Accommodation in ABO-incompatible kidney allografts, a novel mechanism of self-protection against antibody-mediated injury

Impact of preoperative complement-dependent cytotoxicity crossmatch on postoperative outcomes in kidney transplant recipients: A retrospective analysis

ObjectivesThe aim of the present study was to compare the differences in clinical outcomes within 6 months postoperatively between a complement-dependent cytotoxicity <10% group of low-risk kidney transplant patients and a complement-dependent cytotoxicity ≥10% group of relatively high-risk patients.MethodsThe clinical data of 330 patients who underwent kidney transplantation were retrospectively analyzed. The patients were divided into three groups according to the results of complement-dependent cytotoxicity crossmatch: (a) group 1 (complement-dependent cytotoxicity ≥10%); (b) group 2a (5% ≤ complement-dependent cytotoxicity < 10%); and (c) group 2b (complement-dependent cytotoxicity <5%). The clinical outcomes were compared between the three groups.ResultsSignificant differences were noted in serum creatinine levels and estimated glomerular filtration rate between groups 2a and 2b on days (D) 1, 2, 3, and 7 (P < 0.005). From postoperative D1 to month (M) 6, a significant difference (P < 0.05) was noted in urea levels between the three groups. On D3, blood glucose levels were significantly lower in group 2b than in group 2a (P < 0.001); at M6, group 2b exhibited lower blood glucose levels than group 1 (P = 0.043). On D2, group 2b had a lower neutrophil percentage than group 1 (P < 0.05), which was significantly different from those of groups 1 and 2a on D3 (P < 0.05). The percentage and absolute number of lymphocytes in group 2b were significantly higher than those in group 1 (P < 0.01) on D1 and D2. The percentage and absolute number of lymphocytes were significantly higher in group 2b than in groups 1 and 2a on D3 and D7 (P < 0.05).ConclusionsComplement-dependent cytotoxicity <10%, particularly complement-dependent cytotoxicity <5%, was associated with superior attributes compared with complement-dependent cytotoxicity ≥10% in terms of most aspects of postoperative recovery and low incidence of adverse events. However, delayed graft function rate was highest in the complement-dependent cytotoxicity of 5%-10% group. The source of donor kidneys was the most important factor influencing delayed graft function, and a larger cohort with a longer follow-up period may be needed to verify the tendency.

Exploring parvovirus B19 pathogenesis and therapy among kidney transplant recipients: case report and review of literature

We report the case of a 34-year-old male recipient of an ABO-incompatible living donor kidney transplant who was repeatedly hospitalised for anaemia. Acute kidney injury in a patient with severe and recurrent anaemia related to parvovirus B19 infection was diagnosed through viral and histopathological analysis. In view of the patient's impaired immune response due to the immunosuppressive regimen, clinical stabilisation was reached by repeated intravenous immunoglobulin administration as a maintenance therapy in a prolonged course, although viral clearance did not occur. Review of the literature highlighted a variety of pathological renal lesions associated with parvovirus B19 infection, although epidemiological data on parvovirus B19 infection in kidney transplant recipients, standardised diagnostic and therapeutic protocols, and the prospect for specific antiviral therapy are still scarce. Increased awareness of clinical relevance of parvovirus B19 infection in patients who have had a kidney transplant should direct future efforts towards better consideration and comprehension of viral-induced pathogenesis, aimed at effective diagnosis and appropriate therapy.

ABO-incompatible heart transplantation-evolution of a revolution

In the 1990s, neonates born with severe congenital heart disease faced more than 50% mortality awaiting an ABO-compatible (ABOc) transplant donor. This desperate situation, together with knowledge of gaps in the adaptive immune system in early childhood, led to the clinical exploration of intentional ABO-incompatible (ABOi) heart transplantation. In 2001, West et al. reported the first series of 10 infants in Canada. Since then, consideration of ABOi heart donors has become the standard of care for children awaiting transplantation in the first few years of life, resulting in reduced wait times and better organ utilization with noninferior post-transplant outcomes compared to ABOc recipients. This state-of-the-art review discusses the clinical development and evolution, underlying and resulting immunological aspects, current challenges, and future directions of ABOi heart transplantation.

Enzymatic conversion of human blood group A kidneys to universal blood group O

ABO blood group compatibility restrictions present the first barrier to donor-recipient matching in kidney transplantation. Here, we present the use of two enzymes, FpGalNAc deacetylase and FpGalactosaminidase, from the bacterium Flavonifractor plautii to enzymatically convert blood group A antigens from the renal vasculature of human kidneys to 'universal' O-type. Using normothermic machine perfusion (NMP) and hypothermic machine perfusion (HMP) strategies, we demonstrate blood group A antigen loss of approximately 80% in as little as 2 h NMP and HMP. Furthermore, we show that treated kidneys do not bind circulating anti-A antibodies in an ex vivo model of ABO-incompatible transplantation and do not activate the classical complement pathway. This strategy presents a solution to the donor organ shortage crisis with the potential for direct clinical translation to reduce waiting times for patients with end stage renal disease.

Antibody production and tolerance to the α-gal epitope as models for understanding and preventing the immune response to incompatible ABO carbohydrate antigens and for α-gal therapies

This review describes the significance of the α-gal epitope (Galα-3Galβ1-4GlcNAc-R) as the core of human blood-group A and B antigens (A and B antigens), determines in mouse models the principles underlying the immune response to these antigens, and suggests future strategies for the induction of immune tolerance to incompatible A and B antigens in human allografts. Carbohydrate antigens, such as ABO antigens and the α-gal epitope, differ from protein antigens in that they do not interact with T cells, but B cells interacting with them require T-cell help for their activation. The α-gal epitope is the core of both A and B antigens and is the ligand of the natural anti-Gal antibody, which is abundant in all humans. In A and O individuals, anti-Gal clones (called anti-Gal/B) comprise >85% of the so-called anti-B activity and bind to the B antigen in facets that do not include fucose-linked α1-2 to the core α-gal. As many as 1% of B cells are anti-Gal B cells. Activation of quiescent anti-Gal B cells upon exposure to α-gal epitopes on xenografts and some protozoa can increase the titer of anti-Gal by 100-fold. α1,3-Galactosyltransferase knockout (GT-KO) mice lack α-gal epitopes and can produce anti-Gal. These mice simulate human recipients of ABO-incompatible human allografts. Exposure for 2-4 weeks of naïve and memory mouse anti-Gal B cells to α-gal epitopes in the heterotopically grafted wild-type (WT) mouse heart results in the elimination of these cells and immune tolerance to this epitope. Shorter exposures of 7 days of anti-Gal B cells to α-gal epitopes in the WT heart result in the production of accommodating anti-Gal antibodies that bind to α-gal epitopes but do not lyse cells or reject the graft. Tolerance to α-gal epitopes due to the elimination of naïve and memory anti-Gal B cells can be further induced by 2 weeks in vivo exposure to WT lymphocytes or autologous lymphocytes engineered to present α-gal epitopes by transduction of the α1,3-galactosyltransferase gene. These mouse studies suggest that autologous human lymphocytes similarly engineered to present the A or B antigen may induce corresponding tolerance in recipients of ABO-incompatible allografts. The review further summarizes experimental works demonstrating the efficacy of α-gal therapies in amplifying anti-viral and anti-tumor immune-protection and regeneration of injured tissues.

