Review 2: Primary graft dysfunction after lung transplant-pathophysiology, clinical considerations and therapeutic targets

Therapeutic benefits of nitric oxide in lung transplantation

Lung transplantation is an evolutionary procedure from its experimental origin in the twentieth century and is now recognized as an established and routine life-saving intervention for a variety of end-stage pulmonary diseases refractory to medical management. Despite the success and continuous refinement in lung transplantation techniques, the widespread application of this important life-saving intervention is severely hampered by poor allograft quality offered from donors-after-brain-death. This has necessitated the use of lung allografts from donors-after-cardiac-death (DCD) as an additional source to expand the pool of donor lungs. Remarkably, the lung exhibits unique properties that may make it ideally suitable for DCD lung transplantation. However, primary graft dysfunction (PGD), allograft rejection and other post-transplant complications arising from unavoidable ischemia-reperfusion injury (IRI) of transplanted lungs, increase morbidity and mortality of lung transplant recipients annually. In the light of this, nitric oxide (NO), a selective pulmonary vasodilator, has been identified as a suitable agent that attenuates lung IRI and prevents PGD when administered directly to lung donors prior to donor lung procurement, or to recipients during and after transplantation, or administered indirectly by supplementing lung preservation solutions. This review presents a historical account of clinical lung transplantation and discusses the lung as an ideal organ for DCD. Next, the author highlights IRI and its clinical effects in lung transplantation. Finally, the author discusses preservation solutions suitable for lung transplantation, and the protective effects and mechanisms of NO in experimental and clinical lung transplantation.

Acellular ex vivo lung perfusate silences pro-inflammatory signaling in human lung endothelial and epithelial cells

BACKGROUND

Ischemia-reperfusion injury is a key complication following lung transplantation. The clinical application of ex vivo lung perfusion (EVLP) to assess donor lung function has significantly increased the utilization of "marginal" donor lungs with good clinical outcomes. The potential of EVLP on improving organ quality and ameliorating ischemia-reperfusion injury has been suggested.

METHODS

To determine the effects of ischemia-reperfusion and EVLP on gene expression in human pulmonary microvascular endothelial cells and epithelial cells, cell culture models were used to simulate cold ischemia (4 °C for 18 h) followed by either warm reperfusion (DMEM + 10% FBS) or EVLP (acellular Steen solution) at 37 °C for 4 h. RNA samples were extracted for bulk RNA sequencing, and data were analyzed for significant differentially expressed genes and pathways.

RESULTS

Endothelial and epithelial cells showed significant changes in gene expressions after ischemia-reperfusion or EVLP. Ischemia-reperfusion models of both cell types showed upregulated pro-inflammatory and downregulated cell metabolism pathways. EVLP models, on the other hand, exhibited downregulation of cell metabolism, without any inflammatory signals.

CONCLUSION

The commonly used acellular EVLP perfusate, Steen solution, silenced the activation of pro-inflammatory signaling in both human lung endothelial and epithelial cells, potentially through the lack of serum components. This finding could establish the basic groundwork of studying the benefits of EVLP perfusate as seen from current clinical practice.

Impact of pre-lung transplant statin use on the development of primary graft dysfunction

BACKGROUND

Primary graft dysfunction (PGD) is a common occurrence following lung transplantation and contributes to short- and long-term morbidity and mortality. Current management strategies are limited, and robust data to support their use is lacking. Preventative strategies attenuating the recipient's inflammatory state suggest statin therapy may decrease the incidence and severity of PGD. This study aims to evaluate the impact of pre-transplant statin use on the incidence and severity of PGD following lung transplantation.

METHODS

A retrospective cohort study was performed evaluating all patients undergoing bilateral lung transplantation from September 2012 to December 2019. The primary outcome was the incidence of PGD by grade, defined as the highest grade of PGD experienced in the first 72 h. Secondary outcomes included length of intensive care unit and hospital stays and mortality.

RESULTS

Of the 357 patients included in the study, 107 received statin therapy prior to transplant (statin group) and 250 did not (no statin group). PGD occurred in 257 (72%) patients; in the entire cohort, 99 (28%) patients experienced PGD grade 1, 59 (17%) grade 2, and 99 (28%) grade 3. A significantly lower incidence of PGD was observed in the statin group (64.5% vs 75.2%, p = 0.039); however, the association did not remain significant on multinominal analysis for an overall incidence of any PGD (p = 0.275) or incidence of severe PGD (p = 0.240). Statin intensity was not associated with the development of PGD.

CONCLUSIONS

Pre-transplant statin therapy did not appear to impact the development of PGD following lung transplantation. Future prospective studies should further evaluate the impact of statin intensity and duration on the incidence and severity of PGD.

New Aspects of Lung Transplantation: A Narrative Overview Covering Important Aspects of Perioperative Management

The management of lung transplant patients has continued to evolve in recent years. The year 2021 was marked by the publication of the International Consensus Recommendations for Anesthetic and Intensive Care Management of Lung Transplantation. There have been major changes in lung transplant programs over the last few years. This review will summarize the knowledge in anesthesia management of lung transplantation with the most recent data. It will highlight the following aspects which concern anesthesiologists more specifically: (1) impact of COVID-19, (2) future of transplantation for cystic fibrosis patients, (3) hemostasis management, (4) extracorporeal membrane oxygenation management, (5) early prediction of primary graft dysfunction, and (6) pain management.

