Antibody, complement and accommodation in ABO-incompatible transplants

Determination of the clinical relevance of donor epitope-specific HLA-antibodies in kidney transplantation

In kidney transplantation, survival rates are still partly impaired due to the deleterious effects of donor specific HLA antibodies (DSA). However, not all luminex-defined DSA appear to be clinically relevant. Further analysis of DSA recognizing polymorphic amino acid configurations, called eplets or functional epitopes, might improve the discrimination between clinically relevant vs. irrelevant HLA antibodies. To evaluate which donor epitope-specific HLA antibodies (DESAs) are clinically important in kidney graft survival, relevant and irrelevant DESAs were discerned in a Dutch cohort of 4690 patients using Kaplan-Meier analysis and tested in a cox proportional hazard (CPH) model including nonimmunological variables. Pre-transplant DESAs were detected in 439 patients (9.4%). The presence of certain clinically relevant DESAs was significantly associated with increased risk on graft loss in deceased donor transplantations (p < 0.0001). The antibodies recognized six epitopes of HLA Class I, 3 of HLA-DR, and 1 of HLA-DQ, and most antibodies were directed to HLA-B (47%). Fifty-three patients (69.7%) had DESA against one donor epitope (range 1-5). Long-term graft survival rate in patients with clinically relevant DESA was 32%, rendering DESA a superior parameter to classical DSA (60%). In the CPH model, the hazard ratio (95% CI) of clinically relevant DESAs was 2.45 (1.84-3.25) in deceased donation, and 2.22 (1.25-3.95) in living donation. In conclusion, the developed model shows the deleterious effect of clinically relevant DESAs on graft outcome which outperformed traditional DSA-based risk analysis on antigen level.

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.

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.

The emerging role of complement inhibitors in transplantation

The role of complement in the biology of kidney transplantation is becoming more and more significant, especially but not only because we now have access to drugs inhibiting complement. After describing the main characteristics of complement biology, both activation of the complement cascade and the many regulatory factors, we will review the precise role of complement in kidney transplant biology. Complement activation has been involved in ischemia-reperfusion injury, in the recurrence of several diseases such as atypical hemolytic uremic syndrome, C3 glomerulopathies, and antiphospholipid syndrome, as well as the process of antibody-mediated rejection, either acute or chronic. There are many potentially interesting drugs interfering with complement inhibition that have been or may be studied in kidney transplantation. Currently, the bulk of data concerns eculizumab, a monoclonal antibody blocking the complement cascade at the C5. Its efficacy has been demonstrated in the treatment and prevention of recurrence of atypical hemolytic uremic syndrome with an overall good safety profile. Although it has been reported to be efficacious to prevent antibody-mediated rejection, properly designed trials are currently being performed to state this efficacy. In addition, randomized trials are, in the process, regarding the prevention of ischemia-reperfusion injury after kidney transplantation.

New insights in antibody-mediated rejection

PURPOSE OF REVIEW

In the present review, we aim to describe the state of knowledge concerning antibody-mediated rejection (ABMR) spectrum and diagnosis criteria before analyzing the present and future promising leads regarding ABMR prognosis markers and treatment.

RECENT FINDINGS

Recent studies regarding complement-binding donor-specific antibodies and the molecular approach highlighted the unmet need for stratification tools for prognosis and treatment inside ABMR disease.

SUMMARY

ABMR is the leading cause of kidney allograft failure. The recent expansion of its spectrum is related to the paradigm of a continuous process, leading insidiously to a chronic form of ABMR and to the progressive acknowledgement of new entities (such as vascular ABMR, subclinical ABMR, C4d-negative ABMR). Considering the global picture of ABMR, the Banff classification gradually refined the diagnosis criteria so that it now describes a clinically relevant and coherent entity. Nevertheless, if the diagnosis mainly relies on conventional assessment, such as histological findings and circulating donor-specific antibodies, these criteria face serious limitations in terms of stratification of patients at risk of graft loss inside ABMR disease. Recently, new promising tools have emerged in order to identify long-term outcomes at the time of the diagnosis of rejection. In this regard, donor-specific antibodies' complement-fixing ability and the molecular approach contributed significantly. Currently, however, no clinically relevant surrogate marker of treatment efficiency is currently available.

