Abrogation of anti-HLA antibodies via proteasome inhibition. Transplantation. 2009;87:1555-1561. [PMID: 19461494 DOI: 10.1097/tp.0b013e3181a4b91b]

CD38 monoclonal antibody felzartamab for late antibody-mediated rejection: a phase II drug evaluation

INTRODUCTION

Felzartamab is a novel, fully human CD38 monoclonal antibody, currently in development for the treatment of antibody-mediated rejection (AMR) following kidney transplantation.

AREAS COVERED

This review focuses on current phase II trials of felzartamab in AMR and other immune-mediated kidney diseases. Specifically, it discusses the drug's mechanism of action, current phase of clinical development, potential future applications and regulatory status.

EXPERT OPINION

CD38 is an activation marker expressed on the surface of plasma cells and immune cells, including natural killer cells (NK cells) cells. In a recent phase II randomized, placebo-controlled clinical trial, felzartamab demonstrated an acceptable safety and side-effect profile in patients with AMR after kidney transplantation. Efficacy outcomes suggested potential therapeutic benefits, including significant reductions in morphologic and molecular AMR activity. Given the mixed results of previous clinical trials for AMR treatments, the novel approach of targeting both antibody-secreting plasma cells and innate effector cells such as CD38+ NK cells may offer a promising new therapeutic strategy. Felzartamab is also being investigated for the treatment of other antibody-mediated kidney diseases, such as lupus nephritis, primary membranous nephropathy and IgA nephropathy. If proven effective, it could expand the therapeutic options for kidney transplant rejection and primary kidney diseases.

Kidney Transplantation in Multiple Myeloma and Monoclonal Gammopathy of Renal Significance

Recent advances in the treatment of plasma cell disorders (PCDs) have provided a wealth of therapy alternatives and improved overall survival tremendously. Various types of PCDs are associated with kidney injury and end-stage kidney disease in a considerable number of patients. Kidney transplantation (KTx) is the best option for renal replacement therapy in select patients in terms of both quality of life parameters and overall survival. Even with modern therapies, all PCDs carry the risk of hematologic progression, whereas histologic recurrence and graft loss are other prevailing concerns in these patients. The risk of mortality is also higher in some of these disorders compared with KTx recipients who suffer from other causes of kidney disease. Unlike solid cancers, there is no well-defined "waiting time" after hematologic remission before proceeding to KTx. Thus, clinicians are usually reluctant to recommend KTx to patients who develop end-stage kidney disease due to PCDs. This review aims to provide the current evidence on KTx outcomes in patients with monoclonal gammopathy of renal significance and multiple myeloma. Although immunoglobulin light chain amyloidosis is a monoclonal gammopathy of renal significance subtype, KTx outcomes in this group are mentioned in another chapter of this issue.

Ixazomib for Desensitization (IXADES) in Highly Sensitized Kidney Transplant Candidates: A Phase II Clinical Trial

KEY POINTS

Ixazomib treatment resulted in decreases in B-cell subsets and bone marrow lymphocytes. Ixazomib treatment resulted in modest decreases in certain anti-HLA antibody specificities. Ixazomib treatment was tolerated, with modest adverse events.

BACKGROUND

Ixazomib is a second-generation oral proteasome inhibitor approved for treatment of refractory multiple myeloma. We conducted an open-label phase II trial, IXAzomib for DESensitization (IXADES), testing the safety of ixazomib treatment as an approach to decreasing the level and diversity of specificities of anti-HLA antibodies in subjects awaiting kidney transplantation. The trial (NCT03213158) enrolled highly sensitized kidney transplant candidates, defined as subjects with calculated panel reactive antibodies (cPRA) >80%, awaiting kidney transplantation >24 months. The subjects were treated with 12 monthly cycles of ixazomib 3 mg+dexamethasone 20 mg. Efficacy was defined as a decrease of cPRA >20% or kidney transplantation. The safety end point was tolerability.

METHODS

In ten enrolled subjects, no grade IV, five grade III, 11 grade II, and 43 grade I adverse events were noted. The adverse events included infection, transient paresthesia, nausea, vomiting, and diarrhea. The IXADES regimen was not associated with significant change in levels or diversity of anti-HLA antibodies (cPRA).

RESULTS

Although the IXADES regimen did not exhibit a clear impact on levels and diversity of anti-HLA antibodies in this small cohort, the prolonged half-life of IgG could necessitate a longer duration of treatment for accurate evaluation of efficacy.

CONCLUSIONS

In conclusion, treatment with ixazomib/dexamethasone engendered mild-to-moderate toxicity. The impact on anti-HLA was modest and paradoxical in the case of anti-HLA-DR. Clinical trials combining ixazomib with other immunosuppressive agents may be more effective in addressing antibody-mediated processes in kidney transplantation.

