Antibody-mediated Rejection in Lung Transplantation

Acute rejection post lung transplant

PURPOSE OF REVIEW

To review what is currently known about the pathogenesis, diagnosis, treatment, and prevention of acute rejection (AR) in lung transplantation.

RECENT FINDINGS

Epigenomic and transcriptomic methods are gaining traction as tools for earlier detection of AR, which still remains primarily a histopathologic diagnosis.

SUMMARY

Acute rejection is a common cause of early posttransplant lung graft dysfunction and increases the risk of chronic rejection. Detection and diagnosis of AR is primarily based on histopathology, but noninvasive molecular methods are undergoing investigation. Two subtypes of AR exist: acute cellular rejection (ACR) and antibody-mediated rejection (AMR). Both can have varied clinical presentation, ranging from asymptomatic to fulminant ARDS, and can present simultaneously. Diagnosis of ACR requires transbronchial biopsy; AMR requires the additional measuring of circulating donor-specific antibody (DSA) levels. First-line treatment in ACR is increased immunosuppression (pulse-dose or tapered dose glucocorticoids); refractory cases may need antibody-based lymphodepletion therapy. First line treatment in AMR focuses on circulating DSA removal with B and plasma cell depletion; plasmapheresis, intravenous human immunoglobulin (IVIG), bortezomib, and rituximab are often employed.

Hexamerization: explaining the original sin of IgG-mediated complement activation in acute lung injury

Although antibody-mediated lung damage is a major factor in transfusion-related acute lung injury (ALI), autoimmune lung disease (for example, coatomer subunit α [COPA] syndrome), and primary graft dysfunction following lung transplantation, the mechanism by which antigen-antibody complexes activate complement to induce lung damage remains unclear. In this issue of the JCI, Cleary and colleagues utilized several approaches to demonstrate that IgG forms hexamers with MHC class I alloantibodies. This hexamerization served as a key pathophysiological mechanism in alloimmune lung injury models and was mediated through the classical pathway of complement activation. Additionally, the authors provided avenues for exploring therapeutics for this currently hard-to-treat clinical entity that has several etiologies but a potentially focused mechanism.

Development of New Donor-Specific and Human Leukocyte Antigen Antibodies After Transfusion in Adult Lung Transplantation

OBJECTIVES

The development of new human leukocyte antigens (HLAs) and donor-specific antibodies (DSAs) in patients are associated with worse outcomes following lung transplantation. The authors aimed to examine the relationship between blood product transfusion in the first 72 hours after lung transplantation and the development of HLA antibodies, including DSAs.

DESIGN

A retrospective observational study.

SETTING

At a single academic tertiary center.

PARTICIPANTS

Adult lung transplant recipients who underwent transplantation between September 2014 and June 2019.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

A total of 380 patients were included in this study, and 87 (23%) developed de novo donor-specific antibodies in the first year after transplantation. Eighty-five patients (22%) developed new HLA antibodies that were not donor-specific, and 208 patients (55%) did not develop new HLA antibodies in the first year after transplantation. Factors associated with increased HLA and DSA development included donor pulmonary infection, non-infectious indication for transplant, increased recipient body mass index, and a preoperative calculated panel reactive antibody value above 0. Multivariate analysis identified platelet transfusion associated with an increased risk of de novo HLA antibody development compared to the negative group (odds ratio [OR; 95% CI] 1.18 [1.02-1.36]; p = 0.025). Cryoprecipitate transfusion was associated with de novo DSA development compared to the negative group (OR [95% CI] 2.21 [1.32-3.69] for 1 v 0 units; p = 0.002).

CONCLUSIONS

Increased perioperative transfusion of platelets and cryoprecipitate are associated with de novo HLA and DSA development, respectively, in lung transplant recipients during the first year after transplantation.

Immune processes in the pathogenesis of chronic lung allograft dysfunction: identifying the missing pieces of the puzzle

Lung transplantation is the optimal treatment for selected patients with end-stage chronic lung diseases. However, chronic lung allograft dysfunction remains the leading obstacle to improved long-term outcomes. Traditionally, lung allograft rejection has been considered primarily as a manifestation of cellular immune responses. However, in reality, an array of complex, interacting and multifactorial mechanisms contribute to its emergence. Alloimmune-dependent mechanisms, including T-cell-mediated rejection and antibody-mediated rejection, as well as non-alloimmune injuries, have been implicated. Moreover, a role has emerged for autoimmune responses to lung self-antigens in the development of chronic graft injury. The aim of this review is to summarise the immune processes involved in the pathogenesis of chronic lung allograft dysfunction, with advanced insights into the role of innate immune pathways and crosstalk between innate and adaptive immunity, and to identify gaps in current knowledge.

