Lung intragraft donor-specific antibodies as a risk factor for graft loss

The Clinical Significance of HLA Compatibility Scores in Lung Transplantation

Lung transplantation is a life-saving therapeutic option for many chronic end-stage pulmonary diseases, but long-term survival may be limited by rejection of the transplanted organ. Since HLA disparity between donor and recipient plays a major role in rejection, we performed a single center, retrospective observational cohort analysis in our lung transplant cohort (n = 128) in which we calculated HLA compatibility scores for B-cell epitopes (HLAMatchmaker, HLA-EMMA), T-cell epitopes (PIRCHE-II) and missing self-induced NK cell activation (KIR Ligand Calculator). Adjusted Cox proportional hazards model was used to investigate the association between mismatched scores and time to development of donor-specific antibodies (DSA) post-transplant, time to first biopsy-proven acute rejection episode, freedom from CLAD, graft survival and overall survival. For time to first DSA, HLA-EMMA DQB1 scores and PIRCHE-II DQB1 scores were significantly associated with more rapidly developing anti-HLA-DQ antibodies. HLA-EMMA DQB1 score was significantly associated with worse survival. KIR ligand Host-versus-Graft (HvG) mismatches was significantly associated with worse graft survival (CLAD or death) and shorter time to first biopsy-proven rejection when 2 mismatches were present. We demonstrated that HLA-DQB1 compatibility scores and KIR ligand HvG 2 mismatches may allow for identification of recipients at risk of poor long-term outcomes after lung transplantation.

Local intragraft humoral immune responses in chronic lung allograft dysfunction

BACKGROUND

Donor human leukocyte antigen (HLA)-specific antibodies (DSA) and non-HLA antibodies can cause allograft injury, possibly leading to chronic lung allograft dysfunction (CLAD) after lung transplantation. It remains unclear whether these antibodies are produced locally in the graft or derived solely from circulation. We hypothesized that DSA and non-HLA antibodies are produced in CLAD lungs.

METHODS

Lung tissue was prospectively collected from 15 CLAD patients undergoing retransplantation or autopsy. 0.3 g of fresh lung tissue was cultured for 4 days without or with lipopolysaccharide or CD40L: lung culture supernatant (LCS) was sampled. Protein eluate was obtained from 0.3 g of frozen lung tissue. The mean fluorescence intensity (MFI) of DSA and non-HLA antibodies was measured by Luminex and antigen microarray, respectively.

RESULTS

LCS from all 4 patients who had serum DSA at lung isolation were positive for DSA, with higher levels measured after CD40L stimulation (CD40L+LCS). Of these, only 2 had detectable DSA in lung eluate. MFI of non-HLA antibodies from CD40L+LCS correlated with those from lung eluate but not with those from sera. Flow cytometry showed higher frequencies of activated lung B cells in patients whose CD40L+LCS was positive for DSA (n = 4) or high non-HLA antibodies (n = 6) compared to those with low local antibodies (n = 5). Immunofluorescence staining showed CLAD lung lymphoid aggregates with local antibodies contained larger numbers of IgG+ plasma cells and greater IL-21 expression.

CONCLUSIONS

We show that DSA and non-HLA antibodies can be produced within activated B cell-rich lung allografts.

ERS Congress 2024: highlights from the Thoracic Surgery and Lung Transplantation Assembly

Assembly 8, which includes groups 8.01 Thoracic surgery and 8.02 Lung transplantation, arranged many interesting sessions for #ERSCongress 2024, and we highlight some of them in this article https://bit.ly/3AgC5Yv.

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.

Antibody-Mediated Rejection in Lung Transplantation: Diagnosis and Therapeutic Armamentarium in a 21st Century Perspective

Humoral immunity is a major waypoint towards chronic allograft dysfunction in lung transplantation (LT) recipients. Though allo-immunization and antibody-mediated rejection (AMR) are well-known entities, some diagnostic gaps need to be addressed. Morphological analysis could be enhanced by digital pathology and artificial intelligence-based companion tools. Graft transcriptomics can help to identify graft failure phenotypes or endotypes. Donor-derived cell free DNA is being evaluated for graft-loss risk stratification and tailored surveillance. Preventative therapies should be tailored according to risk. The donor pool can be enlarged for candidates with HLA sensitization, with strategies combining plasma exchange, intravenous immunoglobulin and immune cell depletion, or with emerging or innovative therapies such as imlifidase or immunoadsorption. In cases of insufficient pre-transplant desensitization, the effects of antibodies on the allograft can be prevented by targeting the complement cascade, although evidence for this strategy in LT is limited. In LT recipients with a humoral response, strategies are combined, including depletion of immune cells (plasmapheresis or immunoadsorption), inhibition of immune pathways, or modulation of the inflammatory cascade, which can be achieved with photopheresis. Altogether, these innovative techniques offer promising perspectives for LT recipients and shape the 21st century's armamentarium against AMR.

