Advances in diagnosing and managing antibody-mediated rejection

Living Donor Liver Transplantation in Patients with Preformed Donor-Specific Anti-Human Leukocyte Antigen Antibodies Using Preoperative Desensitization Therapy According to Intensity of Donor-Specific Antibodies: A Single-Center Study

BACKGROUND In liver transplantation (LT), preoperative desensitization therapy is considered necessary in patients positive for donor-specific anti-human leukocyte antigen antibodies (DSAs). However, the relationship between DSA intensity and the necessary desensitization therapy is unclear. MATERIAL AND METHODS A total of 37 adult living donor (LD) LTs performed between January 2016 and March 2022 were examined. Mycophenolate mofetil (MMF) was administered preoperatively in DSA-positive cases with positive lymphocyte cross-matching who underwent LDLT. In those with strongly positive DSA (mean fluorescence intensity 10 000), rituximab was administered 2 weeks before LDLT in addition to MMF. Cross-reactive epitope group antigen (CREG)-alone-positive cases were also treated with preoperative MMF when lymphocyte cross-matching was positive. RESULTS Of the 37 patients, 9 were DSA-positive, 7 were CREG-alone-positive, and the others were double-negative. Of 9 DSA-positive cases, desensitization therapy was performed in 7, among which rituximab administration was performed in 3 strongly DSA-positive cases. Of 7 CREG-alone-positive cases, 2 were lymphocyte cross-match-positive and underwent desensitization therapy. The 1-year survival rate was 100% in both DSA- and CREG-alone-positive cases. The frequency of T-cell mediated rejection in DSA-positive, CREG-alone-positive, and double-negative cases was 22%, 43%, and 29%, respectively, with no significant difference. Antibody-mediated rejection occurred in only 1 patient, who was strongly DSA-positive and blood-group incompatible. There was also no significant difference among the 3 groups in terms of the frequency of biliary complications or 90-day mortality. CONCLUSIONS Satisfactory LDLT results were achieved in DSA- and CREG-alone-positive cases following desensitization therapy.

Novel insights in the clinical management of hyperimmune patients before and after transplantation

Despite improvements in anti-Human Leucocyte Antigens antibody detection, identification, and characterization offer a better in peri-operative management techniques, antibodies remain a serious cause of morbidity and mortality for patients both before and after organ transplantation. Hyperimmune patients are disadvantaged by having to wait longer to receive an organ from a suitably matched donor. They could benefit from desensitization protocols in both pre- and post-transplantation period. Clinical studies are underway to highlight which best desensitization strategies could be assure the best outcome in both heart and kidney transplantation. Although most clinical evidence about desensitization strategies by using anti-CD20 monoclonal antibodies, proteasome inhibitors, anti-CD38 monoclonal antibodies, interleukin-6 blockade, cysteine protease and complement inhibitors, comes from kidney transplantation studies, many of the debated novel concepts can be easily applied to desensitization also in heart transplantation. Here, we discuss the candidates and recipients' management by using most common standard of care and novel therapeutics, desensitization endpoints, and strategies for future studies.

Evaluation of Cumulative Effect of Standard Triple Immunosuppression on Prevention of De Novo Donor Specific Antibodies (dnDSA) Production in Children after Kidney Transplantation—A Retrospective and Prospective Study

De novo Donor Specific Antibodies (dnDSA) are associated with inferior graft outcomes. Standard immunosuppression is expected to prevent dnDSA production in low-risk patients. We have evaluated a cumulative effect of a triple immunosuppression (CNI/MMF/Pred), as well as TAC concentration and coefficient of variation on the incidence of dnDSA production. Overall, 67 transplanted patients were evaluated in retrospective (dnDSA for-cause; n = 29) and prospective (dnDSA by protocol; n = 38) groups. In the retrospective group, the eGFR value at first dnDSA detection (median interval—4.0 years post-transplant) was 41 mL/min/1.73 m²; 55% of patients presented biopsy-proven cAMR, and 41% lost the graft within next 2.4 years. Patients from the prospective group presented 97% graft survival and eGFR of 76 mL/min/1.73 m² at 2 years follow-up, an overall incidence of 21% of dnDSA and 18% of acute (T cell) rejection. None of the patients from the prospective group developed cAMR. Median value of Vasudev score within 2 years of follow-up was not significantly higher in dsDSA negative patients, while median value of TAC C₀ > 1–24 months post-transplant was 7.9 in dnDSA negative vs. 7.1 ng/mL in dnDSA positive patients (p = 0.008). Conclusion: dnDSA-negative patients presented a higher exposure to tacrolimus, while not to the combined immunosuppression.

Correlates of survival after autoantibody reduction therapy for acute IPF exacerbations

Background

No medical treatment has proven efficacy for acute exacerbations of idiopathic pulmonary fibrosis (AE-IPF), and this syndrome has a very high mortality. Based on data indicating humoral autoimmune processes are involved in IPF pathogenesis, we treated AE-IPF patients with an autoantibody reduction regimen of therapeutic plasma exchange, rituximab, and intravenous immunoglobulin. This study aimed to identify clinical and autoantibody determinants associated with survival after autoantibody reduction in AE-IPF.

Methods

Twenty-four(24) AE-IPF patients received the autoantibody reduction regimen. Plasma anti-epithelial autoantibody titers were determined by HEp-2 indirect immunofluorescence assays in 22 patients.

Results

Mean age of the patients was 70 + 7 years old, and 70% were male. Beneficial clinical responses that occurred early during therapy were a favorable prognostic indicator: supplemental O₂ flows needed to maintain resting S_aO₂>92% significantly decreased and/or walk distances increased among all 10 patients who survived for at least one year. Plasma anti-HEp-2 autoantibody titers were ~-three-fold greater in survivors compared to non-survivors (p<0.02). Anti-HEp-2 titers >1:160 were present in 75% of the evaluable one-year survivors, compared to 29% of non-survivors, and 10 of 12 patients (83%) with anti-HEP-2 titers <1:160 died during the observation period (Hazard Ratio = 3.3, 95% Confidence Interval = 1.02–10.6, p = 0.047).

