Recommended Treatment for Antibody-mediated Rejection After Kidney Transplantation: The 2019 Expert Consensus From the Transplantion Society Working Group

Rethinking the Diagnosis and Management of Antibody-Mediated Rejection in Multidisciplinary Transplant Meetings: A Global Survey and Banff Working Group Recommendations

INTRODUCTION

The diagnosis of antibody-mediated rejection (AMR) requires input from several transplant professionals. Bringing clinical and laboratory experts together may help standardize care. Yet, little is known about current global practices of multidisciplinary meetings for AMR management.

METHODS

The Banff Antibody-Mediated Injury Working Group approached professional societies worldwide to distribute a survey on the availability, content, participants, perceived value, and barriers to the implementation of multidisciplinary meetings.

RESULTS

Four hundred two transplant professionals from six continents caring for kidney (90.55%), liver (21.14%), pancreas (20.65%), heart (15.17%), and lung (14.18%) transplant recipients participated in the survey, and 302 (75.12%) reported attending multidisciplinary meetings. Multidisciplinary meetings were more prevalent in academic centers, in high- versus low-to-middle-income regions (81.03% and 65.99%, respectively; p < 0.001), and in mid-to-large size transplant programs compared to smaller programs. Perceived value included continued professional development (97.68%) and trainee education (95.70%). AMR was reported to be discussed at these meetings by 217 respondents with case presentations reviewing patient characteristics, histology, and HLA antibody data. A third of the respondents reviewed non-HLA/pathogenic autoantibodies and/or molecular diagnostics, with the latter being more frequently applied in high- versus low-to-middle-income regions (46.71% and 12.31%, respectively; p < 0.001). AMR case presentations allowed diagnosis revision, actionable management plans and were perceived as improving care. The primary barrier to the implementation of multidisciplinary meetings (63.27%) was the unavailability of transplant professionals (e.g., transplant immunologists).

CONCLUSION

Facilitating multidisciplinary meetings through the remote participation of pertinent experts and incentivizing participation through remuneration, protected time, or continued medical education may help standardize AMR diagnosis and harmonize its management.

Complement in Antibody-Mediated Rejection of the Kidney Graft: From Pathophysiology to Clinical Practice

Antibody-mediated rejection (AMR) is a leading cause of kidney graft failure. Complement activation is involved in the AMR process. Our aim is to provide the current understanding of the pathophysiology related to complement-mediated injury in AMR, to present the current evidence regarding complement blockade in AMR management, and to point out emerging therapies and future directions in this area. The complement system plays an important role in the onset and progression of AMR. There is a balance between complement-dependent and -independent mechanisms in the development of rejection lesions. Classic and leptin pathways are involved in this process. C4d positivity is no longer a mandatory feature for AMR diagnosis but remains an independent predictor of negative outcomes. The current evidence regarding AMR treatment is limited. Terminal and proximal complement blockade has gained recognition in clinical practice. Eculizumab and C1 inhibitors are effective in the treatment of AMR as adjuvant therapies to the standard of care. The availability of novel complement inhibitors will lead to more effective and tailored treatment strategies.

Chronic Allograft Nephropathy-A Narrative Review of Its Pathogenesis, Diagnosis, and Evolving Management Strategies

Chronic allograft nephropathy is the leading cause of kidney allograft failure. Clinically, it is characterized by a progressive decline in kidney function, often in combination with proteinuria and hypertension. Histologically, interstitial fibrosis and tubular atrophy, along with features of glomerulosclerosis with occasional double contour appearance, arteriolar hyalinosis, and arteriosclerosis, are characteristic findings. The pathophysiology, though complex and incompletely understood, is thought to involve a sequence of immunologic and non-immunologic injuries eventually leading to tissue remodeling and scarring within the graft. The optimal strategy to prevent chronic allograft nephropathy is to minimize both immune- and non-immune-mediated graft injury.

Spanish guidelines for kidney transplantation in highly sensitized patients with donor-specific anti-HLA antibodies

Highly sensitized patients awaiting kidney transplantation face substantial challenges due to the presence of potential donor-specific anti-HLA antibodies (DSA). These antibodies increase the risk of antibody-mediated rejection (ABMR), but also complicate their access to HLA compatible transplantation. Although advancements in allocation priority programs, such as the Spanish Program for the Access of Highly Sensitized Patients to Kidney Transplantation (PATHI), have introduced virtual crossmatching (v-XM) to streamline compatibility assessments, patients with >99,5 % virtual panel reactive antibodies (vPRA) often remain on waiting lists for extended periods with minimal chances of receiving a transplant. This article summarizes Spanish guidelines for a harmonized and comprehensive framework for the management of highly sensitized patients. These guidelines focus on strategies to facilitate transplantation in the presence of DSA, including a stepwise approach to delist HLA antigens, prioritizing those recognized as "less deleterious" antibodies, to expand transplant options while minimizing immunological risks. Conventional desensitization techniques are discussed, alongside the innovative use of imlifidase to enable transplants in particularly complex cases. Post-transplant monitoring protocols are also exposed, with a focus on early detection of antibody rebound and effective management of ABMR. Ultimately, this resource offers clinicians a structured framework to navigate the intricate challenges of kidney transplantation in high-risk populations, aiming to enhance access to life-saving procedures and improve patient outcomes.

Exploring Net Immunosuppressive Status with Torque Teno Virus Viral Load in Kidney Transplant Recipients with High Molecular Injury

Background/Objectives: New monitoring methods are being developed to improve the kidney transplant outcome. Among them, the measurement of Torque Teno virus load (TTV load) has been associated with the overall immunosuppressive status and the percentage of donor-derived circulating free DNA (dd-cfDNA) with molecular graft injury, mainly related to antibody-mediated rejection (AbMR). Both methods provide complementary information, but they have not been previously used together for the monitoring of kidney transplant recipients (KTx). Methods: A prospective study including 42 KTx performed in our centre was conducted, in which we monitored dd-cfDNA using a targeted NGS assay (AlloSeq cfDNA) in the first month and the TTV load with in-house PCR in the first and third months. Results: Eleven KTx with high molecular injury defined by dd-cfDNA ≥ 1.0% were selected. The TTV load showed a non-significant trend of being lower in AbMR patients (2.91, IQR 4.18 vs. 3.48, IQR 1.47 log10 copies/mL, p = 0.788). No overimmunosuppressed patient developed AbMR, whereas 40% of non-overimmunosuppressed patients showed AbMR (p = 0.428). The TTV load increased more in the AbMR-treated KTx (0.00, IQR 4.71 vs. +6.58, IQR 4.04 log10 copies/mL, p = 0.042) from months one to three, with all AbMR-treated KTx becoming overimmunosuppressed. KTx with opportunistic infections showed higher TTV loads in the third month (5.18, IQR 5.92 vs. 11.53, IQR 3.54 log10 copies/mL, p = 0.024). Conclusions: KTx with molecular injury secondary to rejection tended to be less immunosuppressed, as indicated by a low TTV load. After AbMR therapy, all KTx became overimmunosuppressed and suffered a higher risk of opportunistic infections. Dual monitoring provides useful complementary information for the follow-up of kidney transplant recipients.

Chronic Rejection After Kidney Transplantation

In kidney transplantation, ongoing alloimmune processes-commonly triggered by HLA incompatibilities-can trigger chronic transplant rejection, affecting the microcirculation and the tubulointerstitium. Continuous inflammation may lead to progressive, irreversible graft injury, culminating in graft dysfunction and accelerated transplant failure. Numerous experimental and translational studies have delineated a complex interplay of different immune mechanisms driving rejection, with antibody-mediated rejection (AMR) being an extensively studied rejection variant. In microvascular inflammation, a hallmark lesion of AMR, natural killer (NK) cells have emerged as pivotal effector cells. Their essential role is supported by immunohistologic evidence, bulk and spatial transcriptomics, and functional genetics. Despite significant research efforts, a substantial unmet need for approved rejection therapies persists, with many trials yielding negative outcomes. However, several promising therapies are currently under investigation, including felzartamab, a monoclonal antibody targeting the surface molecule CD38, which is highly expressed in NK cells and antibody-producing plasma cells. In an exploratory phase 2 trial in late AMR, this compound has demonstrated potential in resolving molecular and morphologic rejection activity and injury, predominantly by targeting NK cell effector function. These findings inspire hope for effective treatments and emphasize the necessity of further pivotal trials focusing on chronic transplant rejection.

