Review of bortezomib treatment of antibody-mediated rejection in renal transplantation

Translating B cell immunology to the treatment of antibody-mediated allograft rejection

Antibody-mediated rejection (AMR), including chronic AMR (cAMR), causes ~50% of kidney allograft losses each year. Despite attempts to develop well-tolerated and effective therapeutics for the management of AMR, to date, none has obtained FDA approval, thereby highlighting an urgent unmet medical need. Discoveries over the past decade from basic, translational and clinical studies of transplant recipients have provided a foundation for developing novel therapeutic approaches to preventing and treating AMR and cAMR. These interventions are aimed at reducing donor-specific antibody levels, decreasing graft injury and fibrosis, and preserving kidney function. Innovative approaches emerging from basic science findings include targeting interactions between alloreactive T cells and B cells, and depleting alloreactive memory B cells, as well as donor-specific antibody-producing plasmablasts and plasma cells. Therapies aimed at reducing the cytotoxic antibody effector functions mediated by natural killer cells and the complement system, and their associated pro-inflammatory cytokines, are also undergoing evaluation. The complexity of the pathogenesis of AMR and cAMR suggest that multiple approaches will probably be required to treat these disease processes effectively. Definitive answers await results from large, double-blind, multicentre, randomized controlled clinical trials.

Effect of Plasmapheresis on the Efficacy of Rituximab in Antibody-Mediated Rejection Patients

BACKGROUND

Rituximab and plasmapheresis (PP) suppress and eliminate antibody production in patients experiencing antibody-mediated rejection (AMR). Herein, we discuss a case where rituximab was less effective after PP for treating AMR.

CASE

A 55-year-old male patient underwent kidney transplantation. His renal function remained normal for 1 year. Subsequently, renal function declined, and (donor-specific antibodies showed positive results. A biopsy of the transplanted kidney revealed AMR. On the day of the biopsy, the medical staff administered 200 mg of rituximab, followed by IV immunoglobulin (IVIg) and PP the next day. The time interval between PP + IVIg treatment and rituximab was 12 h. As a result, the B-cell markers CD19 and CD20 did not decrease sufficiently, and the patient's creatinine and glomerular filtration rate muscles did not recover adequately.

CONCLUSION

We report a case in which PP was administered shortly after rituximab injection, resulting in insufficient B-cell inhibition due to the removal of rituximab.

Post-Transplant Monoclonal Gammopathy of Renal Significance: A Case Report

The term monoclonal gammopathy of renal significance has been used to classify the presence of a monoclonal gammopathy or lymphoproliferative disorders that do not meet hematological criteria for myeloma but instead cause kidney damage. Mostly, post-transplant monoclonal gammopathy of renal significance occurs due to recurrent disease. In contrast, the incidence of de novo post-transplant monoclonal gammopathy of renal significance has not been established, as it is considered a rare disease, presenting a unique challenge in terms of diagnosis, management, and potential impact on graft survival. Here, we report a case of de novo monoclonal gammopathy of renal significance diagnosed after kidney transplantation and its complexity due to a concomitant chronic active antibody-mediated rejection.

Effects of invivo CXCR4 Blockade and Proteasome Inhibition on Bone Marrow Plasma Cells in HLA-Sensitized Kidney Transplant Candidates

To date, plasma cell (PC)-targeted therapies have been limited by suboptimal PC depletion and antibody rebound. We hypothesized this is partly because of PC residence in protective bone marrow (BM) microenvironments. The purpose of this proof-of-concept study was to examine the effects of the CXCR4 antagonist, plerixafor, on PC BM residence; its safety profile (alone and in combination with a proteasome inhibitor, bortezomib); and the transcriptional effect on BMPCs in HLA-sensitized kidney transplant candidates. Participants were enrolled into 3 groups: group A (n = 4), plerixafor monotherapy; and groups B (n = 4) and C (n = 4), plerixafor and bortezomib combinations. CD34⁺ stem cell and PC levels increased in the blood after plerixafor treatment. PC recovery from BM aspirates varied depending on the dose of plerixafor and bortezomib. Single-cell RNA sequencing on BMPCs from 3 group C participants pretreatment and posttreatment revealed multiple populations of PCs, with a posttreatment enrichment of oxidative phosphorylation, proteasome assembly, cytoplasmic translation, and autophagy-related genes. Murine studies demonstrated dually inhibiting the proteasome and autophagy resulted in greater BMPC death than did monotherapies. In conclusion, this pilot study revealed anticipated effects of combined plerixafor and bortezomib on BMPCs, an acceptable safety profile, and suggests the potential for autophagy inhibitors in desensitization regimens.

