Monoclonal anti-interleukin-6 receptor antibody attenuates donor-specific antibody responses in a mouse model of allosensitization

Innate immune modulation in transplantation: mechanisms, challenges, and opportunities

Organ transplantation is characterized by a sequence of steps that involve operative trauma, organ preservation, and ischemia-reperfusion injury in the transplant recipient. During this process, the release of damage-associated molecular patterns (DAMPs) promotes the activation of innate immune cells via engagement of the toll-like receptor (TLR) system, the complement system, and coagulation cascade. Different classes of effector responses are then carried out by specialized populations of macrophages, dendritic cells, and T and B lymphocytes; these play a central role in the orchestration and regulation of the inflammatory response and modulation of the ensuing adaptive immune response to transplant allografts. Organ function and rejection of human allografts have traditionally been studied through the lens of adaptive immunity; however, an increasing body of work has provided a more comprehensive picture of the pivotal role of innate regulation of adaptive immune responses in transplant and the potential therapeutic implications. Herein we review literature that examines the repercussions of inflammatory injury to transplantable organs. We highlight novel concepts in the pathophysiology and mechanisms involved in innate control of adaptive immunity and rejection. Furthermore, we discuss existing evidence on novel therapies aimed at innate immunomodulation and how this could be harnessed in the transplant setting.

Tocilizumab for the treatment of chronic antibody mediated rejection in kidney transplant recipients

BACKGROUND

Chronic active antibody-mediated rejection (CAAMR) constitutes a dominant form of late allograft failure. Several treatment strategies directed at CAAMR have been attempted but proven ineffective at delaying kidney function decline or reducing donor-specific antibodies (DSA). We describe our single-center experience using tocilizumab in patients with CAAMR.

METHODS

This is a retrospective analysis using electronic medical records. 38 kidney transplant recipients at Columbia University Irving Medical Center who had been prescribed tocilizumab and followed for at least 3 months between August 2013 through December 2019 were included.

RESULTS

Tocilizumab use was associated with a decrease in the rate of estimated glomerular filtration rate (eGFR) decline in the 6 months following treatment initiation as compared to the 3 months before tocilizumab was initiated (difference between slopes before and after initiation of treatment = 2.6 mL/min/1.73 m² (SE = .8, p = .002) per month for up to 6 months following Tocilizumab initiation). Allograft biopsies showed significant improvement in interstitial inflammation scores (score 1(0,1) to 0 (0,1), p = .03) while other histologic scores remained stable. There was no significant change in proteinuria or DSA titers post-treatment with tocilizumab.

CONCLUSIONS

Treatment of CAAMR with tocilizumab was associated with a decrease in the rate of eGFR decline and a reduction in interstitial inflammation scores in patients with CAAMR.

Clazakizumab for the treatment of chronic active antibody-mediated rejection (AMR) in kidney transplant recipients: Phase 3 IMAGINE study rationale and design

BACKGROUND

Chronic active antibody-mediated rejection (AMR) is a major cause of graft loss with no approved drugs for its treatment. Currently, off-label regimens are used, reflecting the high unmet need for effective therapies based on well-controlled trials. Clazakizumab is a high-affinity, humanized monoclonal antibody that binds interleukin-6 and decreases donor-specific antibody (DSA) production and inflammation. Phase 2 pilot studies of clazakizumab in kidney transplant recipients with chronic active AMR suggest modulation of DSA, stabilization of glomerular filtration rate (GFR), and a manageable safety profile. We report the design of the Phase 3 IMAGINE study (NCT03744910) to evaluate the safety and efficacy of clazakizumab for the treatment of chronic active AMR.

METHODS

IMAGINE is a multicenter, double-blind trial of approximately 350 kidney transplant recipients with chronic active AMR (Banff chronic glomerulopathy [cg] >0 with concurrent positive human leukocyte antigen DSA) randomized 1:1 to receive clazakizumab or placebo (12.5 mg subcutaneous once every 4 weeks). The event-driven trial design will follow patients until 221 occurrences of all-cause graft loss are observed, defined as return to dialysis, graft nephrectomy, re-transplantation, estimated GFR (eGFR) <15 mL/min/1.73m², or death from any cause. A surrogate for graft loss (eGFR slope) will be assessed at 1 year based on prior modeling validation. Secondary endpoints will include measures of pharmacokinetics/pharmacodynamics. Recruitment is ongoing across North America, Europe, Asia, and Australia.

DISCUSSION

IMAGINE represents the first Phase 3 clinical trial investigating the safety and efficacy of clazakizumab in kidney transplant recipients with chronic active AMR, and the largest placebo-controlled trial in this patient population. This trial includes prognostic biomarker enrichment and uniquely utilizes the eGFR slope at 1 year as a surrogate endpoint for graft loss, which may accelerate the approval of a novel therapy for patients at risk of graft loss. The findings of this study will be fundamental in helping to address the unmet need for novel therapies for chronic active AMR.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03744910 . Registered on November 19, 2018.

Rationale for the IMAGINE study for chronic active antibody-mediated rejection (caAMR) in kidney transplantation

Chronic active antibody-mediated rejection (caAMR) in kidney transplantation is a major cause of late graft loss and despite all efforts to date, there is no proven effective therapy. Indeed, the Transplant Society (TTS) consensus opinion called for a conservative approach optimizing baseline immunosuppression and supportive care focused on blood pressure, blood glucose, and lipid control. This review provides the rationale and early evidence in kidney transplant recipients with caAMR that supported the design of the IMAGINE study whose goal is to evaluate the potential impact of targeting the IL6/IL6R pathway.

