Rapid reduction in donor-specific anti-human leukocyte antigen antibodies and reversal of antibody-mediated rejection with bortezomib in pediatric heart transplant patients

Clinical outcomes after a biopsy diagnosis of antibody-mediated rejection in pediatric heart transplant recipients

BACKGROUND

Extending survival after heart transplant (HT) is of paramount importance for childhood recipients of HT. Acute rejection is a significant event, and biopsy remains the most specific means for distinguishing between cellular (ACR) and antibody-mediated rejection (AMR).

METHODS

All children in the Pediatric Heart Transplant Society Registry who underwent HT between January 2015 and June 2022 and had ≥1 rejection episode were included. Survival was compared between AMR and ACR-only. Secondary outcomes of infection, malignancy, and cardiac allograft vasculopathy (CAV) were assessed. Risk factors for graft loss after AMR were identified using Cox proportional hazard modeling.

RESULTS

Among 906 children with rejection, 697 (77%) with complete biopsy information were included. AMR was present on biopsy in 261 (37%) patients; ACR-only was present in 436 (63%). Time to rejection was earlier for AMR, median time from HT to rejection 0.11 versus 0.29 years, p = 0.0006. Survival after AMR in the 1st year was lower than survival after ACR-only. Predictors of graft loss after AMR were younger age at HT, congenital heart disease, and rejection with hemodynamic compromise. There was no difference in time to CAV, infection, or malignancy after rejection between groups.

CONCLUSIONS

The largest analysis of pediatric HT rejection with biopsy data to identify AMR underscores the continued importance of AMR on survival. AMR is associated with higher graft loss versus ACR when occurring in the first-year post-HT. Predictors of graft loss after AMR identify patients who may benefit from increased surveillance or augmented maintenance immunosuppression.

Clinical approach to antibody-mediated rejection from the pediatric heart transplant society

This document is designed to outline the definition, pathogenesis, diagnostic modalities and therapeutic measures to treat antibody-mediated rejection in children postheart transplant METHODS: Literature review was conducted by a Pediatric Heart Transplant Society (PHTS) working group to identify existing pediatric and adult studies on antibody-mediated rejection (AMR). In addition, the centers participating in PHTS were asked to submit their approach to diagnosis and management of pediatric AMR. This document synthesizes information gathered from both these sources to highlight a practical approach to diagnosing and managing a child with AMR postheart transplant. This document may not represent the practice at all centers in the PHTS and serves as a starting point to understand an approach to this clinical scenario.

Measuring human leukocyte antigen alloantibodies: beyond a binary decision

PURPOSE OF REVIEW

Accurate measurement of human leukocyte antigen antibodies is critical for making clinical decisions treating patients awaiting transplantation or monitoring them post transplantation. Single antigen bead assay results are given as Mean Fluorescence Intensity, falling short of providing the required quantitative measure.

RECENT FINDINGS

Titration studies were shown to circumvent the limitation of target-saturation that affect interpretation of single antigen bead assays especially in highly sensitized patients with strong antibodies. In fact, titration information can serve to measure efficacy of antibody removal during pretransplant desensitization using plasmapheresis/intravenous immunoglobulin (PP/IVIg) approaches. Moreover, recent studies indicate that knowing the donor-specific antibody titer has prognostic value that can guide PP/IVIg desensitization treatments. Newer data demonstrates an additional layer of information obtained by titration studies allowing to stratify patients with very high cPRA (>99%) based on the strength of the antibodies present, rather than the breadth. This data can thereby identify patients that are more likely to benefit from desensitization approaches on the transplant wait-list.

SUMMARY

Titration studies have a prognostic value with regards to quantifying antibody strength. Obtaining this information does not require performing the complete set of dilutions. In fact, performing two to three specific dilutions can provide relevant information while maintaining practical cost.

Proteasome Inhibitors: Harnessing Proteostasis to Combat Disease

The proteasome is the central component of the main cellular protein degradation pathway. During the past four decades, the critical function of the proteasome in numerous physiological processes has been revealed, and proteasome activity has been linked to various human diseases. The proteasome prevents the accumulation of misfolded proteins, controls the cell cycle, and regulates the immune response, to name a few important roles for this macromolecular "machine." As a therapeutic target, proteasome inhibitors have been approved for the treatment of multiple myeloma and mantle cell lymphoma. However, inability to sufficiently inhibit proteasome activity at tolerated doses has hampered efforts to expand the scope of proteasome inhibitor-based therapies. With emerging new modalities in myeloma, it might seem challenging to develop additional proteasome-based therapies. However, the constant development of new applications for proteasome inhibitors and deeper insights into the intricacies of protein homeostasis suggest that proteasome inhibitors might have novel therapeutic applications. Herein, we summarize the latest advances in proteasome inhibitor development and discuss the future of proteasome inhibitors and other proteasome-based therapies in combating human diseases.

