Long-term outcome of belatacept therapy in de novo kidney transplant recipients - a case-match analysis

B Cell-mediated Immune Regulation and the Quest for Transplantation Tolerance

Pathophysiologic function of B cells in graft rejection has been well recognized in transplantation. B cells promote alloantigen-specific T-cell response and secrete antibodies that can cause antibody-mediated graft failures and rejections. Therefore, strategies targeting B cells, for example, B-cell depletion, have been used for the prevention of both acute and chronic rejections. Interestingly, however, recent mounting evidence indicates that subsets of B cells yet to be further identified can display potent immune regulatory functions, and they contribute to transplantation tolerance and operational tolerance in both experimental and clinical settings, respectively. In this review, we integrate currently available information on B-cell subsets, including T-cell Ig domain and mucin domain 1-positive transitional and T-cell immunoreceptor with Ig and immunoreceptor tyrosine-based inhibitory motif domain-positive memory B cells, displaying immune regulatory functions, with a focus on transplantation tolerance, by analyzing their mechanisms of action. In addition, we will discuss potential T-cell Ig domain and mucin domain 1-positive and T-cell immunoreceptor with Ig and immunoreceptor tyrosine-based inhibitory motif domain-positive B cell-based strategies for the enhancement of operational tolerance in transplantation patients.

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.

New concepts in chronic antibody-mediated kidney allograft rejection: prevention and treatment

PURPOSE OF REVIEW

Chronic antibody-mediated rejection (AMR) is a cardinal cause of transplant failure, with currently no proven effective prevention or treatment. The present review will focus on new therapeutic concepts currently under clinical evaluation.

RECENT FINDINGS

One interesting treatment approach may be interference with interleukin-6 (IL-6) signaling to modulate B-cell immunity and donor-specific antibody (DSA) production. Currently, a large phase III randomized controlled trial is underway to clarify the safety and efficacy of clazakizumab, a high-affinity anti-IL-6 antibody, in chronic AMR. A prevention/treatment strategy may be costimulation blockade using belatacept to interfere with germinal center responses and DSA formation. In a recent uncontrolled study, belatacept conversion was shown to stabilize renal function and dampen AMR activity. Moreover, preliminary clinical results suggest efficacy of CD38 antibodies to deplete plasma and natural killer cells to treat AMR, with anecdotal reports demonstrating at least transient resolution of active rejection.

SUMMARY

There are promising concepts on the horizon for the prevention and treatment of chronic AMR. The design of adequately powered placebo-controlled trials to clarify the safety and efficacy of such new therapies, however, remains a big challenge, and will rely on the definition of precise surrogate endpoints predicting long-term allograft survival. Mapping the natural history of AMR would greatly help the understanding of who would derive benefits from treatment.

Belatacept for maintenance immunosuppression in cardiothoracic transplantation: The potential frontier

Current immunosuppressive regimens with calcineurin inhibitors have improved the management of patients after transplantation. However, their adverse effects are linked to increased morbidity and limit the long-term survival of heart and lung transplant recipients. Belatacept, a costimulation inhibitor interfering with the interaction between CD28 on T cells and the B7 ligands on antigen presenting cells, has shown success and is currently approved for use in renal transplant recipients. Furthermore, it lacks many of the cardiovascular, metabolic, neurologic, and renal adverse of effects of calcineurin inhibitors that have the largest impact on long-term survival in cardiothoracic transplant. Additionally, it requires no therapeutic drug monitoring and is only administered once a month. Limitations to belatacept use have been observed that must be considered when comparing immunosuppression options. Despite this, maintenance immunosuppression with belatacept has the potential to improve outcomes in cardiothoracic transplant recipients, as it has with kidney transplant recipients. However, no large clinical trials investigating belatacept for maintenance immunosuppression in heart and lung transplant recipients exist. There is a large need for focused research of belatacept in cardiothoracic transplantation. Belatacept is a viable treatment option for maintenance immunosuppression, and it is reasonable to pursue more evidence in cardiothoracic transplant recipients.