The Effect of Clinical Decision Support Intervention on Monitoring for Donor Specific Antibodies

BACKGROUND

Following transplantation, it is recommended that human leukocyte antigen (HLA) donor specific antibody (DSA) monitoring for allograft surveillance be tailored to the patient's antibody-mediated rejection (AMR) risk and immunosuppression needs. However, at our institution, DSA orders were placed more frequently than recommended, with daily duplications due to inconsistent ordering across departments (outpatient, emergency, and inpatient). We evaluated the effectiveness of a non-interruptive clinical decision support (CDS) system integrated with computerized provider order entry (CPOE) in reducing redundant DSA orders.

METHODS

CDS included an indication prompt and test status indicator to help providers review test rationale and flag active orders. We then evaluated its impact of this intervention in 5-month periods before and after implementation, using statistical analyses to assess the differences with a t-test.

RESULTS

In the pre-implementation period, 82.5% (1504/1824) of DSA orders from 473 of 792 patients were duplicates, compared to 79.6% (1415/1778) from 463 of 826 patients post-implementation. After excluding cases without reported DSA and overlapping patients, each group had 466 unique patients. Duplicate orders decreased within 50 days post-implementation but increased beyond this period. Among renal transplant recipients, the fraction of duplicate orders within a week significantly dropped (pre-implementation n = 9, post-implementation n = 26, P = 0.009). DSA levels remained stable, suggesting the intervention did not impact detection rates.

CONCLUSION

The CDS implemented reduced unwarranted duplicate orders within 2 weeks of a prior order without affecting long-term (>50 days) monitoring protocols, demonstrating the effectiveness of non-interruptive CDS-CPOE in improving HLA test ordering.

Predicting the success of antibody removal with therapeutic plasma exchange: The role of serum dilutions

Therapeutic plasma exchange (TPE) remains a primary therapy for addressing circulating donor-specific antibodies against mismatched human leukocyte antigens, which pose a significant challenge to successful transplantation of solid organs and hematopoietic cells. In this study, we aimed to evaluate the response to 5 TPE sessions in patients undergoing desensitization, as well as in patients who developed antibody-mediated rejection posttransplant. Sera collected before and after each TPE session was treated with EDTA and tested using the single-antigen bead assay as undiluted or 1:4, 1:16, 1:64, and 1:256 diluted. The reduction in human leukocyte antigen antibodies correlated with previously established total immunoglobulin G reduction levels. However, we observed that class I antibody levels were reduced by 85% to 90% while class II antibodies were reduced by only 75% to 80% after 5 TPE sessions. We also found that dilutions performed on pretreatment serum were predictive of the response to TPE. This approach was used to design TPE-based desensitization protocols for highly sensitized patients across various organ and tissue types, as well as for treating patients with antibody-mediated rejection. Our data suggest that serum dilution may be an effective method for assessing the likelihood of response to TPE, thereby aiding in the guidance of treatment strategies.

Chronic Antibody-Mediated Rejection and Plasma Cell ER Stress: Opportunities and Challenges with Calcineurin Inhibitors

Chronic alloantibody-mediated rejection (cAMR) remains a major challenge in transplant immunology, with no FDA-approved targeted therapies currently available. Despite advancements in cellular immunosuppression, effective strategies to mitigate alloantibody-mediated rejection are still lacking. This review provides a comprehensive overview of transplant rejection with a particular focus on the pathophysiology and therapeutic landscape of cAMR. We highlight the role of plasma cell-driven alloantibody production and its susceptibility to endoplasmic reticulum (ER) stress, a pathway with potential for therapeutic intervention. Special attention is given to calcineurin inhibitors (CNIs), which, beyond their well-established T-cell inhibitory effects, exhibit differential impacts on ER stress and plasma cell viability. By delineating the mechanistic differences between cyclosporine and tacrolimus in regulating ER stress responses, we propose potential therapeutic implications for optimizing cAMR management. This review underscores the need for innovative strategies targeting plasma cell biology to improve long-term transplant outcomes.

Management of concurrent severe COVID-19 pneumonia and antibody-mediated rejection following kidney transplantation: a case report

Background

Due to its high mutation rate, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has recurrently emerged worldwide in recent years, leading to an increased incidence of rejection following kidney transplantation and a worsened prognosis for recipients. The management of the concomitant occurrence of SARS-CoV-2 infection and rejection in kidney transplant recipients poses significant challenges, with limited available experience on this topic. This study presents a case report highlighting the simultaneous manifestation of severe corona virus disease 2019 (COVID-19) pneumonia and acute antibody-mediated rejection (ABMR) during the early post-transplantation period.

Methods

The recipient underwent the renal transplantation from a deceased donor after brain death and received comprehensive management including antiviral therapy, adjustment of immunosuppressive medications, and relevant supportive care during the course of SARS-CoV-2 infection. In the overlapping period of severe COVID-19 pneumonia and ABMR, we implemented plasma exchange (PE) combined with intravenous immunoglobulin (IVIG) and rituximab treatment, while closely monitoring infection-related indicators and elucidate the impact of PE on SARS-CoV-2 antibodies.

Results

The administration of PE did not significantly impact the level of SARS-CoV-2 IgG antibody. Meanwhile, the combination of PE, IVIG, and rituximab treatment effectively reversed ABMR without exacerbating SARS-CoV-2 infection.

Conclusion

The timely administration of antiviral and anti-rejection therapies in the early stage of renal transplant recipient can lead to favorable outcome in case of SARS-CoV-2 infection and concurrent ABMR.

Omics data integration analysis identified new biological insights into chronic antibody-mediated rejection (CAMR)

BACKGROUND

In the last two decades, many studies based on omics technologies have contributed to defining the clinical, immunological, and histological fingerprints of chronic antibody-mediated rejection (CAMR), the leading cause of long-term kidney allograft failure. However, the full biological machinery underlying CAMR has only been partially defined, likely due to the fact thatsingle-omics technologies capture only specific aspects of the biological system and fail to provide a comprehensive understanding of this clinical complication.

METHODS

This study integrated mass spectrometry-based proteomic profiling of serum samples from 19 patients with clinical and histological evidence of CAMR and 26 kidney transplant recipients with normal graft function and histology (CTR) with transcriptomic analysis of peripheral blood mononuclear cells (PBMCs) from an independent cohort of 10 CAMR and 8 CTR patients. Data analysis was conducted using unsupervised hierarchical clustering (multidimensional scaling with k-means) and Spearman's correlation test. Partial least squares discriminant analysis (PLS-DA) with the importance in projection (VIP) score identified key proteins differentiating CAMR from CTR. ELISA was used to validate the omics results.

RESULTS

Proteomic analysis identified 18 proteins that significantly differentiated CAMR from CTR (p < 0.01): five were more abundant (CHI3L1, LYZ, PRSS2, CPQ, IGLV3-32), while 13 were less abundant (SERPINA5, SERPING1, KNG1, CAMP, VNN1, BTD, WDR1, PON3, AHNAK2, MELTF, CA1, CD44, CUL1). Transcriptomic profiling revealed 6 downregulated and 33 upregulated genes in CAMR versus CTR (p < 0.01). Notably, only 2 biological elements were significantly deregulated in both omics analyses: chitinase-3-like protein 1 (CHI3L1) and plasma protease inhibitor C1 (SERPING1). CHI3L1, previously associated with the severity of tissue damage in kidney diseases, was up-regulated in CAMR in both transcriptomics and proteomics, while SERPING1, a serine esterase inhibitor that blocks the classical and lectin pathway of complement, was up-regulated in CAMR in transcriptomics but down-regulated in proteomics. ELISA validated the omics results, and the ROC curve showed that CHI3L1 has good discrimination power between CAMR and CTR (AUC of ROC curve of 0.81).

CONCLUSIONS

Our multi-omics data, although performed in a relatively small cohort of patients, revealed new systemic biological elements involved in the pathogenesis of CAMR and identified CHI3L1 as a new potential biomarker and/or therapeutic target for this important clinical complication. Future validation of these findings in larger patient cohorts should be conducted to better evaluate their clinical utility.