A fatal case of bortezomib-induced lung toxicity in a young adult heart transplant recipient

Bortezomib is approved for the treatment of multiple myeloma but increasingly used in heart transplant (HTx) recipients with antibody-mediated rejection (AMR). Severe pulmonary toxicity is a rare complication in multiple myeloma patients treated with bortezomib, but has not been described in a solid organ transplant recipient. A 20-year-old man 7 years post-HTx presented with acute rejection with hemodynamic compromise. Endomyocardial biopsy showed mixed rejection (ISHLT grade 2R-3R acute cellular rejection (ACR) and pAMR 1 (I+) with diffuse C4d staining). Two new high MFI circulating MHC class-II donor-specific antibodies (DSA) were detected. Treatment included corticosteroids, antithymocyte globulin, plasmapheresis, IVIG, rituximab, and bortezomib (1.3 mg/m² ). Due to rebound in DSA, a second course of bortezomib was started. Thrombocytopenia and peripheral neuropathy prompted a 50% dose reduction during the 2nd course. Shortly after the 3rd reduced dose, the patient developed hypoxemic respiratory failure. Bronchoscopy revealed pulmonary hemorrhage with negative infectious studies. Chest CT showed bilateral parenchymal disease with bronchiectasis and alveolar bleeding. Despite treatment with high-dose steroids, severe ARDS ensued with multisystem organ failure. The patient expired 23 days after the final dose of bortezomib. Post-mortem lung histology revealed diffuse alveolar damage, pulmonary fibrosis, and hemorrhage. Cardiac histology showed resolving/residual ACR 1R and pAMR 1 (I+). While rare, bortezomib-induced lung toxicity (BILT) can occur in HTx recipients and can carry a high risk of mortality. Drug reaction and immediate drug withdrawal should be considered in patients who develop respiratory symptoms, though optimal management of BILT is unclear.

Memory B Cells and Long-lived Plasma Cells

The importance of B cell and antibody-mediated immune response in the acute and long-term persistence of transplanted solid organs has become increasingly evident in recent years. A variety of therapeutic innovations target antibodies directed toward HLA or blood groups (ABO) to allow better allocation and posttransplant longevity of organs. Antibodies originate from plasma cells (PCs), which are terminally differentiated B cells. Long-term production and persistence of these antibodies is partly due to fast reactivation of previously generated memory B cells; however, there is increasing evidence that some differentiated PCs can persist independently in the bone marrow for years or even decades, producing specific antibodies or even experiencing regeneration without proliferation without need to be replaced by newly differentiating B cells. This review outlines the currently presumed pathways of differentiation, antibody, and memory generation on both B-cell and PC levels. On this background, current therapeutic concepts for antibody reduction before and after solid organ transplantation are considered, to better understand their mechanisms, possible synergisms, and specific risks. Specific differences in regards to ABO versus HLA antibodies as well as practical relevance for generation of desensitization and posttransplant antibody-directed therapy protocols are discussed.

Management of the sensitized pediatric heart transplant patient

Despite advancements in transplant immunosuppression and techniques for managing critically ill patients awaiting heart transplantation, children who are immunologically sensitized to human leukocyte antigen remain at increased risk for morbidity and mortality, both while awaiting and after heart transplant. In this review we will discuss the epidemiology of sensitization, review the immunologic basis and methods of human leukocyte antigen antibody detection, describe outcomes for sensitized pediatric transplant candidates, and consider both pre- and post-transplant management options for sensitized patients.

Allograft outcomes of treated children with kidney transplant who developed plasma cell-rich acute rejection (PCAR): A single center's experience

INTRODUCTION

PCAR is a rare form of ACR that may compromise renal allografts. This review evaluates the outcomes of a protocol used to treat PCAR (Study group), and compares these outcomes with a matched cohort with ACR (Control group).

METHODS

A retrospective analysis of 138 of pRTRs who underwent renal allograft biopsies between January 2008 and November 2016.

RESULTS

Seven biopsies revealed in situ hybridization of EBER-negative PCAR (5%). Three Study group pRTRs lost their grafts within 3 months after rejection (43%). None of the Control group pRTRs lost their graft during this period. At the time of rejection, eGFR was different between the Control and Study groups (27.0 ± 19.9 mL/min per m² vs 40.0 ± 10.6 mL/min/1.73 m² , respectively; P < 0.05). Among Study group pRTRs with functioning allografts (n = 4), treatment resulted in an increase in eGFR from nadir levels (27.0 ± 19.9 vs 55.6 ± 18.3 mL/min/1.73 m² , P < 0.05). In the Study group, complications included neutropenia, BK and EBV viremia, and infusion-related hypotension and hypertension.

SUMMARY

(a) Graft loss in Study group while remaining high (43%) was lower than that reported in the published pediatric literature. (b) Our protocol was associated with improvement in eGFR in all surviving pRTRs within the Study group. (c) No life-threatening complications or malignancy were reported during the observation period.

Costimulatory blockade molecules and B-cell-mediated immune response: current knowledge and perspectives

There is an urgent need for therapeutic agents that target humoral alloimmunity in solid organ transplantation. This includes sensitized patients with preformed donor-specific human leukocyte antigen antibodies and patients who develop de novo donor-specific antibodies, both of which are associated with acute and chronic antibody-mediated rejection and allograft loss. In the last decade, both experimental and clinical studies highlighted the major impact of costimulation molecules in the control of immune responses both in the field of transplantation and autoimmune disease. Although these molecules have been initially developed to control the early steps of T-cell activation, recent evidence also supports their influence at several steps of the humoral response. In this review, we aim to provide an overview of the current knowledge of the effects of costimulatory blockade agents on humoral responses in both autoimmune and allogeneic contexts. We first present the effects of costimulatory molecules on the different steps of alloantibody production. We then summarize mechanisms and clinical results observed using cytotoxic T lymphocyte antigen-4 (CTLA4)-Ig molecules both in transplantation and autoimmunity. Finally, we present the potential interest and implications of other costimulatory family members as therapeutic targets, with emphasis on combinatorial approaches, for the optimal control of the alloantigen-specific humoral response.