[Improving access to kidney transplantation for highly sensitized patients: What place for IL-6 pathway blockade in desensitization protocols?]

BACKGROUND

Desensitization allows kidney transplantation for HLA highly sensitized subjects. Due to the central role of IL-6 in immunological response, tocilizumab (monoclonal antibody directed against IL-6 receptor) could probably improve desensitization efficacy.

METHODS

Pubmed systematic review by using MeSH terms: tocilizumab, clazakizumab, interleukin-6 blockade, kidney transplantation, kidney graft and desensitization.

STUDIES

IL-6 plays a role in humoral response (plasmocyte differentiation induced by lymphocyte T, IL-21 secretion) as well as in cellular response (differentiation of LT Th17 rather than T reg). In desensitization field, tocilizumab was first studied as second-line treatment after failing of standard-of-care (apheresis, rituximab ± IgIV). Recent study showed that tocilizumab as a monotherapy attenuated anti-HLA antibodies rates but was not sufficient to allow transplantation. However, lymphocyte immunophenotyping showed that tocilizumab hindered B cells maturation. Thereby, tocilizumab could improve long-term efficacy of desensitization, by limiting the anti-HLA rebound and so avoiding antibody-mediated rejection. This hypothesis is supported by a recent study which used clazakizumab (monoclonal antibody directed against IL-6) in association with standard-of-care. In that study, clazakizumab was continued after kidney transplantation. Results were encouraging because 9/10 patients were transplanted and there was no donor-specific antibody at 6 months post-transplantation.

CONCLUSION

IL-6 pathway blockade as a monotherapy fails to desensitize HLA highly sensitized kidney transplant candidates. In association with standard-of-care, it does not seem to significatively improve kidney allograft access (short-term efficacy) vs. standard-of-care only. However, it could improve long-term prognosis of HLA incompatible transplantation by orienting the response towards a tolerogenic profile, by hindering B-cell maturation and, thereby, avoiding DSA rebounds after transplantation. This hypothesis needs to be proven by further studies.

Investigational drugs for the treatment of kidney transplant rejection

INTRODUCTION

Kidney transplant rejection remains an important clinical problem despite the development of effective immunosuppressive drug combination therapy. Two major types of rejection are recognized, namely T-cell-mediated rejection (TCMR) and antibody-mediated rejection (ABMR), which have a different pathophysiology and are treated differently. Unfortunately, long-term outcomes of both TCMR and ABMR remain unsatisfactory despite current therapy. Hence, alternative therapeutic drugs are urgently needed.

AREAS COVERED

This review covers novel and investigational drugs for the pharmacological treatment of kidney transplant rejection. Potential therapeutic strategies and future directions are discussed.

EXPERT OPINION

The development of alternative pharmacologic treatment of rejection has focused mostly on ABMR, since this is the leading cause of kidney allograft loss and currently lacks an effective, evidence-based therapy. At present, there is insufficient high-quality evidence for any of the covered investigational drugs to support their use in ABMR. However, with the emergence of targeted therapies, this potential arises for individualized treatment strategies. In order to generate more high-quality evidence for such strategies and overcome the obstacles of classic, randomized, controlled trials, we advocate the implementation of adaptive trial designs and surrogate clinical endpoints. We believe such adaptive trial designs could help to understand the risks and benefits of promising drugs such as tocilizumab, clazakizumab, belimumab, and imlifidase.

Treatment of high fat diet-induced obese pregnant mice with IL-6 receptor antibody does not ameliorate placental function and fetal growth restriction

PROBLEM

Pregnancy complications and adverse birth outcomes are in part fueled by the rise in obesity and its associated co-morbidities in western societies. Fetal healthy development and placental function are disturbed by an obese, inflammatory environment associated with cytokines, such as interleukin-6, causing inadequate supply of nutrients to the fetus and perinatal programming with severe health consequences.

METHOD OF STUDY

Mice received high fat diet (HFD) before and during gestation to induce obesity. We performed an IL-6 receptor antibody (MR16-1) treatment in pregnant obese mice at embryonic days E0.5, E7.5 and E14.5 to investigate whether this could ameliorate HFD-induced and obesity-associated placental dysfunction, evaluated by stereology and western blot, and improve offspring outcome at E15.5 in obese dams.

RESULTS

We observed fewer fetuses below the 10th percentile and placental vascularization was less aggravated following MR16-1 treatment of obese dams, showing slight improvements in labyrinth zone (Lz) vascularization. However, placental dysfunction and fetal growth restriction were still apparent in MR16-1 dams compared to lean control dams. Molecular analysis showed significantly elevated IL-6 level in placentas of MR16-1 treated dams.

CONCLUSION

Treatment with MR16-1 blocks IL-6 signaling in the placenta, but has only limited effects on preventing HFD-associated placental dysfunction and offspring outcomes in mice, suggesting further mechanisms in the deterioration of placental vascularization and fetal nutrient supply as a consequence of maternal obesity.

