Preemptive treatment of de novo donor-specific antibodies in lung transplant patients reduces subsequent risk of chronic lung allograft dysfunction or death

Using a combination of biomarkers to monitor allograft dysfunction in lung transplant recipients

Allograft dysfunction is a major limitation of survival in organ transplant recipients including those who have received lung transplantation. Early detection of allograft dysfunction is thus crucial to improve outcomes in these patients. However, there are several causes of allograft dysfunction with allograft infection and rejection being the two important causes. It is often difficult to distinguish between those causes as the presentation can be similar. Allograft rejection, especially antibody-mediated rejection (AMR) and chronic lung allograft dysfunction (CLAD) are often identified too late where progression has already occurred. Biomarkers like anti-HLA antibodies including donor-specific antibodies (DSA), donor-derived cell-free DNA (dd-cfDNA), immune cell function (ICF) assays and next-generation sequencing for microorganisms allow for early identification of allograft dysfunction as well as differentiate rejection from other processes such as infection. This in turn allows for early intervention and, ideally, improved long-term allograft outcomes. Greater evidence exists for these biomarkers in other solid organ transplantations including kidney and heart transplantation, but application to lung transplant recipients is increasing and seems equally promising. In this review, we evaluate existing evidence for using these biomarkers and share our center practice in utilizing a combination of these biomarkers post-transplantation to assess for allograft dysfunction.

Survival of patients with advanced chronic lung allograft dysfunction and the role of redo transplantation

Background

Lung transplantation (LTx) is a treatment option for end-stage lung disease. Chronic lung allograft dysfunction (CLAD) poses challenges to long-term survival. CLAD is usually progressive with a poor prognosis and limited treatment options. Advanced CLAD is the most common indication for redo lung transplantation (LRT). Decision-making on LRT varies between centers.

Methods

This study aimed to explore key aspects of advanced CLAD management, with a focus on disparities in redo transplantation referral and listing rates. A retrospective cohort study was conducted across follow-up clinics at 2 major European centers, examining patient characteristics, treatment approaches, clinical outcomes, and prognostic factors in individuals with advanced CLAD.

Results

In a cohort of 177 patients with advanced CLAD, bronchiolitis obliterans syndrome was the predominant phenotype (66%). Significant morbidity was observed, with 66% of patients severely disabled and 49% on oxygen therapy. Over a median follow-up of 568 days, 94 patients died, with a 2-year survival rate of only 25%. LRT was pursued in 72 patients, with 31 undergoing the procedure. Post-LRT mortality was high (48%), particularly in patients requiring advanced respiratory support. Key risk factors for mortality included restrictive or mixed CLAD phenotypes (hazard ratio [HR] 2.759), rapid disease progression (HR 49.671), and urgent LRT (HR 0.026).

Conclusions

Advanced CLAD patients face high morbidity and mortality. Redo transplantation seems to offer survival benefit in elective patients. Early referral for redo transplantation and proactive management strategies are essential for improving patient outcomes.

Pseudomonas aeruginosa infection induces intragraft lymphocytotoxicity that triggers lung transplant antibody-mediated rejection

How pathogens inhibit transplant tolerance remains unclear. Here, we found that Pseudomonas aeruginosa infection, but not other common bacterial respiratory infections, increases antibody-mediated rejection (AMR) risk in recipients of lung transplants. To explore this relationship, we performed orthotopic lung transplants in mice, infected recipients with P. aeruginosa, and observed for the development of AMR. Intravital two-photon microscopy showed that P. aeruginosa rapidly invaded bronchial-associated lymphoid tissues, which resulted in acute lymphocytotoxicity, including the death of forkhead box P3 (Foxp3)+CD4+ T cells that are required to suppress AMR. P. aeruginosa-mediated AMR required expression of the type III secretion system (T3SS), which injects exotoxins into the cell cytoplasm. Through a combination of mutagenesis and epitope tagging experiments, we revealed that T3SS exotoxin T ADP ribosyl-transferase activity was sufficient for graft-resident Foxp3+CD4+ T cell apoptosis, leading to myeloid differentiation primary response 88 (Myd88)-dependent generation of T-box expressed in T cells (T-bet)- and C-X-C motif chemokine receptor 3 (CXCR3)-positive germinal center and memory B cells with high donor antigen avidity. We also found that T-bet+ and CXCR3+ B cells were elevated in biopsies from recipients of lung transplants who were diagnosed with AMR. In mice, CXCR3 deficiency restricted to B cells or CXCR3 blockade prevented AMR despite P. aeruginosa infection. Our work has identified a previously unrecognized role of bacterial virulence in lung allograft rejection and suggests potential strategies to prevent AMR for those at high risk of P. aeruginosa infection after transplant.