Treatment with bortezomib for recurrent proliferative glomerulonephritis with monoclonal IgG deposits in kidney allograft. Case report and review of the literature

Proliferative glomerulonephritis with monoclonal immunoglobulin IgG deposits (PGNMID) is an already described form of renal involvement by monoclonal gammopathy. PGNMID is known to recur in kidney allografts. Bortezomib has shown clinical success in the treatment of multiple myeloma. However, its effect for recurrent PGNMID in kidney allografts has rarely been reported. We present the case of a 61-year-old woman who developed recurrent PGNMID 3 weeks after kidney transplantation. This patient was initially treated with steroid pulses (500 mg/day for 2 days) and two cycles of rituximab therapy (200 mg/body). However, disease progression was observed with mesangial matrix expansion and subendothelial deposits by light microscopy and stronger staining for IgG3 and kappa in the mesangial area by Immunofluorescence (IF) microscopy. Thus, we started treatment with bortezomib therapy (1.3 mg/m2, once weekly, on days 1, 8, 15, and 22 in a 5-week cycle, for a total of six cycles). Bortezomib therapy reduced massive proteinuria, although monoclonal immune deposits on IF and the serum creatinine level did not change during the treatment period. Seven months after completion of the first bortezomib course, we decided to prescribe a second course of bortezomib with the same regimen. Each course resulted in a > 50% reduction of proteinuria. Bortezomib may delay the progress of PGNMID in kidney allograft patients.

Bortezomib in autoimmune hemolytic anemia and beyond

Bortezomib is a first-in-class, potent, selective and reversible proteasome inhibitor approved for the treatment of multiple myeloma (MM) and relapsed/refractory mantle cell lymphoma. In these diseases, bortezomib targets plasma cells and lymphocytes reducing tumor burden. Recently, preclinical evidence highlighted its efficacy in reducing long-lived plasma cells responsible of autoantibodies production in several models of autoimmune conditions. These findings paved the way to a number of experiences of bortezomib use in patients with various autoimmune conditions, including autoimmune hemolytic anemia (AIHA). The latter is a nice model of autoimmunity in hematology and is caused by the production of autoantibodies against erythrocytes resulting in various degrees of hemolytic anemia. AIHA is classified in warm and cold forms according to the thermal characteristics of the autoantibody, and first-line treatment mainly relies on steroids for warm cases and the anti-CD20 rituximab for cold ones. Relapsed/refractory cases are still an unmet need, and bortezomib has been proposed in this setting with intriguing efficacy. In this review, we collected available literature on bortezomib use in AIHA and in other immune-mediated hematologic and non-hematologic diseases. Overall, most experiences highlight bortezomib efficacy even in multi-relapsed/refractory patients and suggest to consider its use in AIHA after rituximab failure.

Tackling Chronic Kidney Transplant Rejection: Challenges and Promises

Despite advances in post-transplant management, the long-term survival rate of kidney grafts and patients has not improved as approximately forty percent of transplants fails within ten years after transplantation. Both immunologic and non-immunologic factors contribute to late allograft loss. Chronic kidney transplant rejection (CKTR) is often clinically silent yet progressive allogeneic immune process that leads to cumulative graft injury, deterioration of graft function. Chronic active T cell mediated rejection (TCMR) and chronic active antibody-mediated rejection (ABMR) are classified as two principal subtypes of CKTR. While significant improvements have been made towards a better understanding of cellular and molecular mechanisms and diagnostic classifications of CKTR, lack of early detection, differential diagnosis and effective therapies continue to pose major challenges for long-term management. Recent development of high throughput cellular and molecular biotechnologies has allowed rapid development of new biomarkers associated with chronic renal injury, which not only provide insight into pathogenesis of chronic rejection but also allow for early detection. In parallel, several novel therapeutic strategies have emerged which may hold great promise for improvement of long-term graft and patient survival. With a brief overview of current understanding of pathogenesis, standard diagnosis and challenges in the context of CKTR, this mini-review aims to provide updates and insights into the latest development of promising novel biomarkers for diagnosis and novel therapeutic interventions to prevent and treat CKTR.

Heart Transplant Immunosuppression Strategies at Cedars-Sinai Medical Center

Heart transplant is the optimal treatment for selected patients with end-stage heart failure. Immunosuppression after heart transplantation has significantly reduced the incidence of rejection and improved patient outcomes with the routine use of calcineurin inhibitors. Antimetabolites and proliferation signal inhibitors add to the improvement in patient outcomes as well. The goal of induction therapy is to provide intense immunosuppression when the risk of allograft rejection is highest. Most maintenance immunosuppressive protocols employ a 3-drug regimen consisting of a calcineurin inhibitor, an antimetabolite agent and glucocorticoids. The management of rejection proceeds in a stepwise fashion based on the severity of rejection detected on biopsy and the patient's clinical presentation. This review will cover induction, maintenance, rejection therapy and some special considerations including sensitization, renal sparing protocol, and corticosteroid weaning. It will end in consideration of potential future directions in immunosuppressive strategies to promote patient and graft survival.