From bench to bedside: reversing established antibody responses and desensitization

PURPOSE OF REVIEW

Basic transplant immunology has primarily focused on the definition of mechanisms, but an often-stated aspirational goal is to translate basic mechanistic research into future therapy. Pretransplant donor-specific antibodies (DSA) mediate hyperacute as well as early antibody-mediated rejection (AMR), whereas DSA developing late posttransplantation may additionally mediate chronic rejection. Although contemporary immunosuppression effectively prevents early cellular rejection after transplant in nonsensitized patients, it is less effective at controlling preexisting HLA antibody responses or reversing DSA once established, thus underscoring a need for better therapies.

RECENT FINDINGS

We here review the development of a bench-to-bedside approach involving transient proteasome inhibition to deplete plasma cells, combined with maintenance co-stimulation blockade, with CTLA-4Ig or belatacept, to prevent the generation of new antibody-secreting cells (ASCs).

SUMMARY

This review discusses how this treatment regimen, which was rationally designed and validated to reverse established DSA responses in mouse models, translated into reversing active AMR in the clinic, as well as desensitizing highly sensitized patients on the transplant waitlist.

Emerging drugs for antibody-mediated rejection after kidney transplantation: a focus on phase II & III trials

INTRODUCTION

Antibody-mediated rejection (ABMR) is a leading cause of kidney allograft failure. Its therapy continues to be challenge, and no treatment has been approved for the market thus far.

AREAS COVERED

In this article, we discuss the pathophysiology and phenotypic presentation of ABMR, the current level of evidence to support the use of available therapeutic strategies, and the emergence of tailored drugs now being evaluated in systematic clinical trials. We searched PubMed, Clinicaltrials.gov and Citeline's Pharmaprojects for pertinent information on emerging anti-rejection strategies, laying a focus on phase II and III trials.

EXPERT OPINION

Currently, we rely on the use of apheresis for alloantibody depletion and intravenous immunoglobulin (referred to as standard of care), preferentially in early active ABMR. Recent systematic trials have questioned the benefits of using the CD20 antibody rituximab or the proteasome inhibitor bortezomib. However, there are now several promising treatment approaches in the pipeline, which are being trialed in phase II and III studies. These include interleukin-6 antagonism, CD38-targeting antibodies, and selective inhibitors of complement. On the basis of the information that has emerged so far, it seems that innovative treatment strategies for clinical use in ABMR may be available within the next 5-10 years.

Antibody-mediated rejection after kidney transplantation in children; therapy challenges and future potential treatments

Antibody‐mediated rejection (AMR) remains one of the most critical problems in renal transplantation, with a significant impact on patient and graft survival. In the United States, no treatment has received FDA approval jet. Studies about treatments of AMR remain controversial, limited by the absence of a gold standard and the difficulty in creating large, multi‐center studies. These limitations emerge even more in pediatric transplantation because of the limited number of pediatric studies and the occasional use of some therapies with unknown and poorly documented side effects. The lack of recommendations and the unsharp definition of different forms of AMR contribute to the challenging management of the therapy by pediatric nephrologists. In an attempt to help clinicians involved in the care of renal transplanted children affected by an AMR, we rely on the latest recommendations of the Transplantation Society (TTS) for the classification and treatment of AMR to describe treatments available today and potential new treatments with a particular focus on the pediatric population.

Bortezomib alleviates antibody-mediated rejection in kidney transplantation by facilitating Atg5 expression

Antibody‐mediated rejection (AMR) is one of the most dominant mechanisms responsible for the loss of kidney grafts. Previous researches have shown that donor‐specific antibodies (DSAs) are the major mediators of AMR. In order to prolong the survival time of grafts, it is vital to reduce the incidence of AMR and inhibit the generation of DSAs. We established an animal model of AMR by performing kidney transplantation in pre‐sensitized rats. Then, we investigated the effect of bortezomib (BTZ) on AMR. We found that BTZ could reduce the serum level of DSAs and alleviate post‐transplantation inflammation in peritubular capillaries (PTCs) and glomeruli, which was demonstrated by the reduction of C4d and IgG deposition in PTCs, and the reduced number of B cell and plasma cell in peripheral blood and the transplanted kidney (p < 0.05). Our results also suggested that BTZ increased the number of regulatory T cell (Treg) and significantly reduced the proportion of T helper (Th17) cell (p < 0.05). Besides, BTZ induced the significant upregulation of anti‐inflammatory cytokines but downregulated pro‐inflammatory cytokines (p < 0.05). After dealing with Atg5 siRNA‐lentivirus, the effect of BTZ alleviating AMR was reversed and Th17/Treg proportions were also significantly modulated. Collectively, these findings show that BTZ slows down the process of AMR and Atg5 may be the key mechanism. Furthermore, Atg5 silencing results may be demonstrated that Atg5 alleviated AMR by modulating the ratio of Th17/Treg.

