ABO-incompatible living-donor kidney transplantation in children

Rituximab added to conditioning regimen significantly improves erythroid engraftment in major incompatible ABO-group hematopoietic stem cell transplantation

ABO-group major incompatibility hematopoietic stem cell transplantation (HSCT) increases the risk of delayed red cell engraftment and other immunological complications. In this study, we evaluated the efficacy of pre-transplant infusion of rituximab in patients with ABO-incompatibility in improving red blood cell engraftment after HSCT, measured by time to reach transfusion independence. We performed a retrospective, single-center study including 131 consecutive patients transplanted with major or bidirectional ABO-incompatible grafts between 1st January 2013 and 31st December 2019. Fifty-one patients received an infusion of rituximab during the conditioning regimen, while 80 patients did not receive any additional preventive treatment. Time to transfusion independence was significantly reduced for patients treated with rituximab (1 month, 95% CI, 0.5-2) compared with the control group (3.2 months, 95% CI 1.5-3.2, p = 0.02). By multivariable analysis, rituximab use was associated with a faster red blood cell (RBC) engraftment (RR 1.88, 95% CI 1.17-3.03, p = 0.009), while a pre-transplant anti-donor isohemagglutinins titer >1:128 was associated with delayed transfusion independence (RR 0.61, 95% CI 0.37-0.99, p = 0.05). Although limited by the retrospective nature of the study, the results of this analysis suggest that rituximab added to conditioning regimens is feasible, safe, and able to improve post-transplant red blood cell engraftment.

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.

Prevalence of Pure Red Cell Aplasia Following Major ABO-Incompatible Hematopoietic Stem Cell Transplantation

Background

Pure red cell aplasia (PRCA) is one of the important complications in major ABO-incompatible allogeneic hematopoietic stem cell transplantation (HSCT). The established pathogenic factor of PRCA is the persistence of high anti-donor isohemagglutinins. As previously verified, the conditioning regimen and donor type were the factors associated with the development of PRCA in the small-sized studies. Currently, the prevalence, risk factors, and prognosis of PRCA are still worth studying to provide evidence.

Methods

We conducted a prospective nested case-control study to determine the prevalence, donor-related factors, and the outcomes of PRCA following major ABO-incompatible transplantation. A total of 469 patients who underwent ABO-incompatible grafts were observed.

Results

None of the patients were diagnosed with PRCA with minor or bidirectional ABO-incompatible HSCT. Thirteen of the187 patients (7%; 95% confidence interval [CI], 3.9%–11.9%) developed PRCA following major ABO-incompatible HSCT. Eleven of the 13 patients with PRCA recovered entirely. Donor type was an independent factor associated with post-HSCT PRCA (odds ratio [OR]=0.030; 95% CI, 0.003–0.321; P=0.004). The cumulative incidence rates of post-HSCT PRCA in the context of major ABO-incompatible HSCT were 0.8%, 13.1%, and 27.2% for the haploidentical donor (HID), unrelated donor, and matched related donor, respectively. No significant influence of PRCA on transplantation outcomes was observed.

In conclusion, post-HSCT PRCA is a rare and less threatening complication in major ABO-incompatible HSCT. The majority of patients with PRCA could recover. Additionally, HIDs for recipients may have a low risk of post-HSCT PRCA. This trial was registered at www.chictr.org.cn (#ChiCTR2000041412).

ABO-incompatible pediatric kidney transplantation without antibody removal

BACKGROUND

Because of the severe shortage of suitable deceased donors, ABO-incompatible living donor kidney transplantation (ABOi LDKT) is performed even in pediatric recipients in Japan. We performed pediatric ABOi LDKT using rituximab without anti-A/B antibody removal.

METHODS

Thirteen pediatric recipients (mean age 7.4, range 3.4-15.7, four females) whose baseline anti-A/B IgG titers were ≤ × 64 underwent ABOi LDKT without antibody removal and splenectomy between July 2013 and April 2017 at Toho University. Mycophenolate mofetil (MMF) was initiated on day - 10. Rituximab (100 mg) was administered twice. Basiliximab and triple maintenance immunosuppression (calcineurin inhibitor, MMF, and steroids) were administered. Protocol biopsy was performed at 3 months and 1 year after transplantation. We retrospectively compared the clinical outcomes between these recipients and 37 children (mean age 9.0, range 2.6-18.9, 15 female) who underwent ABO-compatible (ABOc) LDKT during the same period.

RESULTS

The mean follow-up periods of ABOi and ABOc groups were 31.9 ± 13.5 and 28.8 ± 14.4 months, respectively. In the ABOi group, no clinical acute rejection (AR) was noted and subclinical AR was observed in four patients without evidence of acute antibody-mediated rejection. In the ABOc group, clinical and subclinical AR developed in 3 and 10 patients, respectively. No significant difference was identified for the mean eGFR between the ABOi and ABOc groups (98.3 ± 48.8 vs. 86.9 ± 39.4, P = 0.452 at 3 months; 78.2 ± 21.2 vs. 79.7 ± 21.3, at 1 year, P = 0.830). Death-censored graft survival at follow-up was 100% in the ABOi group and 94.6% in the ABOc group. Patient survival during the follow-up period in both the groups was 100%. Late-onset neutropenia (LON) requiring granulocyte colony-stimulating factor occurred more frequently in the ABOi group than in the ABOc group (4 vs. 0 patients) (P < 0.001).

