New insights in antibody-mediated rejection

Expanding role of antibodies in kidney transplantation

The role of antibodies in kidney transplant (KT) has evolved significantly over the past few decades. This role of antibodies in KT is multifaceted, encompassing both the challenges they pose in terms of antibody-mediated rejection (AMR) and the opportunities for improving transplant outcomes through better detection, prevention, and treatment strategies. As our understanding of the immunological mechanisms continues to evolve, so too will the approaches to managing and harnessing the power of antibodies in KT, ultimately leading to improved patient and graft survival. This narrative review explores the multifaceted roles of antibodies in KT, including their involvement in rejection mechanisms, advancements in desensitization protocols, AMR treatments, and their potential role in monitoring and improving graft survival.

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.

New Therapies for Highly Sensitized Patients on the Waiting List

Exposure to HLA alloantigens through pregnancy, blood products, and previous transplantations induce powerful immunologic responses that create an immunologic barrier to successful transplantation. This is commonly detected through screening for HLA antibodies using Luminex beads coated with HLA antigens at transplant evaluation. Currently accepted approaches to desensitization include plasmapheresis/low-dose or high-dose intravenous Ig plus anti-CD20. However, these approaches are often unsuccessful because of the inability to remove high titer circulating HLA antibodies and limit rebound responses by long-lived anti-HLA antibody secreting plasma cells (PCs) and memory B cells (B MEM ). This is especially significant for patients with a calculated panel reactive antibody of 99%-100%. Newer desensitization approaches, such as imlifidase (IgG endopeptidase), rapidly inactivate IgG molecules and create an antibody-free zone by cleaving IgG into F(ab'2) and Fc fragments, thus eliminating complement and cell-mediated injury to the graft. This represents an important advancement in desensitization. However, the efficacy of imlifidase is limited by pathogenic antibody rebound, increasing the potential for antibody-mediated rejection. Controlling antibody rebound requires new strategies that address the issues of antibody depletion and inhibition of B MEM and PC responses. This will likely require a combination of agents that effectively and rapidly deplete pathogenic antibodies and prevent immune cell activation pathways responsible for antibody rebound. Here, using anti-IL-6 receptor (tocilizumab) or anti-IL-6 (clazakizumab) could offer long-term control of B MEM and PC donor-specific HLA antibody responses. Agents aimed at eliminating long-lived PCs (anti-CD38 and anti-B-cell maturation antigen×CD3) are likely to benefit highly HLA sensitized patients. Complement inhibitors and novel agents aimed at inhibiting Fc neonatal receptor IgG recycling will be important in desensitization. Administering these agents alone or in combination will advance our ability to effectively desensitize patients and maintain durable suppression post-transplant. After many years of limited options, advanced therapeutics will likely improve efficacy of desensitization and improve access to kidney transplantation for highly HLA sensitized patients.

Advances in desensitization for human leukocyte antigen incompatible kidney transplantation

PURPOSE OF REVIEW

Human leukocyte antigen (HLA) sensitization is a major barrier to kidney transplantation induced by exposure to alloantigens through pregnancy, blood product exposure and previous transplantations. Desensitization strategies are undertaken to improve the chances of finding compatible organ offers. Standard approaches to desensitization include the use of plasmapheresis/low dose intravenous immunoglobulin (IVIG) or high dose IVIG plus anti-CD20. However, current methods to reduce HLA antibodies are not always successful, especially in those with calculated panel reactive antibody 99-100%.

RECENT FINDINGS

Newer desensitization strategies such as imlifidase [immunoglobulin G (IgG) endopeptidase] rapidly inactivates IgG molecules and creates an "antibody-free zone", representing an important advancement in desensitization. However, pathogenic antibodies rebound, increasing allograft injury that is not addressed by imlifidase. Here, use of anti-IL-6R (tocilizumab) or anti-interleukin-6 (clazakizumab) could offer long-term control of B-memory and plasma cell DSA responses to limit graft injury. Agents aimed at long-lived plasma cells (anti-CD38 and anti-BCMAxCD3) could reduce or eliminate HLA-producing plasma cells from marrow niches. Other agents such as complement inhibitors and novel agents inhibiting the Fc neonatal receptor (FcRn) mediated IgG recycling will likely find important roles in desensitization.

SUMMARY

Use of these agents alone or in combination will likely improve the efficacy and durability of desensitization therapies, improving access to kidney transplantation for immunologically disadvantaged patients.

Influence of HLA-A, B, and -DRB1 genes and panel-reactive antibodies on the waitlist time for kidney transplantation in the state of Sao Paulo-Brazil

BACKGROUND

Brazil ranks second in the absolute number of transplants. However, the supply remains insufficient to meet the demands, resulting in a lengthy waitlist. This study aimed to analyze whether the frequency of human leukocyte antigen (HLA) and the value of calculated panel reactive antibody (cPRA) would influence the waiting time for kidney transplantation.

METHODS

The HLA-A, B, and -DRB1 frequencies and the cPRA value were analyzed in 11,186 kidney transplant candidates included in the waitlist from 2006 to 2016.

RESULTS

The most frequent alleles were HLA-A*02, HLA-B*35, and HLA-DRB1*13. The overall mean length of stay on the list was 986 ± 1001 days. The mean waiting time for the three most frequent alleles of the HLA-A and B loci showed no significant difference when compared with the least frequent alleles; however, for the HLA-DRB1 locus, the most frequent alleles showed a shorter waiting time. In the association between HLA and PRA, the average length of stay on the list increased according to the candidate's degree of sensitization, regardless of the analyzed HLA frequency.

CONCLUSION

The length of stay on the waitlist is influenced by the frequency of the HLA alleles of the DRB1 locus and the degree of sensitization.

Early Versus Late Acute AMR in Kidney Transplant Recipients-A Comparison of Treatment Approaches and Outcomes From the ANZDATA Registry

BACKGROUND

Antibody-mediated rejection (AMR) is a major cause of kidney allograft failure and demonstrates different properties depending on whether it occurs early (<6 mo) or late (>6 mo) posttransplantation. We aimed to compare graft survival and treatment approaches for early and late AMR in Australia and New Zealand.

METHODS

Transplant characteristics were obtained for patients with an AMR episode reported to the Australia and New Zealand Dialysis and Transplant Registry from January 2003 to December 2019. The primary outcome of time to graft loss from AMR diagnosis, with death considered a competing risk, was compared between early and late AMR using flexible parametric survival models. Secondary outcomes included treatments used, response to treatment, and time from AMR diagnosis to death.

RESULTS

After adjustment for other explanatory factors, late AMR was associated with twice the risk of graft loss relative to early AMR. The risk was nonproportional over time, with early AMR having an increased early risk. Late AMR was also associated with an increased risk of death. Early AMR was treated more aggressively than late with more frequent use of plasma exchange and monoclonal/polyclonal antibodies. There was substantial variation in treatments used by transplant centers. Early AMR was reported to be more responsive to treatment than late.

