Antibody-Mediated Rejection of Solid-Organ Allografts

Application of CD38 monoclonal antibody in kidney disease

CD38 antigen is a glycoprotein that found on the surface of several immune cells, and this property makes its monoclonal antibodies have the effect of targeted elimination of immune cells. Therefore, the CD38 monoclonal antibody (such as daratumumab, Isatuximab) becomes a new treatment option for membranous nephropathy, lupus nephritis, renal transplantation, and other refractory kidney diseases. This review summarizes the application of CD38 monoclonal antibodies in different kidney diseases and highlights future prospects.

A minor tweak in transplant surgery protocols alters the cellular landscape of the arterial wall during transplant vasculopathy

Introduction

Transplant vasculopathy (TV) is a major complication after solid organ transplantation, distinguished by an arterial intimal thickening that obstructs the vascular lumen and leads to organ rejection. To date, TV remains largely untreatable, mainly because the processes involved in its development remain unclear. Aortic transplantation in mice, used to mimic TV, relies on highly variable experimental protocols, particularly regarding the type of anastomosis used to connect the donor aorta to the recipient. While the amount of trauma undergone by a vessel can dramatically affect the resulting pathology, the impact of the type of anastomosis on TV in mice has not been investigated in detail.

Methods

In this study, we compare the cellular composition of aortic grafts from BALB/C donor mice transplanted into C57BL/6J recipient mice using two different anastomosis strategies: sleeve and cuff.

Results

While both models recapitulated some aspects of human TV, there were striking differences in the cellular composition of the grafts. Indeed, aortic grafts from the cuff group displayed a larger coverage of the neointimal area by vascular smooth muscle cells compared to the sleeve group. Aortic grafts from the sleeve group contained higher amounts of T cells, while the cuff group displayed larger B-cell infiltrates.

Discussion

Together, these data indicate that a seemingly minor technical difference in transplant surgery protocols can largely impact the cellular composition of the graft, and thus the mechanisms underlying TV after aortic transplantation in mice.

The Clinical Utility of Post-Transplant Monitoring of Donor-Specific Antibodies in Stable Renal Transplant Recipients: A Consensus Report With Guideline Statements for Clinical Practice

Solid phase immunoassays improved the detection and determination of the antigen-specificity of donor-specific antibodies (DSA) to human leukocyte antigens (HLA). The widespread use of SPI in kidney transplantation also introduced new clinical dilemmas, such as whether patients should be monitored for DSA pre- or post-transplantation. Pretransplant screening through SPI has become standard practice and DSA are readily determined in case of suspected rejection. However, DSA monitoring in recipients with stable graft function has not been universally established as standard of care. This may be related to uncertainty regarding the clinical utility of DSA monitoring as a screening tool. This consensus report aims to appraise the clinical utility of DSA monitoring in recipients without overt signs of graft dysfunction, using the Wilson & Junger criteria for assessing the validity of a screening practice. To assess the evidence on DSA monitoring, the European Society for Organ Transplantation (ESOT) convened a dedicated workgroup, comprised of experts in transplantation nephrology and immunology, to review relevant literature. Guidelines and statements were developed during a consensus conference by Delphi methodology that took place in person in November 2022 in Prague. The findings and recommendations of the workgroup on subclinical DSA monitoring are presented in this article.

Transcriptional and spatial profiling of the kidney allograft unravels a central role for FcyRIII+ innate immune cells in rejection

Rejection remains the main cause of premature graft loss after kidney transplantation, despite the use of potent immunosuppression. This highlights the need to better understand the composition and the cell-to-cell interactions of the alloreactive inflammatory infiltrate. Here, we performed droplet-based single-cell RNA sequencing of 35,152 transcriptomes from 16 kidney transplant biopsies with varying phenotypes and severities of rejection and without rejection, and identified cell-type specific gene expression signatures for deconvolution of bulk tissue. A specific association was identified between recipient-derived FCGR3A+ monocytes, FCGR3A+ NK cells and the severity of intragraft inflammation. Activated FCGR3A+ monocytes overexpressed CD47 and LILR genes and increased paracrine signaling pathways promoting T cell infiltration. FCGR3A+ NK cells overexpressed FCRL3, suggesting that antibody-dependent cytotoxicity is a central mechanism of NK-cell mediated graft injury. Multiplexed immunofluorescence using 38 markers on 18 independent biopsy slides confirmed this role of FcγRIII+ NK and FcγRIII+ nonclassical monocytes in antibody-mediated rejection, with specificity to the glomerular area. These results highlight the central involvement of innate immune cells in the pathogenesis of allograft rejection and identify several potential therapeutic targets that might improve allograft longevity.