Tocilizumab in the Treatment of Chronic Antibody-Mediated Rejection Post Kidney Transplantation: Clinical and Histological Monitoring

Introduction: Chronic antibody-mediated rejection (cAMR) has very few effective therapeutic options. Interleukin-6 is an attractive target because it is involved in inflammation and humoral immunity. Therefore, the use of tocilizumab (anti-IL6 receptor, TCZ) is a potential valuable therapeutic option to treat cABMR in kidney-transplant (KT) recipients. Materials and Methods: This single-center retrospective study included all KT recipients that received monthly TCZ infusions in the setting of cABMR, between August 2018 and July 2021. We assessed 12-month renal function and KT histology during follow-up. Results: Forty patients were included. At 12-months, eGFR was not significantly different, 41.6 ± 17 vs. 43 ± 17 mL/min/1.73 m² (p = 0.102) in patients with functional graft. Six patients (15%) lost their graft: their condition was clinically more severe at the time of first TCZ infusion. Histological follow-up showed no statistical difference in the scores of glomerulitis, peritubular capillaritis, and interstitial fibrosis/tubular atrophy (IFTA). Chronic glomerulopathy score however, increased significantly over time; conversely arteritis and inflammation in IFTA ares improved in follow-up biopsies. Conclusion: In our study, the addition of TCZ prevented clinical and histological worsening of cABMR in KT recipients, except for more severely ill patients. Randomized studies are needed to clarify the risk/benefit of TCZ in cABMR.

Immune responses following tocilizumab therapy to desensitize HLA-sensitized kidney transplant candidates

Kidney transplant candidates (KTCs) who are HLA highly sensitized (calculated panel-reactive alloantibodies >95%) have poor access to deceased kidney transplantation. In this single-center prospective study, 13 highly sensitized desensitization-naïve KTCs received IV tocilizumab (8 mg/kg) every 4 weeks. We evaluated tolerability as well as immune responses, that is, T cell, B cell, T follicular helper (Tfh) subsets, blood cytokines (IL-6, soluble IL-6 receptor-sIL-6R-, IL-21), blood chemokines (CXCL10, CXCL13), and anti-HLA alloantibodies. Tocilizumab treatment was well-tolerated except in one patient who presented spondylodiscitis, raising a note of caution. Regarding immune parameters, there were no significant changes of percentages of lymphocyte subsets, that is, CD3⁺ , CD3⁺ /CD4⁺ , CD3⁺ /CD8⁺ T cells, and NK cells. This was also the case for Tfh cell subsets, B cells, mature B cells, plasma cells, pre-germinal center (GC) B cells, and post-GC B cells, whereas we observed a significant increase in naïve B cells (p = .02) and a significant decrease in plasmablasts (p = .046) over the tocilizumab treatment course. CXCL10, CXCL13, IL-21, total IgG, IgA, and IgM levels did not significantly change during tocilizumab therapy; conversely, there was a significant increase in IL-6 levels (p = .03) and a huge increase in sIL-6R (p = .00004). There was a marginal effect on anti-HLA alloantibodies (class I and class II). To conclude in highly sensitized KTCs, tocilizumab as a monotherapy limited B cell maturation; however, it had almost no effect on anti-HLA alloantibodies.

Blockade of IL-6/IL-6R Signaling Attenuates Acute Antibody-Mediated Rejection in a Mouse Cardiac Transplantation Model

Acute antibody-mediated rejection (AAMR) is an important cause of cardiac allograft dysfunction, and more effective strategies need to be explored to improve allograft prognosis. Interleukin (IL)-6/IL-6R signaling plays a key role in the activation of immune cells including B cells, T cells and macrophages, which participate in the progression of AAMR. In this study, we investigated the effect of IL-6/IL-6R signaling blockade on the prevention of AAMR in a mouse model. We established a mouse model of AAMR for cardiac transplantation via presensitization of skin grafts and addition of cyclosporin A, and sequentially analyzed its features. Tocilizumab, anti-IL-6R antibody, and recipient IL-6 knockout were used to block IL-6/IL-6R signaling. We demonstrated that blockade of IL-6/IL-6R signaling significantly attenuated allograft injury and improved survival. Further mechanistic research revealed that signaling blockade decreased B cells in circulation, spleens, and allografts, thus inhibiting donor-specific antibody production and complement activation. Moreover, macrophage, T cell, and pro-inflammatory cytokine infiltration in allografts was also reduced. Collectively, we provided a highly practical mouse model of AAMR and demonstrated that blockade of IL-6/IL-6R signaling markedly alleviated AAMR, which is expected to provide a superior option for the treatment of AAMR in clinic.

Tocilizumab and Desensitization in Kidney Transplant Candidates: Personal Experience and Literature Review

Desensitization (DES) allows kidney transplantation for highly HLA-sensitized subjects. Due to the central role of IL-6 in the immunological response, tocilizumab may improve DES efficacy. Thus, we conducted a PubMed systematic review using the MeSH terms tocilizumab, interleukin-6, kidney transplantation, and desensitization. Tocilizumab (TCZ) was first studied for DES as the second-line treatment after failure of a standard DES protocol (SP) (apheresis, rituximab +/- IVIg). Although TCZ (as a monotherapy) attenuated anti-HLA antibody rates, it did not permit transplantation. However, lymphocyte immuno-phenotyping has shown that TCZ hinders B-cell maturation and thus could improve the long-term efficacy of DES by limiting anti-HLA rebound and so avoid antibody-mediated rejection. This hypothesis is supported by a recent study where clazakizumab, a monoclonal antibody directed against IL-6, was continued after kidney transplantation in association with an SP. Nine out of ten patients were then eligible for transplantation, and there were no donor-specific antibodies at 6 months post-transplantation. In association with an SP, tocilizumab does not seem to significantly improve kidney-allograft access (short-term efficacy) vs. a SP only. However, it could improve the long-term prognosis of HLA-incompatible transplantation by hindering B-cell maturation and, thereby, avoiding donor-specific antibody rebounds post-transplantation.