Accommodation in allogeneic and xenogeneic organ transplantation: Prevalence, impact, and implications for monitoring and for therapeutics

Accommodation refers to acquired resistance of organs or tissues to immune or inflammatory reactions that might otherwise cause severe injury or rejection. As first observed in ABO-incompatible kidney transplants and heterotopic cardiac xenografts, accommodation was identified when organ transplants continued to function despite the presence of anti-graft antibodies and/or other reactants in the blood of recipients. Recent evidence suggests many and perhaps most organ transplants have accommodation, as most recipients mount B cell responses specific for the graft. Wide interest in the impact of graft-specific antibodies on the outcomes of transplants prompts questions about which mechanisms confer protection against such antibodies, how accommodation might be detected and whether and how rejection could be superimposed on accommodation. Xenotransplantation offers a unique opportunity to address these questions because immune responses to xenografts are easily detected and the pathogenic impact of immune responses is so severe. Xenotransplantation also provides a compelling need to apply these and other insights to decrease the intensity and toxicity of immunosuppression that otherwise could limit clinical application.

Protection of transplants against antibody-mediated injuries: from xenotransplantation to allogeneic transplantation, mechanisms and therapeutic insights

Long-term allograft survival in allotransplantation, especially in kidney and heart transplantation, is mainly limited by the occurrence of antibody-mediated rejection due to anti-Human Leukocyte Antigen antibodies. These types of rejection are difficult to handle and chronic endothelial damages are often irreversible. In the settings of ABO-incompatible transplantation and xenotransplantation, the presence of antibodies targeting graft antigens is not always associated with rejection. This resistance to antibodies toxicity seems to associate changes in endothelial cells phenotype and modification of the immune response. We describe here these mechanisms with a special focus on endothelial cells resistance to antibodies. Endothelial protection against anti-HLA antibodies has been described in vitro and in animal models, but do not seem to be a common feature in immunized allograft recipients. Complement regulation and anti-apoptotic molecules expression appear to be common features in all these settings. Lastly, pharmacological interventions that may promote endothelial cell protection against donor specific antibodies will be described.

Outcome of ABO-incompatible kidney transplantation using a modified desensitization protocol without plasmapheresis

OBJECTIVES

Several controversies regarding desensitization strategies for successful ABO-incompatible (ABOi) kidney transplantation still exist. This study aimed to investigate whether pretransplant anti-A/B antibody removal is mandatory in an ABOi kidney transplant recipient with low baseline isoagglutinin titers.

METHODS

We adopted a modified desensitization protocol with two doses of rituximab (RTX, 100 mg/body) without pretransplant antibody removal for ABOi kidney transplant recipients with a titer of ≤1:64 (group A; n = 35) and investigated the feasibility of this protocol by comparing it with the clinical outcomes of patients undergoing standard pretransplant plasmapheresis (group B; n = 21).

RESULTS

There was no significant difference in the rate of antibody-mediated rejection within the first month after transplantation between the two groups (11.4% in group A vs. 2% in group B, p = 0.6019). Moreover, no differences were observed in the short- and long-term graft outcomes between the groups. However, two major critical acute antibody-mediated events occurred in group A; one patient lost the graft due to hyperacute rejection, and the other patient developed thrombotic microangiopathy after surgery. Risk factors predicting these perioperative complications were not identified.

CONCLUSIONS

We conclude that not only B-cell depletion using RTX but also pretransplant antibody removal is still recommended even for patients with low isoagglutinin titers. In addition, a new diagnostic tool is needed for accurate risk stratification.

Current Perspectives in ABO-Incompatible Kidney Transplant

For a long time, ABO incompatible living donor kidney transplantation has been considered contraindicated, due to the presence of isohemagglutinins, natural antibodies reacting with non-self ABO antigens. However, as the demand for kidney transplantation is constantly growing, methods to expand the donor pool have become increasingly important. Thus, in the last decades, specific desensitization strategies for ABOi transplantation have been developed. Nowadays, these regimens consist of transient removal of preformed anti-A or anti-B antibodies by using plasmapheresis or immunoadsorption and B-cell immunity modulation by CD20+ cells depletion with rituximab, in association with maintenance immunosuppression including corticosteroids, tacrolimus and mycophenolate mofetil. The outcome in ABOi kidney transplantation have markedly improved over the years. In fact, although randomized trials are still lacking, recent meta analysis has revealed that there is no difference in terms of graft and patient's survival between ABOi and ABO compatible kidney transplant, even in the long term. However, many concerns still exist, because ABOi kidney transplantation is associated with an increased risk of bleeding and infectious complications, partly related to the effects of extracorporeal treatments and the strong immunosuppression. Thus, a continuous improvement in desensitization strategies, with the aim of minimize the immunosuppressive burden, on the basis of immune pathogenesis, antibodies titers and/or ABO blood group, is warranted. In this review, we discuss the main immune mechanisms involved in ABOi kidney transplantation, the pathogenesis of tolerance and the desensitization regimens, including immunoadsorption and plasmapheresis and the immunosuppressive protocol. Finally, we provide an overview on outcome and future perspectives in ABOi kidney transplant.

Transcriptomic heterogeneity of antibody mediated rejection after heart transplant with or without donor specific antibodies

BACKGROUND

Antibody mediated rejection (AMR) is an increasingly studied cause of graft failure after heart transplantation. AMR diagnosis previously required the detection of circulating donor specific antibodies (DSA); however, the most recent criteria only require pathological findings. This classification defined a subset of patients with AMR, yet without known antibodies. Here, we sought to evaluate differences in the transcriptome profile associated with different types of AMR.

METHODS

RNA sequencing was used on endomyocardial biopsies to analyze and compare transcriptomic profiles associated with different subtypes of AMR defined by immunopathological and histopathological findings, as well as the presence or absence of DSA. Gene expression profiles were characterized for each diagnostic group.

RESULTS

The most divergent gene expression profiles were observed between patients with or without DSA. AMR subtypes associated with DSA showed expression of signature genes involved in monocyte activation and response to interferon. There was also substantial difference between the transcriptomic profiles of AMR defined by histopathological and immunopathological findings, the latter being associated with expression of mucin genes. In contrast, there was no differential RNA expression between patients with pAMR1i without DSA and those without AMR. Likewise, no differential expression was observed between patients with pAMR1h with DSA and pAMR2.

CONCLUSIONS

Overall, our studies reveal different expression profiles in endomyocardial biopsies in relation to some key criteria used to diagnose AMR. These findings support the view that the diagnosis of AMR encompasses several phenotypes that may rely on distinct mechanisms of injury.

Highly individual- and tissue-specific expression of glycoprotein group A and B blood antigens in the human kidney and liver

Background

Currently, research on the quantitative distribution of ABO antigens in different organs and tissues remains limited. We aimed to examine the individual characteristics of blood group glycoprotein A and B antigen expression in human kidneys and livers.

Methods

We obtained human samples, including the renal artery, renal vein, renal tissue, hepatic artery, hepatic vein, portal vein, and hepatic tissue, from 24 deceased organ transplant donors. The expression of the blood group antigens glycoprotein A and B was analysed and compared by Western blotting.

Results

There was no significant difference in the expression between blood group glycoprotein A and B antigens at any of the seven sites (p > 0.05). The expression of both A and B antigens was highest in renal tissue and the portal vein and was lowest in the renal artery. A large difference in glycoprotein antigen expression was observed among various donors or different regions of the same individual. Univariate analysis revealed that glycoprotein A/B antigens were affected by the age and sex of donors and were significantly higher in males and in young people.

Conclusions

Our study found that blood group glycoprotein antigen expression showed certain trends and distinct distribution in the kidney, liver, and vessels among individuals and in different regions of the same individual, which may explain the different clinical outcomes of patients who received ABO-incompatible transplantation.