Reducing Donor-specific Antibody During Acute Rejection Diminishes Long-term Renal Allograft Loss: Comparison of Early and Late Rejection

BACKGROUND

Reduction in donor-specific antibody (DSA) has been associated with improved renal allograft survival after antibody-mediated rejection (AMR). These observations have not been separately analyzed for early and late AMR and mixed acute rejection (MAR). The purpose of this study was to evaluate long-term responses to proteasome inhibitor-based therapy for 4 rejection phenotypes and to determine factors that predict allograft survival.

METHODS

Retrospective cohort study evaluating renal transplant recipients with first AMR episodes treated with proteasome inhibitor-based therapy from January 2005 to July 2015.

RESULTS

A total of 108 patients were included in the analysis. Immunodominant DSA reduction at 14 days differed significantly (early AMR 79.6%, early MAR 54.7%, late AMR 23.4%, late MAR 21.1%, P < 0.001). Death-censored graft survival (DCGS) differed at 3 years postrejection (early AMR 88.3% versus early MAR 77.8% versus late AMR 56.7% versus late MAR 54.9%, P = 0.02). Multivariate analysis revealed that immunodominant DSA reduction > 50% at 14 days was associated with improved DCGS (odds ratio, 0.12, 95% CI, 0.02-0.52, P = 0.01).

CONCLUSIONS

In summary, significant differences exist across rejection phenotypes with respect to histological and DSA responses. The data suggest that DSA reduction may be associated with improved DCGS in both early and late AMR.

CD38 Antibody Daratumumab for the Treatment of Chronic Active Antibody-mediated Kidney Allograft Rejection

BACKGROUND

Late antibody-mediated rejection (AMR) is a major cause of transplant failure. Potential therapeutic targets are plasma cells and natural killer (NK) cells, both expressing high levels of CD38.

METHODS

Here, we report the use of CD38 monoclonal antibody daratumumab (9-mo course) in a kidney allograft recipient diagnosed with smoldering myeloma and anti-HLA class II donor-specific antibody-positive chronic active AMR 13 years after transplantation. Patient monitoring included serial HLA single-antigen testing, peripheral blood immune cell phenotyping, as well as follow-up allograft and bone marrow biopsies at 3 and 9 months, including analyses of rejection-related gene expression patterns.

RESULTS

Daratumumab led to persistent CD138+ cell depletion in the bone marrow and blood and substantially decreased NK cells counts in blood and graft tissue. At the same time, donor-specific antibody in serum disappeared, and in vitro alloantibody production by CD138+ cells enriched from bone marrow aspirates was abrogated. A 3-month follow-up biopsy revealed a complete resolution of microcirculation inflammation (g+ptc: 3 to 0) and molecular AMR activity (AMR score: 0.79 to <0.2). The same biopsy showed (subclinical) tubulointerstitial inflammation, which prompted steroid treatment. Over an observation period of 12 months, graft function stabilized.

CONCLUSIONS

Targeting CD38 for plasma cell and NK cell depletion may be an effective strategy to counteract AMR. Our results may encourage the design of future trials to clarify the role of this innovative treatment concept in organ transplantation.

Recommended Treatment for Antibody-mediated Rejection After Kidney Transplantation: The 2019 Expert Consensus From the Transplantion Society Working Group

With the development of modern solid-phase assays to detect anti-HLA antibodies and a more precise histological classification, the diagnosis of antibody-mediated rejection (AMR) has become more common and is a major cause of kidney graft loss. Currently, there are no approved therapies and treatment guidelines are based on low-level evidence. The number of prospective randomized trials for the treatment of AMR is small, and the lack of an accepted common standard for care has been an impediment to the development of new therapies. To help alleviate this, The Transplantation Society convened a meeting of international experts to develop a consensus as to what is appropriate treatment for active and chronic active AMR. The aim was to reach a consensus for standard of care treatment against which new therapies could be evaluated. At the meeting, the underlying biology of AMR, the criteria for diagnosis, the clinical phenotypes, and outcomes were discussed. The evidence for different treatments was reviewed, and a consensus for what is acceptable standard of care for the treatment of active and chronic active AMR was presented. While it was agreed that the aims of treatment are to preserve renal function, reduce histological injury, and reduce the titer of donor-specific antibody, there was no conclusive evidence to support any specific therapy. As a result, the treatment recommendations are largely based on expert opinion. It is acknowledged that properly conducted and powered clinical trials of biologically plausible agents are urgently needed to improve patient outcomes.

