Current and Future Approaches for Monitoring Responses to Anti-complement Therapeutics

Aberrations in complement system functions have been identified as either direct or indirect pathophysiological mechanisms in many diseases and pathological conditions, such as infections, autoimmune diseases, inflammation, malignancies, and allogeneic transplantation. Currently available techniques to study complement include quantification of (a) individual complement components, (b) complement activation products, and (c) molecular mechanisms/function. An emerging area of major interest in translational studies aims to study and monitor patients on complement regulatory drugs for efficacy as well as adverse events. This area is progressing rapidly with several anti-complement therapeutics under development, in clinical trials, or already in clinical use. In this review, we summarized the appropriate indications, techniques, and interpretations of basic complement analyses, exemplified by a number of clinical disorders.

Ekdahl K, Nilsson B, Teramura Y. Optimization of Islet Microencapsulation with Thin Polymer Membranes for Long-Term Stability

Microencapsulation of islets can protect against immune reactions from the host immune system after transplantation. However, sufficient numbers of islets cannot be transplanted due to the increase of the size and total volume. Therefore, thin and stable polymer membranes are required for the microencapsulation. Here, we undertook the cell microencapsulation using poly(ethylene glycol)-conjugated phospholipid (PEG-lipid) and layer-by-layer membrane of multiple-arm PEG. In order to examine the membrane stability, we used different molecular weights of 4-arm PEG (10k, 20k and 40k)-Mal to examine the influence on the polymer membrane stability. We found that the polymer membrane made of 4-arm PEG(40k)-Mal showed the highest stability on the cell surface. Also, the polymer membrane did not disturb the insulin secretion from beta cells.

P3729The left atrial appendage closure by surgery-2 randomized trial

Background

Since the left atrium appendage (LAA) is the predilection site for clot formation in patients with atrial fibrillation (AF), closure of the LAA during surgery (LAACS) is often performed but not yet demonstrated to protect against stroke. The recent LAACS trial found that LAA closure protected from strokes and silent brain damages on a moderate (n=187) number of patients. However, results based solely on strokes and cerebral transitory ischemic attacks (TIA) was not significant (18% events in the control group compared to 6% in patients where LAA was closed (p=0.07). Furthermore, incomplete closure of the LAA is of concern, with an increased relative risk for stroke (10–25%).

Purpose

Determine if LAA closure added to planned open heart surgery protects against post-operative major stroke and minor stroke.

Methods

Adults scheduled for open-heart surgery who sign informed consent will be included regardless of known AF, provided LAA closure is not previously planned. LAACS-2 is an open, parallel, international multi-center study where patients will be randomized to closure of the LAA (with clip or staple), in addition to planned open-heart surgery. The LAA will remain open in the control group. Randomization will be stratified according to ongoing or expected use of anti-coagulant medication following surgery and classified as coronary artery bypass surgery (CABG) alone, mitral valve surgery or other. The primary endpoint is stroke or TIA occurring over at least two years following surgery. Secondary endpoints are: Total mortality and a combination of stroke, TIA or image of recent cerebral infarction in clinical settings demonstrated post-operatively, until the end follow-up. Occurrence of AF during follow-up will be assessed with prolonged (up to several weeks) monitoring with a three-lead compact sensor.

Studies on percutaneous coronary intervention and CABG, estimate a 3.7% pooled incidence of stroke in the first three years following coronary by-pass operations. Using these estimates and those from the previous LAACS study (3.2% strokes on patients with closed LAA vs 11.3% in the control group, p=0.07), we estimate that LAA closure can be demonstrated to protect from strokes, with a significance level of 0.05 and a 90% power, including 1200–1400 patients in an event-driven study. Expecting a cross-over of 10–20%, we plan to enroll 2000 adults. According to the a priori power-calculations, the LAACS-2 trial is powered: 1) to determine if randomization to closure of the LAA in conjunction with planned open-heart surgery, protects patients from post-operative clinical strokes; and 2) if there is an increased thrombogenic effect of incomplete closure or excessive pouch, since such harm can be identified by including between 359 and 1455 patients.