Conclusions

Autoantibody reduction therapy is associated with rapid reduction of supplemental oxygen requirements and/or improved ability to ambulate in many AE-IPF patients. Facile anti-epithelial autoantibody assays may help identify those most likely to benefit from these treatments.

Abrogating biologics interference in flow cytometric crossmatching

The flow cytometric crossmatch is currently the gold standard for evaluating donor and recipient histocompatibility. The assay however does have limitations and is sensitive to false positive reactions resulting from the presence of non-HLA antibodies or therapy related immune biologics. Such false positive reactions can lead to the inappropriate decline of an acceptable donor organ or unnecessary therapeutic intervention. Here we describe the successful validation of anti-idiotype blocking antibodies in prevention of false positive flow crossmatch results caused by biologic therapy. Blocking antibodies specific for the Fab portion of Rituximab and/or Alemtuzumab were incubated with biologic containing patient serum prior to use in flow cytometric crossmatching. Biologic blocking successfully negated false positive crossmatch results with Rituximab (B cell ave. % change = -97%) or Alemtuzumab (T cell ave. % change = -99%, B cell ave. % change = -95%) infused sera respectively. Simultaneous blocking of these biologics was also successful. A complex case is presented to demonstrate the application of this procedure.

Novel Therapeutic Approaches to Allosensitization and Antibody-mediated Rejection

Modification of pathogenic antibodies for autoimmune diseases illuminated the biologic relevance of B cells, plasma cells, and pathogenic antibodies in autoimmunity. They have also rejuvenated interest in how B cells mediate multiple effector functions that include antibody production, antigen presentation to T cells, costimulation, and the production of immune stimulating and immune modulatory cytokines. Repurposing these drugs from autoimmunity and cancer immunotherapy has yielded important advancements in the care of antibody-mediated rejection patients and novel drug development aimed at HLA desensitization have recently emerged. We now stand on an important threshold that promises many advances in the care of our allosensitized patients. We hope that these initial advances will encourage basic scientist, clinical investigators, industry, National Institutes of Health, our academic societies, and the Food and Drug Administration to continue support of these important objectives. These advances clearly have implications for sensitized patients receiving solid organ transplants and antibody-mediated rejection treatment. Modification of alloimmunity and alloantibodies will also have relevance to xenotransplantation where the xenoantibodies present a formidable obstacle to advancement of this important therapy. Working together, we can advance transplant therapeutics where biologic agents are likely to play novel and important roles. Here, we discuss novel drugs emerging in this area.

Therapeutic Plasma Exchange in Pediatric Renal Transplantation Experience of One Decade and 389 Sessions

OBJECTIVE

There are no specific recommendations for therapeutic plasma exchange (TPE) in children after renal transplantation. The purpose of this study was to report the experience with TPE in a pediatric transplant setting.

MATERIALS AND METHODS

59 patients (mean age 12.5 ± 4.5 years) undergoing renal transplantation. Indications for TPE included the recurrence of nephrotic syndrome (NS; n = 30) and atypical hemolytic uremic syndrome (n = 6), chronic antibody-mediated rejection (cAMR; n = 20), sensitization (n = 2), and immune thrombocytopenia (n = 1). The single-filtration TPE was performed in all cases. In 74.7% of patients, fresh frozen plasma was used as a replacement fluid. In 25.3% of patients, 4% albumin solution was used as a replacement fluid. Criteria for TPE efficacy included a decrease of proteinuria and normalization of renal function in NS; a normalization of platelet count, C3, and hemoglobin concentration in aHUS; improvement in renal function; and reduction of donor-specific antibodies in cAMR; and removal of antiplatelet antibodies in immune thrombocytopenia.

RESULTS

Efficacy results for patients with NS: 59.3% achieved remission, 25.9% achieved partial remission, and 14.8% achieved no remission, respectively. For patients with atypical hemolytic uremic syndrome there was remission in 66.6% and no remission in 33.4%. For patients with cAMR there was remission in 75% and no remission in 25%. Antiplatelet antibodies disappeared after TPE in 1 patient. In 9% of TPE procedures, minor complications were noted. All patients were on posttransplant maintenance immunosuppression and several children received additional treatment (intravenous immunoglobulin therapy or rituximab) during TPE therapy.

CONCLUSION

TPE therapy (combined with immunosuppression) was an effective tool in most pediatric cases after renal transplantation with low incidence of minor adverse events.

De novo glomerular diseases after renal transplantation: How is it different from recurrent glomerular diseases?

The glomerular diseases after renal transplantation can occur de novo, i.e., with no relation to the native kidney disease, or more frequently occur as a recurrence of the original disease in the native kidney. There may not be any difference in clinical features and histological pattern between de novo glomerular disease and recurrence of original glomerular disease. However, structural alterations in transplanted kidney add to dilemma in diagnosis. These changes in architecture of histopathology can happen due to: (1) exposure to the immunosuppression specifically the calcineurin inhibitors (CNI); (2) in vascular and tubulointerstitial alterations as a result of antibody mediated or cell-mediated immunological onslaught; (3) post-transplant viral infections; (4) ischemia-reperfusion injury; and (5) hyperfiltration injury. The pathogenesis of the de novo glomerular diseases differs with each type. Stimulation of B-cell clones with subsequent production of the monoclonal IgG, particularly IgG3 subtype that has higher affinity to the negatively charged glomerular tissue, is suggested to be included in PGNMID pathogenesis. De novo membranous nephropathy can be seen after exposure to the cryptogenic podocyte antigens. The role of the toxic effects of CNI including tissue fibrosis and the hemodynamic alterations may be involved in the de novo FSGS pathophysiology. The well-known deleterious effects of HCV infection and its relation to MPGN disease are frequently reported. The new concepts have emerged that demonstrate the role of dysregulation of alternative complement pathway in evolution of MPGN that led to classifying into two subgroups, immune complex mediated MPGN and complement-mediated MPGN. The latter comprises of the dense deposit disease and the C3 GN disease. De novo C3 disease is rather rare. Prognosis of de novo diseases varies with each type and their management continues to be empirical to a large extent.

