A prospective randomized, controlled trial of eculizumab to prevent ischemia-reperfusion injury in pediatric kidney transplantation

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.

Prompt Thrombo-Inflammatory Response to Ischemia-Reperfusion Injury and Kidney Transplant Outcomes

Introduction

In kidney transplantation (KT), the role of the intravascular innate immune system (IIIS) in response to ischemia-reperfusion injury (IRI) is not well-understood. Here, we studied parallel changes in the generation of key activation products of the proteolytic cascade systems of the IIIS following living donor (LD) and deceased donor (DD) transplantation and evaluated potential associations with clinical outcomes.

Methods

In a cohort study, 63 patients undergoing LD (n = 26) and DD (n = 37) transplantation were prospectively included. Fifteen DD kidneys were preserved with hypothermic machine perfusion (HMP), and the remaining were cold stored. Activation products of the kallikrein-kinin, coagulation, and complement systems were measured in blood samples obtained systemically at baseline and locally from the transplant renal vein at 1, 10, and 30 minutes after reperfusion.

Results

DD kidneys exhibited a prompt and interlinked activation of all 3 cascade systems of IIIS postreperfusion, indicating a robust and local thrombo-inflammatory response to IRI. In this initial response, the complement activation product sC5b-9 exhibited a robust correlation with other IIIS activation markers and displayed a strong association with short-term and mid-term (24-month) graft dysfunction. In contrast, LD kidneys did not exhibit this thrombo-inflammatory response. The use of HMP was associated with reduced thromboinflammation and preserved mid-term kidney function.

Conclusion

Kidneys from DD are vulnerable to a prompt thrombo-inflammatory response to IRI, which adversely affects both short-term and long-term allograft function. Strategies aimed at minimizing graft immunogenicity prior to reperfusion are crucial to mitigate the intricate inflammatory response to IRI.

Complement System and the Kidney: Its Role in Renal Diseases, Kidney Transplantation and Renal Cell Carcinoma

The crosstalk among the complement system, immune cells, and mediators of inflammation provides an efficient mechanism to protect the organism against infections and support the repair of damaged tissues. Alterations in this complex machinery play a role in the pathogenesis of different diseases. Core complement proteins C3 and C5, their activation fragments, their receptors, and their regulators have been shown to be active intracellularly as the complosome. The kidney is particularly vulnerable to complement-induced damage, and emerging findings have revealed the role of complement system dysregulation in a wide range of kidney disorders, including glomerulopathies and ischemia-reperfusion injury during kidney transplantation. Different studies have shown that activation of the complement system is an important component of tumorigenesis and its elements have been proved to be present in the TME of various human malignancies. The role of the complement system in renal cell carcinoma (RCC) has been recently explored. Clear cell and papillary RCC upregulate most of the complement genes relative to normal kidney tissue. The aim of this narrative review is to provide novel insights into the role of complement in kidney disorders.

Advances in the study of B cells in renal ischemia-reperfusion injury

Renal ischemia-reperfusion injury (IRI) is a non-negligible clinical challenge for clinicians in surgeries such as renal transplantation. Functional loss of renal tubular epithelial cell (TEC) in IRI leads to the development of acute kidney injury, delayed graft function (DGF), and allograft rejection. The available evidence indicates that cellular oxidative stress, cell death, microvascular dysfunction, and immune response play an important role in the pathogenesis of IRI. A variety of immune cells, including macrophages and T cells, are actively involved in the progression of IRI in the immune response. The role of B cells in IRI has been relatively less studied, but there is a growing body of evidence for the involvement of B cells, which involve in the development of IRI through innate immune responses, adaptive immune responses, and negative immune regulation. Therefore, therapies targeting B cells may be a potential direction to mitigate IRI. In this review, we summarize the current state of research on the role of B cells in IRI, explore the potential effects of different B cell subsets in the pathogenesis of IRI, and discuss possible targets of B cells for therapeutic aim in renal IRI.

Targeting the Complement Pathway in Kidney Transplantation

The complement system is paramount in the clearance of pathogens and cell debris, yet is increasingly recognized as a key component in several pathways leading to allograft injury. There is thus a growing interest in new biomarkers to assess complement activation and guide tailored therapies after kidney transplantation (KTx). C5 blockade has revolutionized post-transplant management of atypical hemolytic uremic syndrome, a paradigm of complement-driven disease. Similarly, new drugs targeting the complement amplification loop hold much promise in the treatment and prevention of recurrence of C3 glomerulopathy. Although unduly activation of the complement pathway has been described after brain death and ischemia reperfusion, any clinical attempts to mitigate the ensuing renal insults have so far provided mixed results. However, the intervention timing, strategy, and type of complement blocker need to be optimized in these settings. Furthermore, the fast-moving field of ex vivo organ perfusion technology opens new avenues to deliver complement-targeted drugs to kidney allografts with limited iatrogenic risks. Complement plays also a key role in the pathogenesis of donor-specific ABO- and HLA-targeted alloantibodies. However, C5 blockade failed overall to improve outcomes in highly sensitized patients and prevent the progression to chronic antibody-mediated rejection (ABMR). Similarly, well-conducted studies with C1 inhibitors in sensitized recipients yielded disappointing results so far, in part, because of subtherapeutic dosage used in clinical studies. The emergence of new complement blockers raises hope to significantly reduce the negative effect of ischemia reperfusion, ABMR, and nephropathy recurrence on outcomes after KTx.