Perspective

If the LAACS procedure in conjunction with planned open-heart surgery protects against future stroke it should be included in future guidelines.

Acknowledgement/Funding

Innovation Fund Denmark; NovoNordisk Foundation; Ib Mogens Christiansen; Bispebjerg-Frederiksberg Research Fund

Is generation of C3(H2O) necessary for activation of the alternative pathway in real life?

In the alternative pathway (AP) an amplification loop is formed, which is strictly controlled by various fluid-phase and cell-bound regulators resulting in a state of homeostasis. Generation of the "C3b-like" C3(H₂O) has been described as essential for AP activation, since it conveniently explains how the initial fluid-phase AP convertase of the amplification loop is generated. Also, the AP has a status of being an unspecific pathway despite thorough regulation at different surfaces. During complement attack in pathological conditions and inflammation, large amounts of C3b are formed by the classical/lectin pathway (CP/LP) convertases. After the discovery of LP´s recognition molecules and its tight interaction with the AP, it is increasingly likely that the AP acts in vivo mainly as a powerful amplification mechanism of complement activation that is triggered by previously generated C3b molecules initiated by the binding of specific recognition molecules. Also in many pathological conditions caused by a dysregulated AP amplification loop such as paroxysmal nocturnal hemoglobulinuria (PNH) and atypical hemolytic uremic syndrome (aHUS), C3b is available due to minute LP and CP activation and/or generated by non-complement proteases. Therefore, C3(H₂O) generation in vivo may be less important for AP activation during specific attack or dysregulated homeostasis, but may be an important ligand for C3 receptors in cell-cell interactions and a source of C3 for the intracellular complement reservoir.

The Human Platelet as an Innate Immune Cell: Interactions Between Activated Platelets and the Complement System

Platelets play an essential role in maintaining homeostasis in the circulatory system after an injury by forming a platelet thrombus, but they also occupy a central node in the intravascular innate immune system. This concept is supported by their extensive interactions with immune cells and the cascade systems of the blood. In this review we discuss the close relationship between platelets and the complement system and the role of these interactions during thromboinflammation. Platelets are protected from complement-mediated damage by soluble and membrane-expressed complement regulators, but they bind several complement components on their surfaces and trigger complement activation in the fluid phase. Furthermore, localized complement activation may enhance the procoagulant responses of platelets through the generation of procoagulant microparticles by insertion of sublytic amounts of C5b9 into the platelet membrane. We also highlight the role of post-translational protein modifications in regulating the complement system and the critical role of platelets in driving these reactions. In particular, modification of disulfide bonds by thiol isomerases and protein phosphorylation by extracellular kinases have emerged as important mechanisms to fine-tune complement activity in the platelet microenvironment. Lastly, we describe disorders with perturbed complement activation where part of the clinical presentation includes uncontrolled platelet activation that results in thrombocytopenia, and illustrate how complement-targeting drugs are alleviating the prothrombotic phenotype in these patients. Based on these clinical observations, we discuss the role of limited complement activation in enhancing platelet activation and consider how these drugs may provide opportunities for further dissecting the complex interactions between complement and platelets.

A human whole-blood model to study the activation of innate immunity system triggered by nanoparticles as a demonstrator for toxicity

In this review article, we focus on activation of the soluble components of the innate immune system triggered by nonbiological compounds and stress variances in activation due to the difference in size between nanoparticles (NPs) and larger particles or bulk material of the same chemical and physical composition. We then discuss the impact of the so-called protein corona which is formed on the surface of NPs when they come in contact with blood or other body fluids. For example, NPs which bind inert proteins, proteins which are prone to activate the contact system (e.g., factor XII), which may lead to clotting and fibrin formation or the complement system (e.g., IgG or C3), which may result in inflammation and vascular damage. Furthermore, we describe a whole blood model which we have developed to monitor activation and interaction between different components of innate immunity: blood protein cascade systems, platelets, leukocytes, cytokine generation, which are induced by NPs. Finally, we describe our own studies on innate immunity system activation induced by three fundamentally different species of NPs (two types of engineered NPs and diesel NPs) as demonstrator of the utility of an initial determination of the composition of the protein corona formed on NPs exposed to ethylenediaminetetraacetic acid (EDTA) plasma and subsequent analysis in our whole blood model.