C3 complement inhibition prevents antibody-mediated rejection and prolongs renal allograft survival in sensitized non-human primates

Sensitized kidney transplant recipients experience high rates of antibody-mediated rejection due to the presence of donor-specific antibodies and immunologic memory. Here we show that transient peri-transplant treatment with the central complement component C3 inhibitor Cp40 significantly prolongs median allograft survival in a sensitized nonhuman primate model. Despite donor-specific antibody levels remaining high, fifty percent of Cp40-treated primates maintain normal kidney function beyond the last day of treatment. Interestingly, presence of antibodies of the IgM class associates with reduced median graft survival (8 vs. 40 days; p = 0.02). Cp40 does not alter lymphocyte depletion by rhesus-specific anti-thymocyte globulin, but inhibits lymphocyte activation and proliferation, resulting in reduced antibody-mediated injury and complement deposition. In summary, Cp40 prevents acute antibody-mediated rejection and prolongs graft survival in primates, and inhibits T and B cell activation and proliferation, suggesting an immunomodulatory effect beyond its direct impact on antibody-mediated injury.

Donor-specific antibodies in sensitized recipients may cause kidney transplant rejection. Here the authors show that complement component C3 inhibition prolongs graft survival by inhibiting T and B cell proliferation/activation and hence tissue injury, despite antibody levels remaining unaffected.

Effect of Donor and Recipient ABH-Secretor Status on ABO-Incompatible Living Donor Kidney Transplantation

Introduction

ABO blood group antigens within grafts are continuously exposed to anti-A/B antibodies in the serum of recipients after ABO-incompatible (ABOi) kidney transplantation and are instrumental in antibody-mediated rejection. Some individuals secrete soluble blood group antigens into body fluids. In this study, we investigated the effect of donor and recipient secretor status on the outcomes of ABOi kidney transplantation.

Methods

Data of a total of 32 patients with ABOi living donor kidney transplantation were retrospectively collected between 2014 and 2020 in West China Hospital. The genotype and phenotype of both donors and recipients were examined and evaluated with post-transplantation anti-A/B titer changes, graft function, and rejection.

Results

Of the 32 recipients and 32 donors, 23 (71.9%) recipients and 27 (84.4%) donors had secretor genotypes, whereas 9 (28.1%) recipients and 5 (15.6%) donors did not. Anti-A/B titers after ABOi kidney transplantation were not significantly influenced by the secretor status of either donors or recipients. The post-transplantation serum creatinine (Scr) levels and estimated glomerular filtration rate (eGFR) was better in weak- or non-secretor recipients at day 30 (Scr P = 0.047, eGFR P = 0.008), day 90 (Scr P = 0.010, eGFR P = 0.005), and month 9 (eGFR P = 0.008), and recipients from secretor donors had a lower incidence of graft rejection in the first year after ABOi transplantation (P = 0.004).

Conclusions

A weak secretor status phenotype was found in both genotypes, i.e., individuals who secreted soluble antigens as well as those who did not. The recipient ABH-secretor status may have an influence on early posttransplant renal function, and the donor ABH-secretor status might affect the incidence of graft rejection.

A Safe Anti-A2 Titer for a Successful A2 Incompatible Kidney Transplantation: A Single-center Experience and Review of the Literature

Background.

Kidney allocation system allows blood type B candidates accept kidneys from A2/A2B donors. There is no mandate by UNOS on which the anti-A2 level is acceptable. We aimed to investigate the safety of kidney transplant in blood group B patients with anti-A2 titers ≤16.

Methods.

We performed 41 A2-incompatible kidney transplants in blood group B recipients between May 2015 and September 2019. Clinical outcomes were compared with a control group of 75 blood group B recipients who received blood group compatible kidney transplantation at the same period.

Results.

Of the 41 recipients, 85% were male, 48% African American, with a median age of 53 (20–73) y. Thirty-eight (93%) were deceased-donor and 3 (7%) were living-donor kidney transplant recipients. Pretransplant anti-A2 IgG titers were 2 in 16, 4 in 9, 8 in 6, and 16 in 5 and too weak to titer in 5 recipients. Eight patients had pretransplant donor-specific antibodies. During a median follow-up of 32.6 mo (6–57.3) patient and graft survival were 100% and 92% in the A2-incompatible kidney transplant group, and 91% and 92% in the blood group compatible group, respectively. Twelve A2-incompatible recipients underwent a 21 clinically indicated kidney biopsies at a median 28 d (6–390) after transplantation. None of the patients developed acute antibody-mediated rejection and 2 patients (5%) had acute T-cell–mediated rejection. Interestingly, peritubular capillary C4d positivity was seen in 7 biopsies which did not have any findings of acute rejection or microvascular inflammation but not in any of the rejection-free biopsies in the control group. C4d positivity was persistent in 5 of those patients who had follow-up biopsies.

Conclusions.

A2-incompatible transplantation is safe in patients with anti-A2 titers ≤16 with excellent short-term kidney allograft outcomes. C4d positivity is frequent in allograft biopsies without acute rejection.

Characteristics of Immunoglobulin M Type Antibodies of Different Origins from the Immunologic and Clinical Viewpoints and Their Application in Controlling Antibody-Mediated Allograft Rejection

Antibody-mediated allograft rejection (AMR) hinders patient prognosis after organ transplantation. Current studies concerning AMR have mainly focused on the diagnostic value of immunoglobulin G (IgG)-type donor-specific antihuman leukocyte antigen antibodies (DSAs), primarily because of their antigen specificity, whereas the clinical significance of immunoglobulin M (IgM)-type DSAs has not been thoroughly investigated in the context of organ transplantation because of their nonspecificity against antigens. Although consensus regarding the clinical significance and role of IgM antibodies is not clear, as discussed in this review, recent findings strongly suggest that they also have a huge potential in novel diagnostic as well as therapeutic application for the prevention of AMR. Most serum IgM antibodies are known to comprise natural antibodies with low affinity toward antigens, and this is derived from B-1 cells (innate B cells). However, some of the serum IgM-type antibodies reportedly also produced by B-2 cells (conventional B cells). The latter are known to have a high affinity for donor-specific antigens. In this review, we initially discuss how IgM-type antibodies of different origins participate in the pathology of various diseases, directly or through cell surface receptors, complement activation, or cytokine production. Then, we discuss the clinical applicability of B-1 and B-2 cell-derived IgM-type antibodies for controlling AMR with reference to the involvement of IgM antibodies in various pathological conditions.

The First North American Experience Using Glycosorb Immunoadsorption Columns for Blood Group-Incompatible Kidney Transplantation

Background:

Blood group incompatibility (ABOi) is the most common barrier to living donor kidney transplantation. Options for such recipients include kidney paired donation (KPD) or desensitization methodology to reduce blood antibody response.

Objective:

The objective of this study is to report on the first North America experience in ABOi living donor kidney transplantation using Glycosorb ABO immunoadsorption columns.

Design:

Retrospective observational cohort study.

Setting:

Renal transplant program at St. Michael’s Hospital, Unity Health Toronto, University of Toronto.

Patients:

Twenty-six ABOi living donor transplants from August 2011 through February 2020 were undertaken at our center.

Measurements:

Renal allograft and patient survival postdesensitization for ABOi living donor transplants and isohemagglutinin titer reduction.

Methods:

Preoperative immunosuppressive regimen consisted of a single dose of Rituximab 375 mg/m² IV on day −28; tacrolimus, mycophenolic acid, and prednisone to start on day −7. Immunoadsorption treatments with Glycosorb A or B columns were performed on day −7 through day −1 based on anti-A or anti-B titers on Spectra Optia Apheresis System. Immunosuppression included basiliximab, solumedrol followed by oral prednisone, once-daily tacrolimus, and mycophenolic acid. The mean follow-up was 53 months (3-96 months).

Results:

A total of 26 individuals underwent an attempt at desensitization of whom 24 patients underwent immediate transplant. One patient had a rebound in titers and subsequently was transplanted from a blood group compatible living donor. A second patient had an unrelated medical issue and desensitization was discontinued. Five-year patient survival was 96% and death censored allograft survival was 92%. Posttransplant anti-A or anti-B titers were monitored daily for the first 7 days posttransplant and every 2 days from days 7 to 14. There were no acute rejections seen in this cohort of transplant recipients.