Novel insights in the clinical management of hyperimmune patients before and after transplantation

Despite improvements in anti-Human Leucocyte Antigens antibody detection, identification, and characterization offer a better in peri-operative management techniques, antibodies remain a serious cause of morbidity and mortality for patients both before and after organ transplantation. Hyperimmune patients are disadvantaged by having to wait longer to receive an organ from a suitably matched donor. They could benefit from desensitization protocols in both pre- and post-transplantation period. Clinical studies are underway to highlight which best desensitization strategies could be assure the best outcome in both heart and kidney transplantation. Although most clinical evidence about desensitization strategies by using anti-CD20 monoclonal antibodies, proteasome inhibitors, anti-CD38 monoclonal antibodies, interleukin-6 blockade, cysteine protease and complement inhibitors, comes from kidney transplantation studies, many of the debated novel concepts can be easily applied to desensitization also in heart transplantation. Here, we discuss the candidates and recipients' management by using most common standard of care and novel therapeutics, desensitization endpoints, and strategies for future studies.

Complement Inhibition in Kidney Transplantation: Where Are We Now?

Kidney transplantation is a life-saving strategy for patients with end-stage renal disease. Although progress has been made in the field of transplantation medicine in recent decades in terms of surgical techniques and immunosuppression, long-term organ survival remains a challenge. Also, for reasons of organ shortage, there is an unmet need for new therapeutic approaches to improve the long-term survival of transplants. There is increasing evidence that the complement system plays a crucial role in various pathological events after transplantation, including ischemia/reperfusion injury as well as rejection episodes. The complement system is part of the innate immune system and plays a crucial role in the defense against pathogens but is also involved in tissue homeostasis. However, the tightly regulated complement system can become dysregulated or activated by non-infectious stimuli, then targeting the organism's own cells and leading to inflammatory tissue damage that exacerbates injury. In this review, we will highlight the role of the complement system after transplantation and discuss ongoing and potential therapeutic approaches.

Complement-targeting therapeutics for ischemia-reperfusion injury in transplantation and the potential for ex vivo delivery

Organ shortages and an expanding waitlist have led to increased utilization of marginal organs. All donor organs are subject to varying degrees of IRI during the transplant process. Extended criteria organs, including those from older donors and organs donated after circulatory death are especially vulnerable to ischemia-reperfusion injury (IRI). Involvement of the complement cascade in mediating IRI has been studied extensively. Complement plays a vital role in the propagation of IRI and subsequent recruitment of the adaptive immune elements. Complement inhibition at various points of the pathway has been shown to mitigate IRI and minimize future immune-mediated injury in preclinical models. The recent introduction of ex vivo machine perfusion platforms provides an ideal window for therapeutic interventions. Here we review the role of complement in IRI by organ system and highlight potential therapeutic targets for intervention during ex vivo machine preservation of donor organs.

Complement-targeted therapies in kidney transplantation-insights from preclinical studies

Aberrant activation of the complement system contributes to solid-organ graft dysfunction and failure. In kidney transplantation, the complement system is implicated in the pathogenesis of antibody- and cell-mediated rejection, ischemia-reperfusion injury, and vascular injury. This has led to the evaluation of select complement inhibitors (e.g., C1 and C5 inhibitors) in clinical trials with mixed results. However, the complement system is highly complex: it is composed of more than 50 fluid-phase and surface-bound elements, including several complement-activated receptors-all potential therapeutic targets in kidney transplantation. Generation of targeted pharmaceuticals and use of gene editing tools have led to an improved understanding of the intricacies of the complement system in allo- and xeno-transplantation. This review summarizes our current knowledge of the role of the complement system as it relates to rejection in kidney transplantation, specifically reviewing evidence gained from pre-clinical models (rodent and nonhuman primate) that may potentially be translated to clinical trials.

Improving the ischemia-reperfusion injury in vascularized composite allotransplantation: Clinical experience and experimental implications

Long-time ischemia worsening transplant outcomes in vascularized composite allotransplantation (VCA) is often neglected. Ischemia-reperfusion injury (IRI) is an inevitable event that follows reperfusion after a period of cold static storage. The pathophysiological mechanism activates local inflammation, which is a barrier to allograft long-term immune tolerance. The previous publications have not clearly described the relationship between the tissue damage and ischemia time, nor the rejection grade. In this review, we found that the rejection episodes and rejection grade are usually related to the ischemia time, both in clinical and experimental aspects. Moreover, we summarized the potential therapeutic measures to mitigate the ischemia-reperfusion injury. Compare to static preservation, machine perfusion is a promising method that can keep VCA tissue viability and extend preservation time, which is especially beneficial for the expansion of the donor pool and better MHC-matching.

A Novel Porcine Model of Ischemia-Reperfusion Injury After Cross-Clamping the Thoracic Aorta Revealed Substantial Cardiopulmonary, Thromboinflammatory and Biochemical Changes Without Effect of C1-Inhibitor Treatment