Lymphocytic Airway Inflammation in Lung Allografts

Lung transplant remains a key therapeutic option for patients with end stage lung disease but short- and long-term survival lag other solid organ transplants. Early ischemia-reperfusion injury in the form of primary graft dysfunction (PGD) and acute cellular rejection are risk factors for chronic lung allograft dysfunction (CLAD), a syndrome of airway and parenchymal fibrosis that is the major barrier to long term survival. An increasing body of research suggests lymphocytic airway inflammation plays a significant role in these important clinical syndromes. Cytotoxic T cells are observed in airway rejection, and transcriptional analysis of airways reveal common cytotoxic gene patterns across solid organ transplant rejection. Natural killer (NK) cells have also been implicated in the early allograft damage response to PGD, acute rejection, cytomegalovirus, and CLAD. This review will examine the roles of lymphocytic airway inflammation across the lifespan of the allograft, including: 1) The contribution of innate lymphocytes to PGD and the impact of PGD on the adaptive immune response. 2) Acute cellular rejection pathologies and the limitations in identifying airway inflammation by transbronchial biopsy. 3) Potentiators of airway inflammation and heterologous immunity, such as respiratory infections, aspiration, and the airway microbiome. 4) Airway contributions to CLAD pathogenesis, including epithelial to mesenchymal transition (EMT), club cell loss, and the evolution from constrictive bronchiolitis to parenchymal fibrosis. 5) Protective mechanisms of fibrosis involving regulatory T cells. In summary, this review will examine our current understanding of the complex interplay between the transplanted airway epithelium, lymphocytic airway infiltration, and rejection pathologies.

Lung Retransplantation

Lung retransplantation remains the standard treatment of irreversible lung allograft failure. The most common indications for lung retransplantation are acute graft failure, chronic lung allograft dysfunction, and postoperative airway complications. Careful patient selection with regards to indications, anatomy, extrapulmonary organ dysfunction (specifically renal dysfunction), and immunologic consideration are of utmost importance. The conduct of the lung retransplantation operation is arduous with special considerations given to operative approach, type of surgery (single vs bilateral), use of extracorporeal circulatory support, and hematological management. Outcomes have improved significantly for most patients, nearing short and midterm outcomes of primary lung recipients in select cases.

Allograft Dysfunction After Lung Transplantation for COPA Syndrome: A Case Report and Literature Review

COPA syndrome is an autoinflammatory disease with autoimmune and autoinflammatory manifestations affecting lungs, joints, and kidneys. COPA syndrome is caused by heterozygous loss-of-function mutations in the coatmer subunit alpha (COPA) gene, encoding α subunit of coatmer protein complex I (COP-I) coated vesicles. Mutant COPA induces constitutive activation of stimulator of interferon (IFN) genes (STING), leading to systemic inflammation and elevated type I interferon response. We have previously reported a Japanese family of COPA syndrome with a novel V242G mutation. Two out of 4 patients required lung transplantation due to intractable interstitial lung disease (ILD) and respiratory failure. Both of them deceased after lung transplantation, one due to sepsis and the other due to allograft dysfunction possibly caused by the reccurent ILD. The literature review indentified unfavorable outcome of the solid organ transplant in COPA syndrome and its related disease, however, precise clinico-pathological description of these cases has been scarce. Here, we report in detail the clinical course of our cases to clarify the pathophysiology of allograft dysfunction in COPA syndrome and propose potential therapeutic approaches to improve post-transplant graft survival.

Graft dysfunction and rejection of lung transplant, a review on diagnosis and management

Introduction

Lung transplantation has proven to be an effective treatment option for end‐stage lung disease. However, early and late complications following transplantation remain significant causes of high mortality.

Objectives

In this review, we focus on the time of onset in primary graft dysfunction and rejection complications, as well as emphasize the role of imaging manifestations and pathological features in early diagnosis, thus assisting clinicians in the early detection and treatment of posttransplant complications and improving patient quality of life and survival.

Data source

We searched electronic databases such as PubMed, Web of Science, and EMBASE. We used the following search terms: lung transplantation complications, primary graft dysfunction, acute rejection, chronic lung allograft dysfunction, radiological findings, and diagnosis and treatment.

Conclusion

Primary graft dysfunction, surgical complications, immune rejection, infections, and neoplasms represent major posttransplant complications. As the main posttransplant survival limitation, chronic lung allograft dysfunction has a characteristic imaging presentation; nevertheless, the clinical and imaging manifestations are often complex and overlap, so it is essential to understand the temporal evolution of these complications to narrow the differential diagnosis for early treatment to improve prognosis.

Early and late complications after lung transplantation remain essential causes of high mortality. In this review, we focus on the timing of the onset of primary graft dysfunction and rejection complications and highlight the role of imaging manifestations and clinicopathologic features in early diagnosis, thus assisting clinicians in the early detection and treatment of posttransplant complications and improving patient quality of life and survival.