Plasma Cell-Rich Acute Rejection in Renal Transplantation: A Case Report

Plasma cell-rich acute rejection (PCAR) is a rare type of allograft rejection in renal transplantation. It is characterized by the presence of mature plasma cells that compromise more than 10% of inflammatory cells infiltrating the renal graft. The pathogenesis of PCAR is unknown, appears late, and has been related mainly to insufficient immunosuppression or infections. The treatment is not clearly defined, and the graft survival is poor. Here, we report a case series of 3 Spanish patients diagnosed with PCAR accompanied by donor-specific antibodies (DSA) after kidney transplantation. Mean to diagnosis was 2-12 years post-transplantation, and they began with abrupt deterioration of renal function. All patients were women and had preceding viral infection. In addition, two of the three patients recognize a doubtful adherence to immunosuppression. About treatment, 2 of the 3 patients, because the biopsy of the renal graft showed signs suggestive of incipient antibody-mediated rejection (ABMR) (glomerulitis, capilaritis, transplant glomerulopathy), were started with corticosteroids, anti-thymoglobulin, plasmapheresis, and intravenous immunoglobulins. The last patient, who only showed PCAR at biopsy, was treated with corticosteroids and anti-thymoglobulin. After treatment, graft function improved in all of them, but one patient developed an ABMR and another required a dialysis program, all of which indicates the difficulty in management and treatment of PCAR.

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.

Outstanding questions in transplantation: B cells, alloantibodies, and humoral rejection

Over the past three decades, improved immunosuppression has significantly reduced T cell-mediated acute rejection rates, but long-term graft survival rates have seen only marginal improvement. The cause of late graft loss has been under intense investigation, and chronic antibody-mediated rejection (AMR) has been identified as one of the leading causes, thus providing a strong rationale for basic science investigation into donor-specific B cells and antibodies in transplantation and ways to mitigate their pathogenicity. In 2018, the American Society of Transplantation launched a community-wide online discussion of Outstanding Questions in Transplantation, and the topic of B cell biology and donor-specific antibody prevention emerged as a major area of interest to the community, leading to a highly engaged dialogue, with comments from basic and translational scientists as well as physicians (http://community.myast.org/communities/community-home/digestviewer). We have summarized this discussion from a bedside to bench perspective and have organized this review into outstanding questions within the paradigm that AMR is a leading cause of graft loss in the clinic, and points of view that challenge aspects of this paradigm. We also highlight opportunities for basic and translational scientists to contribute to the resolution of these questions, mapping important future directions for the transplant research field.

The PI3Kδ selective inhibitor AS2541019 suppresses donor-specific antibody production in rat cardiac and non-human primate renal allotransplant models

Long-term graft survival after organ transplantation is difficult to achieve because of the development of chronic rejection. One cause of chronic rejection arises from antibody-mediated rejection (AMR), which is dependent on the production of donor-specific antibodies (DSA). Current immunosuppression in organ transplantation is effective in preventing acute T cell-mediated rejection, but the risk of DSA production and graft loss due to AMR remains unchanged. Phosphatidylinositol-3-kinase p110δ (PI3Kδ), a member of the family of PI3K lipid kinases, is a key mediator of B cell activation, proliferation and antibody production. AS2541019 is a novel PI3Kδ selective inhibitor that prevents antibody production by inhibiting B cell immunity. The purpose of this study was to evaluate the inhibitory effect of AS2541019 on DSA production in preclinical rodent and non-human primate allotransplant models. Concomitant administration of AS2541019 with tacrolimus and mycophenolate mofetil (MMF) inhibited de novo DSA production in an ACI-to-Lewis rat cardiac allotransplant model. To predict the efficacy of AS2541019 in clinical practice, we evaluated its effects in cynomolgus monkeys. AS2541019 inhibited B cell proliferation and major histocompatibility complex (MHC) class II expression on B cells in cynomolgus monkeys. Oral administration of AS2541019 inhibited MHC class II expression on peripheral B cells and anti-tetanus toxoid antibody production. In cynomolgus monkey renal allotransplant model, concomitant administration of AS2541019 with tacrolimus and MMF significantly inhibited de novo DSA production. Together, our findings indicate that the PI3Kδ selective inhibitor AS2541019 is a potential candidate for preventing AMR development by inhibiting DSA production.

The therapeutic challenge of late antibody-mediated kidney allograft rejection

Late antibody‐mediated rejection (ABMR) is a cardinal cause of kidney allograft failure, manifesting as a continuous and, in contrast with early rejection, often clinically silent alloimmune process. While significant progress has been made towards an improved understanding of its molecular mechanisms and the definition of diagnostic criteria, there is still no approved effective treatment. In recent small randomized controlled trials, therapeutic strategies with promising results in observational studies, such as proteasome inhibitor bortezomib, anti‐C5 antibody eculizumab, or high dose intravenous immunoglobulin plus rituximab, had no significant impact in late and/or chronic ABMR. Such disappointing results reinforce a need of new innovative treatment strategies. Potential candidates may be the interference with interleukin‐6 to modulate B cell alloimmunity, or innovative compounds that specifically target antibody‐producing plasma cells, such as antibodies against CD38. Given the phenotypic heterogeneity of ABMR, the design of adequate systematic trials to assess the safety and efficiency of such therapies, however, is challenging. Several trials are currently being conducted, and new developments will hopefully provide us with effective ways to counteract the deleterious impact of antibody‐mediated graft injury. Meanwhile, the weight of evidence would suggest that, when approaching using existing treatments for established antibody‐mediated rejection, “less may be more”.

