Evaluation of complement function by ELISA

Reconstitution of the alternative pathway of the complement system enables rapid delineation of the mechanism of action of novel inhibitors

The complement system plays a critical role in the innate immune response, acting as a first line of defense against invading pathogens. However, dysregulation of the complement system is implicated in the pathogenesis of numerous diseases, ranging from Alzheimer's to age-related macular degeneration and rare blood disorders. As such, complement inhibitors have enormous potential to alleviate disease burden. While a few complement inhibitors are in clinical use, there is still a significant unmet medical need for the discovery and development of novel inhibitors to treat patients suffering from disorders of the complement system. A key hurdle in the development of complement inhibitors has been the determination of their mechanism of action. Progression along the complement cascade involves the formation of numerous multimeric protein complexes, creating the potential for inhibitors to act at multiple nodes in the pathway. This is especially true for molecules that target the central component C3 and its fragment C3b, which serve a dual role as a substrate for the C3 convertases and as a scaffolding protein in both the C3 and C5 convertases. Here, we report a step-by-step in vitro reconstitution of the complement alternative pathway using bio-layer interferometry. By physically uncoupling each step in the pathway, we were able to determine the kinetic signature of inhibitors that act at single steps in the pathway and delineate the full mechanism of action of known and novel C3 inhibitors. The method could have utility in drug discovery and further elucidating the biochemistry of the complement system.

Complement C1s as a diagnostic marker and therapeutic target: Progress and propective

The molecules of the complement system connect the effectors of innate and adaptive immunity and play critical roles in maintaining homeostasis. Among them, the C1 complex, composed of C1q, C1r, and C1s (C1qr₂s₂), is the initiator of the classical complement activation pathway. While deficiency of C1s is associated with early-onset systemic lupus erythematosus and increased susceptibility to bacteria infections, the gain-of- function variants of C1r and C1s may lead to periodontal Ehlers Danlos syndrome. As C1s is activated under various pathological conditions and associated with inflammation, autoimmunity, and cancer development, it is becoming an informative biomarker for the diagnosis and treatment of a variety of diseases. Thus, more sensitive and convenient methods for assessing the level as well as activity of C1s in clinic samples are highly desirable. Meanwhile, a number of small molecules, peptides, and monoclonal antibodies targeting C1s have been developed. Some of them are being evaluated in clinical trials and one of the antibodies has been approved by US FDA for the treatment of cold agglutinin disease, an autoimmune hemolytic anemia. In this review, we will summarize the biological properties of C1s, its association with development and diagnosis of diseases, and recent progress in developing drugs targeting C1s. These progress illustrate that the C1s molecule is an effective biomarker and promising drug target.

Anti-PEG antibodies compromise the integrity of PEGylated lipid-based nanoparticles via complement

PEGylation of lipid-based nanoparticles and other nanocarriers is widely used to increase their stability and plasma half-life. However, either pre-existing or de novo formed anti-PEG antibodies can induce hypersensitivity reactions and accelerated blood clearance through binding to the nanoparticle surfaces, leading to activation of the complement system. In this study, we investigated the consequences and mechanisms of complement activation by anti-PEG antibodies interacting with different types of PEGylated lipid-based nanoparticles. By using both liposomes loaded with different (model) drugs and LNPs loaded with mRNA, we demonstrate that complement activation triggered by anti-PEG antibodies can compromise the bilayer/surface integrity, leading to premature drug release or exposure of their mRNA contents to serum proteins. Anti-PEG antibodies also can induce deposition of complement fragments onto the surface of PEGylated lipid-based nanoparticles and induce the release of fluid phase complement activation products. The role of the different complement pathways activated by lipid-based nanoparticles was studied using deficient sera and/or inhibitory antibodies. We identified a major role for the classical complement pathway in the early activation events leading to the activation of C3. Our data also confirm the essential role of amplification of C3 activation by alternative pathway components in the lysis of liposomes. Finally, the levels of pre-existing anti-PEG IgM antibodies in plasma of healthy donors correlated with the degree of complement activation (fixation and lysis) induced upon exposure to PEGylated liposomes and mRNA-LNPs. Taken together, anti-PEG antibodies trigger complement activation by PEGylated lipid-based nanoparticles, which can potentially compromise their integrity, leading to premature drug release or cargo exposure to serum proteins.