Successful transplantation of kidney allografts in sensitized rats after syngeneic hematopoietic stem cell transplantation and fludarabine

Current methods to remove donor-specific HLA antibody (DSA) from sensitized patients remain imperfect. We tested novel approaches to desensitization using an animal model of allogeneic sensitization with skin grafts from dark agouti (DA) to Lewis rats. At the peak IgG alloantibody response we transplanted DA kidneys into nephrectomized Lewis recipients (n = 6) and all died within 10 days from antibody-mediated rejection (AMR). Allogeneic hematopoietic stem cell transplants (HSCT) from DA donors failed to engraft after lethal or sub-lethal irradiation. Sensitized rats given lethal irradiation plus syngeneic green fluorescent protein (GFP) + HSCT had repopulation of blood, spleen, thymus and lymph nodes by GFP+ cells. At 2 months after HSCT, serum DSA levels were reduced 60-70% and DSA (IgG) production in cultured splenocytes was also significantly decreased. However, there was only a modest improvement in graft survival from an average of 6.5 to 13.9 (n = 9) days. Adding seven daily doses of fludarabine to the preconditioning regimen resulted in long-term survival (>90 days) in 7 out of 10 rat kidney allografts. We conclude that syngeneic HSCT performed after preconditioning with irradiation and fludarabine can reduce DSA, prevent DSA rebound and AMR, enabling successful transplantation in animals with strong antibody reactivity to the donor MHC.

Diagnosis and prevention of chronic kidney allograft loss

Kidney transplantation is the best possible treatment for many patients with end-stage renal failure, but progressive dysfunction and eventual allograft loss with return to dialysis is associated with increased mortality and morbidity. Immune injury from acute or chronic rejection and non-immune causes, such as nephrotoxicity from calcineurin inhibitors, ischaemia-reperfusion injury, recurrent glomerular disease, and allograft BK viral infection, are potential threats. Serial monitoring of renal function enables early recognition of chronic allograft dysfunction, and investigations such as therapeutic drug concentrations, urinalysis, imaging, and a diagnostic biopsy should be undertaken before irreversible nephron loss has occurred. Specific interventions targeting the pathophysiological cause of dysfunction include strengthening of immunosuppression for chronic rejection, or calcineurin inhibitor minimisation, substitution, or elimination if nephrotoxicity dominates. Recommended proactive preventive measures are control of hypertension, proteinuria, dyslipidaemia, diabetes, smoking, and other comorbidities. Strategies to maintain transplant function and improve long-term graft survival are important goals of translational research.

ABO antibody titer and risk of antibody-mediated rejection in ABO-incompatible renal transplantation

Therapeutic plasma exchange (TPE) preconditioning with immunosuppressive therapy reduces ABO antibody titers, permitting engraftment of ABO-incompatible (ABO-I) kidney transplants. The posttransplant predictive role of ABO antibody titers for antibody-mediated rejection (AMR) is unknown. This retrospective study evaluated 46 individuals who received TPE to permit ABO-I kidney transplantation. ABO antibody titers were performed using donor-type indicator red cells. Seven individuals (15.2%) experienced clinical or subclinical AMR. There was no significant difference between recipient blood group, number of pretransplant TPE and baseline titer between those with and without AMR. At 1-2 weeks posttransplant the median titer was 64 (range 4 - 512) among individuals with AMR and 16 (range 2 - 256) among individuals without AMR. Total agglutination reactivity score was significantly higher among individuals with AMR (p = 0.046). The risk of AMR was significantly higher among individuals with an elevated posttransplant titer of >or=64 (p = 0.006). The sensitivity of an elevated posttransplant titer was 57.1% with a specificity of 79.5%. The positive predictive value was 33.3% and the negative predictive value was 91.2%. Most individuals with AMR have an elevated titer, however, the positive predictive value of a high titer for AMR is poor.

Therapeutic plasma exchange reduces ABO titers to permit ABO-incompatible renal transplantation

BACKGROUND

Thousands of patients with chronic renal failure die yearly without a kidney transplant due to the severe shortage of donors. Therapeutic plasma exchange (TPE) is performed to permit ABO-incompatible (ABO-I) kidney transplants, but little is known about how well TPE reduces ABO antibodies or complications related to TPE in this clinical setting.

STUDY DESIGN AND METHODS

This retrospective study evaluated 46 individuals that received TPE to permit ABO-I kidney transplant. The number of TPE treatments was based on a goal ABO titer at the anti-human globulin (AHG) phase of 16 or less before surgery.