Mitochondrial responses to brain death in solid organ transplant

Mitochondrial dynamics are central to the pathophysiology of cellular damage and inflammatory responses. In the context of solid organ transplantation, mitochondria are implicated in immune activation in donor organs that occurs after brain death, as they are critical to the regulation of cellular stress response, cell death, and display energetic adaptations through the adjustment of respiratory capacity depending on the cellular milieu. Mitochondrial damage activates mitochondrial systems of fission, fusion, biogenesis, and mitochondrial autophagy, or mitophagy. The mechanistic pathways as well as therapies targeting mitochondrial physiology have been studied as plausible ways to mitigate the negative effects of brain death on donor organs, though there is no summative evaluation of the multiple efforts across the field. This mini-review aims to discuss the interplay of donor brain death, mitochondrial dynamics, and impact on allograft function as it pertains to heart, lung, liver, and kidney transplants.

Development and Evaluation of a Novel Radiotracer 125I-rIL-27 to Monitor Allotransplant Rejection by Specifically Targeting IL-27Rα

Noninvasive monitoring of allograft rejection is beneficial for the prognosis of patients with organ transplantation. Recently, IL-27/IL-27Rα was proved in close relation with inflammatory diseases, and 125I-anti-IL-27Rα mAb our group developed demonstrated high accumulation in the rejection of the allograft. However, antibody imaging has limitations in the imaging background due to its large molecular weight. Therefore, we developed a novel radiotracer (iodine-125-labeled recombinant IL-27) to evaluate the advantage in the targeting and imaging of allograft rejection. In vitro specific binding of 125I-rIL-27 was determined by saturation and competitive assay. Blood clearance, biodistribution, phosphor autoradioimaging, and IL-27Rα expression were studied on day 10 after transplantation (top period of allorejection). Our results indicated that 125I-rIL-27 could bind with IL-27Rα specifically and selectively in vitro. The blood clearance assay demonstrated fast blood clearance with 13.20 μl/h of 125I-rIL-27 staying in the blood after 24 h. The whole-body phosphor autoradiography and biodistribution assay indicated a higher specific uptake of 125I-rIL-27 and a clear radioimage in allograft than in syngraft at 24 h, while a similar result was obtained at 48 h in the group of 125I-anti-IL-27Rα mAb injection. Meanwhile, a higher expression of IL-27Rα was found in the allograft by Western blot. The accumulation of radioactivity of 125I-rIL-27 was highly correlated with the expression of IL-27Rα in the allograft. In conclusion, 125I-rIL-27 could be a promising probe for acutely monitoring allograft rejection with high specific binding towards IL-27Rα on allograft and low imaging background.

Isolated Pre-existing HLA-DP Donor-Specific Antibodies are Associated With Poorer Outcomes in Renal Transplantation

Introduction

The importance of donor-specific antibodies (DSAs) in renal transplantation has long been recognized, but the significance of human leukocyte antigen (HLA)-DP antibodies remains less clear. We performed a retrospective single center study of renal transplants with pre-existing isolated HLA-DP-DSAs to assess clinical outcomes.

Methods

Twenty-three patients with isolated HLA-DP-DSAs were compared with 3 control groups as follows: standard immunological risk (calculated reaction frequency [cRF] < 85%, no current or historical DSA, no repeat mismatched antigens with previous transplants, n = 46), highly sensitized (cRF > 85%, n = 27), and patients with HLA-DP antibodies that were not donor-specific (n = 18). Univariate and multivariate analyses were performed comparing antibody-mediated rejection (ABMR)-free and graft survival. Factors in the final multivariable models included patient group, % cRF, B-cell flow crossmatch (BFXM) positivity and regrafts.