CONCLUSIONS

Late AMR is associated with an increased risk of graft loss and death compared with early AMR. The marked heterogeneity in the treatment of AMR highlights the need for effective, new therapeutic options for these conditions.

Conversion to Belatacept in kidney transplant recipients with chronic antibody-mediated rejection (CAMR)

BACKGROUND

The costimulatory inhibitor Belatacept (Bela) has been shown to be an effective alternative in several clinical situations, including chronic antibody-mediated rejection, calcineurin toxicity, and de novo alloantibody formation. To further explore the usefulness of Belatacept under various clinical scenarios, we performed a retrospective analysis of a prospective database of all recipients who had a BPAR diagnosis of CAMR and were converted to a Belatacept maintenance immunosuppression regimen after kidney transplantation.

MATERIAL AND METHOD

We conducted a retrospective analysis of a prospectively collected database of all kidney transplants adult patients at SUNY Upstate Medical Hospital from 1 January 2013 to 31 December 2021. Our inclusion criteria were the patients who have been diagnosed with CAMR according to their renal biopsy based on the 2013 Banff criteria. The primary objective was to compare the kidney viability and function using GFR between the two interest groups and finally compare the outcomes.

RESULTS

A total of 48 patients met our inclusion criteria based on the kidney biopsy result, which showed chronic antibody-mediated graft rejection (CAMR). Nineteen patients (39.6%) were converted to the Belatacept, and we continued the previous immunosuppression regimen in 29 patients (60.4%). The mean time from the transplant date to the diagnosis of CAMR was 1385 days in the Belatacept group and 914 days for the non-Belatacept group (P = 0.15). The mean GFR comparison at each time point between the groups did not show a significant difference, and Belatacept did not show superiority compared to the standard immunosuppression regimen in terms of kidney function preservation. 1 (5.2%) patient from the Belatacept group and 1 (3.4%) patient from the non-Belatacept group had a biopsy-proven acute rejection (BPAR) after CAMR confirmation, and it was comparable (P = 0.76). De novo synthesis of the DSA rate was 12.5% in the Belatacept group and 15% In the non-Belatacept group, which was comparable. (P = 0.90). The patient survival rate was 100% in both groups.

CONCLUSIONS

We conclude that compared to the standard Tacrolimus/MMF/Prednisone regimen, Belatacept did not significantly benefit in preserving the GFR in long-term follow-ups and stabilizing the DSA production, which is one of the main factors resulting in chronic graft failure.

Complement in ischaemia-reperfusion injury and transplantation

Until recently, the only known condition in which complement could mediate transplant injury was the rare occurrence of antibody-mediated rejection, in which the original concept of antibody immunity against the transplant was supported by complementary proteins present in the serum. This has changed within the last two decades because of evidence that the processes of ischaemia–reperfusion injury followed by T cell–mediated rejection are also critically dependent on components generated by the complement system. We now have a clearer understanding of the complement triggers and effectors that mediate injury, and a detailed map of their local sites of production and activation in the kidney. This is providing helpful guidelines as to how these harmful processes that restrict transplant outcomes can be targeted for therapeutic benefit. Here we review some of the recent advances highlighting relevant therapeutic targets.

Approach to Highly Sensitized Kidney Transplant Candidates and a Positive Crossmatch

Human leukocyte antigen (HLA)-incompatible kidney transplantation offers survival benefit compared with ongoing dialysis. There have been considerable advances in the last decade to allow for increased access to transplant for the HLA-sensitized kidney transplant candidates. These include increased priority in the kidney allocation system, kidney paired donation, and novel desensitization strategies. A better understanding of the role of B cells, plasma cells, and complement and inflammatory cytokines in the pathophysiology of HLA antibody-mediated allograft injury has led to the use of novel therapeutics for desensitization and treatment of antibody-mediated rejection. Here we discuss current approaches to kidney transplantation in HLA-sensitized kidney transplant candidates.

Recipient myeloperoxidase-producing cells regulate antibody-mediated acute versus chronic kidney allograft rejection

Antibody-mediated rejection (ABMR) continues to be a major problem undermining the success of kidney transplantation. Acute ABMR of kidney grafts is characterized by neutrophil and monocyte margination in the tubular capillaries and by graft transcripts indicating NK cell activation, but the myeloid cell mechanisms required for acute ABMR have remained unclear. Dysregulated donor-specific antibody (DSA) responses with high antibody titers are induced in B6.CCR5-/- mice transplanted with complete MHC-mismatched A/J kidneys and are required for rejection of the grafts. This study tested the role of recipient myeloid cell production of myeloperoxidase (MPO) in the cellular and molecular components of acute ABMR. Despite induction of equivalent DSA titers, B6.CCR5-/- recipients rejected A/J kidneys between days 18 and 25, with acute ABMR, whereas B6.CCR5-/-MPO-/- recipients rejected the grafts between days 46 and 54, with histopathological features of chronic graft injury. On day 15, myeloid cells infiltrating grafts from B6.CCR5-/- and B6.CCR5-/-MPO-/- recipients expressed marked phenotypic and functional transcript differences that correlated with the development of acute versus chronic allograft injury, respectively. Near the time of peak DSA titers, activation of NK cells to proliferate and express CD107a was decreased within allografts in B6.CCR5-/-MPO-/- recipients. Despite high titers of DSA, depletion of neutrophils reproduced the inhibition of NK cell activation and decreased macrophage infiltration but increased monocytes producing MPO. Overall, recipient myeloid cells producing MPO regulate graft-infiltrating monocyte/macrophage function and NK cell activation that are required for DSA-mediated acute kidney allograft injury, and their absence switches DSA-mediated acute pathology and graft outcomes to chronic ABMR.

Immunologic Rejection of Transplanted Retinal Pigmented Epithelium: Mechanisms and Strategies for Prevention

Replacement of dysfunctional retinal pigmented epithelium (RPE) with grafts derived from stem cells has the potential to improve vision for patients with retinal disorders. In fact, the potential is such that a great number of groups are attempting to realize this therapy through individual strategies with a variety of stem cell products, hosts, immunomodulatory regimen, and techniques to assess the success of their design. Comparing the findings of different investigators is complicated by a number of factors. The immune response varies greatly between xenogeneic and allogeneic transplantation. A unique immunologic environment is created in the subretinal space, the target of RPE grafts. Both functional assessment and imaging techniques used to evaluate transplants are susceptible to erroneous conclusions. Lastly, the pharmacologic regimens used in RPE transplant trials are as numerous and variable as the trials themselves, making it difficult to determine useful results. This review will discuss the causes of these complicating factors, digest the strategies and results from clinical and preclinical studies, and suggest places for improvement in the design of future transplants and investigations.