Immunoproteasome inhibition induces plasma cell apoptosis and preserves kidney allografts by activating the unfolded protein response and suppressing plasma cell survival factors

Chronic antibody-mediated rejection is the leading cause of allograft dysfunction and loss after kidney transplantation, and current immunosuppressive regimens fail to target the plasma cells that produce alloantibodies. We previously showed that treatment with the immunoproteasome inhibitor ONX 0914 prevented the expansion of plasma cells and prevented chronic allograft nephropathy and organ failure after kidney transplantation in rats, but the mechanism has remained elusive. In the current study, we confirmed a long-term reduction in alloantibody production and improvements in allograft histology in rats treated with ONX 0914 or with the broad-spectrum proteasome inhibitor bortezomib. Plasma cells from allotransplanted rats expressed immunoproteasomes at high levels. Immunoproteasome inhibition with ONX 0914 led to ubiquitin-conjugate accumulation, activation of the unfolded protein response, and induction of apoptosis in plasma cells. In addition, ONX 0914 suppressed the expression of adhesion molecules (VLA-4 and LFA-1), plasma cell survival factors (APRIL and IL-6), and IFN-γ-inducible chemokines in bone marrow, while the APRIL receptor BCMA, the IL-6 receptor, and the chemokine receptors CXCR4 and CXCR3 were down-regulated on plasma cells. Taken together, immunoproteasome inhibition blocked alloantibody production by inducing apoptosis of plasma cells through activating the unfolded protein response and suppressing plasma cell survival factors in the bone marrow.

Targeting B Cells and Plasma Cells in Glomerular Diseases: Translational Perspectives

The unique contributions of memory B cells and plasma cells in kidney diseases remain unclear. In this review, we evaluate the clinical experience with treatments directed at B cells, such as rituximab, and at plasma cells, such as proteasome inhibition, to shed light on the role of these two B lineage compartments in glomerular diseases. Specifically, analysis of these targeted interventions in diseases such as ANCA-associated vasculitis, SLE, and antibody-mediated transplant rejection permits insight into the pathogenetic effect of these cells. Notwithstanding the limitations of preclinical models and clinical studies (heterogeneous populations, among others), the data suggest that memory B and plasma cells represent two engines of autoimmunity, with variable involvement in these diseases. Whereas memory B cells and plasma cells appear to be key in ANCA-associated vasculitis and antibody-mediated transplant rejection, respectively, SLE seems likely to be driven by both autoimmune compartments. These conclusions have implications for the future development of targeted therapeutics in immune-mediated renal disease.

A Randomized Trial of Bortezomib in Late Antibody-Mediated Kidney Transplant Rejection

Late antibody-mediated rejection (ABMR) is a leading cause of kidney allograft failure. Uncontrolled studies have suggested efficacy of the proteasome inhibitor bortezomib, but no systematic trial has been undertaken to support its use in ABMR. In this randomized, placebo-controlled trial (the Bortezomib in Late Antibody-Mediated Kidney Transplant Rejection [BORTEJECT] Trial), we investigated whether two cycles of bortezomib (each cycle: 1.3 mg/m² intravenously on days 1, 4, 8, and 11) prevent GFR decline by halting the progression of late donor-specific antibody (DSA)-positive ABMR. Forty-four DSA-positive kidney transplant recipients with characteristic ABMR morphology (median time after transplant, 5.0 years; pretransplant DSA documented in 19 recipients), who were identified on cross-sectional screening of 741 patients, were randomly assigned to receive bortezomib (n=21) or placebo (n=23). The 0.5-ml/min per 1.73 m² per year (95% confidence interval, -4.8 to 5.8) difference detected between bortezomib and placebo in eGFR slope (primary end point) was not significant (P=0.86). We detected no significant differences between bortezomib- and placebo-treated groups in median measured GFR at 24 months (33 versus 42 ml/min per 1.73 m²; P=0.31), 2-year graft survival (81% versus 96%; P=0.12), urinary protein concentration, DSA levels, or morphologic or molecular rejection phenotypes in 24-month follow-up biopsy specimens. Bortezomib, however, associated with gastrointestinal and hematologic toxicity. In conclusion, our trial failed to show that bortezomib prevents GFR loss, improves histologic or molecular disease features, or reduces DSA, despite significant toxicity. Our results reinforce the need for systematic trials to dissect the efficiency and safety of new treatments for late ABMR.