Limitations:

As our protocol was first initiated as proof of concept, a few recipients had low initial isohemagglutinin titers. This may have contributed to improved clinical outcomes.

Conclusions:

ABO column immunoadsorption with specific columns is a safe and effective method for ABOi living donor kidney transplantation, and an option when KPD is less than ideal.

Trial not registered as this was a retrospective cohort review.

ABO-Incompatible Robotic-Assisted Kidney Transplantation in the Obese Recipient

Objective: The objective of this preliminary study was to report and compare the peri-operative and functional results of ABO-incompatible (ABOi) living-donor robotic-assisted kidney transplantation (RAKT), ABO-compatible (ABOc) living-donor RAKT, and ABOi living-donor open kidney transplantation (OKT).

Materials and Methods: For the present retrospective study, we analyzed data of consecutive patients who underwent ABOi or ABOc-RAKT and ABOi-OKT, from January 2015 to December 2019, in one French academic center. Patients' baseline characteristics, operative, and functional outcomes were compared between ABOi-RAKT, ABOc-RAKT, and ABOi-OKT.

Results: 29 RAKT, including 7 ABOi-RAKT, and 56 ABOi-OKT were performed in our center. Median follow-up was 2.0 years. Median recipient age, pre-emptive kidney transplantation rate, sex ratio and desensitization procedures were similar in ABOi-RAKT, ABOc-RAKT, and ABOi-OKT groups. Recipient BMI at transplantation was statistically higher in ABOi and ABOc-RAKT groups compared to ABOi-OKT. The surgical site complication (principally infection-related) rate was lower in ABOi-RAKT, without statistical differences (0 vs. 8.9%, respectively, in ABOi-RAKT and ABOi-OKT, p = 0.7). The delayed graft function rate was 0% in ABOi-RAKT, 13.6% in ABOc-RAKT, and 10.7% in ABOi-OKT (p = 0.6). The post-transplantation blood transfusion rate was statistically higher in the ABOi-OKT group (14.3 vs. 13.6 vs. 57.1% in ABOi-RAKT, ABOc-RAKT, and ABOi-OKT, respectively, p = 0.001). The kidney graft survival at 1 month and at last follow-up was not different between ABOi-RAKT and ABOi-OKT.

Conclusion: Our data support the use of ABOi-RAKT to restore accessibility to kidney transplantation for obese patients to the greatest extent possible. Large series are required to confirm these encouraging data from a single center.

Current protocols and outcomes of ABO-incompatible kidney transplantation

One of the principal obstacles in transplantation from living donors is that approximately 30% are immunologically incompatible because of the presence in the recipient of antibodies directed against the human leukocyte antigen system of the donor or because of the incompatibility of the ABO system. The aim of this review is to describe the more recent data from the literature on the different protocols used and the clinical outcomes of ABO-incompatible kidney transplantation. Two different strategies are used to overcome these barriers: desensitization of the recipient to remove the antibodies and to prevent their rebound after transplantation and the exchange of organs between two or more pairs. The largest part of this review is dedicated to describing the techniques of desensitization. Even if the first reports of successful renal transplantation between ABO-incompatible pairs have been published by 1980, the number of ABO-incompatible transplants increased substantially in this century because of our improved knowledge of the immune system and the availability of new drugs. Rituximab has substantially replaced splenectomy. The technique of apheresis has improved and more recently a tailored desensitization proved to be the more efficient strategy avoiding an excess of immunosuppression with the related side effects. Recent reports document outcomes for such transplantation similar to the outcomes of standard transplantation.

Peripheral blood transcriptome analysis and development of classification model for diagnosing antibody-mediated rejection vs accommodation in ABO-incompatible kidney transplant

The major obstacle to successful ABO blood group-incompatible kidney transplantation (ABOi KT) is antibody-mediated rejection (AMR). This study aimed to investigate transcriptional profiles through RNA sequencing and develop a minimally invasive diagnostic tool for discrimination between accommodation and early acute AMR in ABOi KT. Twenty-eight ABOi KT patients were selected: 18 with accommodation and 10 with acute AMR at the 10th day posttransplant protocol biopsy. Complete transcriptomes of their peripheral blood were analyzed by RNA sequencing. Candidate genes were selected by bioinformatics analysis, validated with quantitative polymerase chain reaction, and used to develop a classification model to diagnose accommodation. A total of 1385 genes were differentially expressed in accommodation compared with in AMR with P-adjusted < .05. Functional annotation and gene set enrichment analysis identified several immune-related and immunometabolic pathways. A 5-gene classification model including COX7A2L, CD69, CD14, CFD, and FOXJ3 was developed by logistic regression analysis. The model was further validated with an independent cohort and discriminated between accommodation and AMR with 92.7% sensitivity, 85.7% specificity, and 91.7% accuracy. Our study suggests that a classification model based on peripheral blood transcriptomics may allow minimally invasive diagnosis of acute AMR vs accommodation and subsequent patient-tailored immunosuppression in ABOi KT.

Molecular Patterns Discriminate Accommodation and Subclinical Antibody-mediated Rejection in Kidney Transplantation

BACKGROUND

Accommodation in ABO-incompatible (ABOi) transplantation and subclinical antibody-mediated rejection in HLA-incompatible (HLAi) transplantation share several morphological similarities. Because the clinical long-term outcomes differ, we hypothesized different molecular processes involved in ABOi transplantation and subclinical antibody-mediated rejection.

METHODS

Using Illumina Human HT-12 v4 Expression BeadChips, the whole transcriptome was evaluated based on 3-month protocol C4d+ biopsies in otherwise stable ABOi and HLAi kidney grafts, as well as in C4d-negative HLA-compatible grafts exhibiting normal histological findings. Top differently regulated genes were further validated using real-time quantitative polymerase chain reaction in another patient cohort and complement regulatory proteins by immunohistochemistry.

RESULTS

In the case of genes involved in immune response-related biological processes, ABOi and HLAi cohorts had similar transcriptomic profiles to C4d-negative controls. The majority of deregulated genes in the ABOi and HLAi groups consisted of metallothioneins and epithelial transporter genes. Increased expression of epithelial transporters (SLC4A1, SLC4A9, SLC17A3, SLC12A3, and SLC30A2) and class 1 metallothioneins (MT1F, MT1G, and MT1X) in HLAi transplantation was validated by real-time quantitative polymerase chain reaction. In comparison to controls, both incompatible cohorts were characterized by the upregulation of intrarenal complement regulatory genes. CD46 and CD59 transcripts were increased in the ABOi cohort, whereas CD46 solely in HLAi group, and CD59 protein expression was similar in both incompatible groups.

CONCLUSIONS

Several epithelial transporters and metallothioneins discriminate subclinical antibody-mediated rejection in HLAi transplantation from accommodation in ABOi transplantation, which suggest different involved downstream mechanisms and increased risk of injury in HLAi settings. Metallothioneins with their antioxidative properties may help to attenuate the inflammation response induced by donor-specific anti-HLA antibody binding.

Complement activation and long-term graft function in ABO-incompatible kidney transplantation

BACKGROUND

ABO-incompatible and ABO-compatible kidney transplantation are equivalent in terms of short-term graft and patient survival. This is thought to be the result of ABO-incompatible graft accommodation, which occurs when anti-blood group antibodies re-occur after transplantation but somehow do not yield their detrimental effect. The underlying mechanism is unclear, but one of the hypotheses is that this is the result of complement inhibition. Since virtually all ABO-incompatible graft biopsies are C4d positive, this complement inhibition must occur somewhere in the complement cascade after the formation of C4d has already taken place, but where exactly is unclear. It is also unclear whether complement inhibition is complete. Incomplete accommodation could explain why recent studies have shown that long-term graft function in ABO-incompatible transplantation is somewhat inferior to ABO-compatible kidney transplantation.