Advancing risk stratification in kidney transplantation: integrating HLA-derived T-cell epitope and B-cell epitope matching algorithms for enhanced predictive accuracy of HLA compatibility

Introduction

The immune-mediated rejection of transplanted organs is a complex interplay between T cells and B cells, where the recognition of HLA-derived epitopes plays a crucial role. Several algorithms of molecular compatibility have been suggested, each focusing on a specific aspect of epitope immunogenicity.

Methods

Considering reported death-censored graft survival in the SRTR dataset, we evaluated four models of molecular compatibility: antibody-verified Eplets, Snow, PIRCHE-II and amino acid matching. We have statistically evaluated their co-dependency and synergistic effects between models systematically on 400,935 kidney transplantations using Cox proportional hazards and XGBoost models.

Results

Multivariable models of histocompatibility generally outperformed univariable predictors, with a combined model of HLA-A, -B, -DR matching, Snow and PIRCHE-II yielding highest AUC in XGBoost and lowest BIC in Cox models. Augmentation of a clinical prediction model of pre-transplant parameters by molecular compatibility metrics improved model performance particularly considering long-term outcomes.

Discussion

Our study demonstrates that the use of multiple specialized molecular HLA matching predictors improves prediction performance, thereby improving risk classification and supporting informed decision-making in kidney transplantation.

Advancements in noninvasive techniques for transplant rejection: from biomarker detection to molecular imaging

Transplant rejection remains a significant barrier to the long-term success of organ transplantation. Biopsy, although considered the gold standard, is invasive, costly, and unsuitable for routine monitoring. Traditional biomarkers, such as creatinine and troponin, offer limited predictive value owing to their low specificity, and conventional imaging techniques often fail to detect early organ damage, increasing the risk of undiagnosed rejection episodes. Considering these limitations, emerging noninvasive biomarkers and molecular imaging techniques hold promise for the early and accurate detection of transplant rejection, enabling personalized management strategies. This review highlights noninvasive biomarkers that predict, diagnose, and assess transplant prognosis by reflecting graft injury, inflammation, and immune responses. For example, donor-derived cell-free DNA (dd-cfDNA) is highly sensitive in detecting early graft injury, whereas gene expression profiling effectively excludes moderate-to-severe acute rejection (AR). Additionally, microRNA (miRNA) profiling enhances the diagnostic specificity for precise AR detection. Advanced molecular imaging techniques further augment the monitoring of rejection. Fluorescence imaging provides a high spatiotemporal resolution for AR grading, ultrasound offers real-time and portable monitoring, and magnetic resonance delivers high tissue contrast for anatomical assessments. Nuclear imaging modalities such as single photon emission computed tomography and positron emission tomography, enable dynamic visualization of immune responses within transplanted organs. Notably, dd-cfDNA and nuclear medicine imaging have already been integrated into clinical practice, thereby demonstrating the translational potential of these techniques. Unlike previous reviews, this work uniquely synthesizes advancements in both noninvasive biomarkers and molecular imaging, emphasizing their complementary strengths. Biomarkers deliver molecular-level insights, whereas imaging provides spatial and temporal resolution. Together, they create a synergistic framework for comprehensive and precise transplant monitoring. By bridging these domains, this review underscores their individual contributions and collective potential to enhance diagnostic accuracy, improve patient outcomes, and guide future research and clinical applications in transplant medicine.

FCGR2C Q13 and FCGR3A V176 alleles jointly associate with worse natural killer cell-mediated antibody-dependent cellular cytotoxicity and microvascular inflammation in kidney allograft antibody-mediated rejection

Natural killer (NK) cell-mediated antibody-dependent cellular cytotoxicity (ADCC) is a major mechanism of humoral allograft injury. FCGR3A V176/F176 polymorphism influences ADCC activity. Additionally, NK cell FcγRIIc expression, dictated by the Q13/STP13 polymorphism, was never investigated in kidney transplantation. To assess the clinical relevance of FCGR2C Q13/STP13 polymorphism in conjunction with FCGR3A V176/F176 polymorphism, 242 kidney transplant recipients were genotyped. NK cell Fc gamma receptor (FcγR) expression and ADCC activity were assessed. RNA sequencing was performed on kidney allograft biopsies to explore the presence of infiltrating FcγR+ NK cells. The FCGR2C Q13 allele was enriched in antibody-mediated rejection patients. FcγRIIc Q13+ NK cells had higher ADCC activity than FcγRIIc Q13- NK cells. In combination with the high-affinity FCGR3A V176 allele, Q13+V176+ NK cells were the most functionally potent. Q13+ was associated with worse microvascular inflammation and a higher risk of allograft loss. Among V176- patients, previously described in the literature as lower-risk patients, Q13+V176- showed a lower graft survival than Q13-V176- patients. In antibody-mediated rejection biopsies, FCGR2C transcripts were enriched and associated with ADCC-related transcripts. Our results suggest that FCGR2C Q13 in addition to FCGR3A V176 is a significant risk allele that may enhance NK cell-mediated ADCC and contribute to allograft injury and poor survival.

Unlocking Transplant Tolerance with Biomaterials

For patients suffering from organ failure due to injury or autoimmune disease, allogeneic organ transplantation with chronic immunosuppression is considered the god standard in terms of clinical treatment. However, the true "holy grail" of transplant immunology is operational tolerance, in which the recipient exhibits a sustained lack of alloreactivity toward unencountered antigen presented by the donor graft. This outcome is resultant from critical changes to the phenotype and genotype of the immune repertoire predicated by the activation of specific signaling pathways responsive to soluble and mechanosensitive cues. Biomaterials have emerged as a medium for interfacing with and reprogramming these endogenous pathways toward tolerance in precise, minimally invasive, and spatiotemporally defined manners. By viewing seminal and contemporary breakthroughs in transplant tolerance induction through the lens of biomaterials-mediated immunomodulation strategies-which include intrinsic material immunogenicity, the depot effect, graft coatings, induction and delivery of tolerogenic immune cells, biomimicry of tolerogenic immune cells, and in situ reprogramming-this review emphasizes the stunning diversity of approaches in the field and spotlights exciting future directions for research to come.

Incidence, risk factors, management strategies, and outcomes of antibody-mediated rejection in pediatric kidney transplant recipients-a multicenter analysis of the Cooperative European Paediatric Renal Transplant Initiative (CERTAIN)

BACKGROUND

This study by the Cooperative European Paediatric Renal Transplant Initiative (CERTAIN) was designed to determine the incidence, risk factors, current management strategies, and outcomes of antibody-mediated rejection (ABMR) in pediatric kidney transplant recipients (pKTR).

METHODS

We performed an international, multicenter, longitudinal cohort study of data reported to the Cooperative European Paediatric Renal Transplant Initiative (CERTAIN) registry. Three hundred thirty-seven pKTR from 21 European centers were analyzed. Clinical outcomes, including kidney dysfunction, rejection, HLA donor-specific antibodies, BK polyomavirus-associated (BKPyV) nephropathy, and allograft loss, were assessed through 5 years post-transplant.

RESULTS

The cumulative incidence of de novo donor-specific class I HLA antibodies (HLA-DSA) post-transplant was 4.5% in year 1, 8.3% in year 3, and 13% in year 5; the corresponding data for de novo class II HLA-DSA were 10%, 22.5%, and 30.6%, respectively. For 5 years post-transplant, the cumulative incidence of acute ABMR was 10% and that of chronic active ABMR was 5.9%. HLA-DR mismatch and de novo HLA-DSA, especially double positivity for class I and class II HLA-DSA, were significant risk factors for ABMR, whereas cytomegalovirus (CMV) IgG negative recipient and CMV IgG negative donor were associated with a lower risk. BKPyV nephropathy was associated with the highest risk of graft dysfunction, followed by ABMR, T-cell mediated rejection, and older donor age.

CONCLUSIONS

This study provides an estimate of the incidence of de novo HLA-DSA and ABMR in pKTR and highlights the importance of BKPyV nephropathy as a strong risk factor for allograft dysfunction.

Germinal Center B Cells are Uniquely Targeted by Antibody-Suppressor CXCR5+CD8+ T Cells

Background

Alloprimed antibody-suppressor CXCR5+CD8+ T cells (CD8+ TAb-supp cells) downregulate alloantibody production, mediate cytotoxicity of IgG+ B cells, and prolong allograft survival. The purpose of this investigation was to determine which immune-cell subsets are susceptible to CD8+ TAb-supp cell-mediated cytotoxicity or noncytotoxic suppression.