Pseudomonas aeruginosa infection correlates with high MFI donor-specific antibody development following lung transplantation with consequential graft loss and shortened CLAD-free survival

BACKGROUND

Donor-specific antibodies (DSAs) are common following lung transplantation (LuTx), yet their role in graft damage is inconclusive. Mean fluorescent intensity (MFI) is the main read-out of DSA diagnostics; however its value is often disregarded when analyzing unwanted post-transplant outcomes such as graft loss or chronic lung allograft dysfunction (CLAD). Here we aim to evaluate an MFI stratification method in these outcomes.

METHODS

A cohort of 87 LuTx recipients has been analyzed, in which a cutoff of 8000 MFI has been determined for high MFI based on clinically relevant data. Accordingly, recipients were divided into DSA-negative, DSA-low and DSA-high subgroups. Both graft survival and CLAD-free survival were evaluated. Among factors that may contribute to DSA development we analyzed Pseudomonas aeruginosa (P. aeruginosa) infection in bronchoalveolar lavage (BAL) specimens.

RESULTS

High MFI DSAs contributed to clinical antibody-mediated rejection (AMR) and were associated with significantly worse graft (HR: 5.77, p < 0.0001) and CLAD-free survival (HR: 6.47, p = 0.019) compared to low or negative MFI DSA levels. Analysis of BAL specimens revealed a strong correlation between DSA status, P. aeruginosa infection and BAL neutrophilia. DSA-high status and clinical AMR were both independent prognosticators for decreased graft and CLAD-free survival in our multivariate Cox-regression models, whereas BAL neutrophilia was associated with worse graft survival.

CONCLUSIONS

P. aeruginosa infection rates are elevated in recipients with a strong DSA response. Our results indicate that the simultaneous interpretation of MFI values and BAL neutrophilia is a feasible approach for risk evaluation and may help clinicians when to initiate DSA desensitization therapy, as early intervention could improve prognosis.

Complement-activating donor-specific anti-HLA antibodies in solid organ transplantation: systematic review, meta-analysis, and critical appraisal

Introduction

Several studies have investigated the impact of circulating complement-activating anti-human leukocyte antigen donor-specific antibodies (anti-HLA DSAs) on organ transplant outcomes. However, a critical appraisal of these studies and a demonstration of the prognostic value of complement-activating status over anti-HLA DSA mean fluorescence intensity (MFI) level are lacking.

Methods

We conducted a systematic review, meta-analysis and critical appraisal evaluating the role of complement-activating anti-HLA DSAs on allograft outcomes in different solid organ transplants. We included studies through Medline, Cochrane, Scopus, and Embase since inception of databases till May 05, 2023. We evaluated allograft loss as the primary outcome, and allograft rejection as the secondary outcome. We used the Newcastle-Ottawa Scale and funnel plots to assess risk of bias and used bias adjustment methods when appropriate. We performed multiple subgroup analyses to account for sources of heterogeneity and studied the added value of complement assays over anti-HLA DSA MFI level.

Results

In total, 52 studies were included in the final meta-analysis (11,035 patients). Complement-activating anti-HLA DSAs were associated with an increased risk of allograft loss (HR 2.77; 95% CI 2.33-3.29, p<0.001; I²=46.2%), and allograft rejection (HR 4.98; 95% CI 2.96-8.36, p<0.01; I²=70.9%). These results remained significant after adjustment for potential sources of bias and across multiple subgroup analyses. After adjusting on pan-IgG anti-HLA DSA defined by the MFI levels, complement-activating anti-HLA DSAs were significantly and independently associated with an increased risk of allograft loss.

Discussion

We demonstrated in this systematic review, meta-analysis and critical appraisal the significant deleterious impact and the independent prognostic value of circulating complement-activating anti-HLA DSAs on solid organ transplant risk of allograft loss and rejection.