AIM

To unravel the relationship between pre-transplant anti-ABO antibodies, complement activation, and long-term graft function.

METHODS

We included all 27 ABO-incompatible transplantations that were performed between 2008 and 2013 at the Academic Medical Center Amsterdam and the University Medical Center Groningen. For each ABO-incompatible transplantation, we included four ABO-compatible controls matched by age, sex, and transplantation date.

RESULTS

Graft and patient survival were not significantly different. The slope of kidney function during five-year follow-up was also not significantly different, but ABO-incompatible recipients did have a lower kidney function at three months (creatinine clearance 58 vs 69 mL/min, P = 0.02, Modification of Diet in Renal Disease 46 vs 52 mL/min/1.73 m², P = 0.08), due to a high rate of early rejection (33% vs 15%, P = 0.03), mostly T-cell mediated. Pre-transplant anti-ABO IgG titers were positively correlated with C5b-9 staining, which itself was positively correlated with the occurrence of T-cell mediated rejection. This may be the result of concurrent C5a formation, which could function as a costimulatory signal for T-cell activation.

CONCLUSION

Co-stimulation of T-cell activation by ongoing complement activation by anti-ABO antibodies may be responsible for an impaired long-term graft function in ABO-incompatible kidney transplantation.

Latest insights on ABO-incompatible living-donor renal transplantation

This review summarizes the latest insights on ABO‐incompatible living‐donor renal transplantation. Desensitization protocols and clinical outcomes were investigated, and a comparison was made with kidney‐paired donation, which is not permitted in Japan for ethical reasons. Although renal transplantation is greatly beneficial for most patients with end‐stage kidney disease, many of these patients must remain on dialysis therapy for extended periods due to the scarcity of organs from deceased donors. ABO blood type incompatibility was once believed to be a contraindication to renal transplantation due to the increased risk for antibody‐mediated rejection and early graft loss attributable to isoagglutinins. Recently, pretransplant desensitization strategies, such as removal of isoagglutinins and antibody‐producing cells, have achieved successful outcomes, although it remains unclear whether graft survival and patient morbidity are equivalent to those for ABO‐compatible renal transplantation. The present review suggested that ABO‐incompatible living‐donor renal transplantation might be a favorable radical renal replacement therapy for patients with end‐stage kidney disease.

The multifaceted role of complement in kidney transplantation

Increasing evidence indicates an integral role for the complement system in the deleterious inflammatory reactions that occur during critical phases of the transplantation process, such as brain or cardiac death of the donor, surgical trauma, organ preservation and ischaemia-reperfusion injury, as well as in humoral and cellular immune responses to the allograft. Ischaemia is the most common cause of complement activation in kidney transplantation and in combination with reperfusion is a major cause of inflammation and graft damage. Complement also has a prominent role in antibody-mediated rejection (ABMR) owing to ABO and HLA incompatibility, which leads to devastating damage to the transplanted kidney. Emerging drugs and treatment modalities that inhibit complement activation at various stages in the complement cascade are being developed to ameliorate the damage caused by complement activation in transplantation. These promising new therapies have various potential applications at different stages in the process of transplantation, including inhibiting the destructive effects of ischaemia and/or reperfusion injury, treating ABMR, inducing accommodation and modulating the adaptive immune response.

Repeat A2 Into B Kidney Transplantation After Failed Prior A2 Into B Transplant: A Case Report

Kidneys from donors with blood type A2 can be successfully transplanted into blood type B and O recipients without the need for desensitization if the recipient's starting anti-A hemagglutinin titer is within an acceptable range. National kidney allocation policy now offers priority for eligible B recipients to receive A2 or A2B deceased donor kidneys, and therefore, the frequency with which A2 or A2B to B transplants will occur is expected to increase. The precise mechanisms by which antibody-mediated rejection is averted in these cases despite the presence of both circulating anti-A antibody and expression of the A2 antigen on the graft endothelium are not known. Whether this process mirrors proposed mechanisms of accommodation, which can occur in recipients of ABO incompatible transplants, is also not known. Repeated exposure to mismatched antigens after retransplantation could elicit memory responses resulting in antibody rebound and accelerated antibody-mediated rejection. Whether this would occur in the setting of repeated A2 donor exposure was uncertain. Here we report the case of a patient with history of a prior A2 to B transplant which failed owing to nonimmunologic reasons; the patient successfully underwent a repeat A2 to B transplant. Neither rebound in anti-A2 antibody nor clinical evidence of antibody-mediated rejection were observed after the transplant. Current kidney allocation will likely enable more such transplants in the future, and this may provide a unique patient population in whom the molecular mechanisms of incompatible graft accommodation may be investigated.

Molecular Assessment of C4d-Positive Renal Transplant Biopsies Without Evidence of Rejection

Introduction

Immunohistochemical staining for C4d in peritubular capillaries has been part of antibody-mediated rejection (AbMR) definition in the Banff Classification for Allograft Pathology since 2003. However, it has limited sensitivity and specificity, therefore the clinical significance of C4d-positive biopsies without evidence of rejection (C4d+ WER) is unknown. We investigated the transcript levels of genes associated with AbMR in C4d+ WER biopsies from both ABO-compatible and incompatible renal transplant patients.

Methods

RNA was extracted from formalin-fixed paraffin-embedded renal transplant biopsies (n = 125) and gene expression analysis of 35 AbMR-associated transcripts carried out using the NanoString nCounter system.

Results

AbMR-associated transcripts were significantly increased in samples with AbMR or suspicious AbMR. A subgroup of 17 of 35 transcripts that best distinguished AbMR from C4d-negative biopsies without evidence of rejection was used to study C4d+ WER samples. There was no differential expression between C4d-negative and C4d+ WER from both ABO-incompatible and -compatible transplants. The geometric mean of 17 differentially expressed genes was used to assign the C4d+ WER biopsies a high- or low-AbMR transcript score. Follow-up biopsies showed AbMR within 1 year of initial biopsy in 5 of 7 high-AbMR transcript patients but only 2 of 46 low-AbMR transcript patients. In multivariate logistic regression analysis, elevated transcript levels in a C4d+ WER biopsy were associated with increased odds for biopsy-proven AbMR on follow-up (P = 0.032, odds ratio 16.318), whereas factors including donor-specific antibody (DSA) status and time since transplantation were not.

Conclusion

Gene expression analysis in C4d+ WER samples has the potential to identify patients at higher risk of developing AbMR.

Distribution of Anti-ABO Immunoglobulin G Subclass and C1q Antibody in ABO-incompatible Kidney Transplantation

INTRODUCTION

To investigate the correlation between serum anti-ABO immunoglobulin G (IgG) and IgG subclasses, anti-ABO IgG subclasses were measured by flow cytometry (FCM) in ABO-incompatible (ABOi) kidney transplant recipients. We also evaluated baseline anti-ABO C1q antibody.

METHOD

Baseline anti-ABO IgG titers were measured by both FCM and column agglutination technique methods in 18 ABOi kidney transplant recipients. The mean florescence intensity (MFI) ratios of baseline anti-ABO IgG subclasses and anti-ABO C1q antibody were obtained by FCM and followed-up after rituximab treatment, each plasmapheresis (PP) session, and kidney transplantation. Correlation between the values of IgG subclass and total IgG titer was analyzed.