Ischemic injury worsens upon return of blood and innate immunity including the complement system play a central role in ischemia-reperfusion injury (IRI) as in thoracic aortic surgery. Complement component1 inhibitor (C1-INH) has been shown to reduce IRI and is a broad-acting plasma cascade inhibitor. We established a new porcine model of IRI by cross-clamping the thoracic aorta and evaluated the global changes occurring in organ function, systemic inflammatory response and organ damage with or without treatment with C1-INH-concentrate. Twenty-four piglets (8.8-11.1 kg) underwent 45 minutes clamping of the thoracic aorta at the Th8 level. Upfront 12 piglets received human saline and 12 received C1-INH (250 IU/kg) intravenously. Three sham animals received thoracic opening without clamping. Reperfusion lasted 5 hours. We studied ten cardiorespiratory markers, three hematologic markers, eleven inflammatory markers, and twelve organ damage markers over the whole experimental period. Postmortem tissue homogenates from seven organs were examined for inflammatory markers and analysed by two-way repeated-measures ANOVA, area under the curve or unpaired t-tests. By excluding sham and combining treated and untreated animals, the markers reflected a uniform, broad and severe organ dysfunction. The mean and range fold change from before cross-clamp onset to maximum change for the different groups of markers were: cardiorespiratory 1.4 (0.2-3.7), hematologic 1.9 (1.2-2.7), plasma inflammatory 19.5 (1.4-176) and plasma organ damage 2.9 (1.1-8.6). Treatment with C1-INH had only a marginal effect on the IRI-induced changes, reaching statistical significance only for the plasma complement activation product TCC (p=0.0083) and IL-4 (p=0.022) and INF-α (p=0.016) in the colon tissue. In conclusion, the present novel model of porcine global IRI is forceful with regards to central markers and could generally be applicable for pathophysiological studies. C1-INH treatment had no significant effect, but the model allows for future testing of other drugs attenuating IRI globally.

Kidneys in SARS-CoV-2 Era; a challenge of multiple faces

INTRODUCTION

With the evolution of SARS-CoV-2 pandemic, it was believed to be a direct respiratory virus. But, its deleterious effects were observed on different body systems, including kidneys.

AIM OF WORK

In this review, we tried as much as we can to summarize what has been discussed in the literature about the relation between SARS-CoV-2 infection and kidneys since December, 2019.

METHODS

Each part of the review was assigned to one or two authors to search for relevant articles in three databases (Pubmed, Scopus and Google scholar) and collected data were summarized and revised by two independent researchers.

CONCLUSION

The complexity of COVID-19 pandemic and kidney could be attributed to the direct effect of SARS-CoV-2 infection on the kidneys, different clinical presentation, difficulties confronting dialysis patients, restrictions of the organ transplant programs, poor outcomes and bad prognosis in patients with known history of kidney diseases who got infected with SARS-CoV-2. This article is protected by copyright. All rights reserved.

Complement in ischaemia-reperfusion injury and transplantation

Until recently, the only known condition in which complement could mediate transplant injury was the rare occurrence of antibody-mediated rejection, in which the original concept of antibody immunity against the transplant was supported by complementary proteins present in the serum. This has changed within the last two decades because of evidence that the processes of ischaemia–reperfusion injury followed by T cell–mediated rejection are also critically dependent on components generated by the complement system. We now have a clearer understanding of the complement triggers and effectors that mediate injury, and a detailed map of their local sites of production and activation in the kidney. This is providing helpful guidelines as to how these harmful processes that restrict transplant outcomes can be targeted for therapeutic benefit. Here we review some of the recent advances highlighting relevant therapeutic targets.

Renal Delivery of Pharmacologic Agents During Machine Perfusion to Prevent Ischaemia-Reperfusion Injury: From Murine Model to Clinical Trials

Donor organ shortage still remains a serious obstacle for the access of wait-list patients to kidney transplantation, the best treatment for End-Stage Kidney Disease (ESKD). To expand the number of transplants, the use of lower quality organs from older ECD or DCD donors has become an established routine but at the price of increased incidence of Primary Non-Function, Delay Graft Function and lower-long term graft survival. In the last years, several improvements have been made in the field of renal transplantation from surgical procedure to preservation strategies. To improve renal outcomes, research has focused on development of innovative and dynamic preservation techniques, in order to assess graft function and promote regeneration by pharmacological intervention before transplantation. This review provides an overview of the current knowledge of these new preservation strategies by machine perfusions and pharmacological interventions at different timing possibilities: in the organ donor, ex-vivo during perfusion machine reconditioning or after implementation in the recipient. We will report therapies as anti-oxidant and anti-inflammatory agents, senolytics agents, complement inhibitors, HDL, siRNA and H2S supplementation. Renal delivery of pharmacologic agents during preservation state provides a window of opportunity to treat the organ in an isolated manner and a crucial route of administration. Even if few studies have been reported of transplantation after ex-vivo drugs administration, targeting the biological pathway associated to kidney failure (i.e. oxidative stress, complement system, fibrosis) might be a promising therapeutic strategy to improve the quality of various donor organs and expand organ availability.

Role of intracellular complement activation in kidney fibrosis

Increased expression of complement C1r, C1s and C3 in kidney cells plays an important role in the pathogenesis of kidney fibrosis. Our studies suggest that activation of complement in kidney cells with increased generation of C3 and its fragments occurs by activation of classical and alternative pathways. Single nuclei RNA sequencing studies in kidney tissue from unilateral ureteral obstruction mice show that increased synthesis of complement C3 and C5 occurs primarily in renal tubular epithelial cells (proximal and distal), while increased expression of complement receptors C3ar1 and C5ar1 occurs in interstitial cells including immune cells like monocytes/macrophages suggesting compartmentalization of complement components during kidney injury. Although global deletion of C3 and macrophage ablation prevent inflammation and reduced kidney tissue scarring, the development of mice with cell-specific deletion of complement components and their regulators could bring further insights into the mechanisms by which intracellular complement activation leads to fibrosis and progressive kidney disease. LINKED ARTICLES: This article is part of a themed issue on Canonical and non-canonical functions of the complement system in health and disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.14/issuetoc.