C3-Glomerulopathy Autoantibodies Mediate Distinct Effects on Complement C3- and C5-Convertases

C3 glomerulopathy (C3G) is a severe kidney disease, which is caused by defective regulation of the alternative complement pathway. Disease pathogenesis is heterogeneous and is caused by both autoimmune and genetic factors. Here we characterized IgG autoantibodies derived from 33 patients with autoimmune C3 glomerulopathy. Serum antibodies from all 33 patients as well as purified IgGs bound to the in vitro assembled C3-convertase. Noteworthy, two groups of antibodies were identified: group 1 with strong (12 patients) and group 2 with weak binding C3-convertase autoantibodies (22 patients). C3Nef, as evaluated in a standard C3Nef assay, was identified in serum from 19 patients, which included patients from group 1 as well as group 2. The C3-convertase binding profile was independent of C3Nef. Group 1 antibodies, but not the group 2 antibodies stabilized the C3-convertase, and protected the enzyme from dissociation by Factor H. Also, only group 1 antibodies induced C3a release. However, both group 1 and group 2 autoantibodies bound to the C5-convertase and induced C5a generation, which was inhibited by monoclonal anti-C5 antibody Eculizumab in vitro. In summary, group 1 antibodies are composed of C3Nef and C5Nef antibodies and likely over-activate the complement system, as seen in hemolytic assays. Group 2 antibodies show predominantly C5Nef like activities and stabilize the C5 but not the C3-convertase. Altogether, these different profiles not only reveal a heterogeneity of the autoimmune forms of C3G (MPGN), they also show that in diagnosis of C3G not all autoimmune forms are identified and thus more vigorous autoantibody testing should be performed.

Targeting Complement Pathways in Polytrauma- and Sepsis-Induced Multiple-Organ Dysfunction

Exposure to traumatic or infectious insults results in a rapid activation of the complement cascade as major fluid defense system of innate immunity. The complement system acts as a master alarm system during the molecular danger response after trauma and significantly contributes to the clearance of DAMPs and PAMPs. However, depending on the origin and extent of the damaged macro- and micro -milieu, the complement system can also be either excessively activated or inhibited. In both cases, this can lead to a maladaptive immune response and subsequent multiple cellular and organ dysfunction. The arsenal of complement-specific drugs offers promising strategies for various critical conditions after trauma, hemorrhagic shock, sepsis, and multiple organ failure. The imbalanced immune response needs to be detected in a rational and real-time manner before the translational therapeutic potential of these drugs can be fully utilized. Overall, the temporal-spatial complement response after tissue trauma and during sepsis remains somewhat enigmatic and demands a clinical triad: reliable tissue damage assessment, complement activation monitoring, and potent complement targeting to highly specific rebalance the fluid phase innate immune response.