Belatacept/CTLA4Ig: an update and critical appraisal of preclinical and clinical results

INTRODUCTION

The B7/CD28/CTLA4 signaling cascade is the most thoroughly studied costimulatory pathway and blockade with CTLA4Ig (abatacept) or its derivative belatacept has emerged as a valuable option for pharmacologic immune modulation. Several clinical studies have ultimately led to the approval of belatacept for immunosuppression in kidney transplant recipients. Areas covered: This review will discuss the immunological background of costimulation blockade and recent preclinical data and clinical results of CTLA4Ig/belatacept. Expert commentary: The development of belatacept is a major advance in clinical transplantation. However, in spite of promising results in preclinical and clinical trials, clinical use remains limited at present, in part due to increased rates of acute rejection. Recent efforts showing encouraging progress in refining such protocols might be a step toward harnessing the full potential of costimulation blockade-based immunosuppression.

Early barriers to neonatal porcine islet engraftment in a dual transplant model

Porcine islet xenografts have the potential to provide an inexhaustible source of islets for β cell replacement. Proof-of-concept has been established in nonhuman primates. However, significant barriers to xenoislet transplantation remain, including the poorly understood instant blood-mediated inflammatory reaction and a thorough understanding of early xeno-specific immune responses. A paucity of data exist comparing xeno-specific immune responses with alloislet (AI) responses in primates. We recently developed a dual islet transplant model, which enables direct histologic comparison of early engraftment immunobiology. In this study, we investigate early immune responses to neonatal porcine islet (NPI) xenografts compared with rhesus islet allografts at 1 hour, 24 hours, and 7 days. Within the first 24 hours after intraportal infusion, we identified greater apoptosis (caspase 3 activity and TUNEL [terminal deoxynucleotidyl transferase dUTP nick end labeling])-positive cells) of NPIs compared with AIs. Macrophage infiltration was significantly greater at 24 hours compared with 1 hour in both NPI (wild-type) and AIs. At 7 days, IgM and macrophages were highly specific for NPIs (α1,3-galactosyltransferase knockout) compared with AIs. These findings demonstrate an augmented macrophage and antibody response toward xenografts compared with allografts. These data may inform future immune or genetic manipulations required to improve xenoislet engraftment.

No augmentation of indoleamine 2,3-dioxygenase (IDO) activity through belatacept treatment in liver transplant recipients

Belatacept is a second-generation cytotoxic T lymphocyte antigen (CTLA)-4 immunoglobulin (Ig) fusion protein approved for immunosuppression in renal transplant recipients. It was designed intentionally to interrupt co-stimulation via CD28 by binding to its ligands B7·1 and B7·2. Experimental evidence suggests a potential additional mechanism for CTLA-4 Ig compounds through binding to B7 molecules expressed on antigen-presenting cells (APCs) and up-regulation of indoleamine 2,3-dioxygenase (IDO), an immunomodulating enzyme that catalyzes the degradation of tryptophan to kynurenine and that down-regulates T cell immunity. So far it remains unknown whether belatacept up-regulates IDO in transplant recipients. We therefore investigated whether belatacept therapy enhances IDO activity in liver transplant recipients enrolled in a multi-centre, investigator-initiated substudy of the Phase II trial of belatacept in liver transplantation (IM103-045). Tryptophan and kynurenine serum levels were measured during the first 6 weeks post-transplant in liver transplant patients randomized to receive either belatacept or tacrolimus-based immunosuppression. There was no significant difference in IDO activity, as indicated by the kynurenine/tryptophan ratio, between belatacept and tacrolimus-treated patients in per-protocol and in intent-to-treat analyses. Moreover, no evidence was found that belatacept affects IDO in human dendritic cells (DC) in vitro. These data provide evidence that belatacept is not associated with detectable IDO induction in the clinical transplant setting compared to tacrolimus-treated patients.