Acute rejection

Despite induction immunosuppression and the use of aggressive maintenance immunosuppressive regimens, acute allograft rejection following lung transplantation is still a problem with important diagnostic and therapeutic challenges. As well as causing early graft loss and mortality, acute rejection also initiates the chronic alloimmune responses and airway-centred inflammation that predispose to bronchiolitis obliterans syndrome (BOS), also known as chronic lung allograft dysfunction (CLAD), which is a major source of morbidity and mortality after lung transplantation. Cellular responses to human leukocyte antigens (HLAs) on the allograft have traditionally been considered the main mechanism of acute rejection, but the influence of humoral immunity is increasingly recognised. As with other several other solid organ transplants, antibody-mediated rejection (AMR) is now a well-accepted and distinct clinical entity in lung transplantation. While acute cellular rejection (ACR) has defined histopathological criteria, transbronchial biopsy is less useful in AMR and its diagnosis is complicated by challenges in the measurement of antibodies directed against donor HLA, and a determination of their significance. Increasing awareness of the importance of non-HLA antigens further clouds this issue. Here, we review the pathophysiology, diagnosis, clinical presentation and treatment of ACR and AMR in lung transplantation, and discuss future potential biomarkers of both processes that may forward our understanding of these conditions.

Treatment of membranous nephropathy: time for a paradigm shift

In patients with membranous nephropathy, alkylating agents (cyclophosphamide or chlorambucil) alone or in combination with steroids achieve remission of nephrotic syndrome more effectively than conservative treatment or steroids alone, but can cause myelotoxicity, infections, and cancer. Calcineurin inhibitors can improve proteinuria, but are nephrotoxic. Most patients relapse after treatment withdrawal and can become treatment dependent, which increases the risk of nephrotoxicity. The discovery of nephritogenic autoantibodies against podocyte M-type phospholipase A2 receptor (PLA₂R) and thrombospondin type-1 domain- containing protein 7A (THSD7A) antigens provides a clear pathophysiological rationale for interventions that specifically target B-cell lineages to prevent antibody production and subepithelial deposition. The anti-CD20 monoclonal antibody rituximab is safe and achieves remission of proteinuria in approximately two-thirds of patients with membranous nephropathy. In those with PLA₂R-related disease, remission can be predicted by anti-PLA₂R antibody depletion and relapse by antibody re-emergence into the circulation. Thus, integrated evaluation of serology and proteinuria could guide identification of affected patients and treatment with individually tailored protocols. Nonspecific and toxic immunosuppressive regimens will fall out of use. B-cell modulation by rituximab and second-generation anti-CD20 antibodies (or plasma cell-targeted therapy in anti-CD20 resistant forms of disease) will lead to a novel therapeutic paradigm for patients with membranous nephropathy.

Bortezomib in the treatment of antibody-mediated rejection in pediatric kidney transplant recipients: A multicenter Midwest Pediatric Nephrology Consortium study

Antibody-mediated rejection leads to allograft loss after kidney transplantation. Bortezomib has been used in adults for the reversal of antibody-mediated rejection; however, pediatric data are limited. This retrospective study was conducted in collaboration with the Midwest Pediatric Nephrology Consortium. Pediatric kidney transplant recipients who received bortezomib for biopsy-proven antibody-mediated rejection between 2008 and 2015 were included. The objective was to characterize the use of bortezomib in pediatric kidney transplant recipients. Thirty-three patients received bortezomib for antibody-mediated rejection at nine pediatric kidney transplant centers. Ninety percent of patients received intravenous immunoglobulin, 78% received plasmapheresis, and 78% received rituximab. After a median follow-up of 15 months, 65% of patients had a functioning graft. The estimated glomerular filtration rate improved or stabilized in 61% and 36% of patients at 3 and 12 months post-bortezomib, respectively. The estimated glomerular filtration rate at diagnosis significantly predicted estimated glomerular filtration rate at 12 months after adjusting for chronic histologic changes (P .001). Fifty-six percent of patients showed an at least 25% reduction in the mean fluorescence intensity of the immune-dominant donor-specific antibody, 1-3 months after the first dose of bortezomib. Non-life-threatening side effects were documented in 21 of 33 patients. Pediatric kidney transplant recipients tolerated bortezomib without life-threatening side effects. Bortezomib may stabilize estimated glomerular filtration rate for 3-6 months in pediatric kidney transplant recipients with antibody-mediated rejection.