Results

Over a median follow-up of 1197 days, 65% of HLA-DP-DSA patients had ABMR on indication biopsies, and 30% of HLA-DP-DSA patients lost their graft. Pre-existing HLA-DP DSAs remained the single factor associated with ABMR after multivariable analysis (hazard ratio [HR] = 9.578, P = 0.012). Patients with HLA-DP DSAs had increased microvascular scores (P = 0.0346) and worse transplant glomerulopathy (P = 0.015) on biopsy compared with the standard immunological risk group. Furthermore, flow crossmatch (FXM) positivity did not help inform on the risk of graft failure or ABMR in patients with preformed DP-DSA.

Conclusion

Transplants with pre-existing HLA-DP-DSAs should be considered high risk. Routine laboratory tests are unable to further risk stratify these patients. Recipients should be considered for intensified immunosuppression and closely monitored.

Immunotherapy and the Spectrum of Kidney Disease: Should We Individualize the Treatment?

The new targeted cancer therapies including immune checkpoint inhibitors (ICIs) have been demonstrated to improve the survival of oncological patients, even in cases of metastatic cancer. In the past 5 years, several studies have revealed that ICI can produce several immune-mediated toxicities involving different organs, such as the skin, the gastrointestinal tract, the liver, and, of course, the kidney. The most frequent lesion of immunotoxicity in the kidney is acute interstitial nephritis (AIN), although other nephropathies have also been described as a consequence of the use of ICI, such as glomerulonephritis and acute thrombotic microangiopathy, among others. In addition, kidney rejection has also been reported in kidney transplant patients treated with ICI. Normally randomized clinical trials with ICI exclude patients with end-stage kidney disease, namely, patients undergoing dialysis and kidney transplant patients. Several important questions need to be addressed in relation to immunotherapy and patients with kidney disease: (a) when to start corticosteroid therapy in a patient with suspected acute kidney injury (AKI) related to ICI, (b) the moment of nephrologist referral and kidney biopsy indication, (c) management of ICI in patients undergoing dialysis, and (d) the effect of ICI in kidney transplantation, immunosuppressive personalized treatment, and risk of allograft rejection in kidney transplant patients. The objective of this review was to summarize the recently published literature on a wide spectrum of kidney disease patients with cancer and ICI. This review will address three main important groups of individuals with kidney disease and cancer immunotherapy, AKI associated with ICI, patients undergoing dialysis, and kidney transplant recipients. We believe that the information provided in this review will enlighten the personalized ICI treatment in individuals with a broader spectrum of kidney diseases.

Harnessing the B Cell Response in Kidney Transplantation - Current State and Future Directions

Despite dramatic improvement in kidney transplantation outcomes over the last decades due to advent of modern immunosuppressive agents, long-term outcomes remain poor. Antibody-mediated rejection (ABMR), a B cell driven process, accounts for the majority of chronic graft failures. There are currently no FDA-approved regimens for ABMR; however, several clinical trials are currently on-going. In this review, we present current mechanisms of B cell response in kidney transplantation, the clinical impact of sensitization and ABMR, the B cell response under current immunosuppressive regimens, and ongoing clinical trials for ABMR and desensitization treatment.

Microvascular Inflammation of the Renal Allograft: A Reappraisal of the Underlying Mechanisms

Antibody-mediated rejection (ABMR) is associated with poor transplant outcomes and was identified as a leading cause of graft failure after kidney transplantation. Although the hallmark histological features of ABMR (ABMRh), i.e., microvascular inflammation (MVI), usually correlate with the presence of anti-human leukocyte antigen donor-specific antibodies (HLA-DSAs), it is increasingly recognized that kidney transplant recipients can develop ABMRh in the absence of HLA-DSAs. In fact, 40-60% of patients with overt MVI have no circulating HLA-DSAs, suggesting that other mechanisms could be involved. In this review, we provide an update on the current understanding of the different pathogenic processes underpinning MVI. These processes include both antibody-independent and antibody-dependent mechanisms of endothelial injury and ensuing MVI. Specific emphasis is placed on non-HLA antibodies, for which we discuss the ontogeny, putative targets, and mechanisms underlying endothelial toxicity in connection with their clinical impact. A better understanding of these emerging mechanisms of allograft injury and all the effector cells involved in these processes may provide important insights that pave the way for innovative diagnostic tools and highly tailored therapeutic strategies.