Immune surveillance and humoral immune responses in kidney transplantation - A look back at T follicular helper cells

T follicular helper cells comprise a specialized, heterogeneous subset of immune-competent T helper cells capable of influencing B cell responses in lymphoid tissues. In physiology, for example in response to microbial challenges or vaccination, this interaction chiefly results in the production of protecting antibodies and humoral memory. In the context of kidney transplantation, however, immune surveillance provided by T follicular helper cells can take a life of its own despite matching of human leukocyte antigens and employing the latest immunosuppressive regiments. This puts kidney transplant recipients at risk of subclinical and clinical rejection episodes with a potential risk for allograft loss. In this review, the current understanding of immune surveillance provided by T follicular helper cells is briefly described in physiological responses to contrast those pathological responses observed after kidney transplantation. Sensitization of T follicular helper cells with the subsequent emergence of detectable donor-specific human leukocyte antigen antibodies, non-human leukocyte antigen antibodies their implication for kidney transplantation and lessons learnt from other transplantation "settings" with special attention to antibody-mediated rejection will be addressed.

Biomarkers for Chronic Lung Allograft Dysfunction: Ready for Prime Time?

Chronic lung allograft dysfunction (CLAD) remains a major hurdle impairing lung transplant outcome. Parallel to the better clinical identification and characterization of CLAD and CLAD phenotypes, there is an increasing urge to find adequate biomarkers that could assist in the earlier detection and differential diagnosis of CLAD phenotypes, as well as disease prognostication. The current status and state-of-the-art of biomarker research in CLAD will be discussed with a particular focus on radiological biomarkers or biomarkers found in peripheral tissue, bronchoalveolar lavage' and circulating blood' in which significant progress has been made over the last years. Ultimately, although a growing number of biomarkers are currently being embedded in the follow-up of lung transplant patients, it is clear that one size does not fit all. The future of biomarker research probably lies in the rigorous combination of clinical information with findings in tissue, bronchoalveolar lavage' or blood. Only by doing so, the ultimate goal of biomarker research can be achieved, which is the earlier identification of CLAD before its clinical manifestation. This is desperately needed to improve the prognosis of patients with CLAD after lung transplantation.

Assessment of Anti-Human Leukocyte Antigen (HLA)-Antibody-Dependent Humoral Response in Patients before and after Lung Transplantation

Background and Objectives: Testing for anti-human leukocyte antigen (HLA) antibodies both before and after transplantation is of fundamental significance for the success of lung transplantation. The aim of this study was the evaluation of anti-HLA immunization of patients before and after lung transplant who were subjected to qualification and transplantation. Materials and Methods: Prior to the transplantation, patients were examined for the presence of IgG class anti-HLA antibodies (anti-human leukocyte antigen), the so-called panel-reactive antibodies (PRA), using the flow cytometry method. After the transplantation, the class and specificity of anti-HLA antibodies (also IgG) were determined using Luminex. Results: In the group examined, the PRA results ranged from 0.1% to 66.4%. Low (30%) and average (30-80%) immunization was found in only 9.7% of the group examined. Presence of class I anti-HLA antibodies with MFI (mean fluorescence intensity) greater than 1000 was found in 42.7% of the patients examined, while class II anti-HLA antibodies were found in 38.4%. Immunization levels before and after the transplantation were compared. In 10.87% of patients, DSA antibodies (donor-specific antibodies) with MFI of over 1000 were found. Conclusions: It seems that it is possible to confirm the correlation between pre- and post-transplantation immunization with the use of the two presented methods of determining IgG class anti-HLA antibodies by increasing the size of the group studied and conducting a long-term observation thereof.

B Cell Immunity in Lung Transplant Rejection - Effector Mechanisms and Therapeutic Implications

Allograft rejection remains the major hurdle in lung transplantation despite modern immunosuppressive treatment. As part of the alloreactive process, B cells are increasingly recognized as modulators of alloimmunity and initiators of a donor-specific humoral response. In chronically rejected lung allografts, B cells contribute to the formation of tertiary lymphoid structures and promote local alloimmune responses. However, B cells are functionally heterogeneous and some B cell subsets may promote alloimmune tolerance. In this review, we describe the current understanding of B-cell-dependent mechanisms in pulmonary allograft rejection and highlight promising future strategies that employ B cell-targeted therapies.