Bortezomib for refractory acute antibody-mediated rejection in kidney transplant recipients: A single-centre case series

AIM

Acute antibody-mediated rejection (ABMR) after kidney transplantation (KT) is associated with poor allograft survival. Current therapies for ABMR are able to deplete B-lymphocytes but do not target plasma cells. Bortezomib is a proteasome inhibitor that can eliminate plasma cells and has demonstrated utility in the treatment of ABMR.

METHODS

A retrospective study was carried out from 2010 to 2014, including all patients with ABMR refractory to conventional treatment who received bortezomib. Bortezomib (1.3 mg/m(2) ) was administered intravenously on days 1, 4, 8, and 11. Renal function, graft survival, follow-up biopsies, and donor-specific antibodies (DSA) were recorded.

RESULTS

We identified seven patients. Of these, high immunological risk was found in 6 of 7, preformed DSA were found in 5 of 7, flow cytometry crossmatch was positive in 4 of 7, and desensitization before KTx was provided in 6 of 7 patients. ABMR was diagnosed at a median of 90 days (8-167) post-KT. After bortezomib therapy, renal function improved or stabilized in 5 of 7 patients and progressively deteriorated in 2 of 7, leading to haemodialysis after 7 and 11 months, respectively. Follow-up kidney biopsies showed persistence of ABMR in 2 of 7, chronic active ABMR 3 of 7 and inactive chronic lesions in 2 of 7. DSA titres significantly decreased after treatment (P = 0.028). All patients experienced mild adverse events. After a follow-up of 22 ± 18 months, three grafts were lost (42%) and four remained functioning.

CONCLUSION

Bortezomib could be useful as an adjuvant therapy for ABMR refractory to conventional treatment with acceptable mid-term outcomes in these severe cases. More research is needed to develop strategies to better preserve graft function after refractory ABMR.

Rituximab in Combination With Bortezomib, Plasmapheresis, and High-Dose IVIG to Treat Antibody-Mediated Renal Allograft Rejection

Background

Current treatment strategies for antibody-mediated renal allograft rejection (AMR) are not sufficiently effective. In most centers, “standard of care” treatment includes plasmapheresis (PPH) and IVIG preparations. Since several years, modern therapeutics targeting B cells and plasma cells have become available. We investigated, whether combined administration of rituximab and bortezomib in addition to PPH and high-dose IVIG is useful.

Methods

Between November 2011 and January 2013, we treated 10 consecutive patients with biopsy-proven AMR with rituximab (500 mg), bortezomib (4× 1.3 mg/m²), PPH (6×), and high-dose IVIG (1.5 g/kg) (group A). This group was compared with a group of 11 consecutive patients treated with an identical regimen without rituximab between July 2010 and November 2011 (group B).

Results

Median follow-up was 41(33-46) months in group A and 55(47-63) months in group B. At 40 months after treatment, graft survival was 60% in group A and 64% in group B, respectively (P = 0.87). Before and after treatment, serum creatinine, estimated glomerular filtration rate, and proteinuria were not different between groups. A significant reduction in donor-specific HLA antibody mean fluorescence intensity was observed in group A (25.2%, P = 0.046) and B (38.3%, P = 0.01) at 3 months posttreatment. In group A, more patients suffered from side effects compared with group B (infections: 70% vs 18%, P = 0.02).

Conclusions

The addition of rituximab to bortezomib, PPH, and high-dose IVIG did not further improve graft survival. Instead, we observed an increase of side effects. Therefore, combined administration of bortezomib and rituximab in addition to PPH and IVIG should be regarded with caution.

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.

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.

Advances in pharmacotherapy to treat kidney transplant rejection

INTRODUCTION

Current immunosuppressive combination therapy provides excellent prevention of T-cell-mediated rejection following renal transplantation; however, antibody-mediated rejection remains of high concern and accounts for a large number of long-term allograft losses. The recent development of protocol biopsies resulted in the definition of subclinical rejection (SCR), showing histologic evidence for rejection but unremarkable clinical course.

AREAS COVERED

This review describes the current knowledge and evidence of pharmacotherapy to treat kidney allograft rejections and covers SCR treatment options. Each substance is analyzed with regard to its classical indication and further discussed for the treatment of other forms of rejection.

EXPERT OPINION

Despite a lack of randomized trials, early acute T-cell-mediated rejection can be treated effectively in most cases without graft loss. The necessity to treat SCR is currently unclear. Due to a lack of effective therapies, new treatment approaches for antibody-mediated rejection are an urgent medical need to improve long-term outcomes. Future research should aim to better define pathophysiology and histology, stratify risk, and develop rational treatment strategies from randomized controlled trials, in order to establish the value of novel therapies in the arsenal of rejection pharmacotherapy. However, the effective prevention of rejection with minimal side effects still remains the goal in immunosuppression.