Methods

Alloprimed immune-cell subsets were evaluated for susceptibility to CD8+ TAb-supp cell-mediated in vitro cytotoxicity and/or suppression of intracellular cytokine expression. In vivo CD8-mediated cytotoxicity to wild-type germinal center (GC) B cells or wild-type CD4+ T follicular helper cells (TFH cells) was assessed in RAG1 knockout mice. The impact of in vivo adoptive transfer of CD8+ TAb-supp cells into hepatocyte or kidney transplant recipients on the quantity of lymphoid immune-cell subsets was assessed.

Results

CD8+ TAb-supp cells mediated allospecific cytotoxicity to alloprimed GC B cells but not alloprimed extrafollicular plasmablasts, marginal zone B cells, follicular B cells, or plasma cells. CD8+ TAb-supp cells did not mediate cytotoxicity to alloprimed dendritic cells, macrophages, CD4+ TFH cells, CD4+ T follicular regulatory cells, or CD4+ regulatory T cell. CD8+ TAb-supp cells did not suppress CD4+ TFH cell, T follicular regulatory cell, or regulatory T-cell cytokine expression. Adoptive transfer of CD8+ TAb-supp cells into hepatocyte or kidney transplant recipients reduced alloantibody production and the quantity of GC B cells, TFH cells, and plasma cells (but not other B-cell, T-cell, or antigen-presenting cell subsets). The reduction of TFH-cell quantity was dependent on CD8+ TAb-supp cell-mediated major histocompatibility complex-I-dependent cytotoxic killing of GC B cells.

Conclusions

The primary targets of CD8+ TAb-supp cells are GC B cells with downstream reduction of TFH and plasma cells.

Acute kidney injury in paediatric kidney transplant recipients

Acute kidney injury (AKI) in paediatric kidney transplant recipients is common. Infection including urinary tract infection (UTI) and rejection are the most common causes in children. Surgical complications often cause AKI early post-transplant, whereas BK polyomavirus nephropathy rarely occurs in the first month post-transplant. Understanding kidney physiology helps to appreciate the sensitivity of the allograft to AKI, more so than native kidneys. Although the cause of AKI is often multi-factorial, there may be an underlying process that is treatable. Eliciting the aetiology, in this regard, is of paramount importance. Pre-renal and post-renal causes of allograft dysfunction are important to distinguish from intrinsic kidney disease. Clinical information and examination of fluid balance, urine dipstick testing, blood tests, bladder and kidney transplant ultrasound, and kidney transplant biopsy remain vital assessment tools in narrowing the differential diagnosis. A careful prescribed and recreational drug history is always warranted as many drugs including supplements are nephrotoxic. Additional causes such as allograft rejection, recurrent disease, and calcineurin inhibitor toxicity need to be considered in cases of allograft dysfunction, which would not affect the native kidneys. Early detection and assessment of AKI is crucial in promoting recovery. Significant progress has been made in specific pathologies over the last 20 years, which has improved kidney allograft survival rates considerably. Research into identifying AKI biomarkers to assist early diagnosis, before the serum creatinine rises, is ongoing.

Follow-up biopsies with microvascular inflammation and persistent donor specific antibodies identify ongoing rejection in pediatric kidney transplant recipients

BACKGROUND

Inadequate treatment of acute rejection (AR) in pediatric kidney transplant recipients (KTR) can contribute to early allograft failure. Serum creatinine is an insensitive marker of allograft function, especially in the pediatric population, and may not detect ongoing rejection after treatment. We evaluated the utility of follow-up biopsies to detect persistent inflammation and future episodes of rejection.

METHODS

We performed a single-center retrospective review to identify pediatric KTR with biopsy-proven rejection and a subsequent follow-up biopsy, noting type of AR, Banff scores, serum creatinine, and presence of donor specific antibodies (DSA). Outcomes included resolution of AR, change in eGFR, DSA, persistent microvascular inflammation (MVI) and future episodes of AR.

RESULTS

Twelve cases of cellular (TCMR), 9 antibody-mediated (AMR), and 8 mixed cases of AR were identified among 23 KTR. Resolution was noted in 75% with TCMR, significantly higher than AMR (22%) or mixed rejection (13%), p < 0.01. Those without resolution of AR on follow-up biopsy were more likely to have ongoing episodes of AR or graft loss (p = 0.02). Persistence of DSA and MVI was associated with lack of AR resolution (p = 0.01 and p = 0.001, respectively). Those with persistent MVI on follow-up biopsy had higher probability of future AR events or graft loss, p = 0.003.

CONCLUSION

Follow-up biopsies to assess response to AR treatment revealed that most cases of TCMR were successfully treated but that AMR and mixed rejection portend a component of chronicity and more complicated course. Identification of persistent subclinical inflammation predicts future rejection episodes, has adverse effects on graft longevity, and can inform the need for additional treatment. We advocate for implementation of a follow-up biopsy protocol and future study of non-invasive biomarkers paired with protocol biopsies.

Daratumumab followed by tocilizumab for treatment of late antibody-mediated rejection in renal transplant recipients with high or moderate levels of de novo donor-specific antibodies: a pilot study

BACKGROUND

Effective treatment of late antibody-mediated rejection (late AMR) is still an unmet medical need. Clearing donor-specific antibody (DSA) and preventing its rebound is the ideal goal of treatment.

METHODS

We have summarized the clinical data from seven patients with late or chronic active AMR after renal transplantation who received daratumumab (Dara)-based treatment first (Phase 1) and then tocilizumab (TCZ) therapy (Phase 2). Phase 1 consisted of an intensive treatment period (Dara plus PP/IVIG) and a maintenance treatment period (Dara alone). The main clinical indicators were DSA, Banff scores and renal function.

RESULTS

After 4 to 17 weeks of intensive treatment, the MFI values of DSA in five of the seven patients fell below 5,000. During Dara maintenance treatment, only one patient's DSA became negative, and the remaining six patients' DSAs remained relatively stable or showed rebound. However, after TCZ treatment was begun, the DSA eventually became negative in three patients and decreased to low levels (< 3,500) in the other three patients. Also, our treatment stabilized renal function in all patients. At 24-28 months after treatment, renal biopsy showed partial remission of microvascular inflammation in four of six patients. In addition, capillary C4d deposition became negative in all patients (P = 0.001), and the mean score of i-IFTA was significantly reduced (P = 0.012). Other chronic injury scores did not change significantly.

CONCLUSIONS

This new therapy combining Dara and TCZ achieved a good desensitization effect, providing an important reference point for designing better-optimized treatment of late or chronic active AMR in the future.

TRIAL REGISTRATION

This retrospectively study was approved by the Ethics Committee of Tongji Hospital, Wuhan, China (TJ-IRB20230729).

The Promising Effect of Tocilizumab on Chronic Antibody-Mediated Rejection (cAMR) of Kidney Transplant

Background: Chronic antibody-mediated rejection (cAMR) constitutes a serious challenge in the long-term success of organ transplantation. It is associated with donor-specific antibodies (DSAs) which activate a complement pathway in response to the presence of human leukocyte antigens (HLAs) on the graft, which results in chronic inflammation and leads to graft dysfunction. One of the recent promising methods of cAMR treatment is a recombinant humanized anti-interleukin-6 receptor (IL-6R) monoclonal antibody referred to as Tocilizumab (TCZ). The aim of the presented systematic review is to explore the existing knowledge regarding the effect of tocilizumab treatment on cAMR and to perform a meta-analysis of the available data. Methods: A systematic review was performed using the PRISMA 2020 Checklist and Flow diagram. A systematic review protocol was registered in PROSPERO: CRD42024510996. The bias assessment was obtained with Methodical Index for Non-Randomized Studies (MINORS), whereas meta-analysis was performed using MedCalc. Results: Five clinical trials with a total number of 105 patients were included in our review. The mean loss of eGFR in time was -0.141 mL/min/1.73 m2 (95% CI: -0.409 to 0.126; p = 0.298) and was found to be statistically insignificant. The heterogeneity was low and was equal to I2 = 0.00%. The authors demonstrated a reduction in DSA titer by TCZ (-0.266 MFI (95% CI: -0.861 to 0.329; p = 0.377)). In the majority of studies, eGFR stabilization was associated with a reduction in DSAs. Conclusions: TCZ pharmacotherapy insignificantly reduced DSA titer and eGFR. Despite promising outcomes of potential eGFR stabilization, there is a need for large randomized controlled trials comparing standard management of cAMR and tocilizumab treatment.