Differential cytokine and chemokine expression during rejection and infection following intestinal transplantation

BACKGROUND/OBJECTIVES

Rejection and infectious enteritis in intestinal transplant (ITx) patients present with virtually identical symptoms. Currently, the gold standard for differentiating between these two conditions is endoscopy, which is invasive and costly. Our primary aim was to identify differences in peripheral blood cytokines during episodes of acute cellular rejection (ACR) and infectious enteritis in patients with intestinal transplants.

METHODS

This was a prospective, cross-sectional study involving ITx patients transplanted between 2000 and 2016. We studied 63 blood samples collected from 29 ITx patients during periods of normal (n = 24) and abnormal (n = 17) allograft function. PBMCs from whole blood samples were cultured under unstimulated or stimulated conditions with phytohemagglutinin (PHA). The supernatant from these cultures were collected to measure cytokine and chemokine levels using a 38-plex luminex panel.

RESULTS

Our study found that cytokines and chemokines are differentially expressed in normal, ACR, and infectious enteritis samples under unstimulated conditions based on heatmap analysis. Although each cohort displayed distinctive signatures, only MDC (p = 0.037) was found to be significantly different between ACR and infectious enteritis. Upon stimulation of PBMCs, patients with ACR demonstrated increased immune reactivity compared to infectious enteritis; though this did not reach statistical significance.

CONCLUSIONS

To our knowledge, this is the first comprehensive study comparing cytokine expression during acute rejection and infectious enteritis in intestinal transplant recipients. Our results suggest that cytokines have the potential to be used as clinical markers for risk stratification and/or diagnosis of ACR and infectious enteritis.

IL-6 Directed Therapy in Transplantation

Purpose of Review

IL-6 is a pleiotropic, pro-inflammatory cytokine that plays an integral role in the development of acute and chronic rejection after solid organ transplantation. This article reviews the experimental evidence and current clinical application of IL-6/IL-6 receptor (IL-6R) signaling inhibition for the prevention and treatment of allograft injury.

Recent Findings

There exists a robust body of evidence linking IL-6 to allograft injury mediated by acute inflammation, adaptive cellular/humoral responses, innate immunity, and fibrosis. IL-6 promotes the acute phase reaction, induces B cell maturation/antibody formation, directs cytotoxic T-cell differentiation, and inhibits regulatory T-cell development. Importantly, blockade of the IL-6/IL-6R signaling pathway has been shown to mitigate its harmful effects in experimental studies, particularly in models of kidney and heart transplant rejection. Currently, available agents for IL-6 signaling inhibition include monoclonal antibodies against IL-6 or IL-6R and janus kinase inhibitors. Recent clinical trials have investigated the use of tocilizumab, an anti-IL-6R mAb, for desensitization and treatment of antibody-mediated rejection (AMR) in kidney transplant recipients, with promising initial results. Further studies are underway investigating the use of alternative agents including clazakizumab, an anti-IL-6 mAb, and application of IL-6 signaling blockade to clinical cardiac transplantation.

Summary

IL-6/IL-6R signaling inhibition provides a novel therapeutic option for the prevention and treatment of allograft injury. To date, evidence from clinical trials supports the use of IL-6 blockade for desensitization and treatment of AMR in kidney transplant recipients. Ongoing and future clinical trials will further elucidate the role of IL-6 signaling inhibition in other types of solid organ transplantation.

Marginal Impact of Tocilizumab Monotherapy on Anti-HLA Alloantibodies in Highly Sensitized Kidney Transplant Candidates

Background.

Highly HLA–sensitized kidney transplant candidates are difficult to desensitize, which reduces their chances of receiving a transplant.

Methods.

We administered tocilizumab as a monotherapy (8 mg/kg once a mo) to 14 highly sensitized kidney transplant candidates. Highest mean fluorescence intensities of anti-HLA antibodies obtained before and after tocilizumab administration were compared from raw and diluted sera.

Results.

The administration of tocilizumab significantly reduced dominant anti-HLA antibody sensitization. However, this decrease in mean fluorescence intensities was minor compared with the initial values.

Conclusions.

Tocilizumab as a monotherapy was not sufficient to allow highly sensitized kidney–transplant candidates to undergo transplantation and, therefore, was not an effective desensitization method.

DNA-PKcs Inhibition Extends Allogeneic Skin Graft Survival

BACKGROUND

Organ transplantation is life-saving and continued investigations into immunologic mechanisms that drive organ rejection are needed to improve immunosuppression therapies and prevent graft failure. DNA-dependent protein kinase catalytic subunit, DNA dependent-protein kinase catalytic subunit (DNA-PKcs), is a critical component of both the cellular and humoral immune responses. In this study, we investigate the contribution of DNA-PKcs to allogeneic skin graft rejection to potentially highlight a novel strategy for inhibiting transplant rejection.

METHODS

Fully MHC mismatched murine allogeneic skin graft studies were performed by transplanting skin from BalbC mice to C57bl6 mice and treating with either vehicle or the DNA-PKcs inhibitor NU7441. Graft rejection, cytokine production, immune cell infiltration, and donor-specific antibody formation were analyzed.

RESULTS

DNA-PKcs inhibition significantly reduced necrosis and extended graft survival compared with controls (mean survival 14 d versus 9 d, respectively). Inhibition reduced the production of the cytokines interleukin (IL)-2, IL-4, IL-6, IL-10, TNF-α, and IFN-γ and the infiltration of CD3+ lymphocytes into grafts. Furthermore, DNA-PKcs inhibition reduced the number of CD19+ B cells and CD19+ CD138+ plasma cells coinciding with a significant reduction in donor-specific antibodies. At a molecular level, we determined that the immunosuppressive effects of DNA-PKcs inhibition were mediated, in part, via inhibition of nuclear factor kappa-light-chain-enhancer of activated B cells signaling through reduced expression of the p65 subunit.