Proteasome, a Promising Therapeutic Target for Multiple Diseases Beyond Cancer

Proteasome is vital for intracellular protein homeostasis as it eliminates misfolded and damaged protein. Inhibition of proteasome has been validated as a powerful strategy for anti-cancer therapy, and several drugs have been approved for treatment of multiple myeloma. Recent studies indicate that proteasome has potent therapeutic effects on a variety of diseases besides cancer, including parasite infectious diseases, bacterial/fungal infections diseases, neurodegenerative diseases and autoimmune diseases. In this review, recent developments of proteasome inhibitors for various diseases and related structure activity relationships are going to be summarized.

Antibody-Mediated Rejection Treatment With Bortezomib in Renal Transplant Recipients: A Single-Center 24-Month Follow-up Case Report

INTRODUCTION

Antibody-mediated rejection (AMR) is related to a poor prognosis in graft survival, with 27% to 40% of patients experiencing graft loss within the first year. The mechanism of damage in AMR is mediated by donor-specific antibodies (DSA). No standard treatment for AMR exists, and conventional management includes high doses of steroids, plasmapheresis, intravenous immunoglobulin, and either rituximab or bortezomib. Because of the high cost of these medications and the lack of prospective studies to evaluate their efficacy and safety, their routine use is limited. In the following study, we describe the use of bortezomib for the treatment of AMR in 5 renal transplant recipients with a 24-month follow-up and compare this case with the reviewed literature.

MATERIAL AND METHODS

Five cases of AMR diagnosed by biopsy are reported, and these patients received bortezomib at a rate of 1.3 mg/m² on days 1, 4, 8, and 11; plasmapheresis; and 1 patient received 30 g of intravenous immunoglobulin.

RESULTS

All patients received his or her first transplant; 4 were from a cadaveric donor, and 1 patient received thymoglobulin at a standard dose. All patients had maintenance therapy based on cyclosporine, mycophenolate mofetil, and prednisone, with an average baseline creatinine level of 1.3 mg/dL. The average days until rejection event were 952 days.

DISCUSSION AND CONCLUSION

AMR treatment with bortezomib was effective, showing stable renal function at 24 months. Patients had adequate tolerance for administration. So far, these results contrast with the literature reviewed, so additional studies and follow-up are required for a new evaluation.

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.

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”.

Sensitization in Heart Transplantation: Emerging Knowledge: A Scientific Statement From the American Heart Association

Sensitization, defined as the presence of circulating antibodies, presents challenges for heart transplant recipients and physicians. When present, sensitization can limit a transplantation candidate’s access to organs, prolong wait time, and, in some cases, exclude the candidate from heart transplantation altogether. The management of sensitization is not yet standardized, and current therapies have not yielded consistent results. Although current strategies involve antibody suppression and removal with intravenous immunoglobulin, plasmapheresis, and antibody therapy, newer strategies with more specific targets are being investigated.

Bortezomib and Immune Globulin Have Limited Effects on Donor-Specific HLA Antibodies in Haploidentical Cord Blood Stem Cell Transplantation: Detrimental Effect of Persistent Haploidentical Donor-Specific HLA Antibodies

Donor-specific HLA antibodies (DSAs) have been associated with an increased risk of graft failure. To decrease DSA levels and reduce the risk of graft failure in haploidentical cord blood transplantation recipients, we studied the effect of bortezomib (BTZ) and i.v. immune globulin (IVIG) pretransplantation. Between 2012 and 2016, 14 patients with a DSA level >2000 mean fluorescence intensity (MFI) to 1 or more mismatched HLA alleles of haploidentical donors, cord blood donors, or both were treated with BTZ and IVIG. Fourteen patients received a median of 4 doses (range, 2 to 8 doses) of BTZ 1.3 mg/m² and a median total IVIG of 2 g/kg before transplantation. Only 2 of 14 patients attained a reduction in MFI to <2000 with this combination. After additional IVIG (n = 8), rituximab (n = 4), and/or plasmapheresis (n = 11), 12 of 14 patients were desensitized to a DSA level <2000 MFI at the time of engraftment. All obtained initial hematopoietic reconstitution, and no DSA rebound phenomenon was observed. Responders with DSA MFI <2000 to the haploidentical donor by transplantation engrafted at a rate comparable to that of historical controls, whereas engraftment in nonresponders took 3 times as long. BTZ and IVIG alone do not appear sufficient to rapidly induce DSA desensitization, and persistent DSAs to a haploidentical donor lead to delayed count recovery. Our data suggest that additional pretreatment with BTZ and IVIG in combination with the conditioning regimen may help abrogate the rebound phenomenon observed with plasmapheresis.