Desensitization With Imlifidase for HLA-Incompatible Deceased Donor Kidney Transplantation: A Delphi International Expert Consensus

Highly sensitized (HS) patients in need of kidney transplantation (KTx) typically spend a longer time waiting for compatible kidneys, are unlikely to receive an organ offer, and are at increased risk of antibody-mediated rejection (AMR). Desensitization using imlifidase, which is more rapid and removes total body immunoglobulin G (IgG) to a greater extent than other methods, enables transplantation to occur between HLA-incompatible (HLAi) donor-recipient pairs and allows patients to have greater access to KTx. However, when the project was launched there was limited data and clinical experience with desensitization in general and with imlifidase specifically. Hence, this Delphi methodology was used to reach a consensus from a multi-disciplinary team (MDT) of experts from 15 countries on the management of HS patients undergoing imlifidase HLAi from a deceased donor (DD) KTx. This Delphi consensus provides clinical practice guidance on the use of imlifidase in the end-to-end management of HS patients undergoing an HLAi DD KTx and supports centers in the development of guidelines for the utilization and integration of imlifidase into clinical practice.

Early and late antibody mediated rejection: Which game is the complement playing?

The role of the complement system in antibody mediated rejection (AMR) emerged in the last decades, and the demonstration of the presence of complement fragments in renal allograft biopsies is a consolidated diagnostic sign of AMR. However, antibodies against donor antigens may lead to microvascular inflammation and endothelial injury even in the absence of complement activation, and growing evidence suggests that complement-independent mechanisms may be prominent in late (i.e., occurring >6 months after transplantation) vs early AMR. Different donor specific antibodies (DSA) with different biological features and complement activation ability may be involved in late or early AMR. Downregulation of tissue complement inhibitors may happen early after transplantation, partially due to ischemia reperfusion injury, and could facilitate complement activation in early vs late AMR. Clinical and histological features of late AMR and C4d negative AMR seem to converge, and this narrative review analyzes the evidence that supports lower complement activation in late vs early AMR, including differential C4d staining prevalence based on the time after transplantation, differential response to anti-complement therapy and other direct and indirect signs of the complement system activation. The therapeutic approach in early vs late AMR should take into account possible differences in the pathophysiological mechanisms of microvascular inflammation and endothelial injury in early vs late AMR.

Probable antibody-mediated rejection in kidney transplantation is a rare and challenging phenotype to define: Findings from a single-center study

The Banff 2022 consensus introduced probable antibody-mediated rejection (AMR), characterized by mild AMR histologic features and human leukocyte antigen (HLA) donor-specific antibody (DSA) positivity. In a single-center observational cohort study of 1891 kidney transplant recipients transplanted between 2004 and 2021, 566 kidney biopsies were performed in 178 individual HLA-DSA-positive transplants. Evaluated at time of the first HLA-DSA-positive biopsy of each transplant (N = 178), 84 of the 178 (47.2%) of first biopsies were scored as no AMR, 22 of the 178 (12.4%) as probable AMR, and 72 of the 178 (40.4%) as AMR. The majority (77.3%) of probable AMR cases were first diagnosed in indication biopsies. Probable AMR was associated with lower estimated glomerular filtration rate (mL/min/1.73m2) than no AMR (20.2 [8.3-32.3] vs 40.1 [25.4-53.3]; P = .001). The one-year risk of (repeat) AMR was similar for probable AMR and AMR (subdistribution hazard ratio (sHR), 0.99; 0.42-2.31; P = .97) and higher than after no AMR (sHR, 3.05; 1.07-8.73; P = .04). Probable AMR had a higher five-year risk of transplant glomerulopathy vs no AMR (sHR, 4.29; 0.92-19.98; P = 06), similar to AMR (sHR, 1.74; 0.43-7.04; P = .44). No significant differences in five-year risk of graft failure emerged between probable AMR and AMR (sHR, 1.14; 0.36-3.58; P = .82) or no AMR (sHR, 2.46; 0.78-7.74; P = .12). Probable AMR is a rare phenotype, however, sharing significant similarities with AMR in this single-center study. Future studies are needed to validate reproducible diagnostic criteria and associated clinical outcomes to allow for defining best management of this potentially relevant phenotype.

Oxidized ATP Suppresses B Lymphocyte Activity to Attenuate Antibody-mediated Rejection of Kidney Allografts in Mice

BACKGROUND

Antibody-mediated rejection (AMR) is a major cause of renal allograft dysfunction and loss. Targeting B cells and/or donor-specific antibody removal using plasma exchange and anti-CD20 antibodies are increasingly used in clinical practice, but the efficacy remains limited. Recent studies suggest that targeting purinergic P2X7 receptor/ATP axis can have profound immune regulatory effects in transplant models, but the mechanisms involved remain incompletely defined.

METHODS

Purified B cells were isolated from the spleen of Balb/C mice and cultured with oxidized ATP at different concentrations. Proliferation and differentiation of B cells were examined. Effects of oxidized ATP were examined in a presensitized animal model where kidney allograft rejection mimics aspects of clinical AMR. Histopathology was assessed at the time of rejection or on day 5 after kidney transplantation. Infiltrating immune cells in renal allografts were detected by flow cytometry.

RESULTS

Oxidized ATP inhibited B-cell activation and proliferation in vitro, significantly attenuated histological signs of graft injury and prolonged kidney allograft survival. Mechanistically, oxidized ATP inhibited antibody secretion by activated B cells in response to lipopolysaccharide stimulation and markedly suppressed the production of donor-specific antibody in kidney allograft recipients. Oxidized ATP also reduced graft infiltration by other inflammatory cells.

CONCLUSIONS

These findings provide evidence for the involvement of the purinergic P2X7 receptor pathway in AMR and suggest that targeting this pathways may have important clinical implications.

CD38 monoclonal antibody felzartamab for late antibody-mediated rejection: a phase II drug evaluation

INTRODUCTION

Felzartamab is a novel, fully human CD38 monoclonal antibody, currently in development for the treatment of antibody-mediated rejection (AMR) following kidney transplantation.

AREAS COVERED

This review focuses on current phase II trials of felzartamab in AMR and other immune-mediated kidney diseases. Specifically, it discusses the drug's mechanism of action, current phase of clinical development, potential future applications and regulatory status.

EXPERT OPINION

CD38 is an activation marker expressed on the surface of plasma cells and immune cells, including natural killer cells (NK cells) cells. In a recent phase II randomized, placebo-controlled clinical trial, felzartamab demonstrated an acceptable safety and side-effect profile in patients with AMR after kidney transplantation. Efficacy outcomes suggested potential therapeutic benefits, including significant reductions in morphologic and molecular AMR activity. Given the mixed results of previous clinical trials for AMR treatments, the novel approach of targeting both antibody-secreting plasma cells and innate effector cells such as CD38+ NK cells may offer a promising new therapeutic strategy. Felzartamab is also being investigated for the treatment of other antibody-mediated kidney diseases, such as lupus nephritis, primary membranous nephropathy and IgA nephropathy. If proven effective, it could expand the therapeutic options for kidney transplant rejection and primary kidney diseases.

Targeting complement in kidney transplantation: Therapeutic approaches based on preclinical and experimental evidence

The complement system is implicated in various facets of kidney transplantation, including ischemia-reperfusion injury (IRI), delayed graft function, allograft rejection, and chronic allograft injury. IRI, prevalent in cadaveric renal transplantation, leads to acute tubular necrosis and engages innate immunity, including neutrophils and the complement system, fostering a cycle of inflammation and necrosis. Experimental and preclinical evidence suggest that targeting the complement system could offer therapeutic benefits in IRI during kidney transplantation. This article explores potential therapeutic approaches targeting complement pathways in kidney transplantation, drawing from experimental and preclinical research findings.

Transcriptomic Signatures of Antibody-mediated Rejection in Early Biopsies With Negative Histology in HLA-incompatible Kidney Transplantation

Background

Presensitized patients with circulating donor-specific antibodies (DSAs) before transplantation are at risk for antibody-mediated rejection (AMR). Peritransplant desensitization mitigates but does not eliminate the alloimmune response. We examined the possibility that subthreshold AMR activity undetected by histology could be operating in some early biopsies.