CONCLUSIONS

Our data confirm that DNA-PKcs contributes to allogeneic graft rejection and highlight a novel immunologic function for DNA-PKcs in the regulation of nuclear factor kappa-light-chain-enhancer of activated B cells and concomitant cytokine production.

BAFF Inhibition Effectively Suppresses the Development of Anti-HLA.A2 Antibody in the Highly Sensitized Mouse Model

B cell activating factor (BAFF) is a cytokine that plays a role in the survival, proliferation and differentiation of B cells. We proposed to observe the effects of BAFF inhibition on the humoral immune responses of an allosensitized mouse model 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 were treated with anti-BAFF monoclonal antibody (mAb) (named Sandy-2) or control IgG1 antibody. HLA.A2-specific IgG was reduced in BAFF-inhibited mice compared to the control group (Δ-13.62 vs. Δ27.07, p < 0.05). BAFF inhibition also resulted in increased pre-pro and immature B cell proportions and decreased mature B cells in the bone marrow (p < 0.05 vs. control). In the spleen, an increase in transitional B cells was observed with a significant decrease in marginal and follicular B cells (p < 0.05 vs. control). There was no significant difference in the proportions of long-lived plasma and memory B cells. Microarray analysis showed that 19 gene probes were significantly up- (>2-fold, p < 0.05) or down-regulated (≤2-fold, p < 0.05) in the BAFF-inhibited group. BAFF inhibition successfully reduced alloimmune responses through the reduction in alloantibody production and suppression of B cell differentiation and maturation. Our data suggest that BAFF suppression may serve as a useful target in desensitization therapy.

Orosomucoid 1 is involved in the development of chronic allograft rejection after kidney transplantation

Chronic allograft rejection is the most common cause of long-term allograft failure. One reason is that current diagnostics and therapeutics for chronic allograft rejection are very limited. We here show that enhanced NFκB signaling in kidney grafts contributes to chronic active antibody-mediated rejection (CAAMR), which is a major pathology of chronic kidney allograft rejections. Moreover, we found that urinary orosomucoid 1 (ORM1) is a candidate marker molecule and therapeutic target for CAAMR. Indeed, urinary ORM1 concentration was significantly higher in kidney transplant recipients pathologically diagnosed with CAAMR than in kidney transplant recipients with normal histology, calcineurin inhibitor toxicity, or interstitial fibrosis and tubular atrophy. Additionally, we found that kidney biopsy samples with CAAMR expressed more ORM1 and had higher NFκB and STAT3 activation in tubular cells than samples from non-CAAMR samples. Consistently, ORM1 production was induced after cytokine-mediated NFκB and STAT3 activation in primary kidney tubular cells. The loss- and gain-of-function of ORM1 suppressed and promoted NFκB activation, respectively. Finally, ORM1-enhanced NFκB-mediated inflammation development in vivo. These results suggest that an enhanced NFκB-dependent pathway following NFκB and STAT3 activation in the grafts is involved in the development of chronic allograft rejection after kidney transplantation and that ORM1 is a non-invasive candidate biomarker and possible therapeutic target for chronic kidney allograft rejection.

Impact of Tocilizumab (Anti-IL-6R) Treatment on Immunoglobulins and Anti-HLA Antibodies in Kidney Transplant Patients With Chronic Antibody-mediated Rejection

BACKGROUND

Chronic antibody-mediated rejection (cAMR) results in the majority of renal allograft losses. Currently, there are no approved therapies. We recently reported on clinical use of tocilizumab (TCZ) for treatment of cAMR in HLA-sensitized kidney transplant patients. IgG1 and IgG3 subclasses of IgG are potent effectors of complement- and antibody-dependent cellular cytotoxicity, which are critical mediators of AMR. Here, we examined the impact of TCZ treatment for cAMR on total IgG, IgG1-4 subclasses, and anti-HLA-IgG (total and subclasses).

METHODS

Archived plasma obtained pre- and post-TCZ treatment (8 mg/kg, 6×, monthly) from 12 cAMR patients who failed standard of care treatment with intravenous immune globulin + rituximab with or without plasma exchange were tested for total IgG and IgG1-4 by ELISA, anti-HLA-total IgG, IgG3 and IgG4, and donor-specific antibody by Luminex assay. Archived plasma from 14 cAMR patients treated with the standard of care were included as controls.

RESULTS

Total IgG and IgG1-3 were significantly reduced post-TCZ, whereas no reduction was seen post-treatment in the control group. Of 11 patients, 8 (73%) showed reduction of anti-HLA-total IgG and IgG3 post-TCZ, but this was not statistically significant.

CONCLUSIONS

TCZ reduced total IgG and IgG1-3 and anti-HLA-total IgG and IgG3 levels, suggesting that TCZ suppresses Ig production in B cells nonspecifically, likely through inhibition of interleukin 6-mediated signaling to B cells and plasma cells. This may be a contributing factor for the beneficial effect of TCZ on cAMR observed in this patient population.