On the role of the immunoproteasome in transplant rejection

The immunoproteasome is expressed in cells of hematopoietic origin and is induced during inflammation by IFN-γ. Targeting the immunoproteasome with selective inhibitors has been shown to be therapeutically effective in pre-clinical models for autoimmune diseases, colitis-associated cancer formation, and transplantation. Immunoproteasome inhibition prevents activation and proliferation of lymphocytes, lowers MHC class I cell surface expression, reduces the expression of cytokines of activated immune cells, and curtails  T helper 1 and 17 cell differentiation. This might explain the in vivo efficacy of immunoproteasome inhibition in different pre-clinical disease models for autoimmunity, cancer, and transplantation. In this review, we summarize the effect of immunoproteasome inhibition in different animal models for transplantation.

Autologous Mesenchymal Stromal Cells Prevent Transfusion-elicited Sensitization and Upregulate Transitional and Regulatory B Cells

BACKGROUND

We hypothesized that immunomodulatory properties of mesenchymal stromal cells (MSC) may be considered for desensitization.

METHODS

Autologous or allogeneic bone marrow derived MSC were infused via tail vein at 0.5 M (0.5 × 106), 1 M, or 2 M cells/dose on days -2, 3, 6, 9, 12 (prevention) or 14, 17, 20, 23, 26 (treatment) relative to transfusion in a Brown Norway to Lewis rat model (10 groups total, n = 6 per group).

RESULTS

At 4 weeks, pooled analyses demonstrated that autologous and allogeneic MSC were equally effective in reducing IgG1 and IgG2a de novo donor-specific antibody (dnDSA, P < 0.001). Dose-response studies indicated that moderate-dose MSC (5 M total) was most effective in reducing IgG1, IgG2a, and IgG2c dnDSA (P ≤ 0.01). Time course studies determined that preventive and treatment strategies were equally effective in reducing IgG1 and IgG2a dnDSA (P ≤ 0.01). However, individual group analyses determined that moderate-dose (5 M) treatment with autologous MSC was most effective in reducing IgG1, IgG2a, and IgG2c dnDSA (P ≤ 0.01). In this group, dnDSA decreased after 1 week of treatment; regulatory B cells increased in the spleen and peripheral blood mononuclear cells; and transitional B cells increased in the spleen, peripheral blood mononuclear cells, and bone marrow (P < 0.05 for all).

CONCLUSIONS

Our findings indicate that autologous MSC prevent transfusion-elicited sensitization and upregulate transitional, and regulatory B cells. Additional studies are needed to determine the biological relevance of these changes after kidney transplantation.

[THE USE OF BORTEZOMIB FOR THE TREATMENT OF CHRONIC ANTIBODY MEDIATED REJECTION AFTER KIDNEY TRANSPLANTATION]

(Backgrounds) The efficacy of bortezomib for chronic antibody mediated rejection (CAMR) after kidney transplantation is still obscure. (Materials and methods) CAMR were persisted in 5 recipients who were treated with plasma exchange, low dose of IVIG, steroid pulse therapy, and rituximab. 1.3 mg/m² of bortezomib was administered on days 1, 4, 8, 11. Serum creatinine (sCr) levels, anti-HLA antibodies, and histology were analyzed. (Results) Stable sCr levels were obtained in 3 out of 5 recipients. No one lost renal graft function during follow-up periods. Anti-HLA class I antibodies were significantly decreased after bortezomib treatment, however anti-HLA class II antibodies were not changed. Histology showed no improvement at 6 months after bortezomib administration. Two recipients whose sCr levels increased during follow-up had already had interstitial fibrosis and tubular atrophy (IF/TA) in histology before bortezomib treatment. (Conclusions) The use of bortezomib after IF/TA could be detected in histology may not contribute to stabilize renal graft function in CAMR.

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.

Nature and Clonality of the Fluoresceinated Secondary Antibody in Luminex Multiplex Bead Assays Are Critical Factors for Reliable Monitoring of Serum HLA Antibody Levels in Patients for Donor Organ Selection, Desensitization Therapy, and Assessment of the Risk for Graft Loss

Luminex multiplex immunoassays enable simultaneous monitoring of Abs against multiple Ags in autoimmune, inflammatory, and infectious diseases. The assays are used extensively to monitor anti-HLA Abs in transplant patients for donor organ selection, desensitization, and assessing the risk for graft rejection. To monitor IgG Abs, fluoresceinated IgG constant H chain-binding polyclonal F(ab')₂ (IgHPolyFab) is used as the fluoresceinated secondary Ab (2nd-Ab), whereas IgG subclasses are monitored with Fc-specific monoclonal whole IgG (FcMonoIgG). The fluorescent signal from the 2nd-Ab is measured as mean florescence intensity (MFI). When IgHPolyFab is used, the signal is amplified as a result of the binding of multiple polyclonal Fabs to the C region of primary IgH. The reliability of such amplification for Ab measurements was not validated, nor were MFIs compared with 1:1 binding of FcMonoIgG to primary Abs. Comparing the MFIs of anti-HLA Abs obtained with IgHPolyFab and FcMonoIgG against normal human sera, IVIg, and allograft recipients' sera, it was observed that the number of HLA-Abs was notably higher with IgHPolyFab than with FcMonoIgG The MFIs of anti-HLA Abs also remained higher with IgHPolyFab in the normal sera and in IVIg, but the reverse was true when the autologous and allogeneic IgG concentrations were augmented in allograft recipients. Indeed, MFIs of the de novo allo-HLA Abs were markedly higher with FcMonoIgG than with IgHPolyFab. Serum titration established the superiority of FcMonoIgG for monitoring MFIs of de novo allo-HLA Abs in allograft recipients. Avoiding false amplifications of the number and MFIs of anti-HLA IgG with FcMonoIgG may minimize immunosuppressive therapies, maximize the number of donors for patients waiting for allografts, and enable better prediction of graft 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.