Rituximab and Monitoring Strategies for Late Antibody-Mediated Rejection After Kidney Transplantation

Background

There is limited information on treatment strategies and monitoring strategies for late antibody-mediated rejection (ABMR) after kidney transplantation.

Methods

In this observational and nonrandomized study, we compared 78 patients diagnosed with late ABMR (>3 months after transplant) who were treated with standard of care steroids/IVIG (n = 38) ± rituximab (n = 40) at our center between March 1, 2013 and December 31, 2016. All patients had follow-up biopsy and donor-specific antibodies (DSA) monitoring within 3 to 12 weeks.

Results

Patients had biopsy 7.3 ± 7 years after transplant and were followed for 15.9 ± 9.6 months after ABMR was diagnosed. Both treatment strategies were associated with a significant decline in DSA, microvascular inflammation (peritubular capillaritis + glomerulitis), and C4d Banff scores. In univariate regression analyses, rituximab, estimated glomerular filtration rate (eGFR), Banff i, t, v, chronicity (interstitial fibrosis + tubular atrophy + fibrous intimal thickening + allograft glomerulopathy) scores on the first biopsy, and eGFR and Banff v score on follow-up biopsy were associated with graft loss. Multivariate analyses retained only rituximab (hazard ratio, 0.23; 95% confidence interval, 0.06-0.84; P = 0.03) and eGFR at follow-up biopsy (0.84; 95% confidence interval, 0.76-0.92; P < 0.001) as significant predictors of graft loss. Kaplan-Meier analyses demonstrated that the benefit associated with rituximab was apparent after 1 year (15% vs 32% graft loss, P = 0.02).

Conclusion

Treatment of late ABMR with steroids/IVIG ± rituximab was effective in reducing DSA and microcirculation inflammation. The addition of rituximab was associated with better graft survival. Follow-up biopsies could be considered in the management of acute rejection to monitor the effect of therapy. Randomized studies on the best therapeutic options for ABMR are needed.

Plasma Exosomes From HLA-Sensitized Kidney Transplant Recipients Contain mRNA Transcripts Which Predict Development of Antibody-Mediated Rejection

BACKGROUND

Sensitization to HLA remains a significant immunologic barrier to successful transplantation. Identifying immune mechanisms responsible for antibody-mediated rejection (AMR) is an important goal. Here, we explored the possibility of predicting the risk for AMR by measuring mRNA transcripts of AMR-associated genes in plasma exosomes from kidney transplant patients.

METHODS

Total RNA was extracted from exosomes purified from 152 ethylenediaminetetraacetic acid-plasma samples of 64 patients (18 AMR, 8 cell-mediated rejection [CMR], 38 no rejection in desensitized [DES] and non-DES control groups) for reverse transcription into cDNA, preamplification and then real time quantitative polymerase chain reaction (qPCR) for 21 candidate genes. The mRNA transcript levels of each gene were calculated. Comparisons were made among 4 patient groups for each gene and also for a gene combination score based on selected genes.

RESULTS

Among 21 candidate genes, we identified multiple genes (gp130, CCL4, TNFα, SH2D1B, CAV1, atypical chemokine receptor 1 [duffy blood group]) whose mRNA transcript levels in plasma exosomes significantly increased among AMR compared with CMR and/or control patients. A gene combination score calculated from 4 genes of gp130, SH2D1B, TNFα, and CCL4 was significantly higher in the AMR than the CMR (P < 0.0001) and no rejection control groups (P < 0.01 vs DES control, P < 0.05 vs non-DES control).

CONCLUSIONS

Our results suggest that plasma exosomes may contain information indicating clinical conditions of kidney transplant patients. mRNA transcript profiles based on gp130, SH2D1B, TNFα, and CCL4 in plasma exosomes may be used to predict on-going and/or imminent AMR.

Assessment of Tocilizumab (Anti-Interleukin-6 Receptor Monoclonal) as a Potential Treatment for Chronic Antibody-Mediated Rejection and Transplant Glomerulopathy in HLA-Sensitized Renal Allograft Recipients

Extending the functional integrity of renal allografts is the primary goal of transplant medicine. The development of donor-specific antibodies (DSAs) posttransplantation leads to chronic active antibody-mediated rejection (cAMR) and transplant glomerulopathy (TG), resulting in the majority of graft losses that occur in the United States. This reduces the quality and length of life for patients and increases cost. There are no approved treatments for cAMR. Evidence suggests the proinflammatory cytokine interleukin 6 (IL-6) may play an important role in DSA generation and cAMR. We identified 36 renal transplant patients with cAMR plus DSAs and TG who failed standard of care treatment with IVIg plus rituximab with or without plasma exchange. Patients were offered rescue therapy with the anti-IL-6 receptor monoclonal tocilizumab with monthly infusions and monitored for DSAs and long-term outcomes. Tocilizumab-treated patients demonstrated graft survival and patient survival rates of 80% and 91% at 6 years, respectively. Significant reductions in DSAs and stabilization of renal function were seen at 2 years. No significant adverse events or severe adverse events were seen. Tocilizumab provides good long-term outcomes for patients with cAMR and TG, especially compared with historical published treatments. Inhibition of the IL-6-IL-6 receptor pathway may represent a novel approach to stabilize allograft function and extend patient lives.

