Pulmonary retransplantation in paediatric patients: a justified therapeutic option? A single-centre experience

Lung transplantation in children

Lung transplantation is a well-established treatment for children facing advanced lung disease and pulmonary vascular disorders. However, organ shortage remains highest in children. For fitting the small chest of children, transplantation of downsized adult lungs, lobes, or even segments were successfully established. The worldwide median survival after pediatric lung transplantation is currently 5.7 years, while under consideration of age, underlying disease, and peri- and posttransplant center experience, median survival of more than 10 years is reported. Timing of referral for transplantation, ischemia-reperfusion injury, primary graft dysfunction, and acute and chronic rejection after transplantation remain the main challenges.

[Aberrant reparative tissue remodeling: histopathology and molecular pathology]

Not only tumorous infiltrations can lead to destruction of parenchymal organs but also the aberrant proliferation and matrix production of mesenchymal cells and vessels during a dysregulated repair attempt. This fibrogenesis is the result of a complex pathogenesis, which can be investigated in animal models but also in situ to harvest new biomarkers. This article deals particularly with the second method and summarizes molecular pathological findings in various model diseases for aberrant reparative tissue reconstruction. These model diseases include plexiform vasculopathy in pulmonary arterial hypertension (PAH), Quilty lesions in heart transplantation, bronchiolitis obliterans (BO), inflammatory airway remodeling and Epstein-Barr virus (EBV) induced smooth muscle proliferation (posttransplantation smooth muscle tumor, PTSMT).Using in situ molecular pathology, we were able to dismiss an assumed involvement of myofibroblastic cells in vessel reconstruction of the lung in PAH. We could also for the first time perform a comprehensive molecular characterization of the vascular remodeling and prove that plexiform vasculopathy represents a complex-regulated epiphenomenon of excessive pulmonary hypertension. This method also allowed us to describe for the first time the miRNA expression in PAH in a compartment-specific manner and to draw conclusions regarding the damaged overriding regulatory mechanisms. In the same way, we were also able to describe the chimeric character of the complex neoangiogenesis in the donor organ after heart transplantation.After lung transplantation, we identified for the first time a group of tissue-based molecular markers, which can predict later occurrence of BO even in morphologically normal transbronchial biopsies. In addition, we have documented for the first time the molecular characteristics of the morphologically analogous airway reconstruction in lung-transplanted and non-transplanted patients. We could further elucidate the role of matrix metalloproteinases (MMP) and their antagonists in inflammatory airway reconstruction and deduce from this the resulting therapeutic implications. Accordingly, we were able to further clarify the origin, pathogenesis and the malignant potential of EBV-induced PTSMT and for the first time provide an evidence-based therapy recommendation and risk assessment.In summary, this article documents that in situ diagnostics can meet the requirements of the challenging parameters and issues of life sciences. It is to be expected that the technical possibilities will develop analogously to the increasing demands and the in situ method will move further into the focus of molecular pathology.

Differential outcomes with early and late repeat transplantation in the era of the lung allocation score

BACKGROUND

Rates of repeat lung transplantation have increased since implementation of the lung allocation score (LAS). The purpose of this study is to compare survival between repeat (ReTx) and primary (LTx) lung transplant recipients in the LAS era.

METHODS

We extracted data from 9,270 LTx and 456 ReTx recipients since LAS implementation, from the United Network for Organ Sharing registry. Propensity scoring was used to match ReTx and LTx recipients. Kaplan-Meier analysis compared survival between LTx and ReTx groups, with and without stratification based on time between first and second transplant. Multivariable Cox models estimated predictors of survival in lung recipients.

RESULTS

Comparing all ReTx to LTx demonstrates a survival advantage for LTx that is diminished with propensity score matching (p = 0.174). Considering LTx against ReTx greater than 90 days after the initial procedure, there are similar survival results (p < 0.067). In contrast, ReTx within 90 days was associated with a survival disadvantage that persisted despite matching (p = 0.011). In ReTx populations, factors conferring worse outcomes include intensive care unit admission, unilateral transplantation, poor functional status, and primary graft dysfunction as the indication for retransplantation (p < 0.05).

CONCLUSIONS

Late lung retransplantation appears to be as beneficial as primary transplantation in propensity-matched patients. However, survival is severely diminished in those retransplanted less than 90 days after primary transplantation. The utility of early retransplantation needs to be carefully weighed in light of risks.

Managing bronchiolitis obliterans syndrome (BOS) and chronic lung allograft dysfunction (CLAD) in children: what does the future hold?

The success of pediatric lung transplantation continues to be limited by long-term graft dysfunction. Historically this has been characterized as an obstructive spirometric defect in the form of the bronchiolitis obliterans syndrome (BOS). It is recognized, however, that this does not reflect many of the other acknowledged etiologies of chronic lung dysfunction-noting it is the sum of the parts that contribute to respiratory morbidity and mortality after transplant. The term chronic lung allograft dysfunction (CLAD) has been coined to reflect these other entities and, in particular, a group of relatively recently described lung disorders called the restrictive allograft syndrome (RAS). RAS is characterized by a restrictive spirometric defect. Although these entities have not yet been studied in a pediatric setting their association with poor compliance, antibody-mediated rejection (AMR), and post-infectious lung damage (particularly viral) warrants attention by pediatric lung transplant teams. Current therapy for the BOS subset of CLAD is otherwise limited to changing immunosuppressants and avoiding excessive infectious risk by avoiding over-immunosuppression. Long-term macrolide therapy in lung transplantation is not of proven efficacy. Reviewing previous BOS studies to explore restrictive spirometric cases and joint projects via groups like the International Pediatric Lung Transplant Collaborative will be the way forward to solve this pressing problem.

Lung re-transplantation: review

PURPOSE OF REVIEW

Re-transplantation of the lung has come of age. Here, we wish to review the recent literature on the topic and discuss clinical implications.

RECENT FINDINGS

Many large volume transplant centres routinely perform lung re-transplantation with satisfactory outcomes. The main indication is bronchiolitis obliterans syndrome, that is chronic rejection of a previous lung transplant. Other indications, such as primary graft failure or early airway complications, are regarded with more caution, as outcomes compare less favourably with those following primary transplantation.

SUMMARY

Re-transplantation of the lung can be performed safely and with outcomes rivalling those of primary transplants in carefully selected recipients with chronic rejection of a previous transplant.

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.