Natural Killer Cells: Critical Effectors During Antibody-mediated Rejection of Solid Organ Allografts

Antibody-mediated rejection (AMR) is an important cause of graft loss and continues to present a formidable obstacle to successful transplantation. Unresolved problems continue to be the absence of effective strategies to ablate the donor-specific antibody (DSA) response as well as to attenuate the antibody-mediated graft tissue injury. While the properties of DSA that cause greater graft tissue injury and the characteristic microvascular pathology of the graft injury are well documented, the mechanisms underlying the injury mediated by the antibodies remains unclear. Recent transcriptome interrogation of kidney and heart biopsies procured during ongoing AMR has indicated the expression of genes associated with natural killer (NK) cell activation that is absent during T cell-mediated rejection. The expression of NK cell transcripts during AMR correlates with the presence of CD56+ cells in the microcirculation inflammation observed during AMR. Several mouse models have recently demonstrated the role of NK cells in antibody-mediated chronic vasculopathy in heart allografts and the requirement for NK cell activation during acute AMR of kidney allografts. In the latter model, NK cell activation within kidney allografts is regulated by the activation of myeloid cells producing myeloperoxidase. Overall, the studies to date indicate that AMR constitutes a complex series of DSA-induced interactions with components of the innate immune response. The innate immune participants and their expressed effector functions resulting in the rejection are beginning to be identified. The identification of these components should uncover novel targets that can be used to attenuate acute graft tissue injury in the presence of DSA.

Low-vacuum scanning electron microscopy may allow early diagnosis of human renal transplant antibody-mediated rejection

Antibody-mediated rejection (ABMR) is an important cause of both short- and long-term injury to renal allografts. Transplant glomerulopathy (TG) is strongly associated with ABMR and reduced graft survival. Ultrastructural changes in early-stage ABMR include TG as a duplication of the glomerular basement membrane (GBM), which can be observed only by transmission electron microscopy (TEM). Low-vacuum scanning electron microscopy (LVSEM) is a new technique that allows comparatively inexpensive, rapid, and convenient observations with high magnification. We analyzed human renal transplants using LVSEM and evaluated the ultrastructural changes representing TG in ABMR. GBM duplication was more clearly visible in the LVSEM images than in the light microscopy (LM) images. In the ABMR group, the cg score of the Banff classification was higher in 54% (7/13) of specimens for LVSEM images than for LM images. And 4 specimens exhibited duplication of the GBM analyzed by LVSEM, but not by LM. In addition, three-dimensional ultrastructural changes, such as coarse meshwork structures of GBM, were observed in ABMR specimens. The ABMR group also exhibited ultrastructural changes in the peritubular capillary basement membranes. In conclusion, analyses of renal transplant tissues using LVSEM allows the identification of GBM duplication and ultrastructural changes of basement membranes at the electron microscopic level, and is useful for early-stage diagnosis of ABMR.

Plasma volume treated with double filtration plasmapheresis and outcomes of acute antibody-mediated rejection in kidney transplant recipients: A retrospective cohort study

A retrospective cohort study was conducted to evaluate the association between the plasma volume treated by double filtration plasmapheresis and allograft outcomes for the treatment of acute antibody-mediated rejection in kidney transplant recipients. Patients were divided into two groups: group 1, plasma volume treated between 1 and <1.3 total plasma volume and group 2, plasma volume treated ≥1.3 total plasma volume. Primary outcome was ≥50% reduction of serum creatinine rising from baseline value at 1 month. A total of 32 courses (146 sessions) of double filtration plasmapheresis were performed; 17 and 15 courses in group 1 and group 2, respectively. Primary outcome occurred in 41% of group 1 and 40% of group 2 (adjusted risk ratio 1.15 [95%CI, 0.48-2.76]). Graft loss at 1 year did not differ between the two groups (adjusted hazard ratio 0.65 [95%CI, 0.23-1.87]). Infection tendency seemed to be higher in group 2 (40% vs 18%, P = .243).

Inflammaging and Complement System: A Link Between Acute Kidney Injury and Chronic Graft Damage

The aberrant activation of complement system in several kidney diseases suggests that this pillar of innate immunity has a critical role in the pathophysiology of renal damage of different etiologies. A growing body of experimental evidence indicates that complement activation contributes to the pathogenesis of acute kidney injury (AKI) such as delayed graft function (DGF) in transplant patients. AKI is characterized by the rapid loss of the kidney's excretory function and is a complex syndrome currently lacking a specific medical treatment to arrest or attenuate progression in chronic kidney disease (CKD). Recent evidence suggests that independently from the initial trigger (i.e., sepsis or ischemia/reperfusions injury), an episode of AKI is strongly associated with an increased risk of subsequent CKD. The AKI-to-CKD transition may involve a wide range of mechanisms including scar-forming myofibroblasts generated from different sources, microvascular rarefaction, mitochondrial dysfunction, or cell cycle arrest by the involvement of epigenetic, gene, and protein alterations leading to common final signaling pathways [i.e., transforming growth factor beta (TGF-β), p16 ink4a , Wnt/β-catenin pathway] involved in renal aging. Research in recent years has revealed that several stressors or complications such as rejection after renal transplantation can lead to accelerated renal aging with detrimental effects with the establishment of chronic proinflammatory cellular phenotypes within the kidney. Despite a greater understanding of these mechanisms, the role of complement system in the context of the AKI-to-CKD transition and renal inflammaging is still poorly explored. The purpose of this review is to summarize recent findings describing the role of complement in AKI-to-CKD transition. We will also address how and when complement inhibitors might be used to prevent AKI and CKD progression, therefore improving graft function.

Safety, pharmacokinetics, and pharmacodynamic activity of obinutuzumab, a type 2 anti-CD20 monoclonal antibody for the desensitization of candidates for renal transplant

The limited effectiveness of rituximab plus intravenous immunoglobulin (IVIG) in desensitization may be due to incomplete B cell depletion. Obinutuzumab is a type 2 anti-CD20 antibody that induces increased B cell depletion relative to rituximab and may therefore be more effective for desensitization. This open-label phase 1b study assessed the safety, pharmacokinetics, and pharmacodynamics of obinutuzumab in highly sensitized patients with end-stage renal disease. Patients received 1 (day 1, n = 5) or 2 (days 1 and 15; n = 20) infusions of 1000-mg obinutuzumab followed by 2 doses of IVIG on days 22 and 43. Eleven patients received additional obinutuzumab doses at the time of transplant and/or at week 24. The median follow-up duration was 9.4 months. Obinutuzumab was well tolerated, and most adverse events were grade 1-2 in severity. There were 11 serious adverse events (SAEs) in 9 patients (36%); 10 of these SAEs were infections and 4 occurred after kidney transplant. Obinutuzumab plus IVIG resulted in profound peripheral B cell depletion and appeared to reduce B cells in retroperitoneal lymph nodes. Reductions in anti-HLA antibodies, number of unacceptable antigens, and the calculated panel reactive antibody score as centrally assessed using single-antigen bead assay were limited and not clinically meaningful for most patients (NCT02586051).