Approaching the sensitized lung patient: risk assessment for donor acceptance

The presence of HLA antibodies is widely recognized as a barrier to solid organ transplantation, and for lung transplant candidates, it has a significant negative impact on both waiting time and waiting list mortality. Although HLA antibodies have been associated with a broad spectrum of allograft damage, precise characterization of these antibodies in allosensitized candidates may enhance their accessibility to transplant. The introduction of Luminex-based single antigen bead (SAB) assays has significantly improved antibody detection sensitivity and specificity, but SAB alone is not sufficient for risk-stratification. Functional characterization of donor-specific antibodies (DSA) is paramount to increase donor accessibility for allosensitized lung candidates. We describe here our approach to evaluate sensitized lung transplant candidates. By employing state-of-the-art technologies to assess histocompatibility and determine physiological properties of circulating HLA antibodies, we can provide our Clinical Team a better risk assessment for lung transplant candidates and facilitate a "road map" to transplant. The cases presented in this paper illustrate the "individualized steps" taken to determine calculated panel reactive antibodies (cPRA), titer and complement-fixing properties of each HLA antibody present in circulation. When a donor is considered, we can better predict the risk associated with potentially crossing HLA antibodies, thereby allowing the Clinical Team to approach allosensitized lung patients with an individualized medicine approach. To facilitate safe access of sensitized lung transplant candidates to potential donors, a synergy between the histocompatibility laboratory and the Clinical Team is essential. Ultimately, donor acceptance is a decision based on several parameters, leading to a risk-stratification unique for each patient.

Social Support Effects on Neural Stress and Alcohol Reward Responses

Social support (SS), or having people to depend on during times of stress, may offer an emotional and neurological buffer to problem drinking. Specifically, SS may modulate reward and stress-related brain responses to mitigate perceptions of alcohol reward and stress. There is limited evidence, however, on this topic and specifically on brain networks that may modulate SS effects on stress and alcohol reward. Here we present a review of the current literature on this topic as well as data from a large community sample of 115 social drinkers. Findings from a novel fMRI task viewing alcohol cue, stress, and neutral images, in separate blocks, while providing ratings on subjective feelings of alcohol craving, stress, and arousal are included. Lower SS significantly predicted greater alcohol craving during alcohol cue and stress conditions, higher baseline levels of stress, and greater arousal in the alcohol cue, relative to neutral condition. Remarkably, individuals with low SS showed greater reward activation (ventral medial prefrontal cortex (VmPFC) and ventral striatum) during alcohol cue exposure, while those with high SS showed no such activation (p < 0.001, family wise error corrected at 0.05). Furthermore, individuals with lower SS showed greater stress circuit (VmPFC, dorsal striatum, and periaqueductal gray) activation not observed in the high SS groups. Both groups showed increased amygdala activation under stress condition. The findings support the notion that SS is a powerful modulator of stress response and reward motivation. High SS buffers neural and subjective stress responses, while low SS potentiates greater reward seeking with higher alcohol craving and greater brain activation during alcohol cue exposure. Previous research and current results suggest the need to further explore the role of SS in those at risk of developing alcohol use disorder and assess novel prevention strategies to boost SS in at-risk drinkers.

Small Extracellular Vesicles in Transplant Rejection

Small extracellular vesicles (sEV), which are released to body fluids (e.g., serum, urine) by all types of human cells, may stimulate or inhibit the innate and adaptive immune response through multiple mechanisms. Exosomes or sEV have on their surface many key receptors of immune response, including major histocompatibility complex (MHC) components, identical to their cellular origin. They also exhibit an ability to carry antigen and target leukocytes either via interaction with cell surface receptors or intracellular delivery of inflammatory mediators, receptors, enzymes, mRNAs, and noncoding RNAs. By the transfer of donor MHC antigens to recipient antigen presenting cells sEV may also contribute to T cell allorecognition and alloresponse. Here, we review the influence of sEV on the development of rejection or tolerance in the setting of solid organ and tissue allotransplantation. We also summarize and discuss potential applications of plasma and urinary sEV as biomarkers in the context of transplantation. We focus on the attempts to use sEV as a noninvasive approach to detecting allograft rejection. Preliminary studies show that both sEV total levels and a set of specific molecules included in their cargo may be an evidence of ongoing allograft rejection.