Validation of an MPC Polymer Coating to Attenuate Surface-Induced Crosstalk between the Complement and Coagulation Systems in Whole Blood in In Vitro and In Vivo Models

Artificial surfaces that come into contact with blood induce an immediate activation of the cascade systems of the blood, leading to a thrombotic and/or inflammatory response that can eventually cause damage to the biomaterial or the patient, or to both. Heparin coating has been used to improve hemocompatibility, and another approach is 2-methacryloyloxyethyl phosphorylcholine (MPC)-based polymer coatings. Here, the aim is to evaluate the hemocompatibility of MPC polymer coating by studying the interactions with coagulation and complement systems using human blood in vitro model and pig in vivo model. The stability of the coatings is investigated in vitro and MPC polymer-coated catheters are tested in vivo by insertion into the external jugular vein of pigs to monitor the catheters' antithrombotic properties. There is no significant activation of platelets or of the coagulation and complement systems in the MPC polymer-coated one, which was superior in hemocompatibility to non-coated matrix surfaces. The protective effect of the MPC polymer coat does not decline after incubation in human plasma for up to 2 weeks. With MPC polymer-coated catheters, it is possible to easily draw blood from pig for 4 days in contrast to the case for non-coated catheters, in which substantial clotting is seen.

Two subgroups in systemic lupus erythematosus with features of antiphospholipid or Sjögren's syndrome differ in molecular signatures and treatment perspectives

Background

Previous studies and own clinical observations of patients with systemic lupus erythematosus (SLE) suggest that SLE harbors distinct immunophenotypes. This heterogeneity might result in differences in response to treatment in different subgroups and obstruct clinical trials. Our aim was to understand how SLE subgroups may differ regarding underlying pathophysiology and characteristic biomarkers.

Methods

In a cross-sectional study, including 378 well-characterized SLE patients and 316 individually matched population controls, we defined subgroups based on the patients’ autoantibody profile at inclusion. We selected a core of an antiphospholipid syndrome-like SLE (aPL+ group; positive in the lupus anticoagulant (LA) test and negative for all three of SSA (Ro52 and Ro60) and SSB antibodies) and a Sjögren’s syndrome-like SLE (SSA/SSB+ group; positive for all three of SSA (Ro52 and Ro60) and SSB antibodies but negative in the LA test). We applied affinity-based proteomics, targeting 281 proteins, together with well-established clinical biomarkers and complementary immunoassays to explore the difference between the two predefined SLE subgroups.

Results

The aPL+ group comprised 66 and the SSA/SSB+ group 63 patients. The protein with the highest prediction power (receiver operating characteristic (ROC) area under the curve = 0.89) for separating the aPL+ and SSA/SSB+ SLE subgroups was integrin beta-1 (ITGB1), with higher levels present in the SSA/SSB+ subgroup. Proteins with the lowest p values comparing the two SLE subgroups were ITGB1, SLC13A3, and CERS5. These three proteins, rheumatoid factor, and immunoglobulin G (IgG) were all increased in the SSA/SSB+ subgroup. This subgroup was also characterized by a possible activation of the interferon system as measured by high KRT7, TYK2, and ETV7 in plasma. In the aPL+ subgroup, complement activation was more pronounced together with several biomarkers associated with systemic inflammation (fibrinogen, α-1 antitrypsin, neutrophils, and triglycerides).

Conclusions

Our observations indicate underlying pathogenic differences between the SSA/SSB+ and the aPL+ SLE subgroups, suggesting that the SSA/SSB+ subgroup may benefit from IFN-blocking therapies while the aPL+ subgroup is more likely to have an effect from drugs targeting the complement system. Stratifying SLE patients based on an autoantibody profile could be a way forward to understand underlying pathophysiology and to improve selection of patients for clinical trials of targeted treatments.

Electronic supplementary material

The online version of this article (10.1186/s13075-019-1836-8) contains supplementary material, which is available to authorized users.

Evaluation of a Novel Immunoassay for Quantification of C1q for Clinical Diagnostic Use

Objectives: C1q is a valuable biomarker of disease activity in systemic lupus erythematosus (SLE). The “gold standard” assay, rocket immunoelectrophoresis (RIE), is time-consuming, and thus a shift to soluble immune precipitation techniques such as nephelometry has occurred. However, quantification of C1q with these techniques has been questioned as a result of the antibody binding properties of C1q. In the present work, we have compared results using various techniques (RIE, nephelometry, and ELISA) and have developed and validated a new magnetic bead-based sandwich immunoassay (MBSI).