Roles of BATF/JUN/IRF4 complex in tacrolimus mediated immunosuppression on Tfh cells in acute rejection after liver transplantation

Rejection injury is a serious complication after liver transplantation (LTx). Tacrolimus (Tac) is a key immunosuppressive agent in the prevention of liver rejection after transplantation. The basic leucine zipper ATF-like transcription factor (BATF)/JUN/interferon regulatory factor 4 (IRF4) complex serves critical functions in the immune response. This study aimed to explore the role of the BATF/JUN/IRF4 complex in rejection after LTx by treatment with Tac. Herein, DA and Lewis (LEW) rats were used to construct the LTx animal model. The recipient LEW rats were treated with Tac or saline, subcutaneously. Splenic mononuclear cells were treated with Tac at 1 and 10 nM after stimulation with interleukin-6 (IL-6), and the expression of factors associated with the nuclear factor of activated T cells (NFAT)-BATF/JUN/IRF4 and IL-21 were detected. The results demonstrated that Tac prolonged the allografts survival and attenuated inflammation injury, and decreased the percentage frequencies of T follicular helper (Tfh) cells in peripheral blood mononuclear cells and inhibited B-cell lymphoma 6 (Bcl-6) and IL-6 expression in Tfh cells. In addition, Tac inhibited the expression of the BATF/JUN/IRF4 complex, Bcl-6 and IL-21 NFATc1 and NFATc2 were inhibited by Tac, and interacted with the promoter of BATF and IRF4. In conclusion, the attenuation of rejection injury may be dependent on the NFAT-BATF/JUN/IRF4-IL-21 axis, and the BATF/JUN/IRF4 complex participates in the inhibition of IL-21-producing Tfh cells after treatment with Tac. These findings suggest that the BATF/JUN/IRF4 complex-IL-21 axis may be used as a potential target for attenuating rejection injury after LTx.

What have we learned about how to prevent and treat antibody-mediated rejection in kidney transplantation?

Antibody-mediated rejection (ABMR) in kidney transplantation is a major cause of late graft loss, and despite all efforts to date the "standard of care" remains plasmapheresis, IVIg, and steroids, which itself is based on low quality evidence. This review focuses on the risk factors leading to memory and de novo donor-specific antibody (DSA)-associated ABMR, the optimal prevention strategies for ABMR, and advances in  adjunctive and emerging therapies for ABMR. Because new agents require regulatory approval via a Phase 3 randomized control trial (RCT), an overview of progress in innovative trial design for ABMR is provided. Finally, based on the insights gained in the biology of ABMR, current knowledge gaps are identified for future research that could significantly affect our understanding of how to optimally treat ABMR.

T Follicular Helper Cells As a New Target for Immunosuppressive Therapies

Over the past decade, antibody-mediated (humoral) rejection has been recognized as a common cause of graft dysfunction after organ transplantation and an important determinant for graft loss. In humoral alloimmunity, T follicular helper (Tfh) cells play a crucial role, because they help naïve B cells to differentiate into memory B cells and alloantibody-producing plasma cells within germinal centers. In this way, they contribute to the induction of donor-specific antibodies, which are responsible for the humoral immune response to the allograft. In this article, we provide an overview of the current knowledge on the effects of immunosuppressive therapies on Tfh cell development and function, and discuss possible new approaches to influence the activity of Tfh cells. In addition, we discuss the potential use of Tfh cells as a pharmacodynamic biomarker to improve alloimmune-risk stratification and tailoring of immunosuppression to individualize therapy after transplantation.

Interleukin-6, A Cytokine Critical to Mediation of Inflammation, Autoimmunity and Allograft Rejection: Therapeutic Implications of IL-6 Receptor Blockade

The success of kidney transplants is limited by the lack of robust improvements in long-term survival. It is now recognized that alloimmune responses are responsible for the majority of allograft failures. Development of novel therapies to decrease allosensitization is critical. The lack of new drug development in kidney transplantation necessitated repurposing drugs initially developed in oncology and autoimmunity. Among these is tocilizumab (anti-IL-6 receptor [IL-6R]) which holds promise for modulating multiple immune pathways responsible for allograft injury and loss. Interleukin-6 is a cytokine critical to proinflammatory and immune regulatory cascades. Emerging data have identified important roles for IL-6 in innate immune responses and adaptive immunity. Excessive IL-6 production is associated with activation of T-helper 17 cell and inhibition of regulatory T cell with attendant inflammation. Plasmablast production of IL-6 is critical for initiation of T follicular helper cells and production of high-affinity IgG. Tocilizumab is the first-in-class drug developed to treat diseases mediated by IL-6. Data are emerging from animal and human studies indicating a critical role for IL-6 in mediation of cell-mediated rejection, antibody-mediated rejection, and chronic allograft vasculopathy. This suggests that anti-IL-6/IL-6R blockade could be effective in modifying T- and B-cell responses to allografts. Initial data from our group suggest anti-IL-6R therapy is of value in desensitization and prevention and treatment of antibody-mediated rejection. In addition, human trials have shown benefits in treatment of graft versus host disease in matched or mismatched stem cell transplants. Here, we explore the biology of IL-6/IL-6R interactions and the evidence for an important role of IL-6 in mediating allograft rejection.