BAFF signaling drives interstitial transformation of mouse renal tubular epithelial cells in a Pin1-dependent manner

Aberrant expression of B cell–activating factor belonging to TNF superfamily (BAFF) and its receptors results in abnormal biological activities in hematopoietic and non-hematopoietic cells and is closely associated with the occurrence and development of various diseases. However, the biological significance and potential mechanisms underlying BAFF signaling in renal tubular epithelial cells (RTECs) remain unknown. This study aimed to investigate the biological role of BAFF signaling in RTECs. Mice primary RTECs were applied. The proliferation status and apoptotic rates were examined by MTS assay and flow cytometry, respectively. The expression of BAFF and its receptors was analyzed via flow cytometry and sodium ion transport function, and cytokeratin-18 expression was detected through immunofluorescence staining. In addition, Pin1 was knocked down via siRNA and its expression was assessed through reverse transcription PCR. Lastly, western blotting was performed to analyze E-cadherin, ɑ-SMA, and Pin1 expression. Results suggested that BAFF-R was significantly upregulated upon IFN-γ stimulation, and enhancement of BAFF signaling promoted cell survival and reduced their apoptotic rate, while simultaneously reducing the epithelial phenotype and promoting the interstitial transformation of cells. Furthermore, Pin1 was significantly increased, along with the upregulation of BAFF signaling in the RTECs, and participated in interstitial transformation induced by BAFF signaling. Collectively, the present results elucidate the potential mechanism of loss of normal function of RTECs under long-term high dose of BAFF stimulation provides a potential therapeutic target for renal interstitial fibrosis, and underlining mechanisms of shortening of long-term outcomes of kidney allografts via augmenting of BAFF signaling.

Tackling Chronic Kidney Transplant Rejection: Challenges and Promises

Despite advances in post-transplant management, the long-term survival rate of kidney grafts and patients has not improved as approximately forty percent of transplants fails within ten years after transplantation. Both immunologic and non-immunologic factors contribute to late allograft loss. Chronic kidney transplant rejection (CKTR) is often clinically silent yet progressive allogeneic immune process that leads to cumulative graft injury, deterioration of graft function. Chronic active T cell mediated rejection (TCMR) and chronic active antibody-mediated rejection (ABMR) are classified as two principal subtypes of CKTR. While significant improvements have been made towards a better understanding of cellular and molecular mechanisms and diagnostic classifications of CKTR, lack of early detection, differential diagnosis and effective therapies continue to pose major challenges for long-term management. Recent development of high throughput cellular and molecular biotechnologies has allowed rapid development of new biomarkers associated with chronic renal injury, which not only provide insight into pathogenesis of chronic rejection but also allow for early detection. In parallel, several novel therapeutic strategies have emerged which may hold great promise for improvement of long-term graft and patient survival. With a brief overview of current understanding of pathogenesis, standard diagnosis and challenges in the context of CKTR, this mini-review aims to provide updates and insights into the latest development of promising novel biomarkers for diagnosis and novel therapeutic interventions to prevent and treat CKTR.

Case Report: Splenic Irradiation for the Treatment of Chronic Active Antibody-Mediated Rejection in Kidney Allograft Recipients With De Novo Donor-Specific Antibodies

Chronic active antibody-mediated rejection (AMR) in renal transplantation is usually refractory to current conventional treatment with rituximab, plasmapheresis (PP), and intravenous immunoglobulins (IVIG). Splenic irradiation has been reported to be effective in the rescue of early severe acute AMR after kidney transplantation; however, its effect in chronic active AMR has not been reported to date. In order to reduce donor-specific antibody (DSA) and prevent the progression of chronic AMR, we used repetitive low-dose splenic irradiation, together with rituximab and PP/IVIG, in two living-related kidney transplant recipients with pathologically diagnosed chronic active AMR and the presence of long-term class II-de novo DSA. DSA monitoring and repeated renal biopsy revealed significantly reduced DSA levels as well as alleviated glomerulitis and peritubular capillaritis in both patients after treatment, and these therapies may have played a role in delaying the progression of chronic AMR. Although DSA levels in both patients eventually rebounded to some extent after treatment, serum creatinine increased slowly in one patient during the 16-month follow-up period and remained stable in the other during the 12-month follow-up period. Given the poor efficacy of conventional treatment at present, splenic irradiation may still be one of the treatment options for chronic active AMR.