Modulation of NF-κB Signaling as a Therapeutic Target in Autoimmunity

Autoimmune diseases arise from the loss of tolerance to endogenous self-antigens, resulting in a heterogeneous range of chronic conditions that cause considerable morbidity and mortality worldwide. In Western countries, over 5% of the population is affected by some form of autoimmune disease, with enhanced or inappropriate activation of nuclear factor (NF)-κB implicated in a number of these conditions. Although treatment strategies for autoimmunity have improved significantly in recent years, current therapeutics are still not capable of achieving satisfactory disease management in all patients, and as such, the therapeutic modulation of NF-κB is an attractive target in autoimmunity. To date, no NF-κB inhibitors have progressed to the clinic for the treatment of autoimmunity, but a variety of promising approaches targeting multiple stages of the NF-κB pathway are currently being explored. This review focuses on the current strategies being investigated for the inhibition of the NF-κB pathway in autoimmune diseases and considers potential future strategies for the therapeutic targeting of this crucial transcription factor.

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.

Modern approaches to incompatible kidney transplantation

The presence of human-leukocyte antigen (HLA)-antibodies and blood group incompatibility remain a large barrier to kidney transplantation leading to increased morbidity and mortality on the transplant waiting list. Over the last decade a number of new approaches were developed to overcome these barriers. Intravenous immunoglobulin (IVIG) remains the backbone of HLA desensitization therapy and has been shown in a prospective, randomized, placebo controlled trial to improve transplantation rates. Excellent outcomes with the addition of rituximab (anti-B cell) to IVIG based desensitization have been achieved. There is limited experience with bortezomib (anti-plasma cell) and eculizumab (complement inhibition) for desensitization. However, these agents may be good adjuncts for patients who are broadly sensitized with strong, complement-fixing HLA antibodies. Excellent short and long-term outcomes have been achieved in ABO incompatible transplantation with the combination of antibody removal, B cell depletion, and pre-transplant immunosuppression. Kidney paired donation has emerged as a reasonable alternative for programs who cannot provide desensitization or in conjunction with desensitization. Future therapies directed toward cytokines that alter B cell proliferation are under investigation.

Treatment of antibody‐mediated rejection in renal transplant patients: a clinical practice survey

Introduction

Preferences for the testing and treatment of antibody‐mediated rejection (AMR) in renal transplant patients vary among programs and individual practitioners. The description of these preferences and identification of commonalities can contribute to creating a standard of care.

Methods

A survey was distributed through the Transplant Listserv of the American College of Clinical Pharmacy (ACCP) and via email to members of the American Society of Transplantation Community of Pharmacy (AST CoP), collected, and analyzed.

Results

Most clinicians (26/28) test for donor‐specific antibodies (DSAs) when evaluating a patient with possible AMR. Treatments for AMR varied widely among responding clinicians and included intravenous immune globulin (IVIG, n = 25), plasmapheresis (n = 24), rituximab (n = 8), bortezomib (n = 4), rabbit antithymocyte globulin (n = 2), and eculizumab (n = 1). Weight‐based dosing of IVIG averaged 1.8 g/kg total dose. Six centers use rituximab as initial therapy, while two use rituximab if other therapy fails. Four centers use bortezomib as initial therapy, while two centers use it for severe/persistent AMR. One center uses eculizumab as initial therapy and one center uses it for severe AMR.

Conclusion

Methods for the detection of AMR are similar, yet treatment of AMR varies widely. Most centers utilize DSA for detection and a combination of IVIG and plasmapheresis for treatment.

Biologics in renal transplantation

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

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

SIGNIFICANCE

Development of donor-specific antibodies (DSA) after kidney transplantation is associated with reduced allograft survival. A few strategies have been tested in controlled clinical trials for the treatment of antibody-mediated rejection (AMR), and no therapies are approved by regulatory authorities. Thus development of antihumoral therapies that provide prompt elimination of DSA and improve allograft survival is an important goal.

RECENT ADVANCES

Proteasome inhibitor (PI)-based regimens provide a promising new approach for treating AMR. To date, experiences have been limited to off-label bortezomib use in AMR. Key findings with PI-based therapy are that they provide effective primary and rescue therapy for AMR by prompt reduction in immunodominant DSA and improvements in histologic and renal function. Early and late AMR differ immunologically and in response to PI therapy. Bortezomib-related toxicities in renal transplant recipients are similar to those observed in the multiple myeloma population.

