The therapeutic challenge of late antibody-mediated kidney allograft rejection

Abstract

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".

Keywords: antibody-mediated rejection; kidney transplantation; randomized controlled trial; rejection treatment.

Figure 1

Pathogenesis of antibody‐mediated rejection and potential therapeutic targets. A primary trigger of B cell alloimmunity may be the interaction of follicular T helper cells with naive B cells. This leads to B cell proliferation and differentiation, and the generation of B memory cells and antibody‐producing plasma cells. Binding of alloantibodies to the endothelium may trigger direct signalling, induce Fc gamma receptor (FcγR) dependent cellular effects, such as natural killer (NK) cell (and macrophage) activation, and trigger complement activation via the classical pathway (CP). Costimulation blockers, monoclonal antibodies (mAb) that target the interleukin‐6 (IL‐6)/IL‐6 receptor (IL‐6R) axis, or B lymphocyte stimulator may prevent proper B cell activation/differentiation and affect the generation or integrity of plasma cells. IL‐6 antagonists may also enhance the formation of regulatory T cells. Proteasome inhibitors and CD38 mAb may deplete alloantibody‐producing plasma cells, the latter affecting also NK cells and regulatory T cells. Complement inhibitors and membrane filtration target the C1 complex, a key component of the CP, or by interference with the terminal component C5 (eculizumab), the formation of the membrane attack complex and anaphylatoxin C5a. The mode of action of intravenous immunoglobulin is multifaceted and may include interference with B and T cell activation, antibody formation and recycling, as well as complement activation.