IgG Endopeptidase in Highly Sensitized Patients Undergoing Transplantation

BACKGROUND

Donor-specific antibodies create an immunologic barrier to transplantation. Current therapies to modify donor-specific antibodies are limited and ineffective in the most highly HLA-sensitized patients. The IgG-degrading enzyme derived from Streptococcus pyogenes (IdeS), an endopeptidase, cleaves human IgG into F(ab')₂ and Fc fragments inhibiting complement-dependent cytotoxicity and antibody-dependent cellular cytotoxicity, which suggests that IdeS might be useful for desensitization. We report on the combined experience of two independently performed open-label, phase 1-2 trials (conducted in Sweden and the United States) that assessed the efficacy of IdeS with regard to desensitization and transplantation of a kidney from an HLA-incompatible donor.

METHODS

We administered IdeS to 25 highly HLA-sensitized patients (11 patients in Uppsala or Stockholm, Sweden, and 14 in Los Angeles) before the transplantation of a kidney from an HLA-incompatible donor. Frequent monitoring for adverse events, outcomes, donor-specific antibodies, and renal function was performed, as were renal biopsies. Immunosuppression after transplantation consisted of tacrolimus, mycophenolate mofetil, and glucocorticoids. Patients in the U.S. study also received intravenous immune globulin and rituximab after transplantation to prevent antibody rebound.

RESULTS

Recipients in the U.S. study had a significantly longer cold ischemia time (the time elapsed between procurement of the organ and transplantation), a significantly higher rate of delayed graft function, and significantly higher levels of class I donor-specific antibodies than those in the Swedish study. A total of 38 serious adverse events occurred in 15 patients (5 events were adjudicated as being possibly related to IdeS). At transplantation, total IgG and HLA antibodies were eliminated. A total of 24 of 25 patients had perfusion of allografts after transplantation. Antibody-mediated rejection occurred in 10 patients (7 patients in the U.S. study and 3 in the Swedish study) at 2 weeks to 5 months after transplantation; all these patients had a response to treatment. One graft loss, mediated by non-HLA IgM and IgA antibodies, occurred.

CONCLUSIONS

IdeS reduced or eliminated donor-specific antibodies and permitted HLA-incompatible transplantation in 24 of 25 patients. (Funded by Hansa Medical; ClinicalTrials.gov numbers, NCT02224820 , NCT02426684 , and NCT02475551 .).

Potential Roles for C1 Inhibitor in Transplantation

Complement is a major contributor to inflammation and graft injury. This system is especially important in ischemia-reperfusion injury/delayed graft function as well as in acute and chronic antibody-mediated rejection (AMR). The latter is increasingly recognized as a major cause of late graft loss, for which we have few effective therapies. C1 inhibitor (C1-INH) regulates several pathways which contribute to both acute and chronic graft injuries. However, C1-INH spares the alternative pathway and the membrane attack complex (C5–9) so innate antibacterial defenses remain intact. Plasma-derived C1-INH has been used to treat hereditary angioedema for more than 30 years with excellent safety. Studies with C1-INH in transplant recipients are limited, but have not revealed any unique toxicity or serious adverse events attributed to the protein. Extensive data from animal and ex vivo models suggest that C1-INH ameliorates ischemia-reperfusion injury. Initial clinical studies suggest this effect may allow transplantation of donor organs which are now discarded because the risk of primary graft dysfunction is considered too great. Although the incidence of severe early AMR is declining, accumulating evidence strongly suggests that complement is an important mediator of chronic AMR, a major cause of late graft loss. Thus, C1-INH may also be helpful in preserving function of established grafts. Early clinical studies in transplantation suggest significant beneficial effects of C1-INH with minimal toxicity. Recent results encourage continued investigation of this already-available therapeutic agent.

Update on the use of immunoglobulin in human disease: A review of evidence

Human immunoglobulin preparations for intravenous or subcutaneous administration are the cornerstone of treatment in patients with primary immunodeficiency diseases affecting the humoral immune system. Intravenous preparations have a number of important uses in the treatment of other diseases in humans as well, some for which acceptable treatment alternatives do not exist. We provide an update of the evidence-based guideline on immunoglobulin therapy, last published in 2006. Given the potential risks and inherent scarcity of human immunoglobulin, careful consideration of its indications and administration is warranted.

Factors Predicting Risk for Antibody-mediated Rejection and Graft Loss in Highly Human Leukocyte Antigen Sensitized Patients Transplanted After Desensitization

BACKGROUND

Desensitization with intravenous immunoglobulin and rituximab (I+R) significantly improves transplant rates in highly sensitized patients, but antibody-mediated rejection (ABMR) remains a concern.

PATIENTS AND METHODS

Between July 2006 and December 2012, 226 highly sensitized patients received transplants after desensitization. Most received alemtuzumab induction and standard immunosuppression. Two groups were examined: ABMR (n = 181) and ABMR (n = 45, 20%). Risk factors for ABMR, pathology, and outcomes were assessed.

RESULTS

Significant risks for ABMR included previous transplants and pregnancies as sensitizing events, donor-specific antibody (DSA) relative intensity scores greater than 17, presence of both class I and II DSAs at transplant and time on waitlist. The ABMR showed a significant benefit for graft survival and glomerular filtration rate at 5 years (P < 0.0001). Banff pathology characteristics for ABMR patients with or without graft loss did not differ. C4d versus C4d ABMR did not predict graft loss (P = 0.086). Thrombotic microangiopathy (TMA) significantly predicted graft failure (P = 0.045). The ABMR episodes were treated with I+R (n = 25), or, in more severe ABMR, plasma exchange (PLEX)+I+R (n = 20). Graft survival for patients treated with I+R was superior (P = 0.028). Increased mortality was seen in ABMR patients experiencing graft loss after ABMR treatment (P = 0.004). The PLEX + Eculizumab improved graft survival for TMA patients (P = 0.036).

CONCLUSION

Patients desensitized with I+R who remain ABMR have long-term graft and patient survival. The ABMR patients have significantly reduced graft survival and glomerular filtration rate at 5 years, especially TMA. Severe ABMR episodes benefit from treatment with PLEX + Eculizumab. The DSA-relative intensity scores at transplant was a strong predictor of ABMR. Donor-specific antibody avoidance and reduction strategies before transplantation are critical to avoiding ABMR and improving long-term outcomes.