CONCLUSIONS

Pre- and post-transplantation antibody removal is not a prerequisite for successful pediatric ABOi LDKT, at least in patients with a low anti-A/B IgG antibody titer. However, LON caused by rituximab should be monitored.

A donor risk index for graft loss in pediatric living donor kidney transplantation

Pediatric kidney transplant candidates often have multiple potential living donors (LDs); no evidence-based tool exists to compare potential LDs, or to decide between marginal LDs and deceased donor (DD) kidney transplantation (KT). We developed a pediatric living kidney donor profile index (P-LKDPI) on the same scale as the DD KDPI by using Cox regression to model the risk of all-cause graft loss as a function of living donor characteristics and DD KDPI. HLA-B mismatch (adjusted hazard ratio [aHR] per mismatch = 1.04 1.271.55 ), HLA-DR mismatch (aHR per mismatch = 1.02 1.231.49 ), ABO incompatibility (aHR = 1.20 3.268.81 ), donor systolic blood pressure (aHR per 10 mm Hg = 1.01 1.071.18 ), and donor estimated GFR (eGFR; aHR per 10 mL/min/1.73 m2 = 0.88 0.940.99 ) were associated with graft loss after LDKT. Median (interquartile range [IQR]) P-LKDPI was -25 (-56 to 12). 68% of donors had P-LKDPI <0 (less risk than any DD kidney) and 25% of donors had P-LKDPI >14 (more risk than median DD kidney among pediatric KT recipients during the study period). Strata of LDKT recipients of kidneys with higher P-LKDPI had a higher cumulative incidence of graft loss (39% at 10 years for P-LDKPI ≥20, 28% for 20> P-LKDPI ≥-20, 23% for -20 > P-LKDPI ≥-60, 19% for P-LKDPI <-60 [log rank P < .001]). The P-LKDPI can aid in organ selection for pediatric KT recipients by allowing comparison of potential LD and DD kidneys.

Immune Desensitization Allows Pediatric Blood Group Incompatible Kidney Transplantation

BACKGROUND

Blood group incompatible transplantation (ABOi) in children is rare as pretransplant conditioning remains challenging and concerns persist about the potential increased risk of rejection.

METHODS

We describe the results of 11 ABOi pediatric renal transplant recipients in the 2 largest centers in the United Kingdom, sharing the same tailored desensitization protocol. Patients with pretransplant titers of 1 or more in 8 received rituximab 1 month before transplant; tacrolimus and mycophenolate mofetil were started 1 week before surgery. Antibody removal was performed to reduce titers to 1 or less in 8 on the day of the operation. No routine postoperative antibody removal was performed.

RESULTS

Death-censored graft survival at last follow-up was 100% in the ABOi and 98% in 50 compatible pediatric transplants. One patient developed grade 2A rejection successfully treated with antithymocyte globulin. Another patient had a titer rise of 2 dilutions treated with 1 immunoadsorption session. There was no histological evidence of rejection in the other 9 patients. One patient developed cytomegalovirus and BK and 2 others EBV and BK viremia.

CONCLUSIONS

Tailored desensitization in pediatric blood group incompatible kidney transplantation results in excellent outcomes with graft survival and rejection rates comparable with compatible transplants.

ABO incompatible renal transplants: Good or bad?

ABO incompatible kidney transplantation (ABOi-KT) was previously considered to be an absolute contraindication for patients with end-stage kidney disease (ESKD) due to hyperacute rejection related to blood type barrier. Since the first successful series of ABOi-KT was reported, ABOi-KT is performed increasingly all over the world. ABOi-KT has led to an expanded donor pool and reduced the number of patients with ESKD awaiting deceased kidney transplantation (KT). Intensified immunosuppression and immunological understanding has helped to shape current desensitization protocols. Consequently, in recent years, ABOi-KT outcome is comparable to ABO compatible KT (ABOc-KT). However, many questions still remain unanswered. In ABOi-KT, there is an additional residual immunological risk that may lead to allograft damage, despite using current diverse but usually intensified immunosuppressive protocols at the expense of increasing risk of infection and possibly malignancy. Notably, in ABOi-KT, desensitization and antibody reduction therapies have increased the cost of KT. Reassuringly, there has been an evolution in ABOi-KT leading to a simplification of protocols over the last decade. This review provides an overview of the history, outcome, protocol, advantages and disadvantages in ABOi-KT, and focuses on whether ABOi-KT should be recommended as a therapeutic option of KT in the future.