CRITICAL ISSUES

Although preliminary evidence with PI therapy for AMR is encouraging, the evidence is limited. Larger, prospective, randomized controlled trials with long-term follow up are needed. Advancement in endpoints of clinical trial designs and rigorous clinical trials with more standardized adjunct therapies are also required to explore the risks and benefits of AMR treatment modalities.

FUTURE DIRECTIONS

In the next few years, new PIs are likely to be introduced and new approaches would be developed for achieving synergy with PIs. The ultimate goal will be to develop a regimen that delivers reliable, rapid, complete, and durable elimination of DSA with an acceptable safety profile.

Outcomes of combination therapy for chronic antibody-mediated rejection in renal transplantation

AIM

Chronic antibody-mediated rejection (CAMR) in renal transplant patients has poor allograft outcomes. However, treatment strategy has not been established yet. Herein, we present short-term outcomes of combination therapy for CAMR.

METHODS

We identified nine patients with CAMR or suspicious CAMR who were treated with antihumoral therapy from 2010 to 2011 and analyzed their medical records retrospectively.

RESULTS

Five patients had CAMR, and four patients had suspicious CAMR. Severe transplant glomerulopathy (TG) was observed in seven patients. The estimated glomerular filtration rate (eGFR) was decreased in all patients before treatment. We used three different treatment regimens: (i) high-dose intravenous immunoglobulin (IVIG) and rituximab; (ii) high-dose IVIG, rituximab, and bortezomib; and (iii) plasmapheresis with low-dose IVIG, rituximab and bortezomib. After treatment with one of these three regimens, graft function improved or stabilized in six patients, whereas three patients showed further deterioration of eGFR. The third regimen suppressed deterioration of renal function in all patients. Most patients showed no progression of proteinuria. Infectious complications due to Pneumocystis jirovecii pneumonia and herpes zoster occurred in two patients.

CONCLUSION

Combination therapy for CAMR might be effective, even in patients with relatively late-stage CAMR.

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.

Bortezomib for refractory autoimmunity in pediatrics

Therapy of refractory autoimmunity remains challenging. In this study, we evaluated the therapeutic effect of bortezomib, a proteasome inhibitor, by targeting plasma cells in 7 patients (median age, 9.9 years). Four doses of bortezomib were administered at a dose of 1.3 mg/m(2) intravenously (n = 6) or subcutaneously (n = 1) every 72 hours. Bortezomib was administered at a median of 120 days from laboratory confirmation of autoantibodies. All patients had failed 2 or more standard therapies. Rituximab was administered on the first day if B cells were present, and all patients received plasmapheresis 2 hours before bortezomib administration. Six patients experienced resolution of cytopenias. Two of 6 patients experienced recurrence of cytopenias after initial response. Adverse effects include nausea (n = 1), thrombocytopenia (n = 2), Clostridium difficile colitis (n = 1)), febrile neutropenia (n = 1), and cellulitis at the subcutaneous injection site (n = 1). Our experience suggests that bortezomib may be beneficial in the treatment of refractory autoimmunity in children.

Targeting B cells in sensitized kidney transplant patients: state of the art and future perspectives

PURPOSE OF REVIEW

In sensitized kidney transplant recipients, whose number is continuously growing, the negative impact of antibody-mediated rejection is being increasingly recognized. The purpose of this review is to summarize the state of knowledge about the mechanisms of alloantibody production. We will also report the most recent clinical results of current immunosuppressive protocols - either preventive or curative - in this population.

RECENT FINDINGS

Even if progress in access to transplantation and short-term graft survival has been made in sensitized patients using therapeutic strategies targeting both alloantibodies (plasmapheresis and/or intravenous globulins) and B cells (CD20 antibodies), antibody-mediated rejection remains a critical issue frequently compromising renal function and middle-term graft survival. The partial efficacy of such strategies and the presence in sensitized patients of both peripheral memory B cells and bone marrow plasma cells capable of alloantibody synthesis in vitro suggest that, in vivo, alloantibody production most likely involves both cell types, not equally targeted by CD20 antibody-based therapies.

SUMMARY

The need for improved strategies of prevention/treatment of antibody-mediated rejection, have led, based on the actual understanding of alloantibody synthesis, to the use of drugs targeting plasma cells, that is proteasome inhibitors. Preliminary results are contrasted and highlight the necessity for controlled studies in the field of antihumoral therapies.

Down-regulating humoral immune responses: implications for organ transplantation

Alloantibody can be a major barrier to successful organ transplantation; however, therapy to control antibody production or to alter its impact on the allograft remains limited. The goal of this review is to examine the regulatory steps that are involved in the generation of alloreactive B cells, with a specific emphasis on how known mechanisms relate to clinical situations in transplant recipients. Thus, we will examine the process of activation of mature, naïve B cells and how this relates to de novo antibody production. The role of long-lived plasma cells in persistent antibody production and the factors regulating their longevity will be explored. The regulation of memory B cells and their possible roles in alloimmunity also will be assessed. Finally, we will review current therapeutic approaches aimed at controlling alloantibody and assess their efficacy. By examining the pathways to antibody production mechanistically, we hope to identify important gaps in our current knowledge and gain insight into possible new therapeutic approaches to overcoming antibody in transplant patients.