Off-label use of the expensive orphan drug eculizumab in France 2009-2013 and the impact of literature: focus on the transplantation field

PURPOSE

The orphan drug eculizumab (Soliris ®) is one of the most expensive in the world and based on expenditures is classed among the highest in France, a scenario suggestive of off-label use. Given its pharmacological properties, it is likely to be used in organ transplantation. Our purposes were to describe the consumption trends of eculizumab for off-label indications overall and in the organ transplantation field and to assess the impact of publications on the latter use.

METHODS

We carried out a temporal ecological study within the French national hospitalization database (PMSI). First, the trend of eculizumab consumption (2009-2013) was compared to our estimate of the maximum on-label consumption (overall and for transplantation). Second, we evaluated the impact of the publications supporting the effectiveness of eculizumab in the transplantation field on temporal trends of eculizumab consumption.

RESULTS

Eculizumab total consumption exceeded our estimate of the maximum on-label consumption since the end of 2011 and increased until the end of the study. The off-label consumption represented at least 50 % of the total consumption. The off-label consumption in organ transplantation also increased since 2011. The amount of publications grew through the study period, but overall, the evidence level remained low. Statistically, publications were neither associated with the drug consumption for transplantation in the long term nor in the short term.

CONCLUSION

Eculizumab started being notably used for off-label indications in France since the end of 2011, and this use increased until the end of the study. We found only low-level evidence concerning the off-label use of eculizumab in the transplantation field through the studied period.

Post-Transplant Membranous Nephropathy Associated with Chronic Active Antibody-Mediated Rejection and Hepatitis C Infection after Deceased Donor Renal Transplantation

A 53-year-old woman who had undergone deceased donor kidney transplantation twice, at 35 and 43 years of age, presented with renal impairment. She was infected with hepatitis C virus (HCV). The histology of the graft kidney revealed post-transplant membranous nephropathy (MN) with podocytic infolding and antibody-mediated rejection (AMR). IgG subclass staining showed fine granular deposits of IgG1 and IgG3, but not IgG4, in the glomerular capillary walls. Panel reactive antibody scores for human leukocyte antigen class I and class II were 92.67% and 66.68%, respectively. Thus, this case of post-transplanted MN was considered to be associated with AMR and HCV infection.

Targeted complement inhibition and microvasculature in transplants: a therapeutic perspective

Active complement mediators play a key role in graft-versus-host diseases, but little attention has been given to the angiogenic balance and complement modulation during allograft acceptance. The complement cascade releases the powerful proinflammatory mediators C3a and C5a anaphylatoxins, C3b, C5b opsonins and terminal membrane attack complex into tissues, which are deleterious if unchecked. Blocking complement mediators has been considered to be a promising approach in the modern drug discovery plan, and a significant number of therapeutic alternatives have been developed to dampen complement activation and protect host cells. Numerous immune cells, especially macrophages, develop both anaphylatoxin and opsonin receptors on their cell surface and their binding affects the macrophage phenotype and their angiogenic properties. This review discusses the mechanism that complement contributes to angiogenic injury, and the development of future therapeutic targets by antagonizing activated complement mediators to preserve microvasculature in rejecting the transplanted organ.

Achieving incompatible transplantation through desensitization: current perspectives and future directions

The application of life-saving transplantation is severely limited by the shortage of organs, and histoincompatibility. To increase transplant rates in sensitized patients, new protocols for HLA and blood type incompatible (ABOi) desensitization have emerged. These approaches require significant desensitization using intravenous immunoglobulin, rituximab and plasma exchange. In addition, the development of donor-specific antibody responses post transplant is the major cause of allograft failure with return to dialysis. This increases patient morbidity/mortality and cost. Immunotherapeutic agents used for desensitization evolved from drug development in oncology and autoimmune diseases. Currently, there is a renaissance in development of novel drugs likely to improve antibody reduction in transplantation. These include agents that inactivate IgG molecules, anticytokine antibodies, costimulatory molecule blockade, anticomplement agents and therapies aimed at the plasma cell.

Biologics in renal transplantation

The biologics used in transplantation clinical practice include several monoclonal and polyclonal antibodies aimed at specific cellular receptors. The effect of their mechanisms of action includes depleting or blocking specific cell subpopulations, complement system, or removing circulating preformed antibodies and blocking their production. They are used in induction, desensitization ABO-incompatible renal transplantation, rescue therapy of steroid-resistant acute rejection, treatment of posttransplant recurrence of primary disease such as nephrotic syndrome or atypical hemolytic-uremic syndrome, and in late humoral rejection. There are various indications for the use of biologic agents before and early or late after renal transplantation in both high- and low-risk recipients. In the latter situation, the biologics-based induction is used to further minimize immunosuppression maintenance. The targets of several biologic agents are present across a variety of cells, and manipulation of the immune system with biologics may be associated with significant risk of acute and late-onset adverse events; therefore, clinical risk-versus-benefit ratio must be carefully balanced in every case. Several trials on novel biologics are reported in adults but not in the pediatric population.

Genes associated with antibody-dependent cell activation are overexpressed in renal biopsies from patients with antibody-mediated rejection

INTRODUCTION

Antibody-mediated rejection (ABMR) is dependent on complement activating donor-specific anti-HLA antibodies (DSA). This is commonly detected by C4d deposition in allografts. However, recent data define a C4d negative ABMR phenotype suggesting a role for complement-independent DSA injury, antibody-dependent cellular cytotoxicity (ADCC).

METHODS

Here, we established an in vitro ADCC model that identified human ADCC-activated genes using microarray analysis. We subsequently interrogated renal allograft biopsies from patients with ABMR and controls for mRNA expression of the ADCC-activated gene set.