Issues in solid-organ transplantation in children: translational research from bench to bedside

In this review, we identify important challenges facing physicians responsible for renal and cardiac transplantation in children based on a review of the contemporary medical literature. Regarding pediatric renal transplantation, we discuss the challenge of antibody-mediated rejection, focusing on both acute and chronic antibody-mediated rejection. We review new diagnostic approaches to antibody-mediated rejection, such as panel-reactive antibodies, donor-specific cross-matching, antibody assays, risk assessment and diagnosis of antibody-mediated rejection, the pathology of antibody-mediated rejection, the issue of ABO incompatibility in renal transplantation, new therapies for antibody-mediated rejection, inhibiting of residual antibodies, the suppression or depletion of B-cells, genetic approaches to treating acute antibody-mediated rejection, and identifying future translational research directions in kidney transplantation in children. Regarding pediatric cardiac transplantation, we discuss the mechanisms of cardiac transplant rejection, including the role of endomyocardial biopsy in detecting graft rejection and the role of biomarkers in detecting cardiac graft rejection, including biomarkers of inflammation, cardiomyocyte injury, or stress. We review cardiac allograft vasculopathy. We also address the role of genetic analyses, including genome-wide association studies, gene expression profiling using entities such as AlloMap®, and adenosine triphosphate release as a measure of immune function using the Cylex® ImmuKnow™ cell function assay. Finally, we identify future translational research directions in heart transplantation in children.

Therapeutic plasma exchange for the treatment of pediatric renal diseases in 2013

Therapeutic plasma exchange is an extracorporeal treatment modality that removes systemic circulating pathologic factors or replaces absent plasma components and plays a role in many nephrologic conditions. It presents a number of technical challenges in the pediatric population but has become an increasingly common practice in pediatric nephrology over the past several decades. While prospective evidence is often lacking, our increased understanding of the molecular pathogenesis underlying many pediatric renal diseases provides sound reasoning for the use of plasma exchange in treating these conditions. This review will present the currently accepted indications for plasma exchange in children, the technical aspects of the procedure and its potential complications.

Maximising living donation with paediatric blood-group-incompatible renal transplantation

Long-term outcomes for paediatric renal transplant recipients have improved over the last 20 years, with better patient and renal allograft survival. As paediatric renal transplantation programmes have increased over this timeframe, living donation has become the favoured modality for renal replacement therapy and is advocated pre-emptively in as many cases as possible. However, one of the main barriers historically to living donation has been ABO blood-group incompatibility, with the result that patients were listed to be on call for a deceased donor renal transplant. The clinical scenario has now changed so that donors and recipients for renal transplantation can be worked up and listed for paired exchange and/or living-related ABO blood-group-incompatible renal transplantation (ABOi). There is extensive data in adult practice, and increasing evidence in paediatric practice that the short- and medium-term outcomes for both patient and renal allograft survival for ABOi is equivalent to that of blood-group-compatible renal transplantation.

Lessons and insights from ABO-incompatible lung transplantation

With ABO blood group incompatibility (ABOi) between donor and recipient becoming a part of mainstream living-donor renal transplantation, the applicability of ABOi to other areas of transplantation is being reconsidered. Here we present a case of inadvertent ABOi lung retransplantation managed successfully with initial plasmapheresis, antithymocyte globulin and intravenous immunoglobulin; and subsequently with oral cyclophosphamide and sirolimus in addition to tacrolimus and prednisolone. Interestingly, in the setting of solid levels of tacrolimus and sirolimus, the patient developed a fatal thrombotic microangiopathy of uncertain origin subsequent to the cessation of cyclophosphamide at 9 years posttransplant. It is apparent that ABOi lung transplantation can result in surprisingly successful long-term outcomes. Low pretransplant antibody titers likely aid this and, in pediatric neonatal or infant cases, this may not be uncommon. We must proceed cautiously as there are significant risks. Understanding the monitoring, prevention and treatment of lung transplant antibody-mediated rejection, while avoiding the long-term complications of overimmunosuppression, will be the keys to the success of future cases.

Bleeding complications in pediatric ABO-incompatible kidney transplantation

BACKGROUND

ABO-incompatible renal transplantation (ABOi-RTx) following preconditioning with immunoadsorption (IA) and rituximab is a promising approach to facilitate living-related RTx. However, clinical experience is limited in pediatric patients.

METHODS

Three patients underwent living-related ABOi-RTx in our center. Preoperative IA was performed six, ten and 11 times in patient one, two and three, respectively, to achieve isoagglutinin titers of ≤1:8 on the day of transplantation; rituximab was administered once. The immunosuppressive regimen further comprised tacrolimus, mycophenolate, methylprednisolone and basiliximab; immunoglobulin G (IgG) was infused on the day of ABOi-RTx.

RESULTS

All three patients achieved normal renal function within 2-6 days post-RTx. Major postoperative bleeding occurred in two patients, with one requiring repeated blood transfusions and the other a surgical revision 4 h after RTx, despite local citrate anticoagulation use during the preoperative IA procedures in the latter patient. A pyelonephritis-associated increase of the isoagglutinin IgG/IgM titers to 1:64/1:128 led to a biopsy-proven acute humoral rejection in the third patient, which was treated successfully with plasma exchange and methylprednisolone pulses. The estimated glomerular filtration rate at 18, 8 and 23 months post-RTx was 96, 52 and 74 ml/min/1.73 m(2), respectively.

CONCLUSIONS

ABOi-RTx can successfully be performed in pediatric patients after preconditioning with quadruple immunosuppression, rituximab and IA. Caution is required regarding bleeding complications, which are most likely due to the unspecific binding of coagulation factors during repeated IA.