Impact of HLA antibodies on graft survival in long-term renal recipients with functional grafts

OBJECTIVES

Accumulating evidence supports the hypothesis that HLA antibodies play an important role in early renal allograft injury. However, the effects of HLA antibodies on long-term graft survival are still poorly understood. In this study, we examined the impact of HLA antibodies on graft survival in long-term renal recipients with functional grafts for 10 years.

MATERIAL AND METHODS

In this retrospective study, long-term renal recipients were defined as kidney transplant recipients who had normally functioning renal grafts (serum creatinine level <2.0 mg/dl) for 10 years. Posttransplant serum samples from a total of 92 long-term renal allograft recipients on cyclosporine-based triple maintenance drug therapy (121.6 ± 0.886 months) were screened for the specificities of anti-HLA antibodies. The results of HLA antibodies before the transplantation, assessed using the same test method, were compared with those after their transplantations. Moreover, these 92 patients who received cadaveric renal transplant between January 2000 and December 2002 were followed up for about 10 years (range 107-135 months).

RESULTS

27 patients had HLA-I antibodies and 16 patients had HLA-II antibodies before the transplantation, whereas 12 patients had HLA-I antibodies and 18 patients had HLA-II antibodies after the transplantation. Moreover, the types of HLA antibodies were different from those found before the transplantation. In these renal recipients with functioning renal grafts, the estimated glomerular filtration rate was 66.52 ± 14.52 ml/min/1.73 m(2) in the HLA antibody-positive group (n = 23) and 69.09 ± 25.54 ml/min/1.73 m(2) negative in the HLA antibody-negative group (n = 69, p > 0.05). Three patients (3.26%) (3 out of 92) had donor-specific anti-HLA antibodies (DSA). The frequency of DSA in this study was lower than that in the general Chinese Han renal recipient population.

CONCLUSIONS

We find that all HLA antibodies in the long-term renal grafts are newly formed after the transplantation. The HLA antibody status has little impact on the renal graft function in the long-term renal recipients.

Novel immunosuppressive agents in kidney transplantation

Excellent outcomes have been achieved in the field of renal transplantation. A significant reduction in acute rejection has been attained at many renal transplant centers using contemporary immunosuppressive, consisting of an induction agent, a calcineurin inhibitor, an antiproliferative agent plus or minus a corticosteroid. Despite improvements with these regimens, chronic allograft injury and adverse events still persist. The perfect immunosuppressive regimen would limit or eliminate calcineurin inhibitors and/or corticosteroid toxicity while providing enhanced allograft outcomes. Potential improvements to the calcineurin inhibitor class include a prolonged release tacrolimus formulation and voclosporin, a cyclosporine analog. Belatacept has shown promise as an agent to replace calcineurin inhibitors. A novel, fully-human anti-CD40 monoclonal antibody, ASKP1240, is currently enrolling patients in phase 2 trials with calcineurin minimization and avoidance regimens. Another future goal of transplant immunosuppression is effective and safe treatment of allograft rejection. Novel treatments for antibody mediated rejection include bortezomib and eculizumab. Several investigational agents are no longer being pursed in transplantation including the induction agents, efalizumab and alefacept, and maintenance agents, sotrastaurin and tofacitinib. The purpose of this review is to consolidate the published evidence of the effectiveness and safety of investigational immunosuppressive agents in renal transplant recipients.

Acute antibody-mediated rejection in pediatric kidney transplants: a single center experience

aAMR is a potentially devastating complication of kidney transplantation. The incidence of aAMR in children, while thought to be rare, is not well defined, and there is a paucity of data on treatment regimens in children. We retrospectively reviewed the outcomes of our pediatric patients that were treated for aAMR between 2007 and 2009. Three adolescent Hispanic males were found to have aAMR. All three received deceased donor transplants, and all three verbalized non-adherence. Treatment consisted of rituximab, solumedrol, PE, and IVIgG in one patient, and PE, IVIgG, and bortezomib in two patients. The only side effect of therapy noted was mild hypotension with rituximab that resolved after decreasing the infusion rate. There were no reported infections two yr after treatment, and all of the viral monitoring in these patients remained negative.

Minimal effect of bortezomib in reducing anti-pig antibodies in human leukocyte antigen-sensitized patients: a pilot study

BACKGROUND

Bortezomib, a proteasome inhibitor used to treat multiple myeloma, has been administered (± plasma exchange ± intravenous immunoglobulin [IVIg]) in attempts to reduce antibodies against human leukocyte antigens (HLA) in sensitized patients undergoing organ transplantation. To our knowledge, bortezomib has not been investigated for its effect on natural anti-pig antibodies. If bortezomib could reduce the production of anti-pig antibodies, this would likely be beneficial to the outcome of pig organ grafts in primates.