Exploring the knowledge gap of immune checkpoint inhibitors in chronic renal failure: A systematic review of the literature

Targeting the immune system with immune checkpoint inhibitors (ICI) to treat cancer has been lately adopted with a significant improvement of patients' survival. In parallel, the incidence of malignancy in chronic kidney disease (CKD) patients is increasing, but solid evidence concerning the efficacy and safety of ICI in this population is lacking. Moreover, the use of these agents as immunity boosters in kidney graft recipients treated with immunosuppressors is still controversial. We present in this article a review of the pharmacological properties of these drugs and their behavior with kidney failure and dialysis, as well as evidence of their use in different populations of CKD. Most of the available data are limited to case reports and case series. These drugs appear to be safe without dose adjustment in CKD patients and patients on dialysis. A major concern with this therapy in transplanted patients remains the risk of graft rejection.

Protocol Biopsies in Patients With Subclinical De Novo Donor-specific Antibodies After Kidney Transplantation: A Multicentric Study

BACKGROUND

De novo donor-specific antibodies (DSAs) are associated with antibody-mediated rejection (AMR) and allograft loss. Whether monitoring of de novo DSA (dnDSA) paired with systematic kidney biopsy should become routine remains to be established.

METHODS

A retrospective multicentric study (9 French kidney transplant units of the Spiesser group) included patients without graft dysfunction biopsied because of the presence of dnDSA (One Lambda, mean fluorescence intensity [MFI], >1000).

RESULTS

One hundred twenty-three patients (85 male/38 female; mean age, 49.5 ± 13.1 y old) were biopsied after the detection of a dnDSA, 65.3 months (median) after kidney transplantation. Graft function was stable within 3 months before biopsy (estimated glomerular filtration rate, 55.3 ± 18.9 mL/min/1.73 m). Fifty-one subclinical AMRs (sAMRs) (41.4%) were diagnosed, of which 32 (26%) active and 19 (15.5%) chronic active sAMR. Seventy-two biopsies revealed no AMR (58.5%). Predictive factors associated with the diagnosis of active sAMR were MFI of immunodominant DSA >4000, MFI of the sum of DSA >6300, age of the recipient <45 years old, and the absence of steroids at biopsy. The presence of proteinuria >200 mg/g was predictive of chronic active sAMR. The decrease of estimated glomerular filtration rate at 5 years post-biopsy was significantly higher in patients with acute sAMR (-25.2 ± 28.3 mL/min/1.73 m) and graft survival significantly lower.

CONCLUSIONS

Performing a kidney graft biopsy for the occurrence of dnDSA without renal dysfunction leads to the diagnosis of a sAMR in over 40% of cases. Nevertheless, we did not observe any effect of standard treatment in acute sAMR.

Peripheral Blood RNA Sequencing Unravels a Differential Signature of Coding and Noncoding Genes by Types of Kidney Allograft Rejection

Introduction

Peripheral blood (PB) molecular patterns characterizing the different effector immune pathways driving distinct kidney rejection types remain to be fully elucidated. We hypothesized that transcriptome analysis using RNA sequencing (RNAseq) in samples of kidney transplant patients would enable the identification of unique protein-coding and noncoding genes that may be able to segregate different rejection phenotypes.

Methods

We evaluated 37 biopsy-paired PB samples from the discovery cohort, with stable (STA), antibody-mediated rejection (AMR), and T cell-mediated rejection (TCMR) by RNAseq. Advanced machine learning tools were used to perform 3-way differential gene expression analysis to identify gene signatures associated with rejection. We then performed functional in silico analysis and validation by Fluidigm (San Francisco, CA) in 62 samples from 2 independent kidney transplant cohorts.