Distribution of ABO blood group antibody titers in pediatric patients awaiting renal transplantation: implications for organ allocation policy

BACKGROUND

Blood group-incompatible transplantation is one strategy used when a potential recipient does not have a compatible living donor. Current practice includes desensitization strategies to reduce antibody titers. However, when antibodies are low, in cardiac transplantation in neonates for example, no desensitization is required. This study is the first to examine the distribution of ABO blood group antibody titers in a population of pediatric patients on the deceased-donor renal transplantation waiting list.

METHODS

All patients from two pediatric nephrology centers active on the national deceased-donor waiting list had antibody titers (total immunoglobulin load) measured. A simulation modeling the effect of allocating blood group-incompatible deceased-donor kidneys to those patients with titers of 16 or lower was developed.

RESULTS

Twenty-four children were screened; eight (33.3%) had titers of either anti-A or anti-B antibodies of 8 or lower. A further three (12.5%) had either an anti-A or anti-B antibody titer of 16. Blood group A or B patients had lower antibody levels than blood group O patients. In blood group O patients, levels of anti-A antibodies were higher than anti-B antibodies (Wilcoxon signed rank test, P=0.028). The simulation model showed that a change in organ allocation policy would increase pediatric transplant activity by 2.2% and reduce the median waiting time for a transplant.

CONCLUSION

This allocation strategy may be of particular benefit to those pediatric patients who have been on the deceased-donor waiting list for a long time or those with a high calculated reaction frequency.

Outcomes of pediatric ABO-incompatible kidney transplantations are equivalent to ABO-compatible controls

BACKGROUND

Due to the profound shortage of suitable deceased allografts, much effort has been made to investigate whether successful kidney transplantation (KT) is possible across the ABO blood group barrier even for pediatric recipients.

METHODS

We reviewed 52 consecutive ABO incompatible (ABOic) transplantation performed between September 1989 and March 2011. The mean age at transplantation was 10.6 ± 3.9 years (range, 4.4-19.7), with 35 boys and 17 girls. The donor-to-recipient ABO blood antigen incompatibility was as follows: A1/O (n = 17); B/O (n = 13); A1/B (n = 6); B/A1 (n = 1); A1B/B (n = 9); and A1B/A (n = 6). As a control group, data were collected from 271 pediatric ABO compatible (ABOc) living donor KT in the same period.

RESULTS

Overall acute rejection episodes (ARE) among the ABOic group were significantly higher than those of the ABOc group (44% vs 26%; P < .02). However, there was no difference in glomerular filtration rate (GFR) at 1 year after transplantation: 86 ± 31 mL/min for ABOic vs 99 ± 37 mL/min for ABOic, respectively. The 1-y, 5-y, and 10-year patient survival rates were 98%, 92%, and 92% in the ABOic group, respectively, and 99%, 98%, and 97% in the ABOc group, respectively (P = not significant [NS]). The overall 1-, 5-, 10-, and 15-year graft survival rates were 94%, 88%, 86%, and 86% in the ABOic group, respectively, and 95%, 92%, 88%, and 78% in the ABOc group, respectively.

CONCLUSION

ABOic KT provided long-term allograft and patient survivals equivalent to ABOc live donor transplantations.

ABO-incompatible kidney transplantation in children

  We designed a new protocol to enable safe ABO-incompatible kidney transplantation. The new protocol utilizes antigen-specific immunoadsorption rather than unspecific plasma exchange to remove existing anti A/B antibodies and rituximab rather than splenectomy to prevent rebound of antibodies. Sixty patients have so far been successfully transplanted with this protocol and 10 of those have been children. When compared with ABO-compatible transplantations, we could not find any differences in success rate, renal function, or adverse events.

Prevention of pure red cell aplasia after major or bidirectional ABO blood group incompatible hematopoietic stem cell transplantation by pretransplant reduction of host anti-donor isoagglutinins

BACKGROUND

Persistent anti-donor isoagglutinins after major ABO blood group incompatible hematopoietic stem cell transplantation may cause delayed red blood cell engraftment and post-transplant pure red cell aplasia.

DESIGN AND METHODS

We investigated the effect of pretransplant anti-donor isoagglutinin reduction by in vivo absorption and/or plasmapheresis on the incidence of pure red cell aplasia and the time to red blood cell engraftment in 153 hematopoietic stem cell transplant recipients with major ABO incompatibility.

RESULTS

Twelve patients (8%) developed pure red cell aplasia, 3/98 (3%) with, and 9/55 (16%) without prior isoagglutinin reduction (p=0.009). Red blood cell engraftment was faster in patients with isoagglutinin reduction; in addition, peripheral blood hematopoietic stem cell transplantation, acute graft-versus-host disease, and younger age were associated with faster red blood cell engraftment in Cox regression analysis. In patients with pure red cell aplasia the mean red blood cell engraftment occurred after 225 days (p<0.001) and was associated with a simultaneous decrease of anti-donor isoagglutinins. Patients with pure red cell aplasia had higher pretransplant anti-donor isoagglutinin titers (p=0.001) and received more post-transplant red blood cell transfusions (p<0.001).

CONCLUSIONS

Following major ABO incompatible hematopoietic stem cell transplantation, pure red cell aplasia and delayed red blood cell engraftment depend on the levels of anti-donor isoagglutinins and are efficiently prevented by the pretransplant removal of these isoagglutinins. The benefits of reducing the time of transfusion-dependency and transfusion-associated risks must be carefully balanced against the potential side effects of isoagglutinin reduction.