Targeting Inflammation and Oxidative Stress as a Therapy for Ischemic Kidney Injury

Inflammation and oxidative stress are the main pathological processes that accompany ischemic injury of kidneys and other organs. Based on this, these factors are often chosen as a target for treatment of acute kidney injury (AKI) in a variety of experimental and clinical studies. Note, that since these two components are closely interrelated during AKI development, substances that treat one of the processes often affect the other. The review considers several groups of promising nephroprotectors that have both anti-inflammatory and antioxidant effects. For example, many antioxidants, such as vitamins, polyphenolic compounds, and mitochondria-targeted antioxidants, not only reduce production of the reactive oxygen species in the cell but also modulate activity of the immune cells. On the other hand, immunosuppressors and non-steroidal anti-inflammatory drugs that primarily affect inflammation also reduce oxidative stress under some conditions. Another group of therapeutics is represented by hormones, such as estrogens and melatonin, which significantly reduce severity of the kidney damage through modulation of both these processes. We conclude that drugs with combined anti-inflammatory and antioxidant capacities are the most promising agents for the treatment of acute ischemic kidney injury.

Aberrant activation of the complement system in renal grafts is mediated by cold storage

Aberrant complement activation leads to tissue damage during kidney transplantation, and it is recognized as an important target for therapeutic intervention. However, it is not clear whether cold storage (CS) triggers the complement pathway in transplanted kidneys. The goal of the present study was to determine the impact of CS on complement activation in renal transplants. Male Lewis and Fischer rats were used, and donor rat kidneys were exposed to 4 h or 18 h of CS followed by transplantation (CS + transplant). To study CS-induced effects, a group with no CS was included in which the kidney was removed and transplanted back to the same rat [autotransplantation (ATx)]. Complement proteins (C3 and C5b-9) were evaluated with Western blot analysis (reducing and nonreducing conditions) and immunostaining. Western blot analysis of renal extracts or serum indicated that the levels of C3 and C5b-9 increased after CS + transplant compared with ATx. Quite strikingly, intracellular C3 was profoundly elevated within renal tubules after CS + transplant but was absent in sham or ATx groups, which showed only extratubular C3. Similarly, C5b-9 immunofluorescence staining of renal sections showed an increase in C5b-9 deposits in kidneys after CS + transplant. Real-time PCR (SYBR green) showed increased expression of CD11b and CD11c, components of complement receptors 3 and 4, respectively, as well as inflammatory markers such as TNF-α. In addition, recombinant TNF-α significantly increased C3 levels in renal cells. Collectively, these results demonstrate that CS mediates aberrant activation of the complement system in renal grafts following transplantation.NEW & NOTEWORTHY This study highlights cold storage-mediated aberrant activation of complement components in renal allografts following transplantation. Specifically, the results demonstrate, for the first time, that cold storage functions in exacerbation of C5b-9, a terminal cytolytic membrane attack complex, in renal grafts following transplantation. In addition, the results indicated that cold storage induces local C3 biogenesis in renal proximal cells/tubules and that TNF-α promotes C3 biogenesis and activation in renal proximal tubular cells.

Acute Kidney Injury (AKI) before and after Kidney Transplantation: Causes, Medical Approach, and Implications for the Long-Term Outcomes

Acute kidney injury (AKI) is a common finding in kidney donors and recipients. AKI in kidney donor, which increases the risk of delayed graft function (DGF), may not by itself jeopardize the short- and long-term outcome of transplantation. However, some forms of AKI may induce graft rejection, fibrosis, and eventually graft dysfunction. Therefore, various strategies have been proposed to identify conditions at highest risk of AKI-induced DGF, that can be treated by targeting the donor, the recipient, or even the graft itself with the use of perfusion machines. AKI that occurs early post-transplant after a period of initial recovery of graft function may reflect serious and often occult systemic complications that may require prompt intervention to prevent graft loss. AKI that develops long after transplantation is often related to nephrotoxic drug reactions. In symptomatic patients, AKI is usually associated with various systemic medical complications and could represent a risk of mortality. Electronic systems have been developed to alert transplant physicians that AKI has occurred in a transplant recipient during long-term outpatient follow-up. Herein, we will review most recent understandings of pathophysiology, diagnosis, therapeutic approach, and short- and long-term consequences of AKI occurring in both the donor and in the kidney transplant recipient.

Novel strategies to target the humoral alloimmune response

Antibody-mediated rejection (ABMR) represents a major cause of late allograft loss in solid organ transplantation worldwide. This process is driven by donor-specific antibodies (DSA), which develop either de-novo or, in sensitized patients, are preformed at the time of transplantation. Effective targeting of ABMR has been hampered by a lack of robust randomized controlled trials (RCT), required for the regulatory approval of new therapeutics. In this review, we discuss the evidence behind the present "standard" of care and recent progress in the development of novel strategies targeting different aspects of the alloimmune humoral response, including naïve and memory B-cell activation, the germinal centre reaction, plasma cell survival and antibody effector functions. In particular, we focus on co-stimulation blockade and its combination with next-generation proteasome inhibitors, new depleting monoclonal antibodies (anti-CD19, anti-BCMA, anti-CD38, anti-CD138), interleukin-6 blockade, complement inhibition and DSA degradation. These treatment modalities, when used in the appropriate clinical context and combination, have the potential to finally improve long-term allograft survival.