Impacts of single nucleotide polymorphisms in Fc gamma receptor IIA (rs1801274) on lung transplant outcomes among Japanese lung transplant recipients

This study aimed to analyze the influences of single nucleotide polymorphisms (SNPs) in Fc gamma receptor IIA (FCGR2A) on postoperative outcomes after lung transplantation (LTx). We enrolled 191 lung transplant recipients (80 undergoing living-donor lobar lung transplants [LDLLTs] and 111 undergoing deceased-donor lung transplants [DDLTs]) in this study. We identified SNPs in FCGR2A (131 histidine [H] or arginine [R]; rs1801274) and reviewed the infectious complication-free survival after ICU discharge. The SNPs in FCGR2A comprised H/H (n=53), H/R (n=24), and R/R (n=3) in LDLLT, and H/H (n=67), H/R (n=42), and R/R (n=2) in DDLT. Recipients with H/H (H/H group) and those with H/R or R/R (R group) were compared in the analyses of infectious complications. In multivariate analyses, the R group of SNPs in FCGR2A was associated with pneumonia-free survival (HR: 2.52 [95% confidence interval {CI}: 1.35-4.71], p=0.004), fungal infection-free survival (HR: 2.50 [95% CI: 1.07-5.84], p=0.035), and cytomegalovirus infection-free survival (HR: 2.24 [95% CI: 1.07-4.69], p=0.032) in LDLLT but it was not associated with infectious complication-free survival in DDLT. Therefore, in LDLLT, more attention to infectious complications might need to be paid for LTx recipients with H/R or R/R than for those with H/H.

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.

Guiding therapeutic plasma exchange for antibody-mediated rejection treatment in lung transplant recipients - a retrospective study

Antibody-Mediated Rejection (AMR) due to donor-specific antibodies (DSA) is associated with poor outcomes after lung transplantation. Currently, there are no guidelines regarding the selection of treatment protocols. We studied how DSA characteristics including titers, C1q, and mean fluorescence intensity (MFI) values in undiluted and diluted sera may predict a response to therapeutic plasma exchange (TPE) and inform patient prognosis after treatment. Among 357 patients consecutively transplanted without detectable pre-existing DSAs between 01/01/16 and 12/31/18, 10 patients were treated with a standardized protocol of five TPE sessions with IVIG. Based on DSA characteristics after treatment, all patients were divided into three groups as responders, partial responders, and nonresponders. Kaplan-Meier Survival analyses showed a statistically significant difference in patient survival between those groups (P = 0.0104). Statistical analyses showed that MFI in pre-TPE 1:16 diluted sera was predictive of a response to standardized protocol (R²  = 0.9182) and patient survival (P = 0.0098). Patients predicted to be nonresponders who underwent treatment with a more aggressive protocol of eight TPE sessions with IVIG and bortezomib showed improvements in treatment response (P = 0.0074) and patient survival (P = 0.0253). Dilutions may guide clinicians as to which patients would be expected to respond to a standards protocol or require more aggressive treatment.

Clinical relevance of donor-specific antibodies directed at HLA-C: A long road to acceptance

In solid organ transplantation (SOT), the clinical relevance of donor-specific antibodies (DSA) directed at anti-HLA-A, -B, -DR and -DQ antigens is largely recognized while it is still a matter of debate for DSA directed at HLA-C. In this review, we summarize the peculiarities of HLA-C among class I HLA antigens as well as their immunogenicity, which underlie the clinical relevance of HLA-C locus and anti-HLA-C DSA in SOT. Many factors, both intrinsic and extrinsic to the HLA-C gene and HLA-C protein, explain its lower expression in comparison with HLA-A and -B. This lower expression can explain the apparent lower immunogenicity of HLA-C leading to a lower prevalence and strength of anti-HLA-C antibodies. Nevertheless, HLA-C antigens are truly immunogenic and preformed anti-HLA-C DSA are clinically relevant. Indeed, anti-HLA-C DSA are able to bind donor cells and to activate the complement pathway both ex vivo and in vivo. In line with this, numerous clinical studies now show that preformed DSA directed at native HLA-C molecules induce poorer graft outcomes. We then plead for the inclusion of HLA-C in all transplant allocation systems and we propose a strategy to cope with anti-HLA-C DSA in SOT. Beyond SOT, anti-HLA-C antibodies generate a growing interest in the allo-HCT, transfusion and obstetrics fields, while new concepts such as the role of the "missing-self" in solid organ rejection places HLA-C as an inescapable actor in transplant tolerance.