The Effect of Bortezomib on Antibody-Mediated Rejection after Kidney Transplantation

PURPOSE

Recently, bortezomib has been used to treat antibody-mediated rejection (AMR) refractory to conventional treatment such as plasmapheresis, intravenous immunoglobulin, and rituximab. The authors aimed to describe their experiences when bortezomib was used to treat refractory AMR.

MATERIALS AND METHODS

Eleven refractory AMR episodes treated with bortezomib were included in this study. The patients received one or two cycles of bortezomib (1.3 mg/m²) on days 1, 4, 8, and 11.

RESULTS

Bortezomib effectively reduced antibodies against various targets, including human leukocyte antigen (HLA) class I and II, ABO blood group antigen, and angiotensin II type 1 receptor. Antibodies were depleted or reduced significantly in eight AMR episodes. Overall, there was a significant improvement in the mean estimated glomerular filtration rate (eGFR) at 3 months after therapy (36.91±22.15 mL/min/1.73 m²) versus eGFR at time of AMR diagnosis (17.00±9.25 mL/min/1.73 m²; p=0.007). All six early-onset AMR episodes (within 6 months post-transplantation) showed full recovery of allograft function. Additionally, three of the five late-onset AMR episodes (>6 months post-transplantation) showed improved allograft function.

CONCLUSION

Anti-humoral treatment based on bortezomib might be an effective strategy against refractory AMR caused by various types of antibodies. Notably, this treatment could be more effective in early-onset AMR than in late-onset AMR.

The divergent roles of macrophages in solid organ transplantation

PURPOSE OF REVIEW

This review summarizes the phenotype and function of macrophages in the context of solid organ transplantation and will focus on fundamental insights into their paradoxical pro-inflammatory versus suppressive function. We will also discuss the therapeutic potential of regulatory macrophages in tolerance induction.

RECENT FINDINGS

Macrophages are emerging as an essential element of solid organ transplantation. Macrophages are involved in the pathogenesis of ischemia reperfusion injury, as well as both acute and chronic rejection, exacerbating injury through secretion of inflammatory effectors and by amplifying adaptive immune responses. Notably, not all responses associated with macrophages are deleterious to the graft, and graft protection can in fact be conferred by macrophages. This has been attributed to the presence of macrophages with tissue-repair capabilities, as well as the effects of regulatory macrophages.

SUMMARY

The explosion of new information on the role of macrophages in solid organ transplantation has opened up new avenues of research and the possibility of therapeutic intervention. However, the role of myeloid cells in graft rejection, resolution of rejection and tissue repair remains poorly understood. A better understanding of plasticity and regulation of monocyte polarization is vital for the development of new therapies for the treatment of acute and chronic transplant rejection.

The Tao of myeloma

Multiple myeloma is a plasma cell malignancy in which significant advances have been observed during the last 15 years. Our understanding of the disease has been advanced through its molecular characterization. We have also seen improvements in patient care with the development of 2 new classes of active agents, proteasome inhibitors and immunomodulatory drugs (IMiDs), resulting in a significant improvement in overall survival of myeloma patients such that it can now be debated as to whether some subsets of myeloma patients can be cured. However, the advances in our understanding of myeloma biology occurred in parallel with advances in treatment as opposed to being directly informed by the research. Moreover, the molecular characterization of malignant plasma cells would not have predicted the effectiveness of these novel therapies.We hypothesize that proteasome inhibitors and IMiDs are highly active because malignant plasma cells are constrained by many of the characteristics of their normal counterparts and these novel therapies target both normal plasma cell biology and the cancer biology of myeloma. Thus, a better understanding of normal plasma cell biology will likely yield as many actionable targets as mapping the genomic landscape of this disease.

Memory B cells in transplantation

Much of the research on the humoral response to allografts has focused on circulating serum antibodies and the long-lived plasma cells that produce these antibodies. In contrast, the interrogation of the quiescent memory B cell compartment is technically more challenging and thus has not been incorporated into the clinical diagnostic or prognostic toolkit. In this review, we discuss new technologies that have allowed this heretofore enigmatic subset of B cells to be identified at quiescence and during a recall response. These technologies in experimental models are providing new insights into memory B cell heterogeneity with respect to their phenotype, cellular function, and the antibodies they produce. Similar technologies are also allowing for the identification of comparable memory alloreactive B cells in transplant recipients. Although much of the focus in transplant immunology has been on controlling the alloreactive B cell population, long-term transplant patient survival is also critically dependent on protection by pathogen-specific memory B cells. Techniques are available that allow the interrogation of memory B cell response to pathogen re-encounter. Thus, we are poised in our ability to investigate how immunosuppression affects allospecific and pathogen-specific memory B cells, and reason that these investigations can yield new insights that will be beneficial for graft and patient survival.