METHODS

Nine patients received bortezomib either to reduce anti-HLA antibody levels before organ allotransplantation or to treat antibody-mediated rejection. Patients at the Mayo Clinic (Group 1; n = 4) received bortezomib alone, whereas at the UPMC (Group 2; n = 5), this was combined with plasmaphereses ± IVIg in some cases. Anti-pig IgM and IgG levels against wild-type (WT) and α1,3-galactosyltransferase gene knockout (GTKO) pig aortic endothelial cells (flow cytometry-relative mean fluorescence intensity) and anti-Gal IgM and IgG (ELISA-OD480 nm ) were measured pre- and post-bortezomib therapy.

RESULTS

Mean anti-pig IgM levels were 11.2 (WT) and 1.9 (GTKO) pre-bortezomib treatment and 9.4 (WT: P = 0.02) and 1.7 (GTKO: P = 0.33) post-bortezomib treatment, respectively. Mean anti-pig IgG levels were 4.3 (WT) and 1.5 (GTKO) pre-bortezomib treatment and 3.6 (WT: P = 0.21) and 1.4 (GTKO: P = 0.20) post-bortezomib treatment, respectively. Mean anti-Gal IgM and IgG levels were 0.7 and 1.1, respectively, pre-treatment, and 0.6 (P = 0.03) and 1.1 (NS), respectively, post-treatment. When the data were analyzed in Groups 1 and 2 separately, there were no significant differences between the pre- and post-bortezomib levels of anti-pig, anti-non-Gal, or anti-Gal IgM or IgG.

CONCLUSIONS

From this limited study, we conclude that bortezomib might reduce anti-Gal IgM levels in primates, but, in this respect alone, is unlikely to have any significant effect on the outcome of GTKO pig organ transplantation.

Use of bortezomib to treat anti-HLA antibodies in renal transplant patients: a single-center experience

Donor-specific human leukocyte antigen (HLA) antibodies (DSA) are associated with decreased graft survival and may cause graft rejection. Bortezomib, a selective inhibitor of the 26S proteasome developed to treat multiple myeloma, has been used for its anti-plasma cell activity in patients undergoing transplantation. We describe our experience with bortezomib used to reduce anti-HLA antibodies in eight renal transplant patients. Patients received bortezomib (1.3mg/m(2)) on days 1, 4, 8, and 11 beginning when antibodies were detected. It was used alone in one patient and was complemented with plasmapheresis in five patients, with IVIG in one patient, and with IVIG and plasmapheresis in another patient. De novo DSA class II were detected in all eight patients and two also had DSA class I. Antibodies were entirely eliminated in five (62.5%) patients 90 days after treatment but only reduced in the other three (62.5%). Notably, they later increased in one patient. Five (62.5%) patients had AMR, two (25%) had mixed rejection, and one had no rejection. our results suggest that bortezomib is effective for reducing DSA avoiding chronic graft injury.

Failure of bortezomib to cure acute antibody-mediated rejection in a non-compliant renal transplant patient

Bortezomib has appeared recently as a potential active treatment for acute AMR for few years. We reported a patient who received two courses of bortezomib for the treatment of an acute AMR associated with de novo HLA DSA that occurred 18 months after renal transplantation because of non-compliance. Graft biopsy revealed features of acute humoral rejection with plasmocyte infiltration and C4d staining. Bortezomib was associated with corticosteroid pulses, IVIgs, and PP. Despite this rapid management, the patient lost his graft and carried on dialysis. Bortezomib therapy in addition to current therapy of AMR is not always effective in the treatment for late acute AMR in renal transplantation. We discuss on the place of such a treatment and other therapeutic strategies in this indication.

Proteasome inhibition profoundly affects activated human B cells

BACKGROUND

Proteasome inhibitors, although initially developed for the treatment of malignancies, have been found to affect normal plasma cells by efficaciously inducing apoptosis. One proteasome inhibitor, bortezomib, has been used in transplantation settings to deplete human leukocyte antigen antibody-producing plasma cells to reverse humoral allograft rejection.

METHODS

To establish whether proteasome inhibitors are active on B cells, being plasma cell precursors, we examined a set of four proteasome inhibitors, including bortezomib, carfilzomib, ONX 0912, and ONX 0914, for their potential to impact the functionalities of activated B cells in vitro.

RESULTS

All proteasome inhibitors dose-dependently abrogated IgM and IgG production by activated B cells, as well as their proliferation, with varying efficiencies. The bortezomib-induced decline in immunoglobulin production was mainly due to a decrease in the number of B cells capable of immunoglobulin secretion, caused by apoptosis.

CONCLUSIONS

The action of proteasome inhibitors is not confined to plasma cells but also has impact on activated naïve and memory B cells.