Antibody-mediated rejection after cardiac transplant: Treatment with immunoadsorption, intravenous immunoglobulin, and anti-thymocyte globulin

Antibody-mediated rejection of allograft is a poorly understood problem after cardiac transplantation that complicates the postoperative course and impairs the graft function and overall survival. Although plasmapheresis and intravenous immunoglobulins have been used as standard therapies for years, there is no consensus about antibody-mediated rejection therapy and most transplantation centers have their own protocols. We describe herein a successful treatment for an acute antibody-mediated rejection of cardiac allograft combining immunoadsorption, intravenous immunoglobulins, and anti-thymocyte globulin, which manifested with polymorphic ventricular tachycardia and right ventricular dysfunction.

Pathological antibody-mediated rejection in pediatric heart transplant recipients: Immunologic risk factors, hemodynamic significance, and outcomes

Biopsy-diagnosed pAMR has been observed in over half of pediatric HT recipients within 6 years of transplantation. We report the incidence and outcomes of pAMR at our center. All endomyocardial biopsies for all HT recipients transplanted between 2010 and 2015 were reviewed and classified using contemporary ISHLT guidelines. Graft dysfunction was defined as a qualitative decrement in systolic function by echocardiogram or an increase of ≥3 mm Hg in atrial filling pressure by direct measurement. Among 96 patients, pAMR2 occurred in 7 (7%) over a median follow-up period of 3.1 years, while no cases of pAMR3 occurred. A history of CHD, DSA at transplant, and elevated filling pressures were associated with pAMR2. Five-sixths (83%) of patients developed new C1q+ DSA at the time of pAMR diagnosis. There was a trend toward reduced survival, with 43% of patients dying within 2.3 years of pAMR diagnosis.

Pre-clinical evaluation of proteasome inhibitors for canine and human osteosarcoma

Osteosarcoma, a common malignancy in large dog breeds, typically metastasises from long bones to lungs and is usually fatal within 1 to 2 years of diagnosis. Better therapies are needed for canine patients and their human counterparts, a third of whom die within 5 years of diagnosis. We compared the in vitro sensitivity of canine osteosarcoma cells derived from 4 tumours to the currently used chemotherapy drugs doxorubicin and carboplatin, and 4 new anti-cancer drugs. Agents targeting histone deacetylases or PARP were ineffective. Two of the 4 cell lines were somewhat sensitive to the BH3-mimetic navitoclax. The proteasome inhibitor bortezomib potently induced caspase-dependent apoptosis, at concentrations substantially lower than levels detected in the bones and lungs of treated rodents. Co-treatment with bortezomib and either doxorubicin or carboplatin was more toxic to canine osteosarcoma cells than each agent alone. Newer proteasome inhibitors carfilzomib, ixazomib, oprozomib and delanzomib manifested similar activities to bortezomib. Human osteosarcoma cells were as sensitive to bortezomib as the canine cells, but slightly less sensitive to the newer drugs. Human osteoblasts were less sensitive to proteasome inhibition than osteosarcoma cells, but physiologically relevant concentrations were toxic. Such toxicity, if replicated in vivo, may impair bone growth and strength in adolescent human osteosarcoma patients, but may be tolerated by canine patients, which are usually diagnosed later in life. Proteasome inhibitors such as bortezomib may be useful for treating canine osteosarcoma, and ultimately may improve outcomes for human patients if their osteoblasts survive exposure in vivo, or if osteoblast toxicity can be managed.

The clinical impact of donor-specific antibodies in heart transplantation

Donor-specific antibodies (DSA) are integral to the development of antibody-mediated rejection (AMR). Chronic AMR is associated with high mortality and an increased risk for cardiac allograft vasculopathy (CAV). Anti-donor HLA antibodies are present in 3-11% of patients at the time of heart transplantation (HTx), with de novo DSA (predominantly anti-HLA class II) developing post-transplant in 10-30% of patients. DSA are associated with lower graft and patient survival after HTx, with one study suggesting a three-fold increase in mortality in patients who develop de novo DSA (dnDSA). DSA against anti-HLA class II, notably DQ, are at particularly high risk for graft loss. Although detection of DSA is not a criterion for pathologic diagnosis of AMR, circulating DSA are found in almost all cases of AMR. MFI thresholds of ~5000 for DSA against class I antibodies, 2000 against class II antibodies, or an overall cut-off of 5-6000 for any DSA, have been suggested as being predictive for AMR. There is no firm consensus on pre-transplant strategies to treat HLA antibodies, or for the elimination of antibodies after diagnosis of AMR. Minimizing the risk of dnDSA is rational but data on risk factors in HTx are limited. The effect of different immunosuppressive regimens is largely unexplored in HTx, but studies in kidney transplantation emphasize the importance of adherence and maintaining adequate immunosuppression. One study has suggested a reduced risk for dnDSA with rabbit antithymocyte globulin induction. Management of DSA pre- and post-HTx varies but typically most centers rely on a plasmapheresis or immunoadsorption, with or without rituximab and/or intravenous immunoglobulin. Based on the literature and a multi-center survey, an algorithm for a suggested surveillance and therapeutic strategy is provided.