Intentional ABO-incompatible lung transplantation

We report on a case of intentional blood group incompatible lung transplantation. A blood group O cystic fibrosis patient was mechanically ventilated and put on interventional lung assist for severe respiratory decompensation. Since timely allocation of a blood group O donor lung was impossible, an AB deceased donor lung rescue allocation was accepted and the transplant performed using a pre-, peri- and postoperative antibody depletion protocol including plasmapheresis, ivIg administration, rituximab and immunoadsorption. Nine months after the transplant the patient is at home and well.

ABO-incompatible kidney transplantation using antigen-specific immunoadsorption and rituximab: a 3-year follow-up

BACKGROUND

In 2001 a protocol for ABO-incompatible (ABOi) kidney transplantation based on antigen-specific immunoadsorption and rituximab was introduced at our center, short-term results being comparable with those of ABO-compatible (ABOc) living donor kidney transplantation. Of greater importance, however, is long-term graft function, thus far not evaluated. The aim of this study was therefore to assess long-term results of this protocol.

METHODS

Twenty ABOi kidney recipients with more than 12-month follow-up were included in the study: all adult crossmatch negative ABOi kidney recipients (n=15) were compared with an adult ABOc living donor recipient control group (n=30), and all pediatric ABOi kidney recipients (<16 years of age) (n=5) were compared with a group of pediatric ABOc kidney recipients (n=18).

RESULTS

Mean follow-up was three years. There was no significant difference in patient survival, nor in graft survival or in the incidence of acute rejection in any of the groups. In the adult kidney recipients mean glomerular filtration rate was equivalent at all time points (79-83 mL/min), as was Deltas-creatinine. In the pediatric groups, Deltas-creatinine was similar but glomerular filtration rate lower among the ABOi kidney recipients. There was a significant reduction (P<0.0001) without rebound in A/B antibody titers after transplantation (median IgG 1:2 and median IgM 1:1>1 year posttransplant) compared with pretransplant levels (median IgG 1:32 and IgM 1:16).

CONCLUSION

We conclude that ABOi kidney transplantation using antigen-specific immunoadsorption and rituximab is equivalent to ABOc living donor kidney transplantation. ABOi transplantation after this protocol does not have a negative impact on long-term graft function.

Allosensitization does not increase the risk of xenoreactivity to alpha1,3-galactosyltransferase gene-knockout miniature swine in patients on transplantation waiting lists

BACKGROUND

The recent availability of alpha1,3-galactosyltransferase knockout (GalT-KO) miniature swine has eliminated anti-Gal antibodies as the major barrier to xenotransplantation, potentially bringing this modality closer to clinical application. Highly-allosensitized patients, who have poor prospects of receiving a suitable cross-match negative human organ, might be the first patients to benefit from xenotransplantation of porcine organs. However, concerns exist regarding cross-reactivity of alloreactive anti-human leukocyte antigen (HLA) antibodies against xenogeneic swine leukocyte antigen (SLA) antigens. We have investigated this question using sera from such patients on GalT-KO target cells.

METHODS

Using flow cytometry and complement-dependent cytotoxicity (CDC) assays, we have tested a panel of 88 human serum samples from patients awaiting cadaveric renal allotransplantation for reactivity against: 1) human; 2) standard miniature swine; and 3) GalT-KO peripheral blood lymphocytes (PBL) and cultured endothelial cells.

RESULTS

Anti-swine IgM and IgG antibody binding, as well as CDC, were significantly attenuated on GalT-KO versus standard swine. No correlation was found between the degree of anti-human panel reactive antibodies (PRA) and xenoreactivity against either standard or GalT-KO miniature swine. Treatment of sera with dithiothreitol (DTT) showed that the majority of remaining lymphocytotoxicity against GalT-KO swine was mediated by preformed IgM antibodies. Patients with high alloreactivity but low anti-GalT-KO xenoreactivity were readily identified.

CONCLUSIONS

Highly allosensitized patients awaiting renal transplants appear to be at no increased risk of xenosensitization over their non-sensitized cohorts, and could therefore be candidates for xenotransplantation using GalT-KO swine donors.

ABO-histo blood group incompatibility in hematopoietic stem cell and solid organ transplantation

In contrast to solid organ transplantation (SOT), ABO-histo blood group incompatibility is of minor importance for hematopoietic stem cell transplantation (HSCT). Patients receiving ABO-incompatible HSCT are at an increased risk for immune-mediated hematological complications including immediate and delayed hemolysis, late red blood cell engraftment and pure red cell aplasia, but seem not to have a worse overall survival or increased transplant-related mortality. This review gives an overview of the immunological mechanisms leading to complications associated with ABO-incompatible HSCT and describes approaches to prevent them. The current organ shortage in SOT stimulates the exploration of new strategies to expand the donor pool including ABO-incompatible SOT and xenotransplantation. Here, we discuss the hypothesis that ABO-incompatible transplantation may be viewed as a human in vivo model for the humoral immune mechanisms of antigen-mismatched transplantation. ABO-incompatible HSCT and SOT provide excellent possibilities to analyze graft accommodation and transplantation tolerance. Understanding the underlying mechanisms of graft survival in ABO-incompatible transplantation may facilitate new strategies to overcome the immunological barriers in SOT and xenotransplantation.