Immunosuppression in Lung Transplantation

Immunosuppression in lung transplantation is an area devoid of robust clinical data. This chapter will review the history of immunosuppression in lung transplantation. Additionally, it will evaluate the three classes of induction, maintenance, and rescue immunosuppression in detail. Induction immunosuppression in lung transplantation aims to decrease incidence of lung allograft rejection, however infectious risk must be considered when determining if induction is appropriate and which agent is most favorable. Similar to other solid organ transplant patient populations, a multi-drug approach is commonly prescribed for maintenance immunosuppression to minimize single agent drug toxicities. Emphasis of this review is placed on key medication considerations including dosing, adverse effects, and drug interactions. Clinical considerations will be reviewed per drug class given available literature. Finally, acute cellular, antibody mediated, and chronic rejection are reviewed.

Early stage of antibody-mediated rejection after lung transplantation： A case report and literature review

Antibody-mediated rejection (AMR) is a rare and serious complication after lung transplantation, with no characteristic of pathological manifestation, no systematic standard treatment, and the poor efficacy and prognosis. We reported a case of early AMR after lung transplantation and the relevant literature has been reviewed. A male patient presented with symptoms of cold 99 days after transplantation and resolved after symptomatic treatment. He admitted to the hospital 14 days later because of a sudden dyspnea and fever. Anti-bacteria, anti-fungi, anti-virus, and anti-pneumocystis carinii treatment were ineffective, and a dose of 1 000 mg methylprednisolone did not work too. The patient's condition deteriorated rapidly and tracheal intubation was done to maintain breathing. Serum panel reactive antibody and donor specific antibody showed postive in humen leukocyte antigen (HLA) II antibody. Pathological examination after transbronchial transplantation lung biopsy showed acute rejection. Clinical AMR was diagnosed combined the donor-specific antibody with the pathological result. The patient was functionally recovered after combined treatment with thymoglobuline, rituximab, plasmapheresis, and immunoglobulin. No chronic lung allograft dysfunction was found after 3 years follow up. We should alert the occurrence of AMR in lung transplantation recipient who admitted to hospital with a sudden dyspnea and fever while showed no effect after common anti-infection and anti-rejection treatment. Transbronchial transplantation lung biopsy and the presence of serum donor-specific antibody are helpful to the diagnosis. The treatment should be preemptive and a comprehensive approach should be adopted.

Complications of Lung Transplantation: Update on Imaging Manifestations and Management

As lung transplantation has become the most effective definitive treatment option for end-stage chronic respiratory diseases, yearly rates of this surgery have been steadily increasing. Despite improvement in surgical techniques and medical management of transplant recipients, complications from lung transplantation are a major cause of morbidity and mortality. Some of these complications can be classified on the basis of the time they typically occur after lung transplantation, while others may occur at any time. Imaging studies, in conjunction with clinical and laboratory evaluation, are key components in diagnosing and monitoring these conditions. Therefore, radiologists play a critical role in recognizing and communicating findings suggestive of lung transplantation complications. A description of imaging features of the most common lung transplantation complications, including surgical, medical, immunologic, and infectious complications, as well as an update on their management, will be reviewed here. Keywords: Pulmonary, Thorax, Surgery, Transplantation Supplemental material is available for this article. © RSNA, 2021.

Antithymocyte globulin is associated with a lower incidence of de novo donor-specific antibody detection in lung transplant recipients: A single-center experience

Purpose

Induction immunosuppression has improved the long‐term outcomes after lung transplant. This is the first report exploring the association of induction immunosuppression with the development of de novo donor‐specific human leukocyte antigen (HLA) antibodies (DSA) in lung transplant recipients (LTR).

Methods

Sixty‐seven consecutive primary LTR were followed for 3 years posttransplant. A total of 41/67 (61%) LTR‐received induction immunosuppression using a single dose of rabbit Antithymocyte Globulin (rATG; 1.5 mg/kg) within 24 h of transplant. All recipients had a negative flow cytometry crossmatch on the day of transplant. Serum samples at 1, 3, 6, and 12 months posttransplant were assessed for the presence of de novo HLA DSA.

Results

De novo HLA DSA were detected in 22/67 (32.8%) LTR within 1‐year posttransplant. Of these, 9/41 (21.9%) occurred in the induction therapy group and 13/26 (50%) in the noninduction group. Class II DSA were detected in 3/41 (7.3%) LTR who received induction compared to 9/26 (34.6%) LTR without induction immunosuppression (p = .005). Differences in overall survival or freedom from chronic lung allograft dysfunction rates between the two groups were not statistically significant.

Conclusion

Induction immunosuppression utilizing a modified regimen of single‐dose rATG is associated with a significant reduction in de novo DSA production in LTR.

Phosphorylated S6 ribosomal protein expression by immunohistochemistry correlates with de novo donor-specific HLA antibodies in lung allograft recipients

BACKGROUND

Per the ISHLT 2016 definition, a C4d-positive lung biopsy is required to meet criteria for definite antibody-mediated rejection (AMR). Unfortunately, C4d has poor sensitivity and specificity, and low inter-rater reliability. Phosphorylated S6 ribosomal protein (p-S6RP) expressed via the mTOR pathway has been shown to be a biomarker of AMR and correlates with donor-specific antibodies (DSA) in heart allografts. However, p-S6RP immunohistochemistry (IHC) in the setting of pulmonary AMR has yet to be evaluated. We sought to determine whether p-S6RP IHC performed on lung biopsies correlates with de novo DSA.