Kidney-intrinsic factors determine the severity of ischemia/reperfusion injury in a mouse model of delayed graft function

Delayed graft function due to transplant ischemia/reperfusion injury adversely affects up to 50% of deceased-donor kidney transplant recipients. However, key factors contributing to the severity of ischemia/reperfusion injury remain unclear. Here, using a clinically relevant mouse model of delayed graft function, we demonstrated that donor genetic background and kidney-intrinsic MyD88/Trif-dependent innate immunity were key determinants of delayed graft function. Functional deterioration of kidney grafts directly corresponded with the duration of cold ischemia time. The graft dysfunction became irreversible after cold ischemia time exceeded six hours. When cold ischemia time reached four hours, kidney grafts displayed histological features reflective of delayed graft function seen in clinical kidney transplantation. Notably, kidneys of B6 mice exhibited significantly more severe histological and functional impairment than kidneys of C3H or BALB/c mice, regardless of recipient strains or alloreactivities. Furthermore, allografts of B6 mice also showed an upregulation of IL-6, neutrophil gelatinase-associated lipocalin, and endoplasmic reticulum stress genes, as well as an increased influx of host neutrophils and memory CD8 T-cells. In contrast, donor MyD88/Trif deficiency inhibited neutrophil influx and decreased the expression of IL-6 and endoplasmic reticulum stress genes, along with improved graft function and prolonged allograft survival. Thus, kidney-intrinsic factors involving genetic characteristics and innate immunity serve as critical determinants of the severity of delayed graft function. This preclinical murine model allows for further investigations of the mechanisms underlying delayed graft function.

Review: Ischemia Reperfusion Injury-A Translational Perspective in Organ Transplantation

Thanks to the development of new, more potent and selective immunosuppressive drugs together with advances in surgical techniques, organ transplantation has emerged from an experimental surgery over fifty years ago to being the treatment of choice for many end-stage organ diseases, with over 139,000 organ transplants performed worldwide in 2019. Inherent to the transplantation procedure is the fact that the donor organ is subjected to blood flow cessation and ischemia during harvesting, which is followed by preservation and reperfusion of the organ once transplanted into the recipient. Consequently, ischemia/reperfusion induces a significant injury to the graft with activation of the immune response in the recipient and deleterious effect on the graft. The purpose of this review is to discuss and shed new light on the pathways involved in ischemia/reperfusion injury (IRI) that act at different stages during the donation process, surgery, and immediate post-transplant period. Here, we present strategies that combine various treatments targeted at different mechanistic pathways during several time points to prevent graft loss secondary to the inflammation caused by IRI.

The Inhibition of Complement System in Formal and Emerging Indications: Results from Parallel One-Stage Pairwise and Network Meta-Analyses of Clinical Trials and Real-Life Data Studies

This manuscript presents quantitative findings on the actual effectiveness of terminal complement component 5 (C5) inhibitors and complement component 1 (C1) esterase inhibitors through their formal and common “off-label” (compassionate) indications. The results emanated from pairwise and network meta-analyses to present evidence until September 2019. Clinical trials (CT) and real-life non-randomized studies of the effects of interventions (NRSI) are consistent on the benefits of C5 inhibitors and of the absence of effects of C1 esterase inhibitors (n = 7484): Mathematically, eculizumab (surface under the cumulative ranking area (SUCRA) >0.6) and ravulizumab (SUCRA ≥ 0.7) were similar in terms of their protective effect on hemolysis in paroxysmal nocturnal hemoglobinuria (PNH), thrombotic microangiopathy (TMA) in atypical hemolytic uremic syndrome (aHUS), and acute kidney injury (AKI) in aHUS, in comparison to pre-/off-treatment state and/or placebo (SUCRA < 0.01), and eculizumab was efficacious on thrombotic events in PNH (odds ratio (OR)/95% confidence interval (95% CI) in CT and real-life NRSI, 0.07/0.03 to 0.19, 0.24/0.17 to 0.33) and chronic kidney disease (CKD) occurrence/progression in PNH (0.31/0.10 to 0.97, 0.66/0.44 to 0.98). In addition, meta-analysis on clinical trials shows that eculizumab mitigates a refractory generalized myasthenia gravis (rgMG) crisis (0.29/0.13 to 0.61) and prevents new acute antibody-mediated rejection (AMR) episodes in kidney transplant recipients (0.25/0.13 to 0.49). The update of findings from this meta-analysis will be useful to promote a better use of complement inhibitors, and to achieve personalization of treatments with this class of drugs.

Infectious Complications of Biological and Small Molecule Targeted Immunomodulatory Therapies

The past 2 decades have seen a revolution in our approach to therapeutic immunosuppression. We have moved from relying on broadly active traditional medications, such as prednisolone or methotrexate, toward more specific agents that often target a single receptor, cytokine, or cell type, using monoclonal antibodies, fusion proteins, or targeted small molecules. This change has transformed the treatment of many conditions, including rheumatoid arthritis, cancers, asthma, and inflammatory bowel disease, but along with the benefits have come risks. Contrary to the hope that these more specific agents would have minimal and predictable infectious sequelae, infectious complications have emerged as a major stumbling block for many of these agents. Furthermore, the growing number and complexity of available biologic agents makes it difficult for clinicians to maintain current knowledge, and most review articles focus on a particular target disease or class of agent. In this article, we review the current state of knowledge about infectious complications of biologic and small molecule immunomodulatory agents, aiming to create a single resource relevant to a broad range of clinicians and researchers. For each of 19 classes of agent, we discuss the mechanism of action, the risk and types of infectious complications, and recommendations for prevention of infection.