The Role of Long-Lived Plasma Cells in Antibody-Mediated Rejection of Kidney Transplantation: An Update

Background

Antibody-mediated rejection (ABMR) following kidney transplant is closely associated with poor prognosis of the recipients. Long-lived plasma cells (LLPCs) produce alloantibodies as long as life time and play a crucial role in ABMR.

Summary

LLPCs generate from germinal centers and reside in survival niches in the bone marrow as well as the inflamed tissues. They are the main and long-term source of the antibodies. LLPCs mediate ABMR via the generation of preformed antibodies in sensitized patients and de novo antibodies after transplantation. They have been acknowledged as the leading causes of ABMR; however, LLPCs are insensitive to traditional immunosuppressive therapy that removes B cells. Strategies targeting LLPCs, such as antithymocyte globulin, proteasome inhibitors as well as monoclonal antibodies, are promising methods to persistently and thoroughly clear the entire PC pool.

Key Message

LLPCs play an important role in ABMR by producing alloantibodies continually, and targeting LLPCs might be a novel and effective approach against ABMR.

Prediction of renal allograft chronic rejection using a model based on contrast-enhanced ultrasonography

Objective

To evaluate the application of contrast‐enhanced ultrasonography (CEUS) for the diagnosis of renal allograft chronic rejection (CR).

Methods

A total of 104 patients who were suspected to have AR or CR were enrolled in this study (derivation group, n = 66; validation group, n = 38). Before biopsy, all patients received an ultrasound examination.

Results

In the CR group, rising time (RT) and time to peak (TTP) of medulla (RTm and TTPm, respectively) were significantly longer compared to those in the AR group. The kidney volume was significantly decreased in the CR group but was increased in the AR group. In the derivation group, age, change in kidney volume, and TTPm were identified as independent predictors by multivariate analysis. Based on the multivariate analysis results and area under receiver operating characteristic (ROC) curves (AUROCs) of individual markers, we constructed a new index as follows: P = −5.424 + 0.074 × age −9.818 × kidney volume change + 0.115 × TTPm; New Index = e^P/(1 + e^P). The new index discriminates CR from AR and had better AUROCs than any other parameters.

Conclusion

In conclusion, the new index provides a new diagnosis model for CR.

Is antibody-mediated rejection in kidney transplant recipients a risk factor for developing cytomegalovirus or BK virus infection? Results from a case-control study

BACKGROUND

Data are scarce on cytomegalovirus (CMV) and BK virus (BKV) infection after antibody-mediated rejection (ABMR).

OBJECTIVES

We hypothesized that the immunological response in patients with ABMR or the immune modulation associated with its treatment could predispose to CMV and BKV infection. Our objective was to investigate this hypothesis.

STUDY DESIGN

We conducted a single-center, matched case-control study (1:2 ratio) to analyze CMV and BKV replication during the first year after the ABMR diagnosis in kidney transplant recipients. Adult recipients with a histopathological diagnosis of ABMR between 2007-2015 were included as cases. Controls were kidney recipients who underwent transplantation immediately before and after the index case.

RESULTS

Fifty-eight patients diagnosed with ABMR (33 chronic active ABMR and 25 acute ABMR), with their matched controls (116) were included. Forty-four cases received treatment for ABMR, including plasmapheresis (41), immunoglobulins (40), and rituximab (31). Within 1 year after ABMR, cases showed CMV replication more often than controls (9/58, 15.5% vs 7/116, 6%, OR = 4.21, CI 1.10-16.16, p = 0.04). Over the study period, CMV PCR determinations were requested more frequently in cases than controls (46/58, 79.3% vs 63/116, 54.3%, OR = 4.58, CI 1.92-10.9, p = 0.001). On multivariate analysis adjusted for CMV PCR determinations, retransplantation, antithymocyte globulin treatment and methylprednisolone treatment for acute rejection, CMV replication remained more common in cases than in controls (OR = 2.41, CI 0.49-11.73, p = 0.28). There were no differences in BKV replication in either urine or blood.

CONCLUSIONS

ABMR may be a risk factor for CMV but not for BKV replication in kidney transplant recipients.

In the absence of natural killer cell activation donor-specific antibody mediates chronic, but not acute, kidney allograft rejection

Antibody mediated rejection (ABMR) is a major barrier to long-term kidney graft survival. Dysregulated donor-specific antibody (DSA) responses are induced in CCR5-deficient mice transplanted with complete major histocompatibility complex (MHC)-mismatched kidney allografts, and natural killer (NK) cells play a critical role in graft injury and rejection. We investigated the consequence of high DSA titers on kidney graft outcomes in the presence or absence of NK cell activation within the graft. Equivalent serum DSA titers were induced in CCR5-deficient B6 recipients of complete MHC mismatched A/J allografts and semi-allogeneic (A/J x B6) F1 kidney grafts, peaking by day 14 post-transplant. A/J allografts were rejected between days 16-28, whereas B6 isografts and semi-allogeneic grafts survived past day 65. On day 7 post-transplant, NK cell infiltration into A/J allografts was composed of distinct populations expressing high and low levels of the surface antigen NK1.1, with NK1.1_low cells reflecting the highest level of activation. These NK cell populations increased with time post-transplant. In contrast, NK cell infiltration into semi-allogeneic grafts on day 7 was composed entirely of NK1.1_high cells that decreased thereafter. On day 65 post-transplant the semi-allogeneic grafts had severe interstitial fibrosis, glomerulopathy, and arteriopathy, accompanied by expression of pro-fibrogenic genes. These results suggest that NK cells synergize with DSA to cause acute kidney allograft rejection, whereas high DSA titers in the absence of NK cell activation cannot provoke acute ABMR but instead induce the indolent development of interstitial fibrosis and glomerular injury that leads to late graft failure.

The regulation of interferon type I pathway-related genes RSAD2 and ETV7 specifically indicates antibody-mediated rejection after kidney transplantation

CONTEXT

Antibody-mediated rejection (ABMR) after kidney transplantation (KTx) remains the crucial obstacle to successful long-term graft function. The identification of gene signatures involved in ABMR could grant the basis for better prevention and treatment strategies.

OBJECTIVE

The identification of gene signatures in whole blood cells specific for ABMR after KTx.

MATERIALS AND METHODS

Total RNA from blood cells of 16 kidney-transplanted patients with ABMR, stable graft function (SGF), and with T-cell-mediated rejection (TCMR) was isolated. Gene expression was determined by high-throughput sequencing followed by validation and analyses of differentially expressed candidates on mRNA level and on protein level in a large patient cohort (n = 185) in patients with SGF, urinary tract infection (UTI), borderline rejection (BL), TCMR, ABMR, and interstitial fibrosis and tubular atrophy.