Xenotransplantation and ABO incompatible transplantation: The similarities they share

Transplantation of kidney allografts across the ABO barrier has been feasible with the development of technologies for removal of anti-blood group antibodies from the circulation of the recipent. The recipients of ABO incompatible grafts display tolerance, accommodation or rejection of the graft. Understanding the factors that determine the outcome of the immune response against incompatible blood group antigens has required the study of an appropriate experimental animal model. The model used is that of knockout (KO) mice for the alpha1,3galactosyltransferase gene, lacking the alpha-gal epitopes and transplanted with wild type mouse heart expressing the alpha-gal epitope. The alpha-gal epitope (Galalpha1-3Galbeta1-(3)4GlcNAc-R) is one of the most abundant carbohydrate epitopes on cells of non-primate mammals and New World monkeys, where it is synthesized by the glycosylation enzyme alpha1,3galactosyltransferase. In humans, apes and Old World monkeys, this epitope is absent due to an evolutionary event that led to the inactivation of the alpha1,3galactosyltransferase gene in ancestral Old World primates. Instead, humans, apes and Old World monkeys produce a natural antibody, the anti-Gal antibody, that is the most abundant natural antibody in humans (approximately 1% of circulating immunoglobulins) and which specifically interacts with alpha-gal epitopes. The interaction between anti-Gal and alpha-gal epitopes is a major immunologic barrier in xenotransplantation, preventing transplantation of pig organs or tissues (i.e. xenografts) into humans. Anti-Gal antibodies also comprise a large proportion of anti-blood group B activity in A and O individuals. Moreover, in recipients of ABO incompatible grafts, much of the elicited anti-A and anti-B antibodies are in fact anti-Gal antibodies capable of binding also to the incompatible blood group antigens. Since the alpha-gal epitope is very similar in its structure to blood groups A and B, understanding anti-Gal response to alpha-gal epitopes is likely to provide information on the immune response to ABO incompatible antigens. Studies on the immune response to alpha-gal epitopes in KO mice have indicated that this epitope can not activate T cells. Anti-Gal B cells engaging alpha-gal epitopes on transplated wild type mouse heart can be activated to produce their antibodies only if they receive help from T cells that are activated by allogeneic or xenogeneic peptides. If T cell help is not available for several days the B cells are induced to differentiate into cells capable of producing accommodating antibodies. Accommodating anti-Gal antibodies bind to the incompatible carbohydrate antigen but do not induce rejection. Prolonged exposure of anti-Gal B cells to the incompatible alpha-gal epitope on the wild type mouse heart graft induces tolerance due to the deletion of these B cells. These studies imply that similar variation in the availability of T cell help in recipients of ABO incompatible grafts result in rejection, accommodation or tolerance, to the blood group antigen. The studies on immune response to incompatible alpha-gal epitopes have further indicated that tolerance to incompatible blood group antigens can be achieved by gene therapy with autologous bone marrow cells or autologous lymphocytes engineered to express the incompatible blood group antigen. Studies in the mouse model suggest that administration into the patient such autologous cells engineered to express the incompatible transplantation carbohydrate antigen induces deletion of anti-blood group B cells and induction of tolerance, provided that the anti-blood group antibodies are removed. Such tolerance is perpetuated indefinitely by the subsequent transplantation of the organ expressing the incompatible blood group antigen.

Mechanisms and Role of HLA and non-HLA Alloantibodies

The role of alloantibodies against HLA and non-HLA targets is becoming increasingly recognized as critical in the pathogenesis of acute and chronic renal allograft outcomes. This review discusses the antigenic targets, the mechanisms of T and B cell activation that result in the production of antibody, the complement cascade, methods of antibody detection, and the evidence that alloantibody-mediated mechanisms are active in acute and chronic rejection.

ABO-incompatible kidney transplantation of an 8-yr-old girl with donor/recipient-constellation A1B/B

BACKGROUND

Antigen-specific immunoadsorption combined with rituximab offers the possibility for ABO-incompatible kidney transplantation without splenectomy.

PATIENT AND METHOD

An 8-year-old mentally retarded girl with steroid-resistant nephrotic syndrome and focal segmental glomerulosclerosis due to mitochondriopathy poorly tolerated hemodialysis. Paternal blood group A1B was incompatible with blood group B of the child. Therefore, we decided to perform the first ABO-incompatible renal transplantation in a child in Germany using antigen-specific immunoadsorption. Rituximab (1 x 375 mg/m2) was administered 2 weeks before the first immunoadsorption (Glycosorb) ABO A-column). Triple-drug immunosuppression (tacrolimus, mycophenolate mofetil and prednisolone) was simultaneously started with immunoadsorption. Initial tacrolimus levels were targeted between 15 and 20 ng/ml. Before transplantation, six immunoadsorptions were applied on days -9, -7, -4, -3, -2 and -1. Intravenous immunoglobulin (0.5 g/kg) was administered preoperatively. After transplantation, three immunoadsorptions were performed on days +4, +6 and +8.