RESULTS

Before TPE, the median titer of recipient was 32 (range, 2-128) at room temperature (RT) phase and 64 (range, 4-1024) at AHG phase. The first TPE reduced the total agglutination reactivity score at AHG phase by 10.2 percent. Before transplantation, there was a mean of 6.2 +/- 2.5 TPE treatments and total agglutination reactivity score at AHG phase was reduced by 53.5 percent. The median titer remained reduced at 3 to 6 months after transplantation at 4 (range, 0-64) at RT phase and 8 (range, 1-64) at AHG phase. TPE complications were minimal. During at least one procedure, 15 (32.6%) individuals had either urticaria or pruritus, 18 (39.1%) individuals experienced mild citrate-induced hypocalcemia, 5 (10.2%) individuals had hypotension, 6 (13.0%) individuals had nausea or vomiting, and 1 (2.2%) individual had West Nile virus encephalitis.

CONCLUSIONS

With current infectious disease blood screening protocols, TPE has minimal complications and can reduce ABO antibody titers to permit ABO-I renal transplantation.

Four stages and lack of stable accommodation in chronic alloantibody-mediated renal allograft rejection in Cynomolgus monkeys

The etiology of immunologically mediated chronic renal allograft failure is unclear. One cause is thought to be alloantibodies. Previously in Cynomolgus monkeys, we observed a relationship among donor-specific alloantibodies (DSA), C4d staining, allograft glomerulopathy, allograft arteriopathy and progressive renal failure. To define the natural history of chronic antibody-mediated rejection and its effect on renal allograft survival, we now extend this report to include 417 specimens from 143 Cynomolgus monkeys with renal allografts. A subset of animals with long-term renal allografts made DSA (48%), were C4d positive (29%), developed transplant glomerulopathy (TG) (22%) and chronic allograft arteriopathy (CAA) (19%). These four features were highly correlated and associated with statistically significant shortened allograft survival. Acute cellular rejection, either Banff type 1 or 2, did not correlate with alloantibodies, C4d deposition or TG. However, endarteritis (Banff type 2) correlated with later CAA. Sequential analysis identified four progressive stages of chronic antibody-mediated rejection: (1) DSA, (2) deposition of C4d, (3) TG and (4) rising creatinine/renal failure. These new findings provide strong evidence that chronic antibody-mediated rejection develops without enduring stable accommodation, progresses through four defined clinical pathological stages and shortens renal allograft survival.

Can ABO-incompatible organ transplantation pave the way for clinical xenotransplantation?

Because of the apparent mechanistic similarities between antibody-mediated rejection of ABO-incompatible organ allografts and vascularized xenografts, there is hope that strategies to enable transplantation across the ABO barrier may also be effective in curbing xenograft rejection. This paper discusses the molecular similarities and differences between an ABO-incompatible allograft and a porcine xenograft in terms of their interactions with the immune system.

Multicenter experience of ABO-incompatible pediatric cardiac transplantation

Although ABO blood group incompatible cardiac transplantation in neonates and infants reduces waiting list mortality without compromising outcome, the technique has not been adopted by all centers, and to date Toronto remains the only center to have published results from a large case series. We present a review of ABO-incompatible heart transplantation in the United Kingdom (UK) where current recipient selection criteria differ somewhat from those used in the United States (US) and Canada. Between February 2000 and November 2006, 21 ABO-incompatible cardiac transplants were performed in children aged 2-40 months (median 10.0). Immunosuppression followed standard regimens. Pretransplant donor-specific isohemagglutinins of >1:4, (the UNOS cutoff), were present in five patients and reduced by plasma exchange. After transplantation, 19/21 recipients demonstrated persisting deficiency of donor-specific isohemagglutinins. Significant donor-specific isohemagglutinins levels were detected repeatedly in 2/21 recipients who have shown no clinical or biopsy evidence of rejection. All recipients survive without retransplantation and there have been no episodes of humoral rejection. We conclude it is possible for other centers to replicate the excellent results achieved in Toronto and that ABO-incompatible transplantation may be performed successfully in some patients beyond infancy with established isohemagglutinin production providing preoperative antibody removing strategies are used.