Efficacy of a Standardized Regimen of Therapeutic Plasma Exchange and IVIG for Treatment of Antibody-Mediated Rejection in Lung Transplant Recipients

Antibody-mediated rejection (AMR) in lung transplantation has been associated with poor long-term clinical course and is a risk factor for chronic lung allograft dysfunction and graft loss. Appropriate management of AMR is necessary to improve graft survival in lung transplant recipients. There is currently no standardized approach to the treatment of lung AMR, and practices vary by institution. We sought to examine the efficacy of a standardized protocol of plasma exchange (PLEX) and IVIG in decreasing donor-specific antibodies (DSAs) and improving AMR in lung transplant recipients. A retrospective chart review was conducted on all lung transplant recipients who completed a course of PLEX per UT Southwestern AMR protocol between January 2012 and December 2019 for diagnosis of AMR. Data were collected on the patient clinical course, treatment regimen, pre-PLEX DSA, post-PLEX DSA, follow-up (> 1-month post-PLEX) DSA, and pre-and post-PLEX biopsy, when available. Of 527 patients who underwent lung transplantation during the study period, 56 (11%) received an acute course of PLEX every other day per protocol for AMR of lung transplant. Forty (71%) of 56 patients had one episode of AMR requiring PLEX; 16 patients (29%) had repeat episodes of AMR within 6 weeks to 47 months of the first episode. Most patients showed improvement in AMR on biopsy (69%) and a decline in DSA (68%). Our data suggest that treatment with combined PLEX and IVIG protocol appears effective for treating lung AMR.

Update on the immunological mechanisms of primary graft dysfunction and chronic lung allograft dysfunction

PURPOSE OF REVIEW

Primary graft dysfunction (PGD) and chronic lung allograft dysfunction (CLAD) are the leading causes of graft loss in lung transplant recipients. The development of mouse lung transplant models has allowed for the genetic dissection of cellular and molecular pathways that prevent graft survival. This review provides an overview into recent mechanistic insights into PGD and CLAD.

RECENT FINDINGS

Mouse orthotopic lung transplant models and investigations of human lung transplant recipeints have revealed new molecular and cellular targets that promote PGD and CLAD. Donor and recipient-derived innate immune cells promote PGD and CLAD. PGD is driven by communication between classical monocytes and tissue-resident nonclassical monocytes activating alveolar macrophages to release chemokines that recruit neutrophils. Products of cell damage trigger neutrophil NET release, which together with NK cells, antibodies and complement, that further promote PGD. The development of CLAD involves circuits that activate B cells, CD8 + T cells, classical monocytes, and eosinophils.

SUMMARY

Effective targeted management of PGD and CLAD in lung transplant recipient to improve their long-term outcome remains a critical unmet need. Current mechanistic studies and therapeutic studies in mouse models and humans identify new possibilities for prevention and treatment.

Donor Specific Antibodies in Extracorporeal Membrane Oxygenation-Bridged Lung Transplant Recipients

Background

Extracorporeal membrane oxygenation (ECMO) is increasingly used as a bridge to lung transplantation. Although other mechanical circulatory support devices have been associated with anti-human leukocyte antigen antibody formation, including de novo donor-specific antibodies (dnDSA), it is unknown whether ECMO is a sensitizing exposure.

Methods

This was a single-center retrospective cohort study of lung transplant recipients. We compared dnDSA development in ECMO-bridged and non-ECMO exposed recipients. We also assessed differences in chronic lung allograft dysfunction-free survival between ECMO-bridged recipients with and without dnDSA, and between those who developed dnDSA with and without ECMO bridge.