Results

We found 102 genes (63 coding genes and 39 noncoding genes) associated with AMR (54 upregulated), TCMR (23 upregulated), and STA (25 upregulated) perfectly clustered with each rejection phenotype and highly correlated with main histologic lesions (ρ = 0.91). For the genes associated with AMR, we found enrichment in regulation of endoplasmic reticulum stress, adaptive immunity, and Ig class-switching. In the validation, we found that the SIGLEC17P pseudogene and 9 SIGLEC17P-related coding genes were highly expressed among AMR but not in TCMR and STA samples.

Conclusions

This analysis identifies a critical gene signature in PB in kidney transplant patients undergoing AMR, sufficient to differentiate them from patients with TCMR and immunologically quiescent kidney allografts. Our findings provide the basis for new studies dissecting the role of noncoding genes in the pathophysiology of kidney allograft rejection and their potential value as noninvasive biomarkers of the rejection process.

Pre-existing Alloreactive T and B Cells and Their Possible Relevance for Pre-transplant Risk Estimation in Kidney Transplant Recipients

In allogeneic transplantation, genetic disparities between patient and donor may lead to cellular and humoral immune responses mediated by both naïve and memory alloreactive cells of the adaptive immune system. This review will focus on alloreactive T and B cells with emphasis on the memory compartment, their role in relation to kidney rejection, and in vitro assays to detect these alloreactive cells. Finally, the potential additional value of utilizing donor-specific memory T and B cell assays supplementary to current routine pre-transplant risk assessment of kidney transplant recipients will be discussed.

Mechanisms of organ transplant injury mediated by B cells and antibodies: Implications for antibody-mediated rejection

Recent adjustments to the histological diagnosis and the introduction of molecular classification are providing renewed support for the paradigm that antibody-mediated rejection (ABMR) is an important clinical problem for which there is an urgent need for better therapies. Acute ABMR is observed when the graft is exposed to rapid increases in high-titer donor-specific antibodies (DSA) that are most often generated as anamnestic responses in sensitized recipients or de novo responses in nonsensitized patients who are nonadherent. Chronic ABMR is associated with slower increases in DSA, which may be high or low titer and transient or persistent. These DSA elicit cycles of injury and repair that manifest as multilamination of the peritubular capillary basement membrane or arteriopathy manifesting as intimal fibrosis. Mitigating the problem of AMBR requires the anamnestic and de novo DSA responses to be prevented and established DSA responses to be reversed. To this end, a better understanding of the immunobiology of DSA production is necessary and also the development of assays capable of detecting early humoral immune responses.Recent advances in understanding the immunobiology of B cells and areas requiring further investigation that might lead to new therapies or better diagnosis are discussed in this review.

HLA-specific memory B-cell detection in kidney transplantation: Insights and future challenges

Humoral alloimmunity mediated by anti‐human leucocyte antigen (HLA) antibodies is a major challenge in kidney transplantation and impairs the longevity of the transplanted organ. The immunological risk of an individual patient is currently mainly assessed by detection of HLA antibodies in the serum, which are produced by long‐lived bone marrow‐residing plasma cells. However, humoral alloimmunity is complex, and alloreactive memory B cells constitute an additional factor in the interplay of immune cells. These recirculating “silent” cells are responsible for the immunological recall response by differentiating into antibody‐producing cells upon antigen re‐encounter. Historically, due to the lack of appropriate and routinely applicable assays to determine the presence and HLA specificity of alloreactive memory B cells, their contribution to the humoral alloimmune response has clinically often been suspected but could not be determined. In this review, we give an overview of recent advances in techniques to detect alloreactive memory B cells and discuss their strengths and limitations. Furthermore, we summarize experiences with these techniques in alloimmunized individuals and transplant recipients, thereby emphasizing unmet needs to be addressed in future studies.

Diagnostic Performance of Donor-Derived Plasma Cell-Free DNA Fraction for Antibody-Mediated Rejection in Post Renal Transplant Recipients: A Prospective Observational Study

Objective

To evaluate the diagnostic performance of donor-derived plasma cell-free DNA (cfDNA) in discriminating antibody-mediated rejection (ABMR) or de novo donor-specific antibodies (DSA) without histological lesions in kidney allograft recipients.

