections are major risk factors for chronic lung allograft dysfunction (CLAD) after lung transplantation. To shed light on the enigmatic etiology of CLAD, we test the following hypotheses using a new experimental model: (i) Alloimmune-independent pulmonary inflammation reactivates alloimmunity. (ii) Alloimmunity enhances the susceptibility of the graft toward pathogen-associated molecular patterns. Pulmonary Fischer 344 to Lewis rat allografts were treated with lipopolysaccharide (LPS), which consistently results in lesions typical for CLAD. Grafts, local lymph nodes, and spleens were harvested before (day 28) and after LPS application (days 29, 33, and 40) for real-time RT-PCR and immunohistochemistry. Mixed lymphocyte reactions were performed on day 33. Four weeks after transplantation, lung allografts displayed mononuclear infiltrates compatible with acute rejection and overexpressed most components of the toll-like receptor system. Allografts but not secondary lymphoid organs expressed increased levels of Th1-type transcription factors and cytokines. LPS induced macrophage infiltration as well as mRNA expression of pro-inflammatory cytokines and effector molecules of innate immunity. Unexpectedly, T-cell reactivity was not enhanced by LPS. We conclude that prevention of CLAD might be accomplished by local suppression of Th1 cells in stable grafts and by controlling innate immunity during alloimmune-independent pulmonary inflammation.

Lung transplantation

Lung transplantation may be the only intervention that can prolong survival and improve quality of life for those individuals with advanced lung disease who are acceptable candidates for the procedure. However, these candidates may be extremely ill and require ventilator and/or circulatory support as a bridge to transplantation, and lung transplantation recipients are at risk of numerous post-transplant complications that include surgical complications, primary graft dysfunction, acute rejection, opportunistic infection, and chronic lung allograft dysfunction (CLAD), which may be caused by chronic rejection. Many advances in pre- and post-transplant management have led to improved outcomes over the past decade. These include the creation of sound guidelines for candidate selection, improved surgical techniques, advances in donor lung preservation, an improving ability to suppress and treat allograft rejection, the development of prophylaxis protocols to decrease the incidence of opportunistic infection, more effective therapies for treating infectious complications, and the development of novel therapies to treat and manage CLAD. A major obstacle to prolonged survival beyond the early post-operative time period is the development of bronchiolitis obliterans syndrome (BOS), which is the most common form of CLAD. This manuscript discusses recent and evolving advances in the field of lung transplantation.

Inflammatory signalling associated with brain dead organ donation: from brain injury to brain stem death and posttransplant ischaemia reperfusion injury

Brain death is associated with dramatic and serious pathophysiologic changes that adversely affect both the quantity and quality of organs available for transplant. To fully optimise the donor pool necessitates a more complete understanding of the underlying pathophysiology of organ dysfunction associated with transplantation. These injurious processes are initially triggered by catastrophic brain injury and are further enhanced during both brain death and graft transplantation. The activated inflammatory systems then contribute to graft dysfunction in the recipient. Inflammatory mediators drive this process in concert with the innate and adaptive immune systems. Activation of deleterious immunological pathways in organ grafts occurs, priming them for further inflammation after engraftment. Finally, posttransplantation ischaemia reperfusion injury leads to further generation of inflammatory mediators and consequent activation of the recipient's immune system. Ongoing research has identified key mediators that contribute to the inflammatory milieu inherent in brain dead organ donation. This has seen the development of novel therapies that directly target the inflammatory cascade.