Methods

Transcriptome of kidney allograft biopsies performed within the first month in presensitized patients (DSA+) who had received desensitization and did not develop active/probable AMR by histology (R-) was compared with biopsies showing active/probable AMR (R+/DSA+). As negative controls, biopsies without rejection by histology in patients without DSA at transplantation were used (R-/DSA-). RNA sequencing from biopsies selected from the biobank was used in cohort 1 (n = 32) and microarray, including the molecular microscope (Molecular Microscope Diagnostic System [MMDx]) algorithm, in recent cohort 2 (n = 30).

Results

The transcriptome of R-/DSA+ was similar to R+/DSA+ as these groups differed in 14 transcripts only. Contrarily, large differences were found between both DSA+ groups and negative controls. Fast gene set enrichment analyses showed upregulation of the immune system in both DSA+ groups (gene ontology terms: adaptive immune response, humoral immune response, antigen receptor-mediated signaling, and B-cell receptor signaling or complement activation) when compared with negative controls. MMDx assessment in cohort 2 classified 50% of R-/DSA+ samples as AMR and found no differences in AMR molecular scores between R+ and R- DSA+ groups. In imlifidase desensitization, MMDx series showed a gradual increase in AMR scores over time.

Conclusions

Presensitized kidney transplant recipients exhibited frequent molecular calls of AMR in biopsy-based transcript diagnostics despite desensitization therapy and negative histology.

Chimeric HLA antibody receptor T cell therapy for humoral transplant rejection

Antibody-mediated rejection (ABMR) is a significant obstacle to achieving optimal long-term outcomes after solid organ transplantation. The presence of donor-specific antibodies (DSAs), particularly against human leucocyte antigen (HLA), increases the risk of allograft rejection and subsequent graft loss. No effective treatment for ABMR currently exists, warranting novel approaches to target the HLA-specific humoral alloimmune response. Cellular therapies may hold promise to this end. According to publicly available sources as of now, three independent laboratories have genetically engineered a chimeric HLA antibody receptor (CHAR) and transduced it into human T cells, based on the demonstrated efficacy of chimeric antigen receptor T cell therapies in malignancies. These CHAR-T cells are designed to exclusively eliminate B cells that produce donor-specific HLA antibodies, which form the cornerstone of ABMR. CHAR technology generates potent and functional human cytotoxic T cells to target alloreactive HLA-specific B cells, sparing B cells with other specificities. Thus CHAR technology may be used as a selective desensitization protocol and to treat ABMR after solid organ transplantation.

Network meta-analysis of pharmacological treatment for antibody-mediated rejection after organ transplantation

Objective

This study aims to assess the efficacy of pharmacological interventions in mitigating graft injury in transplant patients with antibody-mediated rejection (AMR) through a network meta-analysis (NMA).

Methods

A search was conducted on databases such as Cochrane Library, PubMed, EmBase, and Web of Science for randomized controlled trials (RCTs) on pharmacological interventions for alleviating graft injury following AMR. The search was performed for publications up to April 12, 2024. Two reviewers conducted independent reviews of the literature, extracted data, and assessed the risk of bias (ROB) in the included studies using the ROB assessment tool recommended by the Cochrane Handbook for Systematic Reviews of Interventions 5.1.0. A Bayesian NMA was conducted using R 4.4.0, RStudio software, and the GeMTC package to assess the outcomes in estimated glomerular filtration rate (eGFR), mean fluorescence intensity (MFI), g-score, and infection under pharmacological treatments.

Results

A total of 8 RCTs involving 215 patients and 6 different pharmacological treatments were included in this NMA. The results indicated that the increase in eGFR by eculizumab (SUCRA score: 81) appeared to be more promising. The decrease in MFI by bortezomib (SUCRA score: 72.3), rituximab (SUCRA score: 68.2), and clazakizumab (SUCRA score: 67.1) demonstrated better efficacy. The decrease in g-score by eculizumab (SUCRA score: 74.3), clazakizumab (SUCRA score: 72.2), and C1INH (SUCRA score: 63.6) appeared to have more likelihood. For infection reduction, clazakizumab (SUCRA score: 83.5) and bortezomib (SUCRA score: 66.8) might be better choices.

Conclusion

The results of this study indicate that eculizumab has the potential to enhance eGFR and reduce g-score. Bortezomib demonstrates superior efficacy in reducing MFI. Clazakizumab appears to be more effective in reducing infections.

Systematic review registration

https://www.crd.york.ac.uk/prospero/, identifier CRD42024546483.

EASL Clinical Practice Guidelines on liver transplantation

Liver transplantation (LT) is an established life-saving procedure. The field of LT has changed in the past 10 years from several perspectives, with the expansion of indications, transplantation of patients with acute-on-chronic liver failure, evolution of transplant oncology, the use of donations after cardiac death, new surgical techniques, and prioritisation of recipients on the waiting list. In addition, the advent of organ perfusion machines, the recognition of new forms of rejection, and the attention paid to the transition from paediatric to adult patients, have all improved the management of LT recipients. The purpose of the EASL guidelines presented here is not to cover all aspects of LT but to focus on developments since the previous EASL guidelines published in 2016.

Defining causes of death-censored kidney allograft failure: A 5-year multicentre ANZDATA and clinical cross-sectional study

AIM

Determining specific causes of allograft failure allows a focus on understanding and treating these conditions. Previous studies highlight chronic antibody-mediated rejection as a leading cause of late allograft failure. We sought to define causes of allograft failure in a large cohort of kidney transplant recipients across multiple centres in Australia and New Zealand, including cases previously attributed to chronic allograft nephropathy (CAN).

METHODS

All death-censored allograft failures at 9 participating centres between 1 January 2014 to 31 December 2018 were included. Available clinical and biopsy data were reviewed and the "most likely" cause assigned.

RESULTS

There were 642 death-censored allograft failures in the study period. Of these, 495 (77.1%) had an informative biopsy performed a median of 13.4 months (IQR 2.5-39.1 months) prior to allograft failure. Rejection of any type was the leading cause of allograft failure (47.5%), comprised chiefly of chronic antibody-mediated rejection (37.4%) and chronic T-cell mediated rejection (6.4%). Other leading causes were undifferentiated interstitial fibrosis and tubular atrophy (10.8%), late medical and surgical complications (8.1%) and recurrent or de novo glomerulonephritis (7.0%). Polyoma viral nephropathy and calcineurin inhibitor toxicity each contributed to <2%. Causes of allograft failure previously attributed to CAN (n = 419, 65.3%) had a similar distribution to the overall cohort, with 43.9% attributed to chronic antibody-mediated rejection.

CONCLUSION

To prolong allograft survival, improved strategies are needed to curtail alloimmune responses. Greater understanding of the causes of undifferentiated interstitial fibrosis and tubular atrophy and potential treatments would also be of considerable benefit.

Treatment Response of Donor Specific Antibodies and Forced Expiratory Volume in Lung Transplant Recipients With Antibody Mediated Rejection

BACKGROUND

Antibody-mediated rejection (AMR) is an evolving diagnosis in lung transplantation. The presence of anti-human leukocyte antigen (HLA) donor-specific antibodies (DSAs) does not always correlate with clinical picture, leading to variation in treatment. This study sought to examine anti-HLA DSA response and lung allograft stabilization following AMR treatment.

METHODS

A single-center, retrospective case series was conducted in adult lung transplant recipients treated for clinical and subclinical AMR. The primary outcome was anti-HLA DSA reduction (≥ 25% decrease in mean fluorescence intensity [MFI]). The secondary outcome was forced expiratory volume (FEV1) stabilization (≤ 10% decline) at peak FEV1 and at 6-months post-treatment.

RESULTS

Fifteen bilateral lung transplant recipients were included. Eight (53%) patients achieved the primary outcome with median MFI reduction of -56.7% (interquartile range [IQR] = -41.3 to -69.5). Statistical significance was found on matched pairs analysis between 3 and 6 months post-treatment for anti-HLA DSA reduction. Of the subjects with available data, 7 of 9 (78%) patients had FEV1 stabilization from diagnosis to peak FEV1, and 5 of 7 (71%) patients had stabilization from diagnosis to 6 months post-treatment. A statistically significant decline was found from peak FEV1 post-treatment to 6 months post-treatment (-0.4 L ± 0.2, P = .05). Univariate analysis did not identify predictors affecting anti-HLA DSA response.

