ABO‐incompatible kidney transplantation can be successfully conducted by monitoring IgM isoagglutinin titers during desensitization

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.

Advancement in preoperative desensitization therapy for ABO incompatible kidney transplantation recipients

ABO incompatibility has long been considered an absolute contraindication for kidney transplantation. However, with the increasing number of patients with ESRD in recent years, ABO-incompatible kidney transplantation (ABOi-KT) has expanded the types of donors by crossing the blood group barrier through preoperative desensitization therapy. At present, the desensitization protocols consist of removal of preexisting ABO blood group antibody titers and prevention of ABO blood group antibody return. Studies have suggested similar patient and graft survival among ABOi-KT and ABOc-KT recipients. In this review, we will summarize the effective desensitization regimens of ABOi-KT, aiming to explore effective ways to improve the success rate and the long-term survival rate of ABOi-KT recipients.

Recommendations for living donor kidney transplantation

This Guide for Living Donor Kidney Transplantation (LDKT) has been prepared with the sponsorship of the Spanish Society of Nephrology (SEN), the Spanish Transplant Society (SET), and the Spanish National Transplant Organization (ONT). It updates evidence to offer the best chronic renal failure treatment when a potential living donor is available. The core aim of this Guide is to supply clinicians who evaluate living donors and transplant recipients with the best decision-making tools, to optimise their outcomes. Moreover, the role of living donors in the current KT context should recover the level of importance it had until recently. To this end the new forms of incompatible HLA and/or ABO donation, as well as the paired donation which is possible in several hospitals with experience in LDKT, offer additional ways to treat renal patients with an incompatible donor. Good results in terms of patient and graft survival have expanded the range of circumstances under which living renal donors are accepted. Older donors are now accepted, as are others with factors that affect the decision, such as a borderline clinical history or alterations, which when evaluated may lead to an additional number of transplantations. This Guide does not forget that LDKT may lead to risk for the donor. Pre-donation evaluation has to centre on the problems which may arise over the short or long-term, and these have to be described to the potential donor so that they are able take them into account. Experience over recent years has led to progress in risk analysis, to protect donors' health. This aspect always has to be taken into account by LDKT programmes when evaluating potential donors. Finally, this Guide has been designed to aid decision-making, with recommendations and suggestions when uncertainties arise in pre-donation studies. Its overarching aim is to ensure that informed consent is based on high quality studies and information supplied to donors and recipients, offering the strongest possible guarantees.

Transplant outcomes of 100 cases of living-donor ABO-incompatible kidney transplantation

BACKGROUND

Although ABO-incompatible (ABOi) kidney transplantation (KT) has been performed successfully, a standard preconditioning regimen has not been established. Based on the initial antidonor ABO antibody titers, an individualized preconditioning regimen is developed, and this study explored the efficacy and safety of the regimen.

METHODS

From September 1, 2014, to September 1, 2020, we performed 1668 consecutive living-donor KTs, including 100 ABOi and 1568 ABO-compatible (ABOc) KTs. ABOi KT recipients (KTRs) with a lower antibody titer (≤1:8) were administered oral immunosuppressive drugs (OIs) before KT, while patients with a medium titer (1:16) received OIs plus antibody-removal therapy (plasma exchange/double-filtration plasmapheresis), patients with a higher titer (≥1:32) were in addition received rituximab (Rit). Competing risk analyses were conducted to estimate the cumulative incidence of infection, acute rejection (AR), graft loss, and patient death.

RESULTS

After propensity score analyses, 100 ABOi KTRs and 200 matched ABOc KTRs were selected. There were no significant differences in graft and patient survival between the ABOi and ABOc groups (P  = 0.787, P  = 0.386, respectively). After using the individualized preconditioning regimen, ABOi KTRs showed a similar cumulative incidence of AR (10.0% υs . 10.5%, P  = 0.346). Among the ABOi KTRs, the Rit-free group had a similar cumulative incidence of AR ( P  = 0.714) compared to that of the Rit-treated group. Multivariate competing risk analyses revealed that a Rit-free regimen reduced the risk of infection (HR: 0.31; 95% CI: 0.12-0.78, P  = 0.013). Notably, antibody titer rebound was more common in ABOi KTRs receiving a Rit-free preconditioning regimen ( P  = 0.013) than those receiving Rit. ABOi KTRs with antibody titer rebound had a 2.72-fold risk of AR (HR: 2.72, 95% CI: 1.01-7.31, P  = 0.048). ABOi KTRs had similar serum creatinine and estimated glomerular filtration rate compared to those of ABOc KTRs after the first year.