METHODS

IHC for p-S6RP performed on 26 biopsies from lung transplant recipients with de novo HLA DSA (DSA+) and 28 biopsies from patients with no DSA (DSA-) were evaluated by 3 pathologists who independently scored the degree of alveolar macrophage and pneumocyte staining. Staining in ≥50% of the biopsy as determined by at least 2 pathologists was considered positive.

RESULTS

Twenty-one (81%) DSA+ biopsies stained positive for p-S6RP in pneumocytes and 21 (81%) in macrophages. Six DSA- biopsies (21%) stained positive for p-S6RP in pneumocytes, 6 (21%) were positive in macrophages. Pneumocyte p-S6RP staining was 81% sensitive and 79% specific for DSA. Macrophage staining showed the same sensitivity and specificity but with lower inter-rater agreement (κ = 0.53 vs 0.68).

CONCLUSIONS

This study demonstrates a positive relationship between de novo DSA and p-S6RP expression in pneumocytes and macrophages using IHC. p-S6RP is relatively sensitive and specific, and has superior inter-rater reliability compared to C4d.

Antibody-Mediated Rejection and Sponge Effect in a Redo Lung Transplant Recipient

Long-term survival after lung transplant remains severely limited by chronic lung allograft dysfunction. Antibody-mediated rejection of lung transplant allografts is usually caused by donor-specific antibodies (DSAs) directed toward donor human leukocyte antigens (HLAs). Typically, patients with antibody-mediated rejection have significantly higher circulating DSAs and increased mean fluorescence intensity than those without antibody-mediated rejection. However, some patients with antibody-mediated rejection have low mean fluorescence intensities, partly due to the "sponge effect" related to DSAs binding to HLA molecules within the lung. Herein, we report the case of an 18-year-old, female lung transplant recipient who required retransplantation and developed circulating DSAs directed toward the first allograft but detected in circulation only after retransplantation. The present case draws attention to a rare finding of sponge effect in a patient with antibody-mediated rejection leading to allograft failure.

Antibody-Mediated Rejection Management Following Lung Transplantation

BACKGROUND

Although antibody-mediated rejection (AMR) is described in other solid organ transplant populations, the literature describing the management following lung transplantation is limited.

OBJECTIVE

The purpose of this study is to evaluate the management strategies of AMR in lung transplant recipients.

METHODS

This single-center, retrospective study described the management of AMR in adult lung transplant recipients who received treatment with rabbit antithymocyte globulin, bortezomib, rituximab, intravenous immune globulin (IVIG), and/or plasmapheresis between September 2015 and June 2019.

RESULTS

A total of 270 medication orders for 55 patient admissions were included in the primary outcome analysis. The most commonly used regimen consisted of IVIG, plasmapheresis, and rituximab (49.1%; n = 27), followed by IVIG and plasmapheresis alone (27.3%, n = 15). A total of 51 patients (93%) received plasmapheresis as part of their AMR treatment, with a median of 4 [3, 5] sessions per encounter; 86% of patients with positive donor-specific antibodies (DSAs) had a reduction in DSAs following AMR treatment. Overall, 23.5% of patients had noted allograft failure or need for retransplantation. A total of 10 patients died during the AMR treatment hospital admission, and an additional 11 patients died within 1 year of the initial encounter.

CONCLUSION AND RELEVANCE

This represents the largest report describing management strategies of AMR in lung transplant recipients. Although practice varied, the most commonly used regimen consisted of plasmapheresis, IVIG, and rituximab.

Outcomes Following ATG Therapy for Chronic Lung Allograft Dysfunction

Chronic lung allograft dysfunction (CLAD) is the major factor limiting survival post lung transplantation (LTx) with limited effective therapeutic options. We report our 12-y experience of antithymocyte globulin (ATG) as second-line CLAD therapy.

Single-Center Experience of Outcomes and Prescribing Patterns of IV Immunoglobulin Use in Critically Ill Patients

Supplemental Digital Content is available in the text.

Previous literature has not compared prescribing practices of IV immunoglobulin in medical ICU survivors and nonsurvivors. The objective of this study was to study IV immunoglobulin use in patients admitted to a medical ICU evaluating differences between hospital survivors and nonsurvivors in regards to level of evidence supporting use, prescribing patterns, and cost.