When tissue is the issue: A histological review of chronic lung allograft dysfunction

Although chronic lung allograft dysfunction (CLAD) remains the major life-limiting factor following lung transplantation, much of its pathophysiology remains unknown. The discovery that CLAD can manifest both clinically and morphologically in vastly different ways led to the definition of distinct subtypes of CLAD. In this review, recent advances in our understanding of the pathophysiological mechanisms of the different phenotypes of CLAD will be discussed with a particular focus on tissue-based and molecular studies. An overview of the current knowledge on the mechanisms of the airway-centered bronchiolitis obliterans syndrome, as well as the airway and alveolar injuries in the restrictive allograft syndrome and also the vascular compartment in chronic antibody-mediated rejection is provided. Specific attention is also given to morphological and molecular markers for early CLAD diagnosis or histological changes associated with subsequent CLAD development. Evidence for a possible overlap between different forms of CLAD is presented and discussed. In the end, "tissue remains the (main) issue," as we are still limited in our knowledge about the actual triggers and specific mechanisms of all late forms of posttransplant graft failure, a shortcoming that needs to be addressed in order to further improve the outcome of lung transplant recipients.

Clinical Outcomes of Lung Transplantation in the Presence of Donor-Specific Antibodies

Rationale: There is significant variation in approach to pre-lung transplant donor-specific antibodies (DSA), with some centers declining to cross any DSA. We implemented a protocol for transplantation for candidates with pretransplant DSA so long as a prospective complement-dependent cytotoxicity crossmatch was negative, regardless of number, specificity, class, or mean fluorescence intensity.Objectives: To compare post-transplant outcomes including overall survival, chronic lung allograft dysfunction-free survival, antibody-mediated rejection, and acute cellular rejection in lung transplant recipients where pretransplant DSA was and was not present.Methods: This was a single-center retrospective cohort study. For recipients with pretransplant DSA, if the prospective complement-dependent cytotoxicity crossmatch was negative, the donor offer was accepted and plasmapheresis was performed within 24 hours of transplantation and continued until retrospective crossmatch results returned. Immunosuppression and post-transplant management were not otherwise modified.Results: Of the 203 included recipients, 18 (8.9%) had pretransplant DSA. The median DSA mean fluorescence intensity was 4,000 (interquartile range, 2,975-5,625; total range, 2,100-17,000). The median number of DSA present per patient was one (interquartile range, 1-2). The presence of pretransplant DSA was not associated with increased mortality (hazard ratio, 1.2; 95% confidence interval [CI], 0.4-3.4) or decreased chronic lung allograft dysfunction-free survival (hazard ratio, 1.1; 95% CI, 0.6-2.1). Recipients with pretransplant DSA were more likely to require prolonged mechanical ventilation (adjusted odds ratio, 7.0; 95% CI, 2.3-21.6) and to have antibody-mediated rejection requiring treatment (adjusted odds ratio, 7.5; 95% CI, 1.0-55.8).Conclusions: A protocol of accepting donor offers for lung transplant candidates with preformed, complement-dependent cytotoxicity crossmatch-negative DSA is associated with increased need for prolonged mechanical ventilation and antibody-mediated rejection without affecting short-term overall or chronic lung allograft dysfunction-free survival.

Intragraft donor-specific anti-HLA antibodies in phenotypes of chronic lung allograft dysfunction

INTRODUCTION

Circulating anti-human leukocyte antigen (HLA) serum donor-specific antibodies (sDSAs) increase the risk of chronic lung allograft dysfunction (CLAD) and mortality. Discrepancies between serological and pathological/clinical findings are common. Therefore, we aimed to assess the presence of tissue-bound graft DSAs (gDSAs) in CLAD explant tissue compared with sDSAs.

METHODS

Tissue cores, obtained from explant lungs of unused donors (n=10) and patients with bronchiolitis obliterans syndrome (BOS; n=18) and restrictive allograft syndrome (RAS; n=18), were scanned with micro-computed tomography before elution of antibodies. Total IgG levels were measured via ELISA. Anti-HLA class I and II IgG gDSAs were identified using Luminex single antigen beads and compared with DSAs found in serum samples.