RESULTS

The baseline MFI ratios of total IgG, IgG1, IgG2, IgG3, and IgG4 were 202.46, 62.41, 30.01, 1.04, and 1.13, respectively. The MFI ratios of IgG1, IgG2, and total IgG measured at baseline and pre-PP were positively correlated with the baseline ABO titer was measured using the column agglutination technique. The numbers of PP sessions to reach the target titer were correlated with the baseline IgG and IgG1 levels. IgG1 and IgG2 as well as total IgG were removed effectively after serial PP. Anti-ABO C1q antibody was neither detected nor correlated with total IgG and any IgG subclasses.

CONCLUSIONS

Our findings suggest that IgG1 and IgG2 are the dominant IgG subclass in ABOi kidney transplant recipients. Baseline levels of IgG1 and IgG2 were correlated with baseline total IgG titer. However, anti-ABO C1q antibody was not detected in the present study.

Similar Microvascular Inflammation and Tubulointerstitial Injury in ABO-Incompatible and Matched ABO-Compatible Kidney Allografts

ABO-incompatible (ABOi) kidney transplantation represents a viable tool to increase the donor pool for kidney transplantation, however, increased alloimmune response has been debated. The early outcomes of 25 low-risk ABOi kidney transplant recipients were compared with thoroughly matched 50 ABO-compatible (ABOc) ones. The matching process was based on gender and age of recipients and immunologic parameters, such as panel reactive antibodies, number of human leukocyte antigen mismatches, and transplantation era. Three-month protocol kidney graft biopsy Banff scores and 1-year clinical outcomes were compared. Apart from C4d positivity, no statistically significant differences were found regarding the Banff scores between the two groups. Similarly, microvascular inflammation and tubulointerstitial injury revealed no differences either. The eGFR at 3 months and 1 year was similar in both groups. In conclusion, blood group incompatibility yields no additional microvascular and tubulointerstitial graft injury if desensitization protocol was applied to low-risk kidney transplant recipients.

Accommodation in ABO-incompatible organ transplants

Accommodation refers to a condition in which a transplant (or any tissue) appears to resist immune-mediated injury and loss of function. Accommodation was discovered and has been explored most thoroughly in ABO-incompatible kidney transplantation. In this setting, kidney transplants bearing blood group A or B antigens often are found to function normally in recipients who lack and hence produce antibodies directed against the corresponding antigens. Whether accommodation is owed to changes in anti-blood group antibodies, changes in antigen or a change in the response of the transplant to antibody binding are critically reviewed and a new working model that allows for the kinetics of development of accommodation is put forth. Regardless of how accommodation develops, observations on the fate of ABO-incompatible transplants offer lessons applicable more broadly in transplantation and in other fields.

Defining the phenotype of antibody-mediated rejection in kidney transplantation: Advances in diagnosis of antibody injury

The diagnostic criteria for antibody-mediated rejection (ABMR) are constantly evolving in light of the evidence. Inclusion of C4d-negative ABMR has been one of the major advances in the Banff Classification in recent years. Currently Banff 2015 classification requires evidence of donor specific antibodies (DSA), interaction between DSA and the endothelium, and acute tissue injury (in the form of microvasculature injury (MVI); acute thrombotic microangiopathy; or acute tubular injury in the absence of other apparent cause). In this article we review not only the ABMR phenotypes acknowledged in the most recent Banff classification, but also the phenotypes related to novel pathogenic antibodies (non-HLA DSA, antibody isoforms and subclasses, complement-binding functionality) and molecular diagnostic tools (gene transcripts, metabolites, small proteins, cytokines, and donor-derived cell-free DNA). These novel tools are also being considered for the prognosis and monitoring of treatment response. We propose that improved classification of ABMR based on underlying pathogenic mechanisms and outcomes will be an important step in identifying patient-centered therapies to extend graft survival.

Effects of Neutralization by Soluble ABH Antigens Produced by Transplanted Kidneys From ABO-Incompatible Secretor Donors

BACKGROUND

Grafts survive despite blood group antigens on the transplant being continuously exposed to antibodies in the blood of recipients in ABO-incompatible kidney transplantation (ABOi KT), owing to the mechanism of accommodation. We analyzed the immunodynamics of soluble ABH antigens in allografts from secretor donors and the influence of such immunodynamics on accommodation and subsequent graft survival in ABOi KT.

METHODS

The genotype of a known human β-galactoside α-1,2-fucosyltransferase gene (FUT2), which determines soluble ABH antigen secretor status, was established in 32 donors for ABOi KT at the Severance Hospital, from June 2010 to July 2015. Clinical outcomes of recipients, such as anti-A/B antibody titer change, renal function, and graft survival, were evaluated.

RESULTS

Twenty-five donors were secretors (78.1%), and seven were nonsecretors (21.9%). The frequency of anti-A/B IgG or IgM antibody titer elevation or reduction post-transplantation was not significantly related to donor secretor status. However, IgM titer was rapidly reduced in recipients transplanted from nonsecretor donors (P=0.01), which could be explained by the lack of absorption effect of soluble antigens, enhancing the binding of antibodies to antigens in the allografts. Interestingly, soluble ABH antigens did not affect rejection-free graft survival, which may be due to the nature of β-galactoside α-1,2-fucosyltransferase.

CONCLUSIONS

Soluble ABH antigens produced by transplanted kidneys from secretor donors played a role in inducing accommodation within three months of KT through neutralization; however, major graft outcomes were not affected.

Endothelial Cells in Antibody-Mediated Rejection of Kidney Transplantation: Pathogenesis Mechanisms and Therapeutic Implications

Antibody-mediated rejection (AMR) has been identified as a main obstacle for stable immune tolerance and long survival of kidney allografts. In spite of new insights into the underlying mechanisms of AMR, accurate diagnosis and efficient treatment are still challenges in clinical practice. Endothelium is the first barrier between recipients' immune systems and grafts in vascularized organ transplants. Considering that endothelial cells express a number of antigens that can be attacked by various allo- and autoantibodies, endothelial cells act as main targets for the recipients' humoral immune responses. Importantly, emerging evidence has shown that endothelial cells in transplants could also initiate protective mechanisms in response to immune injuries. A better understanding of the role of endothelial cells during the pathogenesis of AMR might provide novel therapeutic targets. In the present review, we summarize the antigens expressed by endothelial cells and also discuss the activation and accommodation of endothelial cells as well as their clinical implications. Collectively, the progress discussed in this review indicates endothelial cells as promising targets to improve current diagnosis and therapeutic regimens for AMR.

Molecular Assessment of Microcirculation Injury in Formalin-Fixed Human Cardiac Allograft Biopsies With Antibody-Mediated Rejection

Precise diagnosis of antibody-mediated rejection (AMR) in cardiac allograft endomyocardial biopsies (EMBs) remains challenging. This study assessed molecular diagnostics in human EMBs with AMR. A set of 34 endothelial, natural killer cell and inflammatory genes was quantified in 106 formalin-fixed, paraffin-embedded EMBs classified according to 2013 International Society for Heart and Lung Transplantation (ISHLT) criteria. The gene set expression was compared between ISHLT diagnoses and correlated with donor-specific antibody (DSA), endothelial injury by electron microscopy (EM) and prognosis. Findings were validated in an independent set of 57 EMBs. In the training set (n = 106), AMR cases (n = 70) showed higher gene set expression than acute cellular rejection (ACR; n = 21, p < 0.001) and controls (n = 15, p < 0.0001). Anti-HLA DSA positivity was associated with higher gene set expression (p = 0.01). Endothelial injury by electron microscopy strongly correlated with gene set expression, specifically in AMR cases (r = 0.62, p = 0.002). Receiver operating characteristic curve analysis for diagnosing AMR showed greater accuracy with gene set expression (area under the curve [AUC] = 79.88) than with DSA (AUC = 70.47) and C4d (AUC = 70.71). In AMR patients (n = 17) with sequential biopsies, increasing gene set expression was associated with inferior prognosis (p = 0.034). These findings were confirmed in the validation set. In conclusion, biopsy-based molecular assessment of antibody-mediated microcirculation injury has the potential to improve diagnosis of AMR in human cardiac transplants.