Methods: C1q was quantified by nephelometry and the new sandwich immunoassay in 45 serum samples analyzed using RIE. C1q was also assessed in plasma using RIE and sandwich immunoassay in samples from SLE patients with nephritis (n = 69), SLE patients without nephritis (n = 310) as classified by BILAG score, and matched controls (n = 322). In addition, cerebrospinal fluid (CSF) samples from 31 patients, previously analyzed with ELISA, were also analyzed with the MBSI to test the behavior of this new assay in the lower detection range.

Results: We found a strong correlation between the new MBSI, RIE, and ELISA, but not with nephelometry. The MBSI demonstrated lower levels of C1q in SLE patients than in matched controls (p < 0.0001), and patients with nephritis had lower levels than patients without nephritis (p < 0.01). Similarily, RIE showed significant differences between the patient groups (p < 0.0001). An association was also found between the levels of C1q and the SLE disease activity index (SLEDAI). Furthermore, there was good correlation between the values obtained by MBSI and ELISA, in both serum (r = 0.960) and CSF (r = 0.786), underscoring the ability of both techniques to measure low concentrations of C1q with high accuracy.

Conclusion: The sandwich immunoassay correlated well with RIE, but soluble immune precipitation techniques, such as nephelometry, did not appear suitable alternatives, since C1q itself, and possibly anti-C1q antibodies, interfered with the measurements. The new sandwich immunoassay is therefore a good replacement for RIE in monitoring SLE disease activity.

Protective Effects of the Complement Inhibitor Compstatin CP40 in Hemorrhagic Shock

Trauma-induced hemorrhagic shock (HS) plays a decisive role in the development of immune, coagulation, and organ dysfunction often resulting in a poor clinical outcome. Imbalanced complement activation is intricately associated with the molecular danger response and organ damage after HS. Thus, inhibition of the central complement component C3 as turnstile of both inflammation and coagulation is hypothesized as a rational strategy to improve the clinical course after HS.Applying intensive care conditions, anaesthetized, monitored, and protectively ventilated nonhuman primates (NHP; cynomolgus monkeys) received a pressure-controlled severe HS (60 min at mean arterial pressure 30 mmHg) with subsequent volume resuscitation. Thirty minutes after HS, animals were randomly treated with either an analog of the C3 inhibitor compstatin (i.e., Cp40) in saline (n = 4) or with saline alone (n = 4). The observation period lasted 300 min after induction of HS.We observed improved kidney function in compstatin Cp40-treated animals after HS as determined by improved urine output, reduced damage markers and a tendency of less histopathological signs of acute kidney injury. Sham-treated animals revealed classical signs of mucosal edema, especially in the ileum and colon reflected by worsened microscopic intestinal injury scores. In contrast, Cp40-treated HS animals exhibited only minor signs of organ edema and significantly less intestinal damage. Furthermore, early systemic inflammation and coagulation dysfunction were both ameliorated by Cp40.The data suggest that therapeutic inhibition of C3 is capable to significantly improve immune, coagulation, and organ function and to preserve organ-barrier integrity early after traumatic HS. C3-targeted complement inhibition may therefore reflect a promising therapeutic strategy in fighting fatal consequences of HS.

Interpretation of Serological Complement Biomarkers in Disease

Complement system aberrations have been identified as pathophysiological mechanisms in a number of diseases and pathological conditions either directly or indirectly. Examples of such conditions include infections, inflammation, autoimmune disease, as well as allogeneic and xenogenic transplantation. Both prospective and retrospective studies have demonstrated significant complement-related differences between patient groups and controls. However, due to the low degree of specificity and sensitivity of some of the assays used, it is not always possible to make predictions regarding the complement status of individual patients. Today, there are three main indications for determination of a patient's complement status: (1) complement deficiencies (acquired or inherited); (2) disorders with aberrant complement activation; and (3) C1 inhibitor deficiencies (acquired or inherited). An additional indication is to monitor patients on complement-regulating drugs, an indication which may be expected to increase in the near future since there is now a number of such drugs either under development, already in clinical trials or in clinical use. Available techniques to study complement include quantification of: (1) individual components; (2) activation products, (3) function, and (4) autoantibodies to complement proteins. In this review, we summarize the appropriate indications, techniques, and interpretations of basic serological complement analyses, exemplified by a number of clinical disorders.