Modulation of Donor-Specific Antibody Production After Organ Transplantation by Valproic Acid: A Histone Deacetylase Inhibitor

BACKGROUND

Antibody-mediated rejection, mediated by donor-specific antibodies, is emerging as a leading cause for allograft dysfunction in organ transplantation. Histone deacetylase inhibitors (HDACi) have potential immunosuppressive action, but their effects on antibody-mediated rejection and B cell function in organ transplantation have not been fully explored.

METHODS

The impacts of valproic acid (VPA), an HDACi, on isolated murine B cell proliferation, apoptosis, class switch recombination (CSR), differentiation, and secretion of immunoglobulin were investigated in vitro and in vivo. Molecular mechanisms were also explored by analyzing the expression of the activation-induced cytidinedeaminase, B lymphocyte-induced maturation protein-1 (Blimp-1/Pridm1), X-box-binding protein 1 and interferon-regulatory factor 4. Mouse cardiac transplant model was used to evaluate the regulatory effects of VPA on B cell response in vivo.

RESULTS

Valproic acid significantly inhibited B cell CSR, plasma cell differentiation, thereby reduced antibody generation in a dose-dependent manner without altering B cell proliferation and apoptosis in vitro and in vivo. Activation-induced cytidinedeaminase, Blimp-1/Pridm1 and X-box-binding protein 1 expression were repressed by VPA treatment in a dose-dependent manner, whereas no obvious changes were observed on interferon-regulatory factor 4 expression. Although VPA alone did not prolong the graft medium survival time after murine heart transplantation, the low levels of donor-specific antibody, especially IgG in serum and the less numbers of plasma cells in the spleen were observed in VPA-treated mice.

CONCLUSIONS

Valproic acid inhibited B cell CSR and plasma cell differentiation in vitro and in nitrophenyl-chicken gamma globulin-immunized and heart transplant recipient mice. HDACi might be a therapeutic agent targeting B cell response after organ transplantation.

Guidelines on the Use of Therapeutic Apheresis in Clinical Practice-Evidence-Based Approach from the Writing Committee of the American Society for Apheresis: The Seventh Special Issue

The American Society for Apheresis (ASFA) Journal of Clinical Apheresis (JCA) Special Issue Writing Committee is charged with reviewing, updating, and categorizing indications for the evidence-based use of therapeutic apheresis in human disease. Since the 2007 JCA Special Issue (Fourth Edition), the Committee has incorporated systematic review and evidence-based approaches in the grading and categorization of apheresis indications. This Seventh Edition of the JCA Special Issue continues to maintain this methodology and rigor to make recommendations on the use of apheresis in a wide variety of diseases/conditions. The JCA Seventh Edition, like its predecessor, has consistently applied the category and grading system definitions in the fact sheets. The general layout and concept of a fact sheet that was used since the fourth edition has largely been maintained in this edition. Each fact sheet succinctly summarizes the evidence for the use of therapeutic apheresis in a specific disease entity. The Seventh Edition discusses 87 fact sheets (14 new fact sheets since the Sixth Edition) for therapeutic apheresis diseases and medical conditions, with 179 indications, which are separately graded and categorized within the listed fact sheets. Several diseases that are Category IV which have been described in detail in previous editions and do not have significant new evidence since the last publication are summarized in a separate table. The Seventh Edition of the JCA Special Issue serves as a key resource that guides the utilization of therapeutic apheresis in the treatment of human disease. J. Clin. Apheresis 31:149-162, 2016. © 2016 Wiley Periodicals, Inc.

Humoral Compensation after Bortezomib Treatment of Allosensitized Recipients

The efficacy of bortezomib monotherapy in desensitizing kidney transplant candidates with preformed donor-specific antibodies remains unclear. We evaluated the effect of bortezomib on preformed antibodies and upstream components of the B cell response in a primate model sensitized by fully mismatched allogeneic skin transplants to provide mechanistic insights regarding the use of bortezomib as a means of desensitization. Bortezomib treatment given intravenously twice weekly for 1 month (1.3 mg/m² per dose) clearly reduced the numbers of antibody-producing cells and CD38⁺CD19⁺CD20^- plasma cells in the bone marrow (P<0.05), but donor-specific alloantibody levels did not decrease. We observed a rapid but transient induction of circulating IgG⁺ B cells and an increased number of proliferating B cells in the lymph nodes after 1 month of treatment. Notably, bortezomib treatment induced germinal center B cell and follicular helper T cell expansion in the lymph nodes. These data suggest that bortezomib-induced plasma cell depletion triggers humoral compensation.

Significance of Anti-HLA Antibodies on Adult and Pediatric Heart Allograft Outcomes

As methods for human leukocyte antigens (HLA) antibody detection have evolved and newer solid phase assays are much more sensitive, the last 15 years has seen a renewed focus on the importance of HLA antibodies in solid organ transplant rejection. However, there is still much controversy regarding the clinical significance of antibody level as depicted by the mean fluorescence intensity of a patient’s neat serum. Emerging techniques, including those that identify antibody level and function, show promise for the detection of individuals at risk of allograft rejection, determination of the effectiveness of desensitization prior to transplant, and for monitoring treatment of rejection. Here, we review current publications regarding the relevance of donor-specific HLA antibodies (DSA) in adult and pediatric heart transplantation (HT) with graft survival, development of antibody-mediated rejection and cardiac allograft vasculopathy (CAV). The negative impact of DSA on patient and allograft survival is evident in adult and pediatric HT recipients. Many questions remain regarding the most appropriate frequency of assessment of pre- and posttransplant DSA as well as the phenotype of DSA memory vs. true de novo antibody using large multicenter adult and pediatric cohorts and state-of-the-art methodologies for DSA detection and characterization.