Complement activation on endothelium initiates antibody-mediated acute lung injury

Antibodies targeting human leukocyte antigen (HLA)/major histocompatibility complex (MHC) proteins limit successful transplantation and transfusion, and their presence in blood products can cause lethal transfusion-related acute lung injury (TRALI). It is unclear which cell types are bound by these anti-leukocyte antibodies to initiate an immunologic cascade resulting in lung injury. We therefore conditionally removed MHC class I (MHC I) from likely cellular targets in antibody-mediated lung injury. Only the removal of endothelial MHC I reduced lung injury and mortality, related mechanistically to absent endothelial complement fixation and lung platelet retention. Restoration of endothelial MHC I rendered MHC I-deficient mice susceptible to lung injury. Neutrophil responses, including neutrophil extracellular trap (NET) release, were intact in endothelial MHC I-deficient mice, whereas complement depletion reduced both lung injury and NETs. Human pulmonary endothelial cells showed high HLA class I expression, and posttransfusion complement activation was increased in clinical TRALI. These results indicate that the critical source of antigen for anti-leukocyte antibodies is in fact the endothelium, which reframes our understanding of TRALI as a rapid-onset vasculitis. Inhibition of complement activation may have multiple beneficial effects of reducing endothelial injury, platelet retention, and NET release in conditions where antibodies trigger these pathogenic responses.

The impact of C4d testing on tissue adequacy in lung transplant surveillance

BACKGROUND

Surveillance transbronchial biopsies are routinely used to assess lung allograft rejection. While the criteria for diagnosing acute cellular rejection have been well-established, the morphological findings associated with antibody mediated rejection are variable. To increase the sensitivity for antibody mediated rejection, a portion of a biopsy can be used for C4d immunofluorescence testing, along with histologic findings and donor specific antibodies. When the number of alveolar pieces in a biopsy is small, the relative utility of sending one piece for C4d testing is unclear.

METHODS

Pathology reports of 1400 surveillance transbronchial lung biopsies from 2008 to 2017 were reviewed to obtain the number of pieces of alveolar parenchyma in each case. Based on a standard definition of adequacy as five pieces of well-expanded alveolar parenchyma, reports with five fragments were grouped as "adequate", four pieces as a "marginal" sample, and three or less were considered an "inadequate" sample.

RESULTS

Of the 1400 biopsies, 653 specimens had 5 or more pieces of alveolar parenchyma.747 specimens were submitted with less than 5 pieces and 290 of those were considered marginal. In all marginal cases, a piece was withheld for C4d immunofluorescence testing.

CONCLUSIONS

About 21% of specimens would have the recommended 5 pieces of alveolar parenchyma if not for the withholding of pieces for C4d IF testing. Over the span of 10 years, 290 such cases were recorded at our institution. Given this nontrivial impact, it is unclear if C4d immunofluorescence testing should be performed on surveillance transbronchial biopsies when the number of pieces in the specimen is marginal.

Pseudomonas aeruginosa and acute rejection independently increase the risk of donor-specific antibodies after lung transplantation

Factors contributing to donor-specific HLA antibody (DSA) development after lung transplantation have not been systematically evaluated. We hypothesized that the isolation of Pseudomonas aeruginosa in respiratory specimens would increase the risk of DSA development. Our objective was to determine the risk of DSA development associated with the isolation of Pseudomonas aeruginosa after lung transplantation. We conducted a single-center retrospective cohort study of primary lung transplant recipients and examined risk factors for DSA development using Cox regression models. Of 460 recipients, 205 (45%) developed DSA; the majority developed Class II DSA (n = 175, 85%), and 145 of 205 (71%) developed DSA to HLA-DQ alleles. Univariate time-dependent analyses revealed that isolation of Pseudomonas from respiratory specimens, acute cellular rejection, and lymphocytic bronchiolitis are associated with an increased risk of DSA development. In multivariable analyses, Pseudomonas isolation, acute cellular rejection, and lymphocytic bronchiolitis remained independent risk factors for DSA development. Additionally, there was a direct association between the number of positive Pseudomonas cultures and the risk of DSA development. Our findings suggest that pro-inflammatory events including acute cellular rejection, lymphocytic bronchiolitis, and Pseudomonas isolation after transplantation are associated with an increased risk of DSA development.

Antibody-mediated rejection after lung transplantation

Antibody-mediated rejection (AMR) has been identified as a significant form of acute allograft dysfunction in lung transplantation. The development of consensus diagnostic criteria has created a uniform definition of AMR; however, significant limitations of these criteria have been identified. Treatment modalities for AMR have been adapted from other areas of medicine and data on the effectiveness of these therapies in AMR are limited. AMR is often refractory to these therapies, and graft failure and death are common. AMR is associated with increased rates of chronic lung allograft dysfunction (CLAD) and poor long-term survival. In this review, we discuss the history of AMR and describe known mechanisms, application of the consensus diagnostic criteria, data for current treatment strategies, and long-term outcomes. In addition, we highlight current gaps in knowledge, ongoing research, and future directions to address these gaps. Promising diagnostic techniques are actively being investigated that may allow for early detection and treatment of AMR. We conclude that further investigation is required to identify and define chronic and subclinical AMR, and head-to-head comparisons of currently used treatment protocols are necessary to identify an optimal treatment approach. Gaps in knowledge regarding the epidemiology, mechanisms, diagnosis, and treatment of AMR continue to exist and future research should focus on these aspects.