Postoperative management of children after lung transplantation

Pediatric lung transplantation is a highly specialized treatment option at a select few hospitals caring for children. Advancements in surgical and medical approaches in the care of these children have improved their care with only minimal improvement in outcomes which remain the lowest of all solid organ transplants. A crucial time period in the management of these children is in the perioperative period after performance of the lung transplant. Supporting allograft function, preventing infection, maintaining fluid balance, achieving pain control, and providing optimal respiratory support are all key factors required for this highly complex pediatric patient population. We review commonly encountered complications that these patients often experience and provide strategies for management.

Effector immune cells in Chronic Lung Allograft Dysfunction: a Systematic Review

Chronic lung allograft dysfunction (CLAD) remains the major barrier to long‐term survival after lung transplantation and improved insight into its underlying immunological mechanisms is critical to better understand the disease and to identify treatment targets. We systematically searched the electronic databases of PubMed and EMBASE for original research publications, published between January 2000 and April 2021, to comprehensively assess current evidence on effector immune cells in lung tissue and bronchoalveolar lavage fluid from lung transplant recipients with CLAD. Literature search revealed 1351 articles, 76 of which met the criteria for inclusion in our analysis. Our results illustrate significant complexity in both innate and adaptive immune cell responses in CLAD, along with presence of numerous immune cell products, including cytokines, chemokines and proteases associated with tissue remodelling. A clear link between neutrophils and eosinophils and CLAD incidence has been seen, in which eosinophils more specifically predisposed to restrictive allograft syndrome. The presence of cytotoxic and T‐helper cells in CLAD pathogenesis is well‐documented, although it is challenging to draw conclusions about their role in tissue processes from predominantly bronchoalveolar lavage data. In restrictive allograft syndrome, a more prominent humoral immune involvement with increased B cells, immunoglobulins and complement deposition is seen. Our evaluation of published studies over the last 20 years summarizes the complex multifactorial immunopathology of CLAD onset and progression. It highlights the phenotype of several key effector immune cells involved in CLAD pathogenesis, as well as the paucity of single cell resolution spatial studies in lung tissue from patients with CLAD.

Lung Transplantation, Pulmonary Endothelial Inflammation, and Ex-Situ Lung Perfusion: A Review

Lung transplantation (LTx) is the gold standard treatment for end-stage lung disease; however, waitlist mortality remains high due to a shortage of suitable donor lungs. Organ quality can be compromised by lung ischemic reperfusion injury (LIRI). LIRI causes pulmonary endothelial inflammation and may lead to primary graft dysfunction (PGD). PGD is a significant cause of morbidity and mortality post-LTx. Research into preservation strategies that decrease the risk of LIRI and PGD is needed, and ex-situ lung perfusion (ESLP) is the foremost technological advancement in this field. This review addresses three major topics in the field of LTx: first, we review the clinical manifestation of LIRI post-LTx; second, we discuss the pathophysiology of LIRI that leads to pulmonary endothelial inflammation and PGD; and third, we present the role of ESLP as a therapeutic vehicle to mitigate this physiologic insult, increase the rates of donor organ utilization, and improve patient outcomes.

Ischemia-Reperfusion Injury in Lung Transplantation

Lung transplantation has been established worldwide as the last treatment for end-stage respiratory failure. However, ischemia–reperfusion injury (IRI) inevitably occurs after lung transplantation. The most severe form of IRI leads to primary graft failure, which is an important cause of morbidity and mortality after lung transplantation. IRI may also induce rejection, which is the main cause of mortality in recipients. Despite advances in donor management and graft preservation, most donor grafts are still unsuitable for transplantation. Although the pulmonary endothelium is the primary target site of IRI, the pathophysiology of lung IRI remains incompletely understood. It is essential to understand the mechanism of pulmonary IRI to improve the outcomes of lung transplantation. Therefore, we reviewed the state-of-the-art in the management of pulmonary IRI after lung transplantation. Recently, the ex vivo lung perfusion (EVLP) system has been clinically introduced worldwide. Various promising therapeutic strategies for the protection of the endothelium against IRI, including EVLP, inhalation therapy with therapeutic gases and substances, fibrinolytic treatment, and mesenchymal stromal cell therapy, are awaiting clinical application. We herein review the latest advances in the field of pulmonary IRI in lung transplantation.

Ischemia-reperfusion Injury in the Transplanted Lung: A Literature Review

Lung ischemia-reperfusion injury (LIRI) and primary graft dysfunction are leading causes of morbidity and mortality among lung transplant recipients. Although extensive research endeavors have been undertaken, few preventative and therapeutic treatments have emerged for clinical use. Novel strategies are still needed to improve outcomes after lung transplantation. In this review, we discuss the underlying mechanisms of transplanted LIRI, potential modifiable targets, current practices, and areas of ongoing investigation to reduce LIRI and primary graft dysfunction in lung transplant recipients.