RESULTS

From the 570 genes detected, 111 discriminated ABMR from SGF and TCMR. A distinct enrichment of interferon (IFN) type I and type II signature gene set was observed. The expression of candidate genes IFIT1, ETV7, and RSAD2 distinguished ABMR patients from patients with SGF and also TCMR, whereas ETV7 and RSAD2 differentiated ABMR also from BL.

CONCLUSION

The IFN-inducible genes ETV7 and RSAD2 represent specific biomarkers for ABMR episodes after KTx.

New Answers to Old Conundrums: What Antibodies, Exosomes and Inflammasomes Bring to the Conversation. Canadian National Transplant Research Program International Summit Report

Antibody-mediated injury is a major cause of allograft dysfunction and loss. Antibodies to ABH(O) blood group antigens are classic mediators of ABO-incompatible graft rejection, whereas donor-specific anti-HLA antibodies and, more recently, autoantibodies are appreciated as important contributors to allograft inflammation and dysfunction. In August 2016, the International Summit of the Canadian National Transplant Research Program focused on recent advances in the field of antibody-mediated rejection. Here, we describe work presented and discussed at the meeting, with a focus on 3 major themes: the importance of (1) natural antibodies and autoantibodies, (2) tissue injury-derived exosomes and autoimmunity, (3) inflammasome activation and innate immune responses in regulating allograft inflammation and dysfunction. Finally, we explore novel areas of therapeutic intervention that have recently emerged from these 3 major and overlapping fields of transplantation research.

MicroRNA regulation in blood cells of renal transplanted patients with interstitial fibrosis/tubular atrophy and antibody-mediated rejection

Interstitial fibrosis/tubular atrophy (IFTA) is associated with reduced allograft survival, whereas antibody-mediated rejection (ABMR) is the major cause for renal allograft failure. To identify specific microRNAs and their regulation involved in these processes, total RNA from blood cells of 16 kidney transplanted (KTx) patients with ABMR, stable graft function (SGF) and with T-cell mediated rejection (TCMR) was isolated. MicroRNA expression was determined by high-throughput sequencing. Differentially expressed candidate microRNAs were analyzed with RT-PCR in patients with SGF (n = 53), urinary tract infection (UTI) (n = 17), borderline rejection (BL) (n = 19), TCMR (n = 40), ABMR (n = 22) and IFTA (n = 30). From the 301 detected microRNAs, 64 were significantly regulated between the three cohorts. Selected candidate microRNAs miR-223-3p, miR-424-3p and miR-145-5p distinguished TCMR and ABMR from SGF, but not from other pathologies. Most importantly, miR-145-5p expression in IFTA patients was significantly downregulated and displayed a high diagnostic accuracy compared to SGF alone (AUC = 0.891) and compared to SGF, UTI, BL, TCMR and ABMR patients combined (AUC = 0.835), which was verified by cross-validation. The identification of miR-145-5p as IFTA specific marker in blood constitutes the basis for evaluating this potentially diagnostic microRNA as biomarker in studies including high numbers of patients and different pathologies and also the further analysis of fibrosis causing etiologies after kidney transplantation.

Effect of Preformed or De Novo Anti-HLA Antibodies on Function and Graft Survival in Kidney Transplant Recipients

BACKGROUND Donor-specific antibodies (DSA), directed against human leucocyte antigens (HLA), are associated with increased risk for graft rejection in kidney transplantation. Anti-HLA antibodies detection by Luminex™ present high sensitivity and accuracy, but its interpretation after transplantation is not completely clear. The aim of this study was to evaluate the impact of anti-HLA antibodies, preformed or de novo, on renal function, graft survival, and incidence of antibody-mediated acute rejection (AMR). MATERIAL AND METHODS A retrospective cohort of 86 kidney transplant recipients was divided into 3 groups according to the presence of anti-HLA antibodies before transplantation: donor-specific antibodies (DSA+, n=15), non-DSA (non-DSA, n=39), and negative pre-transplant panel reactive antibodies (PRA) that became positive after transplantation (PRA-, n=22). Forty-nine recipients with negative PRA pre- and post-transplantation were excluded. Antibody specificity and intensity of fluorescence (MFI) and their relationship with renal function, proteinuria, AMR, and graft failure were evaluated. RESULTS Among patients who completed 1 year of follow-up, there was no significant difference in serum creatinine, estimated glomerular filtration rate, or proteinuria. AMR incidence was 9.5% in the DSA group, 2.3% in the non-DSA group, and 9.1% in the PRA- group. There was no correlation between fluorescence intensity and/or antibodies class (I or II) with increased risk of AMR. Thirteen grafts failed within 1 year post-transplant, there were 9 deaths due to infection, and only 1 due to AMR (PRA- group, DSA de novo at 3 months). CONCLUSIONS In contrast to previous reports, we did not find a correlation between incidence of AMR and MFI intensity in this series.

Triptolide inhibits donor-specific antibody production and attenuates mixed antibody-mediated renal allograft injury

Donor-specific antibodies (DSAs) are major mediators of renal allograft injury, and strategies to inhibit DSAs are important in promoting long-term graft survival. Triptolide exhibits a wide spectrum of antiinflammatory and immunosuppressive activities, and in autoimmune diseases it inhibits autoantibody levels. In this study, we investigated the suppressive role of triptolide in the generation of DSAs in transplant recipients. We found that triptolide treatment of skin allograft recipients in mice significantly suppressed the development of circulating anti-donor-specific IgG and effectively alleviated DSA-mediated renal allograft injury, which led to prolonged allograft survival. In vitro studies revealed that triptolide inhibited the differentiation of B cells into CD138⁺ CD27⁺⁺ plasma cells; reduced the levels of IgA, IgG, and IgM secreted by plasma cells; and repressed somatic hypermutation and class switch recombination of B cells. Moreover, triptolide-treated recipients showed reduced numbers of B cells, plasma cells, and memory B cells in spleens and decreased numbers of T, B, natural killer (NK) cells, and macrophages infiltrating grafts. These findings highlight the importance of triptolide in suppressing DSAs and establish triptolide as a novel therapeutic agent for antibody-mediated allograft rejection.