IL-21 Receptor Antagonist Inhibits Differentiation of B Cells toward Plasmablasts upon Alloantigen Stimulation

Interaction between T follicular helper (Tfh) cells and B cells is complex and involves various pathways, including the production of IL-21 by the Tfh cells. Secretion of IL-21 results in B cell differentiation toward immunoglobulin-producing plasmablasts. In patients after kidney transplantation, the formation of alloantibodies produced by donor antigen-activated B cells are a major cause of organ failure. In this allogeneic response, the role of IL-21-producing Tfh cells that regulate B cell differentiation is unknown. Here, we tested, in an alloantigen-driven setting, whether Tfh cell help signals control B cell differentiation with its dependency on IL-21. Pre-transplantation patient PBMCs were sorted into pure CD4^posCXCR5^pos Tfh cells and CD19^posCD27^pos memory B cells and stimulated with donor antigen in the presence or absence of an IL-21 receptor (IL-21R) antagonist (αIL-21R). Donor antigen stimulation initiated expression of the activation markers inducible co-stimulator (ICOS) and programmed death 1 (PD-1) on Tfh cells and a shift toward a mixed Tfh2 and Tfh17 phenotype. The memory B cells underwent class switch recombination and differentiated toward IgM- and IgG-producing plasmablasts. In the presence of αIL-21R, a dose-dependent inhibition of STAT3 phosphorylation was measured in both T and B cells. Blockade of the IL-21R did not have an effect on PD-1 and ICOS expression on Tfh cells but significantly inhibited B cell differentiation. The proportion of plasmablasts decreased by 78% in the presence of αIL-21R. Moreover, secreted IgM and IgG2 levels were significantly lower in the presence of αIL-21R. In conclusion, our results demonstrate that IL-21 produced by alloantigen-activated Tfh cells controls B cell differentiation toward antibody producing plasmablasts. The IL-21R might, therefore, be a useful target in organ transplantation to prevent antigen-driven immune responses leading to graft failure.

Tocilizumab (Anti-IL-6R) Suppressed TNFα Production by Human Monocytes in an In Vitro Model of Anti-HLA Antibody-Induced Antibody-Dependent Cellular Cytotoxicity

Background

We previously demonstrated that natural killer (NK) cells activated via FcγRIIIa (CD16) interactions with anti-HLA antibodies binding to peripheral blood mononuclear cells (PBMCs) in the in vitro antibody-dependent cellular cytotoxicity (ADCC) assay produced IFNγ. Here we investigate if other CD16 bearing cells are responsive to alloantigen via alloantibody in the in vitro ADCC and if the ADCC-induced cytokine reactions and cytotoxicity can be modified by the anti-interleukin 6 receptor (IL-6R) monoclonal antibody, Tocilizumab (TCZ).

Methods

Whole blood from a normal individual was incubated overnight with irradiated allo-PBMCs pretreated with anti-HLA antibody positive (in vitro ADCC) or negative sera (mixed lymphocyte reaction [MLR]), with or without TCZ or control IgG. IFNγ+, TNFα+ or IL-6+ cell% in NK cells, monocytes and CD8+ T cells were enumerated by cytokine flow cytometry. ADCC using PBMCs (effector) and Farage B cells (FB, target) with anti-HLA antibody positive sera, with or without TCZ, was measured by flow cytometry.

Results

IFNγ+ and/or TNFα+ cell% in NK cells, monocytes and CD8+ T cells were elevated in the ADCC compared to the MLR condition. IL-6+ cells were significantly increased in ADCC versus MLR (10.2 ± 4.8% vs 2.7 ± 1.5%, P = 0.0003), but only in monocytes. TCZ treatment significantly reduced TNFα+ cell% in monocytes in ADCC, but had no effect on other cytokine+ cells. TCZ showed no effect on cytotoxicity in ADCC.

Conclusions

IFNγ, TNFα, and IL-6 production induced by HLA antibody-mediated CD16 bearing cell activation in NK cells, monocytes, and CD8+ T cells suggests a potential role for ADCC and these inflammatory cytokines in mediation of antibody-mediated rejection. TCZ suppressed TNFα production in monocytes in the ADCC condition, suggesting a role of IL-6/IL-6R pathway in monocytes activation. Inhibition of this pathway could reduce the inflammatory cascade induced by alloantibody, although the inhibitory effect on cytotoxicity is minimal.

Progress in Desensitization of the Highly HLA Sensitized Patient

The presence of HLA antibodies remains a significant and often impenetrable barrier to kidney transplantation, leading to increased morbidity and mortality for patients remaining on long-term dialysis. In recent years, a number of new approaches have been developed to overcome these barriers. Intravenous immunoglobulin (IVIG) remains the lynchpin of HLA desensitization therapy and has been shown in a prospective, randomized, placebo-controlled trial to improve transplantation rates. In addition, IVIG used in low doses with plasma exchange is a reliable protocol for desensitization. Another significant advancement was the addition of rituximab (anti-B-cell therapy) to IVIG and plasma exchange-based desensitization. This approach has significantly improved rates of transplantation and outcomes. There is limited experience with bortezomib (anti-plasma cell therapy) and eculizumab (complement inhibition) for desensitization. However, recent data from a completed trial of eculizumab failed to show a significant benefit for prevention of antibody-mediated rejection compared with standard therapy plus placebo, and bortezomib produced inconsistent results. There is a growing interest in developing new therapeutic agents for desensitization. Newer approaches that address antibody reduction with B-cell depletion are discussed.