RESULTS

Overall, mean fluorescence intensity was higher in RAS eluates compared with BOS and controls (p<0.0001). In BOS, two patients were sDSA⁺/gDSA⁺ and two patients were sDSA^-/gDSA⁺. In RAS, four patients were sDSA⁺/gDSA⁺, one patient was sDSA⁺/gDSA^- and five patients were sDSA^-/gDSA⁺. Serum and graft results combined, DSAs were more prevalent in RAS compared with BOS (56% versus 22%; p=0.04). There was spatial variability in gDSA detection in one BOS patient and three RAS patients, who were all sDSA^-. Total graft IgG levels were higher in RAS than BOS (p<0.0001) and in gDSA⁺ versus gDSA^- (p=0.0008), but not in sDSA⁺ versus sDSA^- (p=0.33). In RAS, total IgG levels correlated with fibrosis (r= -0.39; p=0.02).

CONCLUSIONS

This study underlines the potential of gDSA assessment as complementary information to sDSA findings. The relevance and applications of gDSAs need further investigation.

The Role of Major Histocompatibility Complex in Organ Transplantation- Donor Specific Anti-Major Histocompatibility Complex Antibodies Analysis Goes to the Next Stage

Organ transplantation has progressed with the comprehension of the major histocompatibility complex (MHC). It is true that the outcome of organ transplantation largely relies on how well rejection is managed. It is no exaggeration to say that to be well acquainted with MHC is a shortcut to control rejection. In human beings, MHC is generally recognized as human leukocyte antigens (HLA). Under the current circumstances, the number of alleles is still increasing, but the function is not completely understood. Their roles in organ transplantation are of vital importance, because mismatches of HLA alleles possibly evoke both cellular and antibody-mediated rejection. Even though the control of cellular rejection has improved by recent advances of immunosuppressants, there is no doubt that antibody-mediated rejection (AMR), which is strongly correlated with donor-specific anti-HLA antibodies (DSA), brings a poor outcome. Thus, to diagnose and treat AMR correctly is a clear proposition. In this review, we would like to focus on the detection of intra-graft DSA as a recent trend. Overall, here we will review the current knowledge regarding MHC, especially with intra-graft DSA, and future perspectives: HLA epitope matching; eplet risk stratification; predicted indirectly recognizable HLA epitopes etc. in the context of organ transplantation.

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.

Banff Lung Report: Current knowledge and future research perspectives for diagnosis and treatment of pulmonary antibody-mediated rejection (AMR)

The Lung session of the 2017 14th Banff Foundation for Allograft Pathology Conference, Barcelona focused on the multiple aspects of antibody-mediated rejection (AMR) in lung transplantation. Multidimensional approaches for AMR diagnosis, including classification, histological and immunohistochemical analysis, and donor- specific antibody (DSA) characterization with their current strengths and limitations were reviewed in view of recent research. The group also discussed the role of tissue gene expression analysis in the context of unmet needs in lung transplantation. The current best practice for monitoring of AMR and the therapeutic approach are summarized and highlighted in this report. The working group reached consensus of the major gaps in current knowledge and focused on the unanswered questions regarding pulmonary AMR. An important outcome of the meeting was agreement on the need for future collaborative research projects to address these gaps in the field of lung transplantation.

Improvement in HLA-typing by new sequence-specific oligonucleotides kits for HLA-A, -B, and -DRB1 loci

Polymerase chain reaction sequence-specific oligonucleotide is commonly used for HLA-typing. We replaced our LabType SSO HD (HD) kits with LabType SSO XR (XR) kits (One Lambda, Inc., Canoga Park, California) for HLA-A, -B, and -DRB1 following acquisition of a LABScan3D analyzer. The XR kits have more bead regions than the HD kits, allowing for an extended number of probes and exon coverage. They are claimed to improve typing resolution and to diminish the number of allele ambiguities, including common and well-documented (CWD) and null alleles to be resolved. We retrospectively selected patients who had their first HLA-typing performed with the HD kits and their second determination with the XR kits between 2015 and 2016. Forty-two patients were selected for HLA-A typing comparison, and 48 for HLA-B and 41 for HLA-DRB1. XR kits significantly decreased the number of allele ambiguities for HLA-A and -B. On the other hand, the improvement was limited for the HLA-DRB1 locus. The XR kits did not resolve all the CWD HLA allele ambiguities, which may be important for organ and/or hematopoietic stem cell transplantations. The XR kits eliminated 88%, 62%, and 27% of null allele ambiguities for HLA-A, -B, and -DRB1 loci, respectively. In conclusion, the XR kits allow for a significant improvement of HLA-typing resolution for HLA-A and -B loci in comparison with HD kits. In contrast, the number of oligonucleotides in the XR HLA-DRB1 kit should be extended to include exon 3 at the very least. It could also be interesting to include oligonucleotides allowing HLA-DRB3, 4, and 5 typing.