Results

Among 299 transplant recipients, 48 were ECMO-bridged and 251 were non-ECMO exposed. dnDSA developed in 33.3% of ECMO-bridged and 21.5% of non-ECMO exposed recipients. ECMO was associated with dnDSA development in bivariate (hazard ratio [HR], 2.08, 95% CI, 1.19-3.64, P = .01) but not multivariate analysis after adjusting for known confounders (HR, 1.10, 95% CI, 0.50-2.42, P = .82). Higher posttransplant transfusion volume was independently associated with dnDSA development (HR, 4.68, 95% CI, 2.25-9.72, P < .001). ECMO-bridged recipients with dnDSA did not have worse adjusted chronic lung allograft dysfunction-free survival than those without dnDSA (HR, 0.35, 95% CI, 0.07-1.87, P = .22) or compared to non-ECMO exposed recipients with dnDSA (HR, 0.40, 95% CI, 0.08-2.00, P = .27).

Conclusions

A more restrictive posttransplant transfusion threshold among ECMO-bridged lung transplant recipients may reduce the risk of dnDSA. Surveillance for dnDSA, at least among ECMO-bridged recipients, may only be necessary in the presence of allograft dysfunction.

Pushing the Survival Bar Higher: Two Decades of Innovation in Lung Transplantation

Survival after lung transplantation has significantly improved during the last two decades. The refinement of the already existing extracorporeal life support (ECLS) systems, such as extracorporeal membrane oxygenation (ECMO), and the introduction of new techniques for donor lung optimization, such as ex vivo lung perfusion (EVLP), have allowed the extension of transplant indication to patients with end-stage lung failure after acute respiratory distress syndrome (ARDS) and the expansion of the donor organ pool, due to the better evaluation and optimization of extended-criteria donor (ECD) lungs and of donors after circulatory death (DCD). The close monitoring of anti-HLA donor-specific antibodies (DSAs) has allowed the early recognition of pulmonary antibody-mediated rejection (AMR), which requires a completely different treatment and has a worse prognosis than acute cellular rejection (ACR). As such, the standardization of patient selection and post-transplant management has significantly contributed to this positive trend, especially at high-volume centers. This review focuses on lung transplantation after ARDS, on the role of EVLP in lung donor expansion, on ECMO as a principal cardiopulmonary support system in lung transplantation, and on the diagnosis and therapy of pulmonary AMR.

The diagnosis and management of chronic lung allograft dysfunction

PURPOSE OF REVIEW

Chronic lung allograft dysfunction (CLAD) remains a life-threatening complication following lung transplantation. Different CLAD phenotypes have recently been defined, based on the combination of pulmonary function testing and chest computed tomography (CT) scanning and spurred renewed interests in differential diagnosis, risk factors and management of CLAD.

RECENT FINDINGS

Given their crucial importance in the differential diagnosis, we will discuss the latest development in assessing the pulmonary function and chest CT scan, but also their limitations in proper CLAD phenotyping, especially with regards to patients with baseline allograft dysfunction. Since no definitive treatment exists, it remains important to timely identify clinical risk factors, but also to assess the presence of specific patterns or biomarkers in tissue or in broncho alveolar lavage in relation to CLAD (phenotypes). We will provide a comprehensive overview of the latest advances in risk factors and biomarker research in CLAD. Lastly, we will also review novel preventive and curative treatment strategies for CLAD.

SUMMARY

Although this knowledge has significantly advanced the field of lung transplantation, more research is warranted because CLAD remains a life-threatening complication for all lung transplant recipients.

Fibrotic progression from acute cellular rejection is dependent on secondary lymphoid organs in a mouse model of chronic lung allograft dysfunction

Chronic lung allograft dysfunction (CLAD) remains one of the major limitations to long-term survival after lung transplantation. We modified a murine model of CLAD and transplanted left lungs from BALB/c donors into B6 recipients that were treated with intermittent cyclosporine and methylprednisolone postoperatively. In this model, the lung allograft developed acute cellular rejection on day 15 which, by day 30 after transplantation, progressed to severe pleural and peribronchovascular fibrosis, reminiscent of changes observed in restrictive allograft syndrome. Lung transplantation into splenectomized B6 alymphoplastic (aly/aly) or splenectomized B6 lymphotoxin-β receptor-deficient mice demonstrated that recipient secondary lymphoid organs, such as spleen and lymph nodes, are necessary for progression from acute cellular rejection to allograft fibrosis in this model. Our work uncovered a critical role for recipient secondary lymphoid organs in the development of CLAD after pulmonary transplantation and may provide mechanistic insights into the pathogenesis of this complication.