Safety profile after prolonged C3 inhibition

The central component of the complement cascade, C3, is involved in various biological functions, including opsonization of foreign bodies, clearance of waste material, activation of immune cells, and triggering of pathways controlling development. Given its broad role in immune responses, particularly in phagocytosis and the clearance of microbes, a deficiency in complement C3 in humans is often associated with multiple bacterial infections. Interestingly, an increased susceptibility to infections appears to occur mainly in the first two years of life and then wanes throughout adulthood. In view of the well-established connection between C3 deficiency and infections, therapeutic inhibition of complement at the level of C3 is often considered with caution or disregarded. We therefore set out to investigate the immune and biochemical profile of non-human primates under prolonged treatment with the C3 inhibitor compstatin (Cp40 analog). Cynomolgus monkeys were dosed subcutaneously with Cp40, resulting in systemic inhibition of C3, for 1 week, 2 weeks, or 3 months. Plasma concentrations of both C3 and Cp40 were measured periodically and complete saturation of plasma C3 was confirmed. No differences in hematological, biochemical, or immunological parameters were identified in the blood or tissues of animals treated with Cp40 when compared to those injected with vehicle alone. Further, skin wounds showed no signs of infection in those treated with Cp40. In fact, Cp40 treatment was associated with a trend toward accelerated wound healing when compared with the control group. In addition, a biodistribution study in a rhesus monkey indicated that the distribution of Cp40 in the body is associated with the presence of C3, concentrating in organs that accumulate blood and produce C3. Overall, our data suggest that systemic C3 inhibition in healthy adult non-human primates is not associated with a weakened immune system or susceptibility to infections.

Effects of Low Molecular Weight Heparin and Unfragmented Heparin on Induction of Osteoporosis in Rats

A comparison between the effect of low molecular weight heparin (LMWH) and unfragmented heparin (UH) on induction of osteoporosis was made in 60 rats treated with either UH (2 IU/ g b w), LMWH in 2 doses (2 Xal U/g or 0.4 Xal U/g) or placebo (saline) for 34 days. Studied variables were: bone mineral mass in femora; fragility of humera; zinc and calcium levels in serum and bone ash and albumin in plasma. A significant reduction in bone mineral mass was found in all heparin-treated rats. There was no difference between UH and LMWH in this respect. The effect was dose-dependent in LMWH-treated animals. The zinc contents in bone ash were decreased in all heparin-treated rats as compared with controls. No recognizable pattern was seen in alterations of zinc or calcium in serum. The fragility of the humera, tested as breaking strength did not differ between treatment groups and controls. In conclusion, if dosed according to similar factor Xa inhibitory activities, LMWH induces osteoporosis to the same extent as UH and in a dose-dependent manner. The zinc content in bone ash was decreased after heparin treatment, irrespective of type of heparin given.

Heparin-Induced Osteoporosis in Rats

In order to study the effect of heparin in inducing osteoporosis, 30 female rats were divided in two groups and treated with daily injections of 2 IU heparin/g body weight for 33 and 65 days and compared with the same number of rats acting as controls. The mineral bone mass in the femora of the animals was measured quantitatively. A significant (p <0.001) reduction in bone mineral mass was found in the heparin-treated animals. This effect was present to the same degree after 33 days as after 65 days of treatment. It is concluded that heparin in this dose causes osteoporosis in rats after 33 days and that the described method can be used as an experimental model for further studies on this topic.