Fatal Pneumococcus Sepsis after Treatment of Late Antibody-Mediated Kidney Graft Rejection

Antibody-mediated rejection (ABMR) is a major cause of late renal allograft dysfunction and graft loss. Risks and benefits of treatment of late ABMR have not been evaluated in randomized clinical trials. We report on a 35-year-old patient with deterioration in renal function and progressive proteinuria 15 years after transplantation. Recurrent infections after a splenectomy following traumatic splenic rupture 3 years earlier had led to reduction of immunosuppression. Renal transplant biopsy showed glomerular double contours, 40% fibrosis/tubular atrophy, peritubular capillaritis, and positive C4d staining indicating chronic-active ABMR. ABMR treatment was initiated with steroids, plasmapheresis, and rituximab. Fourteen days later, she presented to the emergency department with fever, diarrhea, vomiting, and hypotension. Despite antibiotic treatment she deteriorated with progressive hypotension, capillary leak with pleural effusion, peripheral edema, and progressive respiratory insufficiency. She died due to septic shock five days after admission. Blood cultures showed Streptococcus pneumoniae, consistent with a diagnosis of overwhelming postsplenectomy infection syndrome, despite protective pneumococcus vaccination titers. We assume that the infection was caused by one of the strains not covered by the Pneumovax 23 vaccination. The increased immunosuppression with B cell depletion may have contributed to the overwhelming course of this infection.

In Vivo Attenuation of Antibody-Mediated Acute Renal Allograft Rejection by Ex Vivo TGF-β-Induced CD4+Foxp3+ Regulatory T Cells

Antibody-mediated rejection (AMR) has emerged as the major cause of renal allograft dysfunction, and more effective strategies need to be explored for improving transplant outcomes. Regulatory T cells (Tregs), consisting of at least natural and induced Treg subsets, suppress effector responses at multiple levels and play a key role in transplantation tolerance. In this study, we investigated the effect of induced Tregs (iTregs) on preventing antibody-mediated renal injury and rejection in a mouse model. We observed that infusion of iTregs markedly attenuated histological graft injury and rejection and significantly improved renal allograft survival. iTregs exhibited a comprehensive ability to regulate immunological disorders in AMR. First, iTreg treatment decreased the levels of circulating antidonor antibody and the antibody deposition within allografts. Second, iTregs significantly reduced cell infiltration including CD4⁺ T cells (including Th1, Th17, and Tfh), CD8⁺IFN-γ⁺ cells, natural killer cells, B cells, and plasma cells, which are involved in the process of AMR. Our results also highlight a predominance of M1 macrophage infiltration in grafts with acute AMR, and M1 macrophage could be reduced by iTreg treatment. Collectively, our data demonstrate, for the first time, that TGF-β-induced Tregs can attenuate antibody-mediated acute renal allograft injury through targeting multiple effectors. Thus, use of iTregs in prevention of AMR in clinical practice could be expected.

Treatment of Antibody-Mediated Rejection After Kidney Transplantation - 10 Years' Experience With Apheresis at a Single Center

Antibody-mediated rejection (AMR) is a major cause of kidney graft failure. We aimed to analyze treatment and outcome of AMR in a national cohort of 75 biopsy-proven acute (43 patients, 57%) or chronic active (32 patients, 43%) AMR episodes between 2000 and 2015. The mean patients' age was 46 ± 16 years, the majority was treated with plasma exchange, 4% received immunoadsorption and 7% received both. The majority received pulse methylprednisolone and low-dose CMV hyperimmune globulin, 20% received bortezomib and 13% rituximab. Concomitant infection was treated in 40% of patients. The immediate treatment outcome was successful in 91%, the 1- and 3-year graft survival rates were 71% and 57%, while 3-year patient survival was 97%. Chronic active AMR was associated with worse graft survival than acute AMR (log rank P = 0.06). To conclude, intensive treatment with apheresis and additional immunosuppression was effective in reversing AMR, but long-term graft survival remains markedly decreased, especially in chronic active AMR.

The mechanisms of rejection in solid organ transplantation

Organ transplantation represents the preferred treatment option for many patients in terminal organ failure. The half-life of transplanted organs, however, is still far from being satisfactory with the vast majority of the organs failing within the first two decades following transplantation. At this stage, it has become apparent that rejection (prevalently mediated by humoral events) remains the primary cause of graft loss after the first year. In this light, studies are underway to better comprehend the immune events underlying graft rejection and novel immunosuppressive strategies are being explored. In this context, therapeutic apheresis techniques, that include therapeutic plasma exchange (TPE), immunoadsorption (IA) and extracorporeal photochemotherapy (ECP), represent an important adjunct in the current immunosuppressive armamentarium. This article briefly reviews our current understanding of the immune process underlying rejection of a solid organ transplant and describes the principal areas of application of therapeutic apheresis techniques in transplantation.

Complement Recognition Pathways in Renal Transplantation

The complement system, consisting of soluble and cell membrane-bound components of the innate immune system, has defined roles in the pathophysiology of renal allograft rejection. Notably, the unavoidable ischemia-reperfusion injury inherent to transplantation is mediated through the terminal complement activation products C5a and C5b-9. Furthermore, biologically active fragments C3a and C5a, produced during complement activation, can modulate both antigen presentation and T cell priming, ultimately leading to allograft rejection. Earlier work identified renal tubule cell synthesis of C3, rather than hepatic synthesis of C3, as the primary source of C3 driving these effects. Recent efforts have focused on identifying the local triggers of complement activation. Collectin-11, a soluble C-type lectin expressed in renal tissue, has been implicated as an important trigger of complement activation in renal tissue. In particular, collectin-11 has been shown to engage L-fucose at sites of ischemic stress, activating the lectin complement pathway and directing the innate immune response to the distressed renal tubule. The interface between collectin-11 and L-fucose, in both the recipient and the allograft, is an attractive target for therapies intended to curtail renal inflammation in the acute phase.

Tracing Donor-MHC Class II Reactive B cells in Mouse Cardiac Transplantation: Delayed CTLA4-Ig Treatment Prevents Memory Alloreactive B-Cell Generation

BACKGROUND

The dual role of B cells as drivers and suppressors of the immune responses have underscored the need to trace the fate of B cells recognizing donor major histocompatibility complex class I and class II after allograft transplantation.

METHODS

In this study, we used donor class II tetramers to trace the fate of I-E-specific B cells after immunization with BALB/c spleen cells or cardiac transplantation, in naive or sensitized C57BL/6 recipients. We combined this approach with genetic lineage tracing of memory B cells in activation-induced cytidine deaminase regulated Cre transgenic mice crossed to the ROSA26-enhanced yellow fluorescent protein reporter mice to track endogenous I-E-specific memory B cell generation.

RESULTS

Immunization with BALB/c splenocytes or heart transplantation induced an expansion and differentiation of I-E-specific B cells into germinal center B cells, whereas BALB/c heart transplantation into sensitized recipients induced the preferential differentiation into antibody-secreting cells. A 10.8-fold increase in the frequency of I-E-specific memory B cells was observed by day 42 postimmunization. Treatment with CTLA4-Ig starting on day 0 or day 7 postimmunization abrogated I-E-specific memory B cell generation and sensitized humoral responses, but not if treatment commenced on day 14.