Update on C1 Esterase Inhibitor in Human Solid Organ Transplantation

Complement plays important roles in both ischemia-reperfusion injury (IRI) and antibody-mediated rejection (AMR) of solid organ allografts. One approach to possibly improve outcomes after transplantation is the use of C1 inhibitor (C1-INH), which blocks the first step in both the classical and lectin pathways of complement activation and also inhibits the contact, coagulation, and kinin systems. C1-INH can also directly block leukocyte-endothelial cell adhesion. C1-INH contrasts with eculizumab and other distal inhibitors, which do not affect C4b or C3b deposition or noncomplement pathways. Authors of reports on trials in kidney transplant recipients have suggested that C1-INH treatment may reduce IRI and delayed graft function, based on decreased requirements for dialysis in the first month after transplantation. This effect was particularly marked with grafts with Kidney Disease Profile Index ≥ 85. Other clinical studies and models suggest that C1-INH may decrease sensitization and donor-specific antibody production and might improve outcomes in AMR, including in patients who are refractory to other modalities. However, the studies have been small and often only single-center. This article reviews clinical data and ongoing trials with C1-INH in transplant recipients, compares the results with those of other complement inhibitors, and summarizes potentially productive directions for future research.

Inflammaging and Complement System: A Link Between Acute Kidney Injury and Chronic Graft Damage

The aberrant activation of complement system in several kidney diseases suggests that this pillar of innate immunity has a critical role in the pathophysiology of renal damage of different etiologies. A growing body of experimental evidence indicates that complement activation contributes to the pathogenesis of acute kidney injury (AKI) such as delayed graft function (DGF) in transplant patients. AKI is characterized by the rapid loss of the kidney's excretory function and is a complex syndrome currently lacking a specific medical treatment to arrest or attenuate progression in chronic kidney disease (CKD). Recent evidence suggests that independently from the initial trigger (i.e., sepsis or ischemia/reperfusions injury), an episode of AKI is strongly associated with an increased risk of subsequent CKD. The AKI-to-CKD transition may involve a wide range of mechanisms including scar-forming myofibroblasts generated from different sources, microvascular rarefaction, mitochondrial dysfunction, or cell cycle arrest by the involvement of epigenetic, gene, and protein alterations leading to common final signaling pathways [i.e., transforming growth factor beta (TGF-β), p16 ink4a , Wnt/β-catenin pathway] involved in renal aging. Research in recent years has revealed that several stressors or complications such as rejection after renal transplantation can lead to accelerated renal aging with detrimental effects with the establishment of chronic proinflammatory cellular phenotypes within the kidney. Despite a greater understanding of these mechanisms, the role of complement system in the context of the AKI-to-CKD transition and renal inflammaging is still poorly explored. The purpose of this review is to summarize recent findings describing the role of complement in AKI-to-CKD transition. We will also address how and when complement inhibitors might be used to prevent AKI and CKD progression, therefore improving graft function.

Tacrolimus reduces atherosclerotic plaque formation in ApoE-/- mice by inhibiting NLRP3 inflammatory corpuscles

Effect of tacrolimus on atherosclerotic plaques and its influence on Nod-like receptor protein 3 (NLRP3) inflammatory pathway were studied by establishing the mouse model of atherosclerosis. The mice were divided into 3 groups: C57BL/6 mouse group (WT group), ApoE^-/- mouse group (ApoE^-/- group) and ApoE^-/- mouse + tacrolimus intervention group (ApoE^-/- + Tac group). The area of atherosclerotic plaques and the pathological morphologic changes were observed. The NLRP3, interleukin-1β (IL-1β), IL-18, NLRP3 inflammatory corpuscles, pro-inflammatory factors IL-1β and IL-18 in the aorta were analyzed. The area of atherosclerotic plaques in ApoE^-/- mice was increased significantly, and it was significantly reduced after tacrolimus intervention. After tacrolimus intervention, the arterial intima became obviously thinner and no obvious cholesterol crystals were observed. The macrophage infiltration in atherosclerotic plaques was significantly increased, and the content of smooth muscle cells was also increased. The levels of serum IL-1β, IL-18 and NLRP3 in ApoE^-/- mice were significantly increased, and they remarkably declined after tacrolimus intervention. ROS content in atherosclerotic plaques was increased in ApoE^-/- mice, and it remarkably declined after tacrolimus intervention. The protein content of NLRP3, ASC, Casp-1, IL-1β and IL-18 in the aorta in ApoE^-/- mice was remarkably increased, and they were inhibited to some extent after tacrolimus intervention. In conclusion, it is speculated that tacrolimus may reduce the formation of AS through inhibiting ROS in macrophages and activation of NLRP3 inflammatory corpuscles and reducing the release of IL-1β and IL-18.

Peritransplant eculizumab does not prevent delayed graft function in deceased donor kidney transplant recipients: Results of two randomized controlled pilot trials

Animal models and observational human data indicate that complement, including C5a, pathogenically participates in ischemia reperfusion (IR) injury that manifests as delayed graft function (DGF) following deceased donor kidney transplantation. We report on the safety/efficacy of anti-C5 monoclonal antibody eculizumab (Ecu) administered in the operating room prior to reperfusion, to prevent DGF in recipients of deceased donor kidney transplants in two related, investigator-sponsored, randomized controlled trials. Eight recipients from a single center were enrolled in a pilot study that led to a 19-subject multicenter trial. Together, 27 deceased donor kidney transplant recipients, 16 Ecu-treated and 11 controls, were treated with rabbit antithymocyte globulin, tacrolimus, mycophenolate mofetil with or without glucocorticoids, and followed for 6 months. Data analysis showed no epidemiological or transplant-related differences between study arms. Ecu was well tolerated with a similar severe adverse event incidence between groups. The DGF rate did not differ between Ecu-treated (44%) and control (45%, P = 1.0) subjects. Serum creatinine reduction in the first week after transplantation, and graft function up to 180-days post-transplant, were also similar. Ecu administration was safe but did not reduce the rate of DGF in a high-risk population of deceased donor recipients.