The Complement System and Antibody-Mediated Transplant Rejection

Complement activation is an important cause of tissue injury in patients with Ab-mediated rejection (AMR) of transplanted organs. Complement activation triggers a strong inflammatory response, and it also generates tissue-bound and soluble fragments that are clinically useful markers of inflammation. The detection of complement proteins deposited within transplanted tissues has become an indispensible biomarker of AMR, and several assays have recently been developed to measure complement activation by Abs reactive to specific donor HLA expressed within the transplant. Complement inhibitors have entered clinical use and have shown efficacy for the treatment of AMR. New methods of detecting complement activation within transplanted organs will improve our ability to diagnose and monitor AMR, and they will also help guide the use of complement inhibitory drugs.

Desensitization in ABO-Incompatible Kidney Transplantation With Low ABO Iso-Agglutinin Titers

BACKGROUND

In ABO-incompatible (ABOi) kidney transplantation (KT) with low iso-agglutinin (IG) titers (IGT), standard pre-conditioning treatment might be excessive. To try to answer this question, we evaluated the pre-conditioning requirements of a group of ABOi KT with low ABO IGT in our center. Our main objective was to assess desensitization requirements for ABOi KT with low IGT (<16) at Hospital Clinic of Barcelona from 2006 to 2014.

METHODS

A retrospective study of desensitization (rituximab and plasma exchange [PE]) requirements for ABOi KT with IGT <16 was conducted.

RESULTS

One and 5 years after KT, patient survival was 100%. Renal graft survival was 90% at 1 and 5 years after KT. Mean PE performed before KT was 1.7 (standard deviation [SD], 1.703); 50% of the patients did not receive PE after transplantation, 30% received 2 sessions of PE, and 20% received only 1. The average is 0.8 (SD, 0.91).Follow-up IG determinations remained with low titers (≤8/8). No rebounds of titers were observed during the first 4 to 6 months after transplantation.

CONCLUSIONS

Recipients with IGT ≤8 required none or only 1 PE session to reach acceptable titers (titers ≤4) to perform ABOi KT safely. This information is useful to assess the possibility of a minimized desensitization protocol in ABOi KT donors with low titers of IG to reduce adverse effects, reduce cost, and simplify pre-transplant logistics.

A Promoter Polymorphism in the CD59 Complement Regulatory Protein Gene in Donor Lungs Correlates With a Higher Risk for Chronic Rejection After Lung Transplantation

Complement activation leads primarily to membrane attack complex formation and subsequent target cell lysis. Protection against self-damage is regulated by complement regulatory proteins, including CD46, CD55, and CD59. Within their promoter regions, single-nucleotide polymorphisms (SNPs) are present that could influence transcription. We analyzed these SNPs and investigated their influence on protein expression levels. A single SNP configuration in the promoter region of CD59 was found correlating with lower CD59 expression on lung endothelial cells (p = 0.016) and monocytes (p = 0.013). Lung endothelial cells with this SNP configuration secreted more profibrotic cytokine IL-6 (p = 0.047) and fibroblast growth factor β (p = 0.036) on exposure to sublytic complement activation than cells with the opposing configuration, whereas monocytes were more susceptible to antibody-mediated complement lysis (p < 0.0001). Analysis of 137 lung transplant donors indicated that this CD59 SNP configuration correlates with impaired long-term survival (p = 0.094) and a significantly higher incidence of bronchiolitis obliterans syndrome (p = 0.046) in the recipient. These findings support a role for complement in the pathogenesis of this posttransplant complication and are the first to show a deleterious association of a donor CD59 promoter polymorphism in lung transplantation.

Acute Cellular Rejection and C4d Positivity in Heart Transplantation : A Manifestation of Asymptomatic Antibody-Mediated Rejection?

OBJECTIVES

The role of routine C4d staining in endomyocardial biopsy specimens is uncertain. The implications of a diagnosis of acute cellular rejection (ACR) with a positive C4d with or without any evidence of antibody-mediated rejection (AMR) are unclear. This study sought to evaluate a distinct phenotype of ACR+/C4d+ in AMR- patients.

METHODS

Data on C4d, ACR, and AMR were collected. Donor-specific antibody (DSA), panel-reactive antibody (PRA), flow crossmatch, and data on ACR and AMR episodes were also reviewed.

RESULTS

Thirty-five patients were followed. Group I with C4d+ biopsy specimens was compared with group II with C4d- biopsy specimens. ACR greater than 1R was higher in group I compared with group II (50% vs 7.4%; P = .01). Clinical suspicion of AMR, positive retrospective crossmatches, and detection of de novo DSA were also higher in group I.

CONCLUSIONS

Our result indicate that C4d and ACR positivity in posttransplant patients may be a harbinger of a subclinical form of asymptomatic AMR.

Strategies to overcome the ABO barrier in kidney transplantation

Kidney transplantation across the ABO blood group barrier was long considered a contraindication for transplantation, but in an effort to increase donor pools, specific regimens for ABO-incompatible (ABOi) transplantation have been developed. These regimens are now widely used as an integral part of the available treatment options. Various desensitization protocols, commonly based on transient depletion of preformed anti-A and/or anti-B antibodies and modulation of B-cell immunity, enable excellent transplant outcomes, even in the long-term. Nevertheless, the molecular mechanisms behind transplant acceptance facilitated by a short course of anti-humoral treatment are still incompletely understood. With the evolution of efficient clinical programmes, tailoring of recipient preconditioning based on individual donor-recipient blood type combinations and the levels of pretransplant anti-A/B antibodies has become possible. In the context of low antibody titres and/or donor A2 phenotype, immunomodulation and/or apheresis might be dispensable. A concern still exists, however, that ABOi kidney transplantation is associated with an increased risk of surgical and infectious complications, partly owing to the effects of extracorporeal treatment and intensified immunosuppression. Nevertheless, a continuous improvement in desensitization strategies, with the aim of minimizing the immunosuppressive burden, might pave the way to clinical outcomes that are comparable to those achieved in ABO-compatible transplantation.

Current progress in ABO-incompatible kidney transplantation

ABO-incompatible kidney transplantation (ABOi KT) was introduced to expand the donor pool and minimize shortage of kidneys for transplantation. Because improved outcomes of ABOi KT were reported in Japan in the early 2000s, the number of ABOi KTs has been increasing worldwide. In addition, a better understanding of immune pathogenesis and subsequent aggressive immunosuppression has helped to make effective desensitization protocols. Current strategies of ABOi KT consist of pretransplant antibody removal using plasmapheresis or immunoadsorption to prevent hyperacute rejection and potent maintenance immunosuppression, such as tacrolimus and mycophenolate mofetil, to inhibit antibody-mediated rejection. Recent outcomes of ABOi KT are comparable with ABO-compatible KT. However, there are still many problems to be resolved. Very high anti-ABO antibody producers are difficult to desensitize. In addition, ABOi KT is associated with an increased risk of infection and possibly malignancy due to aggressive immunosuppression. Optimization of desensitization and patient-tailored immunosuppression protocols are needed to achieve better outcomes of ABOi KT. This review provides an overview of the history, immune mechanism, immunosuppressive protocol, outcomes, current obstacles, and future perspectives in ABOi KT.

Overcoming the ABO incompatibility barrier in pediatric renal transplantation

BACKGROUND

ABO blood type incompatibility between a donor and recipient is generally considered a contraindication to kidney transplantation.