Exploring pre-surgery donor-specific antibodies in the context of organ shortage in liver transplant

BACKGROUND

There is a growing disparity between the number of liver transplant (LT) candidates and availability of suitable liver allografts. Antibody-mediated rejection (AMR), secondary to positive donor-specific antibodies (DSA), remains a concern in liver transplantation. This study aimed to correlate expression of DSA on pre-transplant screening and outcomes of LT, specifically development of AMR in liver allografts and liver function profile in the post-operative period.

METHODS

Data of consecutive patients undergoing orthotopic LT (OLT) at the South Australian Liver Transplant Unit was analysed. All patients underwent DSA testing pre-transplant.

RESULTS

Within a cohort of 96 patients, over a post-OLT median follow-up of 849 days, only 2 patients (2%) developed AMR. While both patients had a positive DSA test preoperatively, overall DSA positivity was noted in 31% patients, with a specificity for prediction of AMR of 0.708. No significant association was noted between AMR (p = 0.092), T cell-mediated rejection/TCMR (p = 0.797) or late hepatic artery thrombosis/LHAT (p = 0.521). There was no significant interaction effect between DSA positivity and serum bilirubin or transaminases over a period of 100 days.

CONCLUSION

AMR following LT is uncommon. A positive DSA pre-transplant does not imply a definite risk of AMR. Also, there does not exist a significant interaction in time between DSA expression and serum bilirubin or transaminase levels. Until there emerges evidence to the contrary, it appears reasonable to consider DSA-positive donors within the broad context of marginal donors in the context of a worldwide shortage of LT donor allografts.

FCGR3A and FCGR2A Genotypes Differentially Impact Allograft Rejection and Patients' Survival After Lung Transplant

Fc gamma receptors (FcγRs) play a major role in the regulation of humoral immune responses. Single-nucleotide polymorphisms (SNPs) of FCGR2A and FCGR3A can impact the expression level, IgG affinity and function of the CD32 and CD16 FcγRs in response to their engagement by the Fc fragment of IgG. The CD16 isoform encoded by FCGR3A [158V/V] controls the intensity of antibody-dependent cytotoxic alloimmune responses of natural killer cells (NK) and has been identified as a susceptibility marker predisposing patients to cardiac allograft vasculopathy after heart transplant. This study aimed to investigate whether FCGR2A and FCGR3A polymorphisms can also be associated with the clinical outcome of lung transplant recipients (LTRs). The SNPs of FCGR2A ([131R/H], rs1801274) and FCGR3A ([158V/F], rs396991) were identified in 158 LTRs and 184 Controls (CTL). The corresponding distribution of genotypic and allelic combinations was analyzed for potential links with the development of circulating donor-specific anti-HLA alloantibodies (DSA) detected at months 1 and 3 after lung transplant (LTx), the occurrence of acute rejection (AR) and chronic lung allograft dysfunction (CLAD), and the overall survival of LTRs. The FCGR3A [158V/V] genotype was identified as an independent susceptibility factor associated with higher rates of AR during the first trimester after LTx (HR 4.8, p < 0.0001, 95% CI 2.37-9.61), but it could not be associated with the level of CD16- mediated NK cell activation in response to the LTR's DSA, whatever the MFI intensity and C1q binding profiles of the DSA evaluated. The FCGR2A [131R/R] genotype was associated with lower CLAD-free survival of LTRs, independently of the presence of DSA at 3 months (HR 1.8, p = 0.024, 95% CI 1.08-3.03). Our data indicate that FCGR SNPs differentially affect the clinical outcome of LTRs and may be of use to stratify patients at higher risk of experiencing graft rejection. Furthermore, these data suggest that in the LTx setting, specific mechanisms of humoral alloreactivity, which cannot be solely explained by the complement and CD16-mediated pathogenic effects of DSA, may be involved in the development of acute and chronic lung allograft rejection.

Development and Optimization of an ELISA to Quantitate C3(H 2 O) as a Marker of Human Disease

Discovery of a C3(H₂O) uptake pathway has led to renewed interest in this alternative pathway triggering form of C3 in human biospecimens. Previously, a quantifiable method to measure C3(H₂O), not confounded by other complement activation products, was unavailable. Herein, we describe a sensitive and specific ELISA for C3(H₂O). We initially utilized this assay to determine baseline C3(H₂O) levels in healthy human fluids and to define optimal sample storage and handling conditions. We detected ~500 ng/ml of C3(H₂O) in fresh serum and plasma, a value substantially lower than what was predicted based on previous studies with purified C3 preparations. After a single freeze-thaw cycle, the C3(H₂O) concentration increased 3- to 4-fold (~2,000 ng/ml). Subsequent freeze-thaw cycles had a lesser impact on C3(H₂O) generation. Further, we found that storage of human sera or plasma samples at 4°C for up to 22 h did not generate additional C3(H₂O). To determine the potential use of C3(H₂O) as a biomarker, we evaluated specimens from patients with inflammatory-driven diseases. C3(H₂O) concentrations were moderately increased (1.5- to 2-fold) at baseline in sera from active systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) patients compared to healthy controls. In addition, upon challenge with multiple freeze-thaw cycles or incubation at 22 or 37°C, C3(H₂O) generation was significantly enhanced in SLE and RA patients' sera. In bronchoalveolar lavage fluid from lung-transplant recipients, we noted a substantial increase in C3(H₂O) within 3 months of acute antibody-mediated rejection. In conclusion, we have established an ELISA for assessing C3(H₂O) as a diagnostic and prognostic biomarker in human diseases.