A Randomized, First-in-Human, Healthy Volunteer Trial of sutimlimab, a Humanized Antibody for the Specific Inhibition of the Classical Complement Pathway

Aberrant activation of the classical complement pathway is the common underlying pathophysiology of orphan diseases such as bullous pemphigoid, antibody‐mediated rejection of organ transplants, cold agglutinin disease, and warm autoimmune hemolytic anemia. Therapeutic options for these complement‐mediated disorders are limited and sutimlimab, a humanized monoclonal antibody directed against complement factor C1s, may be potentially useful for inhibition of the classical complement pathway. A phase I, first‐in‐human, double‐blind, randomized, placebo‐controlled, dose‐escalation trial of single and multiple doses of sutimlimab or placebo was conducted in 64 volunteers to evaluate safety, tolerability, pharmacokinetic, and pharmacodynamic profiles. Single and multiple infusions of sutimlimab were well tolerated without any safety concerns. sutimlimab exhibited a steep concentration–effect relationship with a Hill coefficient of 2.4, and an IC₉₀ of 15.5 μg/mL. This study establishes the foundation for using sutimlimab as a highly selective inhibitor of the classical complement pathway in different diseases.

European Union funded project on the development of a whole complement deficiency screening ELISA-A story of success and an exceptional manager: Mohamed R. Daha

A whole complement ELISA-based assay kit, primarily designed to screen for deficiencies in components of the complement system was developed during a European Union grant involving more than a dozen European scientists and a small-medium enterprise company (Wieslab, which later merged into Eurodiagnostica). The consortium was led by Prof. Mohamed R. Daha who had already guided a preceding European grant which prepared the ground for this endeavor to create a novel and sophisticated complement measurement tool. The final result of the grant was a scientific publication (Seelen et al., 2005, J. Immunol. Methods 296, 187-198) and a commercially available complement deficiency screening kit, WIESLAB(®) Complement system Screen. Thereafter, the group decided to carry on with a grant, located at Innsbruck Medical University, and supported by royalties and unrestricted educational grants from Eurodiagnostica, Malmö, entitled "Search for Applications for WIESLAB(®) Complement system Screen (SAW)" with the aim to look for further applications of this assay. During the latter project the group organized several scientific meetings aimed at evaluating the use of the assay as well as developing further branches of its platform. A look back over almost two decades reveals a great story of excellent research which was also commercially successful, fulfilling the aims of European Union grants. It is also a story of ageless friendship, only possible due to the vision and guidance of an exceptional manager: Moh Daha.

Lessons learned from the porcine CARPA model: constant and variable responses to different nanomedicines and administration protocols

Pigs provide a sensitive and quantitative animal model of complement (C) activation-related pseudoallergy (CARPA) caused by liposomes and a wide range of nanoparticulate drugs or drug nanocarriers (nanomedicines). The tetrad of symptoms (hemodynamic, hematological, laboratory and skin changes) that arise within minutes after i.v. injection of reactogenic nanomedicines (RNMs) are highly reproducible among different pigs but the presence, direction and relative severity of symptoms are very different with different RNMs and their administration schedule. Bolus administration of RNMs usually trigger pulmonary hypertension with or without various degrees of systemic hyper- or hypotension, tachy-or bradycardia, arrhythmia, blood cell and inflammatory mediator changes and skin rash. These reactions can be rapid or protracted, and fully tachyphylactic, semi-tachyphylactic or non-tachyphylactic. Slow infusion usually diminishes the reactions and/or entail delayed, protracted and less severe hemodynamic and other changes. The goal of this review is to present some technical details of the porcine CARPA model, point out its constant and variable parameters, show examples of different reactions, highlight the unique features and capabilities of the model and evaluate its utility in preclinical safety assessment. The information obtained in this model enables the understanding of the complex pathomechanism of CARPA involving simultaneous anaphylatoxin and inflammatory mediator actions at multiple sites in different organs.