CONCLUSIONS

An individualized preconditioning regimen can achieve comparable graft and patient survival rates in ABOi KT with ABOc KT. Rit-free preconditioning effectively prevented AR without increasing the risk of infectious events in those with lower initial titers; however, antibody titer rebound should be monitored.

A New Trial to Measure ABO Antibodies Using Complement-Dependent Cytotoxicity

Background and objectives: The ABO antibody (Ab) titration tests are used in monitoring in ABO-incompatible (ABOi) solid organ transplantation (SOT). However, currently developed ABO Ab tests show Ab binding reactions. This study attempted to measure ABO Ab level using complement-dependent cytotoxicity (CDC). Materials and methods: We studied 93 blood group O serum samples from patients who underwent ABOi SOT from January 2019 to May 2021. Patients’ sera were incubated with A1 or B cells and added to a human complement solution. Supernatants were collected after centrifugation, and free hemoglobin (Hb) was measured by spectrophotometry. We converted plasma Hb value to hemolysis (%), which were compared with ABO Ab titer. Results: We found a mild correlation between hemolysis and ABO Ab titers. In simple regression analysis, the correlation coefficients were within 0.3660−0.4968 (p < 0.0001) before transplantation. In multiple linear regression analysis, anti-A hemolysis (%) was higher in immunoglobulin M (IgM) (β = 12.9) than in immunoglobulin G (IgG) (β = −3.4) (R2 = 0.5216). Anti-B hemolysis was higher in IgM (β = 8.7) than in IgG (β = 0.0) (R2 = 0.5114). There was a large variation in hemolysis within the same Ab titer. Conclusions: CDC can be used in a new trial for ABO Ab measurement. Furthermore, IgM rather than IgG seems to play a significant role in vivo activity, consistent with previous knowledge. Thus, this study may help in the development of the ABO Ab titration supplement test for post-transplant treatment policy establishment and pre-transplant desensitization.

Laboratory support of ABO antibody monitoring for ABO-incompatible solid organ transplantation

The accurate measurement of ABO antibodies is essential for successful ABO-incompatible solid organ transplantation. Titration using two-fold dilution is considered a standard method and is applied in most laboratories. However, this titration method has inherent limitations, including differences in methods between laboratories, a lack of standardization, its semiquantitative nature, and the difficulty of considering the results to be representative of the in vivo activity of ABO antibodies. Various measurement methods other than titration have been developed, and new methods continue to be introduced. Physicians and laboratory specialists who are involved in ABO-incompatible solid organ transplantation need to fully understand these methods for optimal patient management.

A Novel Method of CD31-Combined ABO Carbohydrate Antigen Microarray Predicts Acute Antibody-Mediated Rejection in ABO-Incompatible Kidney Transplantation

Isohemagglutinin assays employing red blood cells (RBCs) are the most common assays used to measure antibody titer in ABO-incompatible kidney transplantation (ABOi KTx). However, ABO antigens expressed on RBCs are not identical to those of kidney and antibody titers do not always correlate with clinical outcome. We previously reported that CD31 was the main protein linked to ABO antigens on kidney endothelial cells (KECs), which was different from those on RBCs. We developed a new method to measure antibody titer using a microarray of recombinant CD31 (rCD31) linked to ABO antigens (CD31-ABO microarray). Mass spectrometry analysis suggested that rCD31 and native CD31 purified from human kidney had similar ABO glycan. To confirm clinical use of CD31-ABO microarray, a total of 252 plasma samples including volunteers, hemodialysis patients, and transplant recipients were examined. In transplant recipients, any initial IgG or IgM antibody intensity >30,000 against the donor blood type in the CD31-ABO microarray showed higher sensitivity, specificity, positive predictive value, and negative predictive value of AABMR, compared to isohemagglutinin assays. Use of a CD31-ABO microarray to determine antibody titer specifically against ABO antigens expressed on KECs will contribute to precisely predicting AABMR or preventing over immunosuppression following ABOi KTx.