Current Expectations for Cardiac Transplantation in Patients With Congenital Heart Disease

Congenital heart disease accounts for 40% of pediatric heart transplants and presents unique challenges to the transplant team. Suitability for transplantation is defined in part by degree of sensitization, pulmonary vascular resistance, and hepatic reserves. The incremental transplant risk for patients with congenital heart disease occurs within the first 3 months, after which survival is equivalent to transplantation for cardiomyopathy. Single ventricle with prior palliation, and especially the failing Fontan, carry the highest risk for transplantation and are least amenable to bridging with mechanical circulatory support. More effective bridging to transplant with mechanical circulatory support will require improvements in the adverse event profile of available pumps and the introduction of miniaturized continuous flow technology. The major barriers to routine long-term survival are chronic allograft failure and allograft vasculopathy. Despite these many challenges, continuing improvements in the care of pediatric heart transplant patients have pushed the median posttransplant survival past 15 years for children and to 20 years for infants.

Interferon Gamma and Contact-dependent Cytotoxicity Are Each Rate Limiting for Natural Killer Cell-Mediated Antibody-dependent Chronic Rejection

Natural killer (NK) cells are key components of the innate immune system. In murine cardiac transplant models, donor-specific antibodies (DSA), in concert with NK cells, are sufficient to inflict chronic allograft vasculopathy independently of T and B cells. In this study, we aimed to determine the effector mechanism(s) required by NK cells to trigger chronic allograft vasculopathy during antibody-mediated rejection. Specifically, we tested the relative contribution of the proinflammatory cytokine interferon gamma (IFN-γ) versus the contact-dependent cytotoxic mediators of perforin and the CD95/CD95L (Fas/Fas ligand [FasL]) pathway for triggering these lesions. C3H/HeJ cardiac allografts were transplanted into immune-deficient C57BL/6 rag-/- γc-/- recipients, who also received monoclonal anti-major histocompatibility complex (MHC) class I DSA. The combination of DSA and wild-type NK cell transfer triggered aggressive chronic allograft vasculopathy. However, transfer of IFN-γ-deficient NK cells or host IFN-γ neutralization led to amelioration of these lesions. Use of either perforin-deficient NK cells or CD95 (Fas)-deficient donors alone did not alter development of vasculopathy, but simultaneous disruption of NK cell-derived perforin and allograft Fas expression resulted in prevention of these abnormalities. Therefore, both NK cell IFN-γ production and contact-dependent cytotoxic activity are rate-limiting effector pathways that contribute to this form of antibody-induced chronic allograft vasculopathy.

Bortezomib decreases the magnitude of a primary humoral immune response to transfused red blood cells in a murine model

BACKGROUND

Few therapeutic options currently exist to prevent or to mitigate transfusion-associated red blood cell (RBC) alloimmunization. We hypothesized that bortezomib, a proteasome inhibitor currently being utilized for HLA alloantibody and ADAMTS13 autoantibody reduction, may be beneficial in a transfusion setting. Herein, we utilized a reductionist murine model to test our hypothesis that bortezomib would decrease RBC alloimmune responses.

STUDY DESIGN AND METHODS

Wild-type mice were treated with bortezomib or saline and transfused with murine RBCs expressing the human KEL glycoprotein. Levels of anti-KEL immunoglobulins in transfusion recipients were measured by flow cytometry. The impact of bortezomib treatment on recipient plasma cells (PCs) and other immune cells was also assessed by flow cytometry and immunofluorescence.

RESULTS

After bortezomib treatment, mice had a 50% reduction in splenic white blood cells and a targeted reduction in marrow PCs. Mice treated with bortezomib before the transfusion of KEL RBCs became alloimmunized in three of three experiments, although their serum anti-KEL IgG levels were 2.6-fold lower than those in untreated mice. Once a primary antibody response was established, bortezomib treatment did not prevent an anamnestic response from occurring.

CONCLUSION

To the extent that these findings are generalizable to other RBC antigens and to humans, bortezomib monotherapy is unlikely to be of significant clinical benefit in a transfusion setting where complete prevention of alloimmunization is desirable. Given the impact on PCs, however, it remains plausible that bortezomib therapy may be beneficial for RBC alloimmunization prevention or mitigation if used in combination with other immunomodulatory therapies.

Role of C1q complement fixing antibody assay in therapeutic plasma exchange management of pediatric cardiac antibody mediated rejection

Pediatric cardiac transplant patients with antibody-mediated rejection (AMR) often undergo therapeutic plasma exchange (TPE) to remove pathologic donor specific antibodies (DSA). In cases where DSA persist, it is unclear how long TPE should be continued. We report a case of a 17-year-old cardiac transplant patient with AMR where use of a C1q complement fixing antibody assay helped guide TPE cessation. This report adds to the existing literature that highlights the potential clinical significance of C1q antibodies in AMR management.