Case Report: Successful Use of Extracorporeal Therapies After ECMO Resuscitation in a Pediatric Kidney Transplant Recipient

The combination of extracorporeal membrane oxygenation (ECMO) and extracorporeal blood purification in children is rarely used due to small total blood volumes, risks of hemodynamic instability and a negative association between volume of blood transfusion and patient outcome. To our knowledge, this is the first description of a multimodal extracorporeal detoxication in the setting of ECMO in a post-kidney-transplant child on immunosuppression. We describe a case of a 30-months old child, who was extracorporeally resuscitated after cardiac arrest during kidney transplantation surgery and additionally treated with a number of extracorporeal blood purification methods (plasma exchange, CytoSorb, and lipopolysaccharide adsorption) in the setting of immunosuppression therapy. This case report shows the successful use of multimodal extracorporeal therapies for a good patient outcome. The lack of response to CytoSorb therapy might suggest an occult infection and not necessarily failure of treatment.

Complement and Complement Targeting Therapies in Glomerular Diseases

The complement cascade is part of the innate immune system whose actions protect hosts from pathogens. Recent research shows complement involvement in a wide spectrum of renal disease pathogenesis including antibody-related glomerulopathies and non-antibody-mediated kidney diseases, such as C3 glomerular disease, atypical hemolytic uremic syndrome, and focal segmental glomerulosclerosis. A pivotal role in renal pathogenesis makes targeting complement activation an attractive therapeutic strategy. Over the last decade, a growing number of anti-complement agents have been developed; some are approved for clinical use and many others are in the pipeline. Herein, we review the pathways of complement activation and regulation, illustrate its role instigating or amplifying glomerular injury, and discuss the most promising novel complement-targeting therapies.

Complement Membrane Attack Complexes Assemble NLRP3 Inflammasomes Triggering IL-1 Activation of IFN-γ-Primed Human Endothelium

RATIONALE

Complement activation contributes to multiple immune-mediated pathologies. In late allograft failure, donor-specific antibody deposits complement membrane attack complexes (MAC) on graft endothelial cells (ECs), substantially increasing their immunogenicity without causing lysis. Internalized MAC stabilize NIK (NF-κB [nuclear factor kappa-light-chain-enhancer of activated B cells]-inducing kinase) protein on Rab5+MAC+ endosomes, activating noncanonical NF-κB signaling. However, the link to increased immunogenicity is unclear.

OBJECTIVE

To identify mechanisms by which alloantibody and internalized MAC activate ECs to enhance their ability to increase T-cell responses.

METHODS AND RESULTS

In human EC cultures, internalized MAC also causes NLRP3 (NOD-like receptor family pyrin domain containing 3) translocation from endoplasmic reticulum to Rab5+MAC+NIK+ endosomes followed by endosomal NIK-dependent inflammasome assembly. Cytosolic NIK, stabilized by LIGHT (lymphotoxin-like inducible protein that competes with glycoprotein D for herpesvirus entry on T cells), does not trigger inflammasome assembly, and ATP-triggered inflammasome assembly does not require NIK. IFN-γ (interferon-γ) primes EC responsiveness to MAC by increasing NLRP3, pro-caspase 1, and gasdermin D expression. NIK-activated noncanonical NF-κB signaling induces pro-IL (interleukin)-1β expression. Inflammasome processed pro-IL-1β, and gasdermin D results in IL-1β secretion that increases EC immunogenicity through IL-1 receptor signaling. Activation of human ECs lining human coronary artery grafts in immunodeficient mouse hosts by alloantibody and complement similarly depends on assembly of an NLRP3 inflammasome. Finally, in renal allograft biopsies showing chronic rejection, caspase-1 is activated in C4d⁺ ECs of interstitial microvessels, supporting the relevance of the cell culture findings.

CONCLUSIONS

In response to antibody-mediated complement activation, IFN-γ-primed human ECs internalize MAC, triggering both endosomal-associated NIK-dependent NLRP3 inflammasome assembly and IL-1 synthesis, resulting in autocrine/paracrine IL-1β-mediated increases in EC immunogenicity. Similar responses may underlie other complement-mediated pathologies.

Pediatric kidney transplantation: early and long-term outcomes following 1187 procedures

AIM

To estimate short- and long-term outcomes of pediatric kidney transplants in Russia considering the maximum available number of cases.

MATERIAL AND METHODS

Retrospective, observational, multi-center study included data about 1187 kidney transplantation procedures (866 - deceased donor, 281 - living donor and 40 - AB0-incompatible living donor) performed in 1065 patients (age 0-17 years) since 1990 till 2017. Patient and graft survival, causes of recipient deaths and graft losses, as well as, the influence of donor type, blood group incompatibility and recipient age on outcomes were analyzed. Results of redo transplantations (n=131) were also investigated.

RESULTS

Annual, 5- , 10- , and 15-year survival of patient was 94, 86, 79 and 69%, respectively; graft survival - 85, 67, 53 and 33%, respectively. Transplantation from related donors including AB0-incompatible cases was associated with 15-30% increase of graft survival (p<0.0001). Up to 23% of children required redo transplantation within 4-5 years after primary procedure and ²/₃ of patients - after 10-15 years. There were no significant differences in outcomes after primary and redo procedures: annual, 5-, 10- and 15-year graft survival was 85, 68, 55, 42 and 85, 62, 45, 19%, respectively (p=0.1164).