RESULTS

Before transplantation, antibody (Ab) titers against paternal erythrocytes (20 degrees C) were reduced from 1 : 64 to 1 : 4 by six antigen-specific immunoadsorptions. After transplantation, we performed three more immunoadsorptions and the Ab titers were stable between 1 : 1 and 1 : 8. One, 2 and 8 months later we observed increases in the Ab titer up to 1 : 32 requiring no change in immunosuppressive therapy. No side effects of immunoadsorption were observed. The girl had excellent initial graft function with a serum creatinine of 55 to 70 micromol/l. Two weeks after transplantation, graft biopsy showed no signs of rejection; there was focal positivity for C4d only. Twelve months after transplantation, renal function was stable, with a serum creatinine of 117 micromol/l. Episodes of rejection or severe infections were absent.

CONCLUSION

ABO-incompatible transplantation using antigen-specific immunoadsorption and rituximab may serve as a suitable alternative for children urgently needing renal transplantation and missing a blood group-compatible donor.

Decay-Accelerating Factor Prevents Acute Humoral Rejection Induced by Low Levels of Anti-αGal Natural Antibodies

BACKGROUND

Hyperacute and delayed vascular rejection due to natural antibodies (NAb) present major obstacles in pig-to-primate xenotransplantation. Although "supraphysiologic" expression of human complement regulatory proteins (CRPs) can prevent hyperacute rejection in discordant xenogenic recipients, their physiologic role in the homologous setting is undefined. We have evaluated the effect of the absence of decay-accelerating factor (DAF) on cardiac allograft rejection in the presence of different levels of antidonor antibodies (Ab).

METHODS

DAF1-deficient (DAF KO; B6129F2 H-2) mice were used as heart graft donors to alpha1,3-galactosyltransferase deficient (GalT KO; B6, H-2) recipients. Heterotopic heart grafting was performed with or without presensitization. Graft survival, histology, and anti-alphaGal Ab levels were monitored.

RESULTS

DAF knockout (KO) but not wild-type (WT) grafts showed hyperacute or acute humoral rejection in nonsensitized GalT KO mice with low levels of anti-alphaGal IgM NAb. However, humoral rejection of both DAF KO and DAF WT donor grafts occurred in presensitized GalT KO recipients.

CONCLUSIONS

The expression of DAF prevents hyperacute rejection in mice with low titers of anti-alphaGal antibody. These studies demonstrate the physiologic role of DAF in preventing humoral rejection in the presence of low levels of NAb and have implications for transplantation of discordant vascularized xenografts.

Antibody-mediated organ-allograft rejection

Recent studies show that alloantibodies mediate a substantial proportion of graft-rejection episodes, contributing to both early and late graft loss. Rejection that is caused by antibody is mediated by different mechanisms from rejection that is caused by T cells, thereby requiring other approaches to treatment and prevention. Antibody induces rejection acutely through the fixation of complement, resulting in tissue injury and coagulation. In addition, complement activation recruits macrophages and neutrophils, causing additional endothelial injury. Antibody and complement also induce gene expression by endothelial cells, which is thought to remodel arteries and basement membranes, leading to fixed and irreversible anatomical lesions that permanently compromise graft function.

Current status of ABO-incompatible kidney transplantation in children

This article reviews the current status of ABO-incompatible kidney transplantation in the pediatric population. ABO blood type incompatibility between a donor and recipient was generally considered a contraindication to kidney transplantation because of the associated high risk for hyperacute rejection. However, due to a severe shortage of suitable cadaveric allografts, much effort has been made over the last decade to investigate whether successful and effective kidney transplantation is possible across the ABO blood group barrier. At present, ABO-incompatible kidney transplantation has been shown to be a valid alternative even for children with end stage renal disease. In this review, we will discuss protocols available for successfully performing ABO-incompatible kidney transplantation in children: (1) pre-transplant extracorporeal immunomodulation with removal of pre-existing anti-A and/or anti-B antibodies; (2) immunosuppressive therapy and anti-rejection therapy; (3) splenectomy and the associated infectious complication in asplenic children. Also, we will speculate regarding the mechanisms underlying accommodation following transplantation.

Successful living donor renal transplantation despite ABO incompatibility and a positive crossmatch

Potential live kidney donors have been rejected when the prospective recipients are blood type or crossmatch incompatible. By utilizing plasmapheresis combined with intravenous immune globulin (PP/IVIg) prior to surgery, donor-specific antibodies against blood group or human leukocyte antigens (HLA) have been removed, thereby allowing successful renal transplantation. A 26-yr-old male with a panel reactive antibody level of 100% and repeated positive crossmatches against deceased donor kidney offers, including zero HLA mismatched donors, successfully underwent ABO-incompatible kidney transplantation from his HLA-identical but nevertheless crossmatch-incompatible sister. The initial anti-A blood group isoagglutinin titers were 128, 256, and 1024 at room temperature, 37 degrees C, and 37 degrees C anti-IgG enhanced, respectively. With an individualized PP/IVIg regimen based on donor-specific antibody titer, however, the relevant antibodies were adequately reduced and hyperacute rejection avoided. Subsequent antibody-mediated rejection, likely directed against a minor histocompatibility antigen, was diagnosed on postoperative day 7 and successfully treated. Neither ABO, or crossmatch incompatibility, or both in combination prohibit kidney transplantation.