Methods

In this prospective single center observational study, we enrolled kidney allograft recipients between November, 2016 and September, 2017 at the First Affiliated Hospital of Sun Yat-sen University. Kidney allograft recipients with ABMR, de novo DSA but no histological lesions or negative DSA, and stable renal function were included. The plasma cfDNA fraction was measured using a targeted, single nucleotide polymorphism (SNP)-based assay. Pathological diagnosis was made according to the 2015 Banff Kidney Rejection Classification. The area under the ROC curve (AUC-ROC) was determined using the bootstrapping method to estimate median and 95% confidence interval (95% CI). The sensitivity, specificity and Youden index, positive predictive value (PPV), and negative predictive value (NPV) were calculated for specific cfDNA fractions.

Results

Totally 37 consecutive patients received kidney allografts, including 18 recipients in the ABMR group and 19 recipients in the stable allograft group (7 DSA-positive and 12 DSA-negative). All patients in the ABMR group were DSA positive and 7 patients in the stable group were DSA positive but had no pathologically proven ABMR. The median donor-derived plasma cfDNA fraction was 2.4% (Q1 1.52% -Q3 3.70%) in the ABMR group, and was significantly higher than that of the stable group (0.65%, Q1 0.57% -Q3 0.97%; P < 0.001), but comparable with that of the DSA-positive patients in the stable allograft group (P = 0.074). The AUC-ROC of cfDNA was 0.90 (95% CI, 0.79–0.98). When a cfDNA threshold of 1% was chosen, it had a sensitivity of 88.9% and a specificity of 73.7%. The PPV was 76.2% and the NPV was 87.5%.

Conclusion

Donor-derived plasma cfDNA fraction increased in kidney allograft recipients with ABMR. Detection of donor-derived plasma cfDNA fraction may contribute to the discrimination between ABMR and stable renal allograft function and may aid early recognition of earlier stage antibody-mediated injury.

Novel insights into non-HLA alloimmunity in kidney transplantation

Recognition of non‐self structures on donor cells represents the main immunological barrier in solid organ transplantation. The human leukocyte antigens (HLA) are considered the most important non‐self (allo)antigens in transplantation. Long‐term graft attrition is mainly caused by the formation of alloreactive antibodies that are directed against non‐self structures (i.e., epitopes) on cell surface proteins. Recently published data provided evidence for a similar importance of non‐HLA mismatches between donors and recipients in acute rejection as well as long‐term kidney allograft survival. These data suggest a broader concept of immunological non‐self that goes beyond HLA incompatibility and expands the current concept of polymorphic non‐self epitopes on cell surface molecules from HLA to non‐HLA targets. Amino acid substitutions caused by single nucleotide variants in protein‐coding genes or complete loss of gene expression represent the basis for polymorphic residues in both HLA and non‐HLA molecules. To better understand these novel insights in non‐HLA alloimmunity, we will first review basic principles of the alloimmune response with a focus on the HLA epitope concept in donor‐specific antibody formation before discussing key publications on non‐HLA antibodies.

The therapeutic challenge of late antibody-mediated kidney allograft rejection

Late antibody‐mediated rejection (ABMR) is a cardinal cause of kidney allograft failure, manifesting as a continuous and, in contrast with early rejection, often clinically silent alloimmune process. While significant progress has been made towards an improved understanding of its molecular mechanisms and the definition of diagnostic criteria, there is still no approved effective treatment. In recent small randomized controlled trials, therapeutic strategies with promising results in observational studies, such as proteasome inhibitor bortezomib, anti‐C5 antibody eculizumab, or high dose intravenous immunoglobulin plus rituximab, had no significant impact in late and/or chronic ABMR. Such disappointing results reinforce a need of new innovative treatment strategies. Potential candidates may be the interference with interleukin‐6 to modulate B cell alloimmunity, or innovative compounds that specifically target antibody‐producing plasma cells, such as antibodies against CD38. Given the phenotypic heterogeneity of ABMR, the design of adequate systematic trials to assess the safety and efficiency of such therapies, however, is challenging. Several trials are currently being conducted, and new developments will hopefully provide us with effective ways to counteract the deleterious impact of antibody‐mediated graft injury. Meanwhile, the weight of evidence would suggest that, when approaching using existing treatments for established antibody‐mediated rejection, “less may be more”.