CONCLUSIONS

The majority of donor-specific memory B cells are generated between days 7 and 14 postimmunization, thus revealing a flexible timeframe whereby delayed CTLA4-Ig administration can inhibit sensitization and the generation of memory graft-reactive B cells.

Relationship between Mean Fluorescence Intensity and C1q/C3d-fixing capacities of anti-HLA antibodies

BACKGROUND

Complement-binding assays are proposed to better stratify the risk of antibody-mediated rejection associated-graft failure. Despite promising clinical results, some have suggested that the MFI of anti-HLA antibodies may influence these tests.

METHODS

We investigated the impact of Abs MFI reduction, induced by plasmapheresis, on C1q- and C3d-binding assays. Sera provided from 7 sensitized kidney transplant patients were analyzed.

RESULTS

Four hundreds and thirty-three SABs were analyzed. Before plasmapheresis, when compared to C1q- SABs, C1q+ SABs had a higher median MFI [17397 (IQR: 14851-18794) vs. 2745 (IQR: 1125-6476), p<0.01]. SABs that remained C1q+ after plasmapheresis had a higher median MFI. Regarding the C3d assay, results were strictly comparable. MFI value was a powerful predictor of both C1q and C3d positivity [AUC 0.97 (CI95% 0.95-0.99) and 0.96, (CI95% 0.93-0.98), respectively].

CONCLUSION

Our data suggest that both C1q- and C3d-binding assays are intimately linked to the MFI of anti-HLA Abs.

Immediate and Catastrophic Antibody-Mediated Rejection in a Lung Transplant Recipient With Anti-Angiotensin II Receptor Type 1 and Anti-Endothelin-1 Receptor Type A Antibodies

Preexisting donor-specific anti-HLA antibodies (DSAs) have been associated with reduced survival of lung allografts. However, antibodies with specificities other than HLA may have a detrimental role on the lung transplant outcome. A young man with cystic fibrosis underwent lung transplantation with organs from a suitable deceased donor. At the time of transplantation, there were no anti-HLA DSAs. During surgery, the patient developed a severe and intractable pulmonary hypertension associated with right ventriular dysfunction, which required arteriovenous extracorporeal membrane oxygenation. After a brief period of clinical improvement, a rapid deterioration in hemodynamics led to the patient's death on postoperative day 5. Postmortem studies showed that lung specimens taken at the end of surgery were compatible with antibody-mediated rejection (AMR), while terminal samples evidenced diffuse capillaritis, blood extravasation, edema, and microthrombi, with foci of acute cellular rejection (A3). Immunological investigations demonstrated the presence of preexisting antibodies against the endothelin-1 receptor type A (ET_A R) and the angiotensin II receptor type 1 (AT₁ R), two of the most potent vasoconstrictors reported to date, whose levels slightly rose after transplantation. These data suggest that preexisting anti-ET_A R and anti-AT₁ R antibodies may have contributed to the onset of AMR and to the catastrophic clinical course of this patient.

Antibody-Mediated Rejection: A Review

BACKGROUND

Chronic antibody injury is a serious threat to allograft outcomes and is therefore the center of active research. In the continuum of allograft rejection, the development of antibodies plays a critical role. In recent years, an increased recognition of molecular and histologic changes has provided a better understanding of antibody-mediated rejection (AMR), as well as potential therapeutic interventions. However, several pathways are still unknown, which accounts for the lack of efficacy of some of the currently available agents that are used to treat rejection.

METHODS

We review the current diagnostic criteria for AMR; AMR paradigms; and desensitization, treatment, and prevention strategies.

RESULTS

Chronic antibody-mediated endothelial injury results in transplant glomerulopathy, manifested as glomerular basement membrane duplication, double contouring, or splitting. Clinical manifestations of AMR include proteinuria and a rise in serum creatinine. Current strategies for the treatment of AMR include antibody depletion with plasmapheresis (PLEX), immunoadsorption (IA), immunomodulation with intravenous immunoglobulin (IVIG), and T cell- or B cell-depleting agents. Some treatment benefits have been found in using PLEX and IA, and some small nonrandomized trials have identified some benefits in using rituximab and the proteasome inhibitor-based therapy bortezomib. More recent histologic follow-ups of patients treated with bortezomib have not shown significant benefits in terms of allograft outcomes. Furthermore, no specific treatment approaches have been approved by the US Food and Drug Administration. Other agents used for more difficult rejections include bortezomib and eculizumab (an anti-C5 monoclonal antibody).

CONCLUSION

AMR is a fascinating field with ample opportunities for research and progress in the future. Despite the use of advanced techniques for the detection of human leukocyte antigen (HLA) or non-HLA donor-specific antibodies, alloimmune response remains an important barrier for successful long-term allograft function. Treatment of AMR with currently available therapies has produced a variety of results, some of them suboptimal, precluding the development of standardized protocols. New therapies are promising, but randomized controlled trials are needed to find surrogate markers and improve the efficacy of therapy.

Renal transplant immunology in the last 20 years: A revolution towards graft and patient survival improvement

To deride the hope of progress is the ultimate fatuity, the last word in poverty of spirit and meanness of mind. There is no need to be dismayed by the fact that we cannot yet envisage a definitive solution of our problems, a resting-place beyond which we need not try to go. -P.B. Medawar, 1969 * Thomas E. Starlz, also known as the Father of Clinical Transplantation, once said that organ transplantation was the supreme exception to the rule that most major advances in medicine spring from discoveries in basic science [Starzl T. The mystique of organ transplantation. J Am Coll Surg 2005 Aug;201(2):160-170]. In fact, the first successful identical-twin kidney transplantation performed by Murray's team in December 1954 (Murray J et al. Renal homotransplantations in identical twins. Surg Forum 1955;6:432-436) was the example of an upside down translation medicine: Human clinical transplantation began and researchers tried to understand the underlying immune response and how to control the powerful rejection pathways through experimental models. In the last 20 years, we have witnessed an amazing progress in the knowledge of immunological mechanisms regarding alloimmune response and an outstanding evolution on the identification and characterization of major and minor histocompatibility antigens. This review presents an historical and clinical perspective of those important advances in kidney transplantation immunology in the last 20 years, which contributed to the improvement in patients' quality of life and the survival of end-stage renal patients. In spite of these significant progresses, some areas still need substantial progress, such as the definition of non-invasive biomarkers for acute rejection; the continuous reduction of immunosuppression; the extension of graft survival, and finally the achievement of real graft tolerance extended to HLA mismatch donor: recipient pairs.

Association of C1q-fixing DSA with late graft failure in pediatric renal transplant recipients

BACKGROUND

We investigated the prognostic value of overall and complement-binding donor-specific HLA antibodies (DSA) in pediatric patients undergoing clinically indicated graft biopsies and their association with graft outcome and specific histological lesions.