Immune response, accommodation, and tolerance to transplantation carbohydrate antigens

The carbohydrate antigens, blood groups A and B, and the alpha-gal epitope (Galalpha1-3Gal) are major risk factors in transplantation. Transplantation across ABO barriers may result in rejection by elicited anti-blood group antibodies, accommodation where elicited anti-blood group antibodies do not reject the graft, or tolerance where no anti-blood group antibodies are produced and the graft is not rejected. alpha1,3Galactosyltransferase knockout mice that lack alpha-gal epitopes but produce the anti-Gal antibody serve as a model for studying these immune responses. Knockout mice underwent transplantation heterotopically with wild-type mouse heart expressing alpha-gal epitopes and subsequently received lymphocytes including naive and memory anti-Gal B cells. The type of elicited immune response was found to be associated with the period that anti-Gal B cells were exposed to alpha-gal epitopes of the graft in the absence of T-cell help. Immediate T-cell help induced production of cytolytic anti-Gal antibodies that reject the graft, whereas delayed T-cell help induced production of accommodating anti-Gal antibodies. In the absence of T-cell help for prolonged periods, anti-Gal B cells exposed to alpha-gal epitopes were deleted, resulting in tolerance. Similar variations in the extent of T-cell help may determine the B-cell response to incompatible A or B antigens. The experimental model further suggests that active tolerance induction before transplantation may be achieved by gene therapy with autologous bone marrow cells or autologous lymphocytes manipulated to express the incompatible transplantation carbohydrate antigen by introduction of the corresponding glycosyltransferase gene into these cells.

Excellent long-term outcome of ABO-incompatible living donor kidney transplantation in Japan

Owing to the severe shortage of cadaveric grafts in Japan, we have performed ABO-incompatible living donor kidney transplantation since 1989. This study assessed short- and long-term outcomes in 441 patients who received ABO-incompatible living donor kidney transplants between January 1989 and December 2001. We compared our results with historical data from 1055 recipients of living kidney transplantation. Overall patient survival rates 1, 3, 5, 7, and 9 years after ABO-incompatible transplantation were 93%, 89%, 87%, 85%, and 84%, respectively. Corresponding overall graft survival rates were 84%, 80%, 71%, 65%, and 59%. After ABO-incompatible transplantation, graft survival rates were significantly higher in patients 29 years or younger than in those 30 years or older and in patients who received anticoagulation therapy than in those who did not receive such therapy. There were no significant differences between A-incompatible and B-incompatible recipients with respect to clinical outcomes. The graft survival rate at 1 year in the historical controls was slightly but not significantly higher than that in our recipients of ABO-incompatible transplants. We conclude that long-term outcome in recipients of ABO-incompatible living kidneys is excellent. Transplantation of ABO-incompatible kidneys from living donors is a radical, but effective treatment for end-stage renal disease.

Mouse-heart grafts expressing an incompatible carbohydrate antigen. II. Transition from accommodation to tolerance

BACKGROUND

Immune response to incompatible ABO antigens on allografts may result in rejection, accommodation, or immune tolerance. Our objective has been to develop a model for studying these three types of immune response to incompatible carbohydrate antigen in alpha1,3-galactosyltransferase knockout (KO) mice. KO mice lack the alpha-gal epitope and can produce the anti-Gal antibody against it after immunization with pig kidney membranes (PKM) that express this epitope.

METHODS

KO mice were transplanted with syngeneic wild-type (WT) heart expressing alpha-gal epitopes. Subsequently, the mice were lethally irradiated and received lymphocytes including memory anti-Gal B cells from PKM immunized KO mice. Immune response to incompatible alpha-gal epitopes on the graft was determined by transplanted-heart function and by production of anti-Gal after PKM immunizations.

RESULTS

Anti-Gal B cells exposed for 1 to 2 weeks to alpha-gal epitopes of WT hearts differentiate into cells producing noncytolytic accommodating antibodies. Exposure for longer periods (2-4 weeks) induces a transition from accommodation into tolerance, indicated by the inability of mice to produce anti-Gal antibodies despite repeated PKM immunizations. WT hearts in accommodating and in tolerized mice continue to function for months.

CONCLUSIONS

In the absence of T-cell help, anticarbohydrate B cells exposed to incompatible carbohydrate antigens of transplanted organs differentiate first into cells capable of producing accommodating antibodies, but, after prolonged exposure, these B cells gradually become tolerized. These findings suggest that prolonged T-cell suppression in recipients of ABO-incompatible allografts may result in a similar induction of tolerance to incompatible blood-group antigens.

Plasma adsorption in critical care

Plasmapheresis therapies such as plasma exchange (PE), double filtration plasmapheresis (DFPP), or immunoadsorption plasmapheresis (IAPP) have become therapeutic tools in critical care. PE or DFPP are limited by their non- or semiselective removal of all plasma components. Replacement fluids such as fresh frozen plasma and albumin are necessary during PE or DFPP. There is the risk of infection and allergic reactions whenever such fluids are used. On the other hand, IAPP is superior to PE and DFPP because it does not require any replacement fluid. There has been development of many adsorbent columns used for removing specific pathogenic substances, and patients with various kinds of critical illness have been treated with IAPP. However, IAPP can be applied only for certain diseases because of the limitations of the commercially available columns. It is concluded that the development of new adsorption therapy may improve the high mortality and morbidity rate in critically ill patients.