The importance of non-HLA antibodies in transplantation

The development of post-transplantation antibodies against non-HLA autoantigens is associated with rejection and decreased long-term graft survival. Although our knowledge of non-HLA antibodies is incomplete, compelling experimental and clinical findings demonstrate that antibodies directed against autoantigens such as angiotensin type 1 receptor, perlecan and collagen, contribute to the process of antibody-mediated acute and chronic rejection. The mechanisms that underlie the production of autoantibodies in the setting of organ transplantation is an important area of ongoing investigation. Ischaemia-reperfusion injury, surgical trauma and/or alloimmune responses can result in the release of organ-derived autoantigens (such as soluble antigens, extracellular vesicles or apoptotic bodies) that are presented to B cells in the context of the transplant recipient's antigen presenting cells and stimulate autoantibody production. Type 17 T helper cells orchestrate autoantibody production by supporting the proliferation and maturation of autoreactive B cells within ectopic tertiary lymphoid tissue. Conversely, autoantibody-mediated graft damage can trigger alloimmunity and the development of donor-specific HLA antibodies that can act in synergy to promote allograft rejection. Identification of the immunologic phenotypes of transplant recipients at risk of non-HLA antibody-mediated rejection, and the development of targeted therapies to treat such rejection, are sorely needed to improve both graft and patient survival.

The Influence of Immunosuppressive Agents on the Risk of De Novo Donor-Specific HLA Antibody Production in Solid Organ Transplant Recipients

Production of de novo donor-specific antibodies (dnDSA) is a major risk factor for acute and chronic antibody-mediated rejection and graft loss after all solid organ transplantation. In this article, we review the data available on the risk of individual immunosuppressive agents and their ability to prevent dnDSA production. Induction therapy with rabbit antithymocyte globulin may achieve a short-term decrease in dnDSA production in moderately sensitized patients. Rituximab induction may be beneficial in sensitized patients, and in abrogating rebound antibody response in patients undergoing desensitization or treatment for antibody-mediated rejection. Use of bortezomib for induction therapy in at-risk patients is of interest, but the benefits are unproven. In maintenance regimens, nonadherent and previously sensitized patients are not suitable for aggressive weaning protocols, particularly early calcineurin inhibitor withdrawal without lymphocyte-depleting induction. Early conversion to mammalian target of rapamycin inhibitor monotherapy has been reported to increase the risk of dnDSA formation, but a combination of mammalian target of rapamycin inhibitor and reduced-exposure calcineurin inhibitor does not appear to alter the risk. Early steroid therapy withdrawal in standard-risk patients after induction has no known dnDSA penalty. The available data do not demonstrate a consistent effect of mycophenolic acid on dnDSA production. Risk minimization for dnDSA requires monitoring of adherence, appropriate risk stratification, risk-based immunosuppression intensity, and prospective DSA surveillance.

Bortezomib Inpatient Prescribing Practices in Free-Standing Children's Hospitals in the United States

This study is a pharmacoepidemiologic description of pediatric bortezomib use. Exposure was identified through billing codes in patients admitted to US children's hospitals that participated with the Pediatric Health Information System between 2004 and 2013. Associated information on underlying diseases, demographics, institutional use, mortality, and physician type was collected. Exposure to bortezomib was identified in 314 patients. Hematologist/Oncologists prescribed half of the bortezomib used. Use increased during the study period. Inpatient volume was positively correlated with bortezomib utilization. Bortezomib use in pediatrics is increasing for a variety of diseases. Variation in use exists across institutions. Further studies are needed to characterize bortezomib's efficacy in pediatric diseases.

Bortezomib-containing regimen for primary treatment of early antibody-mediated cardiac allograft rejection: a case report

Evidence regarding the use of bortezomib-containing schemes in primary treatment of antibody-mediated rejection in heart transplant recipients is scarce. This case report presents the clinical experience with upstream use of bortezomib in primary treatment of early antibody-mediated rejection in an adult heart transplant recipient. Two cycles of bortezomib together with methylprednisolone, immunoadsorption, rituximab, and supplementary doses of intravenous immunoglobulin G reversed signs of heart failure, production of donor-specific antibodies, and findings of antibody-mediated rejection in biopsy. This treatment regimen was tolerated with only mild hematologic toxicity and proved to be successful during a 12-month follow-up. Primary treatment with a bortezomib-containing regimen appears to be a new therapeutic option for severe antibody-mediated rejection in heart transplant recipients. However, the efficacy and safety of this treatment need to be tested in prospective trials.

Assessing Antibody Strength: Comparison of MFI, C1q, and Titer Information

The presence of donor-specific HLA antibodies before or after transplantation may have different implications based on the antibody strength. Yet, current approaches do not provide information regarding the true antibody strength as defined by antigen-antibody dissociation rate. To assess currently available methods, we compared between neat mean fluorescence intensity (MFI) values, C1q MFI values, ethylenediaminetetraacetic acid (EDTA)-treated samples, as well as titration studies and peak MFI values of over 7000 Luminex-based single-antigen HLA antibody data points. Our results indicate that neat MFI values do not always accurately depict antibody strength. We further showed that EDTA treatment (6%) does not always remove all inhibitory factors compared with C1q or titration studies. In this study of patients presenting with multiple antibody specificities, a prozone effect was observed in 71% of the cohort (usually not affecting all antibody specificities within a single serum sample, though). Similar to titration studies, the C1q assay was able to address the issue of potential inhibition; however, its limitation is its low sensitivity and inability to detect the presence of weak antibodies. Titration studies are the only method among the approaches used in this study to provide information suggesting antigen-antibody dissociation rates and are, therefore, likely to provide better indication of true antibody strength.

Changes in the methodology of pre-heart transplant human leukocyte antibody assessment: an analysis of the United Network for Organ Sharing database

BACKGROUND

We sought to investigate temporal trends in the methodology of human leukocyte antibody assessment in heart transplantation.