METHODS

Sera of 62 patients at time of indication biopsy ≥1 year posttransplant were assessed for DSA and C1q-fixing DSA by single-antigen bead (SAB) technology.

RESULTS

Twenty-six patients (42 %) were DSA-positive at time of indication biopsy and nine (15 %) were C1q-positive. At 4 years postbiopsy, patients with C1q-positivity had a low graft survival (11 %) compared to DSA-positive, C1q-negative patients (82 %, p = 0.001) and to DSA-negative patients (88 %, p < 0.001). The majority (89 %) of C1q-positive patients were diagnosed with active chronic antibody-mediated rejection (ABMR). C1q DSA-positivity [adjusted hazard ratio (HR) 6.35], presence of transplant glomerulopathy (HR 9.54), and estimated glomerular filtration rate (eGFR) at the time of indication biopsy (HR 0.91) were risk factors for subsequent graft loss.

CONCLUSIONS

The presence of C1q-positive DSA in the context of an indication biopsy identifies a subgroup of pediatric renal transplant recipients with a markedly increased risk of subsequent graft loss. Because a fraction of DSA-positive patients escape rejection or graft dysfunction, the C1q assay increases the specificity of a positive DSA result regarding unfavorable transplant outcome.

Mechanisms of antibody-mediated acute and chronic rejection of kidney allografts

PURPOSE OF REVIEW

Antibody-mediated rejection is responsible for up to half of acute rejection episodes in kidney transplant patients and more than half of late graft failures. Antibodies cause acute graft abnormalities that are distinct from T cell-mediated rejection and at later times posttransplant, a distinct pathologic lesion is associated with capillary basement membrane multilayering and glomerulopathy. Despite the importance of donor-reactive antibodies as the leading cause of kidney graft failure, mechanisms underlying antibody-mediated acute and chronic kidney graft injury are poorly understood. Here, we review recent insights provided from clinical studies as well as from animal models that may help to identify new targets for therapy.

RECENT FINDINGS

Studies of biopsies from kidney grafts in patients with donor-specific antibody versus those without have utilized analysis of pathologic lesions and gene expression to identify the distinct characteristics of antibody-mediated rejection. These analyses have indicated the presence of natural killer cells and their activation during antibody-mediated rejection. The impact of studies of antibody-mediated allograft injury in animal models have lagged behind these clinical studies, but have been useful in testing the activation of innate immune components within allografts in the presence of donor-specific antibodies.

SUMMARY

Most insights into processes of antibody-mediated rejection of kidney grafts have come from carefully designed clinical studies. However, several new mouse models of antibody-mediated kidney allograft rejection may replicate the abnormalities observed in clinical kidney grafts and may be useful in directly testing mechanisms that underlie acute and chronic antibody-mediated graft injury.

Natural killer cells play a critical role in mediating inflammation and graft failure during antibody-mediated rejection of kidney allografts

While the incidence of antibody-mediated kidney graft rejection has increased, the key cellular and molecular participants underlying this graft injury remain unclear. Rejection of kidney allografts in mice lacking the chemokine receptor CCR5 is dependent on production of donor-specific antibody. Here we determine if cells expressing cytotoxic function contributed to antibody-mediated kidney allograft rejection in these recipients. Wild-type C57BL/6, B6.CCR5(-/-), and B6.CD8(-/-)/CCR5(-/-) mice were transplanted with complete MHC-mismatched A/J kidney grafts, and intragraft inflammatory components were followed to rejection. B6.CCR5(-/-) and B6.CD8(-/-)/CCR5(-/-) recipients rejected kidney allografts by day 35, whereas 65% of allografts in wild-type recipients survived past day 80 post-transplant. Rejected allografts in wild-type C57BL/6, B6.CCR5(-/-), and B6.CD8(-/-)/CCR5(-/-) recipients expressed high levels of VCAM-1 and MMP7 mRNA that was associated with high serum titers of donor-specific antibody. High levels of perforin and granzyme B mRNA expression peaked on day 6 post-transplant in allografts in all recipients, but were absent in isografts. Depletion of natural killer cells in B6.CD8(-/-)/CCR5(-/-) recipients reduced this expression to background levels and promoted the long-term survival of 40% of the kidney allografts. Thus, natural killer cells have a role in increased inflammation during antibody-mediated kidney allograft injury and in rejection of the grafts.

The impact of C4d-negative acute antibody-mediated rejection on short-term prognosis among kidney transplant recipients

AIM

We aimed to investigate the clinical and pathological features of C4d-negative acute antibody-mediated rejection (aAMR), and examined the impact of C4d-negative aAMR on short-term prognosis.

METHODS

From 2005 to 2011, 626 kidney transplantations were performed in our institution and related hospitals. We excluded 174 ABO-incompatible transplantations, and analysed clinical and pathological data from the remaining 452 until December 2013.

RESULTS

During the follow-up period, 39 patients underwent aAMR. We divided them into two groups. According to C4d positivity in each patient's first AMR, we divided the cohort into a C4d-positive aAMR group and a C4d-negative aAMR group, using the new Banff 2013 classification. We compared each aAMR patient's features to controls. Clinical and pathological characteristics were similar in both groups and the short-term outcomes of the two groups were similar, but both were worse than control.

CONCLUSION

C4d-negative aAMR resembles C4d-positive aAMR in terms of clinical and pathological features, and that C4d positivity has no influence on short-term outcome.

Influence of de novo donor-specific antibody on early renal allograft function recovery

BACKGROUND

The aim of the present study is to investigate the impact of de novo donor-specific antibodies (dnDSA) on early graft function, to provide objective reference for early clinical diagnosis and reasonable individualized treatment.

METHODS

305 cases of renal transplant patients for the first time were observed in this study. Follow-up time for all recipients was 6 months after operation. HLA antibody, DSA, renal function were monitored after transplant.

RESULTS

In total of 305 cases, 66 cases (21.64%) were HLA antibody positive and 21 cases (6.89%) showed acute rejection (AR) in 6 months after transplant. The HLA antibody-positive patients included six cases of dnDSA-positive and 60 cases of dnDSA-negative. The incidence of AR was 2.09% (5/239) in HLA antibody-negative patients, 18.33% (11/60) in HLA antibody positive with DSA-negative patients, and 83.33% (5/6) in HLA antibody-positive patients with DSA-positive. There was a big difference between DSA-negative and DSA-positive patients (p < 0.01). The recovery time of AR patients with DSA-positive were longer than DSA-negative patients, and the recovery graft function of AR patient with DSA-positive were not as good as those with DSA-negative.

CONCLUSIONS

The appearance of dnDSA in the early stage of kidney transplantation is a warning sign of AR occurrence. Dynamic monitoring of HLA antibody and DSA could predict the state of graft function, and play an important role in the prevention of AR, timely and effectively.