Expression of complement regulatory proteins in accommodated xenografts induced by anti-alpha-Gal IgG1 in a rat-to-mouse model

Anti-graft antibodies are often associated with graft rejection. Under special conditions, grafts continue to function normally even in the presence of anti-graft antibodies and complement. This condition is termed accommodation. We developed a xenograft accommodation model in which baby Lewis rat hearts are transplanted into Rag/GT-deficient mice, and accommodation is induced by repeated i.v. injections of low-dose anti-alpha-Gal IgG(1). The accommodated grafts survived a bolus dose of anti-alpha-Gal IgG(1), while freshly transplanted second grafts were rejected. To study the mechanism of anti-alpha-Gal IgG(1)-mediated accommodation, both real-time PCR and immunohistochemical staining revealed elevated expression of DAF, Crry and CD59 in the accommodated grafts. In vitro exposure of rat endothelial cells to anti-alpha-Gal IgG(1) also induced the up-regulation of DAF, Crry and CD59, as revealed by Western blot analyses, and was associated with an acquired resistance to antibody and complement-mediated lysis in vitro. Collectively, these studies suggest that the up-regulation of complement regulatory proteins may abrogate complement-mediated rejection and permit the development of xenograft accommodation.

Accommodation of grafts: implications for health and disease

Accommodation refers to the acquired resistance of a graft to immune-mediated injury. It is typically observed after antibodies that would cause rejection of a graft are removed from a recipient and then later return. In addition to being induced in this manner, accommodation can occur spontaneously, without depleting antibodies. Indeed, we postulate spontaneous accommodation may be the most common outcome of clinical organ transplantation. The paper reviews the current understanding of accommodation, emphasizing recent advances and important questions. Among the recent advances are the discoveries of potentially broader relevance of accommodation for biology and immunology and pathways by which accommodation may be achieved. To investigate these pathways and to understand how accommodation begins and how it evolves, clinical organ transplants might offer a useful and incisive model.

Post-transplant anti-HLA class II antibodies as risk factor for late kidney allograft failure

The purpose of this study was to prospectively analyze the relationship between the post-transplant anti-HLA class I and/or class II panel reactive antibodies and graft failure due to chronic allograft nephropathy (CAN). We studied 512 first kidney recipients transplanted at a single center, with a graft functioning for at least 3 years. A single blood sample was collected from each patient for antibody evaluation. The median posttransplant time after blood collection was 4.4 years and did not differ between patients with (n = 91) or without anti-HLA antibodies (n = 421). Female gender, pregnancies and blood transfusions were associated with the presence of anti-HLA class I antibodies. Graft function deterioration was associated with anti-HLA class II antibodies. Multivariate analysis showed independent association for creatinine levels (RR = 7.5), acute rejection (RR = 2.6), recipient male gender (RR = 3.6) and anti-HLA class II antibodies (RR = 2.9) and CAN-associated graft loss. In conclusion, the presence of anti-HLA class II antibodies conferred a risk for graft loss before a decline in renal function and increased the risk of graft failure in patients who already had a decline in graft function. Thus, anti-HLA class II antibody monitoring is a useful tool for the management of long-term kidney recipients.

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.

Humoral rejection of organ allografts

In recent years, the deleterious clinical consequences of recipient de novo alloantibody production against HLA antigens from human organ allografts have been extensively investigated. In kidney transplantation, the identification of the complement C4d fragment in peritubular capillaries as a specific marker for humoral rejection has helped to define and characterize distinct clinical alloantibody-mediated syndromes. This knowledge is relevant for patient management as new therapeutic strategies to remove and control anti-donor antibody production, particularly in the setting of acute humoral rejection, have been reported. For recipients of nonrenal organ allografts such as heart transplant recipients, de novo anti-HLA alloantibody may also be important, although more studies are needed before clear guidelines can be proposed.

Extending options for highly sensitized patients to receive a suitable kidney graft

Highly sensitized patients (anti-HLA) on the kidney waiting list wait longer for a suitable crossmatch negative organ. At the moment there are two strategies to enhance transplantation of these patients. One approach is the determination of acceptable HLA mismatches and application of this knowledge for the selection of crossmatch negative donors, and the second is the desensitization of patients with intravenous immunoglobulin-based protocols to enable transplantation of an organ from a donor towards which antibodies were originally present. Both approaches have advantages and disadvantages and are only successful in a proportion of the patients. The optimal solution is an integrated strategy whereby desensitization is used for those patients for whom the acceptable mismatch approach is not successful.