CASE CHARACTERISTICS

A 12-year-old boy presented with end stage renal disease (blood group B), with the only healthy available donor being mother (blood group AB). The child received renal transplant with mother as the donor, with a designed desensitization and immunosuppressive protocol.

OBSERVATION

At 6 months, child is doing well, with stable graft function.

MESSAGE

ABO-incompatible kidney transplantation is a valid alternative for children with end stage renal disease. This is the first report from India of a Pediatric ABO incompatible renal transplant.

Difference in outcomes after antibody-mediated rejection between abo-incompatible and positive cross-match transplantations

Graft survival seems to be worse in positive cross-match (HLAi) than in ABO-incompatible (ABOi) transplantation. However, it is not entirely clear why these differences exist. Sixty-nine ABOi, 27 HLAi and 10 combined ABOi+HLAi patients were included in this retrospective study, to determine whether the frequency, severity and the outcome of active antibody-mediated rejection (AMR) were different. Five-year death-censored graft survival was better in ABOi than in HLAi and ABOi+HLAi patients (99%, 69% and 64%, respectively, P = 0.0002). Features of AMR were found in 38%, 95% and 100% of ABOi, HLAi and ABOi+HLAi patients that had a biopsy, respectively (P = 0.0001 and P = 0.001). After active AMR, a declining eGFR and graft loss were observed more frequently in HLAi and HLAi+ABOi than in ABOi patients. The poorer prognosis after AMR in HLAi and ABOi+HLAi transplantations was not explained by a higher severity of histological lesions or by a less aggressive treatment. In conclusion, ABOi transplantation offers better results than HLAi transplantation, partly because AMR occurs less frequently but also because outcome after AMR is distinctly better. HLAi and combined ABOi+HLAi transplantations appear to have the same outcome, suggesting there is no synergistic effect between anti-A/B and anti-HLA antibodies.

Differences in chronic intragraft inflammation between positive crossmatch and ABO-incompatible kidney transplantation

BACKGROUND

ABO-incompatible kidney transplantations (ABOiKTxs) seem to have better long-term outcomes than positive crossmatch kidney transplantations (+XMKTxs).

METHODS

This study aimed to assess the differences in chronic injury on histologic findings on 1- and 5-year surveillance biopsies and the clinical outcomes in living-donor kidney transplantations performed between May 1999 and November 2006 including 102 +XMKTxs, 73 ABOiKTxs, and 652 conventional KTxs.

RESULTS

Although 5-year patient survival was similar between groups, graft loss between 1 and 5 years was similar in ABOiKTx (2.6% per year) and conventional KTx (1.7% per yr), and both were lower than that of +XMKTx (5.8% per year). At 5 years, renal function was similar in ABOiKTx and conventional KTx, and both were higher than that of +XMKTx, which had higher rates of inflammation and chronic glomerulopathy on both 1- and 5-year biopsies. Despite having evidence of less chronic injury, ABOiKTx showed a higher rate of intragraft complement activation (C4d deposition) at 5 years compared with +XMKTx (77.8% vs. 18.9%, P<0.001).

CONCLUSION

These data suggest that +XMKTxs have high rates of chronic inflammation at 1 and 5 years after transplantation, which may explain the higher rates of graft loss and lower renal function compared with other factors such as anti-donor antibody or intragraft complement deposition.

One-year protocol biopsies from ABO-incompatible renal allografts compared with a matched cohort of ABO-compatible allografts

Introduction

Early acute antibody-mediated rejection (ABMR) occurs more frequently in ABO-incompatible (ABOi) than in ABO-compatible (ABOc) kidney transplantation. This could lead to increased inflammation/scarring in the ABOi grafts. Protocol biopsy data in ABOi kidney recipients are scarce.

Methods

A single-center retrospective matched cohort study was conducted. Eighty adult living donor (LD) renal transplant recipients without HLA donor-specific antibodies (DSA) transplanted between 2009 and 2012 were included; 20 ABOi and 60 ABOc controls matched for donor age and transplantation year. Protocol biopsies at one yr were scored according to the Banff classification. Three sums of scores were constructed: tubulointerstitial inflammation (t + i = 0 vs. >0), microvascular inflammation (g + ptc = 0 vs. >0), scarring/hyalinosis (ci + ct + cv + ah ≤ 1 vs. >1. Scores and presence of subclinical rejection (SCR) at one yr were compared.

Results

Protocol biopsy findings at one yr in the ABOi vs. ABOc matched control group were not statistically different: (t + i) > 0, 30% vs. 20%; (g + ptc) > 0, 5% vs. 8%; (ci + ct + cv + ah) > 1, 85% vs. 60%, respectively. No transplant glomerulopathy occurred. SCR rate at one yr was 30% vs. 18%, subclinical ABMR 5% vs. 7% (all with de novo HLA DSA).

Conclusion

One-year protocol biopsies of ABOi and ABOc LD recipients do not differ in chronic changes, inflammation, or SCRs.

Complement Interception Across Humoral Incompatibility in Solid Organ Transplantation: A Clinical Perspective

The humoral barrier in transplant biology is the result of preformed donor-specific antibodies (DSAs), directed either against human leukocyte antigens (HLA) or non-HLA antigens such as blood group (ABO) molecules. The term "sensitization" applies to patients carrying these antibodies. Transplantation is widely accepted as a life-saving opportunity for patients with terminal end-organ disease. However, in sensitized patients, transplant outcome is hampered by antibody-mediated rejection (AMR) as a consequence of DSA exposure. Furthermore, sensitized patients have limited access to "matched" organs from the both living and deceased donor pool.Considering the crucial role of the complement system in the pathophysiology of AMR and the availability of complement intervention therapeutics, there is a growing interest in complement-targeting strategies. This review highlights the emerging importance of monitoring and modulation of the complement system in the context of enabling transplantation across humoral incompatibility in sensitized recipients with preformed anti-HLA or natural anti-ABO antibodies. It also discusses the significance of the complement system in the induction of accommodation and further emphasizes current and future perspectives of novel complement therapeutics.

The PROCARE consortium: toward an improved allocation strategy for kidney allografts

Kidney transplantation is the best treatment option for patients with end-stage renal failure. At present, approximately 800 Dutch patients are registered on the active waiting list of Eurotransplant. The waiting time in the Netherlands for a kidney from a deceased donor is on average between 3 and 4 years. During this period, patients are fully dependent on dialysis, which replaces only partly the renal function, whereas the quality of life is limited. Mortality among patients on the waiting list is high. In order to increase the number of kidney donors, several initiatives have been undertaken by the Dutch Kidney Foundation including national calls for donor registration and providing information on organ donation and kidney transplantation. The aim of the national PROCARE consortium is to develop improved matching algorithms that will lead to a prolonged survival of transplanted donor kidneys and a reduced HLA immunization. The latter will positively affect the waiting time for a retransplantation. The present algorithm for allocation is among others based on matching for HLA antigens, which were originally defined by antibodies using serological typing techniques. However, several studies suggest that this algorithm needs adaptation and that other immune parameters which are currently not included may assist in improving graft survival rates. We will employ a multicenter-based evaluation on 5429 patients transplanted between 1995 and 2005 in the Netherlands. The association between key clinical endpoints and selected laboratory defined parameters will be examined, including Luminex-defined HLA antibody specificities, T and B cell epitopes recognized on the mismatched HLA antigens, non-HLA antibodies, and also polymorphisms in complement and Fc receptors functionally associated with effector functions of anti-graft antibodies. From these data, key parameters determining the success of kidney transplantation will be identified which will lead to the identification of additional parameters to be included in future matching algorithms aiming to extend survival of transplanted kidneys and to diminish HLA immunization. Computer simulation studies will reveal the number of patients having a direct benefit from improved matching, the effect on shortening of the waiting list, and the decrease in waiting time.