CONCLUSIONS

Anti-HLA DSA response was achieved in approximately half the cohort. A statistically significant decline in FEV1 was seen from peak FEV1 post-treatment but stabilized in most patients by 6 months. These results highlight the difficulty of DSA management and recovering lung function once lost, however, the finding of FEV1 stabilization after treatment is notable.

Opinions on the Future of Clinical Pig Kidney Xenotransplantation

Based on promising results obtained in primate models, pioneers in the US have now started to explore the new frontier of genetically-edited pig-to-human transplantation. The recent transition of xenotransplantation into clinical medicine has included transplants in brain-dead subjects and the compassionate use of xenotransplants in living recipients without options for allotransplantation. While the barrier of hyperacute rejection seems to be successfully overcome by gene editing of donor pigs, the occurrence of accelerated rejection could pose significant limitations to the success of the procedure. Ultimately, the establishment of efficient and safe strategies to overcome immunologic barriers will, among other critical factors, such as potential xenozoonotic disease transmission or physiological differences, determine whether and for which indications xenotransplantation will be viable. Considering preliminary outcomes of compassionate use xenotransplantions, which may raise questions about how faithfully data from non-human primate models translate into human outcomes, further research in decedents may be necessary before proceeding with additional clinical transplants. Looking ahead, designing systematic trials in xenotransplantation, including the definition of acceptable eligibility criteria for such high-risk transplants, will be an immense challenge, especially in kidney transplantation, where dialysis provides an effective alternative to transplantation in most cases.

Current and emerging tools for simultaneous assessment of infection and rejection risk in transplantation

Infection and rejection are major complications that impact transplant longevity and recipient survival. Balancing their risks is a significant challenge for clinicians. Current strategies aimed at interrogating the degree of immune deficiency or activation and their attendant risks of infection and rejection are imprecise. These include immune (cell counts, function and subsets, immunoglobulin levels) and non-immune (drug levels, viral loads) markers. The shared risk factors between infection and rejection and the bidirectional and intricate relationship between both entities further complicate transplant recipient care and decision-making. Understanding the dynamic changes in the underlying net state of immunity and the overall risk of both complications in parallel is key to optimizing outcomes. The allograft biopsy is the current gold standard for the diagnosis of rejection but is associated with inherent risks that warrant careful consideration. Several biomarkers, in particular, donor derived cell-free-DNA and urinary chemokines (CXCL9 and CXCL10), show significant promise in improving subclinical and clinical rejection risk prediction, which may reduce the need for allograft biopsies in some situations. Integrating conventional and emerging risk assessment tools can help stratify the individual's short- and longer-term infection and rejection risks in parallel. Individuals identified as having a low risk of rejection may tolerate immunosuppression wean to reduce medication-related toxicity. Serial monitoring following immunosuppression reduction or escalation with minimally invasive tools can help mitigate infection and rejection risks and allow for timely diagnosis and treatment of these complications, ultimately improving allograft and patient outcomes.

HLA class, calcineurin inhibitor levels, and the risk of graft failure in kidney recipients with de novo donor-specific antibodies

Introduction

De novo donor-specific HLA antibody (dnDSA) are associated with poor outcomes. Whether this observation applies to both HLA class I and II dnDSA remains unclear.

Methods

We studied 1236 consecutive kidney recipients who had routine anti-HLA antibody surveillance post-transplant.

Results

During the screening period, 55/1236 (4.4%) patients developed dnDSA: 18 (33%) HLA-I only, 33 (60%) HLA-II only, and 4 (7%) both classes. Thirty patients experienced graft loss at a median of 39 months after dnDSA detection: 9/18 (50%) HLA-I only, 17/33 (52%) HLA-II only, and 4/4 (100%) both classes. A control group was created by matching patients with dnDSA to patients who did not develop DSA and had a functioning graft at the time of dnDSA detection in their respective cases. Compared with these controls, the risk estimates of graft loss were similar between patients with HLA-I only and HLA-II only dnDSA (aHR [95% CI] 2.7 [1.1-6.6], p=0.04 and 3.1 [1.5-6.6], p<0.01 respectively). Additionally, the risk of graft loss decreased with increasing CNI trough levels following dnDSA detection (aHR 0.7 [0.6-0.9] for each increase in 1 ng/mL, p=0.02).

Conclusions

The prognosis of patients with dnDSA is similar regardless of the HLA class specificity. Lower calcineurin inhibitor levels predict graft loss in such patients.

Nanoparticle-assisted Targeting Delivery Technologies for Preventing Organ Rejection

Although organ transplantation is a life-saving medical procedure, the challenge of posttransplant rejection necessitates safe and effective immune modulation strategies. Nanodelivery approaches may have the potential to overcome the limitations of small-molecule immunosuppressive drugs, achieving efficacious treatment options for transplant tolerance without compromising overall host immunity. This review highlights recent advances in biomaterial-assisted formulations and technologies for targeted nanodrug delivery with transplant organ- or immune cell-level precision for treating graft rejection after transplantation. We provide an overview of the mechanism of transplantation rejection, current clinically approved immunosuppressive drugs, and their relevant limitations. Finally, we discuss the targeting principles and advantages of organ- and immune cell-specific delivery technologies. The development of biomaterial-assisted novel therapeutic strategies holds considerable promise for treating organ rejection and clinical translation.

Overexpression of miR-451a Aggravates Renal Ischemia-Reperfusion Injury by Targeting KLF1-ACSL4 to Promote Ferroptosis

Ischemia-reperfusion injury (IRI) is a predominant factor leading to delayed graft function (DGF) following kidney transplantation. MicroRNAs (miRNAs) play a pivotal role in the pathogenesis of renal IRI, with ferroptosis being a critical driving force throughout the process. In this study, we utilized bioinformatics methods to construct a network diagram of differentially expressed miRNAs, transcription factors (TFs), and ferroptosis-related genes. An I/R-induced renal injury model in mice and an in vitro H/R-induced HK-2 cell injury model were established. Quantitative real-time PCR (qRT-PCR) and Western blot analysis were used to measure the mRNA and miRNA levels in cells and tissues. The MDA concentration, iron levels, and GSH concentration were measured to evaluate the ferroptosis levels. CCK-8 assays were performed to assess cell viability. Luciferase reporter assays were conducted to validate the downstream targets of miRNA, and chromatin immunoprecipitation assays were performed to verify the interaction between TFs and mRNAs. Both the in vivo and in vitro results demonstrate that miR-451a was significantly enriched in the IRI renal tissues and cells, exacerbating ferroptosis. MiR-451a was found to reduce the expression of Kruppel-like factor 1 (KLF1) by directly binding to the 3'UTR of KLF1 mRNA. Additionally, KLF1 was identified as a negative transcription factor for acyl-CoA synthetase long-chain family member 4 (ACSL4). We demonstrated that IRI induced the upregulation of miR-451a, which reduced KLF1 expression, thereby promoting ferroptosis by upregulating ACSL4 expression, ultimately aggravating IRI-induced renal damage.

Advancing immunosuppression in liver transplantation: A narrative review

Immunosuppression is essential to ensure recipient and graft survivals after liver transplantation (LT). However, our understanding and management of the immune system remain suboptimal. Current immunosuppressive therapy cannot selectively inhibit the graft-specific immune response and entails a significant risk of serious side effects, i.e., among others, de novo cancers, infections, cardiovascular events, renal failure, metabolic syndrome, and late graft fibrosis, with progressive loss of graft function. Pharmacological research, aimed to develop alternative immunosuppressive agents in LT, is behind other solid-organ transplantation subspecialties, and, therefore, the development of new compounds and strategies should get priority in LT. The research trajectories cover mechanisms to induce T-cell exhaustion, to inhibit co-stimulation, to mitigate non-antigen-specific inflammatory response, and, lastly, to minimize the development and action of donor-specific antibodies. Moreover, while cellular modulation techniques are complex, active research is underway to foster the action of T-regulatory cells, to induce tolerogenic dendritic cells, and to promote the function of B-regulatory cells. We herein discuss current lines of research in clinical immunosuppression, particularly focusing on possible applications in the LT setting.