Impact of Transient and Persistent Donor-Specific Antibodies in Lung Transplantation

Lung transplantation (LuTx) is an established treatment for patients with end-stage lung diseases, however, outcomes are limited by acute and chronic rejection. One aspect that has received increasing attention is the role of the host's humoral alloresponse, particularly the formation of de novo donor-specific antibodies (dnDSAs). The aim of this study was to investigate the clinical significance of transient and persistent dnDSAs and to understand their impact on outcomes after LuTx. A retrospective analysis was conducted using DSA screening data from LuTx recipients obtained at the Medical University of Vienna between February 2016 and March 2021. Of the 405 LuTx recipients analyzed, 205 patients developed dnDSA during the follow-up period. Among these, 167 (81%) had transient dnDSA and 38 (19%) persistent dnDSA. Persistent but not transient dnDSAs were associated with chronic lung allograft dysfunction (CLAD) and antibody-mediated rejection (AMR) (p < 0.001 and p = 0.006, respectively). CLAD-free survival rates for persistent dnDSAs at 1-, 3-, and 5-year post-transplantation were significantly lower than for transient dnDSAs (89%, 59%, 56% vs. 91%, 79%, 77%; p = 0.004). Temporal dynamics of dnDSAs after LuTx have a substantial effect on patient outcomes. This study underlines that the persistence of dnDSAs poses a significant risk to graft and patient survival.

Association of positive pre-transplant angiotensin II type 1 receptor antibodies with clinical outcomes in lung transplant recipients

INTRODUCTION

Autoantibodies against the angiotensin II type 1 receptor (AT1R-Ab) have been previously associated with de novo donor-specific antibody (DSA) formation in lung transplantation. However, data regarding the clinical significance of AT1R-Ab in long-term graft function after lung transplantation are lacking.

METHODS

Seventy-one patients who underwent lung transplantation between July 2016 and January 2020 were enrolled in this study. We examined the relationship between pre-transplant AT1R-Ab levels and graft function, clinical outcomes, and human leukocyte antigen (HLA) DSA levels during the first 3 years post-transplantation.

RESULTS

Seventeen (23.9%) patients were AT1R-Ab-positive, and 54 (76.1%) were AT1R-Ab-negative. The median antibody value of the AT1R-Ab-positive group was 18 [18-22.5] U/mL, while that of the AT1R-Ab-negative group was 5.1 [3.5-8.0] U/mL (p < 0.001). There was no significant difference in the median acute cellular rejection (ACR) scores between the two groups (median [interquartile range] 1 [0.8-3] vs. 0.7 [0-1]; p = 0.145). However, there was a significant difference in the distribution of the ACR scores between the two groups (p = 0.015). Most (41.2%) patients in the pre-transplant AT1R-positive group scored above 1. The incidence of de novo DSA was also higher in AT1R-Ab-positive than in AT1R-Ab-negative patients (52.9% vs. 20.4%, p = 0.009). The incidence of chronic lung allograft dysfunction (CLAD) within 3 years was significantly higher in AT1R-Ab-positive than in AT1R-Ab-negative patients (58.3% vs. 11.8%; p < 0.001). In the multivariate Cox regression analysis, AT1R-Ab positivity (hazard ratio, 9.46; 95% confidence interval, 2.89-30.94; p < 0.001) was significantly associated with early CLAD. Furthermore, Kaplan-Meier analysis showed that AT1R-Ab-positive patients had a shorter survival time (χ2 = 39.62, p < 0.001).

CONCLUSION

High AT1R-Ab levels in the pre-transplant serum of lung recipients were associated with the development of de novo HLA-DSA, ACR, early CLAD, and short survival.

Management of donor-specific antibodies in lung transplantation

The formation of antibodies against donor human leukocyte antigens poses a challenging problem both for donor selection as well as postoperative graft function in lung transplantation. These donor-specific antibodies limit the pool of potential donor organs and are associated with episodes of antibody-mediated rejection, chronic lung allograft dysfunction, and increased mortality. Optimal management strategies for clearance of DSAs are poorly defined and vary greatly by institution; most of the data supporting any particular strategy is limited to small-scale retrospective cohort studies. A typical approach to antibody depletion may involve the use of high-dose steroids, plasma exchange, intravenous immunoglobulin, and possibly other immunomodulators or small-molecule therapies. This review seeks to define the current understanding of the significance of DSAs in lung transplantation and outline the literature supporting strategies for their management.