CONCLUSION

It is reasonable to consider the outcomes of transplantations as satisfactory in Russia. However, there is a great potential for improvement. The main problems are high incidence of infectious complications followed by fatal outcomes (41% of all fatal outcomes) and loss of allograft due to primary dysfunction and death of recipients with functioning allografts (19 and 23%, respectively). Primary use of living-related donors for pediatric kidney transplantation seems to be the most effective way to improve both short- and long-term outcomes.

Barriers and Advances in Kidney Preservation

Despite the fact that a significant fraction of kidney graft dysfunctions observed after transplantation is due to ischemia-reperfusion injuries, there is still no clear consensus regarding optimal kidney preservation strategy. This stems directly from the fact that as of yet, the mechanisms underlying ischemia-reperfusion injury are poorly defined, and the role of each preservation parameter is not clearly outlined. In the meantime, as donor demography changes, organ quality is decreasing which directly increases the rate of poor outcome. This situation has an impact on clinical guidelines and impedes their possible harmonization in the transplant community, which has to move towards changing organ preservation paradigms: new concepts must emerge and the definition of a new range of adapted preservation method is of paramount importance. This review presents existing barriers in transplantation (e.g., temperature adjustment and adequate protocol, interest for oxygen addition during preservation, and clear procedure for organ perfusion during machine preservation), discusses the development of novel strategies to overcome them, and exposes the importance of identifying reliable biomarkers to monitor graft quality and predict short and long-term outcomes. Finally, perspectives in therapeutic strategies will also be presented, such as those based on stem cells and their derivatives and innovative models on which they would need to be properly tested.

Perspectives on the Optimal Genetically Engineered Pig in 2018 for Initial Clinical Trials of Kidney or Heart Xenotransplantation

For a clinical trial today, what might realistically be the optimal pig among those currently available? Deletion of expression of the 3 pig carbohydrate antigens, against which humans have natural (preformed) antibodies (triple-knockout pigs), should form the basis of any clinical trial. However, because both complement and coagulation can be activated in the absence of antibody, the expression of human complement- and coagulation-regulatory proteins is likely to be important in protecting the graft further. Any genetic manipulation that might reduce inflammation of the graft, for example, expression of hemeoxygenase-1 or A20, may also be beneficial to the long-term survival of the graft. The transgene for human CD47 is likely to have a suppressive effect on monocyte/macrophage and T-cell activity. Furthermore, deletion of xenoantigen expression and expression of a human complement-regulatory protein are both associated with a reduced T-cell response. Although there are several other genetic manipulations that may reduce the T-cell response further, it seems likely that exogenous immunosuppressive therapy, particularly if it includes costimulation blockade, will be sufficient. We would therefore suggest that, with our present knowledge and capabilities, the optimal pig might be a triple-knockout pig that expressed 1 or more human complement-regulatory proteins, 1 or more human coagulation-regulatory proteins, a human anti-inflammatory transgene, and CD47. Absent or minimal antibody binding is important, but we suggest that the additional insertion of protective human transgenes will be beneficial, and may be essential.

The rational design of affinity-attenuated OmCI for the purification of complement C5

Complement component C5 is the target of the mAb eculizumab and is the focus of a sustained drug discovery effort to prevent complement-induced inflammation in a range of autoimmune diseases. The immune evasion protein OmCI binds to and potently inactivates C5; this tight-binding interaction can be exploited to affinity-purify C5 protein from serum, offering a vastly simplified protocol compared with existing methods. However, breaking the high-affinity interaction requires conditions that risk denaturing or activating C5. We performed structure-guided in silico mutagenesis to identify prospective OmCI residues that contribute significantly to the binding affinity. We tested our predictions in vitro, using site-directed mutagenesis, and characterized mutants using a range of biophysical techniques, as well as functional assays. Our biophysical analyses suggest that the C5–OmCI interaction is complex with potential for multiple binding modes. We present single mutations that lower the affinity of OmCI for C5 and combinations of mutations that significantly decrease or entirely abrogate formation of the complex. The affinity-attenuated forms of OmCI are suitable for affinity purification and allow elution under mild conditions that are nondenaturing or activating to C5. We present the rational design, biophysical characterization, and experimental validation of affinity-reduced forms of OmCI as tool reagents to enable the affinity purification of C5.

Complement Activation in Liver Transplantation: Role of Donor Macrosteatosis and Implications in Delayed Graft Function

The complement system anchors the innate inflammatory response by triggering both cell-mediated and antibody-mediated immune responses against pathogens. The complement system also plays a critical role in sterile tissue injury by responding to damage-associated molecular patterns. The degree and duration of complement activation may be a critical variable controlling the balance between regenerative and destructive inflammation following sterile injury. Recent studies in kidney transplantation suggest that aberrant complement activation may play a significant role in delayed graft function following transplantation, confirming results obtained from rodent models of renal ischemia/reperfusion (I/R) injury. Deactivating the complement cascade through targeting anaphylatoxins (C3a/C5a) might be an effective clinical strategy to dampen reperfusion injury and reduce delayed graft function in liver transplantation. Targeting the complement cascade may be critical in donor livers with mild to moderate steatosis, where elevated lipid burden amplifies stress responses and increases hepatocyte turnover. Steatosis-driven complement activation in the donor liver may also have implications in rejection and thrombolytic complications following transplantation. This review focuses on the roles of complement activation in liver I/R injury, strategies to target complement activation in liver I/R, and potential opportunities to translate these strategies to transplanting donor livers with mild to moderate steatosis.