METHODS

The United Network for Organ Sharing database was queried from June 2004 to March 2013 to obtain pre-heart transplantation human leukocyte antibody results. The % panel reactive antibody for class I and II antibodies was recorded along with the methodology of assessment. Allosensitization was defined as class I and/or II panel reactive antibody of ≥ 10%. The primary outcome measure was graft survival.

RESULTS

During the study period, 12,858 patients with available data underwent heart transplantation. The prevalence of allosensitization increased, with 16.8% in 2005-2006 sensitized at the time of transplantation compared to 23.1% in 2010-2011 (p < 0.001); this occurred in conjunction with an increase in the utilization of flow cytometry (77.2% in 2005-2006; 97.0% in 2010-2011, p < 0.001). Using multivariable analysis, a positive pre-heart transplantation panel reactive antibody by flow cytometry independently predicted graft loss.

CONCLUSIONS

There has been a recent increase in flow cytometric assessment of human leukocyte antibodies prior to heart transplantation, which may be associated with an increase in the prevalence of pre-transplant patients being characterized as allosensitized. Flow cytometry may identify patients with the highest likelihood of graft loss.

Emerging science in paediatric heart transplantation: donor allocation, biomarkers, and the quest for evidence-based medicine

Heart transplantation offers excellent survival benefit to children with end-stage heart failure. With its success, the number of potential recipients continues to exceed the number of available donors. Developing strategies to safely increase donor utilisation is crucial to decreasing wait-list mortality. A new paediatric heart allocation policy is set to be implemented with the goal of prioritising the most urgent listed candidates. Owing to excellent outcomes of ABO-incompatible heart transplantation, the sickest infants will soon receive priority for heart offers irrespective of blood group. Allosensitisation poses unique challenges within the paediatric population; ongoing multi-centre studies are poised to refine our understanding of key risk factors and optimal treatment strategies. Biomarkers for acute cellular rejection, such as donor-specific cell-free DNA, and cardiac allograft vasculopathy, such as VEGF-A, may lead to a decreased need for invasive screening. Ultimately, well-designed and executed randomised control trials of post-transplant immunosuppression are required to improve long-term outcomes after paediatric heart transplantation.

New insights regarding chronic antibody-mediated rejection and its progression to transplant glomerulopathy

PURPOSE OF THIS REVIEW

To discuss new insights regarding chronic antibody-mediated rejection (CAMR) and its progression to transplant glomerulopathy. We will describe the progression to transplant glomerulopathy from a histologic perspective and provide updates on what is known about its pathophysiology, prognosis, and potential therapy.

RECENT FINDINGS

Transplant glomerulopathy is a major contributor to long-term renal allograft loss and is most often associated with CAMR. On the basis of protocol biopsies, we have found that 3.5% of conventional transplants and 27.5% of positive crossmatch kidney transplants have transplant glomerulopathy at 1 year. The pathophysiology of the process is largely unknown, but complement activation was previously thought to be essential. However, CAMR appears to develop despite terminal complement blockade and many C4d negative cases of CAMR have been identified. Thus, complement independent mechanisms, such as direct endothelial cell activation and the infiltration of natural killer cells and monocytes, are likely key to the development of transplant glomerulopathy.

SUMMARY

Transplant glomerulopathy is often the result of CAMR and leads to allograft loss. It is characterized by distinctive histologic changes, and its pathophysiology is a multifaceted process involving both innate and adaptive immunity. Despite advances in the understanding of this condition, no effective therapy exists.

Novel therapeutic and diagnostic management of heart transplant patients

Heart transplantation was performed for the first time 40 years ago and it is now universally considered the "gold standard" treatment for individuals suffering from end-stage heart failure. The increased understanding of the molecular mechanisms and of the role of the immune system in allograft rejection led to an overall improvement of graft survival, which is now around 10 years. The introduction of novel immunosuppressive drugs reduced the rate of acute allograft rejection but did not improve significantly the long-term graft survival. In addition, adverse effects (e.g. infections, cancer and renal failure) associated with immunosuppressive drugs are increasing over time and may affect post-transplantation outcomes. An immunosuppression-free protocol based on tolerance induction is the Holy Grail for heart transplant recipients, but it is still far beyond our reach. In this review, we discuss the landscape of immunological challenges that heart transplanted individuals face and we critically review the novel immunological approaches available to overcome these remaining issues. Some of the novel approaches, successfully tested in preclinical and clinical models, may lead to a prolongation of patient's and heart allograft survival.

HLA desensitization with bortezomib in a highly sensitized pediatric patient

The proteasome inhibitor bortezomib has been used with variable success in the treatment of AMR following heart transplant. There is limited experience with this agent as a pretransplant desensitizing therapy. We report a case of successful HLA desensitization with a bortezomib-based protocol prior to successful heart transplantation. A nine-yr-old boy with dilated cardiomyopathy, not initially sensitized to HLA (cPRA of zero), required three days of ECMO, followed by implantation of a Heartmate II LVAD. Within six wk, the patient developed de novo class I IgG and C1q complement-fixing HLA antibodies with a cPRA of 100%. Two doses of IVIG (2 g/kg) failed to reduce antibody levels, although two courses of a novel desensitization protocol consisting of rituximab (375 mg/m(2) ), bortezomib (1.3 mg/m(2)  × 5 doses), and plasmapheresis reduced his cPRA to 0% and 87% by the C1q and IgG assays, respectively. He underwent heart transplantation nearly two months later. The patient is now >one yr post-transplant, is free of both AMR and ACR, and has no detectable donor-specific antibodies by IgG or C1q. Proteasome inhibition with bortezomib and plasmapheresis may be an effective therapy for HLA desensitization pretransplant.