Choice of ABO Group for Blood Component Transfusion in ABO-Incompatible Solid Organ Transplantation: A Questionnaire Survey in Korea and Guideline Proposal

The number of ABO-incompatible solid organ transplantations (ABOi SOTs) has markedly increased worldwide since the early 2000s. We investigated the choice of ABO group for blood component transfusion in ABOi SOT. We conducted a survey by e-mailing a questionnaire to blood bank specialists at 77 major hospitals in Korea, among whom 34 responded to the survey. In major ABOi SOT, for red blood cells (RBCs), the recipient’s type (70.6%) was the most common choice, followed by group O (29.4%); for platelets, group AB (50.0%) was the most common choice, followed by the donor type (38.2%); for plasma, group AB (55.9%) was the most common choice, followed by the donor type (32.4%). In bidirectional ABOi SOT, for RBCs, the recipient’s type (55.9%) was the most common choice, followed by group O (44.1%); for platelets and plasma, group AB was the most common choice (94.1% and 97.1%, respectively). The policies for transfusion in ABOi SOT were diverse. We suggest a guideline on the choice of ABO group for transfusion in ABOi SOT to secure patient health and enable an efficient use of blood components.

Hyperacute rejection in ABO-incompatible kidney transplantation: Significance of isoagglutinin subclass

INTRODUCTION

ABO-incompatible transplantation has expanded the limited donor pool for kidney transplantation. Despite the successful desensitization protocols and immunosuppression, undesirable cases of hyperacute rejection occurs.

OBJECTIVE

Flow cytometry was used to measure isoagglutinin titer and its IgG subclasses in assessment of the cause of hyperacute rejection in ABO-incompatible kidney transplantation.

MATERIALS AND METHODS

The recipient was admitted for kidney transplantation due to end-stage renal disease. Pre-transplantation work-up for ABO-incompatible kidney transplantation included blood group typing, HLA DNA typing and HLA antibody analyses. HLA crossmatch analysis was conducted using donor lymphocytes and anti-HLA antibody assay using Luminex panel reactive antibody test (One Lambda, Inc., Canoga Park, CA). Desensitization protocol was composed of therapeutic plasma exchange sessions and rituximab.

RESULTS

Despite negative HLA crossmatch results, a case of hyperacute rejection occurred after living donor kidney transplantation. Rejection resulted in immediate removal of graft, and the patient later received a second kidney transplantation. Retrospective evaluation of isoagglutinin titer and its subclasses using flow cytometry identified the cause of rejection to increased IgG1 subclass. Desensitization protocol for ABO-incompatible kidney transplantation now implements further caution for blood group O recipients.

DISCUSSION

Hyperacute rejection resulting from increased IgG1 isoagglutinin subclass has not been previously confirmed using flow cytometry. Unfortunate outcome of this rejection case provides insight to how we should approach and ensure successful ABO-incompatible kidney transplantation.

Challenges in antibody titration for ABO-incompatible renal transplantation

BACKGROUND AND OBJECTIVES

Accurate and regular monitoring of anti-A and anti-B titres pre- and post-transplantation plays a crucial role in the clinical management of patients receiving ABO-incompatible renal transplants. There is no standardized protocol or an external quality assurance program (EQA) currently available for this testing in Australia. The aim of this study was to investigate the diversity of techniques, test platforms and reagents that were currently in use in various laboratories with the aim of developing an EQA.

MATERIALS AND METHODS

An online survey was sent to the participants enrolled with the Royal College of Pathologists of Australasia Quality Assurance Program (RCPAQAP) to assess their interest in participation in the pilot study. A total of 24 participants who expressed interest were sent the group O plasma, A₁ , A₂ and B cells to perform ABO titration using their own methods.

RESULTS

Participants reported a wide range of titre results, from 8 to 1024 for the anti-A titre using A₁ cells, from 2 to 128 for anti-A titre using A₂ cells and from neat to 32 for anti-B titre using B cells.