RESULTS

We identified 13 ADCC-activated genes. Six gene expression assays including 8 of the 13 genes (CCL3, CCL4/CCL4L1/CCL4L2, CD160, IFNG, NR4A3 and XCL1/XCL2) were analyzed in 127 kidney biopsies obtained from HLA-sensitized (HS), non-HS patients and control individuals. Most ADCC-activated genes showed significantly higher expression in the transplant samples compared to the controls (p<0.0005). The gene expression levels were significantly higher in HS and non-HS transplant patients who developed ABMR compared to those who did not (p=0.04-0.002). There was no difference in the gene expression levels between C4d positive and negative ABMR (p=0.26-0.99). Samples from high PRA (>80%) or positive DSA patients showed higher gene expression levels for the ADCC-activated genes compared to low PRA (<80%) and negative DSA patients (p=0.04-0.001).

CONCLUSION

ADCC pathways are active in transplant patients with ABMR, and likely mediate allograft injury, providing a potential mechanism for C4d negative ABMR.

Benefits of rituximab combined with intravenous immunoglobulin for desensitization in kidney transplant recipients

BACKGROUND

Highly HLA-sensitized (HS) patients have difficulty accessing compatible donors, especially deceased donor (DD) transplants. Desensitization protocols (DES) have evolved, but rigorous evaluation is lacking. Here, we examined the efficacy of rituximab as a DES agent in a placebo-controlled trial.

METHODS

Candidates were randomized to IVIG+placebo versus IVIG+rituximab. End points included rates of transplantation, antibody-mediated rejection (ABMR), and renal function. Protocol biopsies were performed at 1 year and analysis of patient and graft survival and donor-specific HLA antibodies (DSA) were performed.

RESULTS

Initially, 15 HS DDs were randomized with 13 receiving transplants. However, we discontinued study entry after five serious adverse events were observed. The study was un-blinded and attribution of patients was noted (IVIG+placebo N=7, IVIG+rituximab N=6). No significant differences were seen in DSA levels at transplant. All ABMR episodes occurred in the IVIG+placebo arm and required intense therapy (P=0.06). The two graft losses were in the placebo group. DSA rebound associated with severe ABMR was seen in three patients in the IVIG+placebo group. No rebound was seen in the IVIG+rituximab group. Renal function at 6 and 12 months showed a significant benefit for IVIG+rituximab (P=0.04).

CONCLUSIONS

Based on limited assessment with acknowledged limitations, both protocols appear effective in achieving levels of DSA allowable for transplantation. However, IVIG+rituximab appeared more effective in preventing DSA rebound and, more importantly, preventing ABMR and development of transplant glomerulopathy.

Protective immunity and use of bortezomib for antibody-mediated rejection in a pediatric kidney transplant recipient

Standard treatments for AMR-rituximab, intravenous immunoglobulin, and/or plasmapheresis-aim to suppress the production and modulate the effect of donor-specific antibodies and remove them, respectively. Proteasome inhibitors such as bortezomib are potent therapeutic agents that target plasma cells more effectively than rituximab to reduce measurable donor-specific antibody production. Little is known in adults, and no data exist in children about effects of proteasome inhibition to treat AMR on protective antibody titers. We present a pediatric renal transplant recipient who received bortezomib for relatively early AMR and whose antibody titers to measles and tetanus were tracked. The AMR was treated successfully, and we noted no clinical decrease in the overall level of protective immunity from pretransplant baseline levels at almost one yr after AMR treatment cessation. Larger studies will elucidate more clearly how proteasome inhibition to treat AMR affects protective immunity in pediatric transplant recipients.

Impact of donor-specific antibodies on the outcomes of kidney graft: Pathophysiology, clinical, therapy

Allo-antibodies, particularly when donor specific, are one of the most important factors that cause both early and late graft dysfunction. The authors review the current state of the art concerning this important issue in renal transplantation. Many antibodies have been recognized as mediators of renal injury. In particular donor-specific-Human Leukocyte Antigens antibodies appear to play a major role. New techniques, such as solid phase techniques and Luminex, have revealed these antibodies from patient sera. Other new techniques have uncovered alloantibodies and signs of complement activation in renal biopsy specimens. It has been acknowledged that the old concept of chronic renal injury caused by calcineurine inhibitors toxicity should be replaced in many cases by alloantibodies acting against the graft. In addition, the number of patients on waiting lists with preformed anti-human leukocyte antigens (HLA) antibodies is increasing, primarily from patients with a history of renal transplant failure already been sensitized. We should distinguish early and late acute antibody-mediated rejection from chronic antibody-mediated rejection. The latter often manifets late during the course of the post-transplant period and may be difficult to recognize if specific techniques are not applied. Different therapeutic strategies are used to control antibody-induced damage. These strategies may be applied prior to transplantation or, in the case of acute antibody-mediated rejection, after transplantation. Many new drugs are appearing at the horizon; however, these drugs are far from the clinic because they are in phase I-II of clinical trials. Thus the pipeline for the near future appears almost empty.

Plasmapheresis-resistant acute humoral rejection successfully treated with anti-C5 antibody

Even if kidney graft survival has improved during the last decades, sensitized pediatric patients are an emerging problem. We describe a 17-yr-old male who lost his first graft due to chronic rejection becoming hyperimmunized (CDC PRA 99.61%). A desensitization protocol based on high-dose IVIG, PP, and two Mabthera(®) infusions was performed with minor response (CDC PRA post-desensitization 80%). One month after his second non-living transplant, he developed a biopsy-proven AMR; post-transplant immunological monitoring showed the presence of donor-specific anti-DQ5 antibodies (DSA, MFI 20.000). He received methylprednisolone pulses and 45 PP sessions without clinical response; eculizumab was then used to salvage a kidney undergoing severe PP-resistant rejection. A biopsy performed after the fourth eculizumab infusion showed complete resolution of AMR. Eculizumab infusions were then continued for the first year post-transplantation. Two yr after transplantation, graft function is stable. Anti-C5 therapy may represent an effective therapeutic option in pediatric patients with PP-resistant AMR.

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.

Donor-specific antibodies: can they predict C4d deposition in pediatric heart recipients?