Human leukocyte antigens and alloimmunization in heart transplantation: an open debate

Considerable advances in heart transplantation outcome have been achieved through the improvement of donor-recipient selection, better organ preservation, lower rates of perioperative mortality and the use of innovative immunosuppressive protocols. Nevertheless, long-term survival is still influenced by late complications. We support the introduction of HLA matching as an additional criterion in the heart allocation. Indeed, allosensitization is an important factor affecting heart transplantation and the presence of anti-HLA antibodies causes an increased risk of antibody-mediated rejection and graft failure. On the other hand, the rate of heart-immunized patients awaiting transplantation is steadily increasing due to the limited availability of organs and an increased use of ventricular assist devices. Significant benefits may result from virtual crossmatch approach that prevents transplantation in the presence of unacceptable donor antigens. A combination of both virtual crossmatch and a tailored desensitization therapy could be a good compromise for a favorable outcome in highly sensitized patients. Here, we discuss the unresolved issue on the clinical immunology of heart transplantation.

Pediatric heart transplantation-indications and outcomes in the current era

Pediatric heart transplantation (HTx) remains an important treatment option in the care of children with end-stage heart disease, whether it is secondary to cardiomyopathy or congenital heart disease (CHD). As surgical outcomes for CHD have improved, the indications for pediatric HTx have had to be dynamic, not only for children with CHD but also for the growing population of adults with CHD. As the field of pediatric HTx has evolved, the outcomes for children undergoing HTx have improved. This is undoubtedly due to the continued research efforts of both single-center studies, as well as research collaboratives such as the International Society for Heart and Lung Transplantation (ISHLT) and the Pediatric Heart Transplant Study (PHTS) group. Research collaboratives are increasingly important in pediatric HTx as single center studies for a limited patient population may not elicit strong enough evidence for practice evolution. Similarly, complications that limit the long term graft survival may occur in a minority of patients thus pooled experience is essential. This review focuses on the indications and outcomes for pediatric HTx, with a special emphasis on studies generated by these research collaboratives.

Pediatric heart transplantation-indications and outcomes in the current era

Pediatric heart transplantation (HTx) remains an important treatment option in the care of children with end-stage heart disease, whether it is secondary to cardiomyopathy or congenital heart disease (CHD). As surgical outcomes for CHD have improved, the indications for pediatric HTx have had to be dynamic, not only for children with CHD but also for the growing population of adults with CHD. As the field of pediatric HTx has evolved, the outcomes for children undergoing HTx have improved. This is undoubtedly due to the continued research efforts of both single-center studies, as well as research collaboratives such as the International Society for Heart and Lung Transplantation (ISHLT) and the Pediatric Heart Transplant Study (PHTS) group. Research collaboratives are increasingly important in pediatric HTx as single center studies for a limited patient population may not elicit strong enough evidence for practice evolution. Similarly, complications that limit the long term graft survival may occur in a minority of patients thus pooled experience is essential. This review focuses on the indications and outcomes for pediatric HTx, with a special emphasis on studies generated by these research collaboratives.

Efficacy of bortezomib for reducing donor-specific antibodies in children and adolescents on a steroid minimization regimen

AMR is increasingly being recognized as an important cause of renal allograft injury, contributing to significant morbidity and graft loss. There are few controlled trials and no well-established treatment guidelines for AMR in renal transplant recipients. We retrospectively reviewed the outcome of four pediatric renal transplant recipients on a steroid minimization immunosuppression protocol treated with bortezomib for elevated DSA and acute AMR from 2012 to 2013. All patients received four doses of bortezomib 1.3 mg/m2 given on days one, four, eight, and 11. All patients also received other treatments prior to bortezomib, which may have included rituximab, methylprednisolone, plasmapheresis, and/or IVIg. While bortezomib in addition to other therapies significantly decreased DSA titers, DSA remained very elevated months after treatment. All four patients had immediate improvement or stabilization of renal function but one eventually lost her graft. There were no adverse events related to bortezomib six months after treatment.

Bortezomib use in a pediatric cardiac transplant center

Data are limited on the efficacy and safety of bortezomib for the treatment of AMR following OHT for pediatric acquired or CHD. Retrospective chart review identified patients who received bortezomib for acute (n = 3, within two wk of diagnosis) and chronic (n = 1, three months after diagnosis) AMR or as part of a desensitization regimen (n = 1). Bortezomib was associated with a 3-66% reduction in class I DSA and a 7-82% reduction in class II DSA. Two of the three acute AMR cases resolved by the first follow-up biopsy. Two patients with AMR resolution are currently well. One patient developed a second episode of AMR, which was unresponsive to bortezomib therapy and required retransplantation for progressive coronary allograft vasculopathy. One patient died shortly after the third cycle from multi-organ failure. The desensitization patient showed transient HLA reduction with two cycles, but died five months after transplant from sepsis. Complications included infection (3/5), peripheral neuropathy (2/5), AKI (2/5), and thrombocytopenia (3/5). Adverse events appear more common in critically ill patients. Bortezomib therapy resulted in variable DSA reduction and AMR resolution in AMR in OHT secondary to pediatric acquired or CHD.