Bronchus-associated lymphoid tissue-resident Foxp3+ T lymphocytes prevent antibody-mediated lung rejection

Antibody-mediated rejection (AMR) is a principal cause of acute and chronic failure of lung allografts. However, mechanisms mediating this oftentimes fatal complication are poorly understood. Here, we show that Foxp3+ T cells formed aggregates in rejection-free human lung grafts and accumulated within induced bronchus-associated lymphoid tissue (BALT) of tolerant mouse lungs. Using a retransplantation model, we show that selective depletion of graft-resident Foxp3+ T lymphocytes resulted in the generation of donor-specific antibodies (DSA) and AMR, which was associated with complement deposition and destruction of airway epithelium. AMR was dependent on graft infiltration by B and T cells. Depletion of graft-resident Foxp3+ T lymphocytes resulted in prolonged interactions between B and CD4+ T cells within transplanted lungs, which was dependent on CXCR5-CXCL13. Blockade of CXCL13 as well as inhibition of the CD40 ligand and the ICOS ligand suppressed DSA production and prevented AMR. Thus, we have shown that regulatory Foxp3+ T cells residing within BALT of tolerant pulmonary allografts function to suppress B cell activation, a finding that challenges the prevailing view that regulation of humoral responses occurs peripherally. As pulmonary AMR is largely refractory to current immunosuppression, our findings provide a platform for developing therapies that target local immune responses.

Complement factor and T-cell interactions during alloimmune inflammation in transplantation

Complement factor and T-cell signaling during an effective alloimmune response plays a key role in transplant-associated injury, which leads to the progression of chronic rejection (CR). During an alloimmune response, activated complement factors (C3a and C5a) bind to their corresponding receptors (C3aR and C5aR) on a number of lymphocytes, including T-regulatory cells (Tregs), and these cell-molecular interactions have been vital to modulate an effective immune response to/from Th1-effector cell and Treg activities, which result in massive inflammation, microvascular impairments, and fibrotic remodeling. Involvement of the complement-mediated cell signaling during transplantation signifies a crucial role of complement components as a key therapeutic switch to regulate ongoing inflammatory state, and further to avoid the progression of CR of the transplanted organ. This review highlights the role of complement-T cell interactions, and how these interactions shunt the effector immune response during alloimmune inflammation in transplantation, which could be a novel therapeutic tool to protect a transplanted organ and avoid progression of CR.

Immunosuppression for Lung Transplantation: Current and Future

Purpose of the review

The number of lung transplantations performed worldwide continues to increase. There is a growing need in these patients for more effective immunosuppressive medications with less toxicity.

Recent findings

This review article summarizes the recent studies and developments in lung transplant immunosuppression. Novel immunosuppressive medications and strategies used in other solid organ transplantations are being trialed in lung transplantation. This includes the use of co-stimulation blockers like belatacept and mTOR inhibitors like everolimus. Calcineurin sparing regimens have been described in an attempt to minimize nephrotoxicity. Assays to measure the bioactivity of immunosuppressive medications to determine the global immune competence, such as Immuknow assay and Gamma interferon response are gaining traction.

Summary

Immunosuppression in lung transplant is evolving with the development of newer drugs and promising strategies to optimize immunosuppression. Further studies with multicenter randomized trials are required to increase the strength of the evidence.

Persistence of de novo donor specific HLA-Antibodies after lung transplantation: a potential marker of decreased patient survival

The impact of de novo donor-specific anti-HLA antibodies (DSA) on outcomes in lung transplantation is still a matter of debate. We hypothesize that differentiating DSA by persistent and transient appearance may offer an additional risk assessment. The clinical relevance of HLA-antibodies was investigated prospectively in 72 recipients with a median follow-up period of 21 months. The presence of HLA-antibodies was analysed by single antigen bead assay prior to and after (3 weeks, 3, 6, 12 and 18 months) transplantation. In 23 patients (32%) de novo DSA were detected. In 10 of these patients (44%) DSA persisted throughout the follow-up period whereas 13 of these patients (56%) had transient DSA. There was a trend towards lower one-year-survival in DSA positive compared to DSA negative patients (83% versus 94%; p=0.199). Remarkably, patients with persistent DSA had significantly reduced survival (one-year survival 60%) compared with both patients without DSA and those with transient DSA (p=0.005). Persistent DSA represented an independent prognostic factor for reduced overall survival in multivariate analysis (HR 8.3, 95% CI 1.8-37.0; p=0.006). Persistence of DSA during the first year after transplantation seems to be more harmful for lung allograft function than transiently detected DSA at an early stage. This article is protected by copyright. All rights reserved.