There is limited evidence regarding the utility of circulating DSA in surveillance for AMR of pediatric heart recipients. Our hypothesis is that quantitation of DSA improves their power for predicting a C4d+, an integral component in the current diagnostic criteria of AMR. All pediatric recipients transplanted between 10/2005 and 1/2011 were retrospectively reviewed for DSA determined within 48 h of EMB. C4d+ was defined as >25% endothelial cell staining by immunohistochemical methods. A total of 183 paired DSA-EMB determinations were identified in 60 patients, a median of three paired studies per patient (range: 1-9). DSA were detected in 60 of these determinations. A receiver-operating characteristic plot identified a threshold single-antibody MFI of >6000 that strongly correlated with C4d+ (p < 0.0001) with a high negative predictive value (0.97) and specificity (0.95). The sensitivity and positive predictive values were 0.71 and 0.60, respectively. The predictive power of single-antigen DSA for C4d deposition was improved in pediatric heart recipients using an institution-specific MFI threshold value. In post-transplant care, quantitative DSA should be an essential component in the surveillance for AMR.

Eculizumab treatment of acute antibody-mediated rejection in renal transplantation: case reports

The occurrence of acute antibody-mediated rejection (AMR), especially in more severe cases, continues to be associated with a poor prognosis for implant survival. Here, we have reported the results of treatment of two patients who developed AMR associated with thrombotic microangiopathy immediately after transplantation. We used a single dose of eculizumab at an early stage jointly with conventional modalities of steroid boluses, plasmapheresis, intravenous immunoglobulin, and rituximab. In both cases, the clinical course was favorable. Eculizumab, a monoclonal antibody with a high affinity for complement protein C5, prevents generation of the final membrane attack complex, blocking this cascade. To date, there are a few reports of the usefulness of eculizumab in AMR. Eculizumab can help to stop endothelial damage, especially in severe cases that show a risk of progression to cortical necrosis, by providing a therapeutic window until the other modalities begin to control the immune response. In our experience, the use of eculizumab can be beneficial in the treatment of AMR.

The paradoxical functions of B cells and antibodies in transplantation

Scarcely anyone would dispute that donor-specific B cells and the Abs that they produce can cause rejection of transplants. Less clear and more controversial, however, is the possibility that donor-specific B cells and the Abs that they produce are one or more means by which transplants can be protected from injury. In this article, we review and discuss this possibility and consider how less well-known functions of B cells and Abs might impact on the design of therapeutics and the management of transplant recipients.

Approach to kidney transplant in sensitized potential transplant recipients

More than one-third of patients on waiting lists for kidney transplant are sensitized. Most have previously formed donor-specific and non-donor-specific serum antibodies and/or positive crossmatch by complement-dependent cytotoxity and/or flow cytometry. Two categories of alloantibodies include antibodies against major histocompatibility complex human leukocyte antigen class 1 and class 2 and antibodies against minor histocompatibility complex. A current positive crossmatch is an absolute contraindication for transplant. Positive historical panel reactive antibody and/or donor-specific antibodies (human leukocyte antigen and minor histocompatibility complex), even in the absence of a historical positive crossmatch, are associated with an increased risk for allosensitization, antibodymediated rejection, and accelerated graft failure. Desensitization protocols are numerous, complex, and expensive. It is recommended to perform a systematic determination of historical and current panel reactive antibody, donor-specific antibodies (human leukocyte antigen and minor histocompatibility complex), and crossmatch by the most sensitive assays. The risk of sensitization may be estimated from the combined results of the crossmatch with the donor and those of the recipient's panel reactive antibody and donor-specific antibodies at baseline. The adoption of a scoring system for risk stratification may facilitate the task of organ allocation for sensitized patients. Recipients with an estimated sensitization risk ≥ high may be referred preferably to the national waiting priority list and informed about the financial and the medical risks that may incur with future transplant. Sensitized patients at high risk for antibody-mediated rejection may benefit from a structured monitoring process involving systematic and regular immunologic, histologic, and functional assessments of the graft after transplant. We recommend the adoption and regular updating of these approaches to ensure safe and appropriate therapeutic standards in these sensitized patients, in accordance with best clinical practice.

Antibody-mediates inhibition of human C1s and the classical complement pathway

Disregulation of complement activation plays a critical role in numerous inflammatory diseases and therefore, inhibition of the complement pathway is of great therapeutic interest. In the classical complement pathway, immune complexes formed by IgM, IgG1, IgG2 and IgG3 antibodies result in the activation of the C1s protease that in turn cleaves C4 and then C4-bound-C2 yielding the proteolytic fragments C4b and C2a which associate to form a C3 convertase enzyme. We report here the engineering of a potent human antibody inhibitor of C1s protease activity. Phage panning of a very large synthetic (F(AB)) antibody fragment library using a truncated version of C1s, comprising the second CCP domain and serine protease domain (CCP₂-SP) and expressed in insect cells, resulted in the isolation of a F(AB) that inhibited the catalytic activity of C1s. An affinity matured variant of the F(AB) format antibody displaying subnanomolar K(D) for C1s was shown to exhibit >80% inhibition of C2 processing at a 5:1 antibody:C1s molar ratio. We show that this engineered antibody, D.35, displays potent inhibition of complement deposition and lysis of Ramos cells by the anti-CD20 therapeutic antibody rituximab relative to the approved, but less-specific, human plasma-derived C1-inhibitor (CINRYZE). C1s inhibitory antibodies should be useful for delineating the role of the classical pathway in disease models and may hold promise as therapeutic agents.