Impact of COVID-19 on anti-HLA antibodies in kidney transplantation

The effects of COVID-19 on the immune profile of kidney transplant recipients are unknown. Immunosuppression adjustment during the illness can increase the risk for de novo donor-specific anti-HLA antibodies (DSA) and acute rejection episodes. This single-center retrospective study includes adult kidney transplant recipients diagnosed with COVID-19 between March 2020 and December 2022, screened for anti-HLA antibodies (AbHLA) pre-transplant and after COVID-19. Analyzed data comprised demographics, immunosuppressive therapy before and during the illness, hospitalization rate, and AbHLA specificity. Two hundred sixty-seven transplant recipients were included and divided according to the pre-transplant AbHLA profile: absent [PRA- (n = 206, 77%)], non-DSA (N = 46, 17%), and DSA+ (n = 15, 6%). The DSA+ group was younger (40.5 ± 16.5; PRA- 50.3 ± 13.4; non-DSA 49.3 ± 11.7 years; p = 0.02). The hospitalization rate was higher in groups with preformed AbHLA (DSA+ n = 8, 53%; non-DSA = 24, 52%; PRA- n = 54, 26%; p < 0.01). Immunosuppression was maintained in 222 (83%), withdrawn in 33 (12%), and reduced in 11 (4%) cases without difference among groups. Twenty-two (8%) cases of de novo DSA were observed after COVID-19 [PRA-, n = 16 (73%) and non-DSA, n = 6 (27%)]. In the DSA+ group, the AbHLA profile remained stable. There were 6 (2%) cases of post-COVID-19 antibody-mediated rejection (DSA+ n = 4, 66%; non-DSA n = 1, 17%, PRA- n = 1, 17%) without T cell-mediated rejection cases. Post-COVID-19 de novo DSA was more frequent in groups without pre-transplant AbHLA, not having association with changes in immunosuppressive therapy.

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.

Use of Tocilizumab in the treatment of chronic active antibody-mediated rejection in pediatric kidney transplant recipients

Chronic active antibody-mediated rejection is one of the leading causes of graft failure and traditional therapies have unclear efficacy. Recent studies suggested that Tocilizumab could stabilize renal function and improve microvascular inflammation. Here we report the outcomes of Tocilizumab therapy in 6 pediatric kidney transplant recipients with biopsy-proven chronic active antibody-mediated rejection resistant to standard treatments. All patients received monthly Tocilizumab infusions for 6 months and were monitored for renal function (creatinine, estimated glomerular filtration rate (eGFR), proteinuria) and Human Leukocyte Antigens (HLA) and non-HLA antibodies at baseline and 3 and 6 months after Tocilizumab initiation. For each patient, a follow-up biopsy was scheduled at the end of the treatment. Renal function did not show stabilization or improvement (mean eGFR 37 ml/min/1.73 m2 pre-Tocilizumab and 27 ml/min/1.73 m2 3 months after-Tocilizumab) and proteinuria remained stable. Moreover, Tocilizumab had no impact on HLA and non-HLA antibodies. Graft loss was observed in 3 patients (50 %) and 4 patients who underwent post-treatment biopsy showed a worsening in overall chronicity scores. In our pediatric series, rescue therapy with Tocilizumab did not appear to be effective in modifying the natural history of chronic active antibody-mediated rejection.

Highly Sensitized Candidates Remain at Risk for Microvascular Inflammation Even When Donor-specific Antibody Is Avoided: A Matched Cohort Study

BACKGROUND

Microvascular inflammation (MVI) is a key feature of antibody-mediated rejection (AMR) among patients with HLA donor-specific antibody (DSA), but MVI at AMR thresholds (Banff glomerulitis [g] + peritubular capillaritis [ptc] score ≥ 2) without DSA has been increasingly recognized. We aimed to determine the incidence of MVI among highly sensitized kidney transplant recipients without DSA.

METHODS

We performed a single-center, retrospective, matched cohort study comparing outcomes of kidney transplant recipients with cPRA ≥90% with preexisting DSA (n = 49), cPRA ≥90% without preexisting DSA (n = 47), and matched controls with cPRA = 0 without preexisting DSA (n = 49). Controls were matched by age, donor type, and transplant date. Indication and surveillance biopsies combined with annual de novo DSA screening were obtained.

RESULTS

Kidney transplant recipients with a cPRA ≥90% and no evidence of preexisting or de novo DSA had a higher incidence of MVI (glomerulitis + peritubular capillaritis ≥ 2) than patients with cPRA = 0 [35% (17/49) versus 12% (6/49), P  = 0.0003] over a median (interquartile range) follow-up of 5 (4-6) y posttransplant. Among this cPRA ≥90% group without DSA, MVI persisted in 54% of cases on follow-up biopsy (7/13), and 24% (4/13) of cases developed transplant glomerulopathy (Banff cg score > 0).

CONCLUSIONS

Highly sensitized transplant recipients have a high incidence of persistent and progressive MVI, even without DSA. The mechanisms underlying these histologic features needs to be elucidated, but this information is important to consider when making decisions about transplantation among highly sensitized individuals.

Donor-Derived Cell-Free DNA as a Companion Biomarker for AMR Treatment With Daratumumab: Case Series

Antibody-mediated rejection (AMR) is among the most frequent causes for graft loss after kidney transplantation. While there are no approved therapies, several case reports with daratumumab and the very recent phase 2 trial of felzartamab in AMR have indicated the potential efficacy of therapeutic interventions targeting CD38. Donor-derived cell-free DNA (dd-cfDNA) is an emerging biomarker with injury-specific release and a short half-life, which could facilitate early diagnosis of AMR and monitoring of treatment response. We describe two cases of patients with chronic active AMR, who were treated with monthly daratumumab infusions, and in whom donor-derived cell-free DNA (dd-cfDNA) was measured longitudinally to monitor treatment response. In both patients, daratumumab treatment led to stabilization of kidney function parameters, a strong decline of dd-cfDNA below the previously established threshold for rejection, and partial or complete histologic resolution of AMR activity. Our case series suggests that dd-cfDNA may be a useful companion biomarker for longitudinal monitoring of anti-CD38 treatment in patients with AMR.

Bortezomib for antibody-mediated rejection of kidney transplant in youth: Associations with donor-specific antibody

BACKGROUND

Antibody-mediated rejection is one of the most significant risk factors for allograft dysfunction and failure in children and adolescents with kidney transplants, yet optimal treatment remains unidentified. To date, there are mixed findings regarding the use of Bortezomib, a plasma cell apoptosis inducer, as an adjunct therapy in the treatment of antibody-mediated rejection.

METHODS

In a retrospective single center study, we reviewed the efficacy and tolerability of bortezomib as adjunct therapy for treatment-refractory antibody-mediated rejection.

RESULTS

Six patients with a median age of 14.6 years (range 6.9-20.1 years) received bortezomib at a mean of 71 months (range 15-83 months) post-kidney transplant. Four patients experienced decline in estimated glomerular filtration rate (eGFR) from 4% to 42%. One patient started bortezomib while on hemodialysis and did not recover graft function, and another patient progressed to hemodialysis 6 months after receiving bortezomib. Although DSA did not completely resolve, there was a statistically significant decline in DSA MFI pre and 12-months post-BZ (p = .012, paired t-test) for the subjects who were not on dialysis at the time of bortezomib. Chronic Allograft Damage Index (CADI) score of ≥3 was seen in all six subjects at their biopsy prior to therapy. No adverse effects were reported.

CONCLUSIONS

Bortezomib was well tolerated and resulted in improvements in MFI of DSA among four pediatric subjects without allograft failure, although no effects were observed on eGFR trajectory. Further studies are needed to clarify whether earlier intervention with bortezomib could prevent renal failure progression.

The Impact of Alloantibodies on Clinical VCA Outcomes and the Need for Immune Tolerance

The functional outcomes and restoration of form after vascularized composite allotransplantation (VCA) have exceeded the results that could be achieved with current autologous surgical techniques. However, the longevity of VCA grafts has been limited due to the development of donor-specific antibodies (DSAs), and chronic rejection and graft failure occur despite long-term immunotherapy. Furthermore, despite widespread consensus that these non-life-saving transplants are beneficial for select patients, the application of VCA is limited by the need for lifelong immunosuppression. Therefore, attempts to achieve drug-free tolerance through safe and effective therapies are critical. This review highlights recent publications regarding alloantibody-mediated rejection (AMR) in various VCAs with a focus on the critical need for novel tolerance-inducing strategies. The development and implementation of effective methods of inducing tolerance, such as the use of anti-CD3 immunotoxins, could drastically improve VCA graft outcomes and recipient quality of life.