Donor-specific HLA antibody-mediated complement activation is a significant indicator of antibody-mediated rejection and poor long-term graft outcome during lung transplantation: a single center cohort study

Complement-mediated allograft injury, elicited by donor-specific HLA antibodies (DSA), is a defining pathophysiological characteristic of allograft damage. We aimed to study DSA-induced complement activation as a diagnostic marker of antibody-mediated rejection (AMR) and a risk stratification tool for graft loss in the context of lung transplantation (LT). We identified 38 DSA-positive patients whose serum samples were submitted for C3d deposition testing via the C3d assay. Among these 38 patients, 15 had AMR (DSAPos AMRPos ). Results were reported for each patient as the C3d ratio for each DSA, the immunodominant DSA, and the C3d ratio for all DSA present in a sample (C3d ratioSUM ). DSAPos AMRPos patients had higher C3d ratioSUM values (58.66 (-1.32 to 118.6) vs. 1.52 (0.30 to 2.74), P = 0.0016) and increased immunodominant C3d ratios (41.87 (1.72 to 82.02) vs. 0.69 (0.21 to 1.19), P = 0.001) when compared with DSAPos AMRNeg patients. Specificity and calculated positive predictive value of the immunodominant C3d ratio and BCMsum tests for AMR diagnosis were both 100% (CI = 17.4-100) in this cohort. Worst graft survival was associated with both immunodominant C3d ratio ≥4 or C3d ratioSUM ≥10 or BCMsum >7000, suggesting that the antibody composition and/or strength are the principal determinants of an HLA DSA's capacity to activate complement.

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.

Detection and clinical impact of human leukocyte antigen antibodies in lung transplantation: A systematic review and meta-analysis

There is significant variability in lung transplant centers' approach to HLA antibodies, creating heterogeneity regarding their clinical significance. Some institutions use beads coated with multiple HLA to screen candidate sera and then use single antigen bead (SAB) to determine antibody identity if the pre-screen is positive. Other centers do not pre-screen, using SAB alone, which may detect low-level antibodies of unknown significance. The primary objective of this study was to review the current literature to identify sources of heterogeneity in the identification of pre- and post-lung transplant HLA antibodies, particularly regarding antibody-detection methods. A random effects model meta-analysis was used to evaluate the relationship between pre-transplant HLA antibodies and the development of de novo donor-specific antibodies (dnDSA) and dnDSA and chronic lung allograft dysfunction (CLAD). Each outcome was stratified by the method of antibody detection (pre-screen followed by SAB vs SAB alone). We identified 13 cohort studies with a total of 3039 patients. The use of pre-screening followed by SAB testing and the use of induction immunosuppression were associated with lower prevalence of dnDSA. Patients with pre-transplant HLA antibodies were more likely to develop dnDSA (hazard ratio [HR] = 1.49, 95% confidence interval [CI]: 1.19-1.86, P < .001). dnDSA was associated with CLAD (HR = 2.02, 95% CI = 1.37-2.97, P < .001). When considering studies using SAB alone, however, pre-transplant antibody status was no longer associated with dnDSA and dnDSA was no longer associated with CLAD. Based on the current literature, SAB-alone testing may detect less clinically relevant antibodies than pre-screening followed by SAB.

Characteristics of Donor-Specific Antibodies Associated With Antibody-Mediated Rejection in Lung Transplantation

Although donor-specific anti-human leukocyte antigen (HLA) antibodies (DSAs) are frequently found in recipients after lung transplantation (LT), the characteristics of DSA which influence antibody-mediated rejection (AMR) in LT are not fully defined. We retrospectively analyzed 206 consecutive LT patients of our center (2010–2013). DSAs were detected by using luminex single antigen beads assay and mean fluorescence intensity was assessed. Within the study population, 105 patients had positive DSA. Patients with and without AMR (AMR^Pos, n = 22, and AMR^Neg, n = 83, respectively) were compared. AMR^Pos patients had significantly greater frequencies of anti-HLA DQ DSA (DQ DSA) than AMR^Neg patients (95 vs 58%, respectively, p < 0.0001). Compared to AMR^Neg patients, AMR^Pos patients had higher DQ DSA sum MFI [7,332 (2,067–10,213) vs 681 (0–1,887), p < 0.0001]. DQ DSA when associated with AMR, had more frequent graft loss and chronic lung allograft dysfunction (CLAD). These data suggest (i) that DSA characteristics clearly differ between AMR^Pos and AMR^Neg patients and (ii) the deleterious impact of DQ DSA on clinical outcome.