Complement-activating donor-specific anti-HLA antibodies and solid organ transplant survival: A systematic review and meta-analysis

BACKGROUND

Anti-human leukocyte antigen donor-specific antibodies (anti-HLA DSAs) are recognized as a major barrier to patients' access to organ transplantation and the major cause of graft failure. The capacity of circulating anti-HLA DSAs to activate complement has been suggested as a potential biomarker for optimizing graft allocation and improving the rate of successful transplantations.

METHODS AND FINDINGS

To address the clinical relevance of complement-activating anti-HLA DSAs across all solid organ transplant patients, we performed a meta-analysis of their association with transplant outcome through a systematic review, from inception to January 31, 2018. The primary outcome was allograft loss, and the secondary outcome was allograft rejection. A comprehensive search strategy was conducted through several databases (Medline, Embase, Cochrane, and Scopus). A total of 5,861 eligible citations were identified. A total of 37 studies were included in the meta-analysis. Studies reported on 7,936 patients, including kidney (n = 5,991), liver (n = 1,459), heart (n = 370), and lung recipients (n = 116). Solid organ transplant recipients with circulating complement-activating anti-HLA DSAs experienced an increased risk of allograft loss (pooled HR 3.09; 95% CI 2.55-3.74, P = 0.001; I2 = 29.3%), and allograft rejection (pooled HR 3.75; 95% CI: 2.05-6.87, P = 0.001; I2 = 69.8%) compared to patients without complement-activating anti-HLA DSAs. The association between circulating complement-activating anti-HLA DSAs and allograft failure was consistent across all subgroups and sensitivity analyses. Limitations of the study are the observational and retrospective design of almost all included studies, the higher proportion of kidney recipients compared to other solid organ transplant recipients, and the inclusion of fewer studies investigating allograft rejection.

CONCLUSIONS

In this study, we found that circulating complement-activating anti-HLA DSAs had a significant deleterious impact on solid organ transplant survival and risk of rejection. The detection of complement-activating anti-HLA DSAs may add value at an individual patient level for noninvasive biomarker-guided risk stratification.

TRIAL REGISTRATION

National Clinical Trial protocol ID: NCT03438058.

Application and interpretation of histocompatibility data in liver transplantation

PURPOSE OF REVIEW

There has been a resurgence of interest in histocompatibility as it applies to liver transplantation. The association of persistent and de-novo donor specific antibody (DSA) and outcomes after liver transplantation continues to be investigated.

RECENT FINDINGS

Consensus continues to evolve regarding the existence of acute and chronic antibody-mediated rejection (AMR) and pathogenicity of DSA and associated pathologic findings after liver transplantation. The presence of persistent high level, complement fixing DSA or emergence of de novo, Class II DSA has been associated with rejection and worse long-term graft and patient survival. Significant adverse associations of DSA extend to patients after simultaneous liver kidney (SLK) transplant as well as in pediatric recipients of liver transplantation. A higher degree of HLA incompatibility has been recently associated with worse outcomes in living donor liver transplant.

SUMMARY

In summary, recent consensus guidelines describe and recognize the existence of acute and chronic AMR and provide a basis upon which to build further investigation. Important adverse outcomes including decreased survival, allograft failure and liver fibrosis have been linked to the presence of DSA. Routine donor and recipient HLA typing and DSA assessment will facilitate diagnosis and provide for baseline data, which may help guide future management. Future investigations may help to clarify the role of therapeutic interventions.

Acute rejection

Despite induction immunosuppression and the use of aggressive maintenance immunosuppressive regimens, acute allograft rejection following lung transplantation is still a problem with important diagnostic and therapeutic challenges. As well as causing early graft loss and mortality, acute rejection also initiates the chronic alloimmune responses and airway-centred inflammation that predispose to bronchiolitis obliterans syndrome (BOS), also known as chronic lung allograft dysfunction (CLAD), which is a major source of morbidity and mortality after lung transplantation. Cellular responses to human leukocyte antigens (HLAs) on the allograft have traditionally been considered the main mechanism of acute rejection, but the influence of humoral immunity is increasingly recognised. As with other several other solid organ transplants, antibody-mediated rejection (AMR) is now a well-accepted and distinct clinical entity in lung transplantation. While acute cellular rejection (ACR) has defined histopathological criteria, transbronchial biopsy is less useful in AMR and its diagnosis is complicated by challenges in the measurement of antibodies directed against donor HLA, and a determination of their significance. Increasing awareness of the importance of non-HLA antigens further clouds this issue. Here, we review the pathophysiology, diagnosis, clinical presentation and treatment of ACR and AMR in lung transplantation, and discuss future potential biomarkers of both processes that may forward our understanding of these conditions.

Update in Chronic Lung Allograft Dysfunction

Chronic lung allograft dysfunction (CLAD) is the major limitation to posttransplant survival. This review highlights the evolving definition of CLAD, risk factors, treatment, and expected outcomes after the development of CLAD.