Posttransplant de novo donor-specific hla antibodies identify pediatric kidney recipients at risk for late antibody-mediated rejection

The emerging role of humoral immunity in the pathogenesis of chronic allograft damage has prompted research aimed at assessing the role of anti-HLA antibody (Ab) monitoring as a tool to predict allograft outcome. Data on the natural history of allografts in children developing de novo Ab after transplantation are limited. Utilizing sera collected pretransplant, and serially posttransplant, we retrospectively evaluated 82 consecutive primary pediatric kidney recipients, without pretransplant donor-specific antibodies (DSA), for de novo Ab occurrence, and compared results with clinical-pathologic data. At 4.3-year follow up, 19 patients (23%) developed de novo DSA whereas 24 had de novo non-DSA (NDSA, 29%). DSA appeared at a median time of 24 months after transplantation and were mostly directed to HLA-DQ antigens. Among the 82 patients, eight developed late/chronic active C4d+ antibody-mediated rejection (AMR), and four C4d-negative AMR. Late AMR correlated with DSA (p < 0.01), whose development preceded AMR by 1-year median time. Patients with DSA had a median serum creatinine of 1.44 mg/dL at follow up, significantly higher than NDSA and Ab-negative patients (p < 0.005). In our pediatric cohort, DSA identify patients at risk of renal dysfunction, AMR and graft loss; treatment started at Ab emergence might prevent AMR occurrence and/or progression to graft failure.

Pushing the boundaries: the current status of ABO-incompatible cardiac transplantation

Since the introduction of intentional ABO-incompatible (ABOi) cardiac transplantation in infants in the late 1990's, the number of patients listed for and undergoing ABOi transplants has increased. This practice has been shown to lead to a reduction in waiting list mortality and increased utilisation of donor organs with equivalent outcomes to ABO-compatible transplants. Differences in the infant immune system provide a window of opportunity for ABOi transplantation. However it is increasingly clear that older patients and those with significant amounts of blood group antibody specific isohaemagglutinins may also benefit. Newer research is now focussing on longer term outcomes of ABOi transplants - in particular the development of graft accommodation or tolerance. This review assesses the current status of ABO-incompatible cardiac transplantation both in infants and in sensitized and older patients.

Donor-specific HLA antibodies and graft function in children after renal transplantation

BACKGROUND

The presence of circulating donor-specific human leukocyte antigen antibodies (HLA-DSA) has been associated with chronic antibody-mediated rejection, leading to progressive graft dysfunction and poor graft survival.The aim of this study was to investigate the incidence and significance of HLA-DSA in paediatric renal transplantation(RTx) patients.

METHODS

A total of 294 post-transplant serum samples from 123 RTx patients were retrospectively analysed for HLA antibodies. Positive samples were further tested for HLADSA by a Luminex Single Antigen bead assay. The antibody findings were correlated to measured glomerular filtration rate(GFR) and clinical outcome.

RESULTS

HLA antibodies were detected in half of the routine samples (140/294) taken 1 month to 10 years after RTx, and 40% (62/140) of these were HLA-DSA. Overall, one-third(42/123) of the patients had HLA-DSA, which mostly(65%) reacted against class II antigens. Detection of HLADSA was not associated with poor GFR at the time of sampling, and no exceptional deterioration of GFR after the HLA-DSA detection was noted in individual patients regardless of the antibody level. The presence of HLA-DSA in the first 2 years posttransplantation was not associated with poorer graft function later on.

CONCLUSION

Detection of HLA antibodies is common in children after RTx, and this finding, as such, does not predict any deterioration of graft function.

The role of B cells in solid organ transplantation

The role of antibodies in chronic injury to organ transplants has been suggested for many years, but recently emphasized by new data. We have observed that when immunosuppressive potency decreases either by intentional weaning of maintenance agents or due to homeostatic repopulation after immune cell depletion, the threshold of B cell activation may be lowered. In human transplant recipients the result may be donor-specific antibody, C4d+ injury, and chronic rejection. This scenario has precise parallels in a rhesus monkey renal allograft model in which T cells are depleted with CD3 immunotoxin, or in a CD52-T cell transgenic mouse model using alemtuzumab to deplete T cells. Such animal models may be useful for the testing of therapeutic strategies to prevent DSA. We agree with others who suggest that weaning of immunosuppression may place transplant recipients at risk of chronic antibody-mediated rejection, and that strategies to prevent this scenario are needed if we are to improve long-term graft and patient outcomes in transplantation. We believe that animal models will play a crucial role in defining the pathophysiology of antibody-mediated rejection and in developing effective therapies to prevent graft injury. Two such animal models are described herein.

Treatment options and strategies for antibody mediated rejection after renal transplantation

Antibody mediated rejection is a significant clinical problem encountered in a subset of renal transplant recipients. This type of rejection has a variable pathogenesis from the presence of donor specific antibodies with no overt disease to immediate hyperacute rejection and many variations between. Antibody mediated rejection is more common in human leukocyte antigen sensitized patients. In general, transplant graft survival after antibody mediated rejection is jeopardized, with less than 50% graft survival 5 years after this diagnosis. A variety of agents have been utilized singly and in combinations to treat antibody mediated rejection with differing results and significant research efforts are being placed on developing new targets for intervention. These same agents have been used in desensitization protocols with some success. In this review, we describe the biology of antibody mediated rejection, review the available agents to treat this form of rejection, and highlight areas of ongoing and future research into this difficult clinical problem.

Regulation of immunity and inflammation by intravenous immunoglobulin: relevance to solid organ transplantation

Intravenous immunoglobulin (IVIg) products are derived from pooled human plasma from thousands of donors and have been used for the treatment of primary immunodeficiency disorders for more than 30 years. IVIg products are also effective in the treatment of autoimmune and inflammatory disorders, however, the precise mechanism(s) of action are not known. Recent data suggest that IVIg has a much broader ability to regulate cellular immunity, including innate and adaptive components. IVIg-induced upregulation of Fcγ receptor IIB on B cells appears to be an important mode of action in suppression of antigen-presenting cell activity and antibody production. IVIg is also a recently recognized modifier of complement activation and injury. Analysis of clinical studies examining the use of IVIg in desensitization protocols and for treatment of antibody-mediated rejection in transplant recipients are supportive. Here, we discuss these important advancements and their relevance to transplant medicine.