Tocilizumab's effect on cognitive deficits induced by intracerebroventricular administration of streptozotocin in Alzheimer's model

Neuroinflammation plays pivotal roles in the pathogenesis of Alzheimer's disease (AD). IL-6 is pleiotropic cytokine which plays significant pathological role in inflammatory diseases and causes prolonged inflammation. Additionally, IL-6 activates microglia cells and enhances the accumulation of amyloid-β peptides. Moreover, IL-6 signal transduction is mediated by membrane-bound and soluble IL-6 receptors. Tocilizumab which is a humanized anti-human IL-6 receptor (IL-6R) monoclonal antibody binds to both of these receptors and inhibits IL-6 signaling by this route. The objective was to investigate tocilizumab's potential effects in the treatment of AD. Male Sprague-Dawley rats were divided into three groups: sham (control), streptozotocin (STZ), and tocilizumab-STZ. We used a single dose of intracerebroventricular (ICV) tocilizumab, beginning 1 h prior to injection of STZ for 3 weeks. The rats in STZ and tocilizumab-STZ groups were given ICV-STZ (3 mg/kg). Behavioral parameters were evaluated on days 17-20 and the rats were sacrificed on day-21 to examine histopathological changes. STZ injection caused significant decrease in the mean escape latency in passive avoidance and also declined the performance improvement in Morris water maze tests. Tocilizumab-STZ group significantly improved learning and spatial memory functions by increasing RLT in the passive avoidance and by shortening escape latency in reaching the platform in the Morris water maze. Histopathological changes were examined using hematoxylin and eosin and immunohistochemical (IHC) stainings. IHC analysis revealed that while protein expressions of amyloid-ß (3.5 ± 0.2) and IL-6 (2.9 ± 0.4) showed intense immune-positivity in STZ group, amyloid-ß (1.3 ± 0.1) and IL-6 (1.5 ± 0.2) immunoreactivities were substantially decreased in tocilizumab treatment group. We conclude that tocilizumab treatment attenuated significantly STZ-induced cognitive impairment and histopathological changes. Further studies would be desirable to investigate clinically relevant protective effects of tocilizumab in AD.

T follicular helper cells in the generation of alloantibody and graft rejection

PURPOSE OF REVIEW

T follicular helper (Tfh) cells are an increasingly relevant CD4 T cell subset responsible for the provision of help to B cells for the generation of an effective humoral immune response. Here we review recent studies that have provided critical insights into the mechanisms of Tfh cell differentiation and function, and introduce newly identified roles for Tfh cells in human disease.

RECENT FINDINGS

Novel molecular regulators of the Tfh cell differentiation program along with new found roles for the costimulatory and coinhibitory inducible T cell costimulator (ICOS), programmed death 1, and cytotoxic T lymphocyte antigen 4 pathways on Tfh cell function have been appreciated. Although circulating Tfh and Tfh-like subset signatures have been linked to numerous immune conditions, extrapolation of these findings to organ transplantation is just beginning.

SUMMARY

The combination of recent progress with regard to Tfh cell biology at the basic science and clinical levels is guiding the elucidation of the role of Tfh cells in the alloimmune response. Application of this knowledge toward the development of novel therapeutic strategies for use in transplantation is imminent.

Further evidence for sustained systemic inflammation in xenograft recipients (SIXR)

INTRODUCTION

In pig-to-baboon heart/artery patch transplantation models, adequate costimulation blockade prevents a T-cell response. After heart transplantation, coagulation dysfunction (thrombocytopenia, reduced fibrinogen, increased D-dimer) and inflammation (increased C-reactive protein [CRP]) develop. We evaluated whether coagulation dysfunction and/or inflammation can be detected following pig artery patch transplantation.

METHODS

Baboons received heart (n = 8) or artery patch (n = 16) transplants from genetically engineered pigs and a costimulation blockade-based regimen. Heart grafts functioned for 15-130 days. Artery recipients were euthanized after 28-84 days. Platelet counts, fibrinogen, D-dimer, and CRP were measured.

RESULTS

Thrombocytopenia and reduced fibrinogen developed only in recipients of hearts not expressing a coagulation-regulatory protein (n = 4), but not in other heart or patch recipients. However, in heart recipients (n = 8), there were sustained increases in D-dimer (<0.5 to 1.9 ug/ml [P < 0.01]) and CRP (0.26-2.2 mg/dl [P < 0.01]). In recipients of artery patches, there were also sustained increases in D-dimer (<0.5 to 1.4 ug/ml [P < 0.01]) and CRP (0.26 to 1.5 mg/dl [P < 0.001]). An IL-6R antagonist suppressed the increase in CRP, but not D-dimer.

CONCLUSION

The pig artery patch model has proved valuable for determining immunosuppressive regimens that prevent sensitization to pig antigens. This model also provides information on the sustained systemic inflammation in xenograft recipients (SIXR). An IL-6R antagonist may help suppress this response.

MCPIP1 Endoribonuclease Activity Negatively Regulates Interleukin-17-Mediated Signaling and Inflammation

Interleukin-17 (IL-17) induces pathology in autoimmunity and infections; therefore, constraint of this pathway is an essential component of its regulation. We demonstrate that the signaling intermediate MCPIP1 (also termed Regnase-1, encoded by Zc3h12a) is a feedback inhibitor of IL-17 receptor signal transduction. MCPIP1 knockdown enhanced IL-17-mediated signaling, requiring MCPIP1's endoribonuclease but not deubiquitinase domain. MCPIP1 haploinsufficient mice showed enhanced resistance to disseminated Candida albicans infection, which was reversed in an Il17ra(-/-) background. Conversely, IL-17-dependent pathology in Zc3h12a(+/-) mice was exacerbated in both EAE and pulmonary inflammation. MCPIP1 degraded Il6 mRNA directly but only modestly downregulated the IL-6 promoter. However, MCPIP1 strongly inhibited the Lcn2 promoter by regulating the mRNA stability of Nfkbiz, encoding the IκBζ transcription factor. Unexpectedly, MCPIP1 degraded Il17ra and Il17rc mRNA, independently of the 3' UTR. The cumulative impact of MCPIP1 on IL-6, IκBζ, and possibly IL-17R subunits results in a biologically relevant inhibition of IL-17 signaling.

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.