Transcriptomic Signature of the CD24hi CD38hi Transitional B Cells Associated With an Immunoregulatory Phenotype in Renal Transplant Recipients

The role of B cells after transplant regarding allograft rejection or tolerance has become a topic of major interest. Recently, in renal transplant recipients, a B cell signature characterized by the overexpression of CD19⁺ CD38^hi CD24^hi transitional B cells has been observed in operationally tolerant patients and in belatacept-treated patients with significantly lower incidence of donor-specific antibodies. The phenotypic and functional characterization of these transitional B cells is far from exhaustive. We present the first transcriptomic and phenotypic analysis associated with this cell phenotype. Three populations were studied and compared: (i) transitional CD24^hi CD38^hi , (ii) CD24⁺ CD38^- , and (iii) CD24^int CD38^int B cells. Transcriptome bioinformatic analysis revealed a particular signature for the CD24^hi CD38^hi population. Phenotypic analysis showed that CD24^hi CD38^hi transitional B cells also expressed CD9, CD10, CD1b and inducible T cell costimulator ligand (ICOS-L) markers. In addition, we found enrichment of IL-10⁺ cells among CD24^hi CD38^hi cells expressing ICOS-L and CD1b, the latter showing regulatory properties. Renal transplant recipients treated with belatacept exhibited significant expression of CD1b. Our results show that transitional CD24^hi CD38^hi B cells exhibit a distinct and specific profile, and this could be helpful for understanding of immune-regulatory mechanisms and immune monitoring in the field of organ transplant and autoimmune disease.

B cells in transplantation

B cell responses underlie the most vexing immunological barriers to organ transplantation. Much has been learned about the molecular mechanisms of B cell responses to antigen and new therapeutic agents that specifically target B cells or suppress their functions are available. Yet, despite recent advances, there remains an incomplete understanding about how B cell functions determine the fate of organ transplants and how, whether or when potent new therapeutics should optimally be used. This gap in understanding reflects in part the realization that besides producing antibodies, B cells can also regulate cellular immunity, contribute to the genesis of tolerance and induce accommodation. Whether non-specific depletion of B cells, their progeny or suppression of their functions would undermine these non-cognate functions and whether graft outcome would suffer as a result is unknown. These questions were discussed at a symposium on "B cells in transplantation" at the 2015 ISHLT annual meeting. Those discussions are summarized here and a new perspective is offered.

Effect of Immunosuppressive Drugs on Humoral Allosensitization after Kidney Transplant

The negative effect of donor-specific antibodies on the success of solid transplant is now clearly established. However, the lack of effective treatment to prevent the development of antibody-mediated lesions deepens the need for clinicians to focus on primary prevention of de novo humoral allosensitization. Among the factors associated with the risk of developing de novo donor-specific antibodies, therapeutic immunosuppression is the most obvious parameter in which improvement is possible. Beyond compliance and the overall depth of immunosuppression, it is likely that the nature of the drugs is also crucial. Here, we provide an overview of the molecular effect of the various immunosuppressive drugs on B cell biology. Clinical data related to the effect of these drugs on de novo humoral allosensitization are also examined, providing a platform from which clinicians can optimize immunosuppression for prevention of de novo donor-specific antibody generation at the individual level.

Belatacept prophylaxis against organ rejection in adult kidney-transplant recipients

End-stage renal disease is a major health problem worldwide, with kidney transplantation being the treatment of choice. Calcineurin inhibitors are still the cornerstone of immunosuppressive therapy. However, they have well-known nephrotoxic affects and increase the risk of cardiovascular disease and cancer. In contrast, belatacept is a biological immunosuppressive agent that inhibits the T-cell co-stimulation. It is approved by the US Food and Drug Administration and the European Medicine Agency for use in adult kidney-transplant recipients to prevent acute rejection. Developmental studies show that belatacept is as efficient as calcineurin inhibitors at preventing acute rejection. In addition, kidney function is better and cardiovascular risk factors are reduced in patients given belatacept. Herein, the authors review the published evidence concerning the efficacy and safety of belatacept and discuss its potential specific indications.