CONCLUSION

There was a wide variation in titre results between and within different technologies. These findings demonstrate the need for an ABO titration EQA. Development of a standard technique and participation in an EQA program should, over time, reduce variation and enable transferrable results across testing centres, which will assist in consistent clinical interpretation and better outcomes for patients.

Evaluation of safety of using incompatible plasma for therapeutic plasma exchange during shortage of AB plasma

BACKGROUND

Criteria for selection of FFP blood type has not been clearly established and use of group AB plasma is preferred by numerous transplantation protocols.

AIMS

This study assesses the safety and efficacy of alternative group A or B plasma in ABO incompatible solid organ transplantation.

MATERIALS & METHODS

Alternative use of group A or B plasma (incompatible plasma) was inevitable during the shortage of group AB plasma. Experience from select number of patients during the period of extreme group AB plasma shortage is described.

RESULTS

The result of alternative use of group A or B plasma was within expectation, showing effective reduction of isoagglutinin titers for pre-operative desensitization and efficacy for treatment of post-operative patients. No immediate hemolytic transfusion reaction was reported.

DISCUSSION

While validation in a larger cohort of patients is necessary, our limited experience have shown satisfactory clinical outcomes without adverse events.

CONCLUSIONS

Use of incompatible group A or B plasma is a viable option when group AB plasma is limited.

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.

Acute Rejection and Infectious Complications in ABO- and HLA-Incompatible Kidney Transplantations

Background

Patients receiving ABO-incompatible (ABOi) or human leukocyte antigen (HLA)-incompatible (HLAi) kidney transplantation (KT) require potent immunosuppression and are thus at a higher risk of infectious complications. We evaluated the clinical outcomes of KT stratified by ABO and HLA incompatibilities and identified the factors associated with the clinical outcomes.

Material/Methods

Recipients who underwent living-related KT between 2012 and 2017 were included and classified into 4 groups: ABO-compatible and HLA-compatible (ABOc/HLAc), HLA-incompatible (ABOc/HLAi), ABO-incompatible (ABOi/HLAc), and ABO-incompatible and HLA-incompatible (ABOi/HLAi). Cox proportional hazards regression analyses were carried out to evaluate the risk factors of acute rejection. Out of the 1732 patients who underwent KT, 1190, 131, 358, and 53 were in the ABOc/HLAc, ABOi/HLAc, ABOc/HLAi, and ABOi/HLAi groups, respectively.

Results

The ABO/HLAi group showed the lowest 5-year graft survival rate (91.7%). Death-censored graft survival was not significantly different among the groups. The mortality rate from infections was significantly higher in the ABOi/HLAi group (7.5%) than the other groups. Antibody-mediated rejection-free graft survival was the lowest in the ABOi/HLAi group, with significant differences compared with the ABOi/HLAc group (P=0.02) and the ABOc/HLAi group (P=0.03). ABOi/HLAi (hazard ratio [HR], 2.63; 95% confidence interval [CI], 1.04–6.65; P<0.01) and combined infection (HR, 1.91; 95% CI, 1.45–2.51; P<0.01) were significant risk factors for acute rejection.

Conclusions

Patients with both ABO and HLA incompatibilities showed inferior rates of overall patient and graft survival due to infectious complications. Infection was a prominent risk factor of acute rejection following KT after adjusting for possible confounders including ABO and HLA incompatibility.

ABO-incompatible living kidney transplantation

ABO-incompatible living kidney transplantation is nowadays a routine procedure to expand living donor pool. The past decades have seen the evolution of desensitization protocol and immunosuppression regimen. Despite increased bleeding events, infectious complications, and rejection episodes reported in some studies, favorable graft and patient survival rate are now achieved, regardless of various protocols among transplant centers. Several issues such as the usage of rituximab and standardization of blood group antibody titration remain to be settled. The deposition of C4d is no longer the histopathologic hallmark of antibody-mediated rejection, which have inspired innovative strategies of peripheral molecular screening and the improvement of histological diagnosis of AMR (antibody-mediated rejection). The better understanding of the underlying mechanism might facilitate the distinction and therapeutic schemes of AMR.