Association of Local Intrapulmonary Production of Antibodies Specific to Donor Major Histocompatibility Complex Class I With the Progression of Chronic Rejection of Lung Allografts

BACKGROUND

Antibody-mediated rejection may lead to chronic lung allograft dysfunction, but antibody-mediated rejection may develop in the absence of detectable donor-specific antibody (DSA) in recipient serum. This study investigated whether humoral immune responses develop not only systemically but locally within rejected lung allografts, resulting in local production of DSA.

METHODS

Lewis rats received orthotopic left lung transplantation from Lewis (syngeneic control) or Brown-Norway (major histocompatibility complex-mismatched allogeneic) donor rats. Rats that underwent allogeneic lung transplantation were subsequently administered cyclosporine until day 14 (short immunosuppression) or day 35 (long immunosuppression). The lung grafts and spleens of recipient animals were tissue cultured for 4 days, and the titer of antibody against donor major histocompatibility complex molecules was assayed by flow cytometry. Explanted lung grafts were also evaluated pathologically.

RESULTS

By day 98, DSA titers in supernatants of lung graft (P = 0.0074) and spleen (P = 0.0167) cultures, but not serum, from the short immunosuppression group were significantly higher than titers in syngeneic controls. Cultures and sera from the long immunosuppression group showed no production of DSA. Microscopically, the lung grafts from the short immunosuppression group showed severe bronchiole obliteration and parenchymal fibrosis, along with lymphoid aggregates containing T and B cells, accompanying plasma cells. These findings suggestive of local humoral immune response were not observed by days 28 and 63.

CONCLUSIONS

DSA can be locally produced in chronically rejected lung allografts, along with intragraft immunocompetent cells. Clinical testing of DSA in serum samples alone may underestimate lung allograft dysfunction.

Application and interpretation of histocompatibility data in thoracic (heart and lung) transplantation

PURPOSE OF REVIEW

The purpose of the review is to update our current understanding and utilization of immunogenetic tools in heart and lung transplant.

RECENT FINDINGS

Increasingly, complex patients have been managed perioperatively for heart and lung transplant using a variety of tests and techniques. Recent treatment regimens and listing strategies have exploited recent laboratory advances. However, the better characterization has led to an even more complex description of sensitized heart and lung candidates. Several recent studies have examined antibody strengths and behavior to guide clinical decision-making and examine postoperative outcomes. Finally, non-human leukocyte antigen antibodies have emerged as possible determinants of allograft outcome in heart and lung transplant.

SUMMARY

Heart and lung transplant candidates with preformed and de-novo posttransplant antibodies continue to represent a challenging and high-risk group of patients. Modern immunogenetic techniques have broadened our understanding and have revealed an even more complex relationship between antibodies, allografts, and outcomes.

A Previous Miscarriage and a Previous Successful Pregnancy Have a Different Impact on HLA Antibody Formation during a Subsequent Successful Pregnancy

Inherited paternal HLA antigens from the semi-allogeneic fetus may trigger maternal immune responses during pregnancy, leading to the production of child-specific HLA antibodies. The prevalence of these HLA antibodies increases with the number of successful pregnancies. In the present study, we investigated the effect of a single prior miscarriage on HLA antibody formation during a subsequent successful pregnancy. Women with a successful pregnancy with one or more prior miscarriages (n = 229) and women with a successful pregnancy without a prior miscarriage (n = 58), and their children were HLA typed. HLA antibody analyses were performed in these women to identify whether HLA antibodies were formed against mismatched HLA class-I antigens of the last child. The percentage of immunogenic antigens was significantly lower after a single successful pregnancy that was preceded by a single miscarriage (n = 18 women) compared to a successful pregnancy that was preceded by a first successful pregnancy (n = 62 women). Thus, our data suggest that a previous miscarriage has a different impact on child-specific HLA antibody formation during a subsequent successful pregnancy than a previous successful pregnancy. The lower immunogenicity in these women cannot be explained by reduced numbers of immunogenic B-cell and T-cell epitopes. In conclusion, our observations indicate that increasing gravidity is not related to an increased prevalence of HLA antibodies in a single successful pregnancy that was preceded by a single prior miscarriage.