Importance of IL-6 inhibition in prevention and treatment of antibody-mediated rejection in kidney allografts

New Therapies for Highly Sensitized Patients on the Waiting List

Exposure to HLA alloantigens through pregnancy, blood products, and previous transplantations induce powerful immunologic responses that create an immunologic barrier to successful transplantation. This is commonly detected through screening for HLA antibodies using Luminex beads coated with HLA antigens at transplant evaluation. Currently accepted approaches to desensitization include plasmapheresis/low-dose or high-dose intravenous Ig plus anti-CD20. However, these approaches are often unsuccessful because of the inability to remove high titer circulating HLA antibodies and limit rebound responses by long-lived anti-HLA antibody secreting plasma cells (PCs) and memory B cells (B MEM ). This is especially significant for patients with a calculated panel reactive antibody of 99%-100%. Newer desensitization approaches, such as imlifidase (IgG endopeptidase), rapidly inactivate IgG molecules and create an antibody-free zone by cleaving IgG into F(ab'2) and Fc fragments, thus eliminating complement and cell-mediated injury to the graft. This represents an important advancement in desensitization. However, the efficacy of imlifidase is limited by pathogenic antibody rebound, increasing the potential for antibody-mediated rejection. Controlling antibody rebound requires new strategies that address the issues of antibody depletion and inhibition of B MEM and PC responses. This will likely require a combination of agents that effectively and rapidly deplete pathogenic antibodies and prevent immune cell activation pathways responsible for antibody rebound. Here, using anti-IL-6 receptor (tocilizumab) or anti-IL-6 (clazakizumab) could offer long-term control of B MEM and PC donor-specific HLA antibody responses. Agents aimed at eliminating long-lived PCs (anti-CD38 and anti-B-cell maturation antigen×CD3) are likely to benefit highly HLA sensitized patients. Complement inhibitors and novel agents aimed at inhibiting Fc neonatal receptor IgG recycling will be important in desensitization. Administering these agents alone or in combination will advance our ability to effectively desensitize patients and maintain durable suppression post-transplant. After many years of limited options, advanced therapeutics will likely improve efficacy of desensitization and improve access to kidney transplantation for highly HLA sensitized patients.

Chronic Active Antibody-mediated Rejection: Opportunity to Determine the Role of Interleukin-6 Blockade

Chronic active antibody-mediated rejection (caAMR) is arguably the most important cause of late kidney allograft failure. However, there are no US Food and Drug Administration (FDA)-approved treatments for acute or chronic AMR and there is no consensus on effective treatment. Many trials in transplantation have failed because of slow and/or inadequate enrollment, and no new agent has been approved by the FDA for transplantation in over a decade. Several lines of evidence suggest that interleukin-6 is an important driver of AMR, and clazakizumab, a humanized monoclonal antibody that neutralizes interleukin-6, has shown promising results in phase 2 studies. The IMAGINE trial (Interleukin-6 Blockade Modifying Antibody-mediated Graft Injury and Estimated Glomerular Filtration Rate Decline) (NCT03744910) is the first to be considered by the FDA using a reasonably likely surrogate endpoint (slope of estimated glomerular filtration rate decline >1 y) for accelerated approval and is the only ongoing clinical trial for the treatment of chronic rejection. This trial offers us the opportunity to advance the care for our patients in need, and this article is a call to action for all transplant providers caring for patients with caAMR.

Advances in desensitization for human leukocyte antigen incompatible kidney transplantation

PURPOSE OF REVIEW

Human leukocyte antigen (HLA) sensitization is a major barrier to kidney transplantation induced by exposure to alloantigens through pregnancy, blood product exposure and previous transplantations. Desensitization strategies are undertaken to improve the chances of finding compatible organ offers. Standard approaches to desensitization include the use of plasmapheresis/low dose intravenous immunoglobulin (IVIG) or high dose IVIG plus anti-CD20. However, current methods to reduce HLA antibodies are not always successful, especially in those with calculated panel reactive antibody 99-100%.

RECENT FINDINGS

Newer desensitization strategies such as imlifidase [immunoglobulin G (IgG) endopeptidase] rapidly inactivates IgG molecules and creates an "antibody-free zone", representing an important advancement in desensitization. However, pathogenic antibodies rebound, increasing allograft injury that is not addressed by imlifidase. Here, use of anti-IL-6R (tocilizumab) or anti-interleukin-6 (clazakizumab) could offer long-term control of B-memory and plasma cell DSA responses to limit graft injury. Agents aimed at long-lived plasma cells (anti-CD38 and anti-BCMAxCD3) could reduce or eliminate HLA-producing plasma cells from marrow niches. Other agents such as complement inhibitors and novel agents inhibiting the Fc neonatal receptor (FcRn) mediated IgG recycling will likely find important roles in desensitization.

SUMMARY

Use of these agents alone or in combination will likely improve the efficacy and durability of desensitization therapies, improving access to kidney transplantation for immunologically disadvantaged patients.

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.

Fine-tuning tumor- and allo-immunity: advances in the use of immune checkpoint inhibitors in kidney transplant recipients

Cancer is a common complication after kidney transplantation. Kidney transplant recipients (KTR) have a 2- to 4-fold higher risk of developing cancer compared to the general population and post-transplant malignancy is the third most common cause of death in KTR. Moreover, it is well known that certain cancer types are overrepresented after transplantation, especially non-melanoma skin cancer. Immune checkpoint inhibitors (ICI) have revolutionized the treatment of cancer, with remarkable survival benefit in a subgroup of patients. ICI are monoclonal antibodies that block the binding of specific co-inhibitory signaling molecules. Cytotoxic T lymphocyte-associated antigen-4 (CTLA-4), programmed cell death protein 1 (PD-1), and its ligand programmed cell death ligand 1 (PD-L1) are the main targets of ICI. Solid organ transplant recipients (SOTR) have been excluded from clinical trials owing to concerns about tumor response, allo-immunity, and risk of transplant rejection. Indeed, graft rejection has been estimated as high as 48% and represents an emerging problem. The underlying mechanisms of organ rejection in the context of treatment with ICI are poorly understood. The search for restricted antitumoral responses without graft rejection is of paramount importance. This review summarizes the current knowledge of the use of ICI in KTR, the potential mechanisms involved in kidney graft rejection during ICI treatment, potential biomarkers of rejection, and how to deal with rejection in clinical practice.

New treatment for antibody-mediated rejection: interleukin-6 inhibitors

Following kidney transplantation, antibody-mediated rejection (AMR) occurs when the antibodies of the immune system attack the transplanted organ, leading to damage of the kidney tissue. De novo human leukocyte antigen donor-specific antibodies (HLA-DSAs) play a key role in AMR. Current therapeutic approaches include intravenous immunoglobulin, anti-CD20 antibodies, and plasmapheresis. In cases resistant to treatment, proteasome inhibitors and C5 inhibitors may be employed. Nevertheless, a pressing need exists for new medications to improve transplant survival and reduce complications. In the context of AMR, interleukin (IL)-6 is instrumental in the development and maturation of B cells into plasma cells, which then produce HLA-DSAs targeting the allograft. IL-6 inhibitors are currently under investigation and show promise due to the essential role of IL-6 in the immune response; however, additional research is necessary.

Combined Use of Tocilizumab and Mesenchymal Stem Cells Attenuate the Development of an Anti-HLA-A2.1 Antibody in a Highly Sensitized Mouse Model

Sensitization to HLA can result in allograft loss for kidney transplantation (KT) patients. Therefore, it is required to develop an appropriate desensitization (DSZ) technique to remove HLA-donor-specific anti-HLA antibody (DSA) before KT. The aim of this research was to investigate whether combined use of the IL-6 receptor-blocking antibody, tocilizumab (TCZ), and bone-marrow-derived mesenchymal stem cells (BM-MSCs) could attenuate humoral immune responses in an allo-sensitized mouse model developed using HLA.A2 transgenic mice. Wild-type C57BL/6 mice were sensitized with skin allografts from C57BL/6-Tg (HLA-A2.1)1Enge/J mice and treated with TCZ, BM-MSC, or both TCZ and BM-MSC. We compared HLA.A2-specific IgG levels and subsets of T cells and B cells using flow cytometry among groups. HLA.A2-specific IgG level was decreased in all treated groups in comparison with that in the allo-sensitized control (Allo-CONT) group. Its decrease was the most significant in the TCZ + BM-MSC group. Regarding the B cell subset, combined use of TCZ and BM-MSC increased proportions of pre-pro B cells but decreased proportions of mature B cells in BM (p < 0.05 vs. control). In the spleen, an increase in transitional memory was observed with a significant decrease in marginal, follicular, and long-lived plasma B cells (p < 0.05 vs. control) in the TCZ + BM-MSC group. In T cell subsets, Th2 and Th17 cells were significantly decreased, but Treg cells were significantly increased in the TCZ+BM-MSC group compared to those in the Allo-CONT group in the spleen. Regarding RNA levels, IL-10 and Foxp3 showed increased expression, whereas IL-23 and IFN-γ showed decreased expression in the TCZ + BM-MSC group. In conclusion, combined use of TCZ and BM-MSC can inhibit B cell maturation and up-regulate Treg cells, finally resulting in the reduction of HLA.A2-specific IgG in a highly sensitized mouse model. This study suggests that the combined use of TCZ and BM-MSC can be proposed as a novel